Stabilizing a glass-ceramic

Abstract

A method of stabilizing a glass-ceramic body, particularly an aluminosilicate body, for use as a telecommunications component in a humid atmosphere, comprises coating the body with an aqueous solution of an alkali metasilicate, with a solution of a silane that is strongly non-polar with respect to water, or with successive applications of the metasilicate and the silane.

We claim:  
     
         1 . A method of stabilizing a glass-ceramic body against irreversible changes in dimension and/or in CTE from exposure to a humid atmosphere, the body having a large, internal surface area, the method comprising coating the body with an aqueous solution of an alkali metasilicate, or with a solution of a silane that is strongly non-polar with respect to water, or with successive applications of the alkali metasilicate and the silane.  
     
     
         2 . A method in accordance with  claim 1  which comprises coating the glass-ceramic body with a non-aqueous solution of a silane that is strongly non-polar with respect to water.  
     
     
         3 . A method in accordance with  claim 2  which comprises coating the glass-ceramic with a dilute solution of an alkali metasilicate prior to applying the dilute solution of a non-polar silane.  
     
     
         4 . A method in accordance with  claim 1  wherein the alkali metasilicate is sodium metasilicate and the silane is (pentafluorophenyl)propyltrimethoxy silane.  
     
     
         5 . A method in accordance with  claim 1  wherein the silane has hydrolyzable groups that react with water on the glass-ceramic surface to form a linkage with the surface.  
     
     
         6 . A method in accordance with  claim 1  which comprises soaking the glass-ceramic body in water for a period of time and drying prior to applying a coating.  
     
     
         7 . A method in accordance with  claim 1  which comprises applying a coating to the surface of the glass-ceramic and determining the effectiveness of the coating by repeatedly measuring the frequency of a selected mechanical resonance mode at spaced intervals of time.  
     
     
         8 . A method in accordance with  claim 1  which comprises providing a non-polar silane having alkoxy groups and a glass-ceramic body having water molecules on its surface, applying a coating of the silane to the glass-ceramic, reacting the alkoxy group on the silane with the water molecules to hydrolyze the alkoxy group, and link the hydrolyzed silane to the glass-ceramic surface.  
     
     
         9 . A method in accordance with  claim 1  wherein the non-polar silane is (pentafluorophenyl)propyltrimethoxy silane.  
     
     
         10 . A glass-ceramic body that has microcracks extending into the body from its surface, and that has a non-polar silane linked to the walls of the microcracks and blocking access of moisture to the microcrack surfaces.  
     
     
         11 . A glass-ceramic body in accordance with  claim 10  wherein the microcracks form a continuous porous network extending into the body from its surface.  
     
     
         12 . A glass-ceramic body in accordance with  claim 10  wherein the silane is hydrolyzed and is linked to hydroxyl ions on the glass-ceramic surface.  
     
     
         13 . A glass-ceramic body in accordance with  claim 10  wherein the non-polar silane is the hydrolyzed product of (pentafluorophenyl)propyltrimethoxy silane.  
     
     
         14 . A glass-ceramic body in accordance with  claim 10  that has a sodium metasilicate coating overlaid with the non-polar silane coating.  
     
     
         15 . A glass-ceramic body in accordance with  claim 10  wherein the glass-ceramic is a member of the aluminosilicate family.  
     
     
         16 . A glass-ceramic body in accordance with  claim 15  wherein the glass-ceramic has a primary crystal phase of beta-eucryptite.  
     
     
         17 . A telecommunications system component comprising an optical element having a positive coefficient of thermal expansion in conjunction with a substrate having a negative coefficient of thermal expansion, the substrate having a microcracked glass-ceramic of the aluminosilicate family having a non-polar silane coating blocking entry of moisture to the microcracks.  
     
     
         18 . A component in accordance with  claim 17  wherein the substrate is a glass-ceramic having a primary crystal phase of beta-eucryptite.  
     
     
         19 . A component in accordance with  claim 17  wherein the silane coating is the hydrolyzed product of (pentafluorophenyl)propyltrimethoxy silane.