Methods for treating ceramic materials and improved treated...

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Reexamination Certificate

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C428S688000, C428S699000, C427S190000, C427S191000, C427S192000, C427S229000, C427S376600, C427S383500, C501S103000

Reexamination Certificate

active

06232004

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods for treating ceramic materials, especially oxide ceramic materials such as zirconia, to stain or darken the material and to impart improved structural and physical properties. The present invention also comprehends ceramic materials treated according to the treatment methods to provide a class of materials having metallic species dispersed in the ceramic structure. Ceramic materials having metallic species dispersed therein exhibit superior structural and physical properties.
BACKGROUND OF THE INVENTION
Ceramic materials have desirable properties for many applications. Zirconia ceramics are especially desirable, because they are generally harder, stronger, more impact resistant, and less reactive with materials in the environment, such as body fluids, than many other ceramics, making them suitable materials for applications where the ceramic components are subjected to harsh environments.
Most untreated oxide ceramic materials, such as zirconia, are light in color. Processing of such ceramic materials, including assembly of oxide ceramic components into assemblies including different materials, may produce discoloration of the ceramic material. Sealing of ceramic components to metallic components, for example, often produces discoloration of the ceramic material. Discolored ceramic materials may exhibit the same desirable properties as ceramic materials having a uniform coloration, but they are far less desirable from a commercial standpoint. It is therefore desirable to darken ceramic materials so that discoloration is not apparent. Darkened ceramic materials may also be preferred for certain applications.
U.S. Pat. No. 5,711,906 discloses a method of manufacturing a black zirconia-based article that incorporates a stabilizer and a pigment. Zirconia powder is mixed with a stabilizer, a pigment formed by a cobalt and iron oxide powder or by a spinel CoFe
2
O
4
powder, and a binder, the mixture is granulated, and the desired article is molded, sintered and polished. The '906 patent also discloses that molded, stabilized zirconia elements will become black if sintered at a temperature of 1,400° to 1,600° C. in a non-oxidizing atmosphere.
U.S. Pat. No. 4,656,145 discloses a black zirconia decorative article produced by sintering an unsintered molded body comprising a zirconia matrix and a stabilizer in a non-oxidizing atmosphere, such as a carbon-containing atmosphere to produce a blackened, sintered article. Blackening agents include zirconium carbide, carbon or a reduction product of zirconia in an amount of 0.001 to 1% by weight. Sintering promoters such as silica, alumina or titania may be incorporated in the unsintered molded body.
SUMMARY OF THE INVENTION
The present invention provides methods for treating ceramic materials, including oxide ceramic materials such as zirconia, with a treatment agent comprising a metallic material, such as titanium. The treatment darkens the ceramic material and, additionally, imparts improved structural and physical properties. According to one aspect, methods of the present invention involve treating a sintered ceramic material by contacting at least one of the ceramic surfaces with a treatment agent comprising a metallic component, and heating the ceramic material, while in contact with the treatment agent, to a temperature at which the ceramic material incorporates metallic species of the metallic component by diffusion to produce a ceramic material having metallic species dispersed in the ceramic structure.
According to another aspect, a green compact of a ceramic material, such as a zirconia material, is treated with a debinding agent, such as a thermal or chemical debinding agent, and the green compact is then sintered in the presence of a treatment agent comprising a metallic component. The metallic component may be introduced using various techniques that are described in greater detail below.
Treatment methods of the present invention may be adapted to treat a variety of oxide ceramic materials, including zirconia ceramics and stabilized zirconia ceramics, alumina, yttria, beryllia, and other oxide ceramics. Zirconia ceramic materials stabilized with yttria, magnesia, ceria or calcia are preferred ceramic materials, and yttria-stabilized zirconia is an especially preferred ceramic material.
Treatment techniques of the present invention involve treating the ceramic material with a treatment agent comprising a metallic species such as titanium, zirconium, nickel, cobalt, manganese, vanadium, chromium, copper, hafnium, silver, aluminum, tantalum, niobium, molybdenum, or a mixture of any of the above metallic species. The treatment agent may be in any form in which one or more metallic components is available for diffusion or dispersion into the ceramic structure under treatment conditions. The metallic component of the treatment agent may take various forms. Metallic, metallic sponge, metallic hydride, and organo-metallic forms of appropriate metallic species are suitable for use as treatment agents. Such treatment agents may be directly contacted to a ceramic material and heated under the appropriate conditions, as described below, to induce diffusion or dispersion of the metallic component into the ceramic structure.
Alternatively, a treatment agent comprising a metallic component may be contacted to or deposited on a ceramic surface, for example, by physical or chemical vapor deposition. Sublimation pumps, including both sputtering and evaporable sublimation pumps, may be used to deposit a treatment layer comprising a suitable metallic component on one or more exposed surfaces of a ceramic material. An evaporable getter or getter device comprising a suitable metallic component may also be used to deposit a treatment layer comprising the metallic component on one or more exposed surfaces of a ceramic material. Suitable getters and gettering devices preferably comprise: zirconium; titanium; barium; hafnium, zirconium-vanadium-iron; zirconium-aluminum; zirconium-iron; zirconium-vanadium-titanium-iron; zirconium-graphite; or any combination of these metallic species.
Ceramic components and surfaces having various conformations and configurations may be treated using the methods of the present invention. Surfaces to be treated are preferably cleaned to remove any foreign or oxidized materials. The ceramic treatment surface(s) to be treated are contacted with a treatment agent comprising a metallic component, such that a metallic species is available for diffusion or dispersion into the ceramic structure under treatment conditions. According to an embodiment wherein the treatment agent comprises metallic particles or metallic sponge or metallic hydride material, or an organometallic material, the metallic material is distributed uniformly on the ceramic surface(s) being treated. Similarly, if a treatment layer comprising a metallic component is deposited on surface(s) of a ceramic material prior to or during treatment using chemical or physical vapor deposition by means of a sublimation pump or a getter or getter device, a layer of uniform thickness is preferred for many applications. For specialized applications where non-uniform diffusion or dispersion of a metallic species into a ceramic material is desired, the treatment layer may be applied in a non-uniform manner, as desired.
An assembly comprising the ceramic material in contact with the treatment agent is heated under vacuum conditions to the desired treatment temperature and held at the treatment temperature for the desired treatment time to induce diffusion of a metallic species into the ceramic structure. Alternatively, methods whereby a metallic species is deposited on the surface of the ceramic material and made available for diffusion or dispersion into the ceramic structure, and then diffused or dispersed into the ceramic structure in an integrated process, may be implemented. In addition to the diffusion or dispersion of metallic species into the ceramic structure, preferred treatment techniques induce

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