Thermal decomposition of Mg(OH)2 and Ca(OH)2 particles produces highly porous calcines that react rapidly with acidic gaseous pollutants at moderate temperatures. Increasing- and constant-temperature gravimetric methods were employed to measure the rates of decomposition of hydroxide particles at temperatures 290-430-degrees-C. The measured data were tested empirically by fitting to the nth-order rate equation of Arrhenius type, and the values of the kinetic parameters were estimated. Differences are explored in the course of the decomposition of magnesium hydroxide and that of calcium hydroxide. The sintering rate of the nascent, hydroxide-derived oxides was measured in a nitrogen atmosphere at temperatures from 400 to 700-degrees-C. An empirical kinetic model has been proposed to correlate the experimental data on the specific surface area of solids. Comparison of the results indicates that particles of MgO exhibit a surface area which is half an order greater than that of CaO sintered under the same conditions.