I have been encountering this persistent problem for a while now, though it looks simple, yet I ain't getting the desired results. Having carried out the carbothermal reduction of fly ash at 1500o C for 5h, the as-synthesized composite's phase composition shows that SiO2 is still present as in raw material (quartz phase 22o & 28o). At this heating temperature, if the SiO2 is not reduced to SiC, it should at least be transformed into another phase (b-cristobalite....); however, the XRD phase analysis indicates that quartz is present at the same position.
Please, someone should help me to provide scientific explanations for that.
Thanks
The phase transformation of quartz to cristobalite varies considerably between different quartz sources. I can tell you in Silicon smelting furnace where quartz is reduced to silicon at 1800 deg C, not all quartz transforms to cristobalite and different quartz sources show different behavior. Usually Si smelters prefer those quartz sources which show less transformation to cristobalite as quartz has got higher mechanical strength in comparison to cristobalite. You can also refer to following paper, fig. 7 where cristobalite formation is negligible in sample qz11 at 1500 deg C. Article Changes in Quartz During Heating and the Possible Effects on...
Arman Seyyedi Thank you very much.
Marcus Sommerfeld, I appreciate your email.
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