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 11, Issue 12 (December 2018)

  • 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 1-162
Export citation of selected articles as:
Open AccessArticle Ferroelectromagnetic Properties of PbFe1/2Nb1/2O3 (PFN) Material Synthesized by Chemical-Wet Technology
Materials 2018, 11(12), 2504; https://doi.org/10.3390/ma11122504 (registering DOI)
Received: 2 November 2018 / Revised: 26 November 2018 / Accepted: 4 December 2018 / Published: 9 December 2018
PDF Full-text (4049 KB) | HTML Full-text | XML Full-text
Abstract
In this work, PbFe1/2Nb1/2O3 (PFN) ceramic samples synthesized by chemically wet method (precipitation from the solution) were obtained. Due to the tendency to form powder agglomerates, the synthesized powder was subjected to ultrasound. The sintering was carried out
[...] Read more.
In this work, PbFe1/2Nb1/2O3 (PFN) ceramic samples synthesized by chemically wet method (precipitation from the solution) were obtained. Due to the tendency to form powder agglomerates, the synthesized powder was subjected to ultrasound. The sintering was carried out under various technological conditions, mainly through controlling the sintering temperature. -X-ray powder-diffraction (XRD), scanning electron microscope (SEM) microstructure analysis, as well as the examinations of dielectric, ferroelectric, and magnetic properties of the PFN ceramics were carried out. Studies have shown that hard ceramic agglomerates can be partially minimized by ultrasound. Due to this treatment, closed porosity decreases, and the ceramic samples have a higher density. Optimization and improvement of the technological process of the PFN material extends the possibility of its use for the preparation of multiferroic composites or multicomponent solid solutions based on PFN. Such materials with functional properties find applications in microelectronic applications, e.g., in systems integrating ferroelectric and magnetic properties in one device. The optimal synthesis conditions of PFN ceramics were determined to be 1050 °C/2 h. Full article
Figures

Figure 1

Open AccessArticle Influence of Ag on the Properties of Ca0.9Yb0.1MnO3 Sintered Ceramics
Materials 2018, 11(12), 2503; https://doi.org/10.3390/ma11122503 (registering DOI)
Received: 14 November 2018 / Revised: 29 November 2018 / Accepted: 5 December 2018 / Published: 9 December 2018
PDF Full-text (2729 KB) | HTML Full-text | XML Full-text
Abstract
In this study, Ca0.9Yb0.1MnO3 + x wt.% Ag (with x = 0, 1, 3, 5, and 10) thermoelectric materials were prepared via the classical ceramic method. In spite of the very high sintering temperature (1300 °C), no significant
[...] Read more.
In this study, Ca0.9Yb0.1MnO3 + x wt.% Ag (with x = 0, 1, 3, 5, and 10) thermoelectric materials were prepared via the classical ceramic method. In spite of the very high sintering temperature (1300 °C), no significant Ag losses were observed following this process. Moreover, Ag addition enhanced cation mobility during sintering due to the formation of a liquid phase. Microstructurally, it was found that Ag decreases porosity; this was confirmed by density measurements. Ag was also found to promote the formation of a Ca2Mn2O5 secondary phase. Despite the presence of this secondary phase, samples with Ag displayed lower electrical resistivity than Ag-free ones, without a drastic decrease in the absolute Seebeck coefficient. The highest thermoelectric performances, which were determined by power factor, were obtained in 1 wt.% Ag samples. These maximum values are slightly higher than the best of those reported in the literature for sintered materials with similar compositions, with the additional advantage of their being obtained using a much shorter sintering procedure. Full article
(This article belongs to the Special Issue Recent Advances in Thermoelectric Materials)
Figures

Graphical abstract

Open AccessArticle A Comparative Study of E-Beam Deposited Gate Dielectrics on Channel Width-Dependent Performance and Reliability of a-IGZO Thin-Film Transistors
Materials 2018, 11(12), 2502; https://doi.org/10.3390/ma11122502 (registering DOI)
Received: 26 October 2018 / Revised: 28 November 2018 / Accepted: 7 December 2018 / Published: 9 December 2018
PDF Full-text (3240 KB) | HTML Full-text | XML Full-text
Abstract
A comparative study on the effects of e-beam deposited gate dielectrics for amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) has been carried out using SiO2, Si3N4, and Ta2O5 dielectric materials.
[...] Read more.
A comparative study on the effects of e-beam deposited gate dielectrics for amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) has been carried out using SiO2, Si3N4, and Ta2O5 dielectric materials. The channel width dependent device electrical performances were investigated using three different sizes of 500 μm, 1000 μm, and 1500 μm. The reliability characteristics were revealed by the threshold voltage variation and drain current variation under positive bias stress. The e-beam deposited high-k dielectric Ta2O5 exhibited the highest stability at the stress voltage of 3 V for 1000 s due to its high capacitance density at 34.1 nF/cm2. The threshold voltage variation along the channel width decreased from SiO2, then Si3N4, to Ta2O5, because of the increased insulating property and density of capacitance. The SiO2-based a-IGZO TFT achieved a high field effect mobility of 27.9 cm2/V·s and on–off current ratio > 107 at the lower channel width of 500 μm. The gate leakage current also decreased with increasing the channel width/length ratio. In addition, the SiO2 gate dielectric-based a-IGZO TFT could be a faster device, whereas the Ta2O5 gate dielectric would be a good candidate for a higher reliability component with adequate surface treatment. Full article
(This article belongs to the Special Issue Transparent Conductive Films and Their Applications)
Figures

Figure 1

Open AccessArticle Effects of an Alternating Magnetic Field/Ag Multi-Alloying Combined Solidification Process on Cu–14Fe Alloy
Materials 2018, 11(12), 2501; https://doi.org/10.3390/ma11122501 (registering DOI)
Received: 7 November 2018 / Revised: 5 December 2018 / Accepted: 6 December 2018 / Published: 9 December 2018
PDF Full-text (3241 KB) | HTML Full-text | XML Full-text
Abstract
An alternating magnetic field (AMF)/Ag multi-alloying combined process was applied to the solidification of Cu–14Fe alloy to study its effects on the microstructure and properties of the resulting samples. The applied AMF and Ag multi-alloying had positive effects on the refinement of the
[...] Read more.
An alternating magnetic field (AMF)/Ag multi-alloying combined process was applied to the solidification of Cu–14Fe alloy to study its effects on the microstructure and properties of the resulting samples. The applied AMF and Ag multi-alloying had positive effects on the refinement of the primary Fe phase and precipitation of Fe solute atoms, respectively. These results indicated that the combined AMF/Ag multi-alloying process was effective to improve the distribution of the primary Fe phase and reduce the Fe content of the Cu matrix, which increased the conductivity of the alloy. The application of the combined AMF/Ag multi-alloying process to the solidification of Cu–Fe alloy provided samples with improved comprehensive properties compared with those of samples solidified using a single process (AMF or Ag multi-alloying). Full article
Figures

Figure 1

Open AccessArticle Facile Fabrication of Amorphous Photonic Structures with Non-Iridescent and Highly-Stable Structural Color on Textile Substrates
Materials 2018, 11(12), 2500; https://doi.org/10.3390/ma11122500 (registering DOI)
Received: 20 November 2018 / Revised: 6 December 2018 / Accepted: 7 December 2018 / Published: 8 December 2018
PDF Full-text (2249 KB) | Supplementary Files
Abstract
Amorphous photonic structures with non-iridescent and highly-stable structural color were fabricated via a simple one-step spray-coating technique. With this strategy, the obtained films on textile substrates presented short-ordered and amorphous photonic structures (APSs) similar to the amorphous nanostructures of avian feathers. The structural
[...] Read more.
Amorphous photonic structures with non-iridescent and highly-stable structural color were fabricated via a simple one-step spray-coating technique. With this strategy, the obtained films on textile substrates presented short-ordered and amorphous photonic structures (APSs) similar to the amorphous nanostructures of avian feathers. The structural color presented the same hue when viewed at different angles and could be well controlled by varying the diameters of the SiO2 nanospheres. The prepared fabrics with structural color exhibited high color stability due to stability in both the assembled physical structure and the refractive index. The high stability of the assembled physical structure was attributed to the cementing effect of Poly(methylmethacrylate-butylacrylate) P(MMA-BA) existing between textile substrate and SiO2 nanospheres and among SiO2 nanospheres, while the high stability in the refractive index was contributed by the liquid-resistance achieved by both the surface roughness and the low-surface-energy of the as-sprayed APSs. With the resistances to external forces and liquid invasion, the non-iridescent brilliant structural color of the as-prepared fabrics could be kept steady. In this study, an approach of fabricating APSs with non-iridescent and stable structural color was established to enhance its potential application in structural coloration of textiles, and other color-related smart textiles. . Full article
Open AccessArticle Hydration Kinetics of Composite Cementitious Materials Containing Copper Tailing Powder and Graphene Oxide
Materials 2018, 11(12), 2499; https://doi.org/10.3390/ma11122499 (registering DOI)
Received: 19 October 2018 / Revised: 4 December 2018 / Accepted: 6 December 2018 / Published: 8 December 2018
PDF Full-text (5024 KB) | HTML Full-text | XML Full-text
Abstract
The hydration heat evolution curves of composite cementitious materials containing copper tailing powder (CT) and graphene oxide (GO) with different contents are measured and analyzed in this paper. The hydration rate and total hydration heat of the composite cementitious materials decrease with the
[...] Read more.
The hydration heat evolution curves of composite cementitious materials containing copper tailing powder (CT) and graphene oxide (GO) with different contents are measured and analyzed in this paper. The hydration rate and total hydration heat of the composite cementitious materials decrease with the increase of CT dosage, but improve with the increase of CT fineness and GO dosage. The hydration process of the cementitious systems undergoes three periods, namely nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), which can be simulated well using the Krstulovic–Dabic model. The hydration rates of the three controlling processes of the composite cementitious system decrease with the increase of CT content, but improve slightly with the increase of CT fineness. GO enhances the controlling effect of the NG process of the cementitious systems with or without CT, thus promotes the early hydration as a whole. Full article
(This article belongs to the Special Issue Thermal Analysis of Materials)
Figures

Graphical abstract

Open AccessCommunication Facile Synthesis of Silver Nanoparticles with High Antibacterial Activity
Materials 2018, 11(12), 2498; https://doi.org/10.3390/ma11122498 (registering DOI)
Received: 22 October 2018 / Revised: 9 November 2018 / Accepted: 6 December 2018 / Published: 8 December 2018
PDF Full-text (2138 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report on a reverse microemulsion method for the synthesis of silver nanocrystals and examine their antibacterial activities. As the molar ratio of water to sodium bis(2-ethylhexyl) sulfosuccinate (AOT) increases to 25, a morphology transition from a sphere-like nanocrystal to a wire-like one
[...] Read more.
We report on a reverse microemulsion method for the synthesis of silver nanocrystals and examine their antibacterial activities. As the molar ratio of water to sodium bis(2-ethylhexyl) sulfosuccinate (AOT) increases to 25, a morphology transition from a sphere-like nanocrystal to a wire-like one was observed. For both the gram-negative and gram-positive bacteria, the wire-like silver nanocrystal showed higher antibacterial activities. We conclude that the morphology of silver nanocrystals dominates their antibacterial activity. Full article
Figures

Figure 1

Open AccessArticle A Self-Adaptive Umbrella Model for Vibration Analysis of Graphene
Materials 2018, 11(12), 2497; https://doi.org/10.3390/ma11122497 (registering DOI)
Received: 11 November 2018 / Revised: 2 December 2018 / Accepted: 4 December 2018 / Published: 8 December 2018
PDF Full-text (4336 KB) | HTML Full-text | XML Full-text
Abstract
The beam finite element and molecular dynamics models are two popular methods to represent the reaction of carbon-carbon bonds in graphene. However, the wrinkles and ripples in geometrical characteristics are difficult take into consideration. The out-planar mechanical properties are neglected in classical models
[...] Read more.
The beam finite element and molecular dynamics models are two popular methods to represent the reaction of carbon-carbon bonds in graphene. However, the wrinkles and ripples in geometrical characteristics are difficult take into consideration. The out-planar mechanical properties are neglected in classical models of graphene. This paper proposes a self-adaptive umbrella model for vibration analysis of graphene. The parameters in the umbrella model are flexible to adapting the geometrical and material characteristics of graphene. The umbrella model consists of shell and beam elements. The honeycomb beam and planar shell model of graphene are included in the self-adaptive umbrella model as particular cases. The sensitivity analysis and results confirmed the rationality and feasibility of the self-adaptive umbrella model. Full article
Figures

Figure 1

Open AccessArticle Regulation of Substrate-Target Distance on the Microstructural, Optical and Electrical Properties of CdTe Films by Magnetron Sputtering
Materials 2018, 11(12), 2496; https://doi.org/10.3390/ma11122496 (registering DOI)
Received: 10 November 2018 / Revised: 2 December 2018 / Accepted: 5 December 2018 / Published: 8 December 2018
PDF Full-text (2527 KB) | HTML Full-text | XML Full-text
Abstract
Cadmium telluride (CdTe) films were deposited on glass substrates by direct current (DC) magnetron sputtering, and the effect of substrate-target distance (Dts) on properties of the CdTe films was investigated by observations of X-ray diffraction (XRD) patterns, atomic force microscopy
[...] Read more.
Cadmium telluride (CdTe) films were deposited on glass substrates by direct current (DC) magnetron sputtering, and the effect of substrate-target distance (Dts) on properties of the CdTe films was investigated by observations of X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), UV-VIS spectra, optical microscopy, and the Hall-effect measurement system. XRD analysis indicated that all samples exhibited a preferred orientation along the (111) plane, corresponding to the zinc blende structure, and films prepared using Dts of 4 cm demonstrated better crystallinity than the others. AFM studies revealed that surface morphologies of the CdTe films were strongly dependent on Dts, and revealed a large average grain size of 35.25 nm and a high root mean square (RMS) roughness value of 9.66 nm for films fabricated using Dts of 4 cm. UV-VIS spectra suggested the energy band gap (Eg) initially decreased from 1.5 to 1.45 eV, then increased to 1.68 eV as Dts increased from 3.5 to 5 cm. The Hall-effect measurement system revealed that CdTe films prepared with a Dts of 4 cm exhibited optimal electrical properties, and the resistivity, carrier mobility, and carrier concentration were determined to be 2.3 × 105 Ω∙cm, 6.41 cm2∙V−1∙S−1, and 4.22 × 1012 cm−3, respectively. Full article
(This article belongs to the Section Thin Films)
Figures

Figure 1

Open AccessArticle Effects of Laser Texture Oxidation and High-Temperature Annealing of TiV Alloy Thin Films on Mechanical and Antibacterial Properties and Cytotoxicity
Materials 2018, 11(12), 2495; https://doi.org/10.3390/ma11122495 (registering DOI)
Received: 21 November 2018 / Revised: 4 December 2018 / Accepted: 6 December 2018 / Published: 8 December 2018
PDF Full-text (49106 KB) | HTML Full-text | XML Full-text
Abstract
Titanium dioxide and vanadium oxides have been applied extensively in industrial and medical fields. The objective of this study was to develop various composite structures of titanium and vanadium oxide (Ti-V-O) coatings on pure titanium through high-temperature annealing and laser texturing oxidation, separately;
[...] Read more.
Titanium dioxide and vanadium oxides have been applied extensively in industrial and medical fields. The objective of this study was to develop various composite structures of titanium and vanadium oxide (Ti-V-O) coatings on pure titanium through high-temperature annealing and laser texturing oxidation, separately; additionally, surface morphologies, tribological and hydrophilic properties, and antibacterial and biocompatibility abilities of these Ti-V-O coatings were evaluated. TiV alloy thin films were deposited on pure titanium and then annealed to form Ti-V-O coatings through thermal oxidation and laser texturing oxidation. Ball-on-disc wear tests and contact angle tests were conducted to evaluate the tribological properties and wettability of the coatings, respectively. The antibacterial activity of the coatings was estimated by SYTO9 nucleic acid staining with Staphylococcus aureus (Gram-positive bacteria). The cell cytotoxicity of the coatings was analyzed following the ISO 10995-5:2009 standard with human skin fibroblast cells. The Ti-V-O coatings, subjected to annealing at 700 °C, demonstrated higher hardness (Hv 1171) and a lower friction coefficient (0.6). The highest hardness (Hv 2711) and the lowest friction coefficient (0.52) were obtained for the Ti-V-O after laser surface texturing oxidation at 100 kHz. The oxide coating obtained from 100 kHz laser texturing oxidation exhibited the lotus effect because of its systematic textured microstructures, and displayed superhydrophobic surface properties. Compared with the unannealed TiV coating, both the samples with high-temperature annealing and laser surface texturing oxidation had excellent antibacterial properties to Staphylococcus aureus. However, the Ti-V-O thin films exhibited notable cell cytotoxicity. Although the cell viability on Ti-V-O coatings were not ideal, this study confirmed improvement in surface hardness, tribology, and antibacterial performance in Ti-V-O coatings, which may have potential for use in biomedical tools, devices, and equipment. Full article
Figures

Figure 1

Open AccessArticle Tunable Luminescent A-SiNxOy Films with High Internal Quantum Efficiency and Fast Radiative Recombination Rates
Materials 2018, 11(12), 2494; https://doi.org/10.3390/ma11122494 (registering DOI)
Received: 18 November 2018 / Revised: 5 December 2018 / Accepted: 6 December 2018 / Published: 8 December 2018
PDF Full-text (5784 KB) | HTML Full-text | XML Full-text
Abstract
In this work, we systematically investigated the Nx bonding defects that induced high photoluminescence internal quantum efficiencies (PL IQEs) and very fast radiative recombination processes in amorphous silicon oxynitride (a-SiNxOy) systems. The luminescent N‒Si‒O bonding-related defect states were
[...] Read more.
In this work, we systematically investigated the Nx bonding defects that induced high photoluminescence internal quantum efficiencies (PL IQEs) and very fast radiative recombination processes in amorphous silicon oxynitride (a-SiNxOy) systems. The luminescent N‒Si‒O bonding-related defect states were checked for the XPS, EPR, and temperature-dependent steady-state PL (TD-SSPL) properties. The PL IQEs were calculated from PL quantum yields through the principle of planar geometry optics, and then confirmed by the TD-SSPL properties. The radiative recombination rates [kr(R)] were determined by combining the PL IQE values and ns-PL lifetimes obtained from time-resolved PL measurements. Both the PL IQE, exceeding 72%, and the fast kr(R) (~108 s−1) are proportional to the concentration of Nx defects, which can be explained by N‒Si‒O bonding states related to the quasi-three-level model, suggesting the possible realization of stimulated light emission in a-SiNxOy systems. Full article
(This article belongs to the Section Optics and Photonics)
Figures

Figure 1

Open AccessArticle Copper-Based Volumetric Filler Dedicated for Ag Paste for Depositing the Front Electrodes by Printing on Solar Si Cells
Materials 2018, 11(12), 2493; https://doi.org/10.3390/ma11122493 (registering DOI)
Received: 20 November 2018 / Revised: 4 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
PDF Full-text (1874 KB)
Abstract
In this work we present research results on a new paste NPCuXX (where: NP—new paste, CuXX—component, XX—a modifier consisting of Ni and other important elements) based on a copper composite (CuXX) for fabrication of front electrodes in silicon solar cells. The CuXX composite
[...] Read more.
In this work we present research results on a new paste NPCuXX (where: NP—new paste, CuXX—component, XX—a modifier consisting of Ni and other important elements) based on a copper composite (CuXX) for fabrication of front electrodes in silicon solar cells. The CuXX composite is obtained by chemical processing of copper powder particles and can be used in two ways: as an additive to commercially available paste or as a base material for a new paste, NPCuXX. The CuXX offers the possibility to exchange up to 30 and 50 wt.% Ag into Cu, which significantly decreases the solar cells material costs, and therefore, the overall solar cell price. Emphasis was placed on a proper mass suitable fabrication process of the CuXX component. The NPCuXX paste has been applied both to conventional cell structures such as aluminum-back surface field (Al-BSF) and passivated emitter and rear contact (PERC), and finally solar cells with front electrodes deposited by screen-printing method were fabricated and characterized by current-voltage techniques. This paper reports the first implementation of the copper volumetric material into a screen print paste used in a high-temperature metallization process to fabricate the front contacts of Si solar cells with a highest fill factor of 77.92 and 77.69% for the abovementioned structures, respectively. Full article
(This article belongs to the Special Issue Materials for Photovoltaic Applications)
Open AccessArticle A Novel Class of Injectable Bioceramics that Glue Tissues and Biomaterials
Materials 2018, 11(12), 2492; https://doi.org/10.3390/ma11122492 (registering DOI)
Received: 16 November 2018 / Revised: 30 November 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
PDF Full-text (4757 KB)
Abstract
Calcium phosphate cements (CPCs) are clinically effective void fillers that are capable of bridging calcified tissue defects and facilitating regeneration. However, CPCs are completely synthetic/inorganic, unlike the calcium phosphate that is found in calcified tissues, and they lack an architectural organization, controlled assembly
[...] Read more.
Calcium phosphate cements (CPCs) are clinically effective void fillers that are capable of bridging calcified tissue defects and facilitating regeneration. However, CPCs are completely synthetic/inorganic, unlike the calcium phosphate that is found in calcified tissues, and they lack an architectural organization, controlled assembly mechanisms, and have moderate biomechanical strength, which limits their clinical effectiveness. Herein, we describe a new class of bioinspired CPCs that can glue tissues together and bond tissues to metallic and polymeric biomaterials. Surprisingly, alpha tricalcium phosphate cements that are modified with simple phosphorylated amino acid monomers of phosphoserine (PM-CPCs) bond tissues up to 40-fold stronger (2.5–4 MPa) than commercial cyanoacrylates (0.1 MPa), and 100-fold stronger than surgical fibrin glue (0.04 MPa), when cured in wet-field conditions. In addition to adhesion, phosphoserine creates other novel properties in bioceramics, including a nanoscale organic/inorganic composite microstructure, and templating of nanoscale amorphous calcium phosphate nucleation. PM-CPCs are made of the biocompatible precursors calcium, phosphate, and amino acid, and these represent the first amorphous nano-ceramic composites that are stable in liquids. Full article
(This article belongs to the Section Biomaterials)
Figures

Graphical abstract

Open AccessArticle Carbide Precipitation during Tempering and Its Effect on the Wear Loss of a High-Carbon 8 Mass% Cr Tool Steel
Materials 2018, 11(12), 2491; https://doi.org/10.3390/ma11122491 (registering DOI)
Received: 7 November 2018 / Revised: 27 November 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
PDF Full-text (4532 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the precipitation of carbide and wear loss of high-carbon 8 mass% Cr tool steel at two tempering conditions (i.e., 773–803 K and 823–853 K) were studied by INCA Steel, EPMA-1720H, XRD, and ML-10 tester. The results show that the particles
[...] Read more.
In this paper, the precipitation of carbide and wear loss of high-carbon 8 mass% Cr tool steel at two tempering conditions (i.e., 773–803 K and 823–853 K) were studied by INCA Steel, EPMA-1720H, XRD, and ML-10 tester. The results show that the particles of test steels include the carbides (Cr7C3 and Cr23C6) and carbides nucleated on Al2O3. When carbides are of the same size, the number of carbides in test steel at a tempering temperature of 773–803 K is greater than that at a tempering temperature of 823–853 K, especially when the size of carbides is less than 5 μm. Compared with the test steel tempered at 823–853 K, the distance between adjacent actual particles reduced by 80.6 μm and the maximum amount of reduction was 9.4% for single wear loss at the tempering temperature of 773–803 K. It can be concluded from thermodynamics results that Al2O3 inclusions began to precipitate in liquid, and the precipitation of carbides was at the solid–liquid region. Al2O3 can be used as the nucleation interface of carbide, thus promoting the formation of carbides. During the cooling of molten steel, a lower temperature can increase the difference of actual solubility product bigger than equilibrium solubility product, thus promoting the carbide formation. Full article
Figures

Figure 1

Open AccessArticle Viscoelastic Mechanical Responses of HMAP under Moving Load
Materials 2018, 11(12), 2490; https://doi.org/10.3390/ma11122490 (registering DOI)
Received: 9 November 2018 / Revised: 1 December 2018 / Accepted: 6 December 2018 / Published: 7 December 2018
PDF Full-text (2857 KB) | HTML Full-text | XML Full-text
Abstract
In order to represent the mechanical response laws of high-modulus asphalt pavement (HMAP) faithfully and objectively, the viscoelasticity of high-modulus asphalt mixture (HMAM) was considered, and the viscoelastic mechanical responses were calculated systematically based on moving load by numerical simulations. The performances of
[...] Read more.
In order to represent the mechanical response laws of high-modulus asphalt pavement (HMAP) faithfully and objectively, the viscoelasticity of high-modulus asphalt mixture (HMAM) was considered, and the viscoelastic mechanical responses were calculated systematically based on moving load by numerical simulations. The performances of the HMAP in resistance to the deformation and the cracking at the bottom layer were compared with the ordinary asphalt pavement. Firstly, Lubao and Honeywell 7686 (H7686) were selected as the high modulus modifiers. The laboratory investigations of Asphalt mix-70 penetration, Asphalt mix-SBS (styrene-butadiene-styrene), HMAM-Lubao and HMAM-H7686 were carried out by dynamic modulus tests and wheel tracking tests. The conventional performances related to the purpose of using the HMAM were indicated. The master curves of the storage moduli were obtained and the viscoelastic parameters were fitted based on viscoelastic theories. Secondly, 3D pavement models based on moving loads for the viscoelastic structures were built using the non-linear finite element software ABAQUS. The wheel path was discretized in time and space to apply the Haversine wave load, and then the mechanical responses of four kinds of asphalt pavement were calculated. Finally, the sensitivity analysis was carried out. The results showed that the addition of the high modulus modifiers can improve the resistance to high-temperature rutting of the pavements. Except for the tensile strain and stress at the bottom of the underlayer, other responses decreased with the increases of the dynamic moduli and the change laws of the tensile strain and stress were affected by the range of the dynamic modulus. The tensile stress at the bottom of the asphalt layer would be too large if the modulus of the layer were too large, and a larger tensile strain would result. Therefore, the range of the modulus must be restricted to avoid the cracking due to excessive tension when using the HMAM. The resistance of the HMAP to deformation was better and the HMAP was less sensitive to load changes and could better withstand the adverse effects inflicted by heavy loads. Full article
(This article belongs to the Special Issue Environment-Friendly Construction Materials)
Figures

Figure 1

Open AccessArticle Fundamentals of Force-Controlled Friction Riveting: Part II—Joint Global Mechanical Performance and Energy Efficiency
Materials 2018, 11(12), 2489; https://doi.org/10.3390/ma11122489 (registering DOI)
Received: 24 October 2018 / Revised: 21 November 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
PDF Full-text (5171 KB) | HTML Full-text | XML Full-text
Abstract
The present work investigates the correlation between energy efficiency and global mechanical performance of hybrid aluminum alloy AA2024 (polyetherimide joints), produced by force-controlled friction riveting. The combinations of parameters followed a central composite design of experiments. Joint formation was correlated with mechanical performance
[...] Read more.
The present work investigates the correlation between energy efficiency and global mechanical performance of hybrid aluminum alloy AA2024 (polyetherimide joints), produced by force-controlled friction riveting. The combinations of parameters followed a central composite design of experiments. Joint formation was correlated with mechanical performance via a volumetric ratio (0.28–0.66 a.u.), with a proposed improvement yielding higher accuracy. Global mechanical performance and ultimate tensile force varied considerably across the range of parameters (1096–9668 N). An energy efficiency threshold was established at 90 J, until which, energy input displayed good linear correlations with volumetric ratio and mechanical performance (R-sq of 0.87 and 0.86, respectively). Additional energy did not significantly contribute toward increasing mechanical performance. Friction parameters (i.e., force and time) displayed the most significant contributions to mechanical performance (32.0% and 21.4%, respectively), given their effects on heat development. For the investigated ranges, forging parameters did not have a significant contribution. A correlation between friction parameters was established to maximize mechanical response while minimizing energy usage. The knowledge from Parts I and II of this investigation allows the production of friction riveted connections in an energy efficient manner and control optimization approach, introduced for the first time in friction riveting. Full article
Figures

Figure 1

Open AccessArticle Comparative Study on the Damage Characteristics of Asphalt Mixtures Reinforced with an Eco-Friendly Basalt Fiber under Freeze-thaw Cycles
Materials 2018, 11(12), 2488; https://doi.org/10.3390/ma11122488 (registering DOI)
Received: 15 November 2018 / Revised: 4 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
PDF Full-text (4700 KB) | HTML Full-text | XML Full-text
Abstract
The main distresses of asphalt pavements in seasonal frozen regions are due to the effects of water action, freeze-thaw cycles, traffic, and so on. Fibers are usually used to reinforce asphalt mixtures, in order to improve its mechanical properties. Basalt fiber is an
[...] Read more.
The main distresses of asphalt pavements in seasonal frozen regions are due to the effects of water action, freeze-thaw cycles, traffic, and so on. Fibers are usually used to reinforce asphalt mixtures, in order to improve its mechanical properties. Basalt fiber is an eco-friendly mineral fiber with high mechanical performance, low water absorption, and an appropriate temperature range. This paper aims to address the freeze-thaw damage characteristics of asphalt mixtures (AC-13) reinforced with eco-friendly basalt fiber, with a length of 6 mm. Based on the Marshall design method and ordinary pavement performances, including rutting resistance, anti-cracking, and moisture stability, the optimum asphalt and basalt fiber contents were determined. Test results indicated that the pavement performances of asphalt mixture exhibited a trend of first increasing and then deceasing, with the basalt fiber content. Subsequently, asphalt mixtures with a basalt fiber content of 0.4% were prepared for further freeze-thaw tests. Through the comparative analysis of air voids, splitting strength, and indirect tensile stiffness modulus, it could be found that the performances of asphalt mixtures gradually declined with freeze-thaw cycles and basalt fiber had positive effects on the freeze-thaw resistance. This paper can be used as a reference for further investigation on the freeze-thaw damage model of asphalt mixtures with basalt fiber. Full article
(This article belongs to the Special Issue Environment-Friendly Construction Materials)
Figures

Figure 1

Open AccessArticle Optimization of Steam-Curing Regime for Recycled Aggregate Concrete Incorporating High Early Strength Cement—A Parametric Study
Materials 2018, 11(12), 2487; https://doi.org/10.3390/ma11122487 (registering DOI)
Received: 14 November 2018 / Revised: 28 November 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
PDF Full-text (3210 KB) | HTML Full-text | XML Full-text
Abstract
This paper investigates the properties of steam cured recycled aggregate concrete (RAC), in an attempt to determine the optimum conditions of the steam-curing cycle for RAC, and incorporating high early strength cement (HESC). Varying conditions of steam curing were employed. The steam-curing cycle
[...] Read more.
This paper investigates the properties of steam cured recycled aggregate concrete (RAC), in an attempt to determine the optimum conditions of the steam-curing cycle for RAC, and incorporating high early strength cement (HESC). Varying conditions of steam curing were employed. The steam-curing cycle was set based on the peak temperature, and the duration for which the peak temperature was maintained. Three peak temperatures were used for steam curing, 50 °C, 60 °C, and 70 °C, maintained for up to two hours. The compressive strength results indicated that the steam-curing cycle employing the peak temperature of 50 °C maintained for one hour with a total duration of four hours was the optimum for strength development, both at the early and late stages of hydration. Determining the optimum steam-curing temperature and duration will help reduce the associated curing cost, thus further economizing the production cost of recycled aggregate concrete. Full article
Figures

Figure 1

Open AccessArticle Glassy Carbon Electrocorticography Electrodes on Ultra-Thin and Finger-Like Polyimide Substrate: Performance Evaluation Based on Different Electrode Diameters
Materials 2018, 11(12), 2486; https://doi.org/10.3390/ma11122486 (registering DOI)
Received: 13 November 2018 / Revised: 3 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
PDF Full-text (3836 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Glassy carbon (GC) has high potential to serve as a biomaterial in neural applications because it is biocompatible, electrochemically inert and can be incorporated in polyimide-based implantable devices. Miniaturization and applicability of GC is, however, thought to be partially limited by its electrical
[...] Read more.
Glassy carbon (GC) has high potential to serve as a biomaterial in neural applications because it is biocompatible, electrochemically inert and can be incorporated in polyimide-based implantable devices. Miniaturization and applicability of GC is, however, thought to be partially limited by its electrical conductivity. For this study, ultra-conformable polyimide-based electrocorticography (ECoG) devices with different-diameter GC electrodes were fabricated and tested in vitro and in rat models. For achieving conformability to the rat brain, polyimide was patterned in a finger-like shape and its thickness was set to 8 µm. To investigate different electrode sizes, each ECoG device was assigned electrodes with diameters of 50, 100, 200 and 300 µm. They were electrochemically characterized and subjected to 10 million biphasic pulses—for achieving a steady-state—and to X-ray photoelectron spectroscopy, for examining their elemental composition. The electrodes were then implanted epidurally to evaluate the ability of each diameter to detect neural activity. Results show that their performance at low frequencies (up to 300 Hz) depends on the distance from the signal source rather than on the electrode diameter, while at high frequencies (above 200 Hz) small electrodes have higher background noises than large ones, unless they are coated with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). Full article
(This article belongs to the Special Issue Glassy Carbon: Microstructure, Properties and Applications)
Figures

Figure 1

Open AccessArticle Preparation and Characterization of Zeolite/TiO2 Cement-Based Composites with Excellent Photocatalytic Performance
Materials 2018, 11(12), 2485; https://doi.org/10.3390/ma11122485
Received: 22 October 2018 / Revised: 22 November 2018 / Accepted: 4 December 2018 / Published: 7 December 2018
Viewed by 29 | PDF Full-text (5825 KB) | HTML Full-text | XML Full-text
Abstract
A zeolite/TiO2 composite (ZTC) was applied to prepare a high-quality photocatalytic cement-based material (PCM). The acetone degradation experiment and micro measurements including XRD(X-Ray Diffractometer), SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer), BET(BET Specific Surface Area Tester), FTIR(Fourier Transform Infrared Spectrometer) were conducted to characterize
[...] Read more.
A zeolite/TiO2 composite (ZTC) was applied to prepare a high-quality photocatalytic cement-based material (PCM). The acetone degradation experiment and micro measurements including XRD(X-Ray Diffractometer), SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer), BET(BET Specific Surface Area Tester), FTIR(Fourier Transform Infrared Spectrometer) were conducted to characterize the photocatalytic efficiency and physicochemical properties of PCM, respectively. Results show that TiO2 particles disperse on the surface of a PCM homogeneously and provide abundant active sites for photocatalytic reactions. Compared to a normal photocatalytic cement-based material (NPCM), the TiO2 content of a PCM is lower and its photocatalytic efficiency is higher. The ZTC frees TiO2 particles from the impacts of cement hydration products and increases the adsorption volume of acetone. The photocatalytic performance of the PCM was stable after repeated tests. Using the ZTC as a photocatalyst has a prominent effect on the photocatalytic performance of the PCM. Full article
(This article belongs to the Section Advanced Composites)
Figures

Figure 1

Open AccessArticle In Vitro Comparison of the Efficacy of Peri-Implantitis Treatments on the Removal and Recolonization of Streptococcus gordonii Biofilm on Titanium Disks
Materials 2018, 11(12), 2484; https://doi.org/10.3390/ma11122484
Received: 19 November 2018 / Revised: 30 November 2018 / Accepted: 1 December 2018 / Published: 6 December 2018
Viewed by 96 | PDF Full-text (1054 KB) | HTML Full-text | XML Full-text
Abstract
Objective: To compare the efficacy of four commonly used clinical procedures in removing Streptococcus gordonii biofilms from titanium disks, and the recolonization of the treated surfaces. Background: Successful peri-implantitis treatment depends on the removal of the dental biofilm. Biofilm that forms after implant
[...] Read more.
Objective: To compare the efficacy of four commonly used clinical procedures in removing Streptococcus gordonii biofilms from titanium disks, and the recolonization of the treated surfaces. Background: Successful peri-implantitis treatment depends on the removal of the dental biofilm. Biofilm that forms after implant debridement may threaten the success of the treatment and the long-term stability of the implants. Methods: S. gordonii biofilms were grown on titanium disks for 48 h and removed using a plastic curette, air-abrasive device (Perio-Flow®), titanium brush (TiBrush®), or implantoplasty. The remaining biofilm and the recolonization of the treated disks were observed using scanning electron microscopy and quantified after staining with crystal violet. Surface roughness (Ra and Rz) was measured using a profilometer. Results: S. gordonii biofilm biomass was reduced after treatment with Perio-Flow®, TiBrush®, and implantoplasty (all p < 0.05), but not plastic curette (p > 0.05), compared to the control group. Recolonization of S. gordonii after treatment was lowest after Perio-Flow®, TiBrush®, and implantoplasty (all p < 0.05 vs. control), but there was no difference between the plastic curette and the control group (p > 0.05). Ra and Rz values ranged from 1–6 µm to 1–2 µm and did not differ statistically between the control, plastic curette, Perio-Flow, and TiBrush groups. However, the implantoplasty group showed a Ra value below 1 µm (p < 0.01, ANOVA, Tukey). Conclusions: Perio-Flow®, TiBrush®, and implantoplasty were more effective than the plastic curette at removing the S. gordonii biofilm and preventing recolonization. These results should influence the surgical management of peri-implantitis. Full article
(This article belongs to the Special Issue Biomaterials and Implant Biocompatibility)
Figures

Figure 1

Open AccessArticle Solid-Liquid Interdiffusion (SLID) Bonding of p-Type Skutterudite Thermoelectric Material Using Al-Ni Interlayers
Materials 2018, 11(12), 2483; https://doi.org/10.3390/ma11122483
Received: 30 October 2018 / Revised: 22 November 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 100 | PDF Full-text (540 KB) | Supplementary Files
Abstract
Over the past few years, significant progress towards implementation of environmentally sustainable and cost-effective thermoelectric power generation has been made. However, the reliability and high-temperature stability challenges of incorporating thermoelectric materials into modules still represent a key bottleneck. Here, we demonstrate an implementation
[...] Read more.
Over the past few years, significant progress towards implementation of environmentally sustainable and cost-effective thermoelectric power generation has been made. However, the reliability and high-temperature stability challenges of incorporating thermoelectric materials into modules still represent a key bottleneck. Here, we demonstrate an implementation of the Solid-Liquid Interdiffusion technique used for bonding Mmy(Fe,Co)4Sb12 p-type thermoelectric material to metallic interconnect using a novel aluminium–nickel multi-layered system. It was found that the diffusion reaction-controlled process leads to the formation of two distinct intermetallic compounds (IMCs), Al3Ni and Al3Ni2, with a theoretical melting point higher than the initial bonding temperature. Different manufacturing parameters have also been investigated and their influence on electrical, mechanical and microstructural features of bonded components are reported here. The resulting electrical contact resistances and apparent shear strengths for components with residual aluminium were measured to be (2.8 ± 0.4) × 10−5 Ω∙cm2 and 5.1 ± 0.5 MPa and with aluminium completely transformed into Al3Ni and Al3Ni2 IMCs were (4.8 ± 0.3) × 10−5 Ω∙cm2 and 4.5 ± 0.5 MPa respectively. The behaviour and microstructural changes in the joining material have been evaluated through isothermal annealing at hot-leg working temperature to investigate the stability and evolution of the contact. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
Figures

Graphical abstract

Open AccessArticle Effect of Shell Growth on the Morphology of Polyvinyl Acetate/Polystyrene Inverted Core-Shell Latex Fabricated by Acrylonitrile Grafting
Materials 2018, 11(12), 2482; https://doi.org/10.3390/ma11122482
Received: 2 October 2018 / Revised: 11 November 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 81 | PDF Full-text (746 KB)
Abstract
A novel strategy for fabricating inverted core-shell structured latex particles was implemented to investigate the morphology and properties of polyvinyl acetate (PVAc)-based latex. In this study, active grafting points were synthesized onto the surface of PVAc latex cores via grafting acrylonitrile (AN) to
[...] Read more.
A novel strategy for fabricating inverted core-shell structured latex particles was implemented to investigate the morphology and properties of polyvinyl acetate (PVAc)-based latex. In this study, active grafting points were synthesized onto the surface of PVAc latex cores via grafting acrylonitrile (AN) to obtain a controllable coating growth of the shell monomer, styrene (St). The effect of shell growth on the morphological evolvement was explored by tuning the time of shell monomer polymerization. Unique particle morphologies, transferring from “hawthorn” type, over “peeled pomegranate” type, to final “strawberry-like” type, were observed and verified by electron microscopy. The morphological structure of latex particles exerted a significant effect on the particle size, phase structure, and mechanical properties of the obtained emulsions. The water-resistance of PVAc-based latex was also evaluated by the water absorption of latex films. More importantly, the experimental results provided a reasonable support for the controlled growth of St monomer, that is, the self-nucleation of dispersive St monomer can be transformed to in-situ coating growth on the PVAc core surface depending on the AN-active grafting points. This fabricating approach provides a reference for dynamical design and control of the latex particle morphology. Full article
Figures

Graphical abstract

Open AccessArticle P-Texture Effect on the Fatigue Crack Propagation Resistance in an Al-Cu-Mg Alloy Bearing a Small Amount of Silver
Materials 2018, 11(12), 2481; https://doi.org/10.3390/ma11122481
Received: 16 November 2018 / Revised: 2 December 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 91 | PDF Full-text (11557 KB)
Abstract
P-texture effect on the fatigue crack propagation (FCP) resistance in an Al-Cu-Mg alloy containing a small amount of Ag, is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattering diffraction (EBSD). Results shows that the
[...] Read more.
P-texture effect on the fatigue crack propagation (FCP) resistance in an Al-Cu-Mg alloy containing a small amount of Ag, is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattering diffraction (EBSD). Results shows that the high intensity P-texture sheet has lower σ0.2b, lower FCP rate and higher damage tolerance than random texture sheet. Fracture analysis indicates that the striations spacing of high intensity P-texture sheet is much smaller than that of random texture sheet and it has a rougher fatigue fracture surface, which causes a significant roughness induced crack closure (RICC) effect. The calculation results manifest that high intensity P-texture sheet possesses a higher crack closure level reaching 0.73 as compared to random texture sheet (only 0.25). The statistical analysis results reveal the P-grains have large twist angle of 105–170° and tilt angle of 5–60° with neighboring grains, which is similar to Goss-grains. This is the fundamental reason that P-texture sheet has the same FCP resistance and induces fatigue crack deflection as Goss-texture sheet. Additionally, the most {111} slipping planes of P-grains are distributed in the range of 30–50° deviating from transverse direction of the sheet. This results in more {111} slipping planes to participate in cyclic plastic deformation, which is beneficial to reduce fatigue damage accumulation and improve the damage tolerance of Al-Cu-Mg-Ag alloy. Full article
Open AccessArticle Highly Conductive and Transparent AZO Films Fabricated by PLD as Source/Drain Electrodes for TFTs
Materials 2018, 11(12), 2480; https://doi.org/10.3390/ma11122480
Received: 19 October 2018 / Revised: 21 November 2018 / Accepted: 1 December 2018 / Published: 6 December 2018
Viewed by 94 | PDF Full-text (2768 KB) | HTML Full-text | XML Full-text
Abstract
Aluminum-doped ZnO (AZO) has huge prospects in the field of conductive electrodes, due to its low price, high transparency, and pro-environment. However, enhancing the conductivity of AZO and realizing ohmic contact between the semiconductor and AZO source/drain (S/D) electrodes without thermal annealing remains
[...] Read more.
Aluminum-doped ZnO (AZO) has huge prospects in the field of conductive electrodes, due to its low price, high transparency, and pro-environment. However, enhancing the conductivity of AZO and realizing ohmic contact between the semiconductor and AZO source/drain (S/D) electrodes without thermal annealing remains a challenge. Here, an approach called pulsed laser deposition (PLD) is reported to improve the comprehensive quality of AZO films due to the high energy of the laser and non-existence of the ion damage. The 80-nm-thick AZO S/D electrodes show remarkable optical properties (transparency: 90.43%, optical band gap: 3.42 eV), good electrical properties (resistivity: 16 × 10−4 Ω·cm, hall mobility: 3.47 cm2/V·s, carrier concentration: 9.77 × 1020 cm−3), and superior surface roughness (Rq = 1.15 nm with scanning area of 5 × 5 μm2). More significantly, their corresponding thin film transistor (TFT) with low contact resistance (RSD = 0.3 MΩ) exhibits excellent performance with a saturation mobility (µsat) of 8.59 cm2/V·s, an Ion/Ioff ratio of 4.13 × 106, a subthreshold swing (SS) of 0.435 V/decade, as well as good stability under PBS/NBS. Furthermore, the average transparency of the unpatterned multi-films composing this transparent TFT can reach 78.5%. The fabrication of this TFT can be suitably transferred to transparent arrays or flexible substrates, which is in line with the trend of display development. Full article
(This article belongs to the Section Thin Films)
Figures

Figure 1

Open AccessArticle Copper Alloy Touch Surfaces in Healthcare Facilities: An Effective Solution to Prevent Bacterial Spreading
Materials 2018, 11(12), 2479; https://doi.org/10.3390/ma11122479
Received: 12 November 2018 / Revised: 30 November 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 117 | PDF Full-text (1910 KB) | HTML Full-text | XML Full-text
Abstract
In the healthcare environment, microorganisms’ cross-transmission between inanimate surfaces and patients or healthcare workers can lead to healthcare-associated infections. A recent interest has grown to create antimicrobial copper touch surfaces, in order to counteract microbial spread in the healthcare environment. For the first
[...] Read more.
In the healthcare environment, microorganisms’ cross-transmission between inanimate surfaces and patients or healthcare workers can lead to healthcare-associated infections. A recent interest has grown to create antimicrobial copper touch surfaces, in order to counteract microbial spread in the healthcare environment. For the first time, five French long-term care facilities were at 50% fitted with copper alloys door handles and handrails. Related to the environmental bacterial contamination, 1400 samples were carried out on copper and control surfaces over three years after copper installation. In addition, some copper door handles were taken from the different facilities, and their specific activity against methicillin-resistant S. aureus (MRSA) was tested in vitro. In comparison to control surfaces, copper door handles and handrails revealed significantly lower contamination levels. This difference was observed in the five long-term care facilities and it persists through the three years of the study. High and extreme levels of bacterial contamination were less frequent on copper surfaces. Although, the antibacterial activity of copper surfaces against MRSA was lowered after three years of regular use, it was still significant as compared to inert control surfaces. Therefore, copper containing surfaces are promising actors in the non-spreading of environmental bacterial contamination in healthcare facilities. Full article
Figures

Figure 1

Open AccessArticle Investigation of the Foam Development Stages by Non-Destructive Testing Technology Using the Freeze Foaming Process
Materials 2018, 11(12), 2478; https://doi.org/10.3390/ma11122478
Received: 12 November 2018 / Revised: 3 December 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 89 | PDF Full-text (6929 KB) | HTML Full-text | XML Full-text
Abstract
With a novel Freeze Foaming method, it is possible to manufacture porous cellular components whose structure and composition also enables them for application as artificial bones, among others. To tune the foam properties to our needs, we have to understand the principles of
[...] Read more.
With a novel Freeze Foaming method, it is possible to manufacture porous cellular components whose structure and composition also enables them for application as artificial bones, among others. To tune the foam properties to our needs, we have to understand the principles of the foaming process and how the relevant process parameters and the foam’s structure are linked. Using in situ analysis methods, like X-ray microcomputed tomography (µCT), the foam structure and its development can be observed and correlated to its properties. For this purpose, a device was designed at the Institute of Lightweight Engineering and Polymer Technology (ILK). Due to varying suspension temperature and the rate of pressure decrease it was possible to analyze the foam’s developmental stages for the first time. After successfully identifying the mechanism of foam creation and cell structure formation, process routes for tailored foams can be developed in future. Full article
(This article belongs to the Special Issue In-Situ X-Ray Tomographic Study of Materials)
Figures

Graphical abstract

Open AccessArticle Damage Determination in Ceramic Composites Subject to Tensile Fatigue Using Acoustic Emission
Materials 2018, 11(12), 2477; https://doi.org/10.3390/ma11122477
Received: 30 October 2018 / Revised: 1 December 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 83 | PDF Full-text (5361 KB) | HTML Full-text | XML Full-text
Abstract
Acoustic emission (AE) has proven to be a very useful technique for determining damage in ceramic matrix composites (CMCs). CMCs rely on various cracking mechanisms which enable non-linear stress–strain behavior with ultimate failure of the composite due to fiber failure. Since these damage
[...] Read more.
Acoustic emission (AE) has proven to be a very useful technique for determining damage in ceramic matrix composites (CMCs). CMCs rely on various cracking mechanisms which enable non-linear stress–strain behavior with ultimate failure of the composite due to fiber failure. Since these damage mechanisms are all microfracture mechanisms, they emit stress waves ideal for AE monitoring. These are typically plate waves since, for most specimens or applications, one dimension is significantly smaller than the wavelength of the sound waves emitted. By utilizing the information of the sound waveforms captured on multiple channels from individual events, the location and identity of the sources can often be elucidated. The keys to the technique are the use of wide-band frequency sensors, digitization of the waveforms (modal AE), strategic placement of sensors to sort the data and acquire important contents of the waveforms pertinent for identification, and familiarity with the material as to the damage mechanisms occurring at prescribed points of the stress history. The AE information informs the damage progression in a unique way, which adds to the understanding of the process of failure for these composites. The AE methodology was applied to woven SiC fiber-reinforced melt-infiltrated SiC matrix composites tested in fatigue (R = 0.1) at different frequencies. Identification of when and where AE occurred coupled with waveform analysis led to source identification and failure progression. For low frequency fatigue conditions, damage progression leading to failure appeared to be due to fiber failure at or near the peak stress of the stress cycle. For higher frequency fatigue conditions, significantly greater amounts of AE were detected compared to low frequency tests a few hours prior to failure. Damage progression leading to failure included AE detected events which occurred on the unloading part of the fatigue cycle near the valley of the stress cycle. These events were associated with 90 tow longitudinal split and shear cracks presumably due to local compressive stresses associated with mating crack surface interactions during unloading. The local region where these occurred was the eventual failure location and the “valley” events appeared to influence the formation of increased local transverse cracking based on AE. Full article
(This article belongs to the Special Issue Damage Detection and Characterization of High Performance Composites)
Figures

Figure 1

Open AccessArticle Autogenous Healing of Early-Age Cementitious Materials Incorporating Superabsorbent Polymers Exposed to Wet/Dry Cycles
Materials 2018, 11(12), 2476; https://doi.org/10.3390/ma11122476
Received: 31 October 2018 / Revised: 30 November 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
Viewed by 136 | PDF Full-text (54243 KB) | HTML Full-text | XML Full-text
Abstract
This study experimentally investigated the autogenous healing performances of cementitious materials incorporating superabsorbent polymers (SAPs) after exposure to eight cycles of wet/dry conditions. In each cycle, cracked cement paste specimens with different SAP dosages were exposed to wet conditions for 1 h, during
[...] Read more.
This study experimentally investigated the autogenous healing performances of cementitious materials incorporating superabsorbent polymers (SAPs) after exposure to eight cycles of wet/dry conditions. In each cycle, cracked cement paste specimens with different SAP dosages were exposed to wet conditions for 1 h, during which capillary water absorption tests were conducted, and then exposed to dry conditions for 47 h. The test results reveal that the initial sorptivity values of the reference, 0.5% SAP, 1.0% SAP, and 1.5% SAP specimens after one cycle were decreased by 22.9%, 36.8%, 42.8%, and 46.3%, respectively, after eight cycles. X-ray micro-computed tomography analysis showed that the crack volume percentages filled with healing products were 1.1%, 1.6%, 2.2%, and 2.9% in the reference, 0.5% SAP, 1.0% SAP, and 1.5% SAP specimens, respectively. As the cycling was repeated, the reduction ratio of the initial sorptivity and the quantity of healing products were increased with increases in SAP dosage. Furthermore, more healing products were distributed near SAP voids than in other sections in the specimens. This study demonstrates that the incorporation of SAPs in cementitious materials can enhance the autogenous healing performances of materials exposed to cyclic wet/dry conditions. Full article
Figures

Figure 1

Open AccessArticle Predicting Viscosity and Surface Tension at High Temperature of Porcelain Stoneware Bodies: A Methodological Approach
Materials 2018, 11(12), 2475; https://doi.org/10.3390/ma11122475
Received: 12 October 2018 / Revised: 30 November 2018 / Accepted: 1 December 2018 / Published: 6 December 2018
Viewed by 123 | PDF Full-text (11541 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The shear viscosity and the glass-vapor surface tension at high temperature are crucial to understand the viscous flow sintering kinetics of porcelain stoneware. Moreover, the pyroplastic deformation depends on the viscosity of the whole body, which is made up of a suspension of
[...] Read more.
The shear viscosity and the glass-vapor surface tension at high temperature are crucial to understand the viscous flow sintering kinetics of porcelain stoneware. Moreover, the pyroplastic deformation depends on the viscosity of the whole body, which is made up of a suspension of crystals dispersed in the melt. The existing fundamental theoretical background, along with semi-empirical constitutive laws for viscous flow sintering and glass densification, can be exploited through different approaches to estimate the physical properties at high temperatures starting from amount and chemical composition of the melt. In this work, a comprehensive attempt to predict the properties of the liquid phase is proposed by means of a detailed overview of existing models for viscosity and surface tension of glasses and melts at high temperature. The chemical composition of the vitreous phase and its physical properties at high temperature are estimated through an experimental approach based on the qualitative and quantitative chemical and phase analyses (by Rietveld refinement of X-ray powder diffraction patterns) of different porcelain-like materials. Repercussions on the firing behavior of ceramic bodies, are discussed. Comparative examples are provided for porcelain stoneware tiles, vitreous china and porcelain bodies, disclosing differences in composition and properties but a common sintering mechanism. Full article
Figures

Figure 1

Back to Top