Surface Composition and Electrical Conductivity of La2CuO4 and CuO Composite on Exposure to ppm Level H2S.

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  • AONO Hiromichi
    Department of Materials Science and Engineering, Faculty of Engineering, Ehime University
  • SAKAMOTO Masatomi
    Department of Material and Biological Chemistry, Faculty of Science, Yamagata University
  • SADAOKA Yoshihiko
    Department of Materials Science and Engineering, Faculty of Engineering, Ehime University

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  • La<sub>2</sub>CuO<sub>4</sub>-CuO複合体の表面組成と伝導度に与えるH<sub>2</sub>S処理効果

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Abstract

A composite material containing La2CuO4 and CuO was directly synthesized by thermal decomposition of a heteronuclear CuLa (dhbaen) (NO3)⋅nH2O complex, where dhbaen is N, N′-bis (3-hydroxysalicylidene)-ethylenediamine. The mean particle size was of the order of 200nm for a sample decomposing at 800°C. The exposure to 7.8ppm H2S at 50°C for 6d (the exposure gas was alternately changed from air to 7.8ppm H2S at 6h intervals for 6d) resulted in the formation of copper sulfide and lanthanum sulfate on the surface. At 100°C, the surfaces were mostly covered with both sulfide and sulfate. Lanthanum sulfate and copper sulfide, without copper sulfate, were formed at temperatures below 200°C. Copper sulfate was detected when the sample was exposed at 250°C. For samples exposed at 100°C, the atomic ratio determined by X-ray photoelectron spectroscopy (XPS) for [S (sulfate)]/[La] was 1.6 on the surface and decreased to 0.01 with increasing depth of Ar sputtering on the surface. The ratio of [S (sulfide)]/[Cu] was 0.99 on the surface and decreased to about 0.45 upon Ar sputtering. However, [S (sulfate)]/[La] and [S (sulfide)]/[Cu] ratios on the surface were 0.03 and 0.39, respectively, for single-phase La2CuO4 prepared by the solid state reaction method after the exposure. It is concluded that the reactions of Cu and La in La2CuO4 with hydrogen sulfide are accelerated by the presence of well-dispersed CuO.

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