Two ways of synthesis of polymer networks based on diglycidyl ether of bisphenol A,bisphenol A,and sulfanilamide: Kinetics study

The kinetics of reactions of ternary systems based on bisphenol A diglycidyl ether, bisphenol A, and a sulfanilamide curing agent were investigated using HPLC, during two different synthesis paths. The influence of tetrabutylphosphonium tetrafluoroborate as a catalyst for the epoxy–phenol reaction was studied. For the same initial composition, polymers differing by the crosslink point distribution and the chain length between crosslinks were synthesized. Different solid‐state behavior is expected in these two categories of networks. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 580–591, 2001     

Properties of PVA-PSA hybrid materials prepared through the incorporation of polysilicic acid (PSA) into polyvinyl alcohol

A quick method of preparing transparent organic-inorganic hybrid material was studied. The hybrid, PVA/PSA, was prepared through incorporating the nanoscaled polysilicic acid (PSA) obtained through hydrolysis and condensation of metasilicate salt directly into a polyvinyl alcohol (PVA). The interfacial force, microstructure, and dynamic mechanical property of the hybrid were studied by means of spectroscopy (FTIR, X-ray diffraction and solid-state ²⁹Si NMR) and dynamic mechanical analysis, and the results were compared with that of the hybrids, PVA/TEOS, prepared through the traditional sol-gel process. It was found that the microstructure of PVA/PSA was different from that of PVA/TEOS because of the different preparation methods. The structures of the crystals in both hybrids were similar to that of the pure PVA. Other physical properties, such as T_g, storage modulus, tensile strength and solvent resistance of the PVA/PSA hybrid, were improved significantly with the addition of the silica content. The extent of improvement was a little lower than that for the PVA/TEOS.     

Preparation and characterization of ordered mesoporous Mg–Al–Co hydrotalcite based catalyst for decarboxylation of jatropha oil

This paper reported preparation of novel order mesoporous Mg–Al–Co hydrotalcite based catalysts through sol–gel procedure using precursors such Mg(NO₃)₂, Al(NO₃)₃ and Co(NO₃)₂ and Na₂CO₃. The catalyst also contained both acidity and basicity being very convenient for decarboxylation process of vegetable oil to green hydrocarbons. The alkaline media was maintained at pH 10 during the processes. Molar ratio of metal cations and temperature of the sol–gel processes were investigated for their effect in the mesoporous structure formation. The results showed that the procedure should be established at 70 °C with the molar Mg/Al/Co ratio of 1/5/0.2. Acidity and basicity of the mesoporous hydrotalcite based catalyst were demonstrated for their co-existence. The as-synthesized material at the suitable conditions was used as catalyst for decarboxylation of jatropha oil to obtain green hydrocarbons mainly belonging to diesel fraction. The decarboxylation was carried out at 400 °C for 3 h in closed auto-pressurized reactor exhibiting a yield of diesel involving hydrocarbons of over 70% after distillation and analysis. The result also confirmed that the acidity and basicity greatly accelerated the activity of the catalyst. Some techniques were used to characterizing the catalyst including XRD, SEM, TEM, TGA, NH₃-TPD, CO₂-TPD and BET, and GC–MS was also used to analyze the main product composition.     

Heterogeneous amino acid-based tungstophosphoric acids as efficient and recyclable catalysts for selective oxidation of benzyl alcohol

A series of organic-inorganic composite catalysts, prepared by modifying tungstophosphoric acid (TPA; H₃PW₁₂O₄₀) with different amino acids such as phenylalanine (Phe), alanine (Ala), and glycine (Gly) were synthesized. The physicochemical and acidic properties of these (MH) _x H_3?x PW₁₂O₄₀ (M=Phe, Ala, and Gly; x=1–3) composite materials were characterized by a variety of different analytical and spectroscopic techniques, namely TGA, XRD, FT-IR, XPS, and NMR, and exploited as heterogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H₂O₂). Among them, the [PheH]H₂PW₁₂O₄₀ catalyst exhibited the best oxidative activity with an excellent BzOH conversion of 99.0% and a desirable benzaldehyde (BzH) selectivity of 99.6%. Further kinetic studies and model analysis by response surface methodology (RSM) revealed that the oxidation of BzOH with H₂O₂ follows a second-order reaction with an activation energy of 56.7 kJ·mol^?1 under optimized experimental variables: BzOH/H₂O₂ molar ratio=1 : 1.5 mol/mol, amount of catalyst=6.1 wt%, reaction time (x₃)=3.8 h, and amount of water (x₄)=30.2 mL.     

Effects of ITO thin films on microstructural and photocatalytic properties of layered TiO2/ITO films prepared via an extended deposition period

This study elucidates how indium tin oxide (ITO) thin film affects the microstructural and photocatalytic properties of layered TiO₂/ITO films prepared by DC magnetron sputtering. Two ITO substrates, as-received ITO (aITO) and in situ sputtered ITO (sITO), are adopted herein. Photocatalytic measurements of methylene blue and dimethyl sulfoxide indicate that the layered TiO₂/sITO film has greater photocatalytic oxidation than the TiO₂/aITO catalyst. According to photoelectrochemical tests, the latter exhibits a completely opposite activity to that of the former. Secondary ion mass spectrometry elemental depth profiles reveal that tin atoms in the sITO film really permeate into the growing TiO₂ film and promote the formation of the crystalline Ti_1−xSn_xO₂ layer. Additionally, cross-sectional transmission electron microscopy images and the selective area diffraction patterns show the difference between the diffusion of tin in the two catalysts. The photocatalytic oxidation capability is further enhanced in the layered TiO₂/sITO film because of an increase in the bandgap energy and a positive shift in the Fermi level energy of the Ti_1−xSn_xO₂ layer. Conversely, tin diffusion is limited in the aITO substrate under controlled conditions, in such a manner that a Schottky barrier can form at the TiO₂/aITO interface. Therefore, photogenerated electrons can be efficiently transferred from the overlaid TiO₂ film to the aITO substrate, producing a remarkable photocurrent density under UV illumination. Microstructural measurements reveal that the growth of the reactive {0 0 1} facets and columnar porous structure are favored by the synergetic effect of ITO substrate and an extended period of deposition. Accordingly, the photocatalytic capabilities are further raised.     

Non-isothermal crystallization kinetics and microwave properties of Bi0.75Y2.25Fe5O12 prepared by coprecipitation

The non-isothermal crystallization kinetics of Bi_0.75Y_2.25Fe₅O₁₂ powder prepared by coprecipitation has been investigated. The activation energy of crystallization was calculated by differential scanning calorimetry (DSC) at different heating rates. Analysis of non-isothermal DSC data presented values of 650 kJ/mol and 2.48 for the activation energy of crystallization and the Avrami exponent, respectively. This Avrami exponent value was consistent with surface and internal crystallizations occurring simultaneouly. The complex permittivity and permeability of Bi_0.75Y_2.25Fe₅O₁₂ were measured at X-band (8–12 GHz) by cavity perturbation technique. For dielectric properties, the real part of permittivity, ?′, was obtained in the range of 13.18–15.28. For magnetic properties, the real part of permeability, μ′, was obtained in the range of 12.21–20.98.     

The Effect of Homogenization on the Corrosion Behavior of Al–Mg Alloy

The effect of homogenization on the corrosion behavior of 5083-O aluminum alloy is presented in this paper. The intergranular corrosion and exfoliation corrosion were used to characterize the discussed corrosion behavior of 5083-O aluminum alloy. The variations in the morphology, the kind and distribution of the precipitates, and the dislocation configurations in the samples after the homogenization were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effects of the highly active grain boundary character distribution and the types of constituent particles on the corrosion are discussed on the basis of experimental observations. The results indicated that the corrosion behavior of 5083-O alloy was closely related to the microstructure obtained by the heat treatment. Homogenization carried out after casting had the optimal effect on the overall corrosion resistance of the material. Nevertheless, all samples could satisfy the requirements of corrosion resistance in marine applications.     

Design,fabrication and performance analysis of a 200 W PEM fuel cell short stack

A PEM fuel cell short stack of 200 W capacity, with an active area of 100 cm² has been designed and fabricated in-house. The status of unit cell performance was 0.55 W cm⁻². Based on the unit cell technology, a short stack has been developed. The proper design of uniform flow distribution, cooling plate and compressed end plate were important to achieve the best performance of the short stack. The performance of four cells stack was analyzed in static and dynamic modes. In the static mode of polarization curve, the stack has peak power density of 0.55 W cm⁻² (220 W) at 0.5 V per cell, when the voltage was scanning from low to high voltage (1.5–3.5 V), and resulted in minimum water flooding inside the stack. In this study a series of dynamic loadings were tested to simulate the vehicle acceleration. The fuel cell performances respond to dynamic loading influenced by the hydrogen/air stoichiometric, back pressure, and dynamic-loading time. It was needed high hydrogen stoichiometric and back pressure to maintain high dynamic performance. In the long-time stable power testing, the stack was difficult to maintain at high performance, due to the water flooding at high output power. An adjusting cathode back-pressure method for purging water was proposed to prevent the water flooding at flow channels and maintain the stable output power at 170 W (0.42 W cm⁻²).     

Modeling and Dynamic Simulations of Doubly Fed Adjustable-Speed Pumped Storage Units

This paper derives the mathematical models of doubly fed adjustable-speed pumped storage units (DFASPSUs) to be utilized in the power system analysis. It adopts the improved induction machine model with ac excitation on the wire-wound rotor as well as the field-oriented control theory for the study and analysis of DFASPSU models. First, the rotor excitation voltage is separated into two components, i.e., the q-axis voltage and the d-axis voltage, so as to control the output active and reactive powers, respectively. Next, a dynamic model of DFASPSU is derived using the swing equation of rotary electric machine and the equation of motion of rotor rotating mass. Finally, computer simulation is carried out to compare its results with practical examples in terms of dynamic characteristics for verifying the correctness of the proposed models.