The effect of pre-compression, pre-heating and particle size on the thermal decomposition kinetics of potassium metaperiodate (KIO4) to potassium iodate (KIO3) has been investigated by thermogravimetric analysis under isothermal conditions. Although the effect of pre-compression was negligible up to an applied pressure of 5 x 10(3) kg cm(-2), the rate increased drastically on a further increase in pressure. Results of pre-heating indicate that gross imperfections are not as easily annealed as point defects. Studies on the effect of particle size emphasize the need for fixing the particle size to enable a meaningful interpretation of the effects of pre-treatment on solid-state reactions. The rate law (Prout-Tompkins model) as well as the mechanism (electron-transfer) for the decomposition of KIO4 remained unaffected by these pretreatments. The alpha-t data of uncompressed and compressed samples of pure KIO4 were also subjected to isoconversional studies for the determination of activation energy values. (C) 2010 Elsevier B.V. All rights reserved.