Solubility of chromium oxide in binary soda-silicate melts

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

“…In order to quantify the rate of the reaction 4, 10 g of Na 2 O-2SiO 2 glass doped with 1 wt.% Cr 2 O 3 was prepared from a mixture of Na 2 O-2SiO 2 glass and Cr 2 O 3 crystals, heated at 1100°C for 24 h in air. This concentration of Cr 2 O 3 being below the saturation level [5][6][7], no crystalline Cr 2 O 3 should be present in the melt. The glass composition was determined by EPMA (Table 1), and the mass fraction of Cr 2 O 3 in the glass was found to be 0.93 ± 0.04.…”

“…This starting material was then used for subsequent time series experiments. The yellow color of the prepared samples suggests that chromium is mainly present in the hexavalent form [5][6][7].…”

“…However, despite the fact that chromia exhibits low solubility in molten glass even at high temperature, there is a general lack of experimental data concerning the factors that affect chromia solubility in molten glasses. This state of art has stimulated specific studies of Cr 2 O 3 solubility in the Na 2 O-xSiO 2 system as a function of temperature (1000-1300°C), glass composition (x = 1.5 to 4), partial pressure of oxygen (10 −18 atm b fO 2 b 0.20 atm) and the addition of other oxides containing network-forming and/or network-modifying cations (B 2 O 3 , Al 2 O 3 or CaO) [3][4][5][6][7]. One of the main results of these recent studies is that the attainment of thermodynamic equilibrium involves a large number of reactions between numerous chromium-bearing species in mineral, liquid and gaseous phases, even in a chemically simple system [5][6][7].…”

“…This complex situation is due to the fact that chromium can exhibit several oxidation states depending on temperature, oxygen fugacity fO 2 , and melt composition. For example, in air, Cr III and/or Cr VI species dominate, while under more reducing conditions, Cr II may coexist with Cr III [5][6][7].…”

“…The reactions that may occur are presented in Fig. 1 [5][6][7]. An essential step towards equilibrium involves the dissolution of crystalline Cr 2 O 3 , to form Cr III oxy-anions in the liquid (Eq.…”