Materials

16 pages, 9640 KiB

Open AccessEditor’s ChoiceArticle

Novel Adsorbent Based on Banana Peel Waste for Removal of Heavy Metal Ions from Synthetic Solutions

by Mihai Negroiu, Anca Andreea Țurcanu, Ecaterina Matei, Maria Râpă, Cristina Ileana Covaliu, Andra Mihaela Predescu, Cristian Mircea Pantilimon, George Coman and Cristian Predescu

Materials 2021, 14(14), 3946; https://doi.org/10.3390/ma14143946 - 14 Jul 2021

Cited by 37 | Viewed by 5037

Abstract

Due to its valuable compounds, food waste has been gaining attention in different applications, such as life quality and environment. Combined with circular economy requirements, a valorization method for waste, especially banana waste, was to convert them into adsorbents with advanced properties. The [...] Read more.

Due to its valuable compounds, food waste has been gaining attention in different applications, such as life quality and environment. Combined with circular economy requirements, a valorization method for waste, especially banana waste, was to convert them into adsorbents with advanced properties. The banana waste, after thermal treatment, was used with high removal performances (100%) for the removal of heavy metals, such as Cr, Cu, Pb, and Zn, but their small particle size makes them very hard to recover and reuse. For this reason, a biopolymeric matrix was used to incorporate the banana waste. The matrix was chosen for its remarkable properties, such as low cost, biodegradability, low carbon footprint, and reduced environmental impact. In this research, different types of materials (simple banana peel ash BPA and combined with biopolymeric matrix, ALG–BPA, CS–BPA) were prepared, characterized, and tested. The materials were characterized by means of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), optical microscopy (OM), scanning electron microscopy (SEM), and tested for the removal of metal ions from synthetic solutions using atomic absorption spectroscopy (AAS). The ALG–BPA material proved to be the most efficient in the removal of heavy metal ions from synthetic solution, reaching even 100% metal removal for Cr, Fe, Pb, and Zn, while the CS-based materials were the least efficient, presenting the best values for Cr and Fe ions with a removal efficiency of 34.14% and 28.38%, respectively. By adding BPA to CS, the adsorption properties of the material were slightly improved, but also only for Cr and Fe ions, to 37.09% and 57.78%. Full article

(This article belongs to the Special Issue Advanced Eco-Technology and Materials in Water Treatment)

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19 pages, 3518 KiB

Open AccessEditor’s ChoiceArticle

Experimental Evaluation of Shrinkage, Creep and Prestress Losses in Lightweight Aggregate Concrete with Sintered Fly Ash

by Rafał Stanisław Szydłowski and Barbara Łabuzek

Materials 2021, 14(14), 3895; https://doi.org/10.3390/ma14143895 - 13 Jul 2021

Cited by 15 | Viewed by 2788

Abstract

The paper presents the experimental results of shrinkage, creep, and prestress loss in concrete with lightweight aggregate obtained by sintering of fly ash. Two concrete mixtures with different proportions of components were tested. Concrete with a density of 1810 and 1820 kg/m³ [...] Read more.

The paper presents the experimental results of shrinkage, creep, and prestress loss in concrete with lightweight aggregate obtained by sintering of fly ash. Two concrete mixtures with different proportions of components were tested. Concrete with a density of 1810 and 1820 kg/m³, and a 28-day strength of 56.9 and 58.4 MPa was obtained. Shrinkage and creep were tested on 150 × 250 × 1000 mm³ beams. Creep was tested under prestressing load for 539 days and concrete shrinkage for 900 days. The measurement results were compared with the calculations carried out according to the Eurocode 2 as well as with the results of other research. A very low creep coefficient and lower shrinkage in relation to the calculation results and the results of other research were found. It was also revealed that there is a clear correlation between shrinkage and creep, and the amount of water in the concrete. The value of the creep coefficient during the load holding period was 0.610 and 0.537, which is 56.0 and 49.3% of the value determined from the standard. The prestressing losses in the analyzed period amounted to an average of 13.0%. Based on the obtained test results, it was found that the tested lightweight aggregate concrete is well suited for prestressed concrete structures. Shrinkage was not greater than that calculated for normal weight concrete of a similar strength class, which will not result in increased loss of prestress. Low creep guarantees low deflection increments over time. Full article

(This article belongs to the Collection Concrete and Building Materials)

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17 pages, 3612 KiB

Open AccessEditor’s ChoiceArticle

Meta-Analysis of Steel Fiber-Reinforced Concrete Mixtures Leads to Practical Mix Design Methodology

by Emilio Garcia-Taengua, Mehdi Bakhshi and Liberato Ferrara

Materials 2021, 14(14), 3900; https://doi.org/10.3390/ma14143900 - 13 Jul 2021

Cited by 6 | Viewed by 2642

Abstract

The analysis of hundreds of SFRC mixtures compiled from papers published over the last 20 years is reported. This paper is focused on the relationships between the size and dosage of steel fibers and the relative amounts of the constituents of SFRC mixtures. [...] Read more.

The analysis of hundreds of SFRC mixtures compiled from papers published over the last 20 years is reported. This paper is focused on the relationships between the size and dosage of steel fibers and the relative amounts of the constituents of SFRC mixtures. Multiple linear regression is applied to the statistical modeling of such relationships, leading to four equations that show considerable accuracy and robustness in estimating SFRC mixture proportions as a function of fiber content and dimensions, maximum aggregate size, and water-to-cement ratio. The main trends described by these equations are discussed in detail. The importance of the interactions between aggregates, supplementary cementitious materials, and fibers in proportioning SFRC mixtures, as well as implications for workability and stability, are emphasized. The simplicity of these data-driven equations makes them a valuable tool to guide the proportioning of SFRC mixtures. Their predictive performance when used together as a data-driven mix design methodology is confirmed using a validation dataset. Full article

(This article belongs to the Special Issue Artificial Intelligence for Cementitious Materials)

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18 pages, 5532 KiB

Open AccessEditor’s ChoiceReview

An Update Review on N-Type Layered Oxyselenide Thermoelectric Materials

by Junqing Zheng, Dongyang Wang and Li-Dong Zhao

Materials 2021, 14(14), 3905; https://doi.org/10.3390/ma14143905 - 13 Jul 2021

Cited by 15 | Viewed by 5142

Abstract

Compared with traditional thermoelectric materials, layered oxyselenide thermoelectric materials consist of nontoxic and lower-cost elements and have better chemical and thermal stability. Recently, several studies on n-type layered oxyselenide thermoelectric materials, including BiCuSeO, Bi₂O₂Se and Bi₆Cu [...] Read more.

Compared with traditional thermoelectric materials, layered oxyselenide thermoelectric materials consist of nontoxic and lower-cost elements and have better chemical and thermal stability. Recently, several studies on n-type layered oxyselenide thermoelectric materials, including BiCuSeO, Bi₂O₂Se and Bi₆Cu₂Se₄O₆, were reported, which stimulates us to comprehensively summarize these researches. In this short review, we begin with various attempts to realize an n-type BiCuSeO system. Then, we summarize several methods to optimize the thermoelectric performance of Bi₂O₂Se, including carrier engineering, band engineering, microstructure design, et al. Next, we introduce a new type of layered oxyselenide Bi₆Cu₂Se₄O₆, and n-type transport properties can be obtained through halogen doping. At last, we propose some possible research directions for n-type layered oxyselenide thermoelectric materials. Full article

(This article belongs to the Special Issue Advances in Thermoelectric Materials and Devices)

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24 pages, 3136 KiB

Open AccessEditor’s ChoiceArticle

Life Cycle Assessment of Sustainable Asphalt Pavement Solutions Involving Recycled Aggregates and Polymers

by Cristina Oreto, Francesca Russo, Rosa Veropalumbo, Nunzio Viscione, Salvatore Antonio Biancardo and Gianluca Dell’Acqua

Materials 2021, 14(14), 3867; https://doi.org/10.3390/ma14143867 - 11 Jul 2021

Cited by 43 | Viewed by 5995

Abstract

The pursuit of sustainability in the field of road asphalt pavements calls for effective decision-making strategies, referring to both the technical and environmental sustainability of the solutions. This study aims to compare the life cycle impacts of several pavement solution alternatives involving, in [...] Read more.

The pursuit of sustainability in the field of road asphalt pavements calls for effective decision-making strategies, referring to both the technical and environmental sustainability of the solutions. This study aims to compare the life cycle impacts of several pavement solution alternatives involving, in the binder and base layers, some eco-designed, hot- and cold-produced asphalt mixtures made up of recycled aggregates in substitution for natural filler and commercial recycled polymer pellets for dry mixture modification. The first step focused on the technical and environmental compatibility assessment of the construction and demolition waste (CDW), jet grouting waste (JGW), fly ash (FA), and reclaimed asphalt pavement (RAP). Then, three non-traditional mixtures were designed for the binder layer and three for the base layer and characterized in terms of the stiffness modulus. Asphalt pavement design allowed for the definition of the functional units of Life Cycle Assessment (LCA), which was applied to all of the pavement configurations under analysis in a “from cradle to grave” approach. The LCA results showed that the best performance was reached for the solutions involving a cold, in-place recycled mixture made up of RAP and JGW in the base layer, which lowered all the impact category indicators by 31% on average compared to those of the traditional pavement solution. Further considerations highlighted that the combination of a cold base layer with a hot asphalt mixture made up of CDW or FA in the binder layer also maximized the service life of the pavement solution, providing the best synergistic effect. Full article

(This article belongs to the Special Issue Sustainable Asphalt Pavements: Materials, Design Methods, and Characterization Techniques)

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9 pages, 2765 KiB

Open AccessEditor’s ChoiceArticle

Magnetic Reversal in Wiegand Wires Evaluated by First-Order Reversal Curves

by Chao Yang, Yuya Kita, Zenglu Song and Yasushi Takemura

Materials 2021, 14(14), 3868; https://doi.org/10.3390/ma14143868 - 11 Jul 2021

Cited by 9 | Viewed by 2614

Abstract

The magnetic structure of Wiegand wires cannot be evaluated using conventional magnetization hysteresis curves. We analyzed the magnetization reversal of a Wiegand wire by measuring the first-order reversal curves (FORCs). A FeCoV Wiegand wire with a magnetically soft outer layer and a hard [...] Read more.

The magnetic structure of Wiegand wires cannot be evaluated using conventional magnetization hysteresis curves. We analyzed the magnetization reversal of a Wiegand wire by measuring the first-order reversal curves (FORCs). A FeCoV Wiegand wire with a magnetically soft outer layer and a hard magnetic core was used in this study. The magnetization reversal of the soft and hard regions in the wire was identified in the FORC diagrams. The magnetization reversal of the dominantly irreversible process of the soft layer and the magnetic intermediate region between the soft and hard regions was clarified. Full article

(This article belongs to the Section Materials Physics)

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21 pages, 12312 KiB

Open AccessEditor’s ChoiceArticle

Applying Mixture of Municipal Incinerator Bottom Ash and Sewage Sludge Ash for Ceramic Tile Manufacturing

by Deng-Fong Lin, Wei-Jhu Wang, Chia-Wen Chen and Kuo-Liang Lin

Materials 2021, 14(14), 3863; https://doi.org/10.3390/ma14143863 - 10 Jul 2021

Cited by 7 | Viewed by 3309

Abstract

Municipal incinerator bottom ash (MIBA) and sewage sludge ash (SSA) are secondary wastes produced from municipal incinerators. Landfills, disposal at sea, and agricultural use have been the major outlets for these secondary wastes. As global emphasis on sustainability arises, many have called for [...] Read more.

Municipal incinerator bottom ash (MIBA) and sewage sludge ash (SSA) are secondary wastes produced from municipal incinerators. Landfills, disposal at sea, and agricultural use have been the major outlets for these secondary wastes. As global emphasis on sustainability arises, many have called for an increasing reuse of waste materials as valuable resources. In this study, MIBA and SSA were mixed with clay for ceramic tile manufacturing in this study. Raw materials firstly went through TCLP (Toxicity Characteristic Leaching Procedure) to ensure their feasibility for reuse. From scanning electron microscopy (SEM), clay’s smooth surface was contrasted with the porous surface of MIBA and SSA, which led to a higher water requirement for the mixing. Specimens with five MIBA mix percentages of 0%, 5%, 10%, 15%, and 20% (wt) and three SSA mix percentages of 0%, 10%, and 20% (wt) were made to compare how the two waste materials affected the quality of the final product and to what extent. Shrinkage tests showed that MIBA and SSA contributed oppositely to tile shrinkage, as more MIBA reduced tile shrinkage, while more SSA encouraged tile shrinkage. However, as the kiln temperature reached 1150 °C, the SiO2-rich SSA adversely reduced the shrinkage due to the glass phase that formed to expand the tile instead. Both MIBA and SSA increased water tile absorption and reduced its bending strength and wear resistance. Increasing the kiln temperature could effectively improve the water absorption, bending strength, and wear resistance of high MIBA and SSA mixes, as SEM showed a more compact structure at higher temperatures. However, when the temperature reached 1100 °C, more pores appeared and seemingly exhausted the benefit brought by the higher temperature. Complex interactions between kiln temperature and MIBA/SSA mix percentage bring unpredictable performance of tile shrinkage, bending strength, and water absorption, which makes it very challenging to create a sample meeting all the specification requirements. We conclude that a mix with up to 20% of SSA and 5% of MIBA could result in quality tiles meeting the requirements for interior or exterior flooring applications when the kiln temperature is carefully controlled. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 4222 KiB

Open AccessEditor’s ChoiceArticle

Evaluating Elastic-Plastic Wavy and Spherical Asperity-Based Statistical and Multi-Scale Rough Surface Contact Models with Deterministic Results

by Nolan Ryan Chu, Robert L. Jackson, Xianzhang Wang, Arup Gangopadhyay and Hamed Ghaednia

Materials 2021, 14(14), 3864; https://doi.org/10.3390/ma14143864 - 10 Jul 2021

Cited by 16 | Viewed by 3436

Abstract

The solution to an elastic-plastic rough surface contact problem can be applied to phenomena such as friction and contact resistance. Many different types of models have therefore been developed to solve rough surface contact. A deterministic approach may accurately describe the entire surface, [...] Read more.

The solution to an elastic-plastic rough surface contact problem can be applied to phenomena such as friction and contact resistance. Many different types of models have therefore been developed to solve rough surface contact. A deterministic approach may accurately describe the entire surface, but the computing time is too long for practical use. Thus, mathematically abbreviated models have been developed to describe rough surface contact. Many popular models employ a statistical methodology to solve the contact problem, and they borrow the solution for spherical or parabolic contact to represent individual asperities. However, it is believed that a sinusoidal geometry may be a more realistic asperity representation. This has been applied to a newer version of the stacked multiscale model and statistical models. While no single model can accurately describe every contact problem better than any other, this work aims to help establish guidelines that determine the best model to solve a rough surface contact problem by applying mathematical and deterministic models to two reference surfaces in contact with a rigid flat. The discrepancies and similarities form the basis of those guidelines. Full article

(This article belongs to the Special Issue Research about Friction and Wear Modeling for Materials)

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15 pages, 5671 KiB

Open AccessEditor’s ChoiceArticle

Curing Assessment of Concrete with Hyperspectral Imaging

by Lisa Ptacek, Alfred Strauss, Barbara Hinterstoisser and Andreas Zitek

Materials 2021, 14(14), 3848; https://doi.org/10.3390/ma14143848 - 9 Jul 2021

Cited by 8 | Viewed by 3884

Abstract

The curing of concrete significantly influences the hydration process and its strength development. Inadequate curing leads to a loss of quality and has a negative effect on the durability of the concrete. Usually, the effects are not noticed until years later, when the [...] Read more.

The curing of concrete significantly influences the hydration process and its strength development. Inadequate curing leads to a loss of quality and has a negative effect on the durability of the concrete. Usually, the effects are not noticed until years later, when the first damage to the structure occurs because of the poor concrete quality. This paper presents a non-destructive measurement method for the determination of the curing quality of young concrete. Hyperspectral imaging in the near infrared is a contactless method that provides information about material properties in an electromagnetic wavelength range that cannot be seen with the human eye. Laboratory tests were carried out with samples with three different curing types at the age of 1, 7, and 27 days. The results showed that differences in the near infrared spectral signatures can be determined depending on the age of the concrete and the type of curing. The data was classified and analyzed by evaluating the results using k-means clustering. This method showed a high level of reliability for the differentiation between the different curing types and concrete ages. A recommendation for hyperspectral measurement and the evaluation of the curing quality of concrete could be made. Full article

(This article belongs to the Special Issue Structural Concrete Material: New Trends for Eco-Efficiency and Performance)

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31 pages, 16563 KiB

Open AccessEditor’s ChoiceArticle

Reduced Order Multiscale Simulation of Diffuse Damage in Concrete

by Giao Vu, Fabian Diewald, Jithender J. Timothy, Christoph Gehlen and Günther Meschke

Materials 2021, 14(14), 3830; https://doi.org/10.3390/ma14143830 - 8 Jul 2021

Cited by 10 | Viewed by 3312

Abstract

Damage in concrete structures initiates as the growth of diffuse microcracks that is followed by damage localisation and eventually leads to structural failure. Weak changes such as diffuse microcracking processes are failure precursors. Identification and characterisation of these failure precursors at an early [...] Read more.

Damage in concrete structures initiates as the growth of diffuse microcracks that is followed by damage localisation and eventually leads to structural failure. Weak changes such as diffuse microcracking processes are failure precursors. Identification and characterisation of these failure precursors at an early stage of concrete degradation and application of suitable precautionary measures will considerably reduce the costs of repair and maintenance. To this end, a reduced order multiscale model for simulating microcracking-induced damage in concrete at the mesoscale level is proposed. The model simulates the propagation of microcracks in concrete using a two-scale computational methodology. First, a realistic concrete specimen that explicitly resolves the coarse aggregates in a mortar matrix was generated at the mesoscale. Microcrack growth in the mortar matrix is modelled using a synthesis of continuum micromechanics and fracture mechanics. Model order reduction of the two-scale model is achieved using a clustering technique. Model predictions are calibrated and validated using uniaxial compression tests performed in the laboratory. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 2402 KiB

Open AccessEditor’s ChoiceArticle

Fracture and Size Effect of PFRC Specimens Simulated by Using a Trilinear Softening Diagram: A Predictive Approach

by Fernando Suárez, Jaime C. Gálvez, Marcos G. Alberti and Alejandro Enfedaque

Materials 2021, 14(14), 3795; https://doi.org/10.3390/ma14143795 - 7 Jul 2021

Cited by 7 | Viewed by 1881

Abstract

The size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram [...] Read more.

The size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram cannot capture the material behaviour on elements with different sizes due to dependence of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be very convenient for reproducing fracture of polyolefin-fibre-reinforced concrete elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of polyolefin-fibre-reinforced concrete specimens of different sizes under three-point bending. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental points of these softening functions are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately. Full article

(This article belongs to the Special Issue Fracture Mechanics of Fiber Reinforced Concrete)

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43 pages, 8205 KiB

Open AccessEditor’s ChoiceReview

3D Concrete Printing: A Systematic Review of Rheology, Mix Designs, Mechanical, Microstructural, and Durability Characteristics

by Atta Ur Rehman and Jung-Hoon Kim

Materials 2021, 14(14), 3800; https://doi.org/10.3390/ma14143800 - 7 Jul 2021

Cited by 185 | Viewed by 16650

Abstract

This paper provides a state-of-the-art report on the up-to-date research on the emerging 3D concrete printing technology from the concrete materials perspective. It reviews the recent research focused on understanding and characterizing the rheological necessities of the concrete printing process and discusses how [...] Read more.

This paper provides a state-of-the-art report on the up-to-date research on the emerging 3D concrete printing technology from the concrete materials perspective. It reviews the recent research focused on understanding and characterizing the rheological necessities of the concrete printing process and discusses how the researchers are tailoring compatible mix proportions for the 3D concrete printing process by using eco-friendly binders, waste aggregates, chemical admixtures, and nano-additives. This paper systematically evaluates anisotropic behavior in the mechanical properties of printed concrete and establishes an order for anisotropic behavior in the compressive, flexural, and tensile strengths along three different axes (X, Y, and Z axes) of printed concrete. It evaluates the ratio of flexural strength to the compressive strength of printed concrete along the above three axes. This article explains the influence of variation of printing process parameters on the mechanical properties and discusses reinforcement approaches used for increasing structural performance. The microstructure at the interface of adjacent layers and also at the interface of the reinforcement-cement matrix is discussed. The recent research on the durability performance of printed concrete is critically discussed and future research needs for 3D concrete printing are identified in this paper. Full article

(This article belongs to the Special Issue Concrete Technology and Mechanical Properties of Concretes)

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13 pages, 7431 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Desulfurized Crumb Rubber/Styrene–Butadiene–Styrene Composite Modified Asphalt Based on Rheological Properties

by Jingyao Yang, Gang Xu, Peipei Kong and Xianhua Chen

Materials 2021, 14(14), 3780; https://doi.org/10.3390/ma14143780 - 6 Jul 2021

Cited by 10 | Viewed by 2448

Abstract

With the growing interest in bituminous construction materials, desulfurized crumb rubber (CR)/styrene–butadiene–styrene (SBS) modified asphalts have been investigated by many researchers as low-cost environmental-friendly road construction materials. This study aimed to investigate the rheological properties of desulfurized CR/SBS composite modified asphalt within various [...] Read more.

With the growing interest in bituminous construction materials, desulfurized crumb rubber (CR)/styrene–butadiene–styrene (SBS) modified asphalts have been investigated by many researchers as low-cost environmental-friendly road construction materials. This study aimed to investigate the rheological properties of desulfurized CR/SBS composite modified asphalt within various temperature ranges. Bending beam rheometer (BBR), linear amplitude sweep (LAS), and multiple stress creep recovery (MSCR) tests were performed on conventional CR/SBS composite modified asphalt and five types of desulfurized CR/SBS modified asphalts. Meanwhile, Burgers’ model and the Kelvin–Voigt model were used to derive nonlinear viscoelastic parameters and analyze the viscoelastic mechanical behavior of the asphalts. The experimental results indicate that both the desulfurized CR/SBS composite modifier and force chemical reactor technique can enhance the crosslinking of CR and SBS copolymer, resulting in an improved high-, intermediate-, and low-temperature performance of desulfurized CR/SBS composite modified asphalt. Burgers’ model was found to be apposite in simulating the creep stages obtained from MSCR tests for CR/SBS composite modified asphalts. The superior high-temperature performance of desulfurized CR/SBS modified asphalt prepared with 4% SBS, 20% desulfurized rubber, and a force chemical reactor time of 45 min contributes to the good high-temperature elastic properties of the asphalt. Therefore, this combination is recommended as an optimal preparation process. In summary, the desulfurization of crumb rubber and using the force chemical reactor technique are beneficial to composite asphalt performance and can provide a new way of utilizing waste tire rubber. Full article

(This article belongs to the Special Issue Experimental Testing and Constitutive Modelling of Pavement Materials)

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12 pages, 7459 KiB

Open AccessEditor’s ChoiceArticle

Durability Study on High-Performance Fiber-Reinforced Mortar under Simulated Wastewater Pipeline Environment

by Tianyu Wang, Yahong Zhao, Baosong Ma and Cong Zeng

Materials 2021, 14(14), 3781; https://doi.org/10.3390/ma14143781 - 6 Jul 2021

Cited by 9 | Viewed by 2456

Abstract

The acid–alkaline-inducd corrosive environments inside wastewater concrete pipelines cause concrete structural deterioration and substantial economic losses all over the world. High-performance concrete/mortar (HPC) was designed to have better resistance to corrosive environments, with enhanced service life. However, the durability of HPC in wastewater [...] Read more.

The acid–alkaline-inducd corrosive environments inside wastewater concrete pipelines cause concrete structural deterioration and substantial economic losses all over the world. High-performance concrete/mortar (HPC) was designed to have better resistance to corrosive environments, with enhanced service life. However, the durability of HPC in wastewater pipeline environments has rarely been studied. A high-performance mortar mixture (M) reinforced by supplemental materials (including fly ash and silica fume) and polyvinyl alcohol (PVA) fibers, together with a mortar mixture (P) consisting of cement, sand and water with similar mechanical performance, were both designed and exposed to simulated wastewater pipeline environments. The visual appearance, dimensional variation, mass loss, mechanical properties, permeable pore volume, and microstructure of the specimens were measured during the corrosion cycles. More severe deterioration was observed when the alkaline environment was introduced into the corrosion cycles. Test results showed that the M specimens had less permeable pore volume, better dimensional stability, and denser microstructure than the P specimens under acid–alkaline-induced corrosive environments. The mass-loss rates of the M specimens were 66.1–77.2% of the P specimens after 12 corrosion cycles. The compressive strength of the M specimens was 25.5–37.3% higher than the P specimens after 12 cycles under corrosive environments. Hence, the high-performance mortar examined in this study was considered superior to traditional cementitious materials for wastewater pipeline construction and rehabilitation. Full article

(This article belongs to the Special Issue Various Substitute Aggregate Materials for Sustainable Concrete)

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21 pages, 5802 KiB

Open AccessEditor’s ChoiceArticle

Chitosan Nanoparticles Functionalized Viscose Fabrics as Potentially Durable Antibacterial Medical Textiles

by Matea Korica, Zdenka Peršin, Lidija Fras Zemljič, Katarina Mihajlovski, Biljana Dojčinović, Snežana Trifunović, Alenka Vesel, Tanja Nikolić and Mirjana M. Kostić

Materials 2021, 14(13), 3762; https://doi.org/10.3390/ma14133762 - 5 Jul 2021

Cited by 27 | Viewed by 3936

Abstract

This research proposed two pretreatments of viscose fabrics: oxidation with 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and coating with TEMPO-oxidized cellulose nanofibrils (TOCN), to introduce functional groups (COOH and CHO) suitable for irreversible binding of chitosan nanoparticles without and with embedded zinc (NCS and NCS + [...] Read more.

This research proposed two pretreatments of viscose fabrics: oxidation with 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and coating with TEMPO-oxidized cellulose nanofibrils (TOCN), to introduce functional groups (COOH and CHO) suitable for irreversible binding of chitosan nanoparticles without and with embedded zinc (NCS and NCS + Zn, respectively) and consequently achieving washing durable antibacterial properties of the chitosan nanoparticles functionalized fabrics. The characterizations of pretreated and chitosan nanoparticles functionalized fabrics were performed by FTIR and XPS spectroscopy, elemental analysis, inductively coupled plasma optical emission spectrometry, zeta potential measurements, scanning electron microscopy, determination of COOH and CHO groups content, and antimicrobial activity under dynamic contact conditions. Influence of pretreatments on NCS and NCS + Zn adsorption, chemical, electrokinetic, and antibacterial properties as well as morphology, and washing durability of NCS and NCS + Zn functionalized fabrics were studied and compared. Washing durability was evaluated through changes in the chitosan and zinc content, zeta potential, and antibacterial activity after 1, 3, and 5 washing cycles. Pretreatments improved washing durability of antibacterial properties of chitosan nanoparticles functionalized fabrics. The NCS and NCS + Zn functionalized pretreated fabrics preserved antibacterial activity against S. aureus after five washing cycles, while antibacterial activity against E. coli was preserved only after one washing cycle in the case NCS + Zn functionalized pretreated viscose fabrics. Full article

(This article belongs to the Special Issue Chitosan-Based Materials)

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14 pages, 36934 KiB

Open AccessEditor’s ChoiceArticle

Effect of Nano-Magnesium Oxide on the Expansion Performance and Hydration Process of Cement-Based Materials

by Yuxun Ye, Yanming Liu, Tao Shi, Zhuojun Hu, Lei Zhong, Haobo Wang and Yaohui Chen

Materials 2021, 14(13), 3766; https://doi.org/10.3390/ma14133766 - 5 Jul 2021

Cited by 25 | Viewed by 3852

Abstract

Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. This article examines the influence [...] Read more.

Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. This article examines the influence of nano-MgO on the long-term consistency, fluidity, expansion stability, hydration, and mechanical properties of 30% fly ash cement-based materials and improves research into nano-MgO as an expansion agent. Expansion performance, flexural and compressive strength, and stability after boiling and autoclave treatment were tested for specimens mixed with a 2, 4, 6, 8 and 10% cementitious material mass of nano-MgO. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were employed to study their hydration process and microstructure. The results showed that nano-MgO had an obvious effect on the consistency, fluidity and expansion performance of cement paste. After curing in water for 365 days and autoclaving thereafter, the hydration of nano-MgO was relatively complete. The volumetric expansion pressure of the magnesium hydroxide (Mg(OH)₂) crystals and the crystallization pressure generated after their continuous precipitation were the main reasons for the expansion of the slurry. Nano-MgO improved the microstructure of cement paste and significantly enhanced its long-term flexural strength and compressive strength. When the content of nano-MgO was less than 10%, the cement with 30% fly ash had good long-term stability with the potential to compensate for the shrinkage of large-volume concrete. Full article

(This article belongs to the Section Construction and Building Materials)

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15 pages, 4068 KiB

Open AccessEditor’s ChoiceArticle

The Durability of Mortar Containing Alkali Activated Fly Ash-Based Lightweight Aggregate

by Puput Risdanareni, Philip Van den Heede, Jianyun Wang and Nele De Belie

Materials 2021, 14(13), 3741; https://doi.org/10.3390/ma14133741 - 4 Jul 2021

Cited by 11 | Viewed by 3044

Abstract

Beneficiating fly ash as valuable construction material such as artificial lightweight aggregate (LWA) could be an alternative solution to increase the utilization of the industrial by-product. However, generally, LWA is characterized by high porosity and a related high water absorption, which on the [...] Read more.

Beneficiating fly ash as valuable construction material such as artificial lightweight aggregate (LWA) could be an alternative solution to increase the utilization of the industrial by-product. However, generally, LWA is characterized by high porosity and a related high water absorption, which on the one hand allows production of lightweight mortar, but on the other hand can affect its performance. Thus, in this research, the durability performance of mortar composed with alkali-activated fly ash-based LWA, and commercial expanded clay (EC) LWA was investigated. The fly ash LWA was prepared in a pan granulator, with a 6-molar solution of NaOH mixed with Na₂SiO₃ in a Na₂SiO₃/NaOH weight ratio of 1.5 being used as activator (FA 6M LWA). The results revealed that mortar containing FA 6M LWA had equivalent mechanical strength with mortar containing EC LWA. The mortar containing FA 6M LWA had comparable capillary water uptake and chloride migration resistance with the reference and EC LWA mortar. Furthermore, the addition of FA 6M LWA was proven to enhance the carbonation resistance in the resulting mortar, due to the denser interfacial transition zone (ITZ) of mortar with LWA. Full article

(This article belongs to the Special Issue Utilisation of Recycled Materials and By-Products in Concrete)

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17 pages, 4829 KiB

Open AccessEditor’s ChoiceArticle

A Textile Waste Fiber-Reinforced Cement Composite: Comparison between Short Random Fiber and Textile Reinforcement

by Payam Sadrolodabaee, Josep Claramunt, Mònica Ardanuy and Albert de la Fuente

Materials 2021, 14(13), 3742; https://doi.org/10.3390/ma14133742 - 4 Jul 2021

Cited by 48 | Viewed by 8750

Abstract

Currently, millions of tons of textile waste from the garment and textile industries are generated worldwide each year. As a promising option in terms of sustainability, textile waste fibers could be used as internal reinforcement of cement-based composites by enhancing ductility and decreasing [...] Read more.

Currently, millions of tons of textile waste from the garment and textile industries are generated worldwide each year. As a promising option in terms of sustainability, textile waste fibers could be used as internal reinforcement of cement-based composites by enhancing ductility and decreasing crack propagation. To this end, two extensive experimental programs were carried out, involving the use of either fractions of short random fibers at 6–10% by weight or nonwoven fabrics in 3–7 laminate layers in the textile waste-reinforcement of cement, and the mechanical and durability properties of the resulting composites were characterized. Flexural resistance in pre- and post-crack, toughness, and stiffness of the resulting composites were assessed in addition to unrestrained drying shrinkage testing. The results obtained from those programs were analyzed and compared to identify the optimal composite and potential applications. Based on the results of experimental analysis, the feasibility of using this textile waste composite as a potential construction material in nonstructural concrete structures such as facade cladding, raised floors, and pavements was confirmed. The optimal composite was proven to be the one reinforced with six layers of nonwoven fabric, with a flexural strength of 15.5 MPa and a toughness of 9.7 kJ/m². Full article

(This article belongs to the Special Issue Sustainability in Construction and Building Materials)

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16 pages, 7174 KiB

Open AccessEditor’s ChoiceArticle

Interface Design in Lightweight SiC/TiSi₂ Composites Fabricated by Reactive Infiltration Process: Interaction Phenomena between Liquid Si-Rich Si-Ti Alloys and Glassy Carbon

by Donatella Giuranno, Sofia Gambaro, Grzegorz Bruzda, Rafal Nowak, Wojciech Polkowski, Natalia Sobczak, Simona Delsante and Rada Novakovic

Materials 2021, 14(13), 3746; https://doi.org/10.3390/ma14133746 - 4 Jul 2021

Cited by 3 | Viewed by 2730

Abstract

To properly design and optimize liquid-assisted processes, such as reactive infiltration for fabricating lightweight and corrosion resistant SiC/TiSi₂ composites, the extensive knowledge about the interfacial phenomena taking place when liquid Si-rich Si-Ti alloys are in contact with glassy carbon (GC) is of [...] Read more.

To properly design and optimize liquid-assisted processes, such as reactive infiltration for fabricating lightweight and corrosion resistant SiC/TiSi₂ composites, the extensive knowledge about the interfacial phenomena taking place when liquid Si-rich Si-Ti alloys are in contact with glassy carbon (GC) is of primary importance. To this end, the wettability of GC by two different Si-rich Si-Ti alloys was investigated for the first time by both the sessile and pendant drop methods at T = 1450 °C. The results obtained, in terms of contact angle values, spreading kinetics, reactivity, and developed interface microstructures, were compared with experimental observations previously obtained for the liquid Si-rich Si-Ti eutectics processed under the same operating conditions. As the main outcome, a different Si content did not seem to affect the final contact angle values. Contrarily, the final developed microstructure at the interface and the spreading kinetics were observed as weakly dependent on the composition. From a practical point of view, Si-Ti alloy compositions with a Si content falling in the simple eutectic region of the Si-Ti phase diagram might be potentially used as infiltrating materials of C- and SiC-based composites. Full article

(This article belongs to the Special Issue Interfacial and Transport Phenomena between Liquid Metal and Solid Structural Materials)

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15 pages, 1427 KiB

Open AccessEditor’s ChoiceArticle

Protection of Concrete Structures: Performance Analysis of Different Commercial Products and Systems

by Denny Coffetti, Elena Crotti, Gabriele Gazzaniga, Roberto Gottardo, Tommaso Pastore and Luigi Coppola

Materials 2021, 14(13), 3719; https://doi.org/10.3390/ma14133719 - 2 Jul 2021

Cited by 17 | Viewed by 3874

Abstract

The increasing demand for reconstructions of concrete structures and the wide availability on the market of surface protective products and systems could lead to misunderstandings in the decision of the most effective solution. Surface protectors have become increasingly widespread in recent years in [...] Read more.

The increasing demand for reconstructions of concrete structures and the wide availability on the market of surface protective products and systems could lead to misunderstandings in the decision of the most effective solution. Surface protectors have become increasingly widespread in recent years in concrete restoration interventions thanks to their properties: they are able to protect the substrate from aggressive agents and consequently extend the useful life of the structures. The aim of this article is first of all to present the surface protective treatments available on the market, outlining their strengths and weaknesses. Subsequently, a characterization of seven different commercial coatings for reinforced-concrete structures is provided, taking into account chemical nature, fields of use and effectiveness, both in terms of physic and elastic performance and resistance to aggressive agents that undermine the durability of the treated concrete elements. Full article

(This article belongs to the Special Issue Corrosion in Concrete: Inhibitors and Coatings)

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10 pages, 3221 KiB

Open AccessEditor’s ChoiceArticle

Structure, Luminescence, and Magnetic Properties of Crystalline Manganese Tungstate Doped with Rare Earth Ion

by Jae-Young Jung, Soung-Soo Yi, Dong-Hyun Hwang and Chang-Sik Son

Materials 2021, 14(13), 3717; https://doi.org/10.3390/ma14133717 - 2 Jul 2021

Cited by 11 | Viewed by 2785

Abstract

The precursor prepared by co-precipitation method was sintered at various temperatures to synthesize crystalline manganese tungstate (MnWO₄). Sintered MnWO₄ showed the best crystallinity at a sintering temperature of 800 °C. Rare earth ion (Dysprosium; Dy³⁺) was added when [...] Read more.

The precursor prepared by co-precipitation method was sintered at various temperatures to synthesize crystalline manganese tungstate (MnWO₄). Sintered MnWO₄ showed the best crystallinity at a sintering temperature of 800 °C. Rare earth ion (Dysprosium; Dy³⁺) was added when preparing the precursor to enhance the magnetic and luminescent properties of crystalline MnWO₄ based on these sintering temperature conditions. As the amount of rare earth ions was changed, the magnetic and luminescent characteristics were enhanced; however, after 0.1 mol.%, the luminescent characteristics decreased due to the concentration quenching phenomenon. In addition, a composite was prepared by mixing MnWO₄ powder, with enhanced magnetism and luminescence properties due to the addition of dysprosium, with epoxy. To one of the two prepared composites a magnetic field was applied to induce alignment of the MnWO₄ particles. Aligned particles showed stronger luminescence than the composite sample prepared with unsorted particles. As a result of this, it was suggested that it can be used as phosphor and a photosensitizer by utilizing the magnetic and luminescent properties of the synthesized MnWO₄ powder with the addition of rare earth ions. Full article

(This article belongs to the Special Issue Synthesis, Characterization, and Degradation of Advanced Optical and Photo-Active Materials)

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9 pages, 433 KiB

Open AccessEditor’s ChoiceArticle

High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

by Mungo Frost, John D. Lazarz, Abraham L. Levitan, Vitali B. Prakapenka, Peihao Sun, Sergey N. Tkachev, Hong Yang, Siegfried H. Glenzer and Arianna E. Gleason

Materials 2021, 14(13), 3683; https://doi.org/10.3390/ma14133683 - 1 Jul 2021

Cited by 1 | Viewed by 3132

Abstract

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports [...] Read more.

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO

_{2}

. Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO

_{2}

are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus,

G_{0}

= 63 (3) GPa, and adiabatic bulk modulus,

K_{S 0}

= 142 (9) GPa, which is considerably lower than the isothermal bulk modulus,

K_{T 0} \sim

230 GPa, determined by high-pressure X-ray diffraction experiments. Full article

(This article belongs to the Special Issue Materials Behavior under Compression)

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16 pages, 6017 KiB

Open AccessEditor’s ChoiceArticle

On Developing a Hydrophobic Rubberized Cement Paste

by Chi-Yao Chen, Zih-Yao Shen and Maw-Tien Lee

Materials 2021, 14(13), 3687; https://doi.org/10.3390/ma14133687 - 1 Jul 2021

Cited by 7 | Viewed by 2703

Abstract

It is well known that most cement matrix materials are hydrophilic. For structural materials, hydrophilicity is harmful because the absorption of water will induce serious damage to these materials. In this study, crumb rubber was pretreated by partial oxidation and used as an [...] Read more.

It is well known that most cement matrix materials are hydrophilic. For structural materials, hydrophilicity is harmful because the absorption of water will induce serious damage to these materials. In this study, crumb rubber was pretreated by partial oxidation and used as an additive to develop a hydrophobic rubberized cement paste. The pretreated crumb rubber was investigated using Fourier-transform infrared spectrometry (FT-IR) to understand the function groups on its surface. The pyrolysis oil adsorbed on the surface of the crumb rubber was observed by FT-IR and nuclear magnetic resonance (NMR) spectroscopy. A colloid probe with calcium silicate hydrate (C–S–H) at the apex was prepared to measure the intermolecular interaction forces between the crumb rubber and the C-S-H using an atomic force microscope (AFM). Pure cement paste, cement paste with the as-received crumb rubber, and cement paste with pretreated crumb rubber were prepared for comparison. FT-IR, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to understand the microstructure of the pastes. The static contact angle was used as the index of the hydrophobicity of the pastes. Experimental results showed that the hardened cement paste containing partially oxidized crumb rubber had excellent hydrophobic properties with an insignificant reduction in the compressive strength. Full article

(This article belongs to the Special Issue Development and Research of Cementitious Materials)

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14 pages, 5625 KiB

Open AccessEditor’s ChoiceArticle

Effect of Gd³⁺ Substitution on Thermoelectric Power Factor of Paramagnetic Co²⁺-Doped Calcium Molybdato-Tungstates

by Bogdan Sawicki, Marta Karolewicz, Elżbieta Tomaszewicz, Monika Oboz, Tadeusz Groń, Zenon Kukuła, Sebastian Pawlus, Andrzej Nowok and Henryk Duda

Materials 2021, 14(13), 3692; https://doi.org/10.3390/ma14133692 - 1 Jul 2021

Cited by 8 | Viewed by 1824

Abstract

A series of Co²⁺-doped and Gd³⁺-co-doped calcium molybdato-tungstates, i.e., Ca_1−3x−yCo_y_xGd_2x(MoO₄)_1−3x(WO₄)_3x (CCGMWO), where 0 < x ≤ 0.2, y = 0.02 and represents vacancy, were successfully [...] Read more.

A series of Co²⁺-doped and Gd³⁺-co-doped calcium molybdato-tungstates, i.e., Ca_1−3x−yCo_y_xGd_2x(MoO₄)_1−3x(WO₄)_3x (CCGMWO), where 0 < x ≤ 0.2, y = 0.02 and represents vacancy, were successfully synthesized by high-temperature solid-state reaction method. XRD studies and diffuse reflectance UV–vis spectral analysis confirmed the formation of single, tetragonal scheelite-type phases with space group I4₁/a and a direct optical band gap above 3.5 eV. Magnetic and electrical measurements showed insulating behavior with n-type residual electrical conductivity, an almost perfect paramagnetic state with weak short-range ferromagnetic interactions, as well as an increase of spin contribution to the magnetic moment and an increase in the power factor with increasing gadolinium ions in the sample. Broadband dielectric spectroscopy measurements and dielectric analysis in the frequency representation showed a relatively high value of dielectric permittivity at low frequencies, characteristic of a space charge polarization and small values of both permittivity and loss tangent at higher frequencies. Full article

(This article belongs to the Special Issue Magnetocaloric and Thermoelectric Properties of Inorganic Materials)

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10 pages, 1221 KiB

Open AccessEditor’s ChoicePerspective

Metal-Organic Frameworks (MOFs)-Based Nanomaterials for Drug Delivery

by Mohammad Reza Saeb, Navid Rabiee, Masoud Mozafari and Ebrahim Mostafavi

Materials 2021, 14(13), 3652; https://doi.org/10.3390/ma14133652 - 30 Jun 2021

Cited by 77 | Viewed by 6543

Abstract

The composition and topology of metal-organic frameworks (MOFs) are exceptionally tailorable; moreover, they are extremely porous and represent an excellent Brunauer–Emmett–Teller (BET) surface area (≈3000–6000 m²·g⁻¹). Nanoscale MOFs (NMOFs), as cargo nanocarriers, have increasingly attracted the attention of scientists [...] Read more.

The composition and topology of metal-organic frameworks (MOFs) are exceptionally tailorable; moreover, they are extremely porous and represent an excellent Brunauer–Emmett–Teller (BET) surface area (≈3000–6000 m²·g⁻¹). Nanoscale MOFs (NMOFs), as cargo nanocarriers, have increasingly attracted the attention of scientists and biotechnologists during the past decade, in parallel with the evolution in the use of porous nanomaterials in biomedicine. Compared to other nanoparticle-based delivery systems, such as porous nanosilica, nanomicelles, and dendrimer-encapsulated nanoparticles, NMOFs are more flexible, have a higher biodegradability potential, and can be more easily functionalized to meet the required level of host–guest interactions, while preserving a larger and fully adjustable pore window in most cases. Due to these unique properties, NMOFs have the potential to carry anticancer cargos. In contrast to almost all porous materials, MOFs can be synthesized in diverse morphologies, including spherical, ellipsoidal, cubic, hexagonal, and octahedral, which facilitates the acceptance of various drugs and genes. Full article

(This article belongs to the Special Issue Advanced Coordination Polymers)

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14 pages, 4680 KiB

Open AccessEditor’s ChoiceArticle

The Fabrication of Portland Composite Cement Based on Pozzolan Napa Soil

by Mawardi Mawardi, Illyas Md Isa, Alizar Ulianas, Edtri Sintiara, Fadhlurrahman Mawardi and Rizky Zalmi Putra

Materials 2021, 14(13), 3638; https://doi.org/10.3390/ma14133638 - 29 Jun 2021

Cited by 2 | Viewed by 2958

Abstract

The objective of this study is to investigate Napa soil’s potential as an alternative additive in producing Portland composite cement. The Napa soil of Tanah Datar district, West Sumatra, Indonesia is a natural material which contains SiO₂ and Al₂O₃ [...] Read more.

The objective of this study is to investigate Napa soil’s potential as an alternative additive in producing Portland composite cement. The Napa soil of Tanah Datar district, West Sumatra, Indonesia is a natural material which contains SiO₂ and Al₂O₃ as its major components. The parameters used were the fineness of the cement particles, the amount left on a 45 μm sieve, the setting time, normal consistency, loss on ignition, insoluble parts, compressive strength and chemical composition. The composition of Napa soils (% w/w) used as variables include 4, 8, 12 and 16%. Furthermore, 8% pozzolan was used as a control in this research. The results showed that the compressive strength of Napa soil cement which contained 4% Napa soil was much better compared to that of the control on the 7th and 20th day. Furthermore, all the analyzed Napa soil cements met the standard of cement as stipulated in Indonesian National Standard, SNI 7064, 2016. Full article

(This article belongs to the Section Materials Chemistry)

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18 pages, 6772 KiB

Open AccessEditor’s ChoiceReview

Shear Band Evolution under Cyclic Loading and Fatigue Property in Metallic Glasses: A Brief Review

by Xiaodi Wang, Shaojie Wu, Ruitao Qu and Zhefeng Zhang

Materials 2021, 14(13), 3595; https://doi.org/10.3390/ma14133595 - 28 Jun 2021

Cited by 6 | Viewed by 2611

Abstract

The fatigue damage and fracture of metallic glasses (MGs) were reported to be dominated by shear band. While there exist several reviews about the fatigue behavior of MGs, an overview that mainly focuses on shear bands under cyclic loading is urgent, and is [...] Read more.

The fatigue damage and fracture of metallic glasses (MGs) were reported to be dominated by shear band. While there exist several reviews about the fatigue behavior of MGs, an overview that mainly focuses on shear bands under cyclic loading is urgent, and is of great importance for the understanding of fatigue mechanisms and properties. In this review paper, based on the previous research results, the shear band evolution under cyclic loading including shear band formation, propagation and cracking, was summarized and elucidated. Furthermore, one strategy of enhancing the fatigue property through manipulating the microstructure to suppress the shear band formation was proposed. Additionally, the applications of the effect of annealing treatment and processing condition on fatigue behaviors were utilized to verify the strategy. Finally, several future directions of fatigue research in MG were presented. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials)

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17 pages, 27769 KiB

Open AccessEditor’s ChoiceArticle

Bonding of Al6061 by Hot Compression Forming: A Computational and Experimental Study of Interface Conditions at Bonded Surfaces

by Brigit Mittelman, Michael Ben-Haroush, Ira Aloush, Linoy Mordechay and Elad Priel

Materials 2021, 14(13), 3598; https://doi.org/10.3390/ma14133598 - 28 Jun 2021

Cited by 2 | Viewed by 2406

Abstract

In recent years, there has been a growing interest in composite components, which may be designed to provide enhanced mechanical and physical effective properties. One of the methods available to produce such components is joining by plastic deformation, which results in metallurgical bonding [...] Read more.

In recent years, there has been a growing interest in composite components, which may be designed to provide enhanced mechanical and physical effective properties. One of the methods available to produce such components is joining by plastic deformation, which results in metallurgical bonding at the interface. However, the portions of the interface that are bonded and the inhomogeneity in the bonding strength achieved at the interface tend to be overlooked. In the present study, Al6061 beams were bonded, by hot compression (300–500 °C) to different degrees of reduction. The compression was followed by tensile debonding experiments and the revealed interface was microscopically characterized in order to determine the areas that were metallurgically bonded. The SEM characterization revealed that the actual bonded area is much smaller than the interface contact area. Thermo-mechanical finite element models of the compression stage were used to investigate the thermo-mechanical fields, which develop along the interface and influence the resulting bonding strength. The principal strain field patterns across the interface area were shown to be similar to the experimentally observed temperature-dependent bonding patterns. In addition, a quantitative criterion for bonding quality was implemented and shown to correlate with the experimental findings. Full article

(This article belongs to the Special Issue Hot Deformation and Microstructure Evolution of Metallic Materials)

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15 pages, 3054 KiB

Open AccessEditor’s ChoiceOpinion

Geopolymer Foams—Will They Ever Become a Viable Alternative to Popular Insulation Materials?—A Critical Opinion

by Michał Łach

Materials 2021, 14(13), 3568; https://doi.org/10.3390/ma14133568 - 25 Jun 2021

Cited by 52 | Viewed by 4989

Abstract

Over the last several years, there has been a large increase in interest in geopolymer materials, which are usually produced from waste materials, and their applications. The possibilities of application of geopolymers seem to be unlimited, and they are used in almost all [...] Read more.

Over the last several years, there has been a large increase in interest in geopolymer materials, which are usually produced from waste materials, and their applications. The possibilities of application of geopolymers seem to be unlimited, and they are used in almost all fields of technology. Their use as insulation materials appears promising due to their complete nonflammability and excellent strength. However, one limitation is their complex manufacturing process and lack of stability of the obtained geopolymer foams as well as difficulties in achieving such good insulation properties possessed by polyurethane foams, polystyrene, and wool. Hundreds of studies have already been performed on insulating geopolymer foams and various types of foaming agents, and their authors reported that foamed insulating geopolymers had a density starting from 200 kg/m³ and thermal conductivity from 0.04 W/mK. However, the repeatability of the obtained results on an industrial scale is questionable. It is still a challenge to obtain a geopolymer material with comparable properties as conventional insulation materials and to overcome the barriers associated with the successful implementation of geopolymer material as insulation in buildings and other applications on a mass scale. This paper provides a comprehensive review of the methods used for the production of foamed geopolymers and the best parameters obtained, as well as a summary of the most important information reported in the scientific literature. It also presents the results of a critical analysis of the feasibility of implementing this technology for mass deployment. In addition, the problems and limitations that are most often encountered with the implementation of geopolymer technology are discussed. Full article

(This article belongs to the Special Issue Functionalized Mineral Materials in Environmental and Civil Engineering, Ceramics, Foundry and Metals)

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12 pages, 2190 KiB

Open AccessEditor’s ChoiceArticle

ZrN Phase Formation, Hardening and Nitrogen Diffusion Kinetics in Plasma Nitrided Zircaloy-4

by Robert Balerio, Hyosim Kim, Andres Morell-Pacheco, Laura Hawkins, Ching-Heng Shiau and Lin Shao

Materials 2021, 14(13), 3572; https://doi.org/10.3390/ma14133572 - 25 Jun 2021

Cited by 5 | Viewed by 2363

Abstract

Plasma nitridation was conducted to modify the surfaces of Zircaloy-4. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman analysis were used to characterize microstructures and phases. Surface indentation and cross-sectional indentation were performed to evaluate mechanical property changes. Nitridation forms a [...] Read more.

Plasma nitridation was conducted to modify the surfaces of Zircaloy-4. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman analysis were used to characterize microstructures and phases. Surface indentation and cross-sectional indentation were performed to evaluate mechanical property changes. Nitridation forms a thin layer of ZrN phase, followed by a much deeper layer affected by nitrogen diffusion. The ZrN phase is confirmed by both TEM and Raman characterization. The Raman peaks of ZrN phase show a temperature dependence. The intensity increases with increasing nitridation temperatures, reaches a maximum at 700 °C, and then decreases at higher temperatures. The ZrN layer appears as continuous small columnar grains. The surface polycrystalline ZrN phase is harder than the bulk by a factor of ~8, and the nitrogen diffusion layer is harder by a factor of ~2–5. The activation energy of nitrogen diffusion was measured to be 2.88 eV. The thickness of the nitrogen-hardened layer is controllable by changing the nitridation temperature and duration. Full article

(This article belongs to the Special Issue Plasma Processing, Synthesis, and Nanomaterials)

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38 pages, 3772 KiB

Open AccessEditor’s ChoiceReview

Removal of Pesticides from Waters by Adsorption: Comparison between Synthetic Zeolites and Mesoporous Silica Materials. A Review

by Magdalena Andrunik and Tomasz Bajda

Materials 2021, 14(13), 3532; https://doi.org/10.3390/ma14133532 - 24 Jun 2021

Cited by 54 | Viewed by 4889

Abstract

Pesticides are pollutants found in wastewater due to increasing agricultural activities over the years. Inappropriate dosing of pesticides results in the dispersal of active ingredients in the environment. The complete removal of pesticides from wastewater is an immediate concern due to their high [...] Read more.

Pesticides are pollutants found in wastewater due to increasing agricultural activities over the years. Inappropriate dosing of pesticides results in the dispersal of active ingredients in the environment. The complete removal of pesticides from wastewater is an immediate concern due to their high toxicity and mobility. At present, adsorption is one of the most widely used methods for pesticide removal, in which synthetic zeolites and mesoporous silica materials are extensively applied. This article presents a systematic and comparative review of the applications and comparison of these adsorbents, based on the data reported in the literature. The paper summarizes the information collected from various studies, including the type of adsorbents and pesticides used, experimental conditions, and results of each work. The studies analyzed were laboratory-based and show potential advantages for the treatment of pesticide-bearing waters using functionalized and unfunctionalized synthetic zeolites and mesoporous silica materials. As a whole, functionalized materials are reported to exhibit better removal performance for different pesticides than conventional materials. It is expected that the results of this review will help researchers to establish a powerful strategy for the abatement of pesticides in wastewater. Full article

(This article belongs to the Special Issue Functionalized Mineral Materials in Environmental and Civil Engineering, Ceramics, Foundry and Metals)

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12 pages, 1561 KiB

Open AccessEditor’s ChoiceArticle

Characterization and Combustion Behavior of Single-Use Masks Used during COVID-19 Pandemic

by Ewa Maria Szefer, Tomasz Mariusz Majka and Krzysztof Pielichowski

Materials 2021, 14(13), 3501; https://doi.org/10.3390/ma14133501 - 23 Jun 2021

Cited by 24 | Viewed by 3101

Abstract

This work aims to study the thermal degradation and combustion behavior of single-use masks commonly used during the COVID-19 pandemic. The sudden increase in plastic waste underlines the crucial need for a proper disposal method. Therefore, to develop a suitable method of thermal [...] Read more.

This work aims to study the thermal degradation and combustion behavior of single-use masks commonly used during the COVID-19 pandemic. The sudden increase in plastic waste underlines the crucial need for a proper disposal method. Therefore, to develop a suitable method of thermal disposal, it is first necessary to identify the primary waste materials and then study their thermal and flammability behaviors using thermal analysis methods. This research focuses on the characterization of individual parts of the masks, their thermal degradation, and pyrolysis processes via FTIR, TG, and MCC analyses. FTIR analysis indicated that all three masks were made out of polypropylene sheets, while two of the ear straps contained polyamide 6. One of the samples was composed mainly of poly (ethylene terephthalate) fiber and thin inner EPDM rubber. The EPDM ear strap left the highest residue and showed the lowest flammability among all samples. The analysis of heat of combustion and thermogravimetry shows that the most heat is generated above 450 °C. Therefore, for the disposal of single-use masks to be effective, it should be carried out in the temperature range from 450 to 750 °C. Full article

(This article belongs to the Section Materials Chemistry)

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18 pages, 3099 KiB

Open AccessEditor’s ChoiceArticle

Chemo-Enzymatic Baeyer–Villiger Oxidation Facilitated with Lipases Immobilized in the Supported Ionic Liquid Phase

by Anna Szelwicka, Anna Wolny, Miroslawa Grymel, Sebastian Jurczyk, Slawomir Boncel and Anna Chrobok

Materials 2021, 14(13), 3443; https://doi.org/10.3390/ma14133443 - 22 Jun 2021

Cited by 11 | Viewed by 3202

Abstract

A novel method for chemo-enzymatic Baeyer–Villiger oxidation of cyclic ketones in the presence of supported ionic liquid-like phase biocatalyst was designed. In this work, multi-walled carbon nanotubes were applied as a support for ionic liquids which were anchored to nanotubes covalently by amide [...] Read more.

A novel method for chemo-enzymatic Baeyer–Villiger oxidation of cyclic ketones in the presence of supported ionic liquid-like phase biocatalyst was designed. In this work, multi-walled carbon nanotubes were applied as a support for ionic liquids which were anchored to nanotubes covalently by amide or imine bonds. Next, lipases B from Candida antarctica, Candida rugosa, or Aspergillus oryzae were immobilized on the prepared materials. The biocatalysts were characterized using various techniques, like thermogravimetry, IR spectroscopy, XPS, elemental analysis, and SEM-EDS microscopy. In the proposed approach, a biocatalyst consisting of a lipase as an active phase allowed the generation of peracid in situ from the corresponding precursor and a green oxidant–hydrogen peroxide. The activity and stability of the obtained biocatalysts in the model oxidation of 2-adamantanone were demonstrated. High conversion of substrate (92%) was achieved under favorable conditions (toluene: n-octanoic acid ratio 1:1 = v:v, 35% aq. H₂O₂ 2 eq., 0.080 g of biocatalyst per 1 mmol of ketone at 20 °C, reaction time 4 h) with four reaction cycles without a drop in its activity. Our ‘properties-by-design’ approach is distinguished by its short reaction time at low temperature and higher thermal stability in comparison with other biocatalysts presented in the literature reports. Full article

(This article belongs to the Special Issue Heterogeneous Catalysts Synthesis and Characterization)

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10 pages, 36578 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of the Composite Mechanism of Nano-Fe₂O₃/Asphalt Based on Molecular Simulation and Experiments

by Yuhao He, Qing Zeng, Yaru Liu, Peng Liu, Yuqin Zeng, Zhenghong Xu and Qicheng Liu

Materials 2021, 14(12), 3425; https://doi.org/10.3390/ma14123425 - 21 Jun 2021

Cited by 1 | Viewed by 2374

Abstract

Asphalt, as an indispensable binder in road paving, plays an important role in transportation development. However, the mechanism of action between the modifier and asphalt cannot be fully explained by the existing test methods. This paper combines molecular simulations with experiments to provide [...] Read more.

Asphalt, as an indispensable binder in road paving, plays an important role in transportation development. However, the mechanism of action between the modifier and asphalt cannot be fully explained by the existing test methods. This paper combines molecular simulations with experiments to provide a research and analysis tool to evaluate the “structure−performance” relationship of asphalt. From the trend of experimental results, the optimal content of Nano-Fe₂O₃ is 1% to 3%. The AFM micrograph of the asphalt material shows that at 3%, the Nano-Fe₂O₃ can be effectively dispersed in the asphalt and the unique “ bee structures “ of the asphalt can be adsorbed around the modifier. Molecular dynamics studies and results show that when Nano-Fe₂O₃ are incorporated into the asphalt and have a strong adsorption force on the colloidal structure of asphalt, the “ bee structures “ can be adsorbed around the Nano-Fe₂O₃. In the range of 208–543 K, the sol-gel structure of asphalt in the Nano-Fe₂O₃/asphalt composite system is gradually disrupted. Full article

(This article belongs to the Section Construction and Building Materials)

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19 pages, 9059 KiB

Open AccessEditor’s ChoiceArticle

A Cellulose-Derived Nanofibrous MnO₂-TiO₂-Carbon Composite as Anodic Material for Lithium-Ion Batteries

by Shun Li, Ming Yang, Guijin He, Dongmei Qi and Jianguo Huang

Materials 2021, 14(12), 3411; https://doi.org/10.3390/ma14123411 - 20 Jun 2021

Cited by 3 | Viewed by 2668

Abstract

A bio-inspired nanofibrous MnO₂-TiO₂-carbon composite was prepared by utilizing natural cellulosic substances (e.g., ordinary quantitative ashless filter paper) as both the carbon source and structural matrix. Mesoporous MnO₂ nanosheets were densely immobilized on an ultrathin titania film precoated [...] Read more.

A bio-inspired nanofibrous MnO₂-TiO₂-carbon composite was prepared by utilizing natural cellulosic substances (e.g., ordinary quantitative ashless filter paper) as both the carbon source and structural matrix. Mesoporous MnO₂ nanosheets were densely immobilized on an ultrathin titania film precoated with cellulose-derived carbon nanofibers, which gave a hierarchical MnO₂-TiO₂-carbon nanoarchitecture and exhibited excellent electrochemical performances when used as an anodic material for lithium-ion batteries. The MnO₂-TiO₂-carbon composite with a MnO₂ content of 47.28 wt % exhibited a specific discharge capacity of 677 mAh g⁻¹ after 130 repeated charge/discharge cycles at a current rate of 100 mA g⁻¹. The contribution percentage of MnO₂ in the composite material is equivalent to 95.1% of the theoretical capacity of MnO₂ (1230 mAh g⁻¹). The ultrathin TiO₂ precoating layer with a thickness ca. 2 nm acts as a crucial interlayer that facilitates the growth of well-organized MnO₂ nanosheets onto the surface of the titania-carbon nanofibers. Due to the interweaved network structures of the carbon nanofibers and the increased content of the immobilized MnO₂, the exfoliation and aggregation, as well as the large volume change of the MnO₂ nanosheets, are significantly inhibited; thus, the MnO₂-TiO₂-carbon electrodes displayed outstanding cycling performance and a reversible rate capability during the Li⁺ insertion/extraction processes. Full article

(This article belongs to the Special Issue Feature Paper in Section Materials Chemistry)

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37 pages, 5670 KiB

Open AccessEditor’s ChoiceReview

Lignin-Based High-Performance Fibers by Textile Spinning Techniques

by Yanhong Jin, Jiaxian Lin, Yu Cheng and Chunhong Lu

Materials 2021, 14(12), 3378; https://doi.org/10.3390/ma14123378 - 18 Jun 2021

Cited by 39 | Viewed by 6079

Abstract

As a major component of lignocellulosic biomass, lignin is one of the largest natural resources of biopolymers and, thus, an abundant and renewable raw material for products, such as high-performance fibers for industrial applications. Direct conversion of lignin has long been investigated, but [...] Read more.

As a major component of lignocellulosic biomass, lignin is one of the largest natural resources of biopolymers and, thus, an abundant and renewable raw material for products, such as high-performance fibers for industrial applications. Direct conversion of lignin has long been investigated, but the fiber spinning process for lignin is difficult and the obtained fibers exhibit unsatisfactory mechanical performance mainly due to the amorphous chemical structure, low molecular weight of lignin, and broad molecular weight distribution. Therefore, different textile spinning techniques, modifications of lignin, and incorporation of lignin into polymers have been and are being developed to increase lignin’s spinnability and compatibility with existing materials to yield fibers with better mechanical performance. This review presents the latest advances in the textile fabrication techniques, modified lignin-based high-performance fibers, and their potential in the enhancement of the mechanical performance. Full article

(This article belongs to the Special Issue Fiber Spinning: Materials & Techniques)

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12 pages, 5455 KiB

Open AccessEditor’s ChoiceArticle

Eco-Friendly Lead-Free Solder Paste Printing via Laser-Induced Forward Transfer for the Assembly of Ultra-Fine Pitch Electronic Components

by Marina Makrygianni, Filimon Zacharatos, Kostas Andritsos, Ioannis Theodorakos, Dimitris Reppas, Nikolaos Oikonomidis, Christos Spandonidis and Ioanna Zergioti

Materials 2021, 14(12), 3353; https://doi.org/10.3390/ma14123353 - 17 Jun 2021

Cited by 9 | Viewed by 3341

Abstract

Current challenges in printed circuit board (PCB) assembly require high-resolution deposition of ultra-fine pitch components (<0.3 mm and <60 μm respectively), high throughput and compatibility with flexible substrates, which are poorly met by the conventional deposition techniques (e.g., stencil printing). Laser-Induced Forward Transfer [...] Read more.

Current challenges in printed circuit board (PCB) assembly require high-resolution deposition of ultra-fine pitch components (<0.3 mm and <60 μm respectively), high throughput and compatibility with flexible substrates, which are poorly met by the conventional deposition techniques (e.g., stencil printing). Laser-Induced Forward Transfer (LIFT) constitutes an excellent alternative for assembly of electronic components: it is fully compatible with lead-free soldering materials and offers high-resolution printing of solder paste bumps (<60 μm) and throughput (up to 10,000 pads/s). In this work, the laser-process conditions which allow control over the transfer of solder paste bumps and arrays, with form factors in line with the features of fine pitch PCBs, are investigated. The study of solder paste as a function of donor/receiver gap confirmed that controllable printing of bumps containing many microparticles is feasible for a gap < 100 μm from a donor layer thickness set at 100 and 150 μm. The transfer of solder bumps with resolution < 100 μm and solder micropatterns on different substrates, including PCB and silver pads, have been achieved. Finally, the successful operation of a LED interconnected to a pin connector bonded to a laser-printed solder micro-pattern was demonstrated. Full article

(This article belongs to the Special Issue Materials Light Life)

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17 pages, 6945 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Sewage Sludge Content and Sintering Temperature on Selected Properties of Lightweight Expanded Clay Aggregate

by Jolanta Latosińska, Maria Żygadło and Przemysław Czapik

Materials 2021, 14(12), 3363; https://doi.org/10.3390/ma14123363 - 17 Jun 2021

Cited by 7 | Viewed by 2549

Abstract

Wastewater treatment processes produce sewage sludge (SS), which, in line with environmental sustainability principles, can be a valuable source of matter in the production of lightweight expanded clay aggregate (LECA). The literature on the influence of SS content and sintering temperature on the [...] Read more.

Wastewater treatment processes produce sewage sludge (SS), which, in line with environmental sustainability principles, can be a valuable source of matter in the production of lightweight expanded clay aggregate (LECA). The literature on the influence of SS content and sintering temperature on the properties of LECA is scarce. This paper aims to statistically evaluate the effects of SS content and sintering temperature on LECA physical properties. Total porosity, pore volume, and apparent density were determined with the use of a density analyzer. A helium pycnometer was utilized to determine the specific density. Closed porosity was calculated. The test results demonstrated a statistically significant influence of the SS content on the specific density and water absorption of LECA. The sintering temperature had a significant effect on the specific density, apparent density, total porosity, closed porosity, total volume of pores, and water absorption. It was proved that a broad range of the SS content is admissible in the raw material mass for the production of LECA. Full article

(This article belongs to the Special Issue Sustainability in Construction and Building Materials)

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21 pages, 22313 KiB

Open AccessEditor’s ChoiceArticle

New Grain Formation Mechanisms during Powder Bed Fusion

by Alexander M. Rausch, Julian Pistor, Christoph Breuning, Matthias Markl and Carolin Körner

Materials 2021, 14(12), 3324; https://doi.org/10.3390/ma14123324 - 16 Jun 2021

Cited by 10 | Viewed by 3330

Abstract

Tailoring the mechanical properties of parts by influencing the solidification conditions is a key topic of powder bed fusion. Depending on the application, single crystalline, columnar, or equiaxed microstructures are desirable. To produce single crystals or equiaxed microstructures, the control of nucleation is [...] Read more.

Tailoring the mechanical properties of parts by influencing the solidification conditions is a key topic of powder bed fusion. Depending on the application, single crystalline, columnar, or equiaxed microstructures are desirable. To produce single crystals or equiaxed microstructures, the control of nucleation is of outstanding importance. Either it should be avoided or provoked. There are also applications, such as turbine blades, where both microstructures at different locations are required. Here, we investigate nucleation at the melt-pool border during the remelting of CMSX-4^® samples built using powder bed fusion. We studied the difference between remelting as-built and homogenized microstructures. We identified two new mechanisms that led to grain formation at the beginning of solidification. Both mechanisms involved a change in the solidification microstructure from the former remelted and newly forming material. For the as-built samples, a discrepancy between the former and new dendrite arm spacing led to increased interdentritic undercooling at the beginning of solidification. For the heat-treated samples, the collapse of a planar front led to new grains. To identify these mechanisms, we conducted experimental and numerical investigations. The identification of such mechanisms during powder bed fusion is a fundamental prerequisite to controlling the solidification conditions to produce single crystalline and equiaxed microstructures. Full article

(This article belongs to the Special Issue Microstructure and Mechanics of Metallic Materials)

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14 pages, 3350 KiB

Open AccessEditor’s ChoiceArticle

Dual Covalent Cross-Linking Networks in Polynorbornene: Comparison of Shape Memory Performance

by Haotian Zhao, Qinghong Zhang, Xinlong Wen, Gongliang Wang, Xiaowen Gong and Xinyan Shi

Materials 2021, 14(12), 3249; https://doi.org/10.3390/ma14123249 - 12 Jun 2021

Cited by 5 | Viewed by 2576

Abstract

In this work, tetrakis(dimethyllamino)ethylene (TDAE) plasticized polynorbornene (PNB) was used as the matrix, sulfur (S) and dicumyl peroxide (DCP) were simultaneously used as crosslinking agents to construct dual covalent cross-linking networks in PNB. The effects of different amounts of cross-linkers on the crosslinking [...] Read more.

In this work, tetrakis(dimethyllamino)ethylene (TDAE) plasticized polynorbornene (PNB) was used as the matrix, sulfur (S) and dicumyl peroxide (DCP) were simultaneously used as crosslinking agents to construct dual covalent cross-linking networks in PNB. The effects of different amounts of cross-linkers on the crosslinking degree, mechanical property, glass transition temperature, and PNB shape memory performance were investigated. Two crosslinking mechanisms were examined by Fourier transform infrared spectrometer and Raman spectrometer. The results showed that sulfur-rich cross-linked PNB exhibited a higher crosslinking degree, tensile strength, and slightly higher glass transition temperature than the DCP-rich system. Cross-linked PNB presented better shape memory performance than the uncross-linked one. Sulfur-rich cross-linked PNB showed even better shape memory behavior than the DCP-rich system, both with a shape fixation ratio of over 99% and a shape recovery ratio of over 90%. The reaction mechanism of sulfur and DCP in cross-linking PNB was different. Sulfur reacted with the α-H in PNB to form monosulfide bonds, disulfide bonds, and polysulfide bonds in PNB and the number of polysulfide bonds increased with increased amounts of sulfur. DCP reacted with the double bonds in PNB to form C-C covalent bond crosslinking networks. The crosslinking mechanism revealed that the sulfur-containing cross-linked bonds, especially polysulfide bonds, were more flexible and bore large deformation, which gave the PNB excellent mechanical properties and ensured a higher shape entropy elastic recovery ratio. Full article

(This article belongs to the Special Issue Self-Healing Materials and Devices)

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23 pages, 4617 KiB

Open AccessEditor’s ChoiceReview

Biological Inspirations: Iron Complexes Mimicking the Catechol Dioxygenases

by Karolina Kałduńska, Anna Kozakiewicz, Magdalena Wujak and Andrzej Wojtczak

Materials 2021, 14(12), 3250; https://doi.org/10.3390/ma14123250 - 12 Jun 2021

Cited by 8 | Viewed by 3737

Abstract

Within the broad group of Fe non-heme oxidases, our attention was focused on the catechol 1,2- and 2,3-dioxygenases, which catalyze the oxidative cleavage of aromatic rings. A large group of Fe complexes with N/O ligands, ranging from N₃ to N₂O [...] Read more.

Within the broad group of Fe non-heme oxidases, our attention was focused on the catechol 1,2- and 2,3-dioxygenases, which catalyze the oxidative cleavage of aromatic rings. A large group of Fe complexes with N/O ligands, ranging from N₃ to N₂O₂S, was developed to mimic the activity of these enzymes. The Fe complexes discussed in this work can mimic the intradiol/extradiol catechol dioxygenase reaction mechanism. Electronic effects of the substituents in the ligand affect the Lewis acidity of the Fe center, increasing the ability to activate dioxygen and enhancing the catalytic activity of the discussed biomimetic complexes. The ligand architecture, the geometric isomers of the complexes, and the substituent steric effects significantly affect the ability to bind the substrate in a monodentate and bidentate manner. The substrate binding mode determines the preferred mechanism and, consequently, the main conversion products. The preferred mechanism of action can also be affected by the solvents and their ability to form the stable complexes with the Fe center. The electrostatic interactions of micellar media, similar to SDS, also control the intradiol/extradiol mechanisms of the catechol conversion by discussed biomimetics. Full article

(This article belongs to the Special Issue Research of Organic Molecules and Materials for Biological Application)

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9 pages, 1173 KiB

Open AccessEditor’s ChoiceArticle

The Formation of Cr-Al Spinel under a Reductive Atmosphere

by Oleksandr Shtyka, Waldemar Maniukiewicz, Radoslaw Ciesielski, Adam Kedziora, Viktar Shatsila, Tomasz Sierański and Tomasz Maniecki

Materials 2021, 14(12), 3218; https://doi.org/10.3390/ma14123218 - 10 Jun 2021

Cited by 6 | Viewed by 2229

Abstract

In the present work, for the first time, the possibility of formation of CrAl₂O₄ was shown from the equimolar mixture of co-precipitated Al₂O₃ and Cr₂O₃ oxides under a reductive environment. The crystallographic properties of [...] Read more.

In the present work, for the first time, the possibility of formation of CrAl₂O₄ was shown from the equimolar mixture of co-precipitated Al₂O₃ and Cr₂O₃ oxides under a reductive environment. The crystallographic properties of the formed compound were calculated using the DICVOL procedure. It was determined that it has a cubic crystal structure with space group Fd-3m and a unit cell parameter equal to 8.22(3) Å. The formed CrAl₂O₄ is not stable under ambient conditions and easily undergoes oxidation to α-Al₂O₃ and α-Cr₂O₃. The overall sequence of the phase transformations of co-precipitated oxides leading to the formation of spinel structure is proposed. Full article

(This article belongs to the Special Issue The Research of Inorganic Nanomaterials)

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13 pages, 10780 KiB

Open AccessEditor’s ChoiceArticle

Covalent Triazine Frameworks Based on the First Pseudo-Octahedral Hexanitrile Monomer via Nitrile Trimerization: Synthesis, Porosity, and CO₂ Gas Sorption Properties

by Isabelle D. Wessely, Alexandra M. Schade, Subarna Dey, Asamanjoy Bhunia, Alexander Nuhnen, Christoph Janiak and Stefan Bräse

Materials 2021, 14(12), 3214; https://doi.org/10.3390/ma14123214 - 10 Jun 2021

Cited by 13 | Viewed by 3480

Abstract

Herein, we report the first synthesis of covalent triazine-based frameworks (CTFs) based on a hexanitrile monomer, namely the novel pseudo-octahedral hexanitrile 1,4-bis(tris(4′-cyano-phenyl)methyl)benzene 1 using both ionothermal reaction conditions with ZnCl₂ at 400 °C and the milder reaction conditions with the strong Brønsted [...] Read more.

Herein, we report the first synthesis of covalent triazine-based frameworks (CTFs) based on a hexanitrile monomer, namely the novel pseudo-octahedral hexanitrile 1,4-bis(tris(4′-cyano-phenyl)methyl)benzene 1 using both ionothermal reaction conditions with ZnCl₂ at 400 °C and the milder reaction conditions with the strong Brønsted acid trifluoromethanesulfonic acid (TFMS) at room temperature. Additionally, the hexanitrile was combined with different di-, tri-, and tetranitriles as a second linker based on recent work of mixed-linker CTFs, which showed enhanced carbon dioxide captures. The obtained framework structures were characterized via infrared (IR) spectroscopy, elemental analysis, scanning electron microscopy (SEM), and gas sorption measurements. Nitrogen adsorption measurements were performed at 77 K to determine the Brunauer-Emmett-Teller (BET) surface areas range from 493 m²/g to 1728 m²/g (p/p₀ = 0.01–0.05). As expected, the framework CTF-hex6 synthesized from 1 with ZnCl₂ possesses the highest surface area for nitrogen adsorption. On the other hand, the mixed framework structure CTF-hex4 formed from the hexanitrile 1 and 1,3,5 tricyanobenzene (4) shows the highest uptake of carbon dioxide and methane of 76.4 cm³/g and 26.6 cm³/g, respectively, at 273 K. Full article

(This article belongs to the Special Issue Advances in Microporous and Mesoporous Materials)

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18 pages, 5543 KiB

Open AccessEditor’s ChoiceArticle

Elemental and Thermochemical Analyses of Materials after Electrical Discharge Machining in Water: Focus on Ni and Zn

by Sergey N. Grigoriev, Marina A. Volosova, Anna A. Okunkova, Sergey V. Fedorov, Khaled Hamdy and Pavel A. Podrabinnik

Materials 2021, 14(12), 3189; https://doi.org/10.3390/ma14123189 - 9 Jun 2021

Cited by 7 | Viewed by 2315

Abstract

The mechanism of the material destruction under discharge pulses and material removal mechanism based on the thermochemical nature of the electrical erosion during electrical discharge machining of conductive materials were researched. The experiments were conducted for two structural materials used in the aerospace [...] Read more.

The mechanism of the material destruction under discharge pulses and material removal mechanism based on the thermochemical nature of the electrical erosion during electrical discharge machining of conductive materials were researched. The experiments were conducted for two structural materials used in the aerospace industry, namely austenite anticorrosion X10CrNiTi18-10 (12kH18N10T) steel and 2024 (D16) duralumin, machined by a brass tool of 0.25 mm in diameter in a deionized water medium. The optimized wire electrical discharge machining factors, measured discharge gaps (recommended offset is 170–175 µm and 195–199 µm, respectively), X-ray photoelectron spectroscopy for both types of materials are reported. Elemental analysis showed the presence of metallic Zn, CuO, iron oxides, chromium oxides, and 58.07% carbides (precipitation and normal atmospheric contamination) for steel and the presence of metallic Zn, CuO, ZnO, aluminum oxide, and 40.37% carbides (contamination) for duralumin. For the first time, calculating the thermochemistry parameters for reactions of Zn(OH)₂, ZnO, and NiO formation was produced. The ability of Ni of chrome–nickel steel to interact with Zn of brass electrode was thermochemically proved. The standard enthalpy of the Ni₅Zn₂₁ intermetallic compound formation (erosion dust) ΔH⁰₂₉₈ is −225.96 kJ/mol; the entropy of the crystalline phase S^c_int is 424.64 J/(mol·K). Full article

(This article belongs to the Special Issue Surface Modification of Metallic Materials)

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14 pages, 4240 KiB

Open AccessEditor’s ChoiceArticle

Assessment of Electrical Resistivity and Oxygen Diffusion Coefficient of Cementitious Materials from Microstructure Features

by Renzhan Zhou, Qiang Li, Jiandong Wang, Kewen Zhou, Rui He and Chuanqing Fu

Materials 2021, 14(12), 3141; https://doi.org/10.3390/ma14123141 - 8 Jun 2021

Cited by 5 | Viewed by 2797

Abstract

A newly proposed modified non-contact electrical resistivity measurement was used to test the resistivity of concrete and cement mortar. The oxygen diffusion coefficients of concrete and mortar were determined by a gas diffusion measurement, and the capillary porosity of concrete and cement mortar [...] Read more.

A newly proposed modified non-contact electrical resistivity measurement was used to test the resistivity of concrete and cement mortar. The oxygen diffusion coefficients of concrete and mortar were determined by a gas diffusion measurement, and the capillary porosity of concrete and cement mortar was measured by mercury intrusion porosimetry (MIP) measurement. The obtained electrical resistivity and capillary porosity results were verified with other researchers’ data, the measured electrical resistivity results can be estimated by a simple equation from the capillary porosity results. The obtained oxygen diffusion coefficient results were quantitatively correlated with capillary porosity and electrical resistivity measurement results. The proposed equations can be practically used to assess the electrical resistivity and oxygen diffusion coefficient. Full article

(This article belongs to the Special Issue Sustainable, Self-Healing, and Functional Building Materials)

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12 pages, 2765 KiB

Open AccessEditor’s ChoiceArticle

Colored Tattoo Ink Screening Method with Optical Tissue Phantoms and Raman Spectroscopy

by Filip Sadura, Maciej S. Wróbel and Katarzyna Karpienko

Materials 2021, 14(12), 3147; https://doi.org/10.3390/ma14123147 - 8 Jun 2021

Cited by 4 | Viewed by 3547

Abstract

Due to the increasing popularity of tattoos among the general population, to ensure their safety and quality, there is a need to develop reliable and rapid methods for the analysis of the composition of tattoo inks, both in the ink itself and in [...] Read more.

Due to the increasing popularity of tattoos among the general population, to ensure their safety and quality, there is a need to develop reliable and rapid methods for the analysis of the composition of tattoo inks, both in the ink itself and in already existing tattoos. This paper presents the possibility of using Raman spectroscopy to examine tattoo inks in biological materials. We have developed optical tissue phantoms mimicking the optical scattering coefficient typical for human dermis as a substitute for an in vivo study. The material employed herein allows for mimicking the tattoo-making procedure. We investigated the effect of the scattering coefficient of the matrix in which the ink is located, as well as its chemical compositions on the spectra. Raman surface line scanning has been carried out for each ink in the skin phantom to establish the spatial gradient of ink concentration distribution. This ensures the ability to detect miniature concentrations for a tattoo margin assessment. An analysis and comparison of the spectra of the inks and the tattooed inks in the phantoms are presented. We recommend the utilization of Raman spectroscopy as a screening method to enforce the tattoo ink safety legislations as well as an early medical diagnostic screening tool. Full article

(This article belongs to the Special Issue Advanced Materials for Biophotonics Applications)

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14 pages, 5650 KiB

Open AccessEditor’s ChoiceArticle

Effect of Confining Conditions on the Hydraulic Conductivity Behavior of Fiber-Reinforced Lime Blended Semiarid Soil

by Abdullah Ali Shaker, Mosleh Ali Al-Shamrani, Arif Ali Baig Moghal and Kopparthi Venkata Vydehi

Materials 2021, 14(11), 3120; https://doi.org/10.3390/ma14113120 - 6 Jun 2021

Cited by 14 | Viewed by 3582

Abstract

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic [...] Read more.

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (k_sat) were determined. For FC fibers, an increase in fiber dosage caused k_sat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, k_sat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering (2nd Edition))

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11 pages, 2499 KiB

Open AccessEditor’s ChoiceArticle

Reinforcing Increase of ΔT_c in MgB₂ Smart Meta-Superconductors by Adjusting the Concentration of Inhomogeneous Phases

by Yongbo Li, Guangyu Han, Hongyan Zou, Li Tang, Honggang Chen and Xiaopeng Zhao

Materials 2021, 14(11), 3066; https://doi.org/10.3390/ma14113066 - 4 Jun 2021

Cited by 8 | Viewed by 3522

Abstract

Incorporating with inhomogeneous phases with high electroluminescence (EL) intensity to prepare smart meta-superconductors (SMSCs) is an effective method for increasing the superconducting transition temperature (T_c) and has been confirmed in both MgB₂ and Bi(Pb)SrCaCuO systems. However, the increase of [...] Read more.

Incorporating with inhomogeneous phases with high electroluminescence (EL) intensity to prepare smart meta-superconductors (SMSCs) is an effective method for increasing the superconducting transition temperature (T_c) and has been confirmed in both MgB₂ and Bi(Pb)SrCaCuO systems. However, the increase of ΔT_c (ΔT_c = T_c ‒ T_cpure) has been quite small because of the low optimal concentrations of inhomogeneous phases. In this work, three kinds of MgB₂ raw materials, namely, ^aMgB₂, ^bMgB₂, and ^cMgB₂, were prepared with particle sizes decreasing in order. Inhomogeneous phases, Y₂O₃:Eu³⁺ and Y₂O₃:Eu³⁺/Ag, were also prepared and doped into MgB₂ to study the influence of doping concentration on the ΔT_c of MgB₂ with different particle sizes. Results show that reducing the MgB₂ particle size increases the optimal doping concentration of inhomogeneous phases, thereby increasing ΔT_c. The optimal doping concentrations for ^aMgB₂, ^bMgB₂, and ^cMgB₂ are 0.5%, 0.8%, and 1.2%, respectively. The corresponding ΔT_c values are 0.4, 0.9, and 1.2 K, respectively. This work open a new approach to reinforcing increase of ΔT_c in MgB₂ SMSCs. Full article

(This article belongs to the Special Issue Advances in Superconducting Materials: Characterization, Properties and Applications)

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12 pages, 760 KiB

Open AccessEditor’s ChoiceArticle

Efficient Triazine Derivatives for Collagenous Materials Stabilization

by Vanessa Gatto, Silvia Conca, Noemi Bardella and Valentina Beghetto

Materials 2021, 14(11), 3069; https://doi.org/10.3390/ma14113069 - 4 Jun 2021

Cited by 15 | Viewed by 3389

Abstract

Nowadays, the need to reduce plastic waste and scantly biodegradable fossil-based products is of great importance. The use of leather as an alternative to synthetic materials is gaining renewed interest, but it is fundamental that any alternative to plastic-based materials should not generate [...] Read more.

Nowadays, the need to reduce plastic waste and scantly biodegradable fossil-based products is of great importance. The use of leather as an alternative to synthetic materials is gaining renewed interest, but it is fundamental that any alternative to plastic-based materials should not generate an additional environmental burden. In the present work, a simple protocol for collagen stabilization mediated by 2-chloro-4,6-diethoxy-1,3,5-triazine (CDET) and a tert-amine has been described. Different tert-amines were tested in combination with CDET in a standard amidation reaction between 2-phenylethylamine and benzoic acid. Best performing condensation systems have been further tested for the cross-linking of both collagen powder and calf hides. The best results were achieved with CDET/NMM giving high-quality leather with improved environmental performances. Full article

(This article belongs to the Special Issue Environmentally Sustainable Solutions to Polymeric Waste Materials)

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21 pages, 9843 KiB

Open AccessEditor’s ChoiceArticle

Laser Beam Drilling of Inconel 718 and Its Effect on Mechanical Properties Determined by Static Uniaxial Tensile Testing at Room and Elevated Temperatures

by Jana Petrů, Marek Pagáč and Martin Grepl

Materials 2021, 14(11), 3052; https://doi.org/10.3390/ma14113052 - 3 Jun 2021

Cited by 5 | Viewed by 2962

Abstract

Particularly in the aerospace industry and its applications, recast layers and microcracks in base materials are considered to be undesirable side effects of the laser beam machining process, and can have a significant influence on the resulting material behavior and its properties. The [...] Read more.

Particularly in the aerospace industry and its applications, recast layers and microcracks in base materials are considered to be undesirable side effects of the laser beam machining process, and can have a significant influence on the resulting material behavior and its properties. The paper deals with the evaluation of the affected areas of the Inconel 718 nickel-base superalloy after its drilling by a laser beam. In addition, measurements and analyses of the mechanical properties were performed to investigate how these material properties were affected. It is supposed that the mechanical properties of the base material will be negatively affected by this accompanying machining process phenomenon. As a verification method of the final mechanical properties of the material, static uniaxial tension tests were performed on experimental flat shape samples made of the same material (Inconel 718) and three different thicknesses (0.5/1.0/1.6 mm) which best represented the practical needs of aerospace sheet metal applications. There was one hole that was drilled with an angle of under 70° in the middle of the sample length. Additionally, there were several sets of samples for each material thickness that were drilled by both conventional and nonconventional methods to emphasize the effect of the recast layer on the base material. In total, 192 samples were evaluated within the experiment. Moreover, different tensile testing temperatures (room as 23 °C and elevated as 550 °C) were determined for all the circumstances of the individual experiments to simulate real operation load material behavior. As a result, the dependencies between the amount of the recast layer and the length of the microcracks observed after the material was machined by laser beam, and the decrease in the mechanical properties of the base material, were determined. Full article

(This article belongs to the Special Issue Composites, Alloys and Advanced Processes for Manufacturing in Aeronautics and Aerospace)

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