Guaranteed reagent grade magnesium basic carbonate with 0, 2, 5 and 10 wt% of ZnO and extra pure grade magnesium basic carbonate and natural magnesite with 0, 2 and 5 wt% of ZnO were calcined at temperatures of 600°C to 1400°C for periods of 7.5 to 240 minutes. The MgO obtained was studied by means of X-ray diffraction and electron microscopy.
In the calcined products of E. P. magnesium basic carbonate the shape of original material was broken at temperatures higher than 800°C and converted clearly into the separated spherical particles of MgO, in contrast with the fact that pseudomorphs were observed over the whole ranges of calcination temperatures on the calcined products of G. R. magnesium basic carbonate and magnesite.
Evidences were also obtained from X-ray analysis that the solid solutions were formed from MgO and added ZnO, and the lattice constants of MgO increased continuously with the increase of the content of ZnO.
The relation between crystallite size (D) of MgO and calcination time (t) could be described by the equation D=Ktⁿ (K: a constant).
The values of n for G. R. magnesium basic carbonate and magnesite increased with the addition of ZnO, but in the case of E. P. magnesium basic carbonate, the variations of n was not almost observed.
The obtained values of n were as follows:
G. R. magnesium basic carbonate: 0.10-0.16
E. P. magnesium basic carbonate: 0.10-0.11
Natural magnesite: 0.22-0.34
The activation energies (Q) for crystallite growth of MgO showed two values in low and high temperature regions for each mixture.
The obtained Q values for low temperature region were 41 to 46kcal/mol and almost constant for all mixtures.
The Q values for high temperature region were decreased with the addition of ZnO and the obtained values were as follows:
G. R. magnesium basic carbonate: 126-59kcal/mol
E. P. magnesium basic carbonate: 180-149kcal/mol
Natural magnesite: 143-81kcal/mol