Article comprising metal oxide glasses and method of making same

This application is a continuation of U.S. Ser. No. 10/211491, filed Aug. 2, 2002, which is a continuation-in-part of U.S. Ser. No. 09/922,526, filed Aug. 2, 2001, now abandoned, the disclosures of which are incorporated herein by reference.

The present invention relates to a metal oxide ceramic and a method of making articles therewith. Examples of articles include kitchenware (e.g., plates), dental brackets, and reinforcing fibers, cutting tool inserts, abrasives, and structural components of gas engines, (e.g., valves and bearings).

A large number of glass and glass-ceramic compositions are known. The majority of oxide glass systems utilize well-known glass-formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅ to aid in the formation of the glass. Some of the glass compositions formed with these glass-formers can be heat-treated to form glass-ceramics. The upper use temperature of glasses and glass-ceramics formed from such glass formers is generally less than 1200° C., typically about 700-800° C. The glass-ceramics tend to be more temperature resistant than the glass from which they are formed.

Although a large number of metal oxides can be obtained in an amorphous state by melting and rapidly quenching, most, because of the need for very high quench rates to provide amorphous rather than crystalline material, cannot be formed into bulk or complex shapes. Generally, such systems are very unstable against crystallization during subsequent reheating and therefore do not exhibit typical properties of glass such as viscous flow. On the other hand, glasses based on the known network forming oxides (e.g., SiO₂ and B₂O₃) are generally relatively stable against crystallization during reheating and, correspondingly, the “working” range where viscous flow occurs can be readily accessed. Formation of large articles from powders of known glass (e.g., SiO₂ and B₂O₃) via viscous sintering at temperatures above glass transition temperature is well known. For example, in the abrasive industry, grinding wheels are made using vitrified bond to secure the abrasive particles together.

It is desirable to provide large articles and/or complex shapes comprising non-traditional glass and glass-ceramic compositions.

Disclosed herein is an article comprising: coalesced first and second glasses, wherein: the first glass comprises at least two different metal oxides, wherein the first glass has a T_g1 and T_x1, and wherein the difference between the T_g1 and the T_x1 is at least 5K, the first glass comprising less than 20% by weight SiO₂, less than 20% by weight B₂O₃, and less than 40% by weight P₂O₅; and the second glass comprises at least two different metal oxides, wherein the second glass has a T_g2 and T_x2, and wherein the difference between the T_g2 and the T_x2 is at least 5K, the second glass comprising less than 20% by weight SiO₂, less than 20% by weight B₂O₃, and less than 40% by weight P₂O₅.

Exemplary first and second glasses include La₂O₃—TiO₂ glass, REO—Al₂O₃ glass, or REO—Al₂O₃—ZrO₂ glass.

The article may comprise glass or glass-ceramic.

Also disclosed herein is a method of making an article, comprising: providing a first glass comprising at least two different metal oxides, wherein the first glass has a T_g1 and T_x1, and wherein the difference between the T_g1 and the T_x1 is at least 5K, the first glass containing less than 20% by weight SiO₂, less than 20% by weight B₂O₃, and less than 40% by weight P₂O₅; and providing a second glass comprising at least two different metal oxides, wherein the second glass has a T₂ and T_x2, and wherein the difference between the T_g2 and the T_x2 is at least 5K, the second glass containing less than 20% by weight SiO₂, less than 20% by weight B₂O₃, and less than 40% by weight P₂O₅; and heating the first and second glasses above the higher of T_g1 and T_g2 to coalesce the first and second glasses.