Preparation of barium hexa-aluminate aerogel
- PDF / 989,025 Bytes
- 5 Pages / 576 x 792 pts Page_size
- 56 Downloads / 202 Views
Barium hexa-aluminate (BaO • 6A12O3) aerogels were prepared using a supercritical drying method and their properties examined. A barium hexa-aluminate aerogel prepared from a double alkoxide of barium and aluminum showed a high specific surface area of 421 m 2 /g. Monolithic barium hexa-aluminate formed. No BaO • A12O3 or alumina was observed, as is often the case in powder processing. The specific surface area of the monolithic barium hexa-aluminate fired at 1400 CC for 2 h was 12 m 2 /g, while that of the barium hexa-aluminate xerogel was only 0.8 m 2 /g. A barium hexa-aluminate aerogel was also prepared using barium by using a chelating agent. This aerogel showed a specific surface area of 454 m 2 /g as-dried. In the case of the chelating agent, BaO • AI2O3 was also detected along with barium hexa-aluminate after firing.
I. INTRODUCTION Recently, materials maintaining a high surface area at temperatures greater than 1000 °C have been investigated.1"3 Alumina has been used as a porous material in many cases. However, its surface area decreases drastically with the formation of a alumina.4'5 It has been reported that the addition of barium oxide to alumina is effective in maintaining high specific surface area compared with alumina itself.6 Machida et al. have reported that barium hexa-aluminate (BaO • 6A12O3) shows high specific surface area.7'8 In particular, BaO • 6A12O3 prepared by the sol-gel method shows a high specific surface area of more than 10 m 2 /g after firing at 1600 °C. The sol-gel method is used to produce nanoscale structure materials.9 We have reported on alumina aerogels with high surface area and their thermal properties.10 In the present study, we determine the properties of BaO • 6A12O3 aerogels prepared by the sol-gel method and supercritical drying. II. EXPERIMENTAL Figure l(a) shows a flow chart of the procedure used to synthesize BaO • 6A12O3 aerogel referred to as double alkoxide. Aluminum tri sec-butoxide [Al(OBusec)3], barium metal, and 2-butanol were mixed and refluxed, with the reaction yielding a double alkoxide of Ba[Al(OBu sec )3] 2n under a dry nitrogen atmosphere. Diethanolamine (DEA) was added to control the speed of hydrolysis [Al(OBu sec ) 3 : DEA = 1:1.5]. Water ^'Present address: Superconductivity Research Laboratory, c/o Japan Fine Ceramics Center, 4-1 Mutsuno 2-Chome Atsuta-ku, Nagoya 456, Japan. b) Present address: Kurosaki Refractories Co., Ltd., 1-1, Higashihama, Yawatanishi, Kitakyushu 806, Japan. 2272
J. Mater. Res., Vol. 9, No. 9, Sep 1994
http://journals.cambridge.org
Downloaded: 09 Apr 2015
[Al(OBu sec ) 3 : H 2 O = 1:3] diluted with 2-butanol was gradually added at 0 °C, and the Ba[Al(OBu sec ) 3 ] 2 and Al(OBu sec ) 3 mixture modified with DEA was hydrolyzed to a BaO • 6A12O3 precursor sol. 1N-NH4OH was added to cause gelation. Ethyl acetoacetate has been used to prepare alumina aerogels since it presents fewer problems during supercritical drying (such as shrinkage) compared with other reagents used for modifiers. However, in the synthesis of the BaO • 6A
Data Loading...
