Effect of the Sintering Additive on Microstructure and Mechanical Properties of Hi‐NicalonTM SiC Fibers in a HfB2 Matrix

This study is focused on the effect of the sintering additive on the microstructure and properties of HfB₂ composites reinforced with SiC Hi–Nicalon fibers. The materials were spark plasma sintered with addition of 5–10 vol% of Si₃N₄ or ZrSi₂. The fibers morphology was examined using scanning and transmission electron microscopy and remarkable differences were observed depending on the additive. Local hardness and Young's modulus were measured by nanoindentation to investigate the fiber mechanical behavior. The introduction of 20 vol% SiC short fibers into the HfB₂ matrix increased the fracture toughness up to 5.4 MPa m^1/2 for the material sintered with ZrSi₂. The room temperature flexural strength of the materials containing fibers slightly decreased when ZrSi₂ was used, but with the addition of Si₃N₄ an improvement of more than the 40%, as compared to the unreinforced material was observed.     

Stability and Oxidation Properties of RE-α-Sialon Ceramics (RE = Y, Nd, Sm, Yb)

Oxidation studies of hot-pressed RE-α-sialons, RE _x -Si_{12-4.5 x} Al_{4.5 x} O_{1.5 x} N_{16-1.5 x} (with x = 0.40 for RE = Nd, Sm, Yb; and x = 0.48 for RE = Y) were carried out in oxygen in a TG apparatus for ca. 20 h. Very good oxidation resistance was found for the Yb-doped samples, with parabolic rate constants K _p similar/congruent 0.09 10^-6-3 10^-6 mg²cm^-4s^-1 in the temperature range 1250-1350°C. The promising performance of this material was corroborated by long-term oxidation experiments (5 days) in air at 1350°C. Although the oxidation kinetics can be described by simple equations related to the parabolic rate law (e.g., the arctan equation, Δ W / A ₀=α arctan bt + c t ), the oxidation process in these materials is likely to be complex. The significantly lower oxidation resistance of the RE = Nd, Sm doped α-sialons, especially at higher temperatures, is related to the formation of melilite, RE₂Si_{3− y} Al _y O_{3+ y} N_{4− y} ( y ∼ 1), in these systems. The melilite phase is also responsible for the thermal instability of the Nd- and Sm-α-sialons.     

Analysis of ubiquinone and tocopherol levels in normal and hyperlipidemic human plasma

The type and amount of lipophilic antioxidants in plasma of hyperlipidemic patients are of great importance since they play a central role in preventing deleterious oxidation of blood lipids and proteins. Isolation and quantitation of lipophilic antioxidants from hyperlipidemic plasma samples meet great obstacles because of increased levels of various intermediary lipid products. This study was designed to develop a rapid and efficient extraction and separation procedure for simultaneous analysis of ubiquinone-9 and-10 as well as α-, δ-, and γ-tocopherol isomers. The levels of ubiquinone-10, α- and γ-tocopherol were analyzed in human plasma samples using high-performance liquid chromatography. Lipid extraction was performed by petroleum ether/methanol/water. After phase separation, ubiquinone was reduced to ubiquinol by sodium borohydride and the lipids were separated on a C18 column. A binary gradient with solvents containing lithium perchlorate was used, and an electrochemical detector was employed for quantitation. This procedure was also efficient for the analysis of antioxidant lipids in samples containing a large number of accumulated and interfering lipid intermediates. Thus, the procedure described here is useful for efficient and rapid quantitation of ubiquinones and tocopherols in human plasma samples, especially those originating from hyperlipidemic patients.     

On the synthesis and characterization of new low temperature curing powder coatings cured with radiation

The synthesis and characterization of a new type of low temperature curing powder coating is described. The type of materials used were mixtures of an amorphous methacrylate-functional prepolymer and crystalline acrylate and methacrylate monomers. The introduction of a crystalline component in an amorphous resin mixture was shown to markedly reduce the melt viscosity and thus enhance the flow properties of the powder coating. Curing experiments showed the advantage of using photoinitiation compared to thermal initiation. The reaction was much faster and the problem with oxygen inhibition could be avoided. Department of Polymer Technology, S-100 44 Stockholm, Sweden.     

Biobased UV-curable coatings based on itaconic acid

A series of renewable unsaturated polyesters were synthesized from itaconic acid (IA), succinic acid, and 1,4-butanediol by solvent-free polycondensation. Previous studies utilizing IA to make polyesters for coating applications have shown great potential; however, the curing and material properties have not been investigated in detail. The aim of this study was to investigate how the curing is affected by the amount of unsaturations and how well itaconate-based polyesters crosslink without the addition of any other unsaturated monomers or reactive diluents. The chemical structures of the polyesters were confirmed with FTIR, ¹H-NMR, and THF–SEC. The degree of curing was studied with FTIR, and the mechanical properties of the crosslinked polyesters were evaluated with DMA, pendulum hardness, and microindentation. The degree of curing was found to be up to 75%, and furthermore, it was found that the final mechanical properties of the crosslinked coatings could be tuned by modifying the IA content in the monomer composition. The results from DMA showed that there is a clear trend between mechanical properties and crosslinking density.     

High-performance removal of acids and furans from wheat straw pretreatment liquid by diananofiltration

Two model solutions and a real stream from the hydrothermal pretreatment of wheat straw were subjected to nanofiltration, and permeate flux, retention and resistance to fouling were evaluated. Three commercial NF membranes were tested, and a pressure of 4 bars (range: 1–20 bars) and a temperature of 20ºC (range: 20–50ºC) were found to provide the best results in terms of retention. A subsequent nanodiafiltration consisting of five cycles enabled one to recover 90% of the monosaccharides (purity >99%). This result showed that diananofiltration could be a promising strategy for the recovery of high-purity streams of monosaccharides from pretreatment liquids.     

Oxidation Kinetics of Nickel Particles: Comparison Between Free Particles and Particles in an Oxide Matrix

The degradation of selective solar absorbers through oxidation has been studied. We compare the oxidation kinetics of nickel particles of various sizes. Both free particles and particles embedded in an oxide matrix were studied. The oxidation kinetics of polycrystalline nickel nanorods was determined by IR spectroscopy in the temperature range 300–500°C. The particles were oxidized when situated in the porous alumina matrix of an electrochemically deposited solar absorber coating. The oxidation kinetics was compared to that of free nanometer-particles at the same temperature and to micron-sized polycrystalline nickel particles, which were studied by thermogravimetry in a wider temperature range. It was found that the rate constant was markedly lower for the particles in the matrix. Implications for the durability of selectively solar absorbing coatings are discussed.     

Hydrogenation of soybean oil with cationic Rh(I)-Phosphine complexes as catalysts — Para-toluene sulfonate and sulfonated styrene resins as counterions

A cationic rhodium(I) complex, viz. Rh NBD diphos⁺ 4-CH₃-C₆H₅SO ₃ ⁻ [NBD = norbornadiene, diphos = (C₆H₅)₂ P-CH₂-CH₂-P(C₆H₅)₂], has been used as a homogeneous catalyst for the hydrogenation of soybean oil in acetone solution. This complex acts almost in the same way as the corresponding ones with ClO ₄ ⁻ or PF ₆ ⁻ as conuterions, i.e., it gives high polyene selectivity and low formation oftrans isomers. Because of the somewhat stronger basic character of the p-toluene-sulfonate ion compared with the perchlorate and hexafluorphosphate ions, the relative proportion of reaction via the so-called monohydride path is larger in the present case. When the ionic complex, Rh NBD diphos⁺, is bound to a solid support, e.g., to the anionic sites of sulfonated polystyrene resins, a nearly total lack of catalytic activity is observed. Possible reasons for these effects are discussed-in terms of π-arene-metal binding and covalent coordination of the sulfonate group.     

The total PFA of the multiwindow harmonicdetector and its application to real data

The authors study the multiwindow spectral analysis method as it applies to the detection of sinusoidal signals. They examine the probability of false alarm P_FA. The total P _FA (sinusoidal frequency unknown) is shown analytically to be bounded below by the order statistics (minimum) of BM/K independent identically distributed (i.i.d.) beta variates, where M is the length of the data record used in the detection, K the number of windows, and B the width of the frequency band of interest. Simulation results indicate a much larger bound, the minimum of BM i.i.d. beta variates. It is shown that for real signals, the assumptions made in the derivation of the detector break down at frequencies close to zero and to half the sampling frequency     

Magnitude estimation of perceived odor intensity: Empirical and theoretical properties.

Four subjects judged the odor intensities of 7 pyridine concentrations and a blank. Computer simulations of a judgment model were compared with the empirical data. The model generates data patterns that closely mimic empirical findings. The following patterns were confirmed: (a) A power function relates magnitude estimates and concentration with an exponent in the range of 0.7 to 1.0. (b) The exponent fluctuates so that the level constant is negatively correlated with the exponent. (c) The standard deviation of the responses is a negatively accelerated function of the mean. (d) The skewness of the responses is relatively high for low concentrations and declines toward zero with increasing concentration. (e) The correlation between responses to successive stimuli is highest when successive concentrations are similar. (PsycINFO Database Record (c) 2010 APA, all rights reserved)