Relation of swelling and Tg depression to the apparent free volume of a particle‐filled,epoxy‐based adhesive

The effect of hygrothermal aging on a particle‐filled, epoxy‐based adhesive was studied using a gravimetric sorption technique. This study has explored moisture sorption characteristics as well as the associated behaviors of swelling and the depression of the glass transition temperature (T_g). We observed that the diffusion of water in this adhesive has a non‐Fickian behavior, and the depression of T_g proceeds to a definite value that is independent of the final equilibrium water content of the system. Our observations suggest that water diffuses into the polymer in a dual‐sorption mode, in which water resides in two populations. In one population, water is considered to occupy apparent free volume of the adhesive, and the second population water infiltrates polymer structure and forms hydrogen‐bonded clusters. Our results show that hygrothermal aging temperature and swelling do not alter the apparent free volume of this adhesive. We conclude that the constant value of T_g depression at saturation implies that only water in the apparent free volume is responsible for the T_g depression, whereas the swelling proceeds through the formation of hydrogen bonds in the adhesive. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1436–1444, 2003     

A novel sintering resistant and corrosion resistant Pt4ZrO2/C catalyst for high temperature PEMFCs

A novel Pt₄ZrO₂/C catalyst was prepared and compared with 20 wt.% Pt/C in terms of the sintering resistance and corrosion resistance. To evaluate their sintering resistance and corrosion resistance properties, an accelerated ageing test (AAT) was performed. The catalysts before and after AAT were characterized by cyclic voltammetry (CV), rotating disk electrode (RDE) and X-ray diffraction (XRD). After AAT, the dissolution rate of Pt and Zr in H₃PO₄ media (105 wt.%, 204 °C) was characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The electrochemical area (ECA) changes of thin film electrodes based on Pt₄ZrO₂/C and Pt/C catalysts were also evaluated using continuous CV sweep technique. All the results showed that Pt₄ZrO₂/C has higher sintering resistance and corrosion resistance than Pt/C. ‘Anchor effect’ is proposed to explain the enhanced effect of ZrO₂ in Pt₄ZrO₂/C binary catalyst compared with Pt/C that contain platinum alone.     

Fully aliphatic polyimides from adamantane‐based diamines for enhanced thermal stability,solubility, transparency,and low dielectric constant

We have synthesized a series of fully aliphatic polyimides (APIs) from bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BOCA) and various aliphatic diamines, including linear aliphatic, flexible alicyclic, and rigid adamantyl diamines. We performed the polymerization reactions using one‐step syntheses in m‐cresol at elevated temperatures without the isolation of poly(amic) acid. The chemical composition and structure of the polymers were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectrometry. The characterization data are reported from analyses using gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and wide‐angle X‐ray diffraction (WXAD) measurements. The polyimides are also subjected to solubility, solution viscosity, tensile strength, transparency, and dielectric constant measurements. The resultant polyimides possess well‐controlled molecular weight, reasonable intrinsic viscosity, good transparency, enhanced solubility, low dielectric constants, and high glass transition temperature, together with marginal thermal and mechanical stability. These properties were enhanced in copolyimides containing equimolar amounts of rigid and flexible moieties. These rigid‐rod APIs derived from the alicyclic dianhydride and aliphatic diamines are promising candidates as advanced materials for future applications in micro‐ and photoelectronic devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3316–3326, 2006     

Effect of scraped-surface tube cooler temperatures on the physical properties of palm oil margarine

The effects of scraped-surface tube cooler temperatures on the isothermal solid fat content (SFC) of palm oil margarine during processing and on margarine consistency (yield value, g/cm²), SFC, and polymorphic changes in storage were studied. SFC was measured in the mixing tank after leaving the tube cooler and the pin worker. The SFC at the tube cooler exit was proportional to the amount of cooling; a higher SFC was produced by more extreme cooling treatment. The SFC of all margarines were reduced in the pin worker, and the reduction was related to the initial SFC profile of palm oil. Margarine samples were stored at 28°C for 28 d and tested daily. Margarine processed at 25°C in the tube cooler had the highest consistency and the least change in SFC, but by the second week crystals had transformed into the β form. Uniform product consistency and SFC were observed in margarines processed at 20 and 15°C. These margarines retained the β′ crystal form for 3 and 4 wk, respectively. The best palm oil margarine was obtained with a tube cooler temperature of 15°C and a residence time of 1.8 min.     

Light-sensitive elastomers modified by 4-(N-dimethylmaleimido)-benzenesulphenyl chloride

New light-sensitive polymers were prepared by modification of four different elastomers with 4-(N-dimethylmaleimido)-benzenesulphenyl chloride (DMI-BSCI). Polydienes modified by DMI-BSCI form block copolymers. These polymers show a strong increase of the glass transition temperature T_g whereby the T_g increase of modified poly(octenamer) is much smaller. Higher modified polydienes have two T_g. Modified poly(octenamers) show a melting temperature dependence T_m on the content of trans double bonds which is characteristic of statistical copolymers. The ratio of rate constants with which trans- and cis-structures in poly(octenamer) are occupied by DMI-BSCI, is

$\text{k}{}_{\mathrm{trans}}\text{k}{}_{\mathrm{cis}}\text{= 0.34}$

     

铝锆炭滑板在浇铸钙处理钢时的化学侵蚀

利用扫描电镜对抗钙处理钢液侵蚀试验后的铝锆炭残样进行了显微结构观察 ,并分析了铝锆炭滑板在钙处理钢液中的化学侵蚀机理。结果表明 :高温下 ,钙处理钢液中的Ca及CaO会与滑板中的Al2 O3 、SiO2 发生反应 ,生成低熔点的 12CaO·7SiO2 (1392℃ )和 2CaO·SiO2 ·Al2 O3 (15 39℃ )等物质 ,这些低熔物被钢水冲刷掉 ,使得滑板表层的Al2O3 和SiO2 含量迅速降低 ,从而导致了滑板的损毁。     

Dishwashing performance of mixed palm stearin sulfonated methyl esters and polyoxyethylene sorbitan esters

The detergency profiles of sodium salt α-sulfonated methyl esters derived from palm stearin (α-SMEPS) and polyoxyethylene (20) sorbitan monoesters (POESE) in mixed micelle systems were evaluated as a function of the weight ratios of α-SMEPS/POESE [polyoxyethylene (20) sorbitan monolaurate (12), polyoxyethylene (20) sorbitan monostearate (18∶0), and polyoxyethylene (20) sorbitan monooleate (18∶1)] at different water hardness values (5.12, 51.2, and 512.0 ppm CaCO₃) and temperatures (20, 30, 45, and 65°C), respectively. All the mixtures of α-SMEPS/POESE (12, 18∶0, and 18∶1) systems exhibited a synergistic effect at 65°C in the absence of hardness. This was evaluated by measuring the percentage of soil removed. The systems showed an increase in detergency with both the temperature and water hardness. Maximal detergency was observed with 5.12 ppm CaCO₃ in the mixed surfactant solution.     

Distributions of Crystal Size from DSC Melting Traces for Polyethylenes

Melting curves, obtained by differential scanning calorimetry, are used to estimate crystal size distributions. The proposed theoretical analysis is applied to different types of polyethylene, including high‐density polyethylene (HDPE), metallocene catalyzed linear low‐density polyethylenes (m‐LLDPE), blends of m‐LLDPEs, and Ziegler‐Natta catalyzed LLDPEs (ZN‐LLDPE). Theoretical predictions are in agreement with experimental results. A generalized melting temperature equation successfully predicts the melting temperatures of all the LLDPEs, although it was initially proposed for homogeneous copolymers with excluded comonomers. A new definition of the heat of fusion for pure crystals is proposed. This heat of fusion can be calculated from the average crystal size or the crystal size number distribution.     

SiO_2微粉中温结合机理的研究

本文研究了ＳｉＯ２微粉、ＳｉＯ２微粉分别与铝酸钙水泥、ｐ－Ａｌ２Ｏ３、ＭｇＯ的混合粉体在３５０℃－１２００℃之间的显微结构。结果表明：ＳｉＯ２微粉及其与其它水化物形成的网状键是高技术浇注料中温强度较高的主要原因。     

CoMoO4负载Mo-V-Cr-Bi氧化物催化剂上甲烷部分氧化的研究

研究了CoMoO4负载Mo-V-Cr-Bi氧化物催化剂上甲烷部分氧化反应,发现反应存在一转折温度,当反应温度低于此温度时,CO是主要产物,而部分氧化产物甲醇的选择性低于20%,而当反应温度高于此温度时,CO的选择性大大降低,而CO2的选择性大大升高,主要产物变为CO2,甲醇的选择性降为0。在O2完全反应的时候,总会有H2生成,特别当反应温度高于转折温度的时候,H2的生成量大大增加。