Dissolution equilibrium of chromium oxide in a soda lime silicate melt exposed to oxidizing and reducing atmospheres

• Experimental procedure for the study of chromium oxide solubility in silicate melts.
• Determination of the time required to reach the dissolution equilibrium.
• Study of solubility/speciation mechanism depending on the oxygen fugacity.
• Determination of compromise time giving access to solubility value.
• Discussion about the mechanism of oxygen diffusion through the melt.

The dissolution equilibrium of chromium oxide (Cr2O3) in a soda lime silicate melt (Na2O–CaO–5SiO2) at 1300 °C was studied in two extreme atmospheres. The samples were subjected to oxidizing (fO2 = air) and reducing (fO2 = Fe/FeO buffer) atmospheres. The equilibrium was expected to be achieved when there was no significant difference of Cr solubility between rim and core of the samples. Under oxidizing condition, dissolution equilibrium would never been obtained since the CrVI and Na tend to volatilize at high temperature. Therefore, a compromising equilibrium time was suggested by taking into account these parameters. The dissolution equilibria for the samples which were subjected to reducing condition were expected to be achieved at 4 h of heat treatment. In both cases, the results are discussed and dissolution mechanisms are proposed regarding the oxygen diffusion through the melt. The oxygen diffusion coefficient (D) was calculated for the samples which were subjected to the reducing atmosphere by taking into account the thickness of grain-free zone existing at the interface. Molecular oxygen probably diffuses within the melt through an interaction with the network oxygen.