Interdiffusivities matrix of CaO-AI2O3-SiO2 melt at 1723 k to 1823 k

Ternary oxide mixtures of lime, alumina, and silica were premelted and quenched to produce glassy cylinders. A diffusion couple was selected from the mixtures of six different compositions in such a way that the average composition could be 40 wt pct CaO-20 wt pct AI₂O₃ = 40 wt pct SiO₂. Penetration curves of the components were measured with a X-ray microprobe analyzer. The interdiffusivities matrix defined with the Matano interface has been obtained from 52 successful diffusion runs at 1723 K to 1823 K as follows; $$ \begin{gathered} \tilde D_{10 - 10}^{30} = 8.9 \times 10^{ - 11} \exp \left( { - \frac{{253,700}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \tilde D_{10 - 20}^{30} = - 2.5 \times 10^{ - 11} \exp \left( { - \frac{{194,300}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \tilde D_{20 - 10}^{30} = - 4.0 \times 10^{ - 11} \exp \left( { - \frac{{177,600}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \tilde D_{20 - 20}^{30} = 6.12 \times 10^{ - 11} \exp \left( { - \frac{{318,400}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \end{gathered} $$ where symbols, 10, 20, and 30 mean CaO, A1₂O₃, and SiO₂, respectively, and the activation energies are in Joules per mole. The diffusion composition paths obtained are discussed in relation to Cooper’s parallelogram. The composition dependency of the above interdiffusivities is estimated from the quasibinary interdiffusivities in all composition ranges of the present oxide system in liquid state.     

Thermodynamic stability of kΒ-alumina

The activity of K₂O in a mixture of α-alumina and KΒ-alumina has been determined using the solid state galvanic cell: ' Ta, Bi-5 mol pct K // α-alumina + KΒ-alumina // In + In₂O₃, Ta in the temperature range 600 to 1000 K. The cell is written such that the right hand electrode is positive. The solid electrolyte consisted of a dispersion of a-alumina (~15 vol pct) in a matrix of KΒ-alumina. The emf of the cell was found to be reversible and to vary linearly with tem-perature. From the emf and auxiliary data on In₂O₃ and K₂O from the literature, the activity of K₂O in the two-phase mixture is obtained as log a_{K 2}O = 2.368 -20,850/T(K) (±0.015) The standard free energy of formation of KΒ-alumina from component oxides is given by K₂O (s) + 9.5 α-Al₂O₃ (s) → K₂O.9.5A1₂O₃ (s) δG‡ = -398,920 + 45.01 T(K) (±1000) J mol^-1