Let's Make a Mullite Matrix - Elkem

hot-M.O.R [MPa]
20
18
16
14
12
10
8
6
4
2
0
0 5 10 15 20 25 30
Time [h]
6%MS, 6% cem. 1200°C
6%MS, 6%cem, 1300°C
8%MS,2.5%cem, 1200°C
8%MS, 2.5%cem, 1300°C
Figure 11: Bauxite-based refractory castables. Hot-M.O.R. as a function of time.
After 24 hours pre-firing, much of the mullitization is considered completed. Figure 12 shows
the hot-M.O.R. of bauxite castables with 3, 6 and 9% microsilica at 6% cement and also one
with 8% microsilica and 2.5% cement as a function of temperature (composition is given in
Table 3 in the Appendix ). The choice of 6% cement in combination with 6% microsilica is
indeed not the best if the hot-strengths shown in Figure 12 are examined. Unless more than
6% microsilica is used, there are no signs of the characteristic strengthening by mullitization.
This is in accordance with the mechanism sketched for the white fused alumina-based
compositions described earlier in this presentation, but as mentioned earlier, some 100°C
lower than in a pure system. The best results are again obtained by a lowering of the cement
content, while maintaining a relatively high microsilica level. Here 2.5% cement together with
8% microsilica was used.
Elkem Materials – page 15