Method to increase the strength of a form body of a 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 in the form body comprising lithium silicate glass or containing lithium silicate glass the lithium ions are replaced by alkali ions of greater diameter to generate a surface compressive stress. To this end the form body is covered with a melt containing an alkali metal for which an aliquoted quantity of salt containing the alkali metal is used.

1 . A form body of lithium silicate glass ceramic comprising a surface compressive stress is generated in the form body through the replacement of lithium ions by alkali ions of greater diameter than the lithium ions wherein:
 (i) the form body is prepared from a glass melt, which comprises at least the following as starting components: SiO 2 , Al 2 O 3 , Li 2 O, K 2 O, at least one nucleating agent and at least one stabilizer;   (ii) a blank is formed from the glass melt during cooling or following cooling to room temperature, said blank then being subject to at least one first heat treatment W1 at a temperature T W1  for a time t W1 , wherein 620° C.≤T W1 ≤800° C., and 1 minute≤t W1 ≤200 minutes to obtain a crystallization having metasilicate crystals, disilicate crystal, or a combination of metasilicate and disilicate crystals;   (iii) the formed blank is at least partially covered with a melt that includes a first salt of an alkali metal phosphate salt and a second salt of a number of alkali metals with ions of greater diameter than lithium ions;   (iv) the at least partially covered formed blank is annealed for a time t at a temperature T where 620° C.≤T≤800° C. and 0.5 hours≤t≤10 hours such that a surface compressive stress to a depth of at least 20 microns in the form body of lithium silicate glass ceramic is generated through the replacement of lithium ions by the number of alkali metal 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, Rb ions and any combination thereof. 
     
     
         3 . The form body according to  claim 1 , wherein the form body or a blank from which the form body is prepared, has a glass phase which includes ZrO 2  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 contains 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, barium, and any combination thereof 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 , fluorides and any combination thereof 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   
                   0-3, 
                 
                     
                   Tb 4 O 7   
                   0-3, 
                 
                     
                   Na 2 O 
                     0-0.5. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         6 . The form body according to  claim 1 , wherein the form body has a glass phase in the range 20-65% by volume. 
     
     
         7 . The form body according to  claim 1 , wherein the form body has 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 the surface 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 . The form body according to  claim 8 , wherein the percentage by weight of the alkali ions diminishes from layer to layer. 
     
     
         10 . The form body according to  claim 1 , wherein the melt includes one or more elements that color the form body. 
     
     
         11 . The form body according to  claim 10 , wherein the one or more coloring elements are one or more lanthanides with the atomic number or numbers in the range 58 to 70. 
     
     
         12 . The method according to  claim 10 , wherein at least one of the one or more coloring elements is an element selected from the group consisting of vanadium, manganese, iron, yttrium, and antimony. 
     
     
         13 . The method according to  claim 1 , wherein the melt includes potassium ions or sodium ions, or a mixture of potassium ions and sodium ions. 
     
     
         14 . The form body according to  claim 1 , wherein the form body or a blank from which the form body is manufactured, is prepared from a glass melt that includes the following components in percentage by weight: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   SiO 2   
                   50-80, 
                 
                     
                   a nucleating agent 
                   0.5-11,  
                 
                     
                   Al 2 O 3   
                    0-10, 
                 
                     
                   Li 2 O 
                   10-25, 
                 
                     
                   K 2 O 
                    0-13, 
                 
                     
                   Na 2 O 
                   0-1, 
                 
                     
                   ZrO 2   
                    8-12, 
                 
                     
                   CeO 2   
                    0-10, 
                 
                     
                   Tb 4 O 7   
                   0-8, 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         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, barium, and any combination thereof 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 , fluorides and any combination thereof 0-6, 
         optionally one or more oxides of the rare earth metals with the atomic numbers 57, 59-64,66-71, 0-5.