Eutectic Formation from Melt Mixtures of Hydrates of Nickel and Cobalt Salts

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  • Watanabe Yasuyuki
    Research Institute for Science and Engineering, Waseda University
  • Hirasawa Izumi
    Department of Applied Chemistry, Faculty of Science and Engineering, Waseda University

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  • ニッケル・コバルト水和塩混合融液からの共晶形成
  • ニッケル ・ コバルト スイワエン コンゴウユウエキ カラ ノ キョウショウ ケイセイ

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Abstract

<p>Based on the idea that eutectic formation is an useful technology for controlling the melting points of latent heat storage materials over a wide temperature range, precise experimental studies were carried out on the inevitability of eutectic composition of salt hydrate mixtures. Phase diagrams were developed from heating curves of two pseudo-binary systems, Ni(NO3)2·6H2O–CoCl2·6H2O and NiCl2·6H2O–Co(NO3)2·6H2O. The melting points of individual hydrates were 53.5, 53.0, 51.5 and 53.5°C, respectively. In the two binary systems, similar simple eutectic formations were recognized under the same conditions of 30°C and equimolar composition. The crystal compositions in the systems changed depending on the binary mixing ratio. At the same time, new crystal phases that were not attributed to either of original salt hexahydrates were also generated, and the contents of the new phases became maximum at the eutectic points. The two eutectics generated were found to have the same crystal composition as each other as analyzed by X-ray powder diffraction patterns. Consequently, it was concluded that the eutectics were formed through the mutually equivalent exchange of dissociated ions. Further, the inevitability of those compositions was determined as the mixing ratio at which the mutually equivalent exchange might be maintained for all dissociated ions.</p>

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