Lithium silicate glass ceramic and lithium silicate glass comprising a pentavalent metal oxide
Lithium silicate glass ceramics and glasses containing specific oxides of pentavalent elements are described which crystallize at low temperatures and are suitable in particular as dental materials.
1. Lithium silicate glass ceramic, which comprises a pentavalent metal oxide selected from Nb 2 O 5 , Ta 2 O 5 and mixtures thereof and comprises less than 2.0 wt.-% K 2 O and which has lithium metasilicate as main crystal phase.
2. Glass ceramic according to claim 1 , wherein lithium silicate glass ceramic is excluded which comprises at least 6.1 wt.-% ZrO 2 .
3. Glass ceramic according to claim 1 , wherein glass ceramic is excluded which comprises at least 8.5 wt.-% transition metal oxide selected from the group consisting of oxides of yttrium, oxides of transition metals with an atomic number from 41 to 79 and mixtures of these oxides.
4. Glass ceramic according to claim 1 , which comprises less than 1.0 wt.-% K 2 O.
5. Glass ceramic according to claim 1 , which comprises less than 1.0 wt.-% Na 2 O.
6. Glass ceramic according to claim 1 , which comprises at least 2.0 wt.-% Nb 2 O 5 or Ta 2 O 5 .
7. Glass ceramic according to claim 1 , which comprises less than 0.1 wt.-% La 2 O 3 .
8. Glass ceramic according to claim 1 , which comprises the pentavalent metal oxide or mixtures thereof in an amount of from 0.1 to 8.2 wt.-%.
9. Glass ceramic according to claim 1 , which comprises 60.0 to 85.0 wt.-% SiO 2 .
10. Glass ceramic according to claim 1 , which comprises 11.0 to 21.0 wt.-% Li 2 O.
11. Glass ceramic according to claim 1 , which comprises 0 to 10.0 wt.-% P 2 O 5 .
12. Glass ceramic according to claim 1 , which comprises at least one of the following components:
Component
wt.-%
SiO 2
66.0 to 77.0
Li 2 O
12.0 to 20.0
pentavalent metal
2.0 to 8.5
oxide or mixtures
P 2 O 5
0 to 7.0
Al 2 O 3
0 to 6.0.
13. Lithium silicate glass ceramic according to claim 1 , which comprises SiO 2 and Li 2 O in a molar ratio of from 1.7 to 3.1.
14. Lithium silicate glass ceramic according to claim 1 , which comprises less than 0.5 wt.-% CaO.
15. Lithium silicate glass ceramic according to claim 1 , which comprises less than 0.5 wt.-% B 2 O 3 .
16. Glass ceramic according to claim 1 , wherein the glass ceramic is present in the form of a powder, a granular material, a blank or a dental restoration.
17. Glass ceramic according to claim 1 , which has lithium metasilicate as a main crystal phase and has more than 5 vol.-%, lithium metasilicate crystals.
18. Lithium silicate glass with nuclei which are suitable for forming lithium metasilicate crystals as main crystal phase, wherein the glass comprises the components of the glass ceramic according to claim 1 .
19. Glass according to claim 18 , wherein the glass is present in the form of a powder, a granular material, a blank or a dental restoration.
20. Process for the preparation of the glass ceramic according to claim 1 , wherein a starting glass or a glass with nuclei is subjected to at least one heat treatment in the range of from 450 to 950° C.
21. Process for the preparation of a lithium silicate glass ceramic which comprises a pentavalent metal oxide selected from Nb 2 O 5 , Ta 2 O 5 and mixtures thereof and comprises less than 2.0 wt.-% K 2 O, wherein
(a) a starting glass is subjected to a heat treatment at a temperature of from 480 to 500° C. in order to form a glass with nuclei, and
(b) the glass with nuclei is subjected to a heat treatment at a temperature of from 650 to 750° C. in order to form the glass ceramic with lithium disilicate as main crystal phase.
22. Process according to claim 21 , wherein the glass ceramic has more than 10 vol.-% lithium disilicate crystals.
23. Process according to claim 21 , wherein the glass ceramic has a fracture toughness, measured as K IC value, of at least 1.6 MPa·m 0.5 .
24. Process of using the glass ceramic according to claim 1 as dental material for the preparation of dental restorations.
25. Process of preparing the dental restorations according to claim 24 , wherein the glass ceramic is shaped by pressing or machining to the desired dental restoration.
26. Process for the preparation of the glass according to claim 18 , wherein a starting glass is subjected to at least one heat treatment in the range of from 450 to 950° C.
27. Process of using the glass according to claim 18 as dental material for the preparation of dental restorations.
28. Process of preparing the dental restorations according to claim 27 , wherein the glass is shaped by pressing or machining to the desired dental restoration.