So far, pure Mn
3O
4 as a raw material for Mn-Zn ferrites has been synthesized by a hydrothermal reaction of H
2O and Mn. But, this method was costly because it needs high temperatures above 120°C and high pressures above 3kg/cm
2. And so it was tried that the pure Mn
3O
4 might be synthesized at not more than 100°C and under an atmospheric pressure by addition of ammonium salts or amino-acids to water with Mn.
Firstly, in N
2 atmosphere, the formation rates of Mn(OH)
2 were measured at various temperatures when ammonium salts or amino-acids (0.05-0.5mol/l) were added into water with Mn. Secondly, the reactions were carried out under an oxygen or air atmosphere and the reaction rates and the reaction products (Mn
3O
4) were examined.
As the results, it has found these reaction rates were dependent on the hydrogen-ion concentration, the oxygen pressure, the variety and concentration of the additions. On this reaction, Mn was oxidized by H
+ and O
2, and the additions, ammonium salts or amino-acids, catalyzed this reaction. These additions complexed with Mn
2+ which was produced by the redox-reaction between water and Mn, and decreased the activity of Mn
2+. And also, the reaction finished for the almost same hours even when the filtrate is used again many times.
By the addition of ammonium salts or amino-acids, it has become easy to synthesize Mn
3O
4 from metal Mn at not more than 100°C, under an atmospheric pressure and within some hours. The Mn
3O
4 obtained by this reaction was of high pulity, so may be applied to the additions for ferrites.
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