Growth of Tabular α‐Al₂O₃ Grains on Porous Alumina Substrate

Abstract

Gradient, porous alumina ceramics were prepared with the characteristics of microsized tabular α‐Al2O3 grains grown on a surface with a fine interlocking feature. The samples were formed by spin‐coating diphasic aluminosilicate sol on porous alumina substrates. The sol consisted of nano‐sized pseudo‐boehmite (AlOOH) and hydrolyzed tetraethyl orthosilicate [Si(OC2H5)4]. After drying and sintering at 1150°–1450°C, the crystallographic and chemical properties of the porous structures were investigated by analytical electron microscopy. The results show that the formation of tabular α‐Al2O3 grains is controlled by the dissolution of fine Al2O3 in the diphasic material at the interface. The nucleation and growth of tabular α‐Al2O3 grains proceeds heterogeneously at the Al2O3/glass interface by ripening nano‐sized Al2O3 particles.

Thermal Reaction of Cristobalite in Nano‐SiO2/α‐Al2O3 Powder Systems for Mullite Synthesis

“…It is well‐known that mullite formation through a solid‐state reaction usually occurs at a higher temperature (above 1500°C) and requires considerable effort and time . A previous study investigated the growth of tabular α‐Al 2 O 3 grain using spin‐coating diphasic aluminosilicate sol on porous alumina substrate. The sol consisted of nanosized pseudo‐boehmite (AlOOH) and hydrolyzed tetraethyl orthosilicate [Si(OC 2 H 5 ) 4 ] and was composed of SiO 2 /Al 2 O 3 in a 2/3 molar ratio.…”

“…The main reason considered is the kinetic energy difference. Although SiO 2 glass was detected by 1280°C treatment in the Yu and Wei's investigation, the provided thermal condition (temperature and duration for reaction) does not meet the required activation energy to trigger the mullization. Furthermore, the use of alumina substrate largely reduced the kinetic energy needed for the growth of α‐Al 2 O 3 grains and can proceeds heterogeneous nucleation and growth of tabular α‐Al 2 O 3 grain at the alumina/glass interface.…”

“…6,7,19 It is well-known that mullite formation through a solidstate reaction usually occurs at a higher temperature (above 1500°C) and requires considerable effort and time. 26 A previous study 27 investigated the growth of tabular a-Al 2 O 3 grain…”

Effect of Potassium Sulfate on the Low‐Temperature Formation of Alpha Alumina Platelets from Bayerite

“…Moreover, a liquid phase can help fast diffusion. Yu and Wei 32 reported that the formation of tabular α‐Al 2 O 3 grains is controlled by the dissolution of fine Al 2 O 3 in the amorphous (Si 1− x Al x )O 2 matrix ( x =0.05). In our present study, according to the TG analysis, as shown in Fig.…”