Crystal Growth of Magnesium Oxide Prepared by the Thermal Decomposition of Magnesium Hydroxide

Abstract The particle size of magnesium oxide crystals prepared by the thermal decompositions of pure precipitated magnesium hydroxide and native brucite at various temperatures between 500 and 900°C has been measured by the X-ray line broadening method, and the effect of the calcination temperature and its duration on the crystal size of magnesium oxide has been examined. It has been found that the particle size of magnesium oxide crystals increasese with the increase in the calcination temperature and that the rate of crystal growth obeys a different law between the earlier stage of the calcination process at a definite temperature and the later stage. It has also been found that the crystal growth of magnesium oxide proceeds proportional to tn, (t: time), where n is 1/6 for the later stage of the calcination of magnesium oxide from precipitated magnesium hydroxide at temperatures ranging from 700 to 900°C and 1/4 for the same calcination of that from brucite. The values of the activation energy calculated by Arrhenius plot are 17 and 32 kcal./mol. for magnesium oxide obtained from precipitated hydroxide and from brucite respectively.