Glass-ceramic compositions designed for radomes

• US 4,304,603 A
• Filed: 08/11/1980
• Issued: 12/08/1981
• Est. Priority Date: 08/11/1980
• Status: Expired due to Term

• Current Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Original Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Inventors: Grossman, David G., Waldron, Richard W.
• Primary Examiner(s): Fisher, Richard V.
• Application Number:
  US06/177,010
• Time in Patent Office: 484 Days
• Field of Search: 65/31, 65/33, 106/39.8
• US Class Current: 501/9
• CPC Class Codes: C03C 10/0045 containing SiO2, Al2O3 and MgO as main constituents
• CPC Class Codes: H01Q 1/42 Housings not intimately mechanically associated with radiating elements, e.g. radome

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 Al₂ O₃ 21-25 SiO₂ 48-53 TiO₂ 9.5-11.5 As₂ O₃ 0-1 ______________________________________

Claims

1. 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°

C. and 8.6×

10⁹ Hz no greater than about 0.00035, a dielectric constant at 25°

C. and 8.6×

10⁹ Hz no more than about 6, a modulus of rupture after fortification in excess of 30,000 psi, a coefficient of thermal expansion (25°

-300°

C.) of less than about 45×

10^-7 /°

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% Al₂ O₃, 48-53% SiO₂, 9.5-11.5% TiO₂, and 0-1% As₂ O₃.

2. A glass-ceramic according to claim 1 consisting essentially, as calculated from the batch of:

space="preserve" listing-type="tabular">______________________________________ MgO 15.8 Al.sub.2 O.sub.3 23.2 SiO.sub.2 49.9 TiO.sub.2 10.7 As.sub.2 O.sub.3 0.4. ______________________________________

3. A method for making a glass-ceramic suitable for the fabrication of radomes exhibiting a loss tangent at 25°

C. and 8.6×

10⁹ Hz no greater than about 0.00035, a dielectric constant at 25°

C. and 8.6×

10⁹ 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°

-300°

C.) of less than about 45×

10^-7 /°

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% Al₂ O₃, 48-53% SiO₂, 9.5-11.5% TiO₂, and 0-1% As₂ O₃ ;

(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°

-1300°

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".

4. A method according to claim 3 wherein said heat treating consists of first heating said glass shape to about 800°

-900°

C. for about 1-6 hours to cause the development of nuclei therein and then heating said shape to about 1150°

-1300°

C. for about 4-12 hours to cause the growth of crystals on said nuclei.

5. A method according to claim 3 wherein said batch consists essentially of:

space="preserve" listing-type="tabular">______________________________________ MgO 15.8 Al.sub.2 O.sub.3 23.2 SiO.sub.2 49.9 TiO.sub.2 10.7 As.sub.2 O.sub.3 0.4. ______________________________________