Method to increase the strength of a form body of lithium silicate glass ceramic
The invention relates to a method to produce 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 method to increase the strength of a medical form body of lithium silicate glass ceramic comprising the steps of:
preparing the form body or a blank from a glass melt that includes 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;
forming the blank from the glass melt during the course of 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/or 1 minute≤t W1 ≤200 minutes;
mixing a viscous solution or dispersion of a salt that includes alkali metal ions with at least one substance selected from the group consisting of 1,4-butanediol, hexanetriol, and a mixture of the two substances to form the paste;
coating at least a portion of the form body with the paste having one or more alkali metals, wherein the at least portion of the form body is in contact with the paste for a time t where t>5 minutes at a temperature T where T≥300° C. so that a surface compressive stress is created in the form body of lithium silicate glass ceramic through the replacement of lithium ions by alkali metal ions of greater diameter; and
removing the paste from the form body;
wherein alkali metal ions are selected from the group consisting of Na, K, Cs, Rb ions and combinations thereof to generate the surface compressive stress.
2. The method according to claim 1 , wherein the coating step, the paste is applied to the form body by spraying on to the form body.
3. The method according to claim 1 , wherein the coating step, the paste is applied to all surfaces of the form body with a thickness D of not less than 0.5 mm.
4. The method according to claim 1 , wherein the paste includes potassium ions, sodium ions or a combination of both potassium ions and sodium ions.
5. The method according to claim 1 , wherein the glass melt further includes at least one coloring metal oxide.
6. The method according to claim 1 , wherein the step of forming the form body or a blank from the glass melt includes the following components in percentage by weight:
SiO 2
50-80,
at least one 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
0-20,
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, 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.
7. The method according to claim 1 , wherein the glass melt includes the following as starting 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.
8. The method according to claim 1 , wherein the forming step, the first heat treatment W1 is carried out in two steps, wherein in particular in a first step a temperature T St1 is set where 630° C.≤T St1 ≤690° C. and/or in a second step a temperature T St2 where 720° C.≤T St2 ≤780° C. and/or a heating rate A St1 up to the temperature T St1 is 1.5 K/minute≤A St1 ≤2.5 K/minute and/or a heating rate A St2 up to the temperature T St2 is 8 K/minute≤T St2 ≤12 K/minute.
9. The method according to claim 1 , wherein the forming step, the lithium silicate glass ceramic blank is subjected, after the first heat treatment W1, to a second heat treatment W2 at a temperature T W2 for a time t W2 , wherein 800° C.≤T W2 ≤1040° C., and/or 2 minutes≤t W2 ≤200 minutes.
10. The method according to claim 1 , wherein the forming step, after the first 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.
11. Use of a paste containing at least one alkali metal salt for coating a form body of lithium silicate glass ceramic material, according to claim 1 .