B-spodumene glass-ceramic materials and process for making the same

Abstract

The present invention relates to glass-ceramic materials, processes for making the same and articles comprising the same. The glass-ceramic material has a composition, by weight of the total composition, comprising 55-68% SiO2; 18-24% Al2O3; 3.3-4.1% Li2O; 1.5-4.0% ZnO; 1.5-5.0% MgO; 2-5% TiO2; 0-2% ZrO2; 0-5% B2O3; 0-8% P2O5; 0-2% Na2O, 0-2% K2O; and at least one component resulting from an effective amount of at least one fining agent; wherein: the total of B2O3 and P2O5 is at least 1.5% by weight, the total of MgO and ZnO is at least about 3.5% by weight, the total of Na2O and K2O is less than about 3.0% by weight, the total of P2O5, B2O3, Na2O and K2O is less than about 11% by weight, the weight ratio of the sum total of Na2O+K2O to the sum total of P2O5+B2O3

Description

Claims

1. A glass-ceramic material having β-spodumene solid solution as the predominant crystalline phase, a CTE from about 25 to about 700° C. of about 10-30×10−7/° C., and a composition, by weight of the total composition, comprising: 55-68% SiO2; 18-24% Al2O3; 3.3-4.1% Li2O; 1.5-4.0% ZnO; 1.5-5.0% MgO; 2-5% TiO2; 0-2% ZrO2; 0-5% B2O3; 0-8% P2O5; 0-2% Na2O, 0-2% K2O; and components resulting from effective amount of at least one fining agent, wherein: the total of B2O3 and P2O5 is at least 1.5% by weight, the total of MgO and ZnO is at least about 3.5% by weight, the total of Na2O and K2O is less than about 3.0% by weight, the total of P2O5, B2O3, Na2O and K2O is less than about 11% by weight, the weight ratio of the sum total of Na2O+K2O to the sum total of P2O5+B2O3

2. A glass-ceramic material according to claim 1 having a composition wherein the total of P2O5, B2O3, Na2O and K2O is less than about 9% by weight and the total of Na2O and K2O is less than about 2% by weight.

3. A glass-ceramic material according to claim 1 having a composition wherein the total of P2O5, B2O3, Na2O and K2O is less than about 7% by weight and the total of Na2O and K2O is less than about 1% by weight.

4. A glass-ceramic material according to claim 1 comprising 0.3-1.2% SnO2 and 0-1% CeO2 as fining agent and essentially free of As2O3 and Sb2O3.

5. A glass-ceramic material according to claim 1, which is opaque and essentially white.

6. A glass-ceramic material according to claim 1, comprising a total of P2O5 and B2O3 higher than or equal to about 2% by weight.

7. A glass-ceramic material according to claim 1, comprising Fe2O3 in the amounts of less than about 900 ppm by weight, advantageously less than about 500 ppm.

8. A glass-ceramic material according to claim 1, comprising more than 85% of β-spodumene and β-quartz solid solutions among all the crystalline phases.

9. A glass-ceramic material according to claim 1, comprising about 3.5-4.1% by weight of Li2O.

10. A glass-ceramic article made of glass-ceramic material according to claim 1.

11. A glass-ceramic article according to claim 10 which is a cooktop plate or a cook utensil.

12. A glass-ceramic article according to claim 11 which is essentially free of As2O3 and Sb2O3.

13. A process for making a glass-ceramic article, comprising the following steps: (i) mixing raw materials in amounts such that upon melting thereof a glass is produced of a composition by weight of the total glass composition, comprising 55-66% SiO2; 18-22% Al2O3; 3.5-4.1% Li2O; 1.8-3.2% ZnO; 1.5-3.0% MgO; 2-5% TiO2; 0-2% ZrO2; 0-4% B2O3; 0-8% P2O5; 0-2% Na2O, 0-2% K2O; and at least one fining agent; wherein: the total of B2O3 and P2O5 is at least 1.5% by weight, the total of MgO and ZnO is at least about 3.5% by weight, the total of Na2O and K2O is less than about 3.0% by weight, the total of P2O5, B2O3, Na2O and K2O is less than about 11% by weight, the weight ratio of the sum total of Na2O+K2O to the sum total of P2O5+B2O3

14. A process according to claim 13, wherein in step (i), the amount of the raw materials is chosen such that upon melting, the composition of the glass has a total of P2O5, B2O3, Na2O and K2O less than about 9% by weight and a total of Na2O ad K2O less than about 2% by weight.

15. A process according to claim 13, wherein in step (i), the amount of the raw materials is chosen such that upon melting, the composition of the glass has a total of P2O5, B2O3, Na2O and K2O less than about 7% by weight and a total of Na2O ad K2O less than about 1% by weight.

16. A process according to claim 13, wherein in step (ii), the mixture of the raw materials is melted at a temperature up to about 1550° C.

17. A process according to claim 13, wherein in step (i), the raw materials mixed are such that the final melted glass comprises about 0.3-1.2% by weight of SnO2 and 0-1% CeO2 of the final total composition of the melted glass, and essentially free of As2O3 and Sb2O3.

18. A process according to claim 13, wherein in step (i), the raw materials mixed are such that the melted glass comprises a total of B2O3 and P2O5 of higher than or equal to about 2% by weight of the final total composition.

19. A process according to claim 13, wherein in step (v), the temperature Tc is between about 930-1050° C.

20. A process according to claim 13, wherein the duration of step (vi) is less than 1 hour.

21. A process according to claim 13, wherein the total of duration of steps (iv), (v) and (vi) is shorter than 2 hours, advantageously shorter than 90 minutes.