Prepartation of Fine Powders of MgO by Means of Freeze-Drying Processing

Abstract

Fine powders of MgO were produced from aqueous solutions of magnesium sulfate by means of "Freeze-Drying Processing" (F.D.P.). In order to determine the thermal decomposition temperature of the sulfates obtained by F.D.P. and the amount of water involved in the F.D.P. powders, and to identify the structure of the finally formed oxides, thermal gravimetry, differencial thermal analysis and X-ray diffraction methods were carried out. The observation of shapes and particle sizes of sulfate and oxide powders was also made by transmission electron microscopy. Mössbauer spectroscopy was applied to investigate the behaviour of water molecules (dehydration) in the process of freeze-drying of the sulfate solutions including ferrous (Fe₂₊) ions. The particle shape was thin plate like and its breadth of 0.1-0.2 μ, and the thickness was decreased with decreasing concentration of the initial solution. As a result, the followings were confirmed: (1) The solution including ferrous ions is not so easily dehydrated as that without ferrous ions. (2) Fine powders of MgFe₂O₄ can be produced as a result of the oxidation of ferrous ions in the process of freeze-drying.