Compositions: ceramic – Ceramic compositions – Devitrified glass-ceramics
Patent
1999-04-09
2000-09-26
Group, Karl
Compositions: ceramic
Ceramic compositions
Devitrified glass-ceramics
501 5, 501 8, 501 10, 65 331, 65 337, 428694ST, C03C 1002, C03C 1004, C03C 1012, G11B 573
Patent
active
061242233
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The field is nanocrystalline glass-ceramics based on .beta.-quartz solid solution and Mg-rich phases having predominantly very highly uniform, ultra-fine-grained microstructure of .beta.-quartz and one or more phases selected from enstatite, spinel, and a Mg-containing phase with a hexacelsian structure.
BACKGROUND OF THE INVENTION
Glass-ceramic materials have found utility in such varied products as cookware, tableware, missile nose cones, protective shields and industrial applications. Recently, an interest has arisen in producing a rigid, glass-ceramic disk as a substrate upon which a layer of magnetic media can be deposited. The ultimate product is an information disk to cooperate with a head pad in a magnetic memory storage device.
U.S. Pat. No. 2,920,961 (Stookey) originally disclosed the preparation of glass-ceramic articles through the heat treatment of precursor glass bodies by the following three general steps: (1) a glass forming batch, customarily containing a nucleating agent, is melted; (2) the melt is simultaneously cooled to a temperature below the transformation range of the glass and an article is shaped therefrom; and, (3) the resulting glass article is heat treated at temperatures above the annealing point of the glass and, frequently, above the softening point of the glass for a sufficient length of time to cause the glass to crystallize in situ. The heat treatment can be so scheduled as to control the size and, in some instances, the identity of the crystals developed. Thus, the crystallization present in a glass-ceramic article can be the result of both the base composition of the precursor glass and the heat treatment the glass body is subjected to.
Glass-ceramic articles containing a spinel-type crystal phase were originally disclosed in U.S. Pat. No. 3,268,315 (Stookey). This patent discloses a method for forming a glass-ceramic material consisting essentially, expressed in terms of weight percent on the oxide basis, of 40-70% SiO.sub.2, 14-34% Al.sub.2 O.sub.3, 8-27% MgO, and 0.4-2.5% Cr.sub.2 O.sub.3, with the total of these constituents constituting at least 95% by weight of the glass material, and subsequent glass-ceramic. The patent further discloses that the glassceramic exhibits a crystallization consisting essentially of at least one crystal phase selected from the group consisting of a magnesium metasilicate (enstatite) and a spinel. U.S. Pat. No. 4,687,749 (Beall) discloses glass-ceramic articles wherein enstatite constitutes the predominant crystal phase. These articles exhibit a high modulus of rupture, a use temperature in excess of 1200.degree. C., and a high fracture toughness. They consist essentially, expressed in terms of weight percent on the oxide basis, of about 20-35% MgO, 2-12% Al.sub.2 O.sub.3, 40-70% SiO.sub.2, and at least one metal oxide in the indicated proportions selected from the group consisting of 0-2% Li.sub.2 O, 0-4% CaO, 0-12% SrO and 0-17% BaO, at least 0.5% Li.sub.2 O being required when present alone and at least 1% SrO and/or BaO being required in the absence of Li.sub.2 O. The compositions include 5-15% TiO.sub.2 and/or ZrO.sub.2 for nucleation purposes.
Spinel-type crystal phase structures have also been disclosed in other patents such as, U.S. Pat. No. 3,873,329 (Beall); U.S. Pat. No. 3,936,287 (Beall et al.); U.S. Pat. No. 3,681,102 (Beall); U.S. Pat. No. 3,585,054 (Karstetter); U.S. Pat. No. 3,681,102 (Beall); U.S. Pat. No. 3,962,514 (Rittler); U.S. Pat. No. 4,059,454 (Reade); U.S. Pat. No. 4,867,750 (Pinckney); U.S. Pat. No. 5,028,567 (Gotoh et al.); and U.S. Pat. No. 5,079194 (Jean et al.). Also, U.K. Pat. No. 1,544,779 (Macmillan et al.).
One particularly desirable property of magnetic disk substrates is the ease with which such substrate can be fine polished. Information disks must be ultra-smooth to permit proper operation of a memory device. The difficulty in obtaining the desired ultra-smooth surface is a major concern in substrate production. One method which has been used in the past is to form glass-
REFERENCES:
patent: 4687749 (1987-08-01), Beall
patent: 5391522 (1995-02-01), Goto et al.
patent: 5476821 (1995-12-01), Beall et al.
patent: 5491116 (1996-02-01), Beall et al.
Beall George H.
Pinckney Linda R.
Corning Incorporated
Group Karl
Peterson Milton M.
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