Glass-ceramic

Abstract

A subject matter of the invention is a glass-ceramic sheet provided, on at least a portion of at least one of its faces, with a coating of thin layers comprising at least one thin functional layer composed of a metal based on niobium metal Nb, or of an oxide based on a niobium oxide NbO.sub.x in which x is at most 0.5, the or each thin functional layer being framed by at least two thin layers made of dielectric materials, the physical thickness of the thin functional layer or, if appropriate, the combined physical thickness of all the thin functional layers being within a range extending from 8 to 15 nm.

Claims

1. An oven, stove or fireplace door comprising a glass-ceramic sheet, comprising, on at least a portion of at least one of its faces, a coating of layers comprising at least one functional layer comprising a niobium metal Nb or a niobium oxide NbO.sub.x in which x is at most 0.5, the at least one functional layer being framed by at least two layers comprising at least one dielectric material, wherein a thickness of the functional layer or a combined thickness of all functional layers ranges from 8 to 15 nm, wherein the glass-ceramic sheet exhibits a light reflection factor of at most 15%, and a light transmission factor of at least 40%, within the meaning of the standard EN 410:1998.

2. The oven, stove or fireplace door of claim 1, wherein the at least one functional layer consists of a niobium metal.

3. The oven, stove or fireplace door of claim 1, wherein the coating comprises only one functional layer.

4. The oven, stove or fireplace door of claim 1, wherein the dielectric materials, which are identical or different, are chosen from oxides, nitrides or oxynitrides of silicon, aluminum, titanium, zirconium, tin, zinc or any one of their mixtures or solid solutions.

5. The oven, stove or fireplace door of claim 1, wherein the dielectric materials, which are identical or different, comprise silicon nitride, titanium oxide, titanium zirconium oxide, zinc tin oxide, titanium silicon nitride, silicon zirconium nitride or silicon oxide.

6. The oven, stove or fireplace door of claim 1, wherein a thickness of each layer of dielectric material ranges from 10 to 100 nm.

7. The oven, stove or fireplace door of claim 1, wherein a layer of blocker is located above and in contact with and/or below and in contact with the at least one functional layer.

8. The oven, stove or fireplace door of claim 7, wherein each layer of blocker consists of titanium.

9. The oven, stove or fireplace door of claim 7, wherein a thickness of each layer of blocker is at most 3 nm.

10. The oven, stove or fireplace door of claim 1, exhibiting a reflection of at least 50% for a wavelength of 3 micrometers.

11. The oven, stove or fireplace door of claim 1, wherein the glass-ceramic sheet is a lithium aluminosilicate glass-ceramic sheet and comprises crystals of -quartz structure.

12. The oven, stove or fireplace door of claim 11, wherein the glass-ceramic sheet has a chemical composition comprising the following constituents within the limits defined below, expressed as percentages by weight: SiO.sub.2 52-75%; Al.sub.2O.sub.3 18-27%; Li.sub.2O 2.5-5.5%; K.sub.2O 0-3%; Na.sub.2O 0-3%; ZnO 0-3.5%; MgO 0-3%; CaO 0-2.5%; BaO 0-3.5% SrO 0-2%; TiO.sub.2 1.2-5.5%; ZrO.sub.2 0-3%; and P.sub.2O.sub.5 0-8%.

Description

(1) The examples which follow illustrate the invention without limiting it.

(2) According to a first example (example 1), a stack composed of the following layers: a dielectric layer of silicon nitride (60 nm), then a titanium blocker (1 nm), then a functional niobium layer (10 nm), then a titanium blocker (1 nm) and finally a dielectric layer of silicon nitride (60 nm), was deposited on a clear glass-ceramic sold under the Keralite brand by the applicant company. The thicknesses are physical thicknesses. The glass-ceramic used is a glass-ceramic of the LAS type comprising crystals of -quartz structure and a vitreous phase as minor component.

(3) All the layers were deposited in a known way by DC magnetron cathode sputtering, the titanium and niobium layers being deposited from targets respectively of titanium and niobium under an argon plasma and the silicon nitride layers being deposited from targets of silicon (doped with 8 atom % of aluminum) under an atmosphere of argon and nitrogen.

(4) The light transmission factor obtained is 51.0% and the light reflection factor is only 3.4%. The reflection for a wavelength of 3 micrometers is greater than 50%.

(5) Example 2 differs from the first in that the physical thickness of the niobium layer is 13 nm. In this case, the light transmission factor is 44.0% and the light reflection factor is 4.2%. The reflection for a wavelength of 3 micrometers is also much greater than 50%.

(6) In the case of examples 1 and 2, the reflection at 3 micrometers is unchanged after a heat treatment at 550 C. for 60 h and no defect visible to the naked eye is observed.

(7) Example 3 differs from example 1 in that the blockers made of titanium are replaced by blockers made of alloy of nickel and chromium, which are also deposited by magnetron cathode sputtering.

(8) Example 4 differs from the above in that the blocker located above the niobium layer is dispensed with.

(9) Example 5 differs from example 1 in that the blocker located above the niobium layer is dispensed with.

(10) In the case of examples 3 to 5, the reflection at 3 micrometers is greater than 50% after deposition of the coating but falls to approximately 30% after a heat treatment at 550 C. These examples are thus less preferred and illustrate both the advantage of positioning a blocker on each side of the niobium layer and the superiority of the titanium.

(11) Examples 6 to 11 reproduce example 1, except that the dielectric materials and their thicknesses are different. In addition, the thickness of the niobium layer is 13 nm. Finally, these stacks do not comprise blockers. The materials tested are silicon and zirconium nitride, silicon oxide, titanium oxide, titanium zirconium oxide, zinc tin oxide and silicon nitride.

(12) The various tests carried out are collated in table 1 below, which shows the nature and the physical thickness of the dielectric layer located under the functional layer (known as dielectric 1), the nature and the physical thickness of the dielectric layer located on the functional layer (known as dielectric 2), the light transmission factor (known as LT), the light reflection factor (known as LR) and the reflection for a wavelength of 3 m. As in the whole of the text, the designation of the layers is not prejudicial to their exact stoichiometry and/or to the presence of minor elements, such as dopants.

(13) TABLE-US-00001 TABLE 1 R, 3 m Dielectric 1 Dielectric 2 LT (%) LR (%) (%) 6 .sup.SiZrN.sub.x (60 nm) .sup.SiZrN.sub.x (60 nm) 50 4 >50 7 .sup.SiO.sub.2 (85 nm) .sup.SiO.sub.2 (85 nm) 35 7 >50 8 TiO.sub.2 (50 nm) TiO.sub.2 (50 nm) 45 7 >50 9 TiZrO.sub.x (50 nm) TiZrO.sub.x (50 nm) 48 10 >50 10 SnZnO.sub.x (60 nm) SnZnO.sub.x (60 nm) 48 4 >50 11 Si.sub.3N.sub.4 (60 nm) SnZnO.sub.x (60 nm) 48 4 >50