Papers by Keyword: Apparent Activation Energy

Abstract: Copper dross are produced by rough decopperizing of blast furnace lead bullion. During liquation separation of copper dross from lead bullion most of arsenic and copper are concentrated in copper dross, arsenic content is approximately 4% As. Currently the processes for arsenic recovery from copper dross are understudied. In this work the focus is given to studying kinetics of the process for recovering arsenic from copper dross by alkaline-sulfide leaching. Alkaline sulfide leaching allows carrying out selective removal of arsenic into solution, keeping at this non-ferrous and precious metals in leaching residue. The studied method of alkaline sulfide leaching of copper dross provides backgrounds for developing technology that would allow processing of copper dross with selective arsenic removal from lead production cycle. By minimizing circulation of this harmful impurity in lead production it is possible to lessen destructive effect of its aggressive compounds on smelting-units refractory. Kinetics of alkaline sulfide leaching of copper dross was understudied up to date. This work is an attempt to fill the gap.

Abstract: The observed enhancements in the high frequency microwave processing alumina compared to those in conventional method at the same sintering temperatures have been studied. Some possible mechanisms responsible for the enhancements were investigated and are discussed in this paper. The enhancements could be associated with the increase either in driving force or in apparent activation energy of diffusion. An experiment to estimate the driving force of sintering is not easy to perform because the force depends not only on the density and grain size but also on the electric field in the materials. Therefore, a series of experiments to estimate the apparent activation energy were performed in high frequencies microwave and in conventional sintering method, as well. It was observed that the apparent activation energy in conventional sintering was much lower than that of microwave sintering. These activation energy values suggested that diffusion rate in microwaves sintering was faster, which led to the higher densification.

Abstract: The dynamic experiments about the conversion of CO₂ from simulated flue gas were carried out in a bubbling reactor containing a kind of adsorption with M dissolving in ethanol and water at atmospheric pressure. Based on the results of product analysis and electrode potentials, the reaction mechanism of CO₂ reduced by M was deduced. The results of dynamic experiments showed that the reaction order was 1.0, the rate constant was 5.91×10^-2 s^-1, and the apparent activation energy was 23.47 kJ·mol^-1.

Abstract: TG analysis was used to investigate the thermal decomposition of switchgrass, which is a potential gasification feedstock. 10 mg switchgrass sample with the particles between 0.45 and 0.70 mm was linearly heated to 873 K at heating rates of 10, 20, 30 K/min, respectively, under high-purity nitrogen. The Kissinger method and three isoconversional methods including Friedman, Flynn-wall-Ozawa, Vyazovkin and Lenikeocink methods were used to estimate the apparent activation energy of switchgrass. With the three isoconversional methods, it can be concluded that the activation energy increases with increasing conversion. The four model free methods reveal activation energies in the range of 70-460 kJ/mol. These activation energy values provide the basic data for the thermo-chemical utilization of the switchgrass.

Abstract: Two methods are used to estimate the concrete strength based upon the maturity concept. The conclusion is that the apparent activation energy E value is key factor in the equivalent age method, larger value of E indicated that the age conversion factor versus temperature function is more nonlinear, and an increase in temperature results in a disproportionate increase in the age conversion factor. It is also shown that there is a unique relationship between maturity and relative strength (ratio of strength to limiting strength), and the relative strength method method-can be used in the prediction for the concrete strength.

Abstract: The larch bark was examined by non-isothermal means to determine the mass loss kinetics of the thermal decomposition with linear temperature programming in nitrogen atmosphere. In this work, mechanism equation of = was used for Coats-Redfern integral method at the different heating rates. The apparent activation energy, pre-exponential factor and the pyrolysis kinetic equations at the different heating rates were obtained. The pyrolysis temperature area was divided into two separate temperature regions for the pyrolysis kinetic equation and the two components were decomposed respectively at the two separate temperature regions. The global mass loss rate of the bark is considered as controlled respectively by the reactions of the two components respectively during the lower and higher temperature ranges. The kinetics of the two components are found to abide by the mechanism equation of =, which gave the best fits to the experimental data. The obtained kinetic equations of the bark at the different heating rates were additionally validated by the reasonable agreement between the experimental and calculated results.

Abstract: The apparent activation energy for densification is a characteristic quantity that elucidates the fundamental diffusion mechanisms during the sintering process. Based on the Arrhenius theory, the activation energy for densification of the pure and La doped α-Al₂O₃ at constant heating-rates sintering has been estimated. Sintering of α-Al₂O₃ and La doped powder has been executed by the way of a push rod type dilatometer. It was shown that the shrinkage and the relative density of the samples decreased with increasing heating rates. At the same sintering condition, the shrinkage of the pure α-Al₂O₃ was higher than that of the La doped. According to the calculation, it was found that the apparent activation energy had a single value and did not depend on the relative density for both samples. The apparent activation energy of the pure α-Al₂O₃ was 374.3kJ/mol, which was lower than that of La doped (966.5kJ/mol). So the densification process for α-Al₂O₃ was retarded due to La doping, which was consistent with experimental results of the shrinkage.

Abstract: In this paper, application of multilayered circuit substrates has been studied, the glass ceramic (50%Al₂O₃-50%glass) with low temperature co-fired and good performance as the raw material was used, by means of calculating the apparent activation energy of densification in the experiment and observing the SEM images of glass ceramic substrate section, the densification mechanism of glass ceramic substrate sintering is analyzed.

Abstract: Deproteinization of natural rubber was achieved in the latex stage. The structure of deproteinized natural rubber (DPNR) was characterized by fourier transform infrared spectroscopy (FTIR). The thermo degradation of DPNR was studied by thermogravimetry analysis (TG) under air atmosphere and nitrogen atmosphere. The kinetic parameters apparent activation energies (Ea) of the thermal decomposition reaction been calculated from the TG curves using the method described by Broido. And the results were compared with the thermo degradation of natural rubber (NR) under the same conditions. The effect of proteins in natural rubber latex on thermal/ thermo-oxidative stability of NR was discussed. The results show that: the absorptions of the proteins in DPNR at 1546 ㎝^-1, compared to NR, become significantly weaker, nearly disappear, which indicates most of proteins has been removed from NR. The thermo degradation of DPNR in nitrogen atmosphere is a one-step reaction. The initial degradation temperature (T₀) 、the maximum degradation temperature（T_p） and the final degradation temperature（T_f）as well as the Ea of DPNR are higher than those of NR, which indicates that DPNR represents a better thermal stability than NR under nitrogen atmosphere. Thermo-oxidative degradation of DPNR and NR are two-step reaction. The characteristic temperatures (T₀, T_p and T_f) of DPNR are lower than those of NR. The Ea during the First Step of Thermooxidative Degradation of DPNR are also lower than those of NR. These results prove that the thermo-oxidative stability of DPNR is worse than that of NR. Protein is the key role to the thermal stability of natural rubber.

Abstract: New initiator of FFM6 is used to initiate the acrylic emulsion polymerization. The influences of concentration of FFM6 (c[I]) and polymerization temperature (T) on polymerization reaction rate (R_p) were discussed. R_p is proportional to (c[I])^1.4 which is different with classical emulsion polymerization whose R_p is proportion to (c[I])^0.4, that indicate polymerization mechanism of the reaction in the study is different with classical mechanism. The value of Ea, 56.4 kJ/mol, is lower than the value of general radical polymerization’s Ea (80.0-96.0 kJ/mol), which indicates the FFM6 can initiate acrylic emulsion polymerization at a lower temperature compared with the other kinds of initiator.