Glass-ceramic compositions designed for radomes
AssigneeCorning Glass Works
InventorsDavid G. Grossman, Richard W. Waldron
Life of this patent
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Abstract
The instant invention is drawn to glass-ceramics especially designed for the fabrication of radomes, wherein cordierite is the predominant crystal phase but which also contain minor amounts of cristobalite, magnesium-aluminum titanate, and rutile, having overall compositions consisting essentially, expressed in weight percent on the oxide basis, of about ______________________________________ MgO 15-18 Al.sub.2 O.sub.3 21-25 SiO.sub.2 48-53 TiO.sub.2 9.5-11.5 As.sub.2 O.sub.3 0-1 ______________________________________
Claims5
A glass-ceramic suitable for the fabrication of radomes with porous surface layers having a depth of about 0.005"-0.015", said glass-ceramic exhibiting a loss tangent at 25.degree. C. and 8.6.times.10.sup.9 Hz no greater than about 0.00035, a dielectric constant at 25.degree. C. and 8.6.times.10.sup.9 Hz no more than about 6, a modulus of rupture after fortification in excess of 30,000 psi, a coefficient of thermal expansion (25.degree.-300.degree. C.) of less than about 45.times.10.sup.-7 /.degree. C., and wherein cordierite constitutes the predominant crystal phase along with minor amounts of cristobalite, magnesium-aluminum titanate, and rutile, said glass-ceramic having an overall composition consisting essentially, expressed in weight percent on the oxide basis, of about 15-18% MgO, 21-25% Al.sub.2 O.sub.3, 48-53% SiO.sub.2, 9.5-11.5% TiO.sub.2, and 0-1% As.sub.2 O.sub.3.
A method for making a glass-ceramic suitable for the fabrication of radomes exhibiting a loss tangent at 25.degree. C. and 8.6.times.10.sup.9 Hz no greater than about 0.00035, a dielectric constant at 25.degree. C. and 8.6.times.10.sup.9 Hz no more than about 6, a modulus of rupture after fortification in excess of 30,000 psi, and a coefficient of thermal expansion (25.degree.-300.degree. C.) of less than about 45.times.10.sup.-7 /.degree. C. which comprises the steps of:
- (a) melting a batch for a glass consisting essentially, expressed in weight percent on the oxide basis, of about 15-18% MgO, 21-25% Al.sub.2 O.sub.3, 48-53% SiO.sub.2, 9.5-11.5% TiO.sub.2, and 0-1% As.sub.2 O.sub.3 ;
- (b) simultaneously cooling the melt at least below the transformation range thereof and forming a glass shape of a desired configuration therefrom;
- (c) heat treating said glass shape at a temperature between about 1000.degree.-1300.degree. C. for a period of time sufficient to cause the in situ crystallization of cordierite as the predominant crystal phase along with minor amounts of cristobalite, magnesium-aluminum titanate, and rutile;
- (d) contacting the surface of said crystallized shape with an alkaline solution to leach out cristobalite therefrom;
- (e) removing said alkaline solution from the surface of said crystallized shape;
- (f) contacting the surface of said crystallized shape with an acid solution to leach out residual glass therefrom;
- (g) removing said acid solution from the surface of said crystallized shape;
- and then
- (h) sequentially repeating steps (d)-(g) a sufficient number of times to produce a porous surface layer having a depth of about 0.005"-0.015".
Dependencies are inferred from the claim text.