Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1996-12-13
1998-07-07
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 69, 501 72, C03C 3087
Patent
active
057768447
DESCRIPTION:
BRIEF SUMMARY
This invention has as its subject glass compositions suitable for being converted into glass ribbon, from which can be cut plates that are highly resistant to heat. These plates may be used for the production of fire-resistant panes or may serve as substrates for the production of plasma screens, electroluminescent screens and cold cathode screens (field-emission displays).
The glass at present used for the production of such substrates is a glass belonging to the family of the silico-sodo-calcic glasses, commonly used for the production of panes intended for buildings or automobile vehicles. Although this type of glass is thoroughly satisfactory with regard to its chemical resistance, planeity and the defects that it does have, its temperature behaviour sometimes leaves something to be desired.
In the production of emissive screens, the substrate is subjected to several thermal treatments which are intended for stabilizing the dimensions of said substrate and fixing a series of films of different compounds, such as enamels, deposited on its surface. The fixing of these films of more or less large thicknesses requires that the temperature of the substrate be raised to values higher than 550.degree. C. Although the coefficient of thermal expansion of the silico-sodo-calcic glass used may be of the same order of value as that of the compounds deposited on its surface, its temperature behaviour is inadequate and it must be supported on a trued plate during the thermal treatments to prevent any deformation.
The glasses used for the manufacture of fire-resistant panes generally belong to the family of the borosilicate glasses. These glasses, which have very good heat resistance and thermal shock resistance are characterized generally by a low coefficient of thermal expansion. This latter characteristic does not allow high stresses to be developed in these glasses by thermal toughening and the increase of their mechanical strength by this means is accordingly limited.
The present invention proposes to overcome the limitations that the use of these known glasses imposes for one or another of the applications indicated above.
Thus, the present invention has as its subject a glass composition enabling a plate or a substrate to be produced, the deformation of which is virtually zero when it is subjected to temperatures between 550.degree. and 600.degree. C.
The present invention has as its subject, notably, a glass composition enabling a plate to be produced, within which stresses at least as high as those that develop in a plate of ordinary silico-sodo-calcic glass can become established by thermal toughening.
The present invention has as its subject a glass composition enabling a substrate to be produced, in which the surface depletion of alkaline ions shall be less than that observed on a substrate produced from an ordinary silico-sodo-calcic glass.
The present invention also has as its subject a glass composition capable of being melted and converted into a ribbon of float glass on a molten metal bath in temperature conditions close to those of an ordinary silico-sodo-calcic glass.
These objectives are attained by means of a glass composition which comprises the following constituents, in the following proportions by weight:
______________________________________ SiO.sub.2 45 to 68%
Al.sub.2 O.sub.3
0 to 20%
ZrO.sub.2 0 to 20%
B.sub.2 O.sub.3
0 to 10%
Na.sub.2 O 2 to 12%
K.sub.2 O 3.5 to 9%
CaO 1 to 13%
MgO 0 to 8%
______________________________________
ZrO.sub.2 remaining equal to or less than 70%, the sum of the oxides
Al.sub.2 O.sub.3 and ZrO.sub.2 being equal to or greater than 2%, the sum
of the contents of the alkaline oxides Na.sub.2 O and K.sub.2 O being
equal to or greater than 8%, said composition comprising, if desired, the
oxides BaO and/or SrO in proportions such that:
approximately 530.degree. C. and a coefficient of expansion
(.alpha..sub.25.degree.-300.degree. C.) lying between 80 and
95.times.10.sup.-7 /.degree.C.
It is commonly accepted that glass no long
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Chemical Abstracts, vol. 98, No. 18, abstract No. 148473a, Mkrtchyan et al., p. 309, May 2, 1983.
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Courtemanche Gilles
Gy Rene
Jousse Didier
Koch Stephanie
Bell Mark L.
Saint-Gobain Vitrage
Troilo Louis M.
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