CaO-SiO2-Al2O3-Na2O-CaF2 Slag

Name: CaO-SiO2-Al2O3-Na2O-CaF2
Diagram No.: 1156
Type of diagram: TTT
Chemical composition in weight %: See the tables
Group: Slags
Note: The beginning and end of crystallization at different temperatures forms a C-shaped curve for all Samples, as predicted by the classical nucleation theory. The obtained TTT diagrams for the onset of crystallization were compared with the TTT diagram obtained by Kashiwaya et al for the Sample with 7% Na2O in Figures 49-51.

The Sample in the Kashiwaya et al study was examined in a smaller temperature range than for the current study. The effect of increasing the basicity (Sample E1), i.e. the content of CaO is shown in Figure 49. Increasing the basicity reduces the time for the beginning of crystallization. The result that increasing the basicity fits well with the theory that lime promotes crystallization by increasing the liquidus temperature and decreasing viscosity. The free amount of oxygen anions is favored by higher basicity. Due to the higher liquidus temperature, the undercooling increases for the same temperature, resulting in a higher nose position of the curve for Sample E3.

The lower content of alumina also decreases the time for the onset of crystallization, especially below 1100C as shown in Figure 50. Alumina is an amphoteric oxide and has been reported at low concentrations to promote a glassy network upon cooling. Reductions of alumina would therefore decrease the viscosity, making mass diffusion faster. This would also increase crystallization as mass diffusion can be assumed to be the rate-controlling step for crystallization.

Comparing Sample E3 with the Sample from Kashiwaya et al. in Figure 51, it is found that increasing the content of Na2O, and adding a small amount CaF2 increases the crystallization quite significantly. This is in good agreement with the conclusions of Kashiwaya on the effect of Na2O on crystallization behavior. The effect of Na2O is clarified in Figure 52. The increased crystallizatio n rate with increasing Na2O content is in good agreement with previous studies. A comparison of the samples in the current study is shown in Figures 52. The incubation time for the onset of crystallization was shorter for both Samples E1 and E2 compared to the samples studied by Kashiwaya.

Reference: Not shown in this demo version.

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