NI_<0.7>Fe_<2.3>O_4フェライトの酸化反応

概要

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Oxidizing reaction of Ni0.7Fe2.3O4 ferrite in a gaseous flow was studied by measuring cation valence, saturation magnetizaton and crystal lattice constant of the samples heattreated at various temperatures between 530° and 1250°C in air, in pure nitrogen, and in nitrogen containing 5 or 0.5vol% oxygen. It was found that oxidation makes the amount of Fe2+, saturation magnetization and crystal lattice constant decrease, and that there are two kinds of reactions for oxidation of the ferrite. One of them is an oxidation in which α-Fe2O3 is separated as the second phase by the amount nearly corresponding to the excess oxygen given at the heat-treatment of the sample. The other is an oxidation in which the second phase is unseparated. By the latter oxidizing reaction the spinel structure of the ferrite becomes to contain cation vacancies on its B-sites (octahedral sites). To calculate the crystal lattice constant of the spinel containing cation vacancies, application of “the mean size of cation vacancies” was suggested.The two reactions proceed as follows:Ni0.72+Fe0.32+Fe23+O4+δ/2O2→3δFe2O3+1/aNi0.7a2+Fe(0.3-2δ)a2+Fe(2-4δ)a3+O4(Oxidation in which the second phase is separated)→1/bNi0.7b2+Fe(0.3-2δ)b2+Fe(2+2δ)b3+CV(3/4)δbO4(Oxidation in which the second phase is unseparated)where, a=1/(1-2δ), b=4/(4+δ), and CV is the cation vacancy.
社団法人日本セラミックス協会の論文
1974-09-01