Composite powders combining boron with BiF3 and Bi in different amounts were prepared by high energy milling. Thermal analysis in an argon-oxygen mixture showed significant oxidation starting about ...200 K lower than for pure boron. Selective oxidation of metallic Bi at low temperatures was observed. Composites containing either Bi or BiF3 ignited more readily than pure boron when heated by a CO2 laser beam. The composites containing BiF3 ignited more readily than boron when in contact with a hot wire. Burn times of particles aerosolized in air and ignited using the CO2 laser were measured as durations of the recorded emission pulses produced by burning particles. Statistical distributions of the measured burn times were correlated with the respective powder's particle size distributions. Compared to elemental boron, burn times of all prepared composites were shorter, including those containing only 10 wt.% of BiF3 or ca. 8 wt.% of Bi, and for most composites combustion temperatures were higher.
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•PEG-functionalized B particle was synthesized for enhancing combustion performance.•Appropriate amount of PEG could improve B ignition and combustion.•The agglomeration of B ...particles could be alleviated with PEG coating.•Mechanism of PEG promoting combustion and lessening aggregation of B was revealed.
Boron (B) has a good practical application prospect in energetic materials due to its high volumetric and gravimetric heating values. However, the challenge of incomplete combustion inhibited its further application because of the existence of surface boron oxides. Herein, polyethylene glycol (PEG), a kind of oxygen-containing organic matter with an average molecular weight of 2000, was used to modify the B particles at a micron level to improve the combustion performance. The effect of PEG contents on the thermal behavior, heat of combustion, ignition and combustion performance, as well as the combustion intensity of boron powder, was studied. The results showed that the appropriate amount of PEG modification could reduce the ignition temperature of boron powder, increase the degree of oxidation, improve the combustion intensity and heat release. Additionally, the agglomeration behavior of B particles could be alleviated but the improvement diminished with the increase of PEG contents. These results revealed that PEG modification was an efficient strategy to facilitate boron ignition and combustion.
The Kissinger method is an overwhelmingly popular way of estimating the activation energy of thermally stimulated processes studied by differential scanning calorimetry (DSC), differential thermal ...analysis (DTA), and derivative thermogravimetry (DTG). The simplicity of its use is offset considerably by the number of problems that result from underlying assumptions. The assumption of a first-order reaction introduces a certain evaluation error that may become very large when applying temperature programs other than linear heating. The assumption of heating is embedded in the final equation that makes the method inapplicable to any data obtained on cooling. The method yields a single activation energy in agreement with the assumption of single-step kinetics that creates a problem with the majority of applications. This is illustrated by applying the Kissinger method to some chemical reactions, crystallization, glass transition, and melting. In the cases when the isoconversional activation energy varies significantly, the Kissinger plots tend to be almost perfectly linear that means the method fails to detect the inherent complexity of the processes. It is stressed that the Kissinger method is never the best choice when one is looking for insights into the processes kinetics. Comparably simple isoconversional methods offer an insightful alternative.
This paper critically analyzes the traditional method of kinetic determination of activation energy by sectioning the recorded differential thermal analysis peak area. This procedure is incorrect ...because it misses the impact of thermal inertia, which changes the shape of the peak's base line from straight to s‐shape. This effect has been known since the Newton cooling law, but the resulting errors persist to be interwoven into all the kinetic methods based on nonisothermal thermoanalytical measurements. Relating to calorimetry, it is necessary here because heat inertia has become a standard part of heat determination via using the Tian historical equation. The role and impact of heat inertia is discussed and analyzed in detail.
► Kinetics concepts are introduced and advices on collecting data are given. ► Methods based on multiple temperature programs are recommended. ► Evaluation of log
A and
f(
α) or
g(
α) for ...isoconversional methods is described. ► Principles of securing reliability of model-fitting computations are offered. ► Problems of kinetic predictions and approaches to solving them are discussed.
The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations offer guidance for reliable evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) from the data obtained by means of thermal analysis methods such as thermogravimetry (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). The recommendations cover the most common kinetic methods, model-free (isoconversional) as well as model-fitting. The focus is on the problems faced by various kinetic methods and on the ways how these problems can be resolved. Recommendations on making reliable kinetic predictions are also provided. The objective of these recommendations is to help a non-expert with efficiently performing analysis and interpreting its results.
•Conjugate thermal analysis and optimization is carried using several coolants.•The numerical method is parallelized using OpenMP for faster results.•Single and multi-objective optimization of ...thermal management characteristics is done.•Cuckoo search optimization and artificial bee colony algorithm is used.•Nanofluids and thermal oils have emerged as the best coolants for optimized thermal characteristics.
Thermal management of heat-generating battery packs involve many operating parameters affecting its performance, efficiency, and maintenance. Heat generation (Qgen), conductivity ratio (Cr), Reynolds number (Re), spacing between the packs (Ws), and coolant Prandtl number (Pr) are the parameters selected as working parameters for conjugate thermal analysis and optimization. The thermal analysis of battery packs is carried out numerically using the finite volume method. Single and multi-objective optimization of thermal management characteristics, namely maximum temperature (Tb, max), average Nusselt number (Nuavg), and coefficient of friction (Fcavg) using Cuckoo search (CS) and artificial bee colony (ABC) algorithm is attempted. For faster numerical analysis, the developed code is parallelized using OpenMP paradigm. 25 coolants having Pr in the range 0.02 to 511.5 belonging to five categories i.e. gases, oils, thermal oils, nanofluids, and liquid metals, are adopted for optimization. Nuavg and Fcavg are not affected by Cr and Qgen, while Tb, max changes significantly. Ws, Pr, and Re impact these characters differently, demanding the need for optimization. Nanofluids and thermal oils have emerged as the best coolants for optimized thermal characteristics at higher heat generations. CS algorithm provided high fitness of objective functions in single-objective optimization, whereas the ABC algorithm converged with high fitness during multi-objective optimization.
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► Higher extractives content in wood promote ignitability at lower temperatures. ► Wood cellulose crystallinity influences on wood thermal stability. ► Cellulose crystallite size ...affects the thermal degradation temperature of wood.
The influence of wood components and cellulose crystallinity on the thermal degradation behavior of different wood species has been investigated using thermogravimetry, chemical analysis and X-ray diffraction. Four wood samples, Pinus elliottii (PIE), Eucalyptus grandis (EUG), Mezilaurus itauba (ITA) and Dipteryx odorata (DIP) were used in this study. The results showed that higher extractives contents associated with lower crystallinity and lower cellulose crystallite size can accelerate the degradation process and reduce the wood thermal stability. On the other hand, the thermal decomposition of wood shifted to higher temperatures with increasing wood cellulose crystallinity and crystallite size. These results indicated that the cellulose crystallite size affects the thermal degradation temperature of wood species.
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