KINETIC-ANALYSIS OF THERMAL-DECOMPOSITION OF MAGNESITE - INFLUENCE OFGENERATED DEFECTS AND THEIR ANNEALING

The excess enthalpy of magnesite accumulated by vibration grinding at low specific grinding energy consumption is due predominantly to an in crease in specific surface area; at higher energy supply, it is caused by changes in the X-ray amorphous phase content, and when the supplie d energy exceeds ca 2000 kJ kg(-1) it is a result of the generation of other kinds of defects. The generated defects are relatively stable b elow 800 K and are the reason for a broad range of distribution of loc al molar Gibbs energies. Thus, at low temperatures only the 'active' p ortion of samples is able to decompose. Defects relax above ca 800 K, with rates comparable with the rate of decomposition itself. According ly, the efficiency of mechanical activation is impressive only below t his temperature.