Elsevier

Thermochimica Acta

Volume 359, Issue 2, 28 August 2000, Pages 161-168
Thermochimica Acta

Effects of dopants on the isothermal decomposition kinetics of potassium metaperiodate

https://doi.org/10.1016/S0040-6031(00)00526-8Get rights and content

Abstract

The isothermal decomposition of potassium metaperiodate (KIO4) has been studied as a function of concentration of the dopants chloride, sulphate and barium, by thermogravimetry (TG) in the temperature range 560–580 K. The decomposition data for both pure and doped KIO4 were found to be best described by the Prout–Tompkins (PT) equation. As the dopant concentration increases, the rate of decomposition remains unaffected with chloride, increases approximately linearly with sulphate and passes through a maximum with barium. However, doping did not change the activation energy of the reaction. The results favour an electron-transfer mechanism for the decomposition.

Introduction

Kinetics of solid-state reactions is greatly modified by pre-treatments such as doping, pre-compression, pre-heating, etc. A knowledge of such effects provides a deep insight not only into the topochemistry but also into the mechanism and control of these reactions. With this view, we have taken up a systematic study of the effects of pre-treatments on the thermal behaviour of several technologically important high energy solids such as halates and perhalates, and have reported some results [1], [2], [3], [4], [5].

Halates and perhalates occupy an important place in modern solid-state chemistry. One particularly important property of these compounds is their thermal decomposition, which is extremely sensitive to the presence of impurities, additives, etc. Periodates form an important class of compounds of the above type. Relatively little is known of their thermal stability, particularly in the presence of impurities, and more data of this kind are, therefore, desirable. In continuation of our investigations on the thermal behaviour of periodates of alkali metals [2], [3], in this paper, we report the effect of the anion dopants chloride and sulphate, and the cation dopant barium on the isothermal decomposition kinetics of potassium metaperiodate (KIO4) in the temperature range 560–580 K.

Section snippets

Experimental

Only AnalaR or “proanalysi” grade reagents were used. A saturated solution of KIO4 in distilled water (2.5 g/100 ml) was prepared at 340 K and allowed to attain equilibrium at room temperature. The clear solution was decanted into a crystallizing dish, placed in a hot air oven maintained at 325±2 K and allowed to undergo slow evaporation. The resulting crystals were removed, washed with acetone, dried and ground gently using a mortar and pestle to fix the particle size in the range 150–170 μm.

Results

The results of the decomposition of pure KIO4 at different temperatures are presented in Fig. 1(A) in the form of αt curves. The decomposition proceeds through three stages: (i) an initial rapid evolution of gas up to α≅0.006, followed by an induction period, (ii) an acceleratory period up to α=0.50, and (iii) the final decay stage. The initial gas evolution is so rapid that it was not possible to determine the kinetics and energetics of the process.

The αt data in the range α=0.05–0.95 (range

Decomposition of pure KIO4

The kinetics of thermal decomposition of KIO4 to KIO3 in vacuum was studied by Phillips and Taylor [14] by measuring the pressure of oxygen evolved as a function of time and they observed a four stage process. The initial two stages were very small amounting only to α=0.006. The third stage which was acceleratory in character, proceeded up to α=0.50 and was then followed by the final decay stage. They observed that the last two stages were best represented by the PT and the contracting cube

Acknowledgements

One of us (K. Muraleedharan) is thankful to University Grants Commission, New Delhi, India for the award of a fellowship.

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