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

Abstract Factors controlling the rate at which chromium oxide reaches saturation in Na 2 O– x SiO 2 liquids have been studied as a function of melt composition and oxygen fugacity. Under an oxidizing atmosphere, liquid Na 2 CrO 4 or Cr 2 O 3 crystals can be in equilibrium with soda-silicate melts, depending on the concentration of sodium in the studied system. Under reducing conditions, NaCrSi 2 O 6 is stabilized in silica-rich melts when T is lower than 1160 °C, while Cr 2 O 3 is in equilibrium with the sodium-rich melts when T is above 1160 °C. The chromium oxide (Cr 2 O 3 ) to pyroxene (NaCrSi 2 O 6 ) transformation is described in terms of the time required to reach chemical and textural equilibrium. Na 2 CrO 4 , NaCrSi 2 O 6 , and Cr 2 O 3 phase stability domains are reported as well as the Na 2 O–SiO 2 –Cr 2 O 3 phase diagram in the studied temperature and fO 2 range.