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Abstract  

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO2 composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO2 composite and PANI are all D3, and the corresponding function is ƒ(α)=1.5(1−α)2/3[1−(1-α)1/3]−1. The correlated kinetic parameters are E a=112.7±9.2 kJ mol−1, lnA=13.9 and E a=81.8±5.6 kJ mol−1, lnA=8.8 for PANI/ZrO2 composite and PANI, respectively.

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Abstract  

In order to enrich the thermokinetic research methods and enlarge the applicable range of the thermokinetic time-parameter method, the integral and differential thermokinetic equations of consecutive first-order reaction have been deduced, and the mathematical models of the time-parameter method for consecutive first-order reactions have been proposed in this paper. The rate constants of two steps can be calculated from the same thermoanalytical curve measured in a batch conduction calorimeter simultaneously with this method. The thermokinetics of saponifications of diester in aqueoushanol solvent has been studied. The experimental results indicate that the time-parameter method for the consecutive first-order reaction is correct.

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Abstract  

The variations of size, intensity, and size distribution of free volumes generated in the network of molecular chains of gelatin at the sol-gel transition were studied by means of the positron annihilation lifetime technique. Although variation in average free-volume radius was not recognized, a variation of free-volume content was observed at the sol-gel transition point of gelatin with an addition of saccharose.

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Abstract  

Nano-ZnO flakes were synthesized by calcination of the precursor of Zn(OH)2 obtained via the reactive ion exchange method between an ion exchange resin and ZnSO4 solution at room temperature. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscope, UV-Vis diffuse reflection spectrum and Na2EDTA titration were used to characterize the structure features and chemical compositions of the as-prepared ZnO. The results show that the as-prepared ZnO flakes have uniform structure and high purity. Heat capacities in the temperature range of 83 to 396 K were measured. The measured heat capacities values were compared with those of coarse crystal powders and the difference between this two heat capacity curves was analyzed.

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Summary  

Single aerosol particles were analyzed in the ambient air of the center of Shanghai by scanning proton microprobe to obtain characteristic X-ray spectra (micro-PIXE) which were considered to be the fingerprints of these aerosol particles. The origin of the lead-containing particles was identified by the combination of the micro-PIXE spectra with pattern recognition technique. It was found that the most of the lead-containing particles were derived from vehicle exhaust, coal combustion and soil dust.

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Abstract  

Differences of size, content and size distribution of free volumes in linear branched and three-armed polystyrenes, synthesized by radical and anionic processes, were observed by positron annihilation lifetime measurements. The temperature dependence of an average free volume radius was quite similar among polystyrenes of different architectures and molecular weight distributions. The free volume radius increased with temperature, from 0.27 nm (T:60 K) to 0.29 nm (T:260 K) and 0.30 nm (T g:363 K), then to 0.35 nm (423 K), showing turning at and transition temperature. The free volume content decreased from 60 K to 220 K to 300 K showing peculiar minimum at 220 K to 300 K depending on the molecular shape, increased above 320 K, upto 340 to 360 K. The free volume contents decreased with an increase of molecular weight and by an addition of oligomer or plasticiser, suggesting differences in relaxation time or molecular motion between the edge and middle portions of molecular chain and filling effect of smaller molecules in free volumes, respectively. The apparent free volume fraction showed clear variations atT andT g. Size distribution of free volumes suggested more complicated behavior of free volume upon the molecular relaxations and filling effect.

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Abstact  

The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$Co_3 O_4 + H_2 \to 3CoO + H_2 O, 3CoO + 3H_2 \to 3Co + 3H_2 O$$ \end{document}
which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step, the activation energy, E a, and the pre-exponential factor, A, were found to be 104.35 kJ mol−1 and 1.18�106∼2.45�109 s−1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be f(α)=3/2(1−α)[−ln(1−α)]1/3 or in the integral form: g(α)=[−ln(1−α)]2/3. For the second step, the activation energy, E a, and the pre-exponential factor, A, were found to be 118.20 kJ mol−1 and 1.75�107∼2.45 � 109s−1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1−α)2 or in the integral form: g(α)=[1−α]−1−1.

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Abstract  

Effects of gaseous hydrogenation on crystallization behavior of melt-spun Mg63Pr15Ni22 amorphous ribbons have been investigated. The crystallization peak temperature T p1 shifted to higher temperature with increasing heating rate for the un-hydrogenated Mg63Ni22Pr15 metallic glass, however, it is nearly unchanged for the hydrogenated sample. The present work indicates that the crystallization is a nucleation-and-growth process for the un-hydrogenated Mg63Ni22Pr15 metallic glass. However, the crystallization of hydrogenated sample begins with nucleation and then diffusion-controlled growth takes place.

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Abstract  

A new method was proposed for determining the most probable mechanism function of a solid phase reaction. According to Coats-Redfern's integral equation Eβ→0 was calculated by extrapolating β to zero using a series of TG curves with different heating rates. Similarly, Eα→0 was calculated according to Ozawa's equation. The most probable mechanism function of the solid phase dehydration of manganese(II) oxalate dihydrate was confirmed to be G(α)=(1-α)1/2 by comparing Eα→0 with Eβ→0.

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Abstract  

In the present study, the effect of primary processing route on the dissolution and precipitation reactions in a commercial Al−Si alloy (designated as A390) is investigated using differential scanning calorimetry (DSC). The Al−Si alloy selected for the present investigation was processed using conventional casting and spray atomization and deposition routes. The results of differential scanning calorimetry conducted on the as-processed samples indicated no significant dissolution reaction for the as-cast A390 alloy when compared to the similar results obtained for as-spray atomized and deposited samples. However, the thermal analysis conducted on the solutionized cast and spray deposited samples exhibited no significant difference in the kinetics of precipitation reactions. The results of the differential thermal analyses were finally rationalized in terms of observed microstructural features.

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