OCR Text |
Show critical viscosity temperature. On the other hand, Figure 2 for slag B shows a markedly different behavior of the measured viscosity, as well as a complete change In the quality of agreement for the two prediction methods. The Watt-Fereday formula prediction is neither in good qualitative or quantitative agreement with the experimental data. The extended viscosity method prediction, though, is in excellent qualitative agreement and in very good quantitative agreement with the viscosity measurements. The viscosity behavior of slag B is typical of the critical viscosity behavior which is exhibited by many slags. Figure 2 shows that the extended viscosity method predicts fairly closely the temperature of critical viscosity. The extended method predicts a temperature of 1325°C, compared with a measured value of 1400°C. In comparison, the method of Hoy, Roberts and Wilkins (8) for predicting the critical viscosity temperature yields a value of 1220°C. The critical viscosity behavior of a slag is a result of a solid phase (usually containing iron) precipitating out of the liquid slag solution. The chemical equilibrium code predicts this process, as can be seen by examining Table 2. The calculated composition for slag B shows a rapid decrease in the percentage of iron in the liquid slag occurring between 1327°C and 1027°C. Thus, the reason the extended method Is able to so closely predict the viscosity behavior of slag B is because the chemical equilibrium code is able to calculate the changing composition of the liquid slag. Discussion The extended viscosity method has been shown to give excellent agreement with a slag having a critical viscosity behavior, but only fair agreement with a slag which does not exhibit this behavior. The main reason for the prediction of higher viscosities than those measured for slag A is that the ideal solution model of the chemical equilibrium code predicts the presence of solids in the slag mixture even at high temperatures. For slag A, anorthite (Ca0»A£203*2Si02) and magnesium aluminate (Mg0*A£203) are the solids present at high temperatures. For slag B, gehlenite (2Ca0»A£203 Si02) and anorthite are the solids existing at high temperatures. This explains the lack of CaO in the liquid composition for these slags in Table 2. The addition of the 3-8 |