Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
6.4
3.2
Journals
Materials
Editor’s Choice
materials-logo

Journal Menu

► Journal Menu

Journal Browser

► Journal Browser
share announcement

Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

Order results
Result details
Results per page
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
31 pages, 16563 KB  
Article
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 4138
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)
►▼ Show Figures

Figure 1

14 pages, 2402 KB  
Article
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 8 | Viewed by 1966
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)
►▼ Show Figures

Figure 1

43 pages, 8205 KB  
Review
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 202 | Viewed by 18853
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)
►▼ Show Figures

Figure 1

13 pages, 7431 KB  
Article
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 11 | Viewed by 2613
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)
►▼ Show Figures

Figure 1

12 pages, 7459 KB  
Article
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 10 | Viewed by 2598
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)
►▼ Show Figures

Figure 1

21 pages, 5802 KB  
Article
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 4295
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)
►▼ Show Figures

Graphical abstract

14 pages, 36934 KB  
Article
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 29 | Viewed by 4116
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)
►▼ Show Figures

Figure 1

15 pages, 4068 KB  
Article
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 3207
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)
►▼ Show Figures

Figure 1

17 pages, 4829 KB  
Article
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 57 | Viewed by 9567
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)
►▼ Show Figures

Figure 1

16 pages, 7174 KB  
Article
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 2867
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)
►▼ Show Figures

Figure 1

15 pages, 1427 KB  
Article
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 21 | Viewed by 4123
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)
►▼ Show Figures

Figure 1

10 pages, 3221 KB  
Article
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 2957
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)
►▼ Show Figures

Graphical abstract

9 pages, 433 KB  
Article
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 3365
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 CeO2. Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO2 are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, G0 = 63 (3) GPa, and adiabatic bulk modulus, KS0 = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, KT0∼ 230 GPa, determined by high-pressure X-ray diffraction experiments. Full article
(This article belongs to the Special Issue Materials Behavior under Compression)
►▼ Show Figures

Figure 1

16 pages, 6017 KB  
Article
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 2883
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)
►▼ Show Figures

Figure 1

14 pages, 5625 KB  
Article
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 1941
Abstract
A series of Co2+-doped and Gd3+-co-doped calcium molybdato-tungstates, i.e., Ca1−3x−yCoyxGd2x(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., Ca1−3x−yCoyxGd2x(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)
►▼ Show Figures

Figure 1

10 pages, 1221 KB  
Perspective
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 84 | Viewed by 6949
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)
►▼ Show Figures

Scheme 1

14 pages, 4680 KB  
Article
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 3312
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)
►▼ Show Figures

Figure 1

18 pages, 6772 KB  
Review
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 7 | Viewed by 2786
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)
►▼ Show Figures

Figure 1

17 pages, 27769 KB  
Article
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 2574
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)
►▼ Show Figures

Figure 1

15 pages, 3054 KB  
Opinion
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 55 | Viewed by 5380
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)
►▼ Show Figures

Figure 1

12 pages, 2190 KB  
Article
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 6 | Viewed by 2543
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)
►▼ Show Figures

Graphical abstract

38 pages, 3772 KB  
Review
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 62 | Viewed by 5395
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)
►▼ Show Figures

Figure 1

12 pages, 1561 KB  
Article
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 3274
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)
►▼ Show Figures

Graphical abstract

18 pages, 3099 KB  
Article
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 12 | Viewed by 3350
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)
►▼ Show Figures

Figure 1

10 pages, 36578 KB  
Article
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 2 | Viewed by 2504
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)
►▼ Show Figures

Figure 1

19 pages, 9059 KB  
Article
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 2842
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)
►▼ Show Figures

Figure 1

37 pages, 5670 KB  
Review
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 42 | Viewed by 6493
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)
►▼ Show Figures

Graphical abstract

12 pages, 5455 KB  
Article
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 3667
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)
►▼ Show Figures

Figure 1

17 pages, 6945 KB  
Article
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 9 | Viewed by 2719
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)
►▼ Show Figures

Figure 1

21 pages, 22313 KB  
Article
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 3540
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)
►▼ Show Figures

Graphical abstract

14 pages, 3350 KB  
Article
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 2757
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)
►▼ Show Figures

Figure 1

23 pages, 4617 KB  
Review
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 4088
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)
►▼ Show Figures

Figure 1

9 pages, 1173 KB  
Article
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 2405
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)
►▼ Show Figures

Figure 1

13 pages, 10780 KB  
Article
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 14 | Viewed by 3745
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)
►▼ Show Figures

Figure 1

18 pages, 5543 KB  
Article
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 2414
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 Scint is 424.64 J/(mol·K). Full article
(This article belongs to the Special Issue Surface Modification of Metallic Materials)
►▼ Show Figures

Figure 1

14 pages, 4240 KB  
Article
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 6 | Viewed by 3005
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)
►▼ Show Figures

Figure 1

12 pages, 2765 KB  
Article
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 3767
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)
►▼ Show Figures

Figure 1

14 pages, 5650 KB  
Article
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 15 | Viewed by 3711
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 (ksat) were determined. For FC fibers, an increase in fiber dosage caused ksat 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, ksat 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))
►▼ Show Figures

Figure 1

11 pages, 2499 KB  
Article
Reinforcing Increase of ΔTc 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 3694
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 (Tc) 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 (Tc) and has been confirmed in both MgB2 and Bi(Pb)SrCaCuO systems. However, the increase of ΔTc (ΔTc = Tc ‒ Tcpure) 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 ΔTc of MgB2 with different particle sizes. Results show that reducing the MgB2 particle size increases the optimal doping concentration of inhomogeneous phases, thereby increasing ΔTc. The optimal doping concentrations for aMgB2, bMgB2, and cMgB2 are 0.5%, 0.8%, and 1.2%, respectively. The corresponding ΔTc values are 0.4, 0.9, and 1.2 K, respectively. This work open a new approach to reinforcing increase of ΔTc in MgB2 SMSCs. Full article
(This article belongs to the Special Issue Advances in Superconducting Materials: Characterization, Properties and Applications)
►▼ Show Figures

Figure 1

12 pages, 760 KB  
Article
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 16 | Viewed by 3673
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)
►▼ Show Figures

Graphical abstract

25 pages, 9433 KB  
Article
Analysis of Crack Width Development in Reinforced Concrete Beams
by Barbara Goszczyńska, Wiesław Trąmpczyński and Justyna Tworzewska
Materials 2021, 14(11), 3043; https://doi.org/10.3390/ma14113043 - 3 Jun 2021
Cited by 22 | Viewed by 4947
Abstract
The reliability and durability of reinforced concrete structures depend on the amount of concrete cracking. The risk associated with cracks generates a need for diagnostic methods for the evaluation of reinforced concrete structures. This paper presents the results of a study of 10 [...] Read more.
The reliability and durability of reinforced concrete structures depend on the amount of concrete cracking. The risk associated with cracks generates a need for diagnostic methods for the evaluation of reinforced concrete structures. This paper presents the results of a study of 10 single-span reinforced concrete beams to follow the process of crack formation and changes in their width. The beams were loaded to failure with two forces in a monotonic manner with unloading and in a cyclic manner. Continuous observation of the crack formation process was provided by the digital image correlation system. The simplified method for estimating the maximum crack width is proposed. The presented results confirmed the stochastic character of the process of crack formation and development. The maximum crack widths calculated on the basis of the proposed formula were on the safe side in relation to those calculated according to Eurocode 2. It was also confirmed that the distances between cracks do not depend on the loading manner. Hence the density function describing the distribution of distances between cracks can be used to assess the condition of reinforced concrete elements. The research has also shown the suitability of the DIC system (ARAMIS) for testing concrete elements. Full article
(This article belongs to the Special Issue Advanced Construction Materials and Processes in Poland)
►▼ Show Figures

Figure 1

15 pages, 2934 KB  
Article
Freeze-Dried Matrices Composed of Degradable Polymers with Surfactant-Loaded Microparticles Based on Pectin and Sodium Alginate
by Natalia Stachowiak, Jolanta Kowalonek and Justyna Kozlowska
Materials 2021, 14(11), 3044; https://doi.org/10.3390/ma14113044 - 3 Jun 2021
Cited by 13 | Viewed by 4758
Abstract
Gelatin/polyvinylpyrrolidone/hydroxyethyl cellulose/glycerol porous matrices with microspheres made of sodium alginate or pectin and sodium alginate were produced. A surfactant was loaded into these microparticles. The microspheres were characterized using optical microscopy, scanning electron microscopy SEM, and laser diffraction particle size analyzer. For the [...] Read more.
Gelatin/polyvinylpyrrolidone/hydroxyethyl cellulose/glycerol porous matrices with microspheres made of sodium alginate or pectin and sodium alginate were produced. A surfactant was loaded into these microparticles. The microspheres were characterized using optical microscopy, scanning electron microscopy SEM, and laser diffraction particle size analyzer. For the matrices, the density, porosity, swelling capacity, dissolution in phosphate saline buffer were determined and SEM, mechanical, and thermogravimetric studies were applied. The results showed that the size of the two-component microspheres was slightly larger than that of single-ingredient microparticles. The images confirmed the spherical shape of the microparticles. The prepared matrices had high water uptake ability and porosity due to the presence of hydrophilic polymers. The presence of microparticles in the matrices caused a decrease in these parameters. Degradation of the composites with the microspheres was significantly faster than the matrix without them. The addition of microparticles increased the stiffness and toughness of the prepared materials. The efficiency of the thermal decomposition main stage was reduced in the samples with microspheres, whereas a char residue increased in these composites. Full article
(This article belongs to the Special Issue Synthesis, Properties and Applications of Functional Polymers)
►▼ Show Figures

Figure 1

21 pages, 9843 KB  
Article
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 7 | Viewed by 3184
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)
►▼ Show Figures

Figure 1

25 pages, 6158 KB  
Article
Experimental and Modelling of Alkali-Activated Mortar Compressive Strength Using Hybrid Support Vector Regression and Genetic Algorithm
by Khaled A. Alawi Al-Sodani, Adeshina Adewale Adewumi, Mohd Azreen Mohd Ariffin, Mohammed Maslehuddin, Mohammad Ismail, Hamza Onoruoiza Salami, Taoreed O. Owolabi and Hatim Dafalla Mohamed
Materials 2021, 14(11), 3049; https://doi.org/10.3390/ma14113049 - 3 Jun 2021
Cited by 9 | Viewed by 3212
Abstract
This paper presents the outcome of work conducted to develop models for the prediction of compressive strength (CS) of alkali-activated limestone powder and natural pozzolan mortar (AALNM) using hybrid genetic algorithm (GA) and support vector regression (SVR) algorithm, for the first time. The [...] Read more.
This paper presents the outcome of work conducted to develop models for the prediction of compressive strength (CS) of alkali-activated limestone powder and natural pozzolan mortar (AALNM) using hybrid genetic algorithm (GA) and support vector regression (SVR) algorithm, for the first time. The developed hybrid GA-SVR-CS1, GA-SVR-CS3, and GA-SVR-CS14 models are capable of estimating the one-day, three-day, and 14-day compressive strength, respectively, of AALNM up to 96.64%, 90.84%, and 93.40% degree of accuracy as measured on the basis of correlation coefficient between the measured and estimated values for a set of data that is excluded from training and testing phase of the model development. The developed hybrid GA-SVR-CS28E model estimates the 28-days compressive strength of AALNM using the 14-days strength, it performs better than hybrid GA-SVR-CS28C model, hybrid GA-SVR-CS28B model, hybrid GA-SVR-CS28A model, and hybrid GA-SVR-CS28D model that respectively estimates the 28-day compressive strength using three-day strength, one day-strength, all the descriptors and seven day-strength with performance improvement of 103.51%, 124.47%, 149.94%, and 262.08% on the basis of root mean square error. The outcome of this work will promote the use of environment-friendly concrete with excellent strength and provide effective as well as efficient ways of modeling the compressive strength of concrete. Full article
(This article belongs to the Collection Alkali‐Activated Materials for Sustainable Construction)
►▼ Show Figures

Figure 1

37 pages, 5320 KB  
Article
Literature Review of the In-Plane Behavior of Masonry Walls: Theoretical vs. Experimental Results
by Thomas Celano, Luca Umberto Argiento, Francesca Ceroni and Claudia Casapulla
Materials 2021, 14(11), 3063; https://doi.org/10.3390/ma14113063 - 3 Jun 2021
Cited by 53 | Viewed by 7267
Abstract
In-plane strength of masonry walls is affected by the resistant mechanisms activated in the walls, i.e., related to flexural or shear behavior. The latter one can occur in the walls according to different failure modes depending on both mortar and unit strengths and [...] Read more.
In-plane strength of masonry walls is affected by the resistant mechanisms activated in the walls, i.e., related to flexural or shear behavior. The latter one can occur in the walls according to different failure modes depending on both mortar and unit strengths and on the type of assembling, i.e., ‘regular’ or ‘irregular’ texture. In this paper, a critical review of the existing design formulations for the in-plane strength of masonry walls is firstly presented, with important information on the achievable failure modes depending on the geometrical and mechanical features of the masonry fabric. Then, experimental tests are collected from the literature and a comparison between theoretical and experimental results is carried out. The presented analyses are aimed to highlight the differences between the existing formulations and to identify the most suitable ones. Full article
(This article belongs to the Section Construction and Building Materials)
►▼ Show Figures

Figure 1

16 pages, 8395 KB  
Article
Non-Destructive Diagnostics of Concrete Beams Strengthened with Steel Plates Using Modal Analysis and Wavelet Transform
by Magdalena Knak, Erwin Wojtczak and Magdalena Rucka
Materials 2021, 14(11), 3014; https://doi.org/10.3390/ma14113014 - 2 Jun 2021
Cited by 13 | Viewed by 2962
Abstract
Externally bonded reinforcements are commonly and widely used in civil engineering objects made of concrete to increase the structure load capacity or to minimize the negative effects of long-term operation and possible defects. The quality of adhesive bonding between a strengthened structure and [...] Read more.
Externally bonded reinforcements are commonly and widely used in civil engineering objects made of concrete to increase the structure load capacity or to minimize the negative effects of long-term operation and possible defects. The quality of adhesive bonding between a strengthened structure and steel or composite elements is essential for effective reinforcement; therefore, there is a need for non-destructive diagnostics of adhesive joints. The aim of this paper is the detection of debonding defects in adhesive joints between concrete beams and steel plates using the modal analysis approach. The inspection was based on modal shapes and their further processing with the use of continuous wavelet transform (CWT) for precise debonding localization and imaging. The influence of the number of wavelet vanishing moments and the mode shape interpolation on damage imaging maps was studied. The results showed that the integrated modal analysis and wavelet transform could be successfully applied to determine the exact shape and position of the debonding in the adhesive joints of composite beams. Full article
(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering (2nd Edition))
►▼ Show Figures

Figure 1

14 pages, 4523 KB  
Article
Application of Additively Manufactured Pentamode Metamaterials in Sodium/Inconel 718 Heat Pipes
by Longfei Hu, Ketian Shi, Xiaoguang Luo, Jijun Yu, Bangcheng Ai and Chao Liu
Materials 2021, 14(11), 3016; https://doi.org/10.3390/ma14113016 - 2 Jun 2021
Cited by 5 | Viewed by 6179
Abstract
In this study, pentamode metamaterials were proposed for thermal stress accommodation of alkali metal heat pipes. Sodium/Inconel 718 heat pipes with and without pentamode metamaterial reinforcement were designed and fabricated. Then, these heat pipes were characterized by startup tests and thermal response simulations. [...] Read more.
In this study, pentamode metamaterials were proposed for thermal stress accommodation of alkali metal heat pipes. Sodium/Inconel 718 heat pipes with and without pentamode metamaterial reinforcement were designed and fabricated. Then, these heat pipes were characterized by startup tests and thermal response simulations. It was found that pentamode metamaterial reinforcement did not affect the startup properties of sodium/Inconel 718 heat pipes. At 650–950 °C heating, there was a successful startup of heat pipes with and without pentamode metamaterial reinforcement, displaying uniform temperature distributions. A further simulation indicated that pentamode metamaterials could accommodate thermal stresses in sodium/Inconel 718 heat pipes. With pentamode metamaterial reinforcement, stresses in the heat pipes decreased from 12.9–62.1 to 10.2–52.4 MPa. As a result, sodium/Inconel 718 heat pipes could be used more confidently. This work was instructive for the engineering application of alkali metal heat pipes. Full article
(This article belongs to the Special Issue Material Design and Defect Control for Metal Additive Manufacturing)
►▼ Show Figures

Figure 1

12 pages, 1691 KB  
Article
Magneto-Optical Transport Properties of Type-II Nodal Line Semimetals
by Yanmei Sun, Jing Li, Hui Zhao, Meimei Wu and Hui Pan
Materials 2021, 14(11), 3035; https://doi.org/10.3390/ma14113035 - 2 Jun 2021
Cited by 4 | Viewed by 2799
Abstract
We investigate the magneto-optical transport properties and Landau levels of type-II nodal line semimetals. The tilted liner dispersion in type-II nodal line semimetals makes the conduction band and valence band asymmetric, and Landau levels are coupling in the presence of a magnetic field. [...] Read more.
We investigate the magneto-optical transport properties and Landau levels of type-II nodal line semimetals. The tilted liner dispersion in type-II nodal line semimetals makes the conduction band and valence band asymmetric, and Landau levels are coupling in the presence of a magnetic field. We find the background of absorption peaks is curved. The oscillation peaks are tailless with the change of magnetic field. Through tuning tilt term, we find the absorption peaks of optical conductivity change from incomplete degenerate structure to splitting double peaks structure. We also find interband absorption peaks is no longer zero in the imaginary part of Hall conductivity. With the change of the tilt term, the contribution of the absorption peak has two forms, one is that the negative peak only appears at high frequencies, and the other is two adjacent peaks with opposite signs. In addition, the resistivity, circularly polarized light and magnetic oscillation of Hall conductivity are studied. Full article
(This article belongs to the Special Issue Feature Papers in Materials Physics)
►▼ Show Figures

Figure 1

16 pages, 3221 KB  
Article
Simulation of the Attrition of Recycled Concrete Aggregates during Concrete Mixing
by Jaime Moreno-Juez, Luís Marcelo Tavares, Riccardo Artoni, Rodrigo M. de Carvalho, Emerson Reikdal da Cunha and Bogdan Cazacliu
Materials 2021, 14(11), 3007; https://doi.org/10.3390/ma14113007 - 1 Jun 2021
Cited by 13 | Viewed by 3435
Abstract
Concrete mixing can lead to mechanical degradation of aggregates, particularly when dealing with recycled concrete aggregates. In this work, the attrition of such materials during mixing is studied by means of experiments and simulations. The effect of the presence of fines, water addition, [...] Read more.
Concrete mixing can lead to mechanical degradation of aggregates, particularly when dealing with recycled concrete aggregates. In this work, the attrition of such materials during mixing is studied by means of experiments and simulations. The effect of the presence of fines, water addition, flow configuration of the mixer (co- or counter-current) and impeller frequency is discussed. Experiments were performed in a laboratory Eirich mixer. Discrete element numerical simulations (DEM) were performed on the same geometry by mimicking the behaviour of the material and, in particular, the cohesion induced by water and the cement paste using either Hertz–Mindlin or Hertz–Mindlin with Johnson–Kendall–Roberts (JKR) contact laws. The combination of the collision energy spectra extracted from the DEM simulations and an attrition model allowed the prediction of the mass loss due to attrition in 1-min experiments. Semi-quantitative agreement was observed between experiments and simulations, with a mean relative error of 26.4%. These showed that higher mass losses resulted from operation at the highest impeller speeds, co-current operation, and also with the wet aggregate. Mixing of the agglomerate in the concrete mix resulted in a significant reduction in attrition when compared to mixing aggregates alone. With further validation, the proposed simulation approach can become a valuable tool in the optimization of mixing by allowing the effects of material, machine and process variables to be studied on the mass loss due to attrition. Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
►▼ Show Figures

Figure 1

14 pages, 7505 KB  
Article
Cancellation of Auxetic Properties in F.C.C. Hard Sphere Crystals by Hybrid Layer-Channel Nanoinclusions Filled by Hard Spheres of Another Diameter
by Jakub W. Narojczyk, Krzysztof W. Wojciechowski, Jerzy Smardzewski, Attila R. Imre, Joseph N. Grima and Mikołaj Bilski
Materials 2021, 14(11), 3008; https://doi.org/10.3390/ma14113008 - 1 Jun 2021
Cited by 13 | Viewed by 3377
Abstract
The elastic properties of f.c.c. hard sphere crystals with periodic arrays of nanoinclusions filled by hard spheres of another diameter are the subject of this paper. It has been shown that a simple modification of the model structure is sufficient to cause very [...] Read more.
The elastic properties of f.c.c. hard sphere crystals with periodic arrays of nanoinclusions filled by hard spheres of another diameter are the subject of this paper. It has been shown that a simple modification of the model structure is sufficient to cause very significant changes in its elastic properties. The use of inclusions in the form of joined (mutually orthogonal) layers and channels showed that the resulting tetragonal system exhibited a complete lack of auxetic properties when the inclusion spheres reached sufficiently large diameter. Moreover, it was very surprising that this hybrid inclusion, which can completely eliminate auxeticity, was composed of components that, alone, in these conditions, enhanced the auxeticity either slightly (layer) or strongly (channel). The study was performed with computer simulations using the Monte Carlo method in the isothermal-isobaric (NpT) ensemble with a variable box shape. Full article
(This article belongs to the Special Issue Advances in Mechanical Metamaterials)
►▼ Show Figures

Figure 1

Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying article 1701-1750 on page 35 of 44.
Back to TopTop