Kinetic and equilibrium factors affecting saturation of chromium oxide in soda-silicate melts

Factors controlling the rate at which chromium oxide reaches saturation in Na2O–xSiO2 liquids have been studied as a function of melt composition and oxygen fugacity. Under an oxidizing atmosphere, liquid Na2CrO4 or Cr2O3 crystals can be in equilibrium with soda-silicate melts, depending on the concentration of sodium in the studied system. Under reducing conditions, NaCrSi2O6 is stabilized in silica-rich melts when T is lower than 1160 °C, while Cr2O3 is in equilibrium with the sodium-rich melts when T is above 1160 °C. The chromium oxide (Cr2O3) to pyroxene (NaCrSi2O6) transformation is described in terms of the time required to reach chemical and textural equilibrium. Na2CrO4, NaCrSi2O6, and Cr2O3 phase stability domains are reported as well as the Na2O–SiO2–Cr2O3 phase diagram in the studied temperature and fO2 range.