Interpretation of the Kaolinite-Mullite Reaction Sequence from Infrared Absorption Spectra

Autor:	P. K. Foster, J. F. Duncan, H. J. Percival
Rok vydání:	1974
Předmět:	Exothermic reaction Materials science Spinel Mineralogy Infrared spectroscopy Recrystallization (metallurgy) Mullite engineering.material Cristobalite Amorphous solid Chemical engineering Materials Chemistry Ceramics and Composites engineering Kaolinite
Zdroj:	Journal of the American Ceramic Society. 57:57-61
ISSN:	1551-2916 0002-7820
DOI:	10.1111/j.1151-2916.1974.tb10813.x
Popis:	The phases in the kaolinite-mullite reaction sequence were reexamined by ir absorption spectrophotometry. Particular attention was paid to the controversial intermediate Al-containing phases. Amorphous materials were leached from fired kaolinite samples with NaOH to help identify crystalline phases. Metakaolinite partially decomposes, releasing amorphous γ-Al2O3 and SiO2, before the “950°C” exothermic reaction in which metakaolinite is completely decomposed. The resulting spinel-type phase, which is associated with amorphous SiO2 and some poorly crystalline “primary” mullite, is γ-Al203 (crystalline) rather than an Al-Si spinel. There is some evidence, however, that a fraction of the γ-Al2O3, may be an Al-Si spinel. At ≥1100°C secondary mullite therefore forms primarily from the γ-Al2O3/amorphous SiO2 reaction and the recrystallization of primary mullite, whereas excess amorphous SiO2 eventually crystallizes as cristobalite.
Databáze:	OpenAIRE
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