Kinetics and Mechanism of Thermal Decomposition of 1-R-Substituted bis(1,1-Dinitromethyl-3-Nitro- 1,2,4-Triazole-5-yl)

Thermal decomposition kinetics of 1-substituted bis(1,1-dinitromethyl-3-Nitro-1,2,4-triazole- 5-yl) in solution of 1,3-dinitrobenzene is studied with manometric method under isothermal conditions. The limiting stage of thermal decomposition is homolytic break of C-NO2 bond in gem-dinitromethyl group; activation parameters of this stage are calculated. The reactivity of investigated compounds is analyzed. Correlation dependences between logarithm of rate constant, activation energy and steric constant of substituent R are obtained

Effect of Nb2O5 Addition to the Electrical Properties of Fe2TiO5 Ceramics-Based NTC Thermistor

The aims of this research is to identify the effect of Nb2O5addition on the electrical properties of Fe2TiO5ceramics-based NTC thermistor.The concentration of Fe2O3and TiO2was proportional to Fe2TiO5, whereas the concentration value of Nb2O5were 0, 0.5 and 1.0 mole %, respectively. Within two hours, the mixed powder was pressed at 4 ton/cm2to form pellets and sintered at 1300 °C in air. It can perceived from the XRD data that the sintered ceramics had single phase of Fe2TiO5, pseudobrookite. From SEM data, it is found that addition of Nb2O5decreases the grain size. The addition of Nb2O5increases thermistor constant, activation energy and electrical resistance of Fe2TiO5ceramics. The values of thermistor constant of Nb2O5added-Fe2TiO5ceramics were relatively large, indicated that the ceramics were aplicable as the NTC thermistor.

Effects of Irradiation on the Electrical Properties of Alpha-Quartz Crystals

A study is made of irradiation effects on α-quartz crystals using the techniques of electrical conductivity and dielectric loss measurements. The initial radiation-induced conductivity (RIC) induced by X-ray irradiation over the temperature range from 94 to 250 K is found to have a nearly constant activation energy of 0.29 ± 0.02 eV. Since a large RIC still results from irradiation at temperatures too low for alkalis to be liberated, it is proposed that the RIC is due to holes (as small polarons) rather than to alkalis. The dielectric loss measurements in Na-swept quartz are used to follow the changes in the relaxation peaks due to the Al-Na defect as a function of radiation dose and annealing. At the same time a low-temperature “irradiation peak” is studied. Restoration of the main Al-Na peak during annealing occurs in two stages: one near 500 K and the other above 600 K. From the observed behavior of the irradiation peak in various crystals, it is concluded that this peak is probably due to alkali centers. Finally, a defect model interpreting the two annealing stages is presented.

An optical study of pre-ignition heat release

The distributions of temperature and velocity are measured by optical methods in an ethylene–air mixture flowing against a uniformly heated surface, in order to determine the profile of heat release rate before ignition. The objective is to deduce the variation of heat release rate with temperature (in a manner analogous to the thermal analysis of flame structure but in absence of the large diffusive flux of active species associated with flames) so as to compare the rate laws with those applying in flames and to investigate their use for predicting ignition in other flow systems. Various practical igniter systems are investigated using cine-interferometry and particle tracking. The results manifest a constant activation energy of 8.8 kcal mol -1 (37 kJ mol -1 ) and differ entirely from the heat release rate laws in equivalent premixed flat flames. The back-diffusion of radicals in the latter gives rise to much higher rates of heat release at low temperatures and no constant 'activation energy' based on concentrations of the primary reactants. The possibility of using such results to predict ignition, on the criterion that beyond this condition temperature would rise with time, without a steady state solution, is discussed. For unidimensional systems a simple analytical solution is proposed in an Appendix by Dr. J. Adler. This yield interesting and plausible predictions of ignition temperature as a function of flow velocity and initial temperature using present results. Computer solutions would be required for more complex system.

Annealing Kinetics of Neutron?Irradiated Aluminium and Copper

Activation energies for the annealing of copper and aluminium following reactor bombardment near 4 OK have been measured in the range from 10 to 40 OK. Both the change in slope method and the isothermal technique method were utilized with the assumption that a constant activation energy existed. Computations of the number of jumps involved from the measured activation energy result in an impossibly small number. It is obvious that the method for determination of the activation energies is not applicable, probably because of the non-uniqueness of the activation energy.

The Degradation of Elastomers. 2. Oxidative Degradation of Natural Rubber Vulcanizates at Different Elongations and Temperatures. II

The results of measurements of stress relaxation in natural rubber vulcanizates are reported. In the earlier work, the conditions were denned under which the drop in tension of a vulcanizate—after a pre-relaxation in pure nitrogen—follows a zero order law when tested in oxygen. The temperature dependence of the rate of relative tension relaxation was determined for 8 different vulcanizates. With a constant activation energy of about 29 kcal/mole, the vulcanizates differed in their relative relaxation rates at most by two powers of ten. Several general observations on the course of tension relaxation under different conditions were made on the grounds of experimental evidence. Good qualitative agreement was found with relations reported by Berry and Watson.

The kinetics of the thermal decomposition of branched-chain paraffin hydrocarbons - I. iso -Butane, iso -pentane and neo -pentane

The branched hydrocarbons iso -butane, iso -pentane and neo -pentane decompose partly by radical chain reactions suppressible by nitric oxide, and partly by molecular reactions. The latter are of the usual unimolecular type with constant activation energy which is interesting in view of the marked contrast with the reactions of the corresponding normal paraffins. The alternative chemical modes of decomposition of iso -butane occur in propor­tions independent of the pressure from 5 to 400 mm. With neo -pentane a single mode pre­dominates at all pressures.

The kinetics of the thermal decomposition of branched-chain paraffin hydrocarbons - II. The isomeric hexanes

In the study of the thermal decomposition of paraffins the contrast of iso -butane with n -butane and of the branched pentanes with normal pentane has led to the investigation of the isomeric hexanes. The nitric oxide-inhibited reaction of neo -hexane possesses a constant, activation energy at different initial pressures and shows a single transition from second to first order with increasing pressure. The reactions of 2:3-dimethyl-butane, 2-methyl-pentane and 3-methyl-pentane show a double-order transition and a rise in activation energy at lower initial pressures, as previously found for the higher normal paraffins.