Reactive Hot Pressing of Alumina-Molybdenum Disilicide Composites

Al₂O₃-MoSi₂ composites were prepared by reactive hot pressing using molybdenum, aluminum, and mullite powders as precursors. The Gibbs free energy was highly negative for the composite-forming reaction, which indicated that the products were stable relative to the reactants. After the reaction, the composites had high relative density, ∼96%. Based on the composite-forming reaction, the composites should have contained 18 vol% MoSi₂ in an Al₂O₃ matrix. Scanning electron microscopy revealed that the MoSi₂ inclusions were elongated, with an average thickness of ∼5 μm and inclusion lengths that ranged from 5 to 50 μm. Average composite strength was 467 MPa, and toughness was 3.7 MPa·m^1/2.     

The effects of quercetin on SW480 human colon carcinoma cells: a proteomic study

Background  

High fruit and vegetable intake is known to reduce the risk of colon cancer. To improve understanding of this phenomenon the action of different phytochemicals on colon cells has been examined. One such compound is quercetin that belongs to the group known as flavonoids. The purpose of this study was to determine the influence of quercetin on the proteome of the SW480 human colon adenocarcinoma cell line, specifically to identify proteins that could be the molecular targets of quercetin in its amelioration of the progression of colon cancer. To this end, two-dimensional gel electrophoresis and mass spectrometry were used to identify proteins that underwent a change in expression following treatment of the cells with 20 μM quercetin. This could elucidate how quercetin may reduce the progression of colon cancer.     

Experimental Design Applied to the Chemical Durability of Sol–Gel-Derived Zirconias

A statistical design was used to investigate the effects of various processing conditions on the chemical durability of sol–gel-derived zirconias. Eight processing variables were investigated: water:alkoxide molar ratio, alcohol:alkoxide molar ratio, nitric acid:alkoxide molar ratio, mixing temperature during hydrolysis, firing temperature, heating rate, soak at firing temperature, and firing atmosphere. Processing variables were set at high and low limits in a main-effects statistical design. The design identified four critical processing variables (listed in descending order of significance): firing temperature, firing atmosphere, water:alkoxide ratio, and nitric acid:alkoxide ratio. Sol–gel-derived zirconias were characterized by differential scanning calorimetry, X-ray diffractometry, and mercury intrusion. Suggestions are offered that may help to explain why these particular processing conditions influenced the chemical durability of sol–gel-derived zirconias.     

The role of interlamellar chain entanglement in deformation-induced structure changes during uniaxial stretching of isotactic polypropylene

In-situ small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD) were carried out to investigate the deformation-induced structure changes of isotactic polypropylene (iPP) films during uniaxial stretching at varying temperatures (room temperature, 60 °C and 160 °C). From the WAXD data, mass fractions of amorphous, mesomorphic and crystal phases were estimated. Results indicate that at room temperature, the dominant structure change is the transformation of folded-chain crystal lamellae (monoclinic α-form) to oriented mesomorphic phase; while at high temperatures (>60 °C); the dominant change is the transformation of amorphous phase to oriented folded-chain crystal lamellae. This behavior may be explained by the relative strength between the interlamellar entangled network of amorphous chains, which probably directly influence the tie chain distribution, and the surrounding crystal lamellae. It appears that during stretching at low temperatures, the interlamellar entanglement network is strong and can cause lamellar fragmentation, resulting in the formation of oriented mesomorphic phase. In contrast, during stretching at high temperatures, the chain disentanglement process dominates, resulting in the relaxation of restrained tie chains and the formation of more folded-chain lamellae.     

Studies on melt spinning. II. Analysis of the deformation and heat transfer processes

A generalized, empirical equation is proposed which takes into account the dependence of elongational viscosity on both elongation rate and temperature. From this, a mathematical model for simulating the melt spinning process has been developed. The model has been tested against experimentally observed velocity profiles in fibers of polystyrene and high-density polyethylene spun into an isothermal chamber. It has been found that predicted velocity profiles agree well with experimentally observed ones. The mathematical model has been used to predict velocity and temperature profiles in fibers spun into a cooling medium. The simultaneous solution of momentum and energy balance equations by means of a numerical integration scheme has generated important information such as distributions of force components involved in spinning and distributions of the total rate of heat transfer along the spinning way.     

Dynamic mechanical and thermal properties of fire-retardant polypropylene

A study of the effect of a series of fire retardants and antimony oxide upon the dynamic mechanical and thermal properties of polypropylene suggests three categories. (1) “Inert Fillers”—These raise the elastis modulus and the heat distortion temperature of polypropylene without shifting its glass transition temperature. The melting point of polypropylene is only depressed by 1–3°C, the heat of fusion and the percentage of crystallinity of polypropylene in these composites is ～10 percent lower at additive concentrations of ～30 percent. Very poor interaction exists between the additive and the thermo-plastic which apparently exist in two separate phases. (2) “Chain Stiffener”—These raise the elastic modulus (～25 percent) and the glass transition (～11°C) for polypropylene; the melting point of polypropylene in the composite is lowered by ～6°C indicative of good interaction between the additive and polypropylene. (3) “Plasticizer”—These lower the room temperature elastic modulus (～20 percent) and the glass transition temperature (～11°C) of polypropylene; the melting point of polypropylene in the composite is depressed by ～10°C indicating good interaction. The efficacy of the “plasticizer” and “chain stiffener” are attributed partially to melting of polypropylene at the processing temperature.     

Phase properties of mixtures of ceramides

Ceramides have been proposed to have a central role in the function of the stratum corneum. Ceramides also influence the phase properties of model skin lipid mixtures, but the relevance of this to the stratum corneum function is controversial. Because the stratum corneum contains several classes of ceramides, the type of ceramides used in model mixtures of stratum corneum lipid lamellae may be important. Thus, the properties of α-hydroxy fatty acid containing (HFAC) and nonhydroxy fatty acid containing (NFAC) ceramides and their mixtures have been investigated. Ceramides were obtained by the conversion of purified bovine brain cerebrosides. Isolated, anhydrous HFAC underwent an endothermic solid to liquid transition at 92°C. With hydration, an endothermic transition at 71.8°C was observed which was accompanied by a reduction in the birefringence. The enthalpy increased from 66 to 89 J/g with a 20-d storage time. These thermal properties are very similar to those observed with hydroxy fatty acid containing cerebrosides. In contrast, anhydrous nonhydroxy fatty acid containing ceramides underwent a broad endothermic transition over the temperature range of 50–90°C. When hydrated, the initial endothermic transition was interrupted by an exothermic transition that was followed immediately by a second endothermic transition. During these thermal changes, there was a loss of birefringence, and with completion of the second endothermic transition, a nonbirefringent liquid was observed. NFAC samples, stored at 70°C for 5 min, cooled, and then rescanned, displayed only one endotherm at 75°C. The thermal behavior of mixtures of HFAC and NFAC was relatively simple, with a progressive decrease and broadening in the temperature of the phase transition as the proportion of NFAC increased up to weight fractions of NFAC of 0.7. At lower weight fractions, a plateau in thetransition temperature as a function of weight fraction was observed. Even at a weight fraction of 0.1 HFAC, no transition to a nonbirefringent liquid state was observed. The high enthalpic changes observed with mixtures of HFAC and NFAC are consistent with the proposed central role that ceramides have in the mechanical and permeability properties of the skin. Moreover, the marked difference in the properties of these two similar lipids may help to explain some of the properties of the stratum corneum.     

Model filled polymers: The effect of particle size on the rheology of filled poly(methyl methacrylate) composites

The effect of size of crosslinked monodisperse spherical polymer particles on the steady shear and dynamic rheology of filled poly(methyl methacrylate) (PMMA) composites was studied for PMMA and polystyrene (PS) particles in the range from 0.1 to 1.3 micron particle size. For PMMA matrices filled with crosslinked PS particles, reduction in filler size increases non‐Newtonian behavior. Particle size effects on the rheology of filled PMMA were much less pronounced for PMMA filler. The rate of growth of steady shear viscosity with aging time was much larger for PMMA filled with PS particles than with PMMA particles. The apparent yield stress of filled PMMA composites was estimated from Casson plots. The yield stress was negligible for PMMA filler but increased with decreasing particle size for PS filler. We suggest that PS particles are rejected by the PMMA matrix and form clusters, causing large enhancements in viscosity and moduli. Polym. Eng. Sci. 44:452–462, 2004. © 2004 Society of Plastics Engineers.     

The kinetics of the catalytic hydrogenation of toluene

The kinetics of the vapour phase hydrogenation of toluene over a silica-supported nickel catalyst have been determined in the temperature range from 100 to 210 °C and at toluene concentrations of 3 to 16 mol-%. The reaction was found to be first order with respect to hydrogen and of a low fractional order in toluene which increased slightly with temperature. From an analysis of the kinetic data an Eley-Rideal type mechanism for the reaction is proposed.