MgO-B_2O_3系の相関係とMgOの粒成長におよぼすB_2O_3添加の効果

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An extremely pure MgO as one of the starting materials was prepared by decomposing magnesium nitrate solution of 99.9% magnesium. No boric compound in magnesia obtained was recognized by the emission spectral analysis. Many mixtures of magnesium nitrate solution and boric acid corresponding to the various mixing ratio of MgO and B_2O_3 were preheated at around 600℃ for 10hrs and then heat-treated at 910°, 1050°, 1300°, 1500°, 1600°, 1700° and 1750°±5℃ for 24 to 72hrs. The lattice constant of MgO and the crystallite size of MgO were measured with the internal standard of 99.999% Si and phases presented in the heat-treated specimens were identified with a X-ray diffractometer using the radiation of Cu K_α. Particle size of periclase was observed with a scanning electron microscope. The shrinkage, apparent porosity of magnesia body after heat-treatment and evaporation of B_2O_3 were also measured for evaluating the effects of the addition of B_2O_3 on the physical properties of sintered magnesia. The compound MgO・B_2O_3 was not detected, but the compounds 3 MgO・B_2O_3, 2 MgO・B_2O_3 and MgO・2 B_2O_3 were recognized. It was confirmed that there was no solid solubility of B_2O_3 in MgO up to the temperature of 1750℃, and the grain growth of periclase was extremely accelerated by the addition of B_2O_3 particularly at the heat treatments of 1500℃. The shrinkage of magnesia body was maximum with the addition of B_2O_3, 2 to 3%, and decreased rapidly with the associate of bubbling of B_2O_3 when the temperature was higher than 1500℃ in specimens containing more than 5wt% B_2O_3. Apparent porosity of magnesia body after heat-treatment at 1750℃ for 24hrs was minimum with the addition of 0.1wt% B_2O_3 to be about 8%. The porosity increased with the increase in the addition of B_2O_3 for the sintered bodies containing higher than 0.1wt% B_2O_3.
社団法人日本セラミックス協会の論文
1972-02-01

MgO-B_2O_3系の相関係とMgOの粒成長におよぼすB_2O_3添加の効果

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