Compositions: ceramic – Ceramic compositions – Refractory
Patent
1993-05-25
1995-01-24
Brunsman, David
Compositions: ceramic
Ceramic compositions
Refractory
501152, C04B 3510, C04B 3550
Patent
active
053842936
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a rare earth oxide-alumina-silica sintered body and a method of producing the same, and more particularly to a rare earth oxide-alumina-silica sintered body having a high strength, an excellent toughness and a dense structure obtained by controlling abnormal growth of crystal grains, which abnormal growth causes the lowering of strength and toughness, and a method of producing the same.
BACKGROUND ART
The oxide ceramics possess high-temperature strength and are excellent in heat resistance, oxidation resistance and corrosion resistance. Such oxide ceramics can reliably be used up to at least a temperature lower by not higher than several hundred degrees centigrade from a melting point thereof. Therefore, rare earth oxides (oxide of rare earth element or a mixture thereof) and alumina are expected to be used as a high-temperature ceramic material. Particularly, a mixed ceramic containing two oxides is considered to be effective as a so-called high-temperature material because the melting point is about 2000.degree. C.
In the mixed oxide ceramics, however, when a mixture of oxides is fired to obtain a sintered body, abnormal growth of crystal grains causes a large crystal grain size of not less than 100 .mu.m, so that there are caused pores which reduce densification. Furthermore, the resulting sintered body is weak in strength, toughness and hardness.
For instance, in case of Ln.sub.4 Al.sub.2 O.sub.3 compounds, Ln is Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and a mixture thereof, and LnAlO.sub.3 compounds, Ln is Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and a mixture thereof, there is a bad drawback that very brittle polycrystalline sintered bodies are only obtained because a twin is formed through martensitic transformation in the sintering.
On the other hand, one of the methods for controlling the abnormal grain growth in the polycrystalline sintered body of the above mixed oxide ceramics is to use a method for controlling an addition of a third substance.
It is an object of the invention to repeatedly establish the above control technique by adding a third substance to properly control the crystal grain size of the sintered body.
DISCLOSURE OF THE INVENTION
As the rare earth oxide-alumina sintered body capable of realizing the above object, the invention aimed at silica (SiO.sub.2) as the third substance and controlled an average crystal grain size of the sintered body into a given size by adding such a substance.
The invention based on such a fundamental thought is a rare earth oxide-alumina-silica sintered body, characterized in that the sintered body is a mixture of rare earth oxide, alumina and silica and an average crystal grain size thereof is not more than 30 .mu.m. Preferably, the sintered body has a compounding composition of 5-95 wt% of rare earth oxide, 94.9-4.9 wt% of alumina and 0.1-10 wt % of silica and an average crystal grain size of not more than 30 .mu.m, and more particularly a compounding composition of 64.9-89.9 wt % of rare earth oxide, 10-35 wt % of alumina and 0.1-10 wt % of silica and an average crystal grain size of not more than 10 .mu.m.
Furthermore, the rare earth oxide-alumina-silica sintered body is preferably a mixture sintered body of Ln.sub.4 Al.sub.2 O.sub.9 compound or LnAlO.sub.3 compound and silica, and more particularly a mixture sintered body of 99.9-90 wt % of Ln.sub.4 Al.sub.2 O.sub.9 compound or LnAlO.sub.3 compound and 0.1-10 wt % of silica.
Such a rare earth oxide-alumina-silica sintered body can be produced by the following method. That is, the production method of rare earth oxide-alumina-silica sintered body is characterized by comprising powder and silica powder; green shaped body; rising rate of 1.degree.-200.degree. C./minute; and 1400.degree.-2000.degree. C. for 0.1-24 hours to form a sintered body.
In this method, the above mixed powder is a mixture of 5-95 wt % of rare earth oxide powder, 94.9-4.9 wt% of alumina powder and 0.1-10 wt % of silica powder.
Preferably, the mixed powder is a
Hirai Toshio
Omori Mamoru
Brunsman David
Jones Deborah
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