Engineered high expansion glass-ceramics having near linear thermal strain and methods thereof
The present invention relates to glass-ceramic compositions, as well as methods for forming such composition. In particular, the compositions include various polymorphs of silica that provide beneficial thermal expansion characteristics (e.g., a near linear thermal strain). Also described are methods of forming such compositions, as well as connectors including hermetic seals containing such compositions.
1. A method comprising:
providing a glass-ceramic mixture configured to provide a glass-ceramic composition comprising of from about 65 wt. % to about 80 wt. % of SiO 2 ; from about 8 wt. % to about 16 wt. % of Li 2 O; from about 2 wt. % to about 8 wt. % of Al 2 O 3 ; from about 1 wt. % to about 8 wt. % of K 2 O; from about 1 wt. % to about 5 wt. % of P 2 O 5 ; from about 0.5 wt. % to about 7 wt. % of B 2 O 3 ; and from about 0.1 wt. % to about 5 wt. % of ZnO;
heating the mixture to a first temperature T 1 of from about 950° C. to about 1050° C.;
rapidly cooling at a rate r 2 greater than about 30° C./minute to a second temperature T 2 of from about 400° C. to about 750° C., thereby minimizing formation of a cristobalite SiO 2 phase within the mixture;
reheating the mixture to a third temperature T 3 of from about 750° C. to about 850° C., thereby facilitating formation of a quartz SiO 2 phase within the mixture; and
cooling the mixture to a fourth temperature T 4 of from about 10° C. to about 500° C., thereby forming a glass-ceramic composition.
2. The method of claim 1 , wherein the rate r 2 is of from about 40° C./minute to about 80° C./minute.
3. The method of claim 1 , further comprising dwelling at the first temperature T 1 for a first period P 1 configured to allow the mixture to flow and fill a cavity.
4. The method of claim 3 , wherein the first period P 1 is of from about 1 minute to about 30 minutes.
5. The method of claim 1 , further comprising dwelling at the second temperature T 2 for a second period P 2 configured to facilitate formation of the quartz SiO 2 phase.
6. The method of claim 5 , wherein the second period P 2 is of from about 1 minute to about 60 minutes.
7. The method of claim 1 , further comprising dwelling at the third temperature T 3 for a third period P 3 configured to facilitate formation of the cristobalite SiO 2 phase.
8. The method of claim 7 , wherein the third period P 3 is of from about 1 minute to about 60 minutes.
9. The method of claim 1 , wherein the glass-ceramic composition comprises of from about 5 wt. % to about 30 wt. % of SiO 2 as a cristobalite phase and about 5 wt. % to about 30 wt. % of SiO 2 as a quartz phase.
10. The method of claim 9 , wherein the ratio, by weight, of the cristobalite phase to the quartz phase is of from about 1:0.5 to about 1:2.
11. The method of claim 1 , wherein the glass-ceramic composition comprises a glass-ceramic preform or a glass-ceramic seal.
12. The method of claim 1 , wherein the heating step is conducted in the presence of a metal.
13. The method of claim 12 , wherein the glass-ceramic composition forms a seal with the metal.
14. The method of claim 13 , wherein the seal is a hermetic seal comprising:
a metal component; and
a glass-ceramic composition disposed on a surface of the metal component, the composition comprising:
from about 65 wt. % to about 80 wt. % of SiO 2 ;
from about 8 wt. % to about 16 wt. % of Li 2 O;
from about 2 wt. % to about 8 wt. % of Al 2 O 3 ;
from about 1 wt. % to about 8 wt. % of K 2 O;
from about 1 wt. % to about 5 wt. % of P 2 O 5 ;
from about 0.5 wt. % to about 7 wt. % of B 2 O 3 ; and
from about 0.1 wt. % to about 5 wt. % of ZnO;
wherein the composition further comprises of from about 5 wt. % to about 30 wt. % of SiO 2 as a cristobalite phase and about 5 wt. % to about 30 wt. % of SiO 2 as a quartz phase.
15. The method of claim 1 , wherein the glass-ceramic composition comprises:
from about 65 wt. % to about 80 wt. % of SiO 2 ;
from about 8 wt. % to about 16 wt. % of Li 2 O;
from about 2 wt. % to about 8 wt. % of Al 2 O 3 ;
from about 1 wt. % to about 8 wt. % of K 2 O;
from about 1 wt. % to about 5 wt. % of P 2 O 5 ;
from about 0.5 wt. % to about 7 wt. % of B 2 O 3 ; and
from about 0.1 wt. % to about 5 wt. % of ZnO;
wherein the composition further comprises of from about 5 wt. % to about 30 wt. % of SiO 2 as a cristobalite phase and about 5 wt. % to about 30 wt. % of SiO 2 as a quartz phase.
16. The method of claim 15 , wherein the ratio, by weight, of the cristobalite phase to the quartz phase is of from about 1:0.5 to about 1:2.
17. The method of claim 16 , wherein the quartz phase comprises α-quartz and/or β-quartz.
18. The method of claim 16 , wherein the cristobalite phase comprises α-cristobalite and/or β-cristobalite.
19. The method of claim 15 , wherein a combined weight percentage for both the cristobalite phase and the quartz phase is of from about 20 wt. % to about 40 wt. %.
20. The method of claim 19 , further comprising of from about 5 wt. % to about 30 wt. % of SiO 2 as an amorphous phase.