Showing papers in "Journal of Materials Science in 2003"
TL;DR: In this paper, a composite material composed of woven Kevlar® fabric impregnated with a colloidal shear thickening fluid (silica particles (450 nm) dispersed in ethylene glycol) was reported to yield a flexible yet penetration resistant composite material.
Abstract: This study reports the ballistic penetration performance of a composite material composed of woven Kevlar® fabric impregnated with a colloidal shear thickening fluid (silica particles (450 nm) dispersed in ethylene glycol). The impregnated Kevlar fabric yields a flexible, yet penetration resistant composite material. Fragment simulation projectile (FSP) ballistic penetration measurements at ∼244 m/s have been performed to demonstrate the efficacy of the novel composite material. The results demonstrate a significant enhancement in ballistic penetration resistance due to the addition of shear thickening fluid to the fabric, without any loss in material flexibility. Furthermore, under these ballistic test conditions, the impregnated fabric targets perform equivalently to neat fabric targets of equal areal density, while offering significantly less thickness and more material flexibility. The enhancement in ballistic performance is shown to be associated with the shear thickening response, and possible mechanisms of fabric-fluid interaction during ballistic impact are identified.
818 citations
TL;DR: In this paper, the antibacterial efficacy of nanosized silver colloidal solution on the cellulosic and synthetic fabrics was examined using TEM observation of silver nanoparticles showed their shape, and size distribution.
Abstract: This paper deals with the antibacterial efficacy of nanosized silver colloidal solution on the cellulosic and synthetic fabrics Two kinds of Bacteria; Gram-positive and Gram-negative, were used TEM observation of silver nanoparticles showed their shape, and size distribution The particles were very small (2–5 nm) and had narrow distribution SEM images of treated fabrics indicated silver nanoparticles were well dispersed on the surfaces of specimens WAXS patterns did not show any peak of silver as the fabric had very small quantity of silver particles However, ICP-MS informed the residual concentration of silver particles on fabrics before/after laundering The antibacterial treatment of the textile fabrics was easily achieved by padding them with nanosized silver colloidal solution The antibacterial efficacy of the fabrics was maintained after many times laundering
624 citations
TL;DR: In this paper, the authors focus on both high temperature as well as dissolved oxygen sensors and compare the different methods of oxygen sensing, discuss underlying principles, and outline the designs and specific applications.
Abstract: Advancement of gas sensor technology over the past few decades has led to significant progress in pollution control and thereby, to environmental protection An excellent example is the control of automobile exhaust emissions, made possible by the use of oxygen gas sensors Since early 1970's there have been sustained studies on oxygen sensors and has led to development of sensors for various applications with varying performance characteristics Solid electrolyte based potentiometric, amperometric and metal oxide based semiconducting resistive type sensors are used for high temperature applications For solution-based pollution monitoring, dissolved oxygen sensors based on Clark electrodes have played a major role More recently, for biological and medical applications, optical oxygen sensors are beginning to have an impact In this review, we focus on both high temperature as well as dissolved oxygen sensors and compare the different methods of oxygen sensing, discuss underlying principles, and outline the designs and specific applications
451 citations
TL;DR: In this paper, the effect of clay contents on the tensile, dynamic mechanical, and thermal properties as well as the barrier properties of the nanocomposites were investigated using wide angle X-ray diffraction and transmission electron microscopy (TEM).
Abstract: As an attempt to develop environmentally friendly polymer hybrids, biodegradable thermoplastic starch (TPS)/clay nanocomposites were prepared through melt intercalation method. Natural montrorillonite (Na+ MMT; Cloisite Na+) and one organically modified MMT with methyl tallow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) were chosen in the nanocomposite preparation. TPS was prepared from natural potato starch by gelatinizing and plasticizing it with water and glycerol. The dispersion of the silicate layers in the TPS hybrids was characterized by using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). It was observed that the TPS/Cloisite Na+ nanocomposites showed higher tensile strength and thermal stability, better barrier properties to water vapor than the TPS/Cloisite 30B nanocomposites as well as the pristine TPS, due to the formation of the intercalated nanostructure. The effect of clay contents on the tensile, dynamic mechanical, and thermal properties as well as the barrier properties of the nanocomposites were investigated.
442 citations
TL;DR: In this paper, an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.
Abstract: Rice husk is an abundantly available waste material in all rice producing countries. In certain regions, it is sometimes used as a fuel for parboiling paddy in the rice mills. The partially burnt rice husk in turn contributes to more environmental pollution. There have been efforts not only to overcome this but also to find value addition to these wastes using them as secondary source of materials. Rice husk contains nearly 20% silica, which is present in hydrated amorphous form. On thermal treatment, the silica converts to crystobalite, which is a crystalline form of silica. However, under controlled burning conditions, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si3N4, elemental Si and Mg2Si. Due to the high pozzolanic activity, this rice husk silica also finds application in high strength concrete as a substitute for silica fume. Possibility of using this silica as filler in polymers is also studied. The present paper is an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on the processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.
432 citations
TL;DR: In this article, the mechanical properties of ice and snow are reviewed and the strength and fracture toughness of snow are compared to those of ice, and the fracture-initiating flaw sizes in snow appear to correlate to the snow cell size.
Abstract: The mechanical properties of ice and snow are reviewed. The tensile strength of ice varies from 0.7–3.1 MPa and the compressive strength varies from 5–25 MPa over the temperature range −10°C to −20°C. The ice compressive strength increases with decreasing temperature and increasing strain rate, but ice tensile strength is relatively insensitive to these variables. The tensile strength of ice decreases with increasing ice grain size. The strength of ice decreases with increasing volume, and the estimated Weibull modulus is 5. The fracture toughness of ice is in the range of 50–150 kPa m1/2 and the fracture-initiating flaw size is similar to the grain size. Ice-soil composite mixtures are both stronger and tougher than ice alone. Snow is a open cellular form of ice. Both the strength and fracture toughness of snow are substantially lower than those of ice. Fracture-initiating flaw sizes in snow appear to correlate to the snow cell size.
420 citations
TL;DR: In this article, the polypropylene/silver nanocomposite fibers were prepared for the attainment of permanent antibacterial activity to common synthetic textile, and the fibers were melt-spun by co-extrusion of polyethylene (PP) and polyamide (Ag) master-batches using general conjugate spinning.
Abstract: The polypropylene/silver nanocomposite fibers were prepared for the attainment of permanent antibacterial activity to common synthetic textile. The fibers were melt-spun by co-extrusion of polypropylene (PP) and PP/Ag master-batches using general conjugate spinning. Master-batches were made up of mixture of PP chips and nano-sized silver powder. The antibacterial efficacy of spun fibers was excellent not when the master-batch used as the core, but when used as the sheath. The antibacterial activity of nano-silver in fibers was evaluated after certain contact time and calculated by percent reduction of two kinds of bacteria; Staphylococus aureus and Klebsiela pneumoniae. For the characterization, differential scanning calorimetry (DSC) and wide-angle X-ray diffractometer (WAXD) were used for analysis of structure, thermal and crystallization behavior of the spun-fibers. Scanning electron microscopy (SEM) was carried out to observe particle distribution on the nanocomposite fibers.
321 citations
TL;DR: In this article, it is shown that the properties (e.g., size, elemental composition) of the geopolymeric and CSH gels forming simultaneously, and the reactivity of the calcium precipitates along the interfacial region, will hold the key in reformulating a new generation of concrete that matches the durability of ancient concrete.
Abstract: It is possible to have geopolymeric gel and calcium silicate hydrate (CSH) gel forming simultaneously within a single system. Scanning electron microscopy was employed in studying the morphology and elemental composition of the two phases. The elemental composition within the different phases was consistent. However, CSH gel formed in such system had a significantly lower Ca/Si ratio than the CSH commonly formed from the hydration of ordinary Portland cement. In addition, there were some calcium precipitate along the interface between the CSH and geopolymeric gels. It is suggested that the properties (e.g., size, elemental composition) of the geopolymeric and CSH gels forming simultaneously, and the reactivity of the calcium precipitates along the interfacial region, will hold the key in reformulating a new generation of concrete that matches the durability of ancient concrete. A chemical mechanism on how the presence of slag in the alkali activation of metakaolin would lead to the formation of both geopolymeric and CSH gels has been proposed.
300 citations
TL;DR: In this article, the preparation methods of supported platinum catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability are reviewed, as well as the effect of these catalysts on fuel cell performance.
Abstract: Supported platinum electrocatalysts are generally used in low temperature fuel cells to enhance the rates of the hydrogen oxidation and oxygen reduction reactions. In such catalysts, the high surface to volume ratios of the platinum particles maximize the area of the surfaces available for reaction. It is the structure and proper dispersal of these platinum particles that make low-loading catalysts feasible for fuel cell operation, lowering the cost of the system. If the platinum particles cannot maintain their structure over the lifetime of the fuel cell, change in the morphology of the catalyst layer from the initial state will result in a loss of electrochemical activity. This loss of activity in the platinum/carbon catalysts due to the agglomeration of platinum particles is considered to be a major cause of the decrease in cell performance, especially in the case of the cathode. In the light of the latest advances on this field, this paper reviews the preparation methods of these catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability.
297 citations
TL;DR: In this paper, casein, a natural protein, was electrospun into ultra-thin fibrous membranes with diameters between 100 and 500 nm by chemical crosslinking with 4,4′-methylenebis(phenyl diisocyanate) (MDI) in THF.
Abstract: Natural proteins such as casein and enzymes cannot be processed into fibrous forms. With the addition of another polymer such as poly(ethylene oxide) (PEO) or poly(vinyl alcohol) (PVA), casein, a natural protein, was electrospun into ultra-thin fibrous membranes. Fibers in these membranes had diameters between 100 and 500 nm. These fibrous membranes were rendered insoluble by chemical crosslinking with 4,4′-methylenebis(phenyl diisocyanate) (MDI) in THF. The electrospinning method has also been utilized for enzyme immobilization on solid support. The lipase encapsulated in the ultra-fine fibrous membranes exhibits higher catalytic activity towards hydrolyzing olive oil than that in the cast films from the same solution.
232 citations
TL;DR: In this paper, the authors focus mainly on the resistive/semiconductive, especially the surface conductive ceramic oxide type gas sensors, and discuss selected applications with an emphasis on sensor design issues.
Abstract: Many types of sensors have been developed to detect chemical species in the gas phase. These include optical based on color change or fluoresence, surface acoustic wave (SAW) devices, electrochemical, chemoresistive/semiconductive, field effect transistors (FET), metal-insulator-semiconductor (MIS) diode devices, and many other. Among these, resistive type sensors based on ceramic oxides are particularly attractive because of their low cost, wide range of applications and potential for use in electronic nose. This article focuses mainly on the resistive/semiconductive, especially the surface conductive ceramic oxide type gas sensors. The main emphasis is on the basic principles involving gas-solid reactions. Also discussed are selected applications with an emphasis on sensor design issues. Since SnO2 can be used as a model system for oxide-based sensors, most of the discussions focuses on this system, though other systems are occasionally highlighted illustrating recent developments.
TL;DR: In this paper, a three-dimensional model for direct laser metal powder deposition process and rapid prototyping is developed, which calculates transient temperature profiles, dimensions of the fusion zone and residual stresses.
Abstract: A three-dimensional model for direct laser metal powder deposition process and rapid prototyping is developed. Both numerical and analytical models are addressed. In the case of numerical modeling, the capabilities of ANSYS parametric design language were employed. The model calculates transient temperature profiles, dimensions of the fusion zone and residual stresses. Model simulations are compared with experimental results acquired on line using an ultra-high shutter speed camera which is able to acquire well-contrasted images of the molten pool, and off-line using metallographical and x-ray diffraction analyses. The experiments showed good agreement with the modeling. The results are discussed to provide suggestions for feedback control and reduction of residual stresses.
TL;DR: In this article, the effect of contact flattening and material properties on the fracture stress calculation for the diametrical compression test used to evaluate compact strength was examined through finite element simulations using linear elastic, elastoplastic, and porous elastplastic models with commercial finite element software.
Abstract: The effect of contact flattening and material properties on the fracture stress calculation for the diametrical compression test used to evaluate compact strength was examined through finite element simulations Two-dimensional simulations were carried out using linear elastic, elastoplastic, and porous elastoplastic models with commercial finite element software A parametric study was performed by varying the elastic modulus (E), Poisson's ratio (ν), contact frictional coefficient (μ), yield stress (σyield), and compact relative density (RD) Stress contours generated from these simulations were compared to the Hertzian and Hondros analytical expressions Linear elastic simulations show excellent agreement with the analytical solutions Significant deviation, however, occurs for the elastoplastic and porous elastoplastic simulations at larger diametrical strain with material plasticity A better understanding of the stress-state of diametrically loaded plastically deforming disks has been demonstrated in this computational and experimental work Results from these finite element simulations confirm that the standard tensile strength calculation: σf = 2P/π Dt, is suitable for linear elastic materials However, the incorporation of plasticity into the material model results in a significant change in the maximum principal stress field (magnitude and location) rendering the Hertzian estimate of tensile strength invalid A map to check the validity of the Hertzian equation is proposed
TL;DR: In this article, the authors used the Membrane Deflection Experiment to test the mechanical response of freestanding thin film gold specimens and obtained stress-strain curves obtained on films 0.3, 0.5, and 0.1 μm thick.
Abstract: The Membrane Deflection Experiment was used to test the mechanical response of freestanding thin film gold specimens. We present stress-strain curves obtained on films 0.3, 0.5, and 0.1 μm thick. Elastic modulus was consistently measured in the range of 53–55 GPa. Several size effects on the mechanical properties were observed including yield stress variations with membrane width and film thickness. It was observed that a width of 2.5 μm and a thickness of 0.5 μm correspond to major transitions in the material deformation behavior.
TL;DR: In this article, the authors used atomic force microscopy (AFM) in combination with image processing to obtain more information about the arrangement of cellulose aggregates (fibrils) in the secondary cell wall layer of spruce wood.
Abstract: Understanding the arrangement of wood polymers within the fiber wall is important for understanding the mechanical properties of the fibers themselves. Due to their high load bearing ability, the arrangement of cellulose fibrils within the cell wall are of special interest. In this work AFM—Atomic Force Microscopy—in combination with image processing has been used to obtain more information about the arrangement of cellulose aggregates (fibrils) in the secondary cell wall layer of spruce wood. The effects of chemical processing on the arrangement of these cellulose aggregates were also studied. Enlargement of cellulose aggregates was found in the initial phase of the kraft cook. This increase in cellulose aggregate dimensions depended mostly on temperature for treatment temperatures above 140°C, regardless of the amount of alkali present. Although hemicelluloses are lost to various degrees under alkaline conditions, the increase in cellulose aggregate size was mainly related to thermally induced rearrangement of the cellulose molecules. The mean side length of cellulose aggregates was found to be around 18 nm in unprocessed wood and 23 nm in processed wood. The cellulose aggregates were assumed to be square shaped in cross section in both cases.
TL;DR: In this article, a setup for contactless transient photoconductivity measurements on powders by the Time Resolved Microwave Photoconductivity (TRMC) method has been realized.
Abstract: A set-up for contactless transient photoconductivity measurements on powders by the Time Resolved Microwave Photoconductivity (TRMC) method has been realized. These measurements have been used as a tool for the investigation of excess charge-carrier lifetimes in TiO2 (anatase and rutile) powders. The influence of laser wavelength and intensity on TRMC decay shows the importance of the fast-recombination processes. The presence of a long time tail in the TRMC signals of the anatase modification of TiO2 is attributed to quenching of this recombination by hole-trapping at the surface. The influence of surface treatment by ethanol and water on TRMC decay evidences that dominant effects are bulk recombination in rutile and surface trapping in anatase. The influence of doping in rutile shows that increasing the doping rate accelerates the decay whatever the doping type is. The doping element acts as an impurity favoring recombination by creation of structural defects. The influence of thermal treatment in anatase shows that increasing the thermal treatment temperature increases the lifetimes. High crystalline quality leads to long charge-carrier lifetimes. The results are discussed in view of their relevance for photocatalysis.
TL;DR: In this article, the authors reviewed the current understanding of the mechanisms of stress corrosion cracking of pipeline steels and considered the similarities, the differences and the influencing factors for the high pH and low pH stress corrosion cracks caused by a concentrated bicarbonate-carbonate solution.
Abstract: This paper reviews the current understanding of the mechanisms of stress corrosion cracking of pipeline steels. The similarities, the differences and the influencing factors are considered for the “high pH” stress corrosion cracking caused by a concentrated bicarbonate-carbonate solution, and for the “low pH” stress corrosion cracking due to a diluter solution. For high pH stress corrosion cracking, it is well accepted that the mechanism involves anodic dissolution for crack initiation and propagation. In contrast, it has been suggested that the low pH stress corrosion cracking is associated with the dissolution of the crack tip and sides, accompanied by the ingress of hydrogen into the pipeline steel. But the precise influence of hydrogen on the mechanism needs to be further studied.
TL;DR: In this paper, the authors showed that depolymerization leads to the breakage of 1,4β-Dglucoside bonds of chitosan in crystal region.
Abstract: Water-soluble chitosan with low molecular weight was prepared by the depolymerization of chitosan with aqueous H2O2 solution. The IR and 1H-NMR studies verify that depolymerization leads to the breakage of 1,4-β-D-glucoside bonds of chitosan. X-ray analysis shows the depolymerization takes place at the surface of the chitosan in crystal region by so called peeling-off process while the amorphous portion is depolymerized by penetrating pattern.
TL;DR: In this article, a thorough analysis of the strengths and limitations of microrheology with the emphasis on high-throughput applications is presented for two representative cases: the rheological screening of aqueous solutions of a block copolypeptide library and the phase diagram of a water/surfactant/salt system.
Abstract: Microrheology can be used for high-throughput screening of the rheological properties of sample libraries of complex fluids Two passive techniques are particularly suitable: video microscopy and diffusing-wave spectroscopy The techniques complement each other very well and can be applied to samples that offer different experimental challenges We offer a thorough analysis of the strengths and limitations of microrheology with the emphasis on high-throughput applications To illustrate the potential of microrheology, results are presented for two representative cases: the rheological screening of aqueous solutions of a block copolypeptide library and the rheological phase diagram of a water/surfactant/salt system
TL;DR: In this paper, the sintering behavior of Ni/Y2O3-ZrO2(YSZ) cermet electrode coating on 3 mol% Y2O 3-ZRO2electrolyte was studied under moist and dry hydrogen atmosphere at 1000°C for up to 2000 h. The results showed that Ni/YSZ cermet electrodes were dominated by agglomeration and grain growth of Ni particles in the cermets.
Abstract: The sintering behavior of Ni/Y2O3-ZrO2(YSZ) cermet electrode coating on 3 mol% Y2O3-ZrO2electrolyte was studied under moist and dry hydrogen atmosphere at 1000°C for up to 2000 h. The sintering behavior of Ni/YSZ cermet electrodes was dominated by the agglomeration and grain growth of Ni particles in the cermets, which was critically related to the content of Ni and YSZ phases in the cermet. For pure Ni electrode coating, the sintering was substantial and cross plane cracks and isolated Ni island were formed after sintering at 1000°C for only 250 h. However with the addition of YSZ phase, the sintering of Ni/YSZ cermet anode coatings was significantly reduced. For the cermet composition of Ni (50 vol%)/YSZ (50 vol%), the change in the surface porosity and pore size distribution after sintering at 1000°C for 2000 h was very small. The microstructural stability of the Ni (50 vol%)/YSZ (50 vol%) cermet electrodes was also demonstrated by the performance stability tested under current load of 250 mAcm−2at 1000°C for over 2500 h.
TL;DR: In this article, a nanocrystalline Mg-Ti alloy was synthesized by mechanical alloying of Mg and Ti powder blends, which resulted in an extended solubility of Ti in Mg, due to the favorable size factor and the isomorphous structure of the two components.
Abstract: Mg-based Mg-Ti binary alloys have been synthesized by mechanical alloying of Mg and Ti powder blends. It was found that mechanical alloying of Mg and Ti results in a nanocrystalline Mg-Ti alloy and an extended solubility of Ti in Mg, due to the favorable size factor and the isomorphous structure of Mg and Ti. In the case of Mg-20at.%Ti, about 12.5% Ti is dissolved in the Mg lattice when the mechanical alloying process reaches a stable state. The rest (about 7.5 at.%) remains as fine particles in the size of 50–150 nm in diameter. Dissolution of 12.5 at.% Ti in the Mg lattice causes a contraction of the unit cell volume from 0.0464 to 0.0442 nm3 and a decrease of the c/a ratio from 1.624 to 1.612 of the hexagonal structure. The supersaturated solid solution Mg-Ti alloy decomposes upon thermal annealing at temperatures above 200°C. Hydrogenation enhances the decomposition process at lower temperatures.
TL;DR: In this paper, the effect of diverse alloying elements on the dissolution of the copper phase (CuAl2) during solution heat treatment was investigated and the first derivate curves were plotted and used to determine the impact of the additives on the precipitation temperature of the aluminum alloy.
Abstract: The hypoeutectic 319 aluminum alloy (Al-7%Si-3.5%Cu) was used in the present study to investigate the effect of diverse alloying elements on the dissolution of the copper phase (CuAl2) during solution heat treatment. Elements such as Sr, Fe and P were added to the base alloy individually and in various combinations. The cooling curves of these alloys were obtained by solidifying the alloy melts in a preheated graphite mold (600°C, cooling rate ∼0.8°C/s). From these the first derivate curves were plotted and used to determine the effect of the additives on the precipitation temperature of the Al-CuAl2 eutectic reaction. Microstructural examination was carried out using optical microscopy, image analysis, and electron probe microanalysis (EPMA), with energy dispersive X-ray (EDX) and wavelength dispersive spectroscopic (WDS) analysis facilities. Samples from different alloys were solution heat treated at 505°C for various times up to 100 hours. The results explicitly reveal that solution heat treatment plays a critical role on the dissolution of the CuAl2 phase. It is found that Sr leads to segregation of the CuAl2 phase away from the Al-Si eutectic regions, which slows down its dissolution during solution heat treatment. The β-Al5FeSi phase platelets act as preferred precipitation sites for the copper phase and hence lessen the degree of segregation. Thus, addition of Fe can accelerate the copper phase dissolution. However, phosphorus addition has a negative effect on CuAl2 dissolution due to (i) its solubility in the CuAl2 phase particles, and (ii) the formation of (Al,P)O2 oxide particles which act as nucleation sites for the precipitation of the block-like CuAl2 phase. It retards the complete dissolution of this copper phase even after 100 hr solution treatment. In the case when phosphorus and iron are added together, the negative effect of phosphorus can be neutralized to some extent.
TL;DR: In this article, the microstructural evolution of a thixomolded magnesium alloy AZ91D during friction stir welding was investigated, which resulted in a homogeneous microstructure consisting of fine recrystallised α-Mg grains in the thixomed material.
Abstract: Microstructural evolution of a thixomolded magnesium (Mg) alloy AZ91D during friction stir welding was investigated. Friction stir welding resulted in a homogeneous microstructure consisting of fine recrystallised α-Mg grains in the thixomolded material. The microstructural homogenisation and refinement was attributed to dynamic recrystallisation accompanied by the dissolution of the eutectic structure during the welding. The grain refinement in the stir zone was effective in increasing the hardness, as predicted by the Hall-Petch equation. The effect of grain size on hardness was smaller than that in conventional and rapidly solidified AZ91. This phenomenon may be explained as being due to the microstructure of the stir zone which consisted of fine equiaxed grains with a high density of dislocations.
TL;DR: In this article, the authors used an alkoxide sol-gel process modified by adding of Degussa P-25 powder, which was characterized by SEM, EDS, XRD and other methods.
Abstract: Thick films of TiO2 were prepared on glass and stainless steel substrates using an alkoxide sol-gel process modified by addition of Degussa P-25 powder. The prepared films were characterized by SEM, EDS, XRD and other methods. The TiO2 films obtained from the powder modified sol were compared to films obtained from the alkoxide sol-gel without modification. The films obtained from the modified sol-gel were about ten times thicker for a single dip coating/heat treatment cycle than the films obtained from the sol without powder addition. The prepared thick films were smooth and free of macrocracking, fracture or flaking. The grain size of these films was uniform and in the range 100–150 nm and the films were a mixture of anatase and rutile TiO2. The films obtained from the powder modified sol on the stainless steel substrate were also much harder compared to the films obtained from sols without modification and displayed excellent adhesion to the substrate.
TL;DR: In this paper, a 3D macroporous bioactive scaffolds have been produced for tissue engineering applications by foaming sol-gel-derived bioactive glasses with the use of a surfactant.
Abstract: Bioactive glasses are known to have the ability to regenerate bone, and to release ionic biological stimuli that promote bone cell proliferation by gene activation, but their use has been restricted mainly to the form of powder, granules or small monoliths Resorbable 3D macroporous bioactive scaffolds have been produced for tissue engineering applications by foaming sol-gel-derived bioactive glasses The foams exhibit a hierarchical structure, with interconnected macropores (10–500 μm), which provide the potential for tissue ingrowth and mesopores (2–50 nm), which enhance bioactivity and release of ionic products The macroporous matrices were produced by the foaming of sol-gel glasses with the use of a surfactant Three glass systems SiO2, SiO2-CaO and SiO2-CaO-P2O5were foamed using various concentrations of surfactant, in order to investigate the effect of surfactant concentration and composition on the structure and properties of the hierarchical construct
TL;DR: In this article, the effects of environmental aging and accelerated aging on tensile and flexural behavior of BFRP and BGRP were studied by exposing the samples in water at 25°C for up to 1600 h and at 75°C at up to 600 h.
Abstract: The effects of environmental aging and accelerated aging on tensile and flexural behavior of bamboo fiber reinforced polypropylene composite (BFRP) and bamboo-glass fiber reinforced polypropylene hybrid composite (BGRP), all with a 30% (by mass) fiber content, were studied by exposing the samples in water at 25°C for up to 1600 h and at 75°C for up to 600 h. Reduction in tensile strength for BFRP and BGRP was 12.2% and 7.5%, respectively, after aging at 25°C for about 1200 h. Tensile and flexural strength of BFRP and BGRP were reduced by 32%, 11.7%, and 27%, 7.5% respectively, after aging at 75°C for 600 h. While the strengths of the bamboo fiber reinforced composites reduce with sorption time and temperature, the environmental degradation process can be delayed by adding a small amount of glass fiber. Moisture sorption and strength reduction are further suppressed by using maleic anhydride polypropylene (MAPP) as a coupling agent in both types of composite system.
TL;DR: An epoxy functionalized hyperbranched polymer (HBP) was used to toughen a conventional epoxy resin, diglycidyl ether of bisphenol A (DGEBA) cured with diethyltoluene-2,6-diamine (DETDA).
Abstract: An epoxy-functionalized hyperbranched polymer (HBP) was used to toughen a conventional epoxy resin, diglycidyl ether of bisphenol A (DGEBA) cured with diethyltoluene-2,6-diamine (DETDA). There was little change in gel time as a result of addition of HBP, even though the HBP reacts at a slower rate with amine hardeners compared to DGEBA alone. Phase separation was investigated for various HBP contents and as a function of cure conditions as well. The thermal and dynamic viscoelastic behavior of the modified matrices have been examined and compared to the DGEBA epoxy matrix. It appears that the HBP which phase separates does not react as fully as when it is reacted with the amine alone. Nonetheless, good improvement in impact strength as a result of incorporation of HBP were observed and explained in terms of morphological behavior for a DGEBA matrix modified with various amounts of HBP.
TL;DR: In this paper, the authors present a brief overview of a probabilistic design methodology for brittle structures, review the literature for evidence of Probabilistic behavior in the mechanical properties of MEMS (especially strength), and investigate whether evidence exists that a probablistic Weibull effect exists at the structural microscale.
Abstract: The objective of this work is to present a brief overview of a probabilistic design methodology for brittle structures, review the literature for evidence of probabilistic behavior in the mechanical properties of MEMS (especially strength), and to investigate whether evidence exists that a probabilistic Weibull effect exists at the structural microscale. Since many MEMS devices are fabricated from brittle materials, that raises the question whether these miniature structures behave similar to bulk ceramics. For bulk ceramics, the term Weibull effect is used to indicate that significant scatter in fracture strength exists, hence requiring probabilistic rather than deterministic treatment. In addition, the material's strength behavior can be described in terms of the Weakest Link Theory (WLT) leading to strength dependence on the component's size (average strength decreases as size increases), and geometry/loading configuration (stress distribution). Test methods used to assess the mechanical properties of MEMS, especially strength, are reviewed. Four materials commonly used to fabricate MEMS devices are reviewed in this report. These materials are polysilicon, single crystal silicon (SCS), silicon nitride, and silicon carbide.
Journal Article•
TL;DR: In vitro simulations of the biocompatibility of two types of stainless steel and their individual metal components were carried out in simulated physiological solution containing complexing agents, including EDTA and proteins to increase the dissolution of pure metals and stainless steels.
Abstract: The present work is devoted to the problem of biodegradation of orthopaedic implants manufactured from stainless steel. In vitro simulations of the biocompatibility of two types of stainless steel, AISI 304 and AISI 316L, and their individual metal components, i.e. iron, chromium, nickel and molybdenum, were carried out in simulated physiological solution (Hank's) containing complexing agents. Knowledge of the effects of the chemical and biological complexing agents, EDTA and proteins, respectively, on the corrosion resistance of a metal should provide a better understanding of the processes occurring in vivo on its surface. The behavior of stainless steels and metal components was studied under open circuit and under potentiostatic conditions. The concentration of dissolved corrosion products in the form of released ions was determined by differential pulse polarography (DPP) and atomic emission spectrometry using inductively coupled plasma (ICP-AES). The composition of solid corrosion products formed on the surface was analyzed by energy dispersive X-ray spectroscopy (EDS) and their morphology was viewed by scanning electron microscopy (SEM). The addition of EDTA and proteins to physiological solution increased the dissolution of pure metals and stainless steels. The effect of particular protein differs on different metals and alloys.
TL;DR: In this paper, the phase composition of aging products in alloys with Mg : Si > 1 agrees well with the equilibrium phase composition at a temperature of annealing, however, the sequence of precipitation in the alloys having Mg: Si < 1 is more complicated.
Abstract: The Al–Cu–Mg–Si alloying system is a base for a diverse group of commercial alloys which acquire their properties after quenching and aging. Therefore, the knowledge of the phase composition of hardening precipitates and the conditions under which they are formed is very important. ast reference data were analyzed along with experimental results and calculations of phase equilibria. Different alloys were compared based on the composition of the supersaturated solid solution. It is shown that the phase composition of aging products in alloys with Mg : Si > 1 agrees well with the equilibrium phase composition at a temperature of annealing. However, the sequence of precipitation in the alloys with Mg : Si < 1 is more complicated. The hardening in these alloys occurs with precipitation of the β″ and θ′ phases and their precursors. The former phase may contain copper and later transforms either to β′ and β (Mg2Si) or to Q phase depending on the amount of copper and annealing temperature.