Chemically strengthened lithium disilicate-petalite glass-ceramics

Abstract

Ion-exchanged glass ceramic articles described herein have a stress that decreases with increasing distance according to a substantially linear function from a depth of about 0.07 t to a depth of about 0.26 t from the outer surface of the ion-exchanged glass ceramic article from a compressive stress to a tensile stress. The stress transitions from the compressive stress to the tensile stress at a depth of from about 0.18 t to about 0.25 t from the outer surface of the ion-exchanged glass ceramic article. An absolute value of a maximum compressive stress at the outer surface of the ion-exchanged glass article is from 1.8 to 2.2 times an absolute value of a maximum central tension (CT) of the ion-exchanged glass article, and the glass ceramic article has a fracture toughness of 1 MPa√m or more as measured according to the double cantilever beam method.

What is claimed is: 
     
         1 . A method of strengthening a glass ceramic article having a crystal phase selected from the group consisting of petalite, lithium disilicate, and combinations thereof comprises:
 applying an ion exchange medium to the glass ceramic article, wherein the ion exchange medium comprises greater than 0 wt % and less than or equal to 20 wt % NaNO 3 , from 80 wt % to less than 100 wt % KNO 3 , and from 0.01 wt % to 0.5 wt % LiNO 3 .   
     
     
         2 . The method according to  claim 1 , wherein the ion exchange medium has a temperature of from 380° C. to 550° C. 
     
     
         3 . The method according to  claim 1 , wherein the ion exchange medium is applied to the glass ceramic article for a time of from 2 hours to 16 hours. 
     
     
         4 . The method according to  claim 1 , wherein the ion exchange medium is a second ion exchange medium, and the method further comprises: applying a first ion exchange medium to the glass ceramic article wherein the first ion exchange medium comprises NaNO 3 , KNO 3 , and from 0.01 wt % to 0.5 wt % LiNO 3 , and wherein applying the second ion exchange medium is performed after applying the first ion exchange medium. 
     
     
         5 . The method according to  claim 4 , wherein the first ion exchange medium comprises greater than 20 wt % NaNO 3 . 
     
     
         6 . The method according to  claim 4 , wherein the second ion exchange medium comprises greater than 95 wt % and less than 100 wt % KNO 3  and greater than 0 wt % and less than 5 wt % NaNO 3 . 
     
     
         7 . A method of strengthening a glass ceramic article having a crystal phase selected from the group consisting of petalite, lithium disilicate, and combinations thereof, comprises: applying an ion exchange medium to the glass ceramic article, wherein the ion exchange medium comprises greater than 20 wt % and less than or equal to 50 wt % NaNO 3 , from 50 wt % to less than 80 wt % KNO 3 , and from 0.01 wt % to 0.5 wt % LiNO 3 . 
     
     
         8 . The method according to  claim 7 , wherein the ion exchange medium has a temperature of from 380° C. to 550° C. 
     
     
         9 . The method according to  claim 7 , wherein the ion exchange medium is applied to the glass ceramic article for a time of from 2 hours to 16 hours. 
     
     
         10 . The method according to  claim 7 , wherein the ion exchange medium comprises from 30 wt % to 50 wt % NaNO 3  and from 50 wt % to 70 wt % KNO 3 .