Compositions: ceramic – Ceramic compositions – Devitrified glass-ceramics
Patent
1998-03-20
2000-05-09
Group, Karl
Compositions: ceramic
Ceramic compositions
Devitrified glass-ceramics
501 7, 501 68, 65477, 65 337, 65 338, C03C 1012, C03C 1014
Patent
active
060604123
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a crystallizable glass, a crystallized glass, and a crystallized glass article, and to a method of manufacturing the crystallized glass article.
BACKGROUND TECHNIQUE
A crystallized glass is a material containing various crystals precipitated in a glass and exhibiting unique properties which the glass does not have. For example, precipitation of crystals of .beta.-quartz solid solution or .beta.-spodumene solid solution provides a crystallized glass having an extremely low thermal expansion or a negative thermal expansion. Moreover, the crystallized glass generally has a high mechanical strength as compared with the glass because of presence of those crystals.
In recent years, it has been attempted to precisely form the crystallized glass having such excellent properties into the shape of a thin rod, a narrow tube, a thin plate, or the like for application in the field of products, such as electronics parts and precision machine parts, which require precise dimensional accuracy.
As a method of precisely forming the glass, a forming process called redrawing is known. This process comprises the steps of preparing a glass preform with an adequate precision and heating the glass preform to a temperature higher than a softening point of the glass to perform draw forming. This process is widely used in successively producing those glass products which are required to have high precision.
In case of a conventional crystallized glass, however, it is difficult to perform the redraw forming in the manner similar to that for the glass due to the following reasons. Specifically, the conventional crystallized glass has various problems such as difficulty in softening and deformation, difficulty in drawing because of undesirable increase of devitrification during heating, and wide change in physical and chemical properties caused by variation of the amount of crystals dependent on heating. It is therefore proposed to redraw a so-called mother glass, that is, a glass before it is processed into the crystallized glass. However, the glass of this kind is designed to be easily crystallized by heating. Therefore, heating the mother glass for the redraw forming inevitably causes the undesirable devitrification to occur so that not only the dimensions but also the physical and chemical properties are difficult to be controlled.
Under the circumstances, precise forming of the crystallized glass can not presently be achieved by the redraw forming but inevitably requires machining similar to that used for ceramics, resulting in the high cost.
In view of the above-mentioned situation, it is a first object of this invention to provide a crystallizable glass which can be shaped by the redraw forming after crystallization.
It is a second object of this invention to provide a crystallized glass which can be shaped by the redraw forming.
It is a third object of this invention to provide a crystallized glass article obtained by the redraw forming.
It is a fourth object of this invention to provide a method of manufacturing a crystallized glass article by the redraw forming.
DISCLOSURE OF THE INVENTION
As a result of a great deal of studies repeatedly pursued, the present inventor has specified essential requirements which a redrawable crystallized glass must have, based on the knowledge that the crystallized glass is required to have two important conditions, namely, to be easily softened by heating to become drawable and to have a stable crystal phase even when it is heated, so as to be formable by the redrawing.
Specifically, a crystallizable glass according to the present invention has a property of being transformed into a crystallized glass which contains precipitated crystals with a maximum grain size not greater than 5 .mu.m and a glass phase at a ratio of 10 to 85 vol %, and which has a softening point lower than a melting point of a predominant precipitated crystal.
A crystallized glass according to the present invention contains precipitated crystals with a maximum grain size not
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patent: 5173453 (1992-12-01), Beall et al.
patent: 5336643 (1994-08-01), Goto et al.
patent: 5446008 (1995-08-01), Krolla et al.
patent: 5508235 (1996-04-01), Marker
patent: 5691256 (1997-11-01), Taguchi et al.
Group Karl
Nippon Electric Glass Co. Ltd.
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