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Stability of CaNiSi 2 O 6 (“Niopside”) and Activity–Composition Relations of CaMgSi 2 O 6 – CaNiSi 2 O 6 Solid Solutions at 1350°C
Author(s) -
Pretorius Eugene B.,
Muan Arnulf
Publication year - 1992
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1992.tb04210.x
Subject(s) - diopside , enstatite , non blocking i/o , solid solution , wollastonite , forsterite , olivine , nickel , materials science , analytical chemistry (journal) , phase (matter) , mineralogy , chemistry , metallurgy , physics , chondrite , meteorite , raw material , biochemistry , organic chemistry , astronomy , catalysis , chromatography
A complete solid‐solution series exists between diopside (CaMgSi 2 O 6 ) and its nickel analogue, “niopside”(CaNiSi 2 O 6 ). Activity–composition relations within this solid solution, and the stability of the end member CaNiSi 2 O 6 , have been determined by equilibrating CaNiSi 2 O 6 with SiO 2 , CaSiO 3 , and metallic Ni in atmospheres of known oxygen pressures. Within limits of accuracy of the experiments, the solution is ideal at 1350°C. From the experimental data obtained in the present investigation, the standard free energy (Δ G °) of formation of CaNiSi 2 O 6 according to the equation CaO + NiO + 2SiO 2 = CaNiSi 2 O 6 is calculated to be Δ G °=−165862 + 42.40 T J. Experiments in the system CaO–NiO–SiO 2 have shown that the nickel analogue of the phase pseudo‐enstatite (MgSiO 3 ) is unstable with respect to SiO 2 and nickel olivine (Ni 2 SiO 4 ), and the nickel analogues of the phases akermanite (Ca 2 MgSi 2 O 7 ) and monticellite (CaMgSiO 4 ) are unstable relative to the phase assemblage pseudo‐wollastonite (CaSiO 3 ) plus NiO. In the system CaO–MgO–NiO–SiO 2 , however, substitution of Ni for Mg in these phases was observed. The percentage substitution of Ni for Mg in the phases is given in parentheses: diopside (100%), olivine (100%), enstatite (18%), akermanite (20%), and monticellite (57%).