The solubility of water vapour in CaO-SiO2-Al2O3-MgO slag system

The solubility of water Vapour in the CaO-SiO2-Al2O3-MgO quaternary slag system was measured using an inert gas fusion technique with thermal conductivity detection. The stags were equilibrated with argon-water vapour mixture corresponding to 0.157 bar of water vapour pressure at 1873 K. The slag solubility of water vapour is proportional to the square root of vapour pressure. Since the hydroxyl capacity of slag, COH shows an independence on the relative amount of CaO or MgO in slag, the contributions of CaO and MgO on the hydroxyl capacity are equivalent on a molar basis. Whereas, Al2O3 shows a better effect on the hydroxyl capacity than SiO2. A linear relationship between hydroxyl capacity and slag basicity in logarithmic scale was obtained with the slope of 1/2, confirming the water vapour dissolution reaction into a basic slag as (O2-) + H2O(g) = 2(OH-). The correlation between hydroxyl capacity and slag components was derived in terms of their contributing weight factors. The measured Values of C'(OH) agree well with the calculated ones using the interaction energies of alpha(H-Al) = -38300 and alpha(H-Mg) = -22700 J determined with the aid of the regular solution model. In addition, the correlation between hydroxyl capacity and sulphide capacity was empirically derived as a formula of logC(OH) = 1/2logC(s) + (4.38 +/- 0.25) through the thermodynamic expression of both capacities by virtue of the common oxygen ion activity.