Previous Issue

E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Table of Contents

Materials, Volume 12, Issue 6 (March-2 2019)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-89
Export citation of selected articles as:
Open AccessArticle Highly Selective CMOS-Compatible Mid-Infrared Thermal Emitter/Detector Slab Design Using Optical Tamm-States
Materials 2019, 12(6), 929; https://doi.org/10.3390/ma12060929 (registering DOI)
Received: 31 January 2019 / Revised: 8 March 2019 / Accepted: 18 March 2019 / Published: 20 March 2019
PDF Full-text (3145 KB) | HTML Full-text | XML Full-text
Abstract
In this work, we propose and evaluate a concept for a selective thermal emitter based on Tamm plasmons suitable for monolithic on-chip integration and fabrication by conventional complementary metal oxide semiconductor (CMOS)-compatible processes. The original design of Tamm plasmon structures features a purely [...] Read more.
In this work, we propose and evaluate a concept for a selective thermal emitter based on Tamm plasmons suitable for monolithic on-chip integration and fabrication by conventional complementary metal oxide semiconductor (CMOS)-compatible processes. The original design of Tamm plasmon structures features a purely one-dimensional array of layers including a Bragg mirror and a metal. The resonant field enhancement next to the metal interface corresponding to optical Tamm states leads to resonant emission at the target wavelength, which depends on the lateral dimensions of the bandgap structure. We demonstrate the application of this concept to a silicon slab structure instead of deploying extended one dimensional layers thus enabling coupling into slab waveguides. Here we focus on the mid-infrared region for absorption sensing applications, particularly on the CO2 absorption line at 4.26 µm as an example. The proposed genetic-algorithm optimization process utilizing the finite-element method and the transfer-matrix method reveals resonant absorption in case of incident modes guided by the slab and, by Kirchhoff’s law, corresponds to emittance up to 90% depending on different choices of the silicon slab height when the structure is used as a thermal emitter. Although we focus on the application as an emitter in the present work, the structure can also be operated as an absorber providing adjusted lateral dimensions and/or exchanged materials (e.g., a different choice for metal). Full article
(This article belongs to the Special Issue Materials for Sources and Detectors in the GIGA-TERA-MIR Range)
Figures

Figure 1

Open AccessArticle Magnetic Field Patterning of Nickel Nanowire Film Realized by Printed Precursor Inks
Materials 2019, 12(6), 928; https://doi.org/10.3390/ma12060928 (registering DOI)
Received: 28 February 2019 / Revised: 12 March 2019 / Accepted: 13 March 2019 / Published: 20 March 2019
PDF Full-text (3366 KB) | HTML Full-text | XML Full-text
Abstract
This paper demonstrates an easily prepared novel material and approach to producing aligned nickel (Ni) nanowires having unique and customizable structures on a variety of substrates for electronic and magnetic applications. This is a new approach to producing printed metallic Ni structures from [...] Read more.
This paper demonstrates an easily prepared novel material and approach to producing aligned nickel (Ni) nanowires having unique and customizable structures on a variety of substrates for electronic and magnetic applications. This is a new approach to producing printed metallic Ni structures from precursor materials, and it provides a novel technique for nanowire formation during reduction. This homogeneous solution can be printed in ambient conditions, and it forms aligned elemental Ni nanowires over large areas upon heating in the presence of a magnetic field. The use of templates or subsequent purification are not required. This technique is very flexible, and allows the preparation of unique patterns of nanowires which provides opportunities to produce structures with enhanced anisotropic electrical and magnetic properties. An example of this is the unique fabrication of aligned nanowire grids by overlaying layers of nanowires oriented at different angles with respect to each other. The resistivity of printed and cured films was found to be as low as 560 µΩ∙cm. The saturation magnetization was measured to be 30 emu∙g−1, which is comparable to bulk Ni. Magnetic anisotropy was induced with an axis along the direction of the applied magnetic field, giving soft magnetic properties. Full article
(This article belongs to the Section Advanced Nanomaterials)
Figures

Graphical abstract

Open AccessReview Removal of Hazardous Oxyanions from the Environment Using Metal-Oxide-Based Materials
Materials 2019, 12(6), 927; https://doi.org/10.3390/ma12060927 (registering DOI)
Received: 11 February 2019 / Revised: 11 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
PDF Full-text (4297 KB) | HTML Full-text | XML Full-text
Abstract
Scientific development has increased the awareness of water pollutant forms and has reawakened the need for its effective purification. Oxyanions are created by a variety of redox-sensitive metals and metalloids. These species are harmful to living matter due to their toxicity, nondegradibility, and [...] Read more.
Scientific development has increased the awareness of water pollutant forms and has reawakened the need for its effective purification. Oxyanions are created by a variety of redox-sensitive metals and metalloids. These species are harmful to living matter due to their toxicity, nondegradibility, and mobility in aquatic environments. Among a variety of water treatment techniques, adsorption is one of the simplest, cheapest, and most effective. Since metal-oxide-based adsorbents poses a variety of functional groups onto their surface, they were widely applied in ions sorption. In this paper adsorption of harmful oxyanions by metal oxide-based materials according to literature survey was studied. Characteristic of oxyanions originating from As, V, B, W and Mo, their probable adsorption mechanisms and comparison of their sorption affinity for metal-oxide-based materials such as iron oxides, aluminum oxides, titanium dioxide, manganium dioxide, and various oxide minerals and their combinations are presented in this paper. Full article
(This article belongs to the Special Issue Multifunctional Oxide-Based Materials: From Synthesis to Application)
Figures

Graphical abstract

Open AccessArticle Microstructure, Thermal, and Corrosion Behavior of the AlAgCuNiSnTi Equiatomic Multicomponent Alloy
Materials 2019, 12(6), 926; https://doi.org/10.3390/ma12060926 (registering DOI)
Received: 14 February 2019 / Revised: 12 March 2019 / Accepted: 13 March 2019 / Published: 20 March 2019
PDF Full-text (3703 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents the microstructure and corrosion behavior of an AlTiNiCuAgSn new equiatomic multicomponent alloy. The alloy was obtained using the vacuum arc remelting (VAR) technique in MRF-ABJ900 equipment. The microstructural analysis was performed by optical and scanning electron microscopy (SEM microscope, SEM-EDS) [...] Read more.
The paper presents the microstructure and corrosion behavior of an AlTiNiCuAgSn new equiatomic multicomponent alloy. The alloy was obtained using the vacuum arc remelting (VAR) technique in MRF-ABJ900 equipment. The microstructural analysis was performed by optical and scanning electron microscopy (SEM microscope, SEM-EDS) and the phase transformations were highlighted by dilatometric analysis and differential thermal analysis (DTA). The results show that the as-cast alloy microstructure is three-phase, with an average microhardness of 487 HV0.1/15. The obtained alloy could be included in the group of compositionally complex alloys (CCA). The corrosion resistance was studied using the potentiodynamic method in saline solution with 3.5% NaCl. Considering the high corrosion resistance, the obtained alloy can be used for surface coating applications. Full article
(This article belongs to the Special Issue High Entropy Materials: From Fundamentals to Applications)
Figures

Figure 1

Open AccessArticle Use of Ladle Furnace Slag and Other Industrial By-Products to Encapsulate Chloride in Municipal Solid Waste Incineration Fly Ash
Materials 2019, 12(6), 925; https://doi.org/10.3390/ma12060925 (registering DOI)
Received: 2 February 2019 / Revised: 8 March 2019 / Accepted: 17 March 2019 / Published: 20 March 2019
PDF Full-text (4335 KB) | HTML Full-text | XML Full-text
Abstract
Municipal solid waste incineration fly ash (MSWIFA) is a hazardous by-product of waste incineration. The objective of this research is to encapsulate the chloride in MSWIFA and to develop a utilizable construction material using MSWIFA, ground granulated blast-furnace slag (GGBFS), ladle furnace slag [...] Read more.
Municipal solid waste incineration fly ash (MSWIFA) is a hazardous by-product of waste incineration. The objective of this research is to encapsulate the chloride in MSWIFA and to develop a utilizable construction material using MSWIFA, ground granulated blast-furnace slag (GGBFS), ladle furnace slag (LFS), and gypsum. A secondary objective of the work is to explain the hydration and encapsulation mechanisms in this material system using isothermal calorimetry (IC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and ion chromatography (IC). The predominant hydration products are ettringite, Friedel’s salt, and C-S-H gel, with Friedel’s salt and C-S-H dominating in systems high in LFS and ettringite and C-S-H gel dominating in systems low in LFS. The chloride encapsulation showed a strong correlation with the Friedel’s salt amount; however, some encapsulation was also likely due to physical binding in the C-S-H gel. In a system with 30% MSWIFA (by mass), the optimal amount of LFS for strength and chloride encapsulation is 20%–40% (by mass). Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
Figures

Figure 1

Open AccessArticle Fast Removal of Propranolol from Water by Attapulgite/Graphene Oxide Magnetic Ternary Composites
Materials 2019, 12(6), 924; https://doi.org/10.3390/ma12060924 (registering DOI)
Received: 25 February 2019 / Revised: 14 March 2019 / Accepted: 16 March 2019 / Published: 20 March 2019
PDF Full-text (4054 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a novel adsorbent attapulgite/graphene oxide magnetic composite (ATP/Fe3O4/GO) was synthesized for removing propranolol (PRO) from aqueous water. The factors affecting the PRO adsorption process onto ATP/Fe3O4/GO including pH, ionic strength, sorbent dosage, [...] Read more.
In this work, a novel adsorbent attapulgite/graphene oxide magnetic composite (ATP/Fe3O4/GO) was synthesized for removing propranolol (PRO) from aqueous water. The factors affecting the PRO adsorption process onto ATP/Fe3O4/GO including pH, ionic strength, sorbent dosage, and humic acid were systematically investigated by batch experiments. Meanwhile, magnetic attapulgite (ATP/Fe3O4) and magnetic graphene oxide (GO/Fe3O4) were prepared for the comparison of the adsorption performance for PRO. The structural and surface characteristics of the resulting materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential measurements, and scanning electron microscope. The results showed that the adsorption rate of PRO onto ATP/Fe3O4/GO was up to 99%, faster and higher than that of other adsorbents involved at neutral pH. Moreover, the adsorption kinetics were better fitted with pseudo-first-order kinetic model than the second-order kinetic model. The adsorption data were fitted well with the Freundlich isotherm equations, implying that the adsorption process was heterogeneous. The adsorption reaction was endothermic and spontaneous according to the thermodynamic parameters. All results indicated that ATP/Fe3O4/GO was a promising adsorbent for removing PRO from water. Full article
(This article belongs to the Section Advanced Composites)
Figures

Figure 1

Open AccessArticle Ambient Cured Fly Ash Geopolymer Coatings for Concrete
Materials 2019, 12(6), 923; https://doi.org/10.3390/ma12060923 (registering DOI)
Received: 28 January 2019 / Revised: 4 March 2019 / Accepted: 12 March 2019 / Published: 20 March 2019
PDF Full-text (5712 KB) | HTML Full-text | XML Full-text
Abstract
The reinforced concrete structures that support transport, energy and urban networks in developed countries are over half a century old, and are facing widespread deterioration. Geopolymers are an affordable class of materials that have promising applications in concrete structure coating, rehabilitation and sensing, [...] Read more.
The reinforced concrete structures that support transport, energy and urban networks in developed countries are over half a century old, and are facing widespread deterioration. Geopolymers are an affordable class of materials that have promising applications in concrete structure coating, rehabilitation and sensing, due to their high chloride, sulphate, fire and freeze-thaw resistances and electrolytic conductivity. Work to date has, however, mainly focused on geopolymers that require curing at elevated temperatures, and this limits their ease of use in the field, particularly in cooler climates. Here, we outline a design process for fabricating ambient-cured fly ash geopolymer coatings for concrete substrates. Our technique is distinct from previous work as it requires no additional manufacturing steps or additives, both of which can bear significant costs. Our coatings were tested at varying humidities, and the impacts of mixing and application methods on coating integrity were compared using a combination of calorimetry, x-ray diffraction and image-processing techniques. This work could allow geopolymer coatings to become a more ubiquitous technique for updating ageing concrete infrastructure so that it can meet modern expectations of safety, and shifting requirements due to climate change. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Figures

Figure 1

Open AccessArticle Effect of Hot-Pressing Temperature on Characteristics of Straw-Based Binderless Fiberboards with Pulping Effluent
Materials 2019, 12(6), 922; https://doi.org/10.3390/ma12060922 (registering DOI)
Received: 10 February 2019 / Revised: 10 March 2019 / Accepted: 12 March 2019 / Published: 20 March 2019
PDF Full-text (1657 KB) | HTML Full-text | XML Full-text
Abstract
This study aimed to improve straw-based fiberboard properties without resins by adding pulping effluent as well as to investigate the difference among boards under variable hot-pressing temperatures. The characterization of fiberboards produced from wheat straw under pressing temperatures ranging from 160 to 200 [...] Read more.
This study aimed to improve straw-based fiberboard properties without resins by adding pulping effluent as well as to investigate the difference among boards under variable hot-pressing temperatures. The characterization of fiberboards produced from wheat straw under pressing temperatures ranging from 160 to 200 °C was first described. The surface appearance, surface chemistry, thermal transitions, and mechanical performance of the boards were evaluated to investigate the effect of varying hot-pressing temperature. The results indicated that the surface color of boards became darker when the temperature was above 190 °C. Additionally, Fourier transform infrared (FT-IR) measurements showed that more low-molecular constituents and hydrogen bonds were produced under higher pressing temperatures. Furthermore, the physical and mechanical property data were analyzed statistically using one-way analysis of variance (ANOVA) and Tukey’s tests (α = 0.05). The results demonstrated that straw-based fiberboards with effluent under 190 °C exhibited superior strength and water resistance capacities, and showed great potential in commercial decorating and packaging applications. Full article
(This article belongs to the Section Biomaterials)
Figures

Graphical abstract

Open AccessArticle Physical, Chemical, Microstructural and Rheological Properties of Reactive Terpolymer-Modified Bitumen
Materials 2019, 12(6), 921; https://doi.org/10.3390/ma12060921 (registering DOI)
Received: 25 February 2019 / Revised: 8 March 2019 / Accepted: 12 March 2019 / Published: 20 March 2019
Viewed by 34 | PDF Full-text (8280 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the change in the physical, chemical, microstructural, and rheological properties of a road bitumen modified with reactive terpolymer (Elvaloy®RET) was investigated. For this purpose, four different Elvaloy®RET percentages (0%, 0.4%, 0.8%, and 1.2% by wt.) were [...] Read more.
In this study, the change in the physical, chemical, microstructural, and rheological properties of a road bitumen modified with reactive terpolymer (Elvaloy®RET) was investigated. For this purpose, four different Elvaloy®RET percentages (0%, 0.4%, 0.8%, and 1.2% by wt.) were mixed with B 160/220 bitumen. Firstly, the obtained samples were subjected to a short and long-term aging process using a rotating thin-film oven test and pressurized aging vessel, respectively. Then, the engineering characteristics of the samples were investigated using X-ray diffraction, scanning electron microscopy, and conventional and Superpave bitumen tests. The results showed that Elvaloy®RET reacted with the main macromolecular groups in the bitumen, and that the modified bitumens behaved as a homogenous single phase structure as a result of this reaction. Conventional tests showed that Elvaloy®RET-modified bitumens were much harder than pure bitumen and had better aging resistance. Furthermore, the penetration classes of these bitumens changed and their temperature sensitivities decreased significantly. Rheological tests showed that the Elvaloy®RET additive increased the resistance of the bitumen against fatigue cracking and particularly permanent deformation. Moreover, the high temperature performance class of the bitumen also increased. However, parallel to the hardening of the bitumen, a reduction in its resistance to cracking at low temperature was observed. Full article
(This article belongs to the Section Construction and Building Materials)
Figures

Graphical abstract

Open AccessArticle Tribological Characterization of Micron-/Nano-Sized WC-9%Co Cemented Carbides Prepared by Spark Plasma Sintering at Elevated Temperatures
Materials 2019, 12(6), 920; https://doi.org/10.3390/ma12060920 (registering DOI)
Received: 12 January 2019 / Revised: 3 March 2019 / Accepted: 4 March 2019 / Published: 20 March 2019
Viewed by 63 | PDF Full-text (4068 KB) | HTML Full-text | XML Full-text
Abstract
The present study investigates the high temperature tribological performance of spark plasma sintered, nano- and micron-sized tungsten carbide (WC) bonded by 9 wt.% cobalt (Co). The composites were fabricated using a two-step procedure of mixing followed by spark plasma sintering (SPS). Ball-on-disc wear [...] Read more.
The present study investigates the high temperature tribological performance of spark plasma sintered, nano- and micron-sized tungsten carbide (WC) bonded by 9 wt.% cobalt (Co). The composites were fabricated using a two-step procedure of mixing followed by spark plasma sintering (SPS). Ball-on-disc wear tests were conducted at a normal load of 30 N, linear speed of 0.1 m/s under dry conditions and at three different temperatures (room temperature, 300 °C and 600 °C). Field emission scanning electron microscopy (FESEM), optical profilometry and energy dispersive X-ray (EDS) spectroscopy were used to analyze the surface morphology and the wear track area. At room temperature, it was observed that the nano-sized WC composites exhibited better wear resistance than the micron-sized WC composites. The wear resistance of the nano-sized samples declined significantly relative to that of the micron-sized samples with an increase in temperature. This decline in performance was attributed to the higher surface area of nano-sized WC particles, which underwent rapid oxidation at elevated temperatures, resulting in poor wear resistance. The wear rate observed at 600 °C for the micron-sized WC composites was 75% lower than that of the nano-sized cemented carbide. Oxidative wear was observed to be the predominant wear mechanism for both cemented carbide samples at elevated temperatures. Full article
Figures

Figure 1

Open AccessFeature PaperArticle Bone Tissue Engineering in a Perfusion Bioreactor Using Dexamethasone-Loaded Peptide Hydrogel
Materials 2019, 12(6), 919; https://doi.org/10.3390/ma12060919
Received: 31 January 2019 / Revised: 10 March 2019 / Accepted: 18 March 2019 / Published: 19 March 2019
Viewed by 117 | PDF Full-text (1430 KB)
Abstract
The main goal of this study was the formation of bone tissue using dexamethasone (DEX)-loaded [COCH3]-RADARADARADARADA-[CONH2] (RADA 16-I) scaffold that has the ability to release optimal DEX concentration under perfusion force. Bone-marrow samples were collected from three patients during [...] Read more.
The main goal of this study was the formation of bone tissue using dexamethasone (DEX)-loaded [COCH3]-RADARADARADARADA-[CONH2] (RADA 16-I) scaffold that has the ability to release optimal DEX concentration under perfusion force. Bone-marrow samples were collected from three patients during a hip arthroplasty. Human mesenchymal stem cells (hMSCs) were isolated and propagated in vitro in order to be seeded on scaffolds made of DEX-loaded RADA 16-I hydrogel in a perfusion bioreactor. DEX concentrations were as follows: 4 × 10−3, 4 × 10−4 and 4 × 10−5 M. After 21 days in a perfusion bioreactor, tissue was analyzed by scanning electron microscopy (SEM) and histology. Markers of osteogenic differentiation were quantified by real-time polymerase chain reaction (RT-PCR) and immunocytochemistry. Minerals were quantified and detected by the von Kossa method. In addition, DEX release from the scaffold in a perfusion bioreactor was assessed. The osteoblast differentiation was confirmed by the expression analysis of osteoblast-related genes (alkaline phosphatase (ALP), collagen I (COL1A1) and osteocalcin (OC). The hematoxylin/eosin staining confirmed the presence of cells and connective tissue, while SEM revealed morphological characteristics of cells, extracellular matrix and minerals—three main components of mature bone tissue. Immunocytochemical detection of collagen I is in concordance with given results, supporting the conclusion that scaffold with DEX concentration of 4 × 10−4 M has the optimal engineered tissue morphology. The best-engineered bone tissue is produced on scaffold loaded with 4 × 10−4 M DEX with a perfusion rate of 0.1 mL/min for 21 days. Differentiation of hMSCs on DEX-loaded RADA 16-I scaffold under perfusion force has a high potential for application in regenerative orthopedics. Full article
(This article belongs to the Special Issue Scaffold Materials for Tissue Engineering)
Open AccessArticle The Study of Buckling and Post-Buckling of a Step-Variable FGM Box
Materials 2019, 12(6), 918; https://doi.org/10.3390/ma12060918
Received: 27 February 2019 / Revised: 15 March 2019 / Accepted: 15 March 2019 / Published: 19 March 2019
Viewed by 96 | PDF Full-text (778 KB)
Abstract
This work concerns the analysis of a thin-walled box made of ceramic and step-variable functionally graded material (FGM) subjected to compression. The components of the box taken into account were pure alumina and aluminium-alumina graded material. The problem was solved on the basis [...] Read more.
This work concerns the analysis of a thin-walled box made of ceramic and step-variable functionally graded material (FGM) subjected to compression. The components of the box taken into account were pure alumina and aluminium-alumina graded material. The problem was solved on the basis of a finite element method and Koiter’s asymptotic theory using a semi-analytical method (SAM). It analysed both the buckling state and the post-buckling state of the box. In addition, three conditions were considered: The presence of alumina outside or inside of the box and a mixed case. The obtained results were presented and discussed. Full article
(This article belongs to the Special Issue Behavior of Metallic and Composite Structures)
Open AccessArticle Database of Shear Experiments on Steel Fiber Reinforced Concrete Beams without Stirrups
Materials 2019, 12(6), 917; https://doi.org/10.3390/ma12060917 (registering DOI)
Received: 26 February 2019 / Revised: 7 March 2019 / Accepted: 11 March 2019 / Published: 19 March 2019
Viewed by 122 | PDF Full-text (2243 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Adding steel fibers to concrete improves the capacity in tension-driven failure modes. An example is the shear capacity in steel fiber reinforced concrete (SFRC) beams with longitudinal reinforcement and without shear reinforcement. Since no mechanical models exist that can fully describe the behavior [...] Read more.
Adding steel fibers to concrete improves the capacity in tension-driven failure modes. An example is the shear capacity in steel fiber reinforced concrete (SFRC) beams with longitudinal reinforcement and without shear reinforcement. Since no mechanical models exist that can fully describe the behavior of SFRC beams without shear reinforcement failing in shear, a number of empirical equations have been suggested in the past. This paper compiles the existing empirical equations and code provisions for the prediction of the shear capacity of SFRC beams failing in shear as well as a database of 488 experiments reported in the literature. The experimental shear capacities from the database are then compared to the prediction equations. This comparison shows a large scatter on the ratio of experimental to predicted values. The practice of defining the tensile strength of SFRC based on different experiments internationally makes the comparison difficult. For design purposes, the code prediction methods based on the Eurocode shear expression provide reasonable results (with coefficients of variation on the ratio tested/predicted shear capacities of 27–29%). None of the currently available methods properly describe the behavior of SFRC beams failing in shear. As such, this work shows the need for studies that address the different shear-carrying mechanisms in SFRC and its crack kinematics. Full article
(This article belongs to the Section Construction and Building Materials)
Figures

Figure 1

Open AccessArticle Mechanical and Cytocompatibility Evaluation of UHMWPE/PCL/Bioglass® Fibrous Composite for Acetabular Labrum Implant
Materials 2019, 12(6), 916; https://doi.org/10.3390/ma12060916
Received: 24 January 2019 / Revised: 26 February 2019 / Accepted: 8 March 2019 / Published: 19 March 2019
Viewed by 106 | PDF Full-text (4092 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a fibrous composite was developed as synthetic graft for labral reconstruction treatment, comprised of ultra-high molecular weight polyethylene (UHMWPE) fabric, ultrafine fibre of polycaprolactone (PCL), and 45S5 Bioglass®. This experiment aimed to examine the mechanical performance and cytocompatibility [...] Read more.
In this study, a fibrous composite was developed as synthetic graft for labral reconstruction treatment, comprised of ultra-high molecular weight polyethylene (UHMWPE) fabric, ultrafine fibre of polycaprolactone (PCL), and 45S5 Bioglass®. This experiment aimed to examine the mechanical performance and cytocompatibility of the composite. Electrospinning and a slurry dipping technique were applied for composite fabrication. To assess the mechanical performance of UHMWPE, tensile cyclic loading test was carried out. Meanwhile, cytocompatibility of the composite on fibroblastic cells was examined through a viability assay, as well as SEM images to observe cell attachment and proliferation. The mechanical test showed that the UHMWPE fabric had a mean displacement of 1.038 mm after 600 cycles, approximately 4.5 times greater resistance compared to that of natural labrum, based on data obtained from literature. A viability assay demonstrated the predominant occupation of live cells on the material surface, suggesting that the composite was able to provide a viable environment for cell growth. Meanwhile, SEM images exhibited cell adhesion and the formation of cell colonies on the material surface. These results indicated that the UHMWPE/PCL/Bioglass® composite could be a promising material for labrum implants. Full article
(This article belongs to the Special Issue Bioceramics: Bioinert, Bioactive, and Coatings)
Figures

Figure 1

Open AccessArticle Advantages of the Application of the Temper Bead Welding Technique During Wet Welding
Materials 2019, 12(6), 915; https://doi.org/10.3390/ma12060915
Received: 7 February 2019 / Revised: 12 March 2019 / Accepted: 13 March 2019 / Published: 19 March 2019
Viewed by 106 | PDF Full-text (5104 KB) | HTML Full-text | XML Full-text
Abstract
Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check [...] Read more.
Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check the influence of temper bead welding (TBW) on the weldability of the investigated steel. Non-destructive and destructive tests showed that S460ML steel has a high susceptibility to cold cracking. In all joints, hardness in the heat-affected zone (HAZ) was extended to the 400 HV10 values. Microscopic testing showed the presence of microcracks in the HAZ of all welded joints. TBW was chosen as the method to improve the weldability of the investigated steel. This technique allows for the reduction of the maximum hardness in the HAZ below the critical value of 380 HV10, as stated by the EN-ISO 15614-1:2017. It was determined that for S460ML steel, from the point of view of weldability, the pitch between two beads should be in the range 75%–100%. Also, if the pitch between two beads increases, the hardness, grain size, and number of cracks decreases. In all specimens where the hardness of the HAZ was below 380 HV10, there were no microcracks. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
Figures

Figure 1

Open AccessArticle Oxidation Resistance and Microstructure Evaluation of a Polymer Derived Ceramic (PDC) Composite Coating Applied onto Sintered Steel
Materials 2019, 12(6), 914; https://doi.org/10.3390/ma12060914
Received: 21 February 2019 / Revised: 7 March 2019 / Accepted: 12 March 2019 / Published: 19 March 2019
Viewed by 88 | PDF Full-text (4477 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Powder metallurgy is a competitive technology to produce ferrous near net shape parts for diverse engineering applications. However, their inherent porosity increases the susceptibility to oxidation and sealing their surface is mandatory to avoid premature degradation. Alongside, polymer derived ceramics (PDCs), such as [...] Read more.
Powder metallurgy is a competitive technology to produce ferrous near net shape parts for diverse engineering applications. However, their inherent porosity increases the susceptibility to oxidation and sealing their surface is mandatory to avoid premature degradation. Alongside, polymer derived ceramics (PDCs), such as silicon-carbonitride, have drawn attention concerning their high temperature and chemical stability. However, PDCs undergo volume shrinkage during ceramization that leads to defect formation. The shrinkage can be compensated by the addition of fillers, which are also capable of tailoring the ceramic resulting properties. This work evaluates the processing of PDC-based coatings loaded with ZrO2 and glass fillers to compensate for the shrinkage, densify the coating and seal the sintered steel surface. Therefore, polymeric slurries were sprayed onto sintered steel substrates, which were pyrolyzed at different temperatures for microstructural and oxidation resistance evaluation. Microstructural modifications caused by the enhanced glass viscous flow during pyrolysis at 800 °C resulted in more homogeneous, dense and protective coatings, which reduced the mass gain up to 40 wt% after 100 h of oxidation at 450 °C in air in comparison to the uncoated substrate. Moreover, no macrocracks or spallation were detected, confirming the feasibility of PDC composite barrier coatings for sintered steels. Full article
(This article belongs to the Special Issue Novel Metal Carbide/Carbonitride Materials)
Figures

Figure 1

Open AccessArticle Parametric Modeling of Biomimetic Cortical Bone Microstructure for Additive Manufacturing
Materials 2019, 12(6), 913; https://doi.org/10.3390/ma12060913
Received: 21 February 2019 / Revised: 12 March 2019 / Accepted: 15 March 2019 / Published: 19 March 2019
Viewed by 186 | PDF Full-text (5753 KB) | HTML Full-text | XML Full-text
Abstract
In this work we present a novel algorithm for generating in-silico biomimetic models of a cortical bone microstructure towards manufacturing biomimetic bone via additive manufacturing. The software provides a tool for physicians or biomedical engineers to develop models of cortical bone that include [...] Read more.
In this work we present a novel algorithm for generating in-silico biomimetic models of a cortical bone microstructure towards manufacturing biomimetic bone via additive manufacturing. The software provides a tool for physicians or biomedical engineers to develop models of cortical bone that include the inherent complexity of the microstructure. The correspondence of the produced virtual prototypes with natural bone tissue was assessed experimentally employing Digital Light Processing (DLP) of a thermoset polymer resin to recreate healthy and osteoporotic bone tissue microstructure. The proposed tool was successfully implemented to develop cortical bone structure based on osteon density, cement line thickness, and the Haversian and Volkmann channels to produce a user-designated bone porosity that matches within values reported from literature for these types of tissues. Characterization of the specimens using a Scanning Electron Microscopy with Focused Ion Beam (SEM/FIB) and Computer Tomography (CT) revealed that the manufacturability of intricated virtual prototype is possible for scaled-up versions of the tissue. Modeling based on the density, inclination and size range of the osteon and Haversian and Volkmann´s canals granted the development of a dynamic in-silico porosity (13.37–21.49%) that matches with models of healthy and osteoporotic bone. Correspondence of the designed porosity with the manufactured assessment (5.79–16.16%) shows that the introduced methodology is a step towards the development of more refined and lifelike porous structures such as cortical bone. Further research is required for validation of the proposed methodology model of the real bone tissue and as a patient-specific customization tool of synthetic bone. Full article
(This article belongs to the Special Issue Advances in Bone Substitute Biology, Production, and Materials)
Figures

Graphical abstract

Open AccessArticle Evaluation and Selection of De-Icing Salt Based on Multi-Factor
Materials 2019, 12(6), 912; https://doi.org/10.3390/ma12060912
Received: 18 February 2019 / Revised: 13 March 2019 / Accepted: 14 March 2019 / Published: 19 March 2019
Viewed by 99 | PDF Full-text (2145 KB) | HTML Full-text | XML Full-text
Abstract
De-icing salts can greatly ease traffic congestion but introduce corrosion of concrete and damage to plant growth. The decision of which de-icing salt to use becomes a crucial issue. In this study, several representative de-icing salts were investigated, and the effects of de-icing [...] Read more.
De-icing salts can greatly ease traffic congestion but introduce corrosion of concrete and damage to plant growth. The decision of which de-icing salt to use becomes a crucial issue. In this study, several representative de-icing salts were investigated, and the effects of de-icing ability, salt freezing corrosion on concrete, and plant growth were comprehensively tested. Finally, the decision of de-icing salt was made based on analytic hierarchy process (AHP). Results show that de-icing salts achieving the best de-icing effect are not the same at different concentrations. De-icing salts of 3% concentration have the greatest corrosion to concrete. Notably, magnesium chloride and calcium magnesium acetate have the least impact on plants among all studied de-icing salts. Using AHP, ethylene glycol and calcium magnesium acetate are selected as optimal items under different priorities. Full article
(This article belongs to the Special Issue Sustainability in Construction and Building Materials)
Figures

Figure 1

Open AccessFeature PaperArticle Room Temperature Synthesis of V-Doped TiO2 and Its Photocatalytic Activity in the Removal of Caffeine under UV Irradiation
Materials 2019, 12(6), 911; https://doi.org/10.3390/ma12060911
Received: 21 February 2019 / Revised: 13 March 2019 / Accepted: 16 March 2019 / Published: 19 March 2019
Viewed by 93 | PDF Full-text (1047 KB) | HTML Full-text | XML Full-text
Abstract
In this work, the influence of simple acids in the room temperature sol-gel synthesis of TiO2 was investigated and the efficiency of prepared photocatalysts was evaluated in the removal of caffeine. To improve the photoactivity of TiO2, vanadium-doped TiO2 [...] Read more.
In this work, the influence of simple acids in the room temperature sol-gel synthesis of TiO2 was investigated and the efficiency of prepared photocatalysts was evaluated in the removal of caffeine. To improve the photoactivity of TiO2, vanadium-doped TiO2 (VTiO2) samples were obtained starting from different amount of vanadyl sulphate as a dopant source. The samples were centrifuged, washed and finally dried at room temperature, and no calcination step was carried out. The prepared photocatalysts were characterized by different techniques (X-ray powder diffraction (XRD), specific surface area (SSA), ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) and Raman). VTiO2 photocatalysts were tested in the photocatalytic removal of aqueous solutions containing caffeine. The photocatalytic tests were carried out in a recirculating batch cylindrical photoreactor irradiated by a UV LEDs strip (nominal power of 12 W and wavelength emission peak at about 365 nm) surrounding the external surface of the reactor. The optimized VTiO2 photocatalyst was able to reach a caffeine degradation of about 96% after 360 min of UV light irradiation with a total organic carbon (TOC) removal of 72%. Full article
Figures

Figure 1

Open AccessArticle Binary Oxides Prepared by Microwave-Assisted Solution Combustion: Synthesis, Characterization and Catalytic Activity
Materials 2019, 12(6), 910; https://doi.org/10.3390/ma12060910
Received: 25 February 2019 / Revised: 11 March 2019 / Accepted: 15 March 2019 / Published: 19 March 2019
Viewed by 97 | PDF Full-text (9958 KB) | HTML Full-text | XML Full-text
Abstract
Three different alumina-based Ni, Cu, Co oxide catalysts with metal loading of 10 wt %, and labeled 10Ni–Al, 10Co–Al and 10Cu–Al, were prepared by microwave-assisted solution combustion. Their morphological, structural and surface properties were deeply investigated by complementary physico-chemical techniques. Finally, the three [...] Read more.
Three different alumina-based Ni, Cu, Co oxide catalysts with metal loading of 10 wt %, and labeled 10Ni–Al, 10Co–Al and 10Cu–Al, were prepared by microwave-assisted solution combustion. Their morphological, structural and surface properties were deeply investigated by complementary physico-chemical techniques. Finally, the three materials were tested in CO oxidation used as test reaction for comparing their catalytic performance. The 10Cu–Al catalyst was constituted of copper oxide phase, while the 10Ni–Al and 10Co–Al catalysts showed the presence of “spinels” phases on the surface. The well-crystallized copper oxide phase in the 10Cu–Al catalyst, obtained by microwave synthesis, allowed for obtaining very high catalytic activity. With a CO conversion of 100% at 225 °C, the copper containing catalyst showed a much higher activity than that usually measured for catalytic materials of similar composition, thus representing a promising alternative for oxidation processes. Full article
(This article belongs to the Special Issue Materials for Clean Processes in Energy)
Figures

Graphical abstract

Open AccessArticle Nanocomplexes of Graphene Oxide and Platinum Nanoparticles against Colorectal Cancer Colo205, HT-29, HTC-116, SW480, Liver Cancer HepG2, Human Breast Cancer MCF-7, and Adenocarcinoma LNCaP and Human Cervical Hela B Cell Lines
Materials 2019, 12(6), 909; https://doi.org/10.3390/ma12060909
Received: 26 February 2019 / Revised: 11 March 2019 / Accepted: 15 March 2019 / Published: 19 March 2019
Viewed by 105 | PDF Full-text (4797 KB) | HTML Full-text | XML Full-text
Abstract
Inefficient drug administration into cancer cells is related to the chemoresistance of cancer cells caused by genetic mutations including genes involved in drug transport, enzyme metabolism, and/or DNA damage repair. The objective of the present study was to evaluate the properties of platinum [...] Read more.
Inefficient drug administration into cancer cells is related to the chemoresistance of cancer cells caused by genetic mutations including genes involved in drug transport, enzyme metabolism, and/or DNA damage repair. The objective of the present study was to evaluate the properties of platinum (NP-Pt), graphene oxide (GO), and the nanocomplex of GO functionalized with platinum nanoparticles (GO-NP-Pt) against several genetically, phenotypically, and metabolically different cancer cell lines: Colo205, HT-29, HTC-116, SW480, HepG2, MCF-7, LNCaP, and Hela B. The anticancer effects toward the cancer cell lines were evaluated by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxyanilide salt (XTT) and bromodeoxyuridine (BrdU) assays and measurements of cell apoptosis and morphology deformations. The NP-Pt and GO could effectively be introduced to cancer cells, but more effective delivery was observed after GO-NP-Pt treatment. The delivery of the GO-NP-Pt nanocomplex significantly decreased the viability of Colo 205 and HepG2 cells, but did not increase the cytotoxicity of other investigated cancer cells. The nanocomplex GO-NP-Pt also significantly increased the apoptosis of Colo 205 and HepG2 cancer cells. The obtained results suggest that the nanocomplex GO-NP-Pt is a remarkable nanostructure that can improve the delivery of Pt nanoparticles into cancer cells and has potential anticancer applications. Full article
(This article belongs to the Special Issue Advanced Cancer Nanotechnology)
Figures

Graphical abstract

Open AccessFeature PaperReview Regenerative Endodontic Procedures Using Contemporary Endodontic Materials
Materials 2019, 12(6), 908; https://doi.org/10.3390/ma12060908
Received: 4 February 2019 / Revised: 28 February 2019 / Accepted: 13 March 2019 / Published: 19 March 2019
Viewed by 119 | PDF Full-text (4678 KB) | HTML Full-text | XML Full-text
Abstract
Calcium hydroxide apexification and Mineral Trioxide Aggregate (MTA) apexification are classical treatments for necrotic immature permanent teeth. The first tend to fail for lack of compliance given the high number of sessions needed; the second has technical difficulties such as material manipulation and [...] Read more.
Calcium hydroxide apexification and Mineral Trioxide Aggregate (MTA) apexification are classical treatments for necrotic immature permanent teeth. The first tend to fail for lack of compliance given the high number of sessions needed; the second has technical difficulties such as material manipulation and overfilling. With both techniques, the root development is interrupted leaving the tooth with a fragile root structure, a poor crown-to-root ratio, periodontal breakdown, and high risk of fracture, compromising long-term prognosis of the tooth. New scientific literature has described a procedure that allows complete root development of these specific teeth. This regenerative endodontic procedure (REP) proposes the use of a combination of antimicrobials and irrigants, no canal walls instrumentation, induced apical bleeding to form a blood clot and a tight seal into the root canal to promote healing. MTA is the most used material to perform this seal, but updated guidelines advise the use of other bioactive endodontic cements that incorporate calcium and silicate in their compositions. They share most of their characteristics with MTA but claim to have fewer drawbacks with regards to manipulation and aesthetics. The purpose of the present article is to review pertinent literature and to describe the clinical procedures protocol with its variations, and their clinical application. Full article
(This article belongs to the Special Issue Contemporary Endodontic Materials)
Figures

Figure 1

Open AccessReview Advanced Electric Discharge Machining of Stainless Steels: Assessment of the State of the Art, Gaps and Future Prospect
Materials 2019, 12(6), 907; https://doi.org/10.3390/ma12060907
Received: 9 February 2019 / Revised: 28 February 2019 / Accepted: 13 March 2019 / Published: 19 March 2019
Viewed by 126 | PDF Full-text (13064 KB) | HTML Full-text | XML Full-text
Abstract
Electric discharge machining (EDM) is a material removal process that is especially useful for difficult-to-cut materials with complex shapes and is widely used in aerospace, automotive, surgical tools among other fields. EDM is one of the most efficient manufacturing processes and is used [...] Read more.
Electric discharge machining (EDM) is a material removal process that is especially useful for difficult-to-cut materials with complex shapes and is widely used in aerospace, automotive, surgical tools among other fields. EDM is one of the most efficient manufacturing processes and is used to achieve highly accurate production. It is a non-contact thermal energy process used to machine electrically conductive components irrespective of the material’s mechanical properties. Studies related to the EDM have shown that the process performance can be considerably improved by properly selecting the process material and operating parameters. This paper reviews research studies on the application of EDM to different grades of stainless steel materials and describes experimental and theoretical studies of EDM that have attempted to improve the process performance, by considering material removal rate, surface quality and tool wear rate, amongst others. In addition, this paper examines evaluation models and techniques used to determine the EDM process conditions. This review also presents a discussion on developments in EDM and outlines the likely trend for future research. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Figures

Figure 1

Open AccessArticle Prototype Orthopedic Bone Plates 3D Printed by Laser Melting Deposition
Materials 2019, 12(6), 906; https://doi.org/10.3390/ma12060906
Received: 4 February 2019 / Revised: 12 March 2019 / Accepted: 14 March 2019 / Published: 19 March 2019
Viewed by 133 | PDF Full-text (8117 KB) | HTML Full-text | XML Full-text
Abstract
Laser melting deposition is a 3D printing method usually studied for the manufacturing of machine parts in the industry. However, for the medical sector, although feasible, applications and actual products taking advantage of this technique are only scarcely reported. Therefore, in this study, [...] Read more.
Laser melting deposition is a 3D printing method usually studied for the manufacturing of machine parts in the industry. However, for the medical sector, although feasible, applications and actual products taking advantage of this technique are only scarcely reported. Therefore, in this study, Ti6Al4V orthopedic implants in the form of plates were 3D printed by laser melting deposition. Tuning of the laser power, scanning speed and powder feed rate was conducted, in order to obtain a continuous deposition after a single laser pass and to diminish unwanted blown powder, stuck in the vicinity of the printed elements. The fabrication of bone plates is presented in detail, putting emphasis on the scanning direction, which had a decisive role in the 3D printing resolution. The printed material was investigated by optical microscopy and was found to be dense, with no visible pores or cracks. The metallographic investigations and X-ray diffraction data exposed an unusual biphasic α+β structure. The energy dispersive X-ray spectroscopy revealed a composition very similar to the one of the starting powder material. The mapping of the surface showed a uniform distribution of elements, with no segregations or areas with deficient elemental distribution. The in vitro tests performed on the 3D printed Ti6Al4V samples in osteoblast-like cell cultures up to 7 days showed that the material deposited by laser melting is cytocompatible. Full article
Figures

Graphical abstract

Open AccessArticle Construction Materials from Vitrified Lignite Fly Ash in Plasmatron Plasma Reactor
Materials 2019, 12(6), 905; https://doi.org/10.3390/ma12060905
Received: 12 February 2019 / Revised: 3 March 2019 / Accepted: 8 March 2019 / Published: 19 March 2019
Viewed by 115 | PDF Full-text (4360 KB) | HTML Full-text | XML Full-text
Abstract
This article presents results of an investigation of vitrified (melted) fly ash samples from lignite (brown coal) in a plasmatron plasma reactor, to determine its mechanical and chemical properties. The XRF elemental analysis results of sample tests, from before the vitrification process and [...] Read more.
This article presents results of an investigation of vitrified (melted) fly ash samples from lignite (brown coal) in a plasmatron plasma reactor, to determine its mechanical and chemical properties. The XRF elemental analysis results of sample tests, from before the vitrification process and after the vitrification process are shown. The experiments were carried out in a plasma plasmatron reactor with a total power of 65 kW, enabling testing on a quarter technical scale. During the tests, samples of fly ash of about 4 kg mass were processed under selected process conditions. Produced samples of vitrified materials were analyzed in accordance to the requirements for building/construction materials. Results from this investigation confirm its quality to be used as concrete and cement filler, as an addition, and as synthetic aggregate, safe for the environment and neutral for cements. Also the most important leaching of heavy metals to water was analyzed which confirmed meeting of all of requirements necessary to use this material in building materials. Full article
(This article belongs to the Special Issue Sustainability in Construction and Building Materials)
Figures

Figure 1

Open AccessArticle Peptide Controlled Shaping of Biomineralized Tin(II) Oxide into Flower-Like Particles
Materials 2019, 12(6), 904; https://doi.org/10.3390/ma12060904
Received: 11 February 2019 / Revised: 5 March 2019 / Accepted: 13 March 2019 / Published: 18 March 2019
Viewed by 186 | PDF Full-text (1387 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The size and morphology of metal oxide particles have a large impact on the physicochemical properties of these materials, e.g., the aspect ratio of particles affects their catalytic activity. Bioinspired synthesis routes give the opportunity to control precisely the structure and aspect ratio [...] Read more.
The size and morphology of metal oxide particles have a large impact on the physicochemical properties of these materials, e.g., the aspect ratio of particles affects their catalytic activity. Bioinspired synthesis routes give the opportunity to control precisely the structure and aspect ratio of the metal oxide particles by bioorganic molecules, such as peptides. This study focusses on the identification of tin(II) oxide (tin monoxide, SnO) binding peptides, and their effect on the synthesis of crystalline SnO microstructures. The phage display technique was used to identify the 7-mer peptide SnBP01 (LPPWKLK), which shows a high binding affinity towards crystalline SnO. It was found that the derivatives of the SnBP01 peptide, varying in peptide length and thus in their interaction, significantly affect the aspect ratio and the size dimension of mineralized SnO particles, resulting in flower-like morphology. Furthermore, the important role of the N-terminal leucine residue in the peptide for the strong organic–inorganic interaction was revealed by FTIR investigations. This bioinspired approach shows a facile procedure for the detailed investigation of peptide-to-metal oxide interactions, as well as an easy method for the controlled synthesis of tin(II) oxide particles with different morphologies. Full article
Figures

Graphical abstract

Open AccessArticle Tribological Properties of Molybdenum Disulfide and Helical Carbon Nanotube Modified Epoxy Resin
Materials 2019, 12(6), 903; https://doi.org/10.3390/ma12060903
Received: 28 January 2019 / Revised: 8 March 2019 / Accepted: 14 March 2019 / Published: 18 March 2019
Viewed by 152 | PDF Full-text (8905 KB) | HTML Full-text | XML Full-text
Abstract
In this study, epoxy resin (EP) composites were prepared by using molybdenum disulfide (MoS2) and helical carbon nanotubes (H-CNTs) as the antifriction and reinforcing phases, respectively. The effects of MoS2 and H-CNTs on the friction coefficient, wear amount, hardness, and [...] Read more.
In this study, epoxy resin (EP) composites were prepared by using molybdenum disulfide (MoS2) and helical carbon nanotubes (H-CNTs) as the antifriction and reinforcing phases, respectively. The effects of MoS2 and H-CNTs on the friction coefficient, wear amount, hardness, and elastic modulus of the composites were investigated. The tribological properties of the composites were tested using the UMT-3MT friction testing machine, non-contact three-dimensional surface profilometers, and nanoindenters. The analytical results showed that the friction coefficient of the composites initially decreased and then increased with the increase in the MoS2 content. The friction coefficient was the smallest when the MoS2 content in the EP was 6%, and the wear amount increased gradually. With the increasing content of H-CNTs, the friction coefficient of the composite material did not change significantly, although the wear amount decreased gradually. When the MoS2 and H-CNTs contents were 6% and 4%, respectively, the composite exhibited the minimum friction coefficient and a small amount of wear. Moreover, the addition of H-CNTs significantly enhanced the hardness and elastic modulus of the composites, which could be applied as materials in high-temperature and high-pressure environments where lubricants and greases do not work. Full article
Figures

Figure 1

Open AccessArticle Method of Optimisation for Ambient Temperature Cured Sustainable Geopolymers for 3D Printing Construction Applications
Materials 2019, 12(6), 902; https://doi.org/10.3390/ma12060902
Received: 12 February 2019 / Revised: 12 March 2019 / Accepted: 14 March 2019 / Published: 18 March 2019
Viewed by 164 | PDF Full-text (4899 KB) | HTML Full-text | XML Full-text
Abstract
Since the initial introduction of geopolymers, these materials have been characterised as environmentally-friendly sustainable substitutes for ordinary Portland cement (OPC). There is a routine increase in the application of geopolymers, especially in advanced technologies. Because of its better rheological characteristics compared to OPC, [...] Read more.
Since the initial introduction of geopolymers, these materials have been characterised as environmentally-friendly sustainable substitutes for ordinary Portland cement (OPC). There is a routine increase in the application of geopolymers, especially in advanced technologies. Because of its better rheological characteristics compared to OPC, geopolymers are appropriate materials for extrusion-based 3D printing technologies. This paper focuses on the optimisation of an ambient temperature cured geopolymer for 3D printing construction applications. The effects of mixture parameters, including the type of hydroxide solution (HS), the type of silicate solution (SS) and the mass ratio of SS to HS on the workability, extrudability, shape retention ability and mechanical performance of different geopolymer mixtures were investigated. Accordingly, an optimum mixture was identified for geopolymers cured at ambient temperatures. Mechanical properties of the optimised mixture, including flexural and compressive strengths, were measured in different directions with respect to the printed layers. Further, uniaxial tension tests were also conducted on the optimised mixture to measure its interlayer bond strength. The results showed that among the activators investigated, the sodium-based activator composed of sodium hydroxide and sodium silicate solutions, with a SiO2/Na2O ratio of 3.22, was the most effective activator, providing appropriate workability and extrudability, along with reasonable strength and a high shape retention ability. The acquired mechanical properties exhibited anisotropic behaviour in different testing direction. The strength of the interlayer bond was found to be adequate to avoid interfacial shear failure. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
Figures

Figure 1

Open AccessArticle Synthesis of Nanocrystalline AZ91 Magnesium Alloy Dispersed with 15 vol.% Submicron SiC Particles by Mechanical Milling
Materials 2019, 12(6), 901; https://doi.org/10.3390/ma12060901
Received: 2 March 2019 / Revised: 13 March 2019 / Accepted: 15 March 2019 / Published: 18 March 2019
Viewed by 144 | PDF Full-text (6514 KB) | HTML Full-text | XML Full-text
Abstract
The development of a magnesium matrix composite with a high content of dispersions using conventional liquid-phase process is a great challenge, especially for nanometer/submicron particles. In this work, mechanical milling was employed to prepare nanocrystalline AZ91 dispersed with 15 vol.% submicron SiC particles [...] Read more.
The development of a magnesium matrix composite with a high content of dispersions using conventional liquid-phase process is a great challenge, especially for nanometer/submicron particles. In this work, mechanical milling was employed to prepare nanocrystalline AZ91 dispersed with 15 vol.% submicron SiC particles (SiCp/AZ91). AZ91 with no SiCp was applied as a comparative study with the same mechanical milling. In order to investigate the mechanism of dispersing, the morphology evolution of powders and the corresponding SiCp distribution were observed. As the scanning electron microscope (SEM) analysis exhibited, the addition of SiCp accelerated the smashing of AZ91 particles, which promoted the dispersion of SiCp in AZ91. Thus, after mechanical milling, 15 vol.% SiCp, which was smashed from 800 to 255 nm, got uniformly distributed in the Mg matrix. Based on X-ray diffraction (XRD) results, part of the Mg17Al12 precipitate got dissolved, and an Al-supersaturated Mg solid solution was formed. The transmission electron microscopy (TEM) results showed that the ultimate Mg grain (32 nm) of milled SiCp/AZ91 was much smaller than that of milled AZ91 (64 nm), which can be attributed to a pinning effect of submicron SiCp. After mechanical milling, the hardness of SiCp/AZ91 reached 185 HV, which was 185% higher than the original AZ91 and 33% higher than milled AZ91, due to fine Mg grain and submicron dispersions. Full article
(This article belongs to the Section Advanced Nanomaterials)
Figures

Figure 1

Open AccessArticle Correlation of Macroscopic Fracture Behavior with Microscopic Fracture Mechanism for AHSS Sheet
Materials 2019, 12(6), 900; https://doi.org/10.3390/ma12060900
Received: 30 January 2019 / Revised: 7 March 2019 / Accepted: 13 March 2019 / Published: 18 March 2019
Viewed by 133 | PDF Full-text (5817 KB) | HTML Full-text | XML Full-text
Abstract
This research aims to correlate the macroscopic fracture phenomenon with its microscopic fracture mechanism for an advanced high-strength steel (AHSS) TRIP 780 sheet by applying a combined experimental-numerical approach. Six specimens with different shapes were tensioned to fracture and the main deformation areas [...] Read more.
This research aims to correlate the macroscopic fracture phenomenon with its microscopic fracture mechanism for an advanced high-strength steel (AHSS) TRIP 780 sheet by applying a combined experimental-numerical approach. Six specimens with different shapes were tensioned to fracture and the main deformation areas of specimens were subjected to stress states ranging from lower to higher stress triaxiality. The final fracture surface feature for each specimen was obtained to characterize the macroscopic fracture modes at different stress states. The scanning electron microscope (SEM) fractographies of fracture surfaces were detected to reveal the microscopic fracture mechanisms. The stress triaxiality evolution was applied to correlate of fracture mode and fracture mechanism by comparing the macroscopic fracture features as well as micro-defect changes. An increase of stress triaxiality leads to voids extension and then results in a voids-dominant fracture. The micro-shear-slip tends to appear in the stress triaxiality level lower than that of pure shear stress state. The fracture behavior of a practice deformation process was the result of interplay between shear-slip fracture and void-dominant fracture. The unified relationship between average void sizes and stress triaxiality was obtained. The void growth was predicted by the Rice–Tracey model with higher precision. Full article
Figures

Figure 1

Materials EISSN 1996-1944 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top