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29‐Si and 27‐Al Magic‐Angle Spinning Nuclear Magnetic Resonance Study of the Thermal Transformations of Pyrophyllite
Author(s) -
SánchezSoto Pedro J.,
Sobrados Isabel,
Sanz Jesús,
PérezRodríguez José L.
Publication year - 1993
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.1151-2916.1993.tb06604.x
Subject(s) - pyrophyllite , mullite , cristobalite , materials science , magic angle spinning , thermal decomposition , nuclear magnetic resonance spectroscopy , amorphous solid , aluminium silicate , differential thermal analysis , nmr spectra database , magic angle , crystallography , nuclear magnetic resonance , chemistry , mineralogy , spectral line , diffraction , ceramic , metallurgy , stereochemistry , quartz , physics , organic chemistry , astronomy , optics
The thermal transformation of pyrophyllite was analyzed using 27‐Al and 29‐Si MAS‐NMR spectroscopies, thermal analysis (DTA‐TG), dilatometry, and X‐ray diffraction techniques. Above 800°C, dehydroxylation of pyrophyllite is the origin of a broad component in the 27‐Al NMR spectra which is associated with a distorted pentahedral coordination of Al. At 1000°C, tetrahedral sheet breakdown takes place and a partial segregation of amorphous SiO 2 is detected by NMR spectroscopy. This process permits rearrangements of aluminum ions and favors the formation of small disordered nuclei of mullite. The 27‐Al NMR signals observed at 59.5, 40.7, and 1 ppm have been assigned to 4‐ and 6‐coordinated Al in mullite, and the 29‐Si NMR signals observed at −110 and −88 ppm are assigned to well‐crystallized mullite and cristobalite, respectively, formed during thermal decomposition of pyrophyllite.