Study on the Formation mechanism of Tabular Al2O3 and Prismatic Mullite Formation on Alumina Substrate
Date Issued
2007
Date
2007
Author(s)
Yu, Bang-Ying
DOI
zh-TW
Abstract
In this study, diphasic aluminum silicate sol (M) was coating on porous or dense alumina substrate to form a covering layer (DAS) and then sintered at 1280oC, which was below eutectic temperature (1560oC) of Al2O3-SiO system. A gradient, porous Al2O3 substrate was prepared with the characteristics of micro-sized tabular grains on surface, fine interlocking of Al2O3 grains in matrix. Acicular mullite grains were formed on dense Al2O3 substrate with interlocking structure.
The sample was made by spin-coating alumina substrates with diphasic gel made by pseudo-boehmite (AlOOH) and hydrolyzed TEOS [Si(OC2H5)4]. After drying and sintering at different heat treatments, which at the temperature 1280oC, the crystallography and microstructure of the porous structure was investigated by analytical electron microscopy (AEM), X-ray differactometry (XRD), and scanning electron microscopy (SEM). Detailed micro-beam compositional and structural analyses were conducted in order to verify the glassy phase and abnormal Al2O3/ mullite grains.
The abnormal grain growth of Al2O3 grains is possibly due to the transient SiO2-glass phase during sintering above 1250oC. The formation of tabular grains is due to a heterogeneous nucleation from faceted grain of Al2O3/Glass interface, ripening from transient Al2O3 nano-crystals through amorphous SiO2 glass. The reactions are limited to regions where the density is higher, and results in a perpendicular growth of plate-like grains on the substrate. Ostwald ripening in association with the rearrangement of small transient
Subjects
氧化鋁
片狀
莫來石
稜角狀
氧化鋁基材
生長機制
alumina
tabular
mullite
prismatic
alumina substrate
formation mechanism
Type
thesis