Effect of Addition of Oxides on Low-Temperature Oxidation of Molybdenum Disilicide

A type of aluminosilicate that has a good wetting property for molybdenum disilicide (MoSi₂) was added to a MoSi₂ matrix to study the effects on the microstructure and low-temperature oxidation. It was found that the composites had not only good low-temperature oxidation resistance but also high thermal shock resistance when the added oxides formed a network microstructure in the matrix. There was no appreciable oxidation gain for MoSi₂/oxide composites with a network microstructure at 773 K for 2500 h. The results indicate that microstructure design is a simple and effective solution to preventing the low-temperature oxidation of MoSi₂.     

Scaling Analysis for the Axial Displacement and Pressure of Flextensional Transducers

We have examined the axial displacement, Δ h , and maximum axial pressure, P _max, of flextensional transducers such as the moonies and the rainbows with both scaling and mechanical analyses. For a constant electric field E across the transducer, Δ h / t ∝ E / t ² where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and Δ h / t , the relative axial displacement. Thus, for a constant voltage V across the transducer, Δ h / t ∝ V / t ³. As for the maximum pressure, P _max t ² for the rainbows and P _max∝ wt for the moonies where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and w the thickness of the piezoelectric disk of the moonie. These predictions agree well with the experimental results found in the rainbows and the moonies. Our analysis showed that although the rainbows and the moonies differ in design and processing, the underlying physics for the enhancement in the axial displacement are essentially the same: The nonuniform distribution of d ₃₁ through the thickness of the transducer causes the transducer to arch or flatten with an applied electrical field, which leads to the enhancement in the axial displacement. The only difference is that, for the transducer to arch, the applied field is in the opposite direction to the polarization in the rainbows but in the same direction as the polarization in the moonies.     

烧成系统NOx的形成及排放控制技术介绍

煤燃烧过程中污染物的形成、迁徙、排放和抑制规律、NOx污染控制技术等是煤燃烧领域重点研究的内容。文章分析了水泥工业回转窑中煤粉燃烧过程中NOx的形成机理，并针对NOx的形成机理和影响因素，探讨了水泥工业相关的低NOx燃烧技术。目前，较为实际的方法是采取空气分级燃烧技术和设计出科学的燃烧器二种。     

Temperature-dependent diffusion coefficient of soluble substances during ethanol extraction of clove

The temperature dependence of the diffusion coefficient of ethanol-soluble substances from ground cloves (particle size 250 μm) during extraction was estimated by fitting batch extraction data at several temperatures (27.8, 40, 50, and 60°C) to a previously developed mass transfer model. The model was based on spherical geometry of particles. Nonlinear regression analysis was used to develop an equation that describes the diffusivity as a function of temperature. The temperature dependence ofD _A was of the Arrhenius type.     

Calendering of non-newtonian fluids

The calendering of non-Newtonian fluids by two rotating cylinders to produce thin films of fluids finds wide application in polymer sheet-making and food-drying industries. Theoretical work has previouly been devoted to the symmetrical case where the cylinders are of equal diameters rotating at the same speed. The present work proposes a new one-film theory of calendering of power law fluids for unequal radii and surface velocities of the calendering cylinders. The relationship between the dimensionless thickness of the calendered fluid, Δ_e^* and that of the incoming fluid, Δ_i^* is shown to be a function of the ratio of the surface velocities of the cylinders and the power law index. The result further shows that Δ_e^* tends to asymptote after the second decade of Δ_i^*     

Alternative hydrocarbon solvents for cottonseed extraction: Plant trials

Hexane has been used for decades to extract oil from cottonseed and is still the solvent of choice for the edible-oil industry. Due to increased regulations as a result of the 1990 Clean Air Act and potential health risks, the edible-oil extraction industry urgently needs an alternate hydrocarbon solvent to replace hexane. Based on laboratory-scale extraction tests, two hydrocarbon solvents, heptane and isohexane, were recommended as potential replacements for hexane. A cottonseed processing mill with a 270 MT/day (300 tons/day) capacity agreed to test both solvents with their expander-solvent process. Extraction efficiencies of isohexane and heptane, judged by extraction time and residual oil in meal, refined and bleached color of miscella refined oil, and solvent loss, were comparable to that of hexane. However, fewer problems were encountered with the lower-boiling isohexane than with the higher-boiling heptane. With isohexane, the daily throughput increased more than 20%, and natural gas consumption decreased more than 40% as compared to hexane.     

Decane reforming reaction over Pt,Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite

Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on NaY- and HY-zeolite were examined as a catalyst for producing gasoline from n-decane via simultaneous reforming and cracking. The catalysts were prepared by calcining and reducing metal-ion-exchanged Y-zeolite with O₂ and H₂ at 300°C., respectively. Thus prepared catalysts were characterized by hydrogen chemisorption and temperature programmed desorption of ammonia. Pt-Ni/NaY and Pt-Ir/NaY bimetallic catalysts offered the improved activity maintenance compared to Pt/NaY monometallic catalyst. The catalysts supported on HY-zeolite showed higher selectivity toward C₅–C₇ and skeletal isomers of C₅–C₇- and C₈–C₁₀ than those of the catalysts supported on NaY-zeolite, which is a desired characteristic for increasing octane value of gasoline these days. However, deactivation with reaction time was much more pronounced on HY-zeolite-supported catalyst. When the catalyst was prcsulfided with H,S, the stability with time on stream was enhanced and the selectivity was quite different from that of the catalyst before presulfiding. The acidity of Y-zeolite and presulfiding of catalyst greatly influenced the activny, selectivity and stability of Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite in n-decane reforming reaction.     

Surface morphology and nodule formation mechanism of cellulose acetate membranes by atomic force microscopy

By the use of atomic force microscopy (AFM), formation mechanism of nodular structure in cellulose acetate membranes was systematically investigated. Elementary factors affecting the nodule formation were delineated on the basis of both kinetic and thermodynamic considerations. It was shown that (1) the exact nature of nodular structure is thermodynamic equilibrium glassy state; nodular structure will vanish in the rubbery state; (2) the thermodynamic factor affecting nodule formation is the membrane formation temperature; with the membrane formation temperature decreasing, more chain segments are able to form nodular structures; (3) nodule formation is dependent on the segment rearrangement; variation of the solvent environment is the major kinetic factor affecting the segment rearrangement and nodule formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1328–1335, 2003     

超细粉体微胶囊红磷阻燃剂的研制

红磷经湿法研磨预处理，在一定pH值（9．0－9．5），表面活性剂用量为0．8％－1．0％，2200Hz超声波振荡15min后，采用蜜胺树脂预聚体原位法包覆，制得了微胶囊红磷阻燃剂的超细粉体，其平均粒径为2．186um，并探讨了预处理，PH值，表面活性剂及超声波对粒度的影响。     

Crystalline morphology and isothermal crystallization kinetics of poly(ethylene terephthalate)/clay nanocomposites

A poly(ethylene terephthalate) (PET)/montmorillonite clay nanocomposite was synthesized via in situ polymerization. Microscopic studies revealed that in an isothermal crystallization process, some crystallites in the nanocomposite initially were rod‐shaped and later exhibited three‐dimensional growth. The crystallites in the nanocomposite were irregularly shaped, rather than spherulitic, being interlocked together without clear boundaries, and they were much smaller than those of neat PET. With Avrami analysis, the isothermal crystallization kinetic parameters (the Avrami exponent and constant) were obtained. The rate constants for the nanocomposite demonstrated that clay could greatly increase the crystallization rate of PET. The results for the Avrami exponent were consistent with the observation of the rodlike crystallites in the PET/clay nanocomposite during the initial stage. Wide‐angle X‐ray scattering and Fourier transform infrared studies showed that, in comparison with neat PET, the crystal lattice parameters and crystallinity of the nanocomposite did not change significantly, whereas more defects may have been present in the crystalline regions of the nanocomposite because of the presence of the clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1381–1388, 2004