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Resolution of Thermal Peaks of Kaolinite in Thermomechanical Analysis and Differential Thermal Analysis Studies
Author(s) -
Chakraborty Akshoy K.
Publication year - 1992
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1992.tb07238.x
Subject(s) - differential thermal analysis , kaolinite , thermomechanical analysis , materials science , thermal , thermal analysis , differential (mechanical device) , composite material , mineralogy , thermal expansion , geology , thermodynamics , metallurgy , diffraction , physics , optics
The recent findings for the kaolinite metakaolinite, cubic‐mullite, and orthorhombic‐mullite reaction series have been thoroughly examined by differential thermomechanical analysis (DTMA) and differential thermal analysis (DTA). Metakaolinite shows two differential contraction peaks in the vicinity of 980°C caused by final dehydroxylation at the endothermic dip just before 980°C in DTA with expulsion of 35–37 wt% SiO 2 , formation of a defect aluminosilicate phase and simultaneous contraction of the latter phase, and crystallization of cubic mullite at the 980°C exotherm in DTA. Mullitization takes place in two simultaneous reaction steps: (i) polymorphic transformation of cubic mullite to orthorhombic mullite during the ∼1250°C exotherm shown by DTA which coincides with the differential expansion peak in DTMA and (ii) nucleation followed by crystallization of orthorhombic mullite from the residual aluminosilicate compact phase during the ∼1330°C exotherm shown by DTA. The aluminosilicate formed during the large differential contraction at 1100°–1400°C as shown by DTMA. These results, obtained by the two physical techniques, corroborate earlier findings of the kaolinite transformation series.