Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
1996-09-06
2001-09-04
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S097200, C501S097300
Reexamination Certificate
active
06284690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a slurry Si-base composition for use in producing an Si
3
N
4
ceramic, which composition contains water as a dispersion medium. Also, the present invention relates to a dense Si
3
N
4
ceramic of a high strength produced from the above slurry Si-base composition and processes for producing these.
2. Description of the Prior Art
Alcohols have been employed as a dispersion medium for ensuring an effective dispersion of a silicon (Si) powder in the mixing/molding step when a ceramic is produced from the silicon powder as a starting material, as described in Mat. Res. Soc. Symp. Proc., vol. 60, pp. 51-61 (1986). However, from the industrial point of view, the process in which use is made of an alcohol must be provided with expensive explosionproof facilities, which constitute a cause of the increase of product cost.
On the other hand, Japanese Patent Laid-Open Nos. 261662/1991 and 212279/1989 proposed processes in which water not requiring explosionproof facilities is used as a dispersion medium. These processes produce a sintered body of Si
3
N
4
through dispersion of an Si powder in water, addition of an organic binder, a nitriding agent, etc. so as to obtain a slurry, dehydration of the slurry, molding and heating for sintering the molding.
However, the above processes described in Japanese Patent Laid-Open Nos. 261662/1991 and 212279/1989 fail to add a sintering aid required for densification of the resulting sintered body. Therefore, for example, as clearly set forth in Japanese Patent Laid-Open No. 261662/1991, the obtained sintered body of Si
3
N
4
cannot help having a multiplicity of minute pores dispersed therein. Consequently, the flexural strength of the sintered body of Si
3
N
4
is anticipated to be very low. Actually, only a flexural strength as low as 600 MPa or less has been realized.
The reason for the failure to add a sintering aid to the water-base slurry in the above conventional processes would be that the dispersion of Si powder and sintering aid is poor in water as different from that in an alcohol, thereby causing the resultant specimen to have a nonuniform density therein.
SUMMARY OF THE INVENTION
In view of the above circumstances to now, objects of the present invention are to provide a slurry Si-base composition for production of a ceramic of Si
3
N
4
which uses water as a dispersion medium and contains a sintering aid by improving the dispersion of powder in water and further to provide an inexpensive dense Si
3
N
4
ceramic of a high strength which is produced from the above Si-base composition.
The slurry Si-base composition provided by the present invention for attaining the above objects comprises an Si powder having a thickness of a surface oxide film ranging from 1.5 to 15 nm, 50 to 90% by weight of water, 0.2 to 7.5% by weight, in terms of oxide, of a sintering aid and 0.05 to 3% by weight of a dispersant, the Si-base composition having a pH value adjusted to 8-12.
This slurry Si-base composition is produced by a process which comprises subjecting Si powder to oxidation treatment at 200 to 800° C. in air, adding 50 to 90% by weight of water, 0.2 to 7.5% by weight, in terms of oxide, of a sintering aid and 0.05 to 3% by weight of a dispersant to the Si powder and performing such a pH adjustment that the resultant mixture has a pH value of 8 to 12.
Further, the use of the above slurry Si-base composition not only enables producing a ceramic of Si
3
N
4
at a lowered cost without the need to install explosionproof facilities but also allows the obtained Si
3
N
4
ceramic to be dense, uniform and highly strong. Specifically, an Si
3
N
4
ceramic having a relative density of at least 96% and a flexural strength of at least 800 MPa can be obtained.
REFERENCES:
patent: 4943401 (1990-07-01), Edler et al.
patent: 5055432 (1991-10-01), Edler et al.
patent: 5387562 (1995-02-01), Dillinger et al.
patent: 1212279 (1989-08-01), None
patent: 3261662 (1991-11-01), None
patent: WOX9105203 (1991-07-01), None
Copy of Haggerty et al Article “Processing . . . Powders” pp. 51 to 61 (1986).
Nakahata Seiji
Yamakawa Akira
Bierman, Muserlian and Lucas
Group Karl
Sumitomo Electric Industries Ltd.
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