Method for preparing ceramic mixed-oxide materials, particularly

Details Method for preparing ceramic mixed-oxide materials, particularly Method for preparing ceramic mixed-oxide materials, particularly

1995-02-15

1997-03-04

Bell, Mark L.

Compositions: ceramic

Ceramic compositions

Refractory

501102, 501105, 501108, 501126, 501127, 501128, 501133, 501134, 501152, 501153, 501154, 75252, 75254, C04B 3501

Patent

active

056078870

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/SE93/00618, filed Jul. 7, 1993.


FIELD OF INVENTION

The present invention refers to a method for preparing ceramic mixed-oxide materials, particularly intended to be used as matrix material in composite ceramic products, by mixing and co-milling of a metal and a ceramic oxide material and subsequent reaction-sintering in an oxidizing atmosphere.


BACKGROUND OF THE INVENTION

In the preparation of ceramic oxide materials of the kind referred to by mixing and co-milling of a metal and a ceramic oxide material and subsequent reaction-sintering, it has always keen desirable to use the metal in a particulate form with the smallest possible particle size Therefore, in many cases it has been attempted to use milled aluminum having a flake shape. A disadvantage of these processes has been, however, that the flakes smear and adhere to the millingbodies due to the softness of the metal and, hence, also mostly remain in a flake shape. See e.g., Nils Claussen et al. "Low-shrinkage Reaction-Bonded Alumina", J. Europ. Caram. Soc., 5, 1989, pages 29-35. See also other articles of and with Nils Claussen and his research group, such as "Tailoring of Reaction-Bonded Al.sub.2 O.sub.3 Ceramics" Corem Eng Sci Proc, 11, pages 806-820, 1990.
Another way to achieve a better homogeneity between metal and oxide materials in the present connection has been suggested for example, by the US firm Lanxide Corp., Newark, Del., USA and implies that an oxidation of the metal is carried out in melted form. See "Formation of Lanxide ceramic composite materials", J. Mater Res, 1, 1986, pages 81-89. Furthermore, Swedish patent No. 8103269-0 discloses a method of preparing shapes of silicon nitride based materials.


SUMMARY OF THE INVENTION

Since the fine-division of the metal that , in which in most cases, constitutes the step that is difficult to surmount for achieving the goals aimed at, the present invention now suggests a different way of overcoming the difficulties. The feature essentially distinguishing the present invention is that the metal is used in the form of an alloy with an element that is to be present in the final oxide material. In this connection, it is a particular advantage of the invention that the element that the metal is to be alloyed with, is selected such that the alloy obtained becomes brittle so as to facilitate the milling. The subsequent reaction-sintering furthermore can be improved by adding a catalyst metal to the alloy.


DETAILED DESCRIPTION OF THE INVENTION

Thus, the basic idea of the present invention is to mill, together with a suitable oxide compound, a brittle metal alloy into fine particle sizes. In the subsequent reaction-sintering, the metal is oxidized to its corresponding ceramic composition.
Examples of materials that may be employed in the method of the present invention are illustrated by referring to a test with an Al:Si-alloy (88:12) that, together with Al.sub.2 O.sub.3 was successfully milled to fine-size particles. Dry-pressed bodies of this composition were oxidized. It turned out that all of the Si, together with a portion of Al, formed mullite. Furthermore, this occurs already at a temperature below 1400.degree. C. in air atmosphere.
Other ceramic materials that can be manufactured according to the same principles are Al.sub.2 TiO.sub.5, 3Y.sub.2 O.sub.3.5Al.sub.2 O.sub.3 (YAG), Mg.sub.2 Al.sub.4 Si.sub.5 O.sub.18 (coerdirite), MgAl.sub.2 O.sub.4 (spinel), LiAlSi.sub.2 O.sub.6 (.beta.-spodumene) and CaZrO.sub.3 (T.sub.m >2300.degree. C.).
By the invention, it might be achieved that the milling of a pulverulent metal alloy with predetermined brittleness provides particles of sub-micron size (<1 .mu.m). This provides for a really homogenous distribution of the metals in the alloy and, hence reduces the temperature of the transformation to the corresponding ceramic composition. The homogenous distribution furthermore promotes this transformation. Moreover, when preparing an alloy powder having an added catalyst metal the reactivity might be further

REFERENCES:
patent: 4217113 (1980-08-01), Suh et al.
patent: 4557884 (1985-12-01), Petrak et al.
patent: 4605634 (1986-08-01), DeAngelis
patent: 5338712 (1994-08-01), MacMillan et al.

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