Effects of dopants on the isothermal decomposition kinetics of potassium metaperiodate
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 α–t 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 α–t 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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Effect of semiconducting metal oxide additives on the kinetics of thermal decomposition of sodium oxalate under isothermal conditions
2012, Thermochimica ActaCitation Excerpt :Required quantity of the pre-compressed oxide was thoroughly mixed with sodium oxalate (particle size: 106–125 μm), in an agate mortar, to get 1 wt% mixture. Thermogravimetric measurements in static air were carried out on a custom-made thermobalance fabricated in this laboratory [15,29]. A major problem [30] of the isothermal experiment is that a sample requires some time to reach the experimental temperature.
Kinetic studies on the thermal decomposition of aluminium doped sodium oxalate under isothermal conditions
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Influence of trivalent ion dopants on the thermal decomposition kinetics of potassium bromate
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Effect of pre-treatments on isothermal decomposition kinetics of potassium metaperiodate
2010, Thermochimica Acta