Solid-state Reaction Models Research Articles

Kinetic analysis of thermal decomposition reactions: I. Thermal decomposition of potassium bromate

The kinetics of the thermal decomposition of potassium bromate were studied using isothermal and dynamic thermogravimetric techniques. Kinetic analysis of isothermal data in view of various solid-state reaction models showed that the reaction is best described by phase-boundary controlled and random nucleation models. Kinetic analysis of dynamic TG curves were discussed and a critical comparison was made of three methods: the direct differential method and two integral methods, one of Coats and Redfern and the other of Ozawa. The results showed that the Ozawa method gives better correlation and the results are in good agreement with those obtained under isothermal thermogravimetric conditions.

Solid-state polyamidation of dodecamethylenediammonium adipate

The solid-state polyamidation of nylon salts comprises an attractive research field. The low sublimation rate of dodecamethylenediamine ensures salt stability and accurate relationships between amine end-group analysis and extent of the reaction. This accuracy is further enhanced by studying the solid-state polyamidation of dodecamethylenediammonium adipate (DMA), a nylon salt with a low melting point. Reaction rate was found to be influenced drastically by temperature, but the temperature range to effect true solid-state reaction is actually limited. Even at temperatures significantly below the melting point of DMA, a transition of the process, from the solid to the melt state, was clearly observed. Kinetic data obtained were tested against well known solid-state and melt reaction models. Nevertheless, none of them can exclusively describe the polyamidation studied, possibly because the true reaction model should take into consideration the process leading to the solid-melt transition observed.

Rate‐Controlling Factors in the Carbothermic Preparation of UO2‐UC2‐C Microspheres

Rate‐controlling factors in the conversion of UO2+ C microspheres to UC2+ C were investigated using a fluidized‐bed furnace (13 cm in diam.). Examination by X‐ray diffraction, ion microprobe, and microstructural observation revealed that the conversion of UO2 to UC2 began at the surface of the microsphere and progressed toward the central unreacted core. Kinetic models for solid state reactions in spheres were evaluated by using quantitative mass spectrometric data on the rate of evolution of CO during conversion. This analysis revealed that the rate of conversion was controlled by reaction at the outer surface of the microsphere. Also, decreased partial pressures of CO accelerated the rate of reaction.

The distinguishability of selected kinetic models for isothermal solid-state reactions

Data generated from selected model expressions for solid-state kinetics have been analysed in terms of expressions of closely-related form to test distinguishability of the models on which the expressions are based. Random errors have then been introduced into these data and the data have been re-analyzed in terms of the original and closely-related expressions. As is to be expected, introduction of errors decreases distinguishability further and estimates have been made of the accuracy of measurement of the extent of reaction, α, required, the most suitable ranges of α to use, from plots of residuals, and the acceptable levels of various statistical parameters, for reliable distinction between alternative models.

Kinetics and Mechanism of the Reaction Between Zinc Oxide and Barium Carbonate

The kinetics of reaction between BaCO3 and ZnO were studied using thermogravimetric analysis to monitor the percent reaction versus time. Solid state reaction models based on (a) product growth controlled by diffusion through a continuous product layer, (b) product growth controlled by phase boundary reactions, and (c) the concept of an order of reaction, were invalid for the reaction studied. The kinetics of the reaction were described by the kt=–ln (1 –x)⅔ nuclei growth equation. The defect nature of the zinc oxide studied was altered by doping with Li2O and Cr2O3. The activation energy for the reaction of BaCO3 and pure ZnO was 54.6 kcal/mole. The changes in activation energy with the type and amount of ZnO doping cannot be accounted for by the quasi‐chemical theory of solids.