Thermal Decomposition of Triethylindium

Russian Journal of General Chemistry - Thermal decomposition of triethylindium has been studied under static conditions. The temperature dependence of the thermal decomposition rate is described by...     

Temperature dependence of relative modulus in filled polymer systems

The temperature dependence of relative modulus observed in filled thermoset, thermoplastic, and polyelectrolyte salt matrices is explained on the basis of induced stresses produced by the differences in the thermal expansion coefficients of the constituent materials. The analysis is based on the assumption that the modulus of the matrix in a filled polymer is less than that of the unfilled polymer. The temperature dependence of relative modulus is expressed as a function of the difference in thermal expansion coefficients, the volume fraction, the relative modulus in the unstressed state, and mechanical properties of the phases. Agreement is good between the analysis and experimental results for three systems: epoxy and glass, polyethylene and wollastonite, and a polyelectrolyte salt with mica and asbestos.     

The influence of oxygen pressure on the kinetics of the thermal decomposition of Co3O4

The kinetics of the thermal decomposition of Co₃O₄ has been examined in the 1123–1200 K temperature and 2.66–20.73 kPa oxygen pressure range. The kinetics of this process has been deseribed in terms of a mixed-control model of reaction. The values of activation energies of diffusion and chemical reaction as well as the observed activation energy have been given. The strong dependence of the decomposition rate on temperature and oxygen pressure has been explained.     

Thermal stability of tert-butyl peroxypivalate

The thermal stability of tert-butyl peroxypivalate (TBPP) has been investigated in relation to peroxide—diluent compositions in the range 100—10% by weight of peroxide. TBPP was selected because the simple decomposition pattern of the pure product facilitates an interpretation of the concentration dependence. Differential thermal analyses, isothermal and adiabatic storage tests have been used analysis of the decomposition. From the experimental results it is found that the total heat of decomposition is proportional to the peroxide concentration, the activation energy is independent of concentration, and the reaction order varies slightly with concentration. The type of diluent influences the reaction rate. The results are applicable in the 290—360 K temperature range. For the determination of decomposition characteristics, a modified first order equation which takes into account the fraction of diluent can bew used for TBPP—diluent compositions.     

Effect of Impurities on Thermal Decomposition Kinetics of Mineral Fertilizers Based on (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>HPO<Subscript>4</Subscript> in Self-Generated Atmosphere

The effect of impurities on the thermal decomposition kinetics of mineral fertilizers based on (NH₄)₂HPO₄ in self-generated atmosphere was studied by the methods of thermogravimetry and differential thermal analysis. Results are presented of isothermal measurements made in the temperature range 100–110°C. An analysis of the experimental data made it possible to suggest reaction models of the decomposition and to reveal a dependence of the activation energy on the degree of decomposition. A strong deviation of the temperature dependence of rate constants from the Arrhenius law was observed. Conclusions were made on the basis of the study about the influence exerted by impurities on the thermal decomposition of mineral fertilizers based on (NH₄)₂HPO₄ in the self-generated atmosphere and reasons for the deviation from the Arrhenius law.     

L'analyse thermique a vitesse de decomposition constante

A general method of thermal analysis is presented, whose aim is to reduce at will pressure and temperature gradients inside the sample submitted to thermolysis. The basic idea is to control the sample temperature so as to keep constant a parameter related to the decomposition rate. Attention is specially called on the case when the controlled parameter is pressure, which allows to monitor at the same time two parameters (pressure and decomposition rate). As an example, one apparatus is described, working in the pressure range between 20 and 10^?3 torr. This method of Constant Rate Thermal Analysis (CRTA) appears to be specially suited for thermal analysis under controlled vacuum, for the preparation of well defined porous samples, and for the study of decomposition mechanisms.     

Optical method for measuring thermal accommodation coefficients using a whispering-gallery microresonator

A novel optical method has been developed for the measurement of thermal accommodation coefficients in the temperature-jump regime. The temperature dependence of the resonant frequency of a fused-silica microresonator's whispering-gallery mode is used to measure the rate at which the microresonator comes into thermal equilibrium with the ambient gas. The thermal relaxation time is related to the thermal conductivity of the gas under some simplifying assumptions and measuring this time as a function of gas pressure determines the thermal accommodation coefficient. Using a low-power tunable diode laser of wavelength around 1570 nm to probe a microsphere's whispering-gallery mode through tapered-fiber coupling, we have measured the accommodation coefficients of air, helium, and nitrogen on fused silica at room temperature. In addition, by applying thin-film coatings to the microsphere's surface, we have demonstrated that accommodation coefficients can be measured for various gases on a wide range of modified surfaces using this method.     

The pressure dependence of the thermal decomposition of N2O

The pressure dependence of the thermal decomposition of nitrous oxide was investigated behind shock waves at temperatures between 1570 K and 3100 K and pressures from 0.3 atm to 450 atm. Nitrous oxide concentration profiles were measured using IR emission from the 4.5-μm ν₁ band of N₂O. The pressure dependence of the measured rate constant was described using simple Lindemann fits, resulting in the following low- and high-pressure limiting rate coefficients: These values were used to extrapolate current measurements of the rate coefficient to lower temperatures, where the agreement with past work is excellent. Therefore the limiting rate coefficients given above should be suitable for kinetic modeling over a temperature range of 800–2000 K and pressures up to 450 atm. © 1996 John Wiley & Sons, Inc.     

Dynamic and controlled rate thermal analysis of hydrozincite and smithsonite

The understanding of the thermal stability of zinc carbonates and the relative stability of hydrous carbonates including hydrozincite and hydromagnesite is extremely important to the sequestration process for the removal of atmospheric CO₂. The hydration-carbonation or hydration-and-carbonation reaction path in the ZnO-CO₂-H₂O system at ambient temperature and atmospheric CO₂ is of environmental significance from the standpoint of carbon balance and the removal of green house gases from the atmosphere. The dynamic thermal analysis of hydrozincite shows a 22.1% mass loss at 247°C. The controlled rate thermal analysis (CRTA) pattern of hydrozincite shows dehydration at 38°C, some dehydroxylation at 170°C and dehydroxylation and decarbonation in a long isothermal step at 190°C. The CRTA pattern of smithsonite shows a long isothermal decomposition with loss of CO₂ at 226°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of zinc carbonate minerals via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. The CRTA technology offers a mechanism for the study of the thermal decomposition and relative stability of minerals such as hydrozincite and smithsonite.     

Use of the quartz crystal microbalance for kinetic studies of thermal decomposition of solids

A quartz crystal microbalance has been proposed for studies on the temperature dependence of the linear rate of a reaction interface advance in topochemical reactions of the thermal decomposition of solids. A quartz crystal microbalance has been used in investigations of the CuSO₄ · 5H₂O dehydration. The data agree fairly well with those available in the literature. Advantages and disadvantages of the method proposed are discussed.     

A new method of synthesis of BiFeO<Subscript>3</Subscript> prepared by thermal decomposition of Bi[Fe(CN)<Subscript>6</Subscript>]·4H<Subscript>2</Subscript>O

In order to investigate the formation of the multiferroic BiFeO₃, the thermal decomposition of the inorganic complex Bismuth hexacyanoferrate (III) tetrahydrate, Bi[Fe(CN)₆]·4H₂O has been studied. The starting material and the decomposition products were characterized by IR spectroscopy, thermal analysis, laboratory powder X-ray diffraction, and microscopic electron scanning. The crystal structures of these compounds were refined by Rietveld analysis. BiFeO₃ were synthesized by the decomposition thermal method at temperature as low as 600 °C. There is a clear dependence of the type and amount of impurities that are present in the samples with the time and temperature of preparation.     

Thermal investigation of silicone rubber containing imide-siloxane copolymers

Dynamic mechanical thermal analysis and isothermal thermogravimetry yield useful information on the temperature dependence of the mechanical properties and thermal stability of silicone rubbers. In the thermal mechanical relaxation spectra, only one characteristic phenomenon may be observed. Isothermal thermogravimetry reveals that the thermal degradation is a first-order reaction. The experimental results provide a possibility for the calculation of overall (apparent) reaction rate constants characteristic of the thermal decomposition process, and for the calculation of half-time values.     

Thermoanalytical studies of silver and lead jarosites and their solid solutions

Dynamic and controlled rate thermal analysis has been used to characterise synthesised jarosites of formula [M(Fe)₃(SO₄)₂(OH)₆] where M is Pb, Ag or Pb–Ag mixtures. Thermal decomposition occurs in a series of steps. (a) dehydration, (b) well defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of water formation reveal the subtle nature of dehydration and dehydroxylation. CRTA offers a better resolution and a more detailed interpretation of the decomposition processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal separation of the dehydroxylation steps, since in these cases a higher energy (higher temperature) is needed to drive out gaseous decomposition products through a decreasing space at a constant, pre-set rate.     

Kinetic study of the decomposition of Prussian Blue electrocatalytic layer during cathodic reduction of hydrogen peroxide

Kinetic study on the decomposition of Prussian Blue electrocatalytic layer during electrochemical reduction of hydrogen peroxide has been studied in relation to biosensor application of this electrocatalyst. The decomposition has been shown to proceed as a nearly exponential decay process and the corresponding first-order rate coefficients were determined. It has been shown that the decomposition proceeds about 10 times faster in pH 7.3 buffer solution as compared to pH 5.5 buffer. A linear dependence of the decomposition rate on the concentration of hydrogen peroxide has been found.      

Theoretical study of the competitive decomposition and isomerization of 1-hexyl radical

The ground-state potential energy surface of the 1-hexyl system, including the main decomposition and isomerization processes, has been calculated with the MPW1K, BB1K, MPWB1K, MPW1B95, BMK, M05-2X and CBS-QB3 methods. On the basis of these data, thermal rate coefficients of different reaction channels and branching ratios were then calculated using the master equation formulation at 250–2,500 K. The results clearly point out that the 1,5 H atom transfer reaction of 1-hexyl radical with exothermicity proceeds through the lowest reaction barrier, whereas the decomposition processes are thermodynamically unfavorable with large endothermicity. The temperature effect is important on the relative importance of different reactions in the 1-hexyl system. In the low-temperature range of 250–900 K, isomerization reactions, especially 1,5 H atom transfer reaction of 1-hexyl radical, are dominating and responsible for over 82.17% of all the reactions, due to their smaller reaction barriers than those of the decomposition reactions. Furthermore, an equilibrium process involving the isomeric forms of the hexyl radicals appearing at relative low temperature was validated theoretically. However, isomerization and decomposition processes are kinetically competitive and simultaneously important under normal pyrolysis conditions.     

Interpretation of the vibrational relaxation of H2 in H2 within the semiclassical effective mass approach

The temperature dependence of the rate coefficients for vibrational relaxation of H2 in neat H2 is interpreted within the semiclassical effective mass approach. Across the temperature range of 80-3000 K, the experimental rate coefficients vary by five orders of magnitude and fall onto a strongly nonlinear Landau-Teller plot. This behavior is explained by the nonclassical nature of the energy release and by a substantial participation of rotation of the colliding partners in inducing the vibrational transition. A single fitting parameter, the optimal reduced mass, permits one to represent the temperature dependence of the rate coefficient within a factor of 2. This parameter is found to be close to that obtained from a simple model suggested by Sewell et al. [J. Chem. Phys. 99, 2567 (1993)].     

Thermal decomposition behaviors and dust explosion characteristics of nano-polystyrene

With the development of nano-powder technology, polymeric nano-materials are widely used in various industries, while not much research on their thermal decomposition and dust explosion characteristics has been conducted. The thermal behaviors and explosion characteristic parameters of the nano-polystyrene (nano-PS) with a typical particle size of 90 nm were studied by employing thermogravimetric analysis (TG), MIE-D 1.2 minimum ignition energy (MIE) test device, and 20-L spherical dust explosion test equipment. The results showed that the thermal decomposition of the nano-PS occurred in a two-step process which was different from the single process for conventional PS. Meanwhile, the reaction rate of the thermal decomposition for nano-PS increased with the heating rate. The TG and DTG curves shifted to the higher-temperature zone when the heating rate increased, and the initial temperature, final temperature, temperature at the maximum rate, and the maximum rate also increased. The sensitivity parameter of the minimum ignition energy of nano-PS varied as the dust concentration altered, and the most sensitive explosive concentration was about 200 g m⁻³. Also, nano-PS was proved to be quite sensitive to the electrostatic spark, as its calculated MIE value was as low as 11 mJ. For the severity parameters, the explosion pressure and its rising rate of nano-PS tended to increase at first and then decrease with the increase in dust concentrations. According to the risk classification standard, the explosion risk class of nano-PS was St2. The results were further extensively compared to other previous works. The results demonstrated both the higher explosion possibility and severity of nano-PS. This study could provide guidance for the safety management of nano-PS in its manufacture, storage, and handling process.

     

Effect of iron-containing catalysts on thermal decomposition of cured GAP-AP propellants

The effects of various burning rate catalysts on thermal decomposition of cured glycidyl azide polymer (GAP)-ammonium perchlorate (AP) propellants have been studied by means of thermal analysis and a modified vacuum stability test (MVST). Four types of iron-containing catalysts examined in this paper are catocene, ferrocenecarboxaldehyde (FCA), ferrocene, and ferric oxide. Results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) revealed that the catalysts play an important role in the decomposition of both AP and GAP. The peak decomposition temperature (T _m) of DTA curves and onset decomposition temperature (T _o) of TG patterns considerably shifted to a lower temperature as the concentration of catalysts increased in the propellants. The endothermic temperature of AP, however, is unaffected by the presence of burning rate catalysts in all cases. The activation energy of decomposition of the propellants in range of 80 to 120°C is determined, based on the MVST results.