| The chemical activity of Na(,2)O in the Na(,2)O-SiO(,2) system at 1300(DEGREES)C and 1400(DEGREES)C has been determined. A modified transpiration technique was used, in which paddle-stirring of the slag was incorporated to avoid slag-surface depletion of Na(,2)O during the experiments. The data gathered in these experiments were used to calculate the activity of silica, the Gibbs energy of mixing, and the enthalpy of mixing, as a function of comparison from silica saturation to X(,Na(,2)O) of 0.4. The system shows a very negative deviation from Raoultian ideality. At the disilicate composition (DELTA)G('0)/RT is -6.3 at 1300(DEGREES)C and -6.1 at 1400(DEGREES)C. The heat of mixing at the same composition is estimated to be -28.0 kJ.; The information gathered in the above binary system was then used in an encapsulation-type study to generate iso-activity lines in the ternary systems Na(,2)O-CaO-SiO(,2) and Na(,2)O-MgO-SiO(,2). An impregnated low porosity graphite crucible served as the equilibration chamber. The study encompassed the acid region from silica saturation down to approximately X(,SiO(,2)) = 0.6. At constant Na(,2)O-to-SiO(,2) ratios, additions of CaO and MgO both raised the activity coefficient of Na(,2)O. Application of the Richardson model of ideal mixing in silicates to the Na(,2)O-CaO-SiO(,2) system suggests that the cationic mixing takes place between Ca('2+) ions and Na('+) - Na('+) paired-ion units.; The encapsulation-type studies were also conducted on blast-furnace-type slags having molar V ratios (slag basicity) ranging from 0.5 to 1.0, and having two levels of Al(,2)O(,3) content (10 and 20 wt pct). The 'sodium capacity', C(,Na), of a slag has been defined, and it has been determined for all blast-furnace-type slags studied. A decrease in V ratio results in a significant increase in C(,Na). At fixed basicity, replacement of SiO(,2) by Al(,2)O(,3) results in a measurable decrease in C(,Na). Estimates of the temperature variation of C(,Na) have been made. These estimates have been compared with blast-furnace operating data and their relevance has been discussed. |
