Search Results

You are looking at 1 - 10 of 119 items

  • Author: K. Jacob x
Clear All Modify Search

This book combines practical advice with historical underpinnings of current educational practice and should be required reading for those who work closely with college students.

Abstract

Phase relations in the pseudotemary system CaO-CoO-SiO2 have been established at 1323 K. Three quaternary oxides were found to be stable: CaCoSi2O6 with clinopyroxene (Cpx), Ca2CoSi2O7 with melilite (Mel), and CaCoSiO4 with olivine (Ol) structures. The Gibbs energies of formation of the quaternary oxides from their component binary oxides were measured using solid-state galvanic cells incorporating yttria-stabilized zirconia as the solid electrolyte in the temperature range of 1000-1324 K. The results can be sum­marized as follows:

CoO (rs) + CaO (rs) + 2SiO2 (Qtz) → CaCoSi2O6 (Cpx), ΔG0 f = - 117920 + 11.26T (± 150) J/mol

CoO (rs) + 2CaO (rs) + 2SiO2 (Qtz) → Ca2CoSi2O7 (Mel), ΔG0 f = -192690 + 2.38T (±130) J/mol

CoO (rs) + CaO (rs) + SiO2 (Qtz) → CaCoSiO4 (Ol), ΔG0 f = -100325 + 2.55T (±100) J/mol

where rs = rock salt (NaCl) structure and Qtz = quartz. The uncertainty limits correspond to twice the standard error estimate.

The experimentally observed miscibility gaps along the joins CaO-CoO and CaCoSiO4- CO2SiO4 were used to calculate the excess free energies of mixing for the solid solutions Caχ-CO1-χ-O and (Caγ-Co1-γ)CoSiO4: ΔGE = X(1 - X)[31975X + 26736(1 - X)] J/mol and ΔGE = 23100 (±250) Y(1- Y) J/mol. A T-X phase diagram for the binary CaO-CoO was computed from the thermodynamic information; the diagram agrees with information available in the literature. The computed miscibility gap along the CaCoSiO4-Co2SiO4 join is associated with a critical temperature of 1389 (± 15) K. Stability fields for the various solid solutions and the quaternary compounds are depicted on chemical-potential dia­grams for SiO2, CaO, and CoO at 1323 K.