DECOMPOSITION KINETICS OF ALKALINE-EARTH HYDROXIDES AND SURFACE-AREA OF THEIR CALCINES

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 gravimetri c methods were employed to measure the rates of decomposition of hydro xide particles at temperatures 290-430-degrees-C. The measured data we re tested empirically by fitting to the nth-order rate equation of Arr henius type, and the values of the kinetic parameters were estimated. Differences are explored in the course of the decomposition of magnesi um hydroxide and that of calcium hydroxide. The sintering rate of the nascent, hydroxide-derived oxides was measured in a nitrogen atmospher e at temperatures from 400 to 700-degrees-C. An empirical kinetic mode l has been proposed to correlate the experimental data on the specific surface area of solids. Comparison of the results indicates that part icles of MgO exhibit a surface area which is half an order greater tha n that of CaO sintered under the same conditions.