4.2 Distribution of Ca and Al Between Si and CaO-Al 2 O 3 Slags
4.2.2 Phases Present in the Metal Equilibrated with 35-65 wt% and 45-
The metals from the experiments with the 35-65 CaO-Al2O3 slag had three prominent phases: a Si2Al2Ca phase, one Al-rich phase, and one Si-rich phase, which was the matrix.
For the metal from the experiments with 45-55 CaO-Al2O3slags, three phases were also present; a Si2Ca phase, a Si2Al2Ca phase and a Si-rich phase, which was the matrix.
Samples from all experiments were imaged with backscatter electrons. Only some of the images will be presented here, and the rest can be found in appendix B.1 and appendix B.2. Also, all values presented in the following figures are from the EPMA-analysis. All error bars indicate a 95 % confidence interval based on two replicate splits.
(a)Sample 35-65-2, imaged with 40x magnification, marked with 1, 2, 3 showing the phases present. The orange circle denotes a pore.
(b)Sample 35-65-24-2, imaged with 200x magnifi-cation, showing the present phases more clearly.
Figure 4.22:BSE images, showing an overview of the phases present at 40x and 200x for the sample 35-65-24-2, where the Al-rich phase has a red outline.
(a)Sample 45-55-24-2, imaged with 40x magnifica-tion, marked with points for the present phases.
(b)Sample 45-55-24-2, imaged with 200x magnifi-cation, showing the present phases more clearly.
Figure 4.23: BSE images, showing an overview of the phases present at 40x and 200x for the samples 45-55-24-2.
Figure 4.22 and 4.23 shows the phases present in the metal from sample 35-65-24-2 and 45-55-24-2 (metal/slag ratio 1/1), and is an illustration of all phases present in the metal from both slag experiments. In figure 4.22, the points 1, 2, and 3 denotes the Si2Al2Ca phase, the Si-matrix and the Al-rich phase, respectively. In 4.23, the points 1, 2, and 3 denotes the Si2Ca phase, the Si2Al2Ca phase and the Si-matrix.
Table 4.4: Composition of the Al-rich phase in the Si-metal equilibrated with 35-65 wt% CaO-Al2O3slag.
Sample Si Al Ca
35-65-24 1.95 97.70±0.08 0.40 35-65-60 2.79 96.31±0.22 0.23 35-65-120 2.63 97.23±0.88 0.19 35-65-180 3.04 97.06±0.14 0.14 35-65-240 2.04 98.27±0.24 0.19
Table 4.4 shows the composition of the Al-rich phase in the Si-metal equilibrated with 35-65 wt% CaO-Al2O3slag. The concentration of Al in this phase is relatively constant at 96-98 wt% Al, with traces of Si and Ca.
Table 4.5:Composition of the mixed phase (Si2Al2Ca) in the metal from the experiments performed with 35-65 CaO-Al2O3slag (point 1 in figure 4.22).
Sample Si Al Ca
35-65-24 37.78±0.13 36.30±0.16 26.57±0.21 35-65-60 38.59±0.04 36.28±0.08 26.90±0.05 35-65-120 38.27±0.20 36.40±0.04 26.96±0.18 35-65-180 38.38±0.29 36.26±0.23 26.55±0.13 35-65-240 38.49±0.21 36.04±0.25 26.81±0.25
Table 4.6:Composition of the mixed phase (Si2Al2Ca) in the metal from the experiments performed with 45-55 CaO-Al2O3slag (point 2 in figure 4.23).
Sample Si Al Ca
Table 4.7:Composition of the Si2Ca phase in the metal from the experiments performed with 45-55 CaO-Al2O3slag (point 1 in figure 4.23).
45-55-240 57.83±0.23 1.13±0.23 41.48±0.28
Table 4.5 and table 4.6 shows the composition of the Si2Al2Ca phase present in the metals from 35-65 wt% CaO-Al2O3and the 45-55 wt% CaO-Al2O3experiments. It is clear that the composition of the Si2Al2Ca phase is independent of metal/slag ratio for both slag compositions. Also, the same goes for the Si2Ca phase in the metal from 45-55 wt% slag series; the composition of the phase is relatively independent of the metal/slag ratio.
25 phase in the metal equilibrated with 35-65 wt% CaO-Al2O3slag as a function of the SiO2concentration in the equilibrated slag.
(b) The concentration of Si, Al and Ca in the Si2Al2Ca phase in the metal equilibrated with 45-55 wt% CaO-Al2O3slag as a function of the SiO2 con-centration in the equilibrated slag.
Figure 4.24:Comparison of the mixed phases in both metal series as a function of the SiO2 concen-tration in both equilibrated slags.
(a) The concentration of Si, Al and Ca in the Si2Al2Ca phase in the metal equilibrated with 35-65 wt% CaO-Al2O3slag as a function of the Al2O3
(b) The concentration of Si, Al and Ca in the Si2Al2Ca phase in the metal equilibrated with 45-55 wt% CaO-Al2O3slag as a function of the Al2O3 con-centration in the equilibrated slag.
Figure 4.25: Comparison of the Si2Al2Ca phase in both metal series as a function of the Al2O3
concentration in both equilibrated slags.
25
(a) The concentration of Si, Al and Ca in the Si2Al2Ca phase in the metal equilibrated with 35-65 wt% CaO-Al2O3slag as a function of the CaO
(b) The concentration of Si, Al and Ca in the Si2Al2Ca phase in the metal equilibrated with 45-55 wt% CaO-Al2O3slag as a function of the CaO con-centration in the equilibrated slag.
Figure 4.26:Comparison of the mixed phases (Si2Al2Ca) in both metal series as a function of the CaO concentration in both equilibrated slags.
As seen from figure 4.24, 4.25 and 4.26, the amount of Si, Al and Ca in the Si-Al-Ca-rich phase in the metal from both series does not change significantly with increasing SiO2, Al2O3or CaO-content in the equilibrated slags.
Figure 4.27:The Si-Al-Ca phase diagram with the marked composition of both the Si2Al2Ca phases in the metal from both slag experiments.
Figure 4.28:The Si-Al-Ca phase diagram with the marked composition of the Si2Ca phase.
Figure 4.29:Marked composition of the Al-rich phase in the Si metal equilibrated with 35-65 wt%
CaO-Al2O3slag. [23]
Figure 4.27 shows the approximate marked composition of the mixed phase (Si2Al2Ca) phase present for both the metal from 35-65 wt% CaO-Al2O3and 45-55 CaO-Al2O3from the compositions listed in table 4.5 and 4.6. It is seen that the composition when assuming about 40 wt% Si, 35 wt% Al and 25 wt% Ca will be the Si2Al2Ca phase, which agrees well with the modeled results (see section 4.3.1). Figure 4.28 shows the approximate marked composition of the Si-Ca rich phase in the Si-Al-Ca phase diagram, when assuming about 60 wt% Si, and 40 wt% Ca. The theoretical composition is the just above the phase line between the SiCa and Si2Ca, however, the modeled results shows that this is the Si2Ca phase.
In figure 4.29, the composition of the Al-rich phase is marked, and at room temperature, it is seen that there will be an Al-Si phase which mainly composes of∼97.5 wt% Al, with
∼2.5 wt% Si, and in the present case, traces of Ca.
In addtition to the phases presented here, one Si-rich phases (the matrix) were present in both metals equilibrated with 35-65 wt% CaO-Al2O3slag (point 2 in figure 4.22) and with 45-55 wt% CaO-Al2O3 (point 3 in figure 4.23). The concentration of both these phases were∼100 wt% Si.