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Desiliconization of Mullite Felt
Author(s) -
Zaykoski James,
Talmy Inna,
Norr Marriner,
Wuttig Manfred
Publication year - 1991
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.1151-2916.1991.tb06779.x
Subject(s) - mullite , whisker , whiskers , materials science , thermal diffusivity , temperature gradient , evaporation , helium , composite material , analytical chemistry (journal) , porosity , phase (matter) , concentration gradient , mineralogy , chemistry , thermodynamics , chromatography , ceramic , physics , organic chemistry , quantum mechanics
High‐temperature evaporation from 80% porous, rigid mullite (3Al 2 O 3 ·2SiO 2 ) whisker felt was studied under vacuum and at various helium pressures using gravimetry, X‐ray diffractometry, SEM, and EDS. Heat treatments at 1350° to 1550°C resulted in evaporation of SiO 2 from mullite with a rate strongly dependent on temperature and pressure. A concentration gradient of SiO 2 was observed through the cross section of samples after heating under vacuum, indicating that SiO 2 preferentially evaporated from whiskers on the periphery of the samples. The SiO 2 concentration gradient was accompanied by sharp microstructural changes across the specimens. The gradient was decreased by raising the ambient helium pressure during heat treatment. A mathematical model was developed to predict the SiO 2 concentration profile. The model agrees well with experimental results and demonstrates that the diffusivity of SiO 2 in the vapor phase controls the gradient of SiO 2 through the cross section of mullite felt.