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Volume 13, August-1

Materials, Volume 13, Issue 16 (August-2 2020) – 214 articles

Cover Story (view full-size image): Hyaluronic acid, curcumin, and usnic acid are separately utilized as effective biological agents in medicine, and materials based on their blending have wider therapeutic effects than individual ones. In this study, for the first time, native hyaluronic acid-based nanofibers containing curcumin and usnic acid were successfully prepared by the electrospinning technique. Additionally, unstable and hydrophobic curcumin and usnic acid were loaded into the hydrophilic hyaluronic acid matrix without utilizing the activating (catalyzing) agents. The investigation of fibers based on pure hyaluronic acid with active pharmaceutical ingredients will lay the groundwork for the development of highly effective wound dressings with transdermal drug delivery. View this paper
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Open AccessArticle
Effect of pH Cycling Frequency on Glass–Ceramic Corrosion
Materials 2020, 13(16), 3655; https://doi.org/10.3390/ma13163655 - 18 Aug 2020
Viewed by 437
Abstract
The effect of pH changes on the chemical durability of dental glass–ceramic materials was evaluated using weight loss and ion release levels. The hypothesis that increased pH changes will exhibit greater corrosion was investigated. The ion concentration was analyzed using inductively coupled plasma [...] Read more.
The effect of pH changes on the chemical durability of dental glass–ceramic materials was evaluated using weight loss and ion release levels. The hypothesis that increased pH changes will exhibit greater corrosion was investigated. The ion concentration was analyzed using inductively coupled plasma atomic emission spectrometer (ICP). The surface compositions were investigated using X-ray photoelectron spectroscopy (XPS). The surface morphologies were examined using scanning electron microscopy (SEM). Dental glass–ceramics were tested in constant immersion, 3-day cycling, and 1-day cycling with pH 10, pH 2, and pH 7 for 3, 15, and 30 days. The 1-d cycling group demonstrated the highest levels of weight loss compared with 3-d cycling and constant immersion. For the ion release, Si4+ and Ca2+ had the highest rates of release in 1-d cycling, whereas the Al3+ release rate with constant pH 2 was highest. The alteration/passivation layer that was formed on the surface of disks possibly prevented further dissolution of pH 10 corroded disks. XPS analysis demonstrated different surface compositions of corroded disks in pH 10 and pH 2. Si4+, K+, Na+, Al3+, and Ca2+ were detected on the surface of corroded pH 10 disks, whereas a Si4+ and P5+-rich surface formed on corroded pH 2 disks. SEM results demonstrated rougher surfaces for corroded disks in cycling conditions and pH 2 constant immersion. In conclusion, increased pH changes significantly promote the corrosion of dental glass–ceramic materials. Full article
(This article belongs to the Special Issue Corrosion Science in Biomedical Materials)
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Open AccessArticle
Reversible Aggregation of Molecular-Like Fluorophores Driven by Extreme pH in Carbon Dots
Materials 2020, 13(16), 3654; https://doi.org/10.3390/ma13163654 - 18 Aug 2020
Viewed by 458
Abstract
The origin of carbon-dots (C-dots) fluorescence and its correlation with the dots structure still lack a comprehensive model. In particular, the core-shell model does not always fit with the experimental results, which, in some cases, suggest a molecular origin of the fluorescence. To [...] Read more.
The origin of carbon-dots (C-dots) fluorescence and its correlation with the dots structure still lack a comprehensive model. In particular, the core-shell model does not always fit with the experimental results, which, in some cases, suggest a molecular origin of the fluorescence. To gain a better insight, we have studied the response of molecular-like fluorophores contained in the C-dots at extreme pH conditions. Citric acid and urea have been employed to synthesize blue and green-emitting C-dots. They show a different emission as a function of the pH of the dispersing media. The photoluminescence has been attributed to molecular-like fluorophores: citrazinic acid and 4-hydroxy-1H-pyrrolo[3,4-c]-pyridine-1,3,6-(2H,5H)-trione. 3D and time-resolved photoluminescence, ultraviolet–visible (UV–vis) spectroscopy, and dynamic light scattering have been used to determine the aggregation state, quantum yield and emission properties of the C-dots. The dependence of the C-dots blue and green components on the chemical environment indicates that the origin of fluorescence is due to molecular-like fluorophores. Full article
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Open AccessArticle
The Effect of Electrolytic Hydrogenation on Mechanical Properties of T92 Steel Weldments under Different PWHT Conditions
Materials 2020, 13(16), 3653; https://doi.org/10.3390/ma13163653 - 18 Aug 2020
Cited by 1 | Viewed by 444
Abstract
In the present work, the effects of electrolytic hydrogen charging of T92 steel weldments on their room-temperature tensile properties were investigated. Two circumferential weldments between the T92 grade tubes were produced by gas tungsten arc welding using the matching Thermanit MTS 616 filler [...] Read more.
In the present work, the effects of electrolytic hydrogen charging of T92 steel weldments on their room-temperature tensile properties were investigated. Two circumferential weldments between the T92 grade tubes were produced by gas tungsten arc welding using the matching Thermanit MTS 616 filler material. The produced weldments were individually subjected to considerably differing post-welding heat treatment (PWHT) procedures. The first-produced weldment was conventionally tempered (i.e., short-term annealed below the Ac1 critical transformation temperature of the T92 steel), whereas the second one was subjected to its full renormalization (i.e., appropriate reaustenitization well above the T92 steel Ac3 critical transformation temperature and subsequent air cooling), followed by its conventional subcritical tempering. From both weldments, cylindrical tensile specimens of cross-weld configuration were machined. The room-temperature tensile tests were performed for the individual welds’ PWHT states in both hydrogen-free and electrolytically hydrogen-charged conditions. The results indicated higher hydrogen embrittlement susceptibility for the renormalized-and-tempered weldments, compared to the conventionally tempered ones. The obtained findings were correlated with performed microstructural and fractographic observations. Full article
(This article belongs to the Special Issue History, Developments and Trends in the Heat Treatment of Steel)
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Open AccessArticle
Non-Destructive Testing of the Longest Span Soil-Steel Bridge in Europe—Field Measurements and FEM Calculations
Materials 2020, 13(16), 3652; https://doi.org/10.3390/ma13163652 - 18 Aug 2020
Cited by 1 | Viewed by 476
Abstract
The article describes interdisciplinary and comprehensive non-destructive diagnostic tests of final bridge inspection and acceptance proposed for a soil-steel bridge made of corrugated sheets, being the European span length record holder (25.74 m). As an effect of an original concept a detailed and [...] Read more.
The article describes interdisciplinary and comprehensive non-destructive diagnostic tests of final bridge inspection and acceptance proposed for a soil-steel bridge made of corrugated sheets, being the European span length record holder (25.74 m). As an effect of an original concept a detailed and precise information about the structure short-term response was collected. Periodic diagnostics of bridge deformations was done one year after it was built. Load test design was based on numerical simulations performed by means of finite element method (FEM). In situ measurements were done with the aid of: inductive sensors, optical total station, and terrestrial laser scanner. The results produced by terrestrial laser scanning were used to build a precise image of structure deformation in 3D space during the tests. The accuracy of laser mapping was significantly increased using the information coming from total station and inductive sensors. These have higher accuracy and therefore can be used as reference. Thus, new quality in measurements is introduced. Good correspondence between in situ values and FEM estimations was achieved. Therefore, such a combination of testing methods can be used in non-destructive diagnostics of structures and is an interesting alternative for the standard approach, in which the measurements are done in limited number of points. Full article
(This article belongs to the Special Issue Non-Destructive Testing of Structures)
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Open AccessArticle
Influence of Rare Earth Element (Y) on Microstructure and Corrosion Behavior of Hot Extrusion AZ91 Magnesium Alloy
Materials 2020, 13(16), 3651; https://doi.org/10.3390/ma13163651 - 18 Aug 2020
Cited by 1 | Viewed by 464
Abstract
The influence of rare earth element (RE) Y on the microstructure and corrosion behavior of extruded AZ91 Mg alloy was surveyed via morphology characterization and corrosion performance measurements. The results indicate the corrosion resistance of the transversal section of AZ91 Mg alloy containing [...] Read more.
The influence of rare earth element (RE) Y on the microstructure and corrosion behavior of extruded AZ91 Mg alloy was surveyed via morphology characterization and corrosion performance measurements. The results indicate the corrosion resistance of the transversal section of AZ91 Mg alloy containing Y was improved compared with AZ91 Mg alloy without Y. The corrosion resistance of the longitudinal section of AZ91 Mg alloy with Y was lower than that of AZ91 Mg alloy without Y. The change of corrosion resistance can be attributed to the dispersion and volume fraction of the second phase, the effect of cathodic reduction rate, and the refined second phase. Full article
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Open AccessArticle
Nitrogen-Enriched Cr1−xAlxN Multilayer-Like Coatings Manufactured by Dynamic Glancing Angle Direct Current Magnetron Sputtering
Materials 2020, 13(16), 3650; https://doi.org/10.3390/ma13163650 - 18 Aug 2020
Cited by 1 | Viewed by 459
Abstract
Multilayer-like CrN and Cr1−xAlxN coatings with different Al contents were deposited onto a stainless steel substrate using dynamic glancing angle deposition direct current magnetron sputtering (DGLAD dcMS) in a N rich atmosphere to understand the role of Al on [...] Read more.
Multilayer-like CrN and Cr1−xAlxN coatings with different Al contents were deposited onto a stainless steel substrate using dynamic glancing angle deposition direct current magnetron sputtering (DGLAD dcMS) in a N rich atmosphere to understand the role of Al on the growth of the films and mechanical properties of the nitrides with a multilayer architecture. Chemical analysis by means of energy dispersive analysis (EDS) and glow discharge optical emission spectroscopy (GDOES) depth profiling revealed that while CrN samples were close to stoichiometric, the Cr1−xAlxN coatings presented excess N between 70 and 80% at. An expressive change in texture was observed as the CrN coating changed its preferred orientation from (111) to (200) with the addition of Al, followed by a modification in morphology from grains with faceted pyramidal tops in CrN to dome-shaped grains in Cr1−xAlxN coatings. Multilayer-like nanostructures of corrugated grains were produced with a periodicity of approximately 30 nm using dynamic glancing angle deposition. The deposition rate was drastically reduced with an increase of Al, meanwhile, the best mechanical performance was achieved for the coating with a higher content of Al, with hardness up to 27 GPa and a higher value of maximum resistance to plastic deformation. Full article
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Open AccessArticle
Influence of General Mineral Condition on Collagen-Guided Alveolar Crest Augmentation
Materials 2020, 13(16), 3649; https://doi.org/10.3390/ma13163649 - 18 Aug 2020
Viewed by 478
Abstract
The local regeneration of bone defects is regulated by general hormone, enzyme, ion, and vitamin levels. General diseases and dysregulation of the human mineral system can impact this process, even in alveolar crest. The aim of this study is to investigate a relation [...] Read more.
The local regeneration of bone defects is regulated by general hormone, enzyme, ion, and vitamin levels. General diseases and dysregulation of the human mineral system can impact this process, even in alveolar crest. The aim of this study is to investigate a relation between bone density, measured in two-dimensional X-rays, and general mineral condition of patients. The study included 42 patients on whom tooth extractions were performed. Data were divided into two groups: the region where collagen scaffold (BRM) was used and the reference region of intact normal bone (REF). Two-dimensional intraoral radiographs were taken in all cases just after the surgery (00 M) and 12 months later (12 M). Thyrotropin (TSH), parathormone (PTH), Ca2+ in serum, HbA1c, vitamin 25(OH)D3, and spine densitometry were checked. Digital texture analysis in MaZda 4.6 software was done. Texture Index (TI: BRM 1.66 ± 0.34 in 00 M, 1.51 ± 0.41 in 12 M, and REF 1.72 ± 0.28) and Bone Index (BI: BRM 0.73 ± 0.17 in 00 M, 0.65 ± 0.22 41 in 12 M, and REF 0.80 ± 0.14) were calculated to evaluate bone regeneration process after 12 months of healing (TI (p < 0.05) and BI (p < 0.01) are lower in BRM 12 M than in REF). This showed a relation between BI and TSH (R2 = 26%, p < 0.05), as well as a between BI and patient age (R2 = 65%, p < 0.001), and a weak relation between TI and TSH level (R2 = 10%, p < 0.05). This study proved that a collagen scaffold can be successfully used in alveolar crest regeneration, especially in patients with a high normal level of TSH in the middle-aged population. Full article
(This article belongs to the Special Issue Numerical and Biomechanical Analysis in Bioengineering)
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Open AccessArticle
Effect of Different Filler Wires on Mechanical Property and Conductivity of Aluminum-Copper Joints
Materials 2020, 13(16), 3648; https://doi.org/10.3390/ma13163648 - 18 Aug 2020
Viewed by 387
Abstract
The 1060 aluminum and T2 copper were joined by the pulsed double electrode gas metal arc welding (DE-GMAW) brazing method by using four types of filler wires, namely pure aluminum (Al) ER1100, aluminum-magnesium (Al–Mg) ER5356, aluminum-silicon (Al–Si) ER4043, and Al–Si ER4047, respectively. The [...] Read more.
The 1060 aluminum and T2 copper were joined by the pulsed double electrode gas metal arc welding (DE-GMAW) brazing method by using four types of filler wires, namely pure aluminum (Al) ER1100, aluminum-magnesium (Al–Mg) ER5356, aluminum-silicon (Al–Si) ER4043, and Al–Si ER4047, respectively. The effects of different types of filler wires on intermetallic compounds, microhardness tensile strength, and conductivity of joints were investigated. The results showed that a lot of brittle intermetallic compounds laying in the copper side brazing interface zone were generated using pure Al, Al–Mg, and Al–Si filler wires, which caused the change of microhardness, tensile strength, and the conductivity of joints. Meanwhile, with the increase in Si elements contents for Al–Sifiller wires, the thickness of the intermetallic compound layers decreased obviously, which was only up to 3 µm and the conductivity of the joints decreased. In addition, the microhardness, tensile strength, and the conductivity of the joints, when using Al–Sifiller wires, was higher than that using pure Al and Al–Mg filler wires. Hence, in comparison to the pure filler wires and Al–Mg filler wires, the Al–Si filler wires were more suitable for Al–Cu joints by DE-GMAW as Si element content was lower. Full article
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Open AccessArticle
Experimental Analysis of the Function of a Window with a Phase Change Heat Accumulator
Materials 2020, 13(16), 3647; https://doi.org/10.3390/ma13163647 - 17 Aug 2020
Viewed by 493
Abstract
The article presents the results of long-term field tests and their mathematical analysis regarding the impacts of innovative phase change materials on the energy efficiency of composite windows with various glazing parameters. Research was conducted on six glazing combinations throughout the heating season [...] Read more.
The article presents the results of long-term field tests and their mathematical analysis regarding the impacts of innovative phase change materials on the energy efficiency of composite windows with various glazing parameters. Research was conducted on six glazing combinations throughout the heating season in a temperate climate in Rzeszów (Poland). The empirical results obtained during the spring months showed an improvement in the monthly heat balance for windows with phase change materials compared to the reference window by as much as 34.09%. In addition, the empirical results allowed the development and verification of a mathematical model describing the transport and distribution of heat within a window with a phase change heat accumulator. The model was made using equations of non-stationary heat flow and an explicit finite difference method using calorimetric thermograms describing the phase change eutectic mixture used in the research. Carrying out the Snedecor–Fischer test proved the statistical adequacy of the developed model in 4 out of 6 tested combinations of glazing units. Good matching of the empirical and theoretical quantities was also confirmed using the quasi-Newton method. The article is a solution to the problem of the effective use of solar energy within transparent building partitions, while presenting a useful mathematical tool that determines potential thermal gains in various climatic conditions. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle
Blastfurnace Hybrid Cement with Waste Water Glass Activator: Alkali–Silica Reaction Study
Materials 2020, 13(16), 3646; https://doi.org/10.3390/ma13163646 - 17 Aug 2020
Viewed by 482
Abstract
Hybrid systems represent a new sustainable type of cement combining the properties of ordinary Portland cement and alkali-activated materials. In this study, a hybrid system based on blast furnace slag and Portland clinker was investigated. The economic aspects and appropriate waste management resulted [...] Read more.
Hybrid systems represent a new sustainable type of cement combining the properties of ordinary Portland cement and alkali-activated materials. In this study, a hybrid system based on blast furnace slag and Portland clinker was investigated. The economic aspects and appropriate waste management resulted in the usage of technological waste from water glass production (WG-waste) as an alkaline activator. Although the Portland clinker content was very low, the incorporation of this by-product significantly improved the mechanical properties. Nevertheless, the high amount of alkalis in combination with possible reactive aggregates raises concerns about the risk of alkali–silica reaction (ASR). The results obtained from expansion measurement, the uranyl acetate fluorescence method, and microstructure characterization revealed that the undesirable effects of alkali–silica reaction in mortars based on the hydration of hybrid cement are minimal. Full article
(This article belongs to the Special Issue Alkali‐Activated Materials for Sustainable Construction)
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Open AccessArticle
Structural Property Study for GeSn Thin Films
Materials 2020, 13(16), 3645; https://doi.org/10.3390/ma13163645 - 17 Aug 2020
Viewed by 588
Abstract
The structural properties of GeSn thin films with different Sn concentrations and thicknesses grown on Ge (001) by molecular beam epitaxy (MBE) and on Ge-buffered Si (001) wafers by chemical vapor deposition (CVD) were analyzed through high resolution X-ray diffraction and cross-sectional transmission [...] Read more.
The structural properties of GeSn thin films with different Sn concentrations and thicknesses grown on Ge (001) by molecular beam epitaxy (MBE) and on Ge-buffered Si (001) wafers by chemical vapor deposition (CVD) were analyzed through high resolution X-ray diffraction and cross-sectional transmission electron microscopy. Two-dimensional reciprocal space maps around the asymmetric (224) reflection were collected by X-ray diffraction for both the whole structures and the GeSn epilayers. The broadenings of the features of the GeSn epilayers with different relaxations in the ω direction, along the ω-2θ direction and parallel to the surface were investigated. The dislocations were identified by transmission electron microscopy. Threading dislocations were found in MBE grown GeSn layers, but not in the CVD grown ones. The point defects and dislocations were two possible reasons for the poor optical properties in the GeSn alloys grown by MBE. Full article
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Open AccessArticle
A Preliminary Characterisation of Innovative Semi-Flexible Composite Pavement Comprising Geopolymer Grout and Reclaimed Asphalt Planings
Materials 2020, 13(16), 3644; https://doi.org/10.3390/ma13163644 - 17 Aug 2020
Cited by 1 | Viewed by 418
Abstract
This article considers semi-flexible composite (SFC) pavement materials made with reclaimed asphalt planings (RAP) and geopolymer cement-based grouts. Geopolymer grouts were developed and used to fill the internal void structure of coarse RAP skeletons with varying levels of porosity. The geopolymer grouts were [...] Read more.
This article considers semi-flexible composite (SFC) pavement materials made with reclaimed asphalt planings (RAP) and geopolymer cement-based grouts. Geopolymer grouts were developed and used to fill the internal void structure of coarse RAP skeletons with varying levels of porosity. The geopolymer grouts were formulated at ambient temperature using industrial by-products to offer economic and environmental savings relative to conventional Portland cement-based grouting systems. They were characterised on flowability, setting time, and compressive strength. The effect of grout and RAP on SFC material performance was evaluated using permeable porosity, compressive strength, and ultrasonic pulse velocity. SFC performance was significantly influenced by both grout type and RAP content. Improved performance was associated with mixtures of high-flowability/high-strength grout and low RAP content. A practical limitation was identified for combination of grout with low-flowability/fast-setting time and well-compacted RAP skeletons. Solids content exceeding 49% by volume was not feasible, owing to inadequate grout penetration. A suite of SFC materials was produced offering performance levels for a range of practical pavement applications. Preliminary relationships enabling prediction of SFC elastic modulus based on strength and/or ultrasonic pulse velocity test data are given. A pavement design is given using SFC as a sub-base layer for an industrial hardstanding. Full article
(This article belongs to the Special Issue Novel Materials and Technologies for the Urban Roads of the Future)
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Open AccessArticle
Cement-Modified Loess Base for Intercity Railways: Mechanical Strength and Influencing Factors Based on the Vertical Vibration Compaction Method
Materials 2020, 13(16), 3643; https://doi.org/10.3390/ma13163643 - 17 Aug 2020
Viewed by 414
Abstract
Cement-modified loess has been used in the recent construction of an intercity high-speed railway in Xi’an, China. This paper studies the mechanical strength of cement-modified loess (CML) compacted by the vertical vibration compaction method (VVCM). First, the reliability of VVCM in compacting CML [...] Read more.
Cement-modified loess has been used in the recent construction of an intercity high-speed railway in Xi’an, China. This paper studies the mechanical strength of cement-modified loess (CML) compacted by the vertical vibration compaction method (VVCM). First, the reliability of VVCM in compacting CML is evaluated, and then the effects of cement content, compaction coefficient, and curing time on the mechanical strength of CML are analyzed, establishing a strength prediction model. The results show that the correlation of mechanical strength between the CML specimens prepared by VVCM in the laboratory and the core specimens collected on site is as high as 83.8%. The mechanical strength of CML initially show linear growth with increasing cement content and compaction coefficient. The initial growth in CML mechanical strength is followed by a later period, with mechanical strength growth slowing after 28 days. The mechanical strength growth properties of the CML can be accurately predicted via established strength growth equations. The results of this study can guide the design and construction of CML subgrade. Full article
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Open AccessArticle
Effect of Phosphate-Based Inhibitor on Corrosion Kinetics and Mechanism for Formation of Passive Film onto the Steel Rebar in Chloride-Containing Pore Solution
Materials 2020, 13(16), 3642; https://doi.org/10.3390/ma13163642 - 17 Aug 2020
Viewed by 410
Abstract
In the present study, different contents, i.e., 1–3% of 0.5 M ammonium phosphate mono basic (APMB), were used as corrosion inhibitor to reduce the corrosion of steel rebar. Electrochemical impedance spectroscopy (EIS) results showed that up to 24 h of exposure, polarization resistance [...] Read more.
In the present study, different contents, i.e., 1–3% of 0.5 M ammonium phosphate mono basic (APMB), were used as corrosion inhibitor to reduce the corrosion of steel rebar. Electrochemical impedance spectroscopy (EIS) results showed that up to 24 h of exposure, polarization resistance (Rp) and passive/oxide film resistance (Ro) gradually decreased in simulated concrete pore (SCP) + 3.5 wt.% NaCl solution owing to the reduction in pH of the solution. The steel rebar exposed in 2% inhibitor containing SCP + 3.5 wt.% NaCl solution exhibited 90% inhibition efficiency after 1 h of exposure. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed the formation of thermodynamically very stable and sparingly soluble goethite (α-FeOOH), maghemite (γ-Fe2O3), and iron phosphate (FePO4) as passive/oxide film onto the steel rebar surface exposed to 2% inhibitor containing SCP + 3.5 wt.% NaCl solution. Full article
(This article belongs to the Special Issue Corrosion and Corrosion Inhibition of Metals and Their Alloys)
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Open AccessReview
Collagen-Based Materials Modified by Phenolic Acids—A Review
Materials 2020, 13(16), 3641; https://doi.org/10.3390/ma13163641 - 17 Aug 2020
Viewed by 469
Abstract
Collagen-based biomaterials constitute one of the most widely studied types of materials for biomedical applications. Low thermal and mechanical parameters are the main disadvantages of such structures. Moreover, they present low stability in the case of degradation by collagenase. To improve the properties [...] Read more.
Collagen-based biomaterials constitute one of the most widely studied types of materials for biomedical applications. Low thermal and mechanical parameters are the main disadvantages of such structures. Moreover, they present low stability in the case of degradation by collagenase. To improve the properties of collagen-based materials, different types of cross-linkers have been researched. In recent years, phenolic acids have been studied as collagen modifiers. Mainly, tannic acid has been tested for collagen modification as it interacts with a polymeric chain by strong hydrogen bonds. When compared to pure collagen, such complexes show both antimicrobial activity and improved physicochemical properties. Less research reporting on other phenolic acids has been published. This review is a summary of the present knowledge about phenolic acids (e.g., tannic, ferulic, gallic, and caffeic acid) application as collagen cross-linkers. The studies concerning collagen-based materials with phenolic acids are summarized and discussed. Full article
(This article belongs to the Special Issue Biopolymers: Synthesis, Properties and Biological Applications)
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Open AccessReview
Hydrogen Sulfide (H2S) Removal via MOFs
Materials 2020, 13(16), 3640; https://doi.org/10.3390/ma13163640 - 17 Aug 2020
Cited by 1 | Viewed by 605
Abstract
The removal of the environmentally toxic and corrosive hydrogen sulfide (H2S) from gas streams with varying overall pressure and H2S concentration is a long-standing challenge faced by the oil and gas industries. The present work focuses on H2 [...] Read more.
The removal of the environmentally toxic and corrosive hydrogen sulfide (H2S) from gas streams with varying overall pressure and H2S concentration is a long-standing challenge faced by the oil and gas industries. The present work focuses on H2S capture using a relatively new type of material, namely metal-organic frameworks (MOFs), in an effort to shed light on their potential as adsorbents in the field of gas storage and separation. MOFs hold great promise as they make possible the design of structures from organic and inorganic units, but also as they have provided an answer to a long-term challenging objective, i.e., how to design extended structures of materials. Moreover, in designing MOFs, one may functionalize the organic units and thus, in essence, create pores with different functionalities, and also to expand the pores in order to increase pore openings. The work presented herein provides a detailed discussion, by thoroughly combining the existing literature on new developments in MOFs for H2S removal, and tries to provide insight into new areas for further research. Full article
(This article belongs to the Special Issue Metal Oxides for Heterogeneous Catalysis)
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Open AccessArticle
Analysis of Nonlinear Transient Energy Effect on Thermoelectric Energy Storage Structure
Materials 2020, 13(16), 3639; https://doi.org/10.3390/ma13163639 - 17 Aug 2020
Viewed by 364
Abstract
In complex flight conditions, due to the large amount of unusable heat generated by aerodynamic heating, the thermal protection system of an aircraft needs to withstand a large temperature shock, which brings great challenges to the design of the structure. In order to [...] Read more.
In complex flight conditions, due to the large amount of unusable heat generated by aerodynamic heating, the thermal protection system of an aircraft needs to withstand a large temperature shock, which brings great challenges to the design of the structure. In order to effectively utilize the irregular aerodynamic heat, and improve structural heat conduction, a composite structure is formed by using phase change energy storage materials on the basis of the thermoelectric structure, which transforms the aerodynamic waste heat into stable electric energy for the internal system. Through the study of the response of nonlinear transient energy, it is found that the thermoelectric and mechanical properties of the new structure can be improved by adding phase change energy storage materials. Under actual flight conditions, the new structure can reduce the maximum temperature by 180 K and the maximum thermal stress by 110 Mpa. The mechanical properties of the structure are effectively improved, the service life of the structure is prolonged, and the waste heat can be converted into stable electrical energy output to improve the thermoelectric output performance. On the premise of ensuring conversion efficiency, the output power of the new structure has been improved by 64.8% through structural optimization under actual flight conditions. Full article
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Open AccessArticle
Effect of Aging Time on Microstructure and Mechanical Properties in a Cu-Bearing Marine Engineering Steel
Materials 2020, 13(16), 3638; https://doi.org/10.3390/ma13163638 - 17 Aug 2020
Viewed by 401
Abstract
This study elucidated the structure–property relationship in a Cu-bearing marine engineering steel that was water cooled and then aged at 500 °C for 0.5–3 h. The microstructural features, tensile properties and impact properties were comparatively investigated as a function of aging time. When [...] Read more.
This study elucidated the structure–property relationship in a Cu-bearing marine engineering steel that was water cooled and then aged at 500 °C for 0.5–3 h. The microstructural features, tensile properties and impact properties were comparatively investigated as a function of aging time. When the aging period was increased, the Cu precipitates underwent coarsening, and a stable face-centered cubic (fcc) formation occurred. Additionally, the tensile properties were significantly improved at the expense of low temperature toughness, which can be attributed to the presence of nano-sized Cu precipitates. The increment of yield strength mainly derived from Cu precipitate–dislocation interaction strengthening effects (232 MPa for 1 h and 199 MPa for 3 h.) during aging process. Therefore, optimization of mechanical properties was achieved by controlling the parameters of aging process. The peak age hardening condition (i.e., at 500 °C for 1 h) resulted in the yield strength of 755 MPa, tensile strength of 812 MPa, elongation of 26.3% and impact energy of 78 J at −80 °C. Full article
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Open AccessArticle
Tearable and Fillable Composite Sponges Capable of Heat Generation and Drug Release in Response to Alternating Magnetic Field
Materials 2020, 13(16), 3637; https://doi.org/10.3390/ma13163637 - 17 Aug 2020
Viewed by 434
Abstract
Tearable and fillable implants are used to facilitate surgery. The use of implants that can generate heat and release a drug in response to an exogenous trigger, such as an alternating magnetic field (AMF), can facilitate on-demand combined thermal treatment and chemotherapy via [...] Read more.
Tearable and fillable implants are used to facilitate surgery. The use of implants that can generate heat and release a drug in response to an exogenous trigger, such as an alternating magnetic field (AMF), can facilitate on-demand combined thermal treatment and chemotherapy via remote operation. In this study, we fabricated tearable sponges composed of collagen, magnetite nanoparticles, and anticancer drugs. Crosslinking of the sponges by heating for 6 h completely suppressed undesirable drug release in saline at 37 °C but allowed drug release at 45 °C. The sponges generated heat immediately after AMF application and raised the cell culture medium temperature from 37 to 45 °C within 15 min. Heat generation was controlled by switching the AMF on and off. Furthermore, in response to heat generation, drug release from the sponges could be induced and moderated. Thus, remote-controlled heat generation and drug release were achieved by switching the AMF on and off. The sponges destroyed tumor cells when AMF was applied for 15 min but not when AMF was absent. The tearing and filling properties of the sponges may be useful for the surgical repair of bone and tissue defects. Moreover, these sponges, along with AMF application, can facilitate combined thermal therapy and chemotherapy. Full article
(This article belongs to the Special Issue Advanced Composite Biomaterials)
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Open AccessArticle
Corrosion Resistance of Concrete Reinforced by Zinc Phosphate Pretreated Steel Fiber in the Presence of Chloride Ions
Materials 2020, 13(16), 3636; https://doi.org/10.3390/ma13163636 - 17 Aug 2020
Viewed by 379
Abstract
This paper aims to provide new insight into a method to improve the chloride ion corrosion resistance of steel fiber reinforced concrete. The steel fiber was pretreated by zinc phosphate before the preparation of the fiber reinforced concrete. Interfacial bond strength, micro-hardness and [...] Read more.
This paper aims to provide new insight into a method to improve the chloride ion corrosion resistance of steel fiber reinforced concrete. The steel fiber was pretreated by zinc phosphate before the preparation of the fiber reinforced concrete. Interfacial bond strength, micro-hardness and micro-morphology properties were respectively analyzed in the steel fiber reinforced concrete before and after the chloride corrosion cycle test. The results show that the chloride ion corrosion resistance of the steel fiber was enhanced by zinc phosphate treatment. Compared to plain steel fiber reinforced concrete under chloride ion corrosion, the interfacial bond strength of the concrete prepared by steel fiber with phosphating treatment increased by 15.4%. The thickness of the interface layer between the pretreated steel fiber and cement matrix was reduced by 50%. The micro-hardness of the weakest point in the interface area increased by 54.2%. The micro-morphology of the interface area was almost unchanged before and after the corrosion. The steel fiber reinforced concrete modified by zinc phosphate can not only maintain the stability of the microstructure when corroded by chloride ion but also presents good bearing capacity. Full article
(This article belongs to the Special Issue Corrosion in Concrete: Inhibitors and Coatings)
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Open AccessReview
Si-QD Synthesis for Visible Light Emission, Color Conversion, and Optical Switching
Materials 2020, 13(16), 3635; https://doi.org/10.3390/ma13163635 - 17 Aug 2020
Viewed by 423
Abstract
This paper reviews the developing progress on the synthesis of the silicon quantum dots (Si-QDs) via the different methods including electrochemical porous Si, Si ion implantation, and plasma enhanced chemical vapor deposition (PECVD), and exploring their featured applications for light emitting diode (LED), [...] Read more.
This paper reviews the developing progress on the synthesis of the silicon quantum dots (Si-QDs) via the different methods including electrochemical porous Si, Si ion implantation, and plasma enhanced chemical vapor deposition (PECVD), and exploring their featured applications for light emitting diode (LED), color-converted phosphors, and waveguide switching devices. The characteristic parameters of Si-QD LED via different syntheses are summarized for discussion. At first, the photoluminescence spectra of Si-QD and accompanied defects are analyzed to distinguish from each other. Next, the synthesis of porous Si and the performances of porous Si LED reported from different previous works are compared in detail. Later on, the Si-QD implantation in silicide (SiX) dielectric films developed to solve the instability of porous Si and their electroluminescent performances are also summarized for realizing the effect of host matrix to increase the emission quantum efficiency. As the Si-ion implantation still generates numerous defects in host matrix owing to physical bombardment, the PECVD method has emerged as the main-stream methodology for synthesizing Si-QD in SiX semiconductor or dielectric layer. This method effectively suppresses the structural matrix imperfection so as to enhance the external quantum efficiency of the Si-QD LED. With mature synthesis technology, Si-QD has been comprehensively utilized not only for visible light emission but also for color conversion and optical switching applications in future academia and industry. Full article
(This article belongs to the Special Issue Silicon Nanoparticles: Synthesis and Application)
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Open AccessFeature PaperReview
Thermal Conductivity and Cure Kinetics of Epoxy-Boron Nitride Composites—A Review
Materials 2020, 13(16), 3634; https://doi.org/10.3390/ma13163634 - 17 Aug 2020
Viewed by 541
Abstract
Epoxy resin composites filled with thermally conductive but electrically insulating particles play an important role in the thermal management of modern electronic devices. Although many types of particles are used for this purpose, including oxides, carbides and nitrides, one of the most widely [...] Read more.
Epoxy resin composites filled with thermally conductive but electrically insulating particles play an important role in the thermal management of modern electronic devices. Although many types of particles are used for this purpose, including oxides, carbides and nitrides, one of the most widely used fillers is boron nitride (BN). In this review we concentrate specifically on epoxy-BN composites for high thermal conductivity applications. First, the cure kinetics of epoxy composites in general, and of epoxy-BN composites in particular, are discussed separately in terms of the effects of the filler particles on cure parameters and the cured composite. Then, several fundamental aspects of epoxy-BN composites are discussed in terms of their effect on thermal conductivity. These aspects include the following: the filler content; the type of epoxy system used for the matrix; the morphology of the filler particles (platelets, agglomerates) and their size and concentration; the use of surface treatments of the filler particles or of coupling agents; and the composite preparation procedures, for example whether or not solvents are used for dispersion of the filler in the matrix. The dependence of thermal conductivity on filler content, obtained from over one hundred reports in the literature, is examined in detail, and an attempt is made to categorise the effects of the variables and to compare the results obtained by different procedures. Full article
(This article belongs to the Special Issue Advances in Thermoset Materials)
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Open AccessArticle
Effect of Rare Earth on Microstructure and Wear Resistance of In-Situ-Synthesized Mo2FeB2 Ceramics-Reinforced Fe-Based Cladding
Materials 2020, 13(16), 3633; https://doi.org/10.3390/ma13163633 - 17 Aug 2020
Viewed by 344
Abstract
Mo2FeB2 ceramics-reinforced Fe-based cladding with various rare earth (RE) concentrations were prepared by the carbon arc surfacing process. The effects of RE content on the microstructure, phase composition, hardness and wear resistance of the cladding were systematically discussed. Meanwhile, the [...] Read more.
Mo2FeB2 ceramics-reinforced Fe-based cladding with various rare earth (RE) concentrations were prepared by the carbon arc surfacing process. The effects of RE content on the microstructure, phase composition, hardness and wear resistance of the cladding were systematically discussed. Meanwhile, the area fraction and grain size of Mo2FeB2 phase were exactly measured. Moreover, the refining mechanism of rare earth Y was analyzed. Results revealed that the claddings consisted of Mo2FeB2, FeCr, MoB and CrB. Adding the rare-earth Y decreased the grain sizes of Mo2FeB2 phase. Furthermore, grain-refining effects of Mo2FeB2 phase were significant when the RE content was 2% and hard phases evenly distributed in the cladding. In addition, the maximum microhardness value of claddings was about 1078 HV. The claddings with 2% RE contents had better wear resistance, which was equivalent to a sintered sample. Full article
(This article belongs to the Special Issue Wear Resistance Surface Layers and Coatings on Metals and Alloys)
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Open AccessArticle
Balling Behavior of Selective Laser Melting (SLM) Magnesium Alloy
Materials 2020, 13(16), 3632; https://doi.org/10.3390/ma13163632 - 17 Aug 2020
Viewed by 423
Abstract
Macroscopic surface morphology and balling mechanism of AZ61 magnesium alloy prepared by Selective laser melting (SLM) have been investigated. This article studied and analyzed the surface morphology and balling phenomenon of Mg in the laser processing from the aspects of Mg inherent metal [...] Read more.
Macroscopic surface morphology and balling mechanism of AZ61 magnesium alloy prepared by Selective laser melting (SLM) have been investigated. This article studied and analyzed the surface morphology and balling phenomenon of Mg in the laser processing from the aspects of Mg inherent metal properties and laser processing. In terms of laser processing, the results show that, in the direction of increasing scanning speed, the energy density decreases, and the phenomenon of balling and porosity on the surface of the magnesium alloy is serious. When the energy density is 133.9–187.5 J/mm3, balling particles are significantly reduced. It can be seen from the low-magnification SEM image that, even at a scanning speed of 250 mm/s (Ev is 187.5 J/mm3), there are still a few small-sized balling particles on the surface. Therefore, in terms of inherent metal properties, the wettability, capillary instability, thermodynamic, and kinetic analysis of the balling behavior of Mg and other metal (Al, Fe, Cu, Ni, Ti) droplets in the SLM process has been carried out, and the dynamic model of magnesium droplet spreading/solidification was established basic on the result of experiment and metal inherent properties. The results show that SLMed magnesium alloy is a competitive process of melt diffusion and solidification. The final result depends on the intrinsic properties of the magnesium alloy and the applied laser processing parameters. The spreading process of Mg melt is very fast. Although the solidification time of Mg melts changes slowly with the increase of metal droplet temperature, the spreading speed is still very fast due to the low melt density, so the balling phenomenon of SLMed Mg can be controlled to a certain extent. Theoretically calculated, the solidification time of Mg melt droplet is longer than the wetting time at 1173 K (900 °C), so the spreading process is dominant, which can minimize the balling and realize the densification of SLMed Mg. The dynamic spreading of molten pool, the analysis of wetting and solidification process, and the establishment of SLM balling model can provide reference for the design of the SLM forming parameters of Mg and other different metals. Full article
(This article belongs to the Special Issue Additive Manufacturing Materials and Their Applications)
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Open AccessArticle
Phase Transition in Iron Thin Films Containing Coherent Twin Boundaries: A Molecular Dynamics Approach
Materials 2020, 13(16), 3631; https://doi.org/10.3390/ma13163631 - 17 Aug 2020
Cited by 2 | Viewed by 409
Abstract
Using molecular dynamics (MD) simulation, the austenitic and martensitic phase transitions in pure iron (Fe) thin films containing coherent twin boundaries (TBs) have been studied. Twelve thin films with various crystalline structures, thicknesses and TB fractions were investigated to study the roles of [...] Read more.
Using molecular dynamics (MD) simulation, the austenitic and martensitic phase transitions in pure iron (Fe) thin films containing coherent twin boundaries (TBs) have been studied. Twelve thin films with various crystalline structures, thicknesses and TB fractions were investigated to study the roles of the free surface and TB in the phase transition. In the austenitic phase transition, the new phase nucleates mainly at the (112)bcc TB in the thicker films. The (111¯)bcc free surface only attends to the nucleation, when the film is extremely thin. The austenitic transition temperature shows weak dependence on the film thickness in thicker films, while an obvious transition temperature decrease is found in a thinner film. TB fraction has only slight influence on the austenitic temperature. In the martensitic phase transition, both the (1¯10)fcc free surface and (111)fcc TB attribute to the new body-center-cubic (bcc) phase nucleation. The martensitic transition temperature increases with decreased film thickness and TB fraction does not influent the transition temperature. In addition, the transition pathways were analyzed. The austenitic transition obeys the Burgers pathway while both the Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) relationship are observed in the martensitic phase transition. This work may help to understand the mechanism of phase transition in the Fe nanoscaled system containing a pre-existing defect. Full article
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Open AccessArticle
Dissolution of Metals in Different Bromide-Based Systems: Electrochemical Measurements and Spectroscopic Investigations
Materials 2020, 13(16), 3630; https://doi.org/10.3390/ma13163630 - 17 Aug 2020
Viewed by 415
Abstract
The dissolution of the main metals (Cu, Zn, Sn, Pb and Fe) found in waste printed circuit boards (WPCBs) was investigated by electrochemical corrosion measurements (potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)) in different bromide-based systems that could be used as lixiviants in [...] Read more.
The dissolution of the main metals (Cu, Zn, Sn, Pb and Fe) found in waste printed circuit boards (WPCBs) was investigated by electrochemical corrosion measurements (potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)) in different bromide-based systems that could be used as lixiviants in hydrometallurgical route of metals recovery. The analysis of the corrosion products was carried out by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. All measurements showed that the addition of bromine in the electrolyte favors to great extents the dissolution process of all studied metals as compared to bromine-free electrolytes. In the investigated experimental conditions, the highest dissolution rates of the metals were obtained in acidic KBr solution containing 0.01 mol/L bromine and they decreased in the following order: Zn >> Sn > Pb > Fe > Cu. The XRD and XPS chemical assessment allowed the identification of the dissolution products formed on the metallic surfaces after exposure to the electrolytes. They consisted mainly of oxides in the case of Cu, Zn, Sn and Fe, while the presence of PbBr2 was also noticed on the lead surface. Based on the results of EIS and surface investigations, several models explaining the corrosion behavior of the metals were proposed and discussed. The obtained results demonstrate that all studied metals could be successfully leached using brominated solutions, providing a viable alternative for the selective and efficient recovery of the base metals from WPCBs through a multi-step hydrometallurgical processing route. Full article
(This article belongs to the Special Issue Corrosion and Corrosion Inhibition of Metals and Their Alloys)
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Open AccessArticle
Evaluation of Hot Workability of Nickel-Based Superalloy Using Activation Energy Map and Processing Maps
Materials 2020, 13(16), 3629; https://doi.org/10.3390/ma13163629 - 17 Aug 2020
Cited by 1 | Viewed by 469
Abstract
The stress-strain curves for nickel-based superalloy were obtained from isothermal hot compression tests at a wide range of deformation temperatures and strain rates. The material constants and deformation activation energy of the investigated superalloy were calculated. The accuracy of the constitutive equation describing [...] Read more.
The stress-strain curves for nickel-based superalloy were obtained from isothermal hot compression tests at a wide range of deformation temperatures and strain rates. The material constants and deformation activation energy of the investigated superalloy were calculated. The accuracy of the constitutive equation describing the hot deformation behavior of this material was confirmed by the correlation coefficient for the linear regression. The distribution of deformation activation energy Q as a function of strain rate and temperature for nickel-based superalloy was presented. The processing maps were generated upon the basis of Prasad stability criterion for true strains ranging from 0.2 to 1 at the deformation temperatures range of 900–1150 °C, and strain rates range of 0.01–100 s−1. Based on the flow stress curves analysis, deformation activation energy map, and processing maps for different true strains, the undesirable and potentially favorable hot deformation parameters were determined. The microstructural observations confirmed the above optimization results for the hot workability of the investigated superalloy. Besides, the numerical simulation and industrial forging tests were performed in order to verify the obtained results. Full article
(This article belongs to the Special Issue Forging Processes of Materials)
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Open AccessArticle
Fibroblast-Like-Synoviocytes Mediate Secretion of Pro-Inflammatory Cytokines via ERK and JNK MAPKs in Ti-Particle-Induced Osteolysis
Materials 2020, 13(16), 3628; https://doi.org/10.3390/ma13163628 - 17 Aug 2020
Viewed by 441
Abstract
Biomaterials are designed to replace and augment living tissues in order to provide functional support to skeletal deformities. However, wear debris produced from the interfaces of metal implants initiates inflammatory bone loss, causing periprosthetic osteolysis. Lately, fibroblast-like synoviocytes (FLS) have been shown to [...] Read more.
Biomaterials are designed to replace and augment living tissues in order to provide functional support to skeletal deformities. However, wear debris produced from the interfaces of metal implants initiates inflammatory bone loss, causing periprosthetic osteolysis. Lately, fibroblast-like synoviocytes (FLS) have been shown to play a role in wear-debris-induced osteolysis. Thus, here we have tried to understand the underlying mechanism of FLS involvement in wear-debris-induced osteolysis. Our results demonstrate that the effects of Ti particle (1:100 cell-to-Ti particle ratio) on FLS can induce Cox-2 expression and activate NFkB signaling. Moreover, the mRNA expression of pro-inflammatory cytokines such as IL-6, IL-8, IL-11, IL-1β, and TNFα was found to be elevated. However, among these pro-inflammatory cytokines, the mRNA and protein levels of only IL-6, IL-1β, and TNFα were found to be significantly higher. Ti particles activated extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases (MAPKs) as an early response in FLS. Co-inhibition of ERK and JNK signaling pathways by their specific inhibitors (PD9805 and SP600125, respectively) resulted in the suppression of mRNA and protein levels of IL-6, IL-1β, and TNFα in FLS. Taken together, targeting ERK and JNK MAPKs in FLS might provide a therapeutic option for reducing the secretion of bone-resorbing pro-inflammatory cytokines, thus preventing periprosthetic osteolysis. Full article
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Open AccessArticle
Dynamics Studies of Nitrogen Interstitial in GaN from Ab Initio Calculations
Materials 2020, 13(16), 3627; https://doi.org/10.3390/ma13163627 - 17 Aug 2020
Viewed by 434
Abstract
Understanding the properties of defects is crucial to design higher performance semiconductor materials because they influence the electronic and optical properties significantly. Using ab initio calculations, the dynamics properties of nitrogen interstitial in GaN material, including the configuration, migration, and interaction with vacancy [...] Read more.
Understanding the properties of defects is crucial to design higher performance semiconductor materials because they influence the electronic and optical properties significantly. Using ab initio calculations, the dynamics properties of nitrogen interstitial in GaN material, including the configuration, migration, and interaction with vacancy were systematically investigated in the present work. By introducing different sites of foreign nitrogen atom, the most stable configuration of nitrogen interstitial was calculated to show a threefold symmetry in each layer and different charge states were characterized, respectively. In the researches of migration, two migration paths, in-plane and out-of-plane, were considered. With regards to the in-plane migration, an intermediated rotation process was observed first time. Due to this rotation behavior, two different barriers were demonstrated to reveal that the migration is an anisotropic behavior. Additionally, charged nitrogen Frenkel pair was found to be a relatively stable defect complex and its well separation distance was about 3.9 Å. Part of our results are in good agreement with the experimental results, and our work provides underlying insights of the identification and dynamics of nitrogen interstitial in GaN material. This study of defects in GaN material is useful to establish a more complete theory and improve the performance of GaN-based devices. Full article
(This article belongs to the Special Issue First-Principle and Atomistic Modelling in Materials Science)
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Open AccessArticle
Analysis of the Physicochemical and Mineralogical Properties of the Materials Used in the Preparation of Recoblocks
Materials 2020, 13(16), 3626; https://doi.org/10.3390/ma13163626 - 17 Aug 2020
Viewed by 399
Abstract
The construction sector generates 14,000 t/d of construction waste in Mexico City, these materials do not have real applications and end up accumulating in landfills. This work, the objective of which was to analyze the physicochemical and mineralogical properties of soil and construction [...] Read more.
The construction sector generates 14,000 t/d of construction waste in Mexico City, these materials do not have real applications and end up accumulating in landfills. This work, the objective of which was to analyze the physicochemical and mineralogical properties of soil and construction waste used in the manufacture of Recoblocks, is divided in five stages. First, the excavation material was submitted to field tests. Physical and chemical tests were then carried out on construction waste. Subsequently, the optimal mixture for making Recoblocks was determined. Next, Recoblocks were evaluated and compared with blocks made with water only, without mucilage of Opuntia ficus, and finally a feasibility study was performed. The X-ray diffraction study showed the presence of plagioclase, minerals that improve bending resistance, hardness, durability, as well as resistance to stress in a material. Compared to blocks manufactured without mucilage, the use of Opuntia ficus mucilage increased the compressive strength of the material by 59%, as well as the erodibility. Recoblocks are an environmentally friendly option because they are based on recycled materials, dried under the sun, which eliminates the use of brick oven. The production cost per unit is just USD 0.19, so it is a viable option as a building material. Full article
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