Method to increase the strength of a form body of lithium silicate glass ceramic

Abstract

The invention relates to a medical form body of lithium silicate glass ceramic. To increase its strength it is proposed that a surface compressive stress is created in a form body of lithium silicate glass, or containing lithium silicate glass, through the replacement of lithium ions by alkali metal ions of greater diameter. For this purpose the form body is covered with a paste that contains alkali metal.

1 . A form body in the form of a medical or dental object or a part thereof, of lithium silicate glass ceramic, comprises a surface compressive stress that is generated in the form body through the replacement of lithium ions by alkali ions of greater diameter. 
     
     
         2 . The form body according to  claim 1 , wherein the alkali metal ions are selected from the group consisting of Na, K, Cs, Ions, and combinations of ions thereof. 
     
     
         3 . The form body according to  claim 1 , wherein a glass phase of the form body or a blank from which the form body is prepared from, includes at least one stabilizer that increases the strength of the form body, the concentration of which in the starting composition of the form body is 8-12% by weight. 
     
     
         4 . The form body according to  claim 1 , wherein the form body is prepared from a glass melt that includes the following components in percentage by weight 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   SiO 2   
                       52-70, 
                 
                     
                   P 2 O 5   
                    0.5-11, 
                 
                     
                   Al 2 O 3   
                   0.5-5, 
                 
                     
                   Li 2 O 
                       13-22, 
                 
                     
                   K 2 O 
                   0.5-8, 
                 
                     
                   Na 2 O 
                      0-0.5, 
                 
                     
                   ZrO 2   
                     4-16, 
                 
                     
                   CeO 2   
                   0.5-8, 
                 
                     
                   Tb 4 O 7   
                   0.5-6, 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         optionally an oxide or a number of oxides of an earth alkali metal or a number of earth alkali metals selected from the group consisting of magnesium, calcium, strontium, and barium 0-20, 
         optionally one or more additives selected from the group consisting of B 2 O 3 , MnO 2 , Fe 2 O 3 , V 2 O 5 , TiO 2 , Sb 2 O 3 , ZnO, SnO 2  and fluorides 0-6, 
         optionally one or more oxides of the rare earth metals with the atomic numbers 57, 59-64, 66-71 0-5. 
       
     
     
         5 . The form body according to  claim 1 , wherein the form body is prepared from a glass melt that includes the following components in percentage by weight 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   SiO 2   
                   58.1 ± 2.0,  
                 
                     
                   P 2 O 5   
                   5.0 ± 1.5, 
                 
                     
                   Al 2 O 3   
                   4.0 ± 2.5, 
                 
                     
                   Li 2 O 
                   16.5 ± 4.0,  
                 
                     
                   K 2 O 
                   2.0 ± 0.2, 
                 
                     
                   ZrO 2   
                   10.0 ± 0.5,  
                 
                     
                   CeO 2   
                   1.5 ± 0.6, 
                 
                     
                   Tb 4 O 7   
                   1.2 ± 0.4, 
                 
                     
                   Na 2 O 
                   0.2-0.5. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         6 . The form body according to  claim 1 , wherein the form body has a glass phase in the range 20-85% by volume. 
     
     
         7 . The form body according to  claim 1 , wherein the form body includes lithium silicate crystals between 35% and 80% by volume of the body. 
     
     
         8 . The form body according to  claim 1 , wherein the percentage of alkali ions replacing the lithium ions, commencing from a surface of the form body down to a depth of 10 μm is in the range 5-20% by weight, and/or at a depth between 8 and 12 μm from the surface the percentage of alkali ions is in the range 5-10% by weight, and/or at a layer depth of between 12 and 14 μm from the surface the percentage of alkali ions is in the range 4-8% by weight, and/or at a depth from the surface between 14 and 18 μm the percentage of alkali ions is in the range 1-3% by weight. 
     
     
         9 . Use of a paste comprising at least one alkali metal salt for coating a form body of lithium silicate glass ceramic material, according to  claim 1 .