OP磁石に関する研究(第4報) : OP磁石を生成する固相反応
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概要
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OP magnet is industrially manufactured by nitric acid method. That is, the mixture of nitrate solutions of Fe and Co is prefired up to 850°C in air after evaporation and drying. The resulting powder is then pressed (compacted) to desired shape and fired above 1000°C in air of about 1mm Hg.<BR>The chief constituents of the prefired powder are CoFe<SUB>2</SUB>O<SUB>4</SUB> and a-Fe<SUB>2</SUB>O<SUB>3</SUB>, while the fired magnet consists of a solid solution CoFe<SUB>2</SUB>O<SUB>4</SUB>-Fe<SUB>2</SUB>O<SUB>4</SUB> of spinel structure, the composition being approximately CO<SUB>0.75</SUB>-Fe<SUB>2.25</SUB>O<SUB>4</SUB>. Hence, the main reaction during firing-reaction of magnet formation-was considered to be<BR>6 CoFe<SUB>2</SUB>O<SUB>4</SUB>+3 Fe<SUB>2</SUB>O<SUB>3</SUB>→8 Co<SUB>0.75</SUB>Fe<SUB>2.25</SUB>O<SUB>4</SUB>+1/2O<SUB>2</SUB>.<BR>Authors studied about the reaction by assuming that the reaction velocity is controlled mainly by the diffusion velocity of Fe and Co ions in the solid solution, and that evolution of oxygen has no great influence upon the reaction velocity, and found that the so-called Janders equation holds good in this case. The activation energy of the reaction was calculated to be 41Kcal/mol.
- 社団法人 粉体粉末冶金協会の論文