查看更多>>摘要：The thermal stability of nitroguanidine (NQ) with different morphologies was studied using a self-developed isothermal decomposition gas manometric device at both high and low temperatures. At 443.15-463.15 K, the total decomposition of needle-like NQ (N-NQ) and hexagonal block-shaped NQ (H-NQ) proceeded in two stages: a fast decomposition stage after heating, and a much slower decomposition stage later. It was indicated that all the models for N-NQ and H-NQ at the first stage followed the Avrami-Erofeev equation but with different values of n, while all the models at the second stage conformed to Parabola order. The decomposition rate of H-NQ was faster than N-NQ after heating, showing a better stability of N-NQ. At 373.15-413.15 K, the initial decomposition kinetics were calculated. The activation energy calculated by mode-fitting method was 146.33 kJ/mol and 182.71 kJ/mol for N-NQ and H-NQ, respectively, which was consistent with the results obtained through model-free method. The average activation free energy (Delta G(not equal)), enthalpy (Delta H-not equal) and entropy (Delta S-not equal) for N-NQ were 148.30 kJ/mol, 142.03 kJ/mol, and -15.81 J/(mol.K), respectively, while they were 139.61 kJ/mol, 184.42 kJ/mol, and 107.14 J/(mol.K) for H-NQ. The storage life of N-NQ and H-NQ at 298.15 K were extrapolated to 21.58 and 29.44 years, respectively.
Usachev, S., VLomakin, S. M.Koverzanova, E., VShilkina, N. G....
8页
查看更多>>摘要：This study was aimed to investigate the effect of reduced graphene oxide (rGO) on the pyrolysis of polylactide composites (PLA4042D/rGO) prepared in solution. GC-MS analysis of PLA4042D/rGO pyrolysis products showed that introduction of rGO into the composition with PLA leads to a significant change in the ratio of main degradation products. A sharp decrease of five-membered dioxolanones accompanied by a growth in the content of lactides and cyclic oligomeric lactides was observed in PLA4042D/rGO pyrolysis products as compared with pristine PLA. DSC studies of PLA4042D crystallization in the melt showed that the adsorption of PLA macromolecules on rGO surface can cause the decrease in their segmental mobility. Apparently, a decrease in the segmental mobility of PLA chains hinders the formation of dioxolanones via the intramolecular nonradical ester interchange reaction. At the same time, the role of intermolecular reactions with the formation of cyclic oligomers of lactides increases.
查看更多>>摘要：At present, the kinetic approaches of accelerating rate calorimetry (ARC) are restricted to model-fitting methods, and the n-order reaction model is mainly used to estimate the kinetic parameters. However, the model-fitting method has the problems related to model selection and falling into a local optimum. To address these issues, kinetic analysis methods are introduced into ARC data treatment, and the kinetic parameters of complex reactions are solved by a model-free and model-fitting fusion method. First, the Friedman method is used to calculate the activation energy E-alpha. Then, A(alpha) and the overall mathematical function f(alpha) are obtained through the compensation effect. It provides references for the selection of the reaction model and initial values of model fitting, and the kinetic parameters are estimated through two-step model fitting. The fitting in steps realizes the decoupling of E and A and reduces the data dimensions. These help to reduce the chance of falling into a local optimum and lower the experience requirements. Finally, numeric simulations and the experimental results showed the effectiveness of the method.
查看更多>>摘要：Thermal conductivity of kerosene-based nanofluids is experimentally studied in the paper. Aluminum (Al), alumina (Al2O3) and titanium dioxide (TiO2) nanoparticles were dispersed respectively in RP3 aviation kerosene, and thermal conductivity of those nanofluids was measured in a wide range of fluid temperature and particle mass fraction. The increase rate of thermal conductivity of kerosene-based nanofluids reached 60% at a temperature of 403 K. The thermal conductivity of nanofluids changes with different particles, particle size, particle concentration and temperature et al. The change rules are given in this paper in detail. Meanwhile, the experimental results of thermal conductivity are compared with the theoretical model proposed in our previous work originally for water-based nanofluids, and the comparison results are found to be good.
Penzik, M. V.Donskoy, I. G.Kozlov, A. N.Kozlova, M. A....
15页
查看更多>>摘要：The purpose of this article is to study experimentally the oxidation process of wood of different degrees of thermal conversion. We compared experimental data of thermogravimetric analysis in the oxidizing environment of raw wood, cellulose, lignin, and wood samples of different degrees of thermal conversion. Thermally treated wood samples were obtained by heating raw pine wood in an inert atmosphere to a given temperature (250, 300, 350, 400, 500 degrees C), followed by rapid quenching in water. All obtained samples were studied by the thermal analysis combined with mass spectrometry (TGA-MS) in inert and oxidizing environments; technical (moisture content, ash content, volatile yield, or W, A, V) and elemental analysis (C, H, O) data were obtained. We propose a new method for kinetic analysis of biomass decomposition: the change in the leading decomposition mechanisms is monitored by the change in the composition of the detected products. Differences between the thermochemical behavior of biomass, its individual components (cellulose and lignin), and their thermal degradation products are discussed.
Wongthonglueang, ThanaphonRousset, PatrickCommandre, Jean-MichelVan De Steene, Laurent...
8页
查看更多>>摘要：Self-heating and spontaneous combustion of torrefied biomass are direct hazards related to the production, storage and transport of torrefied biomass. In this study, we investigated the effect of combined air oxidation and water sorption on self-heating of torrefied agricultural residue biomass at 60, 120 and 180 ??C cooling temperatures by measuring weight change and heat flow using thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Our results showed that the effect of water adsorption predominated at 60 ??C. When the gas stream was changed from nitrogen to humid nitrogen, the weight of the torrefied biomass increased rapidly associated with heat generation. Conversely, at 180 ??C, the effect of air oxidation predominated and the torrefied biomass decreased rapidly when it was exposed to dry air associated with heat generation. The effect of water adsorption decreased with an increase in the cooling temperature whereas the effect of air oxidation increased with an increase in temperature. The higher torrefaction severity increases the self-heating propensity. The air oxidation and water adsorption may lead to the self-heating of torrefied biomass.
NSTL
Elsevier