Generally, Pb is volatile above 900oC. therefore, deviation from its stiochiometric amount is quite obvious while sintering or calcining at high temperature. How the MgO is able to sealed the alumina crucible. I mean I tried the same method to seal the crucible but how do i confirm weather my sealing is perfect or not?

what should be the specification of MgO powders i.e, size or mess to be chosen? Can anybody tell me the detail procedure? inside the sealed chamber should we put only small quantity of volatile material like PbO or as prepared powder of PbTiO3?