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Influence of Thermal Aging on Microstructural Development of Mullite Containing Alkalis
Author(s) -
Baudín Carmen,
Villar María Pilar
Publication year - 1998
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.1151-2916.1998.tb02690.x
Subject(s) - mullite , microstructure , materials science , annealing (glass) , sintering , grain growth , dissolution , grain boundary , mineralogy , metallurgy , composite material , chemical engineering , chemistry , ceramic , engineering
The influence of annealing treatments at temperatures of 900°C up to 1630°C on the microstructure of a 3Al 2 O 3 2SiO 2 mullite that contains a small amount of alkali (<3 wt%) has been studied. Annealing treatments of a base mullite material at the sintering temperature (1630°C) and at two temperatures lower (900°C) and higher (1200°C) than the lowest invariant points of the SiO 2 ‐Al 2 O 3 ‐Na 2 O system have been performed. Microstructures have been characterized by using scanning and transmission electron microscopy. Special attention has been given to grain‐boundary characteristics‐particularly the amount, composition, and distribution of the remaining glasses. Aging of this material at high temperature leads to a redistribution of the microstructure toward an equilibrium that involves the dissolution of the mullite grains, formation of a liquid phase, and liquid‐phase grain growth. As the aging temperature increases, liquid‐phase grain growth progressively overcomes the effect of the dissolution of mullite and a bimodal microstructure with an increasing number of large, tabular grains develops.