High-pressure decompositions in cobalt and nickel silicates |
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Authors: | Eiji Ito |
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Institution: | Institute for Thermal Spring Research, Okayama University Tottori-ken 682-02 Japan |
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Abstract: | High-pressure stability relations in cobalt and nickel silicates have been studied over the pressure range 130–330 kbar employing a double-staged split-sphere-type high-pressure apparatus.γ-Co2SiO4 and γ-Ni2SiO4 decompose directly into their constituent oxide mixtures (rocksalt plus stishovite) 175 kbar and 280 kbar, respectively. The result that γ-Ni2SiO4 has a wider stability field in pressure than γ-Co2SiO4, is consistent with simple crystal-field theory.The experimental precision is high enough to show that the decomposition boundary of γ-Co2SiO4 has a positive slope (dP/dT > 0) and a preliminary determination of the boundary curve is P(kbar) = 0.065 T (°C) + 110.No positive evidence for the existence of high-pressure forms of CoSiO3 and NiSiO3 has been obtained in these quenching experiments, and they finally decompose into constituent oxide mixtures as in the cases of orthosilicates. |
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