Method to increase the strength of a form body of a lithium silicate glass ceramic
AssigneeDENTSPLY SIRONA Inc.
InventorsStefan Fecher, Lothar Völkl
Life of this patent
Estimating the term…
Abstract
The invention relates to a method to derive 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.
Claims18
A method to increase the strength of a form body of lithiumlithiun silicate glass ceramic, or a part thereof comprising the steps of:
- preparing the form body from a glass melt which comprises at least the following as starting components:
- SiO2, Al2O3, Li2O, K2O, at least one nucleating agent and at least one stabilizer, wherein the stabilizer is ZrO2 in the range of 6 to 14% by weight of the starting components;
- forming a blank 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 TW1 for a time tW1, wherein 620° C.≤TW1≤800° C., and 1 minute≤tW1≤200 minutes to obtain a crystallization having metasilicate crystals, disilicate crystal, or a combination of metasilicate and disilicate crystals;
- providing a melt including 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, wherein the ions of greater diameter than lithium ions is selected from the group consisting of Na, K, Cs, Rb and combinations thereof ions;
- and wherein an aliquoted quantity of the first salt and the second salt is used for the melt;
- laying the form body in a first receptacle having perforations, and then
- (i) immersing the first receptacle with the form body in the melt or
- (ii) introducing the first receptacle with the form body into the salt and the salt is then melted or
- (iii) laying the first receptacle with the form body on the salt or the salt body and the salt is melted at the same time as immersion of the form body in the melt that is forming;
- annealing the at least a portion of the form body that is in contact with the melt for a time t at a temperature T where 620° C.≤T≤800° C. and 0.5 hours≤t≤10 hours;
- replacing lithium ions of the form blank with the ions of greater diameter than lithium ions selected from the group consisting of Na, K, Cs, Rb and combinations thereof ions to generate a surface compressive stress to a depth of at least 20 microns in the form body of lithium silicate glass ceramic through the replacement of lithium ions by the number of alkali metal ions of greater diameter, wherein the replaced lithium ions from the form blank are bound to the alkali metal phosphate salt to reduce the lithium ion content in the melt by precipitating lithium phosphate;
- and
- removing the melt from the at least a portion of the form body.
The method according to claim , further comprising the step of laying the form body on the salt before melting of the salt.
The method according to dawn 15, wherein after the first and/or second heat treatment step, the form body is prepared from the blank through grinding and/or milling or pressing, wherein the heat treatment step or steps is/are carried out during or after pressing.
Use of a capsule filled with at least one alkali metal salt to create a surface stress in a form body of a lithium silicate ceramic material through the replacement of lithium ions by a number of alkali metal ions of greater diameter than the lithium ions, in that the form body is covered by a salt of alkali metal phosphate ions and the number of alkali metals ions of greater diameter than the lithium ions melted in the capsule, wherein the number of alkali metal ions of greater diameter than lithium ions is selected from the group consisting of Na, K, Cs, Rb and combinations thereof ions and wherein:
- (i) the form body is prepared from a glass melt which comprises at least the following as starting components:
- SiO2, Al2O3, K2O, at least one nucleating agent and at least one stabilizer, wherein the stabilizer is ZrO2 in the range of 6 to 14% by weight of the starting components;
- (ii) the 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 TW1 for a time tW1, wherein 620° C.≤TW1≤800° C., and/or 1 minute≤tW1≤200 minutes;
- (iii) the lithium silicate glass ceramic blank is subjected, after the first heat treatment W1l, to a second heat treatment W2 at a temperature TW2 for a time tW2, wherein 800° C.≤TW2≤1040° C., and/or 2 minutes≤tW2≤200 minutes to obtain a crystallization having metasilicate crystals, disilicate crystal, or a combination of metasilicate and disilicate crystals;
- and
- (iv) lithium ions of the form blank are replaced with the number of alkali metal ions of greater dimeter than lithium ions is selected from the group consisting of Na, K, Cs, Rb and combinations thereof ions to generate a surface compressive stress to a depth of at least 10 microns in the form body of lithium silicate glass ceramic through the replacement of 5-20% by weight lithium ions through a depth of 10 microns by the number of alkali metal ions of greater diameter, wherein the replaced lithium ions from the form blank are bound to the alkali metal phosphate ions to reduce the lithium ion content in the melt by precipitating lithium phosphate.
Dependencies are inferred from the claim text.