内田 寛

Magnesium silicon nitride (MgSiN2) powder was prepared by carbothermally reducing a magnesium metasilicate whose chemical composition corresponded to MgO . SiO2 or MgSiO3. About 0.2 g of the powder mixture of magnesium metasilicate and carbon (C) with the molar ratio of C to MgO . SiO2 equal to 6.0 was heated at 1250 degrees C for 7 h in nitrogen atmosphere. The crystalline phase of the carbothermally reduced powder was only MgSiN2. The residual carbon could be removed by heating the powder at 600 degrees C for 1 h in air. The yield of MgSiN2 powder was similar to 70%. The resulting powder contained 3.22 mol% oxygen. The primary particle sizes were ranging from 0.1 to 0.5 mu m.

Magnesium silicon nitride (MgSiN_2) was synthesized by the nitridation of powders in the magnesium (Mg) -silicon (Si) system. Although an Mg and Si powder with an Mg/Si ratio of 1.0 ( = stoichiometric ratio of MgSiN_2) was heated up to 1400℃ in nitrogen (N_2) , a single phase of MgSiN_2 could not be obtained, due to evaporation of Mg during heating. On the basis of the information that Mg_2Si formed as an intermediate phase during the synthesis of MgSiN_2, an Mg_2Si powder was heated at a temperature between 600 and 1600℃ for 1h in N_2. Although MgSiN_2 and other phases such as Si and amorphous Mg_3N_2 were present in the temperature range of 900℃ to 1300℃, the powder heated at 1400℃ consisted of only MgSiN_2 phase. The chemical composition of the powder heated at 1400℃ for 1h was almost stoichiometric; the content of the oxygen was as low as 0.76 mol%. The powder consisted of agglomerates with sizes of 〜5μm; these agglomerates were furthermore composed of primary particles with an average size of 0.54 μm. The oxidation resistant temperature of MgSiN_2 was estimated to be 〜830℃. The MgSiN_2 powder had good resistivity to hydration.