Preparation of Crystals of Alkaline Earth Oxides and Related Compounds

摘要

Processes developed during the period of the project for the purification of BaO, SrO, and CaO are described. These involve, with some variations, dissolution, precipitation of heavy metals and transition metals with (NH4)2S, filtration upon a millipore filter, recrystallization of the alkaline earth nitrates from HNO3 solution, precipitation of the carbonates with CO2 and thermal decomposition to the oxides. Analysis by atomic absorption spectrometry and nuclear activation analysis demonstrates that, except for the presence of other alkaline earths, the purity of the starting material for crystal growth is markedly improved by this treatment. Apparatus for crystal growth from the molten oxides, by the Czochralski method, and from oxide powders by the Verneuil method using a plasma torch, has been constructed. By means of a double-resonance method in which the magnitude of the magnetic circular dichroism is changed by simultaneous ESR excitation, the 4.3 eV optical absorption band in MgO has been definitely shown to be due to Fe(3+). (Author)