β″-アルミナの特性と微細構造に及ぼすSiO_2及びFe_2O_3の影響

概要

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In order to decrease the cost of β-alumina for solid electrolytes of AMTEC (alkali metal thermo-electric converter), it is desirable to use low purity starting materials. In this paper, we investigated the influence of impurities such as SiO_2 and Fe_2O_3,which are usually contained in low purity alumina, for several hundreds ppm, on properties and microstructure of β"-alumina. The content of β"-alumina phase and the density decreased with the addition of SiO_2,and the resistivity of β"-alumina increased even with the addition of amounts of SiO_2 as small as 500 ppm. Additional SiO_2 formed as a glassy phase at multiple grain junctions, but no secondary phase was observed at boundaries between two adjacent grains. Si segregated along the grain boundaries. It was suggested that the segregated Si suppressed the sintering and increased the resistivity. The addition of Fe_2O_3 did not affect the properties such as content of β"-alumina phase, density and resistance, but the addition of Fe_2O_3 in ≥ 0.5 mass% resulted in grain growth. Because Fe ions were suggested dissolved in spinel block of β"-alumina, it was considered that Fe_2O_3 did not influence the properties of β"-alumina.
社団法人日本セラミックス協会の論文
2002-02-01