GLASS CERAMIC ARTICLE, METHOD FOR PRODUCING SAME, AND USE THEREOF

Abstract

Sheet-like glass ceramic article are provided that include surfaces with a thickness between the surfaces between 0.5 mm and 1.9 mm and a core. The articles have a first microstructure provided on each of the surfaces and have a second microstructure in the core with a second thickness (d.sub.2). The first microstructures extend inwardly from the surfaces towards the core and has a first thickness (d.sub.1). The first microstructure has a difference from the second microstructure selected from a group consisting of: a crystalline phase type, a crystalline phase amount, crystalline phase size distribution, crystalline phase orientation, crystalline phases composition, crystalline inclusion, an amorphous phase type, an amorphous phase percentage amount, an amorphous phase composition, and any combinations thereof. The difference results in a first coefficient of linear thermal expansion of the first microstructure that is smaller than a second coefficient of linear thermal expansion of the second microstructure.

Claims

1. A sheet-like glass ceramic article, comprising: surfaces with a thickness between the surfaces between 0.5 mm and 1.9 mm; a core located between the surfaces; a first microstructure provided on each of the surfaces, the first microstructure extending inwardly from the surfaces towards the core and has a first thickness (d.sub.1); and a second microstructure in the core with a second thickness (d.sub.2); wherein the first microstructure has a difference from the second microstructure selected from a group consisting of: a crystalline phase type, a crystalline phase amount, crystalline phase size distribution, crystalline phase orientation, crystalline phases composition, crystalline inclusion, an amorphous phase type, an amorphous phase percentage amount, an amorphous phase composition, and any combinations thereof, and wherein the difference results in a first coefficient of linear thermal expansion of the first microstructure that is smaller than a second coefficient of linear thermal expansion of the second microstructure.

2. The glass ceramic article of claim 1, further comprising an optical transmittance (τ.sub.vis) of at least 85% at a measurement thickness of 1 mm.

3. The glass ceramic article of claim 1, further comprising scattering, determined in transmission, that is not more than 3% at a glass measurement thickness of 1 mm.

4. The glass ceramic article of claim 1, further comprising a crack initiation load (CIL) between 0.5 N and 1.0 N.

5. The glass ceramic article of claim 4, wherein the crack initiation load (CIL) is determined at a glass measurement thickness of 1.9 mm.

6. The glass ceramic article of claim 1, wherein at least one of the surfaces is polished and has a roughness of not more than 0.2 nm (RMS, Ra).

7. The glass ceramic article of claim 1, wherein the glass ceramic article comprises a glass ceramic material with constituents, in wt %: TABLE-US-00005 Al.sub.2O.sub.3  18 to 23 Li.sub.2O 2.5 to 4.2 SiO.sub.2  60 to 69 ZnO   0 to 2 Na.sub.2O   0 to 1.5 K.sub.2O   0 to 1.5 Na.sub.2O + K.sub.2O 0.2 to 1.5 MgO   0 to 1.5 CaO + SrO + BaO   0 to 4 B.sub.2O.sub.3   0 to 2 TiO.sub.2   2 to 5 ZrO.sub.2 0.5 to 2.5 P.sub.2O.sub.5   0 to 3 R.sub.2O.sub.3   0 to 1, MnO.sub.2   0 to 0.3 Fe.sub.2O.sub.3   0 to 0.3 SnO.sub.2   0 to less than 0.6, and a total of TiO.sub.2 + ZrO.sub.2 + SnO.sub.2 that amounts to between 3.8 and 6 wt %, and wherein R = lanthanide.

8. The glass ceramic article of claim 7, wherein the lanthanide is Nd.

9. The glass ceramic article of claim 1, wherein the first microstructure comprises high-quartz solid solution as a first main crystal phase and/or wherein the second microstructure comprises keatite solid solution as a second main crystal phase

10. The glass ceramic article of claim 9, wherein the first main crystal phase has a crystallite size from 0.01 μm to 0.1 μm and/or the second main crystal phase has a crystallite size from 0.05 μm to 0.8 μm.

11. The glass ceramic article of claim 1, wherein the glass ceramic article comprises a glass ceramic material with constituents, in wt %: TABLE-US-00006 SiO.sub.2  45 to 62 Al.sub.2O.sub.3  20 to 40 MgO   5 to 16 Li.sub.2O 0.3 to 6 TiO.sub.2   0 to 10 MoO.sub.3   0 to 2 ZrO.sub.2   0 to 4 B2O.sub.3   0 to 1 P.sub.2O.sub.5   0 to 1 Nd.sub.2O.sub.5   0 to 0.2.

12. The glass ceramic article of claim 11, wherein the glass ceramic material further comprises a constituent selected from a group consisting of WO.sub.3, SnO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, As.sub.2O.sub.3, and any mixtures thereof.

13. The glass ceramic article of claim 11, wherein the glass ceramic material comprises: high-quartz solid solution as a main crystal phase with a crystal phase that is at least 45 vol % and at most 90 vol %; and a fraction of amorphous phase that is at least 10 vol % and at most 55 vol %, wherein the first microstructure has a higher lithium content than the second microstructure.

14. The glass ceramic article of claim 1, wherein the glass ceramic article comprises a glass ceramic material with constituents, in wt %: TABLE-US-00007 Al.sub.2O.sub.3 10 to 40 CaO + BaO + MgO  0 to 18 Na.sub.2O + K.sub.2O  5 to 40 SiO.sub.2 25 to 75 TiO.sub.2 less than 10 ZrO.sub.2 less than 10.

15. The glass ceramic article of claim 14, wherein the glass ceramic material comprises nepheline or a nepheline-like crystal phase as a main crystal phase, wherein the first microstructure has an increased potassium content compared to the second microstructure and/or the first microstructure has a crystal phase content that is different from that of the second microstructure.

16. The glass ceramic article of claim 1, wherein the glass ceramic article comprises a glass ceramic material with constituents, in wt %, on an oxide basis: TABLE-US-00008 Li.sub.2O  3.0 to 4.5 Na.sub.2O    0 to 1.5 K.sub.2O    0 to 1.5 Na.sub.2O + K.sub.2O  0.2 to 2.0 MgO    0 to 2.0 CaO    0 to 1.5 SrO    0 to 1.5 BaO    0 to 2.5 ZnO    0 to 2.5 B.sub.2O.sub.3    0 to 1.0 Al.sub.2O.sub.3   19 to 25 SiO.sub.2   55 to 69 TiO.sub.2  1.4 to 2.7 ZrO.sub.2  1.3 to 2.5 SnO.sub.2    0 to 0.4 SnO.sub.2 + TiO.sub.2 less than 2.7 P.sub.2O.sub.5    0 to 3.0 Nd.sub.2O.sub.3 0.001 to 0.4 CoO    0 to 0.005 Fe.sub.2O.sub.3 not more than 0.04 ZrO.sub.2 + 0.87(TiO.sub.2 + SnO.sub.2)  3.65 to 4.3.

17. The glass ceramic article of claim 16, wherein the glass ceramic material comprises: high-quartz solid solution as a main crystal phase with a crystal phase fraction that is at least 45 vol % and at most 90 vol %; and a fraction of amorphous phase of at least 10 vol % and at most 55 vol %, wherein the first microstructure has crystals that are oriented in a directional manner and the second microstructure has crystals that are oriented randomly.

18. The glass ceramic article of claim 1, wherein the glass ceramic article is configured for a use selected from a group consisting of: a protective glass for a mobile terminal, a cover sheet for an entertainment electronics device, a cover sheet for a display device, a cover sheet for a computer screen, a cover sheet for a measurement device, a cover sheet for a TV set, a cover sheet for a mobile device, a cover sheet for a mobile terminal, a cover sheet for a mobile data processing device, a cover sheet for a cell phone, a cover sheet for a mobile computer, a cover sheet for a palmtop, a cover sheet for a laptop, a cover sheet for a tablet computer, a cover sheet for a wearable computing device, a cover sheet for a watch, a cover sheet for a time measuring device, a protective glazing for a machine, a protective glazing for a high-speed train, a safety glazing for an automobile, a safety glazing for a diving watch, a safety glazing for a submarine, and a cover plate for an explosion-proof device.

19. A method for producing a glass ceramic article, comprising the steps of: providing a starting material comprising a ceramizable glass and/or a glass ceramic material; performing a thermal treatment to generate crystallization nuclei at a temperature T.sub.KB over a duration t.sub.KB; performing a thermal treatment for crystallizing a crystalline precursor phase at a temperature T.sub.KV over a duration t.sub.KV; performing a thermal treatment for crystallizing in keatite solid solution at a temperature T.sub.KK over a duration t.sub.KK; and determining the duration t.sub.KK based on a relative percentage expansion of the ceramizable glass and/or of the glass ceramic material; wherein the method further comprises a step selected from a group consisting of: determining the duration t.sub.KK as a time up to which a relative change in length of a sample of the glass ceramic material at a given temperature T.sub.KK assumes a maximum value, starting the duration t.sub.KK at a point in time at which the glass ceramic material has reached the maximum temperature T.sub.KK which is also isothermal from this point in time and ends at the point in time at which the relative change in length of the sample of the glass ceramic material has reached a maximum, starting the duration t.sub.KK a point in time at which the glass ceramic material has reached the maximum temperature T.sub.KK which is also isothermal from this point in time, determining an end of the thermal treatment duration t.sub.KK for a given temperature T.sub.KK from a curve of a percentage value of relative change in length of a sample of the glass ceramic material and two tangents to the curve, wherein one of the two tangents is applied to a linear part of a first or second slope of the curve, and the other of the two tangents is applied to a temporally subsequent plateau of the curve, and wherein the thermal treatment duration t.sub.KK ends in the middle of an interval which is spanned by the points at which the tangents just no longer touch the curve, as seen from higher temperatures; defining an end of the duration t.sub.KK as at a point in time defined by a point of intersection of tangents from a curve of a percentage value of relative change in length of a sample of the glass ceramic material; and any combinations thereof.

20. A method for producing a glass ceramic article, comprising: providing a starting material comprising a ceramizable glass and/or a glass ceramic material; performing a first thermal treatment to generate crystallization nuclei at a temperature in a range from 300 to 800° C. and over a duration of 10-300 min; performing a second thermal treatment for volume crystallization in a range from 500 to 1200° C. for a duration of 10-300 min; and cooling to room temperature at a cooling rate of 1 to 100 K/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] FIG. 1 is a schematic view, not drawn to scale, showing a section through a sheet-like glass ceramic article; and

[0118] FIG. 2 shows a scanning micrograph of an exemplary glass ceramic article, illustrating crack deflection.

DETAILED DESCRIPTION

[0119] FIG. 1 is a schematic view showing a section through a sheet-like glass ceramic article 1 according to embodiments.

[0120] According to the first aspect of the present disclosure, the glass ceramic article 1 may, for example, have a coefficient of thermal expansion a of less than 1.5*10.sup.−6/K, in the range from 20° C. to 700° C. A first microstructure 2 is provided on each of the surfaces 11, 12 of the article 1. This microstructure extends inwardly from the surface 11 or 12 towards the core 3 and has a thickness d.sub.1. The core 3 defines a second microstructure which has a thickness dz.

[0121] The first microstructure 2 differs from the second microstructure (or core) 3 by the type and/or the amount and/or the size distribution and/or the orientation and/or the composition of the crystalline phases and/or crystals included in the respective microstructure, and/or by the type and/or the percentage amount and/or the composition of an amorphous, for example glassy phase. As a result, there is a difference in the resulting coefficients of linear thermal expansion of the first microstructure 2 and the second microstructure 3, the coefficient of linear thermal expansion of the first microstructure 2 preferably being lower than the coefficient of linear thermal expansion of the second microstructure 3.

[0122] More generally, without being limited to a specific aspect of the present specification, the coefficient of thermal expansion of the first microstructure may be between −3*10.sup.−6/K and +3*10.sup.−6/K according to one embodiment. Furthermore, according to one embodiment, the coefficient of thermal expansion of the second microstructure may generally be between 1.5*10.sup.−6/K and 8*10.sup.−6/K, without being limited to a specific aspect of the present disclosure.

[0123] For a glass ceramic article according to the second aspect, for example, the coefficient of thermal expansion of the first microstructure may be designed to be greater than 0, for example about 1.13*10.sup.−6/K, and the coefficient of thermal expansion of the core or second microstructure may be about 2*10.sup.−6/K. The first microstructure may have a thickness of 70 μm, for example. However, it is also possible that the glass ceramic article according to the second aspect is designed such that the coefficient of thermal expansion is even below 0, for example about −0.023*10.sup.−6/K, and that the coefficient of thermal expansion of the core or second microstructure is about 2*10.sup.−6/K or more, for example 2.2*10.sup.−6/K. The thickness of the first microstructure may, for example, also be more than 70 μm, such as 130 μm. The coefficients of thermal expansion may again change in the glass ceramics or glass ceramic articles according to the second aspect, in particular in the first microstructure, when the ion exchange effect is taken into account. That is because the potassium ion that is diffusing in is larger than the exchanged sodium ion. However, these expansion coefficients are very difficult to measure. For example, compressive stresses may be greater than 70 MPa here, such as 74 MPa, or greater than 200 MPa, such as about 205 MPa for a thickness of about 1.9 mm, about 190 MPa for a thickness of 1 mm, about 160 MPa for a thickness of 0.5 mm. Depending on the exact composition, however, these values may also differ so that, for example, a compressive stress of about 73 MPa may result on the surface for a thickness of approximately 1.9 mm, about 73 MPa for a thickness of approximately 1 mm, about 66 MPa for a thickness of about 0.5 mm.

[0124] This must also be taken into account for the coefficients of thermal expansion of a glass ceramic article according to the third aspect. If the thermal expansion coefficients of surface layer 2 and of core 3 of the non-ion-exchanged glass ceramic article are given, the result is an expansion coefficient of about 11.9*10.sup.−6/K for the first microstructure 2 here, and of 10.5*10.sup.−6/K for the second microstructure 3. However, this will be different in the ion-exchanged state, and furthermore, with the resulting compressive stress caused by the ion exchange, there will be no tensile stress resulting on the surface in this case either, but rather a compressive stress. Therefore, to be more correct, the coefficient of thermal expansion would have to be replaced here by a “chemical expansion coefficient” which, however, cannot be determined metrologically or only with difficulty, as already mentioned above. The first microstructure 2 may have a thickness of more than 10 μm, for example, depending on the precise conditions of the ion exchange, for example 18 μm Greater thicknesses are also conceivable and possible.

[0125] For a glass ceramic article according to the fourth aspect, for example, a resulting coefficient of thermal expansion of approximately −1.67*10.sup.−6/K can be obtained in a direction perpendicular to the surface, for example, and of 0.33*10.sup.−6/K in the direction parallel to the surface, by the targeted directional crystallization in a near-surface area, that is in the first microstructure 2, which may have a thickness of about 20 μm, for example, in particular for a lithium-rich high-quartz solid solution as the crystal phase. In the bulk, a coefficient of thermal expansion of about 0.34*10.sup.−6/K is resulting in this case. In this way, the compressive stress on the surface can be adjusted to be up to 205 MPa or even more, for example. However, depending on the precise implementation, other values are also possible here, which may also vary with the thickness of the glass ceramic article 1. For example, a compressive stress of approximately 90 MPa may result on the surface for a thickness of about 1.9 mm, approximately 88 MPa for a thickness of about 1 mm, and approximately 85 MPa for a thickness of 0.5 mm.

[0126] FIG. 2 shows a scanning micrograph of an exemplary glass ceramic article, illustrating crack deflection. This was obtained for a glass ceramic article with a composition according to the first aspect here, but with a greater thickness. As can be seen, the crack does not extend across the glass ceramic, but is deflected. As mentioned above, this highly advantageous microstructure was surprisingly also obtained for glass ceramics or glass ceramic articles of a different thickness and optionally different composition.

LIST OF REFERENCE NUMERALS

[0127] 1 Sheet-like glass ceramic article [0128] 11 Upper surface of glass ceramic article [0129] 12 Lower surface of glass ceramic article [0130] 2 First microstructure [0131] 3 Core, second microstructure