WO2014132122A2

WO2014132122A2 - Non-opaque arsenic-free beta-spodumene glass ceramic exhibiting brown-grey coloration

Info

Publication number: WO2014132122A2
Application number: PCT/IB2014/000228
Authority: WO
Inventors: Marie Jacqueline Monique Comte; Philippe Lehuede
Original assignee: Eurokera
Priority date: 2013-02-28
Filing date: 2014-02-28
Publication date: 2014-09-04
Also published as: CN105143126A; JP2016516650A; JP6325005B2; KR102143194B1; EP2961703B1; CN105143126B; KR20150123884A; WO2014132122A3; ES2942635T3; EP2961703A2

Abstract

Methods, compositions, and articles provide for LAS-type glass-ceramics having specific thermo-mechanical, optical and coloration characteristics to yield generally brown-grey products. The glass-ceramic materials may include as colorants iron oxide, vanadium oxide, chromium oxide, cobalt oxide, nickel oxide and/or cerium oxide.

Description

NON-OPAQUE ARSENIC-FREE BETA-SPODUMENE

GLASS CERAMIC EXHIBITING BROWN-GREY COLORATION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Application Serial No. 61/770,499 filed on February 28, 2013, the entire content of which is hereby incorporated by reference.

BACKGROUND

[0002] The present disclosure relates to glass-ceramics of the lithium aluminosilicate (LAS) type, having a generally brown- grey color and containing a solid solution of beta-spodumene as the predominant crystalline phase. The disclosure also relates to articles made from such glass-ceramics, precursor glasses for such glass-ceramics, and methods for obtaining such glass-ceramics and related articles.

SUMMARY

[0003] One of the desirable properties of glass-ceramic materials is their thermo-mechanical ability to sustain repeated and rapid temperature changes up to very high

temperatures, which can be as high as. 600-800°C. Although originally developed for other purposes, LAS type glass- ceramics have become the material of choice for certain products in the domestic market, such as glass-ceramic

cooktops . The thermo-mechanical properties of LAS type glass ceramics dovetail nicely with the use of this material in cooktop applications. [0004] Many such cooktops employ radiant elements or other heating elements beneath a top surface of the glass-ceramic. Consequently, to be effective, the glass-ceramic material should exhibit the additional properties of: good

transmission efficiency in the visible and infrared spectrums, very low coefficient of thermal expansion (CTE), and

optionally particular coloration properties in reflection

(defined by the parameters L*, a* and b*) .

[0005] Thus, properties of a viable glass-ceramic material for use in the domestic market, such as for cooktops, involve aesthetic considerations. Although aesthetics are often dismissed as unimportant by some, such considerations are as important as performance characteristics so far as

marketability is concerned. For example, in the domestic market, the color of a glass-ceramic material may be the deciding factor as to whether a product is commercially sustainable.

[0006] In terms of aesthetic considerations, specifically color, the state of the cooktop art offers three options:

transparent black glass-ceramic (with lightness, L*, below 25), white glass-ceramic (with lightness L* higher than 60), and non-colored transparent glass-ceramic with an opaque decorative layer on a backside thereof to provide a desirable color and/or to obscure internal components, such as

electrical components, beneath the cooktop. Notably, however, until now there have been no commercial products exhibiting a generally brown-grey coloration with a range of lightness L* between about 25 to 45, good^" transmission efficiency in the visible and infrared spectrums, and a very low coefficient of thermal expansion (CTE) . [0007] It is noted that although cooktops are one use for the one or more glass-ceramic embodiments disclosed herein, the contemplated applications may extend to other areas, including cookware, pots, pans, etc.,, as well as to packaging for consumer electronics, for example.

[0008] Accordingly, there are needs in the art for new methods and apparatus for providing glass-ceramic of desirable

aesthetic and performance characteristics;

BRIEF DESCRIPTION OF THE FIGURES

[0009] For the purposes of illustration, there are forms shown in the drawings that are presently preferred, it being

understood, however, that the embodiments disclosed and described herein are not limited to the^' precise arrangements and instrumentalities shown.

[0010] FIG. 1 is a table of compositions suitable for use as a glass precursor, and/or a glass-ceramic material, in accordance with one or more embodiments described and/or disclosed herein;

[0011] FIG. 2 is a table of^' characteristics of glass-ceramic materials produced using a glass ceramming process of the precursor glass compositions of FIG. 1 in accordance with one or more embodiments described and/or disclosed herein;

[0012] FIG. 3 is a chart illustrating the relationship between lightness L* of the glass ceramic materials produced and the specific maximum ceramming temperature employed in forming same in accordance with one or more embodiments described and/or disclosed herein; [0013] FIG. 4 is a chart illustrating the relationship between the blue-yellow hue and the green-red hue in glass ceramic materials as a function of the quantities of iron oxide

(Fe203) and chromium oxide (Cr203) in accordance with one or more embodiments described and/or disclosed herein;

[0014] FIG. 5 is a table of compositions used for purposes of comparison with one or more embodiments herein; and

[0015] FIG. 6 is a table of characteristics of glass-ceramic materials produced using the compositions of FIG. 5 after a ceramming process of the precursor glasses.

DETAILED DESCRIPTION General Considerations

[0016] While the production of glass . ceramics has-been carried out for many years, the engineering parameters for producing a generally brown-grey glass ceramic of specific . lightness , L*, transmission, and coefficient of thermal expansion (CTE) have until now been elusive in the art. In this regard, a

discussion is provided herein of the requisite processes, compositions, and/or other parameters for producing the aforementioned glass-ceramics.

[0017] A glass-ceramic is a polycrystalline material produced via a ceramming process (i.e., a controlled rather than spontaneous crystallization) of a precursor glass. The general process for producing a glass-ceramic material

involves three basic steps: (i) forming a precursor glass via appropriate melting (and fining) processes; (ii) cooling and shaping the precursor glass into a desired form; and (iii) ceramming (heat treatment) , wherein the precursor glass partly crystallizes and forms a glass-ceramic.

Glass-Ceramic System

[0018] A wide variety of glass-ceramic systems exists, e.g., the Li20 x A1203 x nSi02-System (LAS system), the MgO x A1203 x nSi02-System (MAS system) , and the ZnO x A1203 x nSi02- System (ZAS system), to name a few.

[0019] The desired system in connection with the embodiments disclosed herein is the Li20 x A1203 x nSi02-System (LAS system) . The LAS system mainly refers to a mix of lithium oxide, aluminum oxide, and silicon oxide with additional components, e.g., glass-phase forming agents such as Zr02, Ti02, MgO, ZnO, BaO, SrO, CaO, K20, Na20, P205, B203, V205, Fe203, Cr203, CoO, NiO, Ce02, and/or Sn02^'.

[0020] In most cases, nucleation agents and fining agents are added to the precursor glass composition. Nucleation agents aid and control the crystallization process and the fining agents are employed to remove gas bubbles from the glass melt. By way of example, one or more embodiments herein may employ Zr02 and/or Ti02 as nucleation agents in the precursor glass process.

[0021] Many conventional precursor glass compositions may employ arsenic oxide (As203) and/or antimony oxide (Sb203) as fining agents during the step of melting a vitrifiable load of raw materials into a precursor glass. In connection with the protection of the environment, it is desired to avoid the use of As203 and Sb203, which are highly toxic compounds. Some prior work has been done in connection with producing glass- ceramic without arsenic and/or antimony in the composition, at processing temperatures, times, atmospheres, etc., suitable to achieve desirable transmission, lightness, CTE, etc. However, one skilled in the art will learn from the disclosure herein that one cannot indiscriminately substitute fining agents and expect that the coloration of the resultant glass-ceramic will not be affected. Indeed, significant care must be taken as to process parameters and compositions in order to arrive at a desired brown-grey coloration.

[0022] By way of example, one or more embodiments herein may employ tin oxide (Sn02) as a fining agent in the precursor glass process. Tin oxide is a more powerful reducing agent than alternatives such as arsenic trioxide and antimony trioxide, and therefore its influence on the coloration and optical transmission properties of the glass-ceramic is different from that of the other compounds. Indeed, although Sn02 may have an initial function as a fining agent, the presence of the compound may indirectly affect coloring and light transmission of the glass-ceramic by reducing colorants such as vanadium oxide (V205) and iron oxide (Fe203) present during ceramming. The effects of V205 and Fe203 on coloration will be discussed in more detail later herein.

[0023] After crystallization, the dominant crystal-phase in LAS type glass-ceramic is a high-quartz solid solution, and when the glass-ceramic is subjected to a more intense heat treatment, the high-quartz solid solution transforms into a keatite-solid solution (which is sometimes called beta- spodumene) . This transition is non-reversible and

reconstructive, which means that bonds in the crystal-lattice are broken and new bonds are arranged. [0024] In an LAS type glass-ceramic, it is possible to adjust the CTE over a wide range by adjusting the initial glass composition, the nature and amount of the crystalline phases and the amount and composition of the residual glass. For purposes of one or more embodiments herein, a low or even zero CTE is desired, which may be obtained by controlling the ceramming heat treatment process to balance the negative and positive CTE contributions of the dominant crystalline phase of the LAS glass-ceramic and residual glass phase (s) . Once again, however, one cannot indiscriminately adjust the

ceramming temperatures to account for desired CTE without considering the effect that such may have on the coloration of the resultant glass-ceramic. Indeed, it has been discovered that the ceramming temperatures have a significant effect on the lightness, L*., and the color of the resultant glass- ceramic.

[0025] In view of the foregoing, various embodiments have been discovered that provide for glass-ceramics, free of arsenic and/or of antimony, having very desirable integrated visible transmission, optical transmission, infra-red transmission, coefficient of thermal expansion, lightness, and coloration.

EXPERIMENTS

[0026] In connection with the development of the embodiments herein, a number of experiments were conducted on numerous samples of material. In particular, a number of glass samples of varying composition were subject to ceramming at different temperatures in order to evaluate the aforementioned

characteristics. Glass Compositions

[ 0027 ] The specific glass compositions utilized to produce the precursor glasses, and/or glass-ceramic materials of the examples herein are listed in the table shown in FIG. 1. The compositions all belong to the LAS system with the . following preferred composition ranges (in weight %) : 60-72% Si02, 18- 23% A1203, 2.5-4.5% Li20, 0-2.5% Zr02, 1.5-4% Ti02, 0-3% MgO, 0-3% ZnO, 0-5% BaO, 0-5% SrO (with 0 < BaO+SrO < 5), 0-2% CaO, 0-1.5% K20, 0-1.5% Na20 (optionally with 0 < CaO+K20+Na20 < 1.5 or 1.25 or 1.0), 0-5% P205, 0-2% B203, 0-0.3% V205, 0.1- 0.4% Fe203, 0.01-0.04% Cr203, 0-0.05% CoO, 0-0.3% NiO, 0-0.2% Ce02, and/or 0-0.6% Sn02.

[ 0028 ] The Zr02 and Ti02 components are used for. nucleation, and the Sn02 is used as a fining component.

[ 0029] The V205, Fe203, Cr203, CoO, NiO, and/or Ce02 are used for coloring. Fe203 and Cr203 were specifically chosen to develop a brown-grey coloration after ceramming.

[ 0030] Notably, the compositions of FIG. 1 contain Sn02 as a fining agent. The amount of Sn02 present may be significant in order to achieve the desired fining functionality; however, any devitrification should be. minimized or even avoided and the influence of the Sn02 on the integrated optical

transmission should be controlled. Indeed, Sn02 is capable of reducing the vanadium oxide and the iron oxide present during ceramming, although due to the high raw material cost for Sn02, its use is advantageously minimized. A Sn0₂ content of up to about 0.6%, e.g., from about 0.1% to 0.4% by weight may be used. Preferably, the embodiments herein contain one of: (i) from about 0.1% to about 0.3% by weight of Sn02; (ii) from about 0.2% to about 0.3% by weight of Sn02; and (iii) about- 0.2% to about 0.4% by weight.

[0031] Accordingly, the disclosed glass-ceramics contain neither As203 nor Sb203 in any significant amount (i.e., they may contain only traces of one and/or the other of these toxic compounds) . If traces of one or the other are present, then such may likely be quantified as As203 + Sb203 is less than about 1000 ppm, preferably less than 500 ppm.

Processing Conditions

[0032] Each of the samples was subject to the following basic process. First the raw materials were melted by preheating in a furnace at 1550°C, followed by heating for 30 minutes at 1550°C, heating for 60 minutes from 1550°C to 1650°C, and heating for 360 minutes at 1650°C. Next, the glass was rolled to a thickness of between about 4-6 mm, and then annealed, at 650°C for about 1 hour.

[0033] Finally, the samples were cerammed in a static furnace in accordance with the following cycle: (i) rapid heating from room temperature to about 655°C for about 20 to 40 minutes; (ii) nucleation from about 650°C to about 820°C for about 15 to 30 minutes; (iii) heating from about 820°C to the maximum ceramming temperature for about 10 to 20 minutes

(notably, the maximum ceramming temperature can vary from about 950°C to about 1060°C); (iv) crystallization at the maximum ceramming temperature for about 5 to 15 minutes; and (v) rapid cooling from about 20 to 40 minutes to room

temperature . [0034] By way of further specifics, the thermal cycle may be :■ (i) rapid heating from room temperature to about 655°C for about 25 minutes; (ii) heating from about 650°C to about 820°C for about 24 minutes; (iii) heating from about 820°C to the maximum ceramming temperature for about 12 to 15 minutes; (iv) crystallization at the maximum ceramming temperature for about 8 minutes; (v) rapid cooling down to about 900°C for about 5 minutes; and (vi) rapid cooling (from about 20 to 40) minutes to room temperature .

Experimental Results

[0035] FIG. 2 is a table showing certain characteristics of each glass-ceramic sample as well as the associated maximum ceramming temperature. Notably, the maximum ceramming

temperature varied between about 1025-1040°C. Given the glass composition system discussed above, and given that the

ceramming treatment used thermal cycles higher than 950°C, the resulting material of all the samples presented a

crystallographic structure that was mainly composed of beta- spodumene glass-ceramic.

Coefficient of Thermal Expansion

[0036] As noted above, one of the desired characteristics of the glass-ceramic is a coefficient of thermal expansion (CTE) of lower than about 15xlO-7/°C (measured between about 20°C to about 700°C) . As shown in FIG. 2, the achieved CTE was indeed less than about 15xlO-7/°C. Such a CTE, however, is higher than for beta-quartz glass ceramic material (which is

generally obtained using lower ceramming temperatures) . In general, beta-quartz glass ceramic material exhibits a CTE close to zero. It has been discovered that in order to obtain a CTE of less than about 15xlO-7/°C, or less than about 11x10- 7/°C, in a beta-spodumene glass-ceramic, it is preferable to limit the content of the Na20, K20 and/or CaO as evidenced by comparing Examples 2 and 6.

Lightness L*

[0037] Additionally and/or alternatively, another of the desired characteristics of the glass-ceramic is a lightness L* between about 20-40. By way of example, the lightness L* may be measured in reflection using a white background with illuminant D65 at 10° observer conditions. As illustrated in FIG. 3, it has been discovered that the glass-ceramic

materials formed from the glass compositions of FIG. 1 will exhibit a lightness L* that varies as a function of ceramming temperature. Indeed, as shown in FIG. 3, Example 1 (labeled "1") shows that if the ceramming temperature is varied between about 950°C to about 1060°C, the lightness L* values will vary from about 20 to about 45. The relationship between lightness L* and ceramming temperature is also exhibited in Examples 2 and 3 in FIG. 3. The increasing value of the lightness L* is caused by a resultant increase of the diffusion back- scattering of the light by the material arising from the increase of the ceramming temperature. Thus, using a

ceramming temperature of less than about 950°C produces a glass-ceramic material with a lightness L* of less than 20 and using a ceramming temperature of greater than 1060°C produces a glass-ceramic that is too opaque, having a lightness of greater than 45. Light Transmission Characteristics

[0038] Additionally and/or alternatively, other

characteristics of the glass-ceramics are related to certain light transmission characteristics, which may be quantified, for example, using the known illuminant D65, 2° observer test on, for example, 4-5.5 mm thick samples. Such transmission^' characteristics include integrated visible transmission (Tl), which may be measured between about 380-780 nm; optical transmission measured at about 625 nm; optical transmission measured at about 950 nm; and/or infra-red optical

transmission, which may be measured at about 1600 nm.

[0039] By way of example, the integrated visible transmission (Tl) may be one of: (i) between about 0.3% to about 6%; (ii) between about 0.4% to about 5%; (iii) between about 0.5% to about 5%; (iv) between about 0.6% to about 4%; (v) between about 0.7% to about 3%; and (vi) between about 0.8% to about 2%. Notably, the range of 0.8% to about 2% is preferred when, for example, one wishes to permit an observer to see with some level of clarity, for example, heating elements glowing below a radiant cooktop without being distracted or overwhelmed by them. Indeed, in some embodiments it may be desirable to permit some level of light transmission for seeing through the glass-ceramic, but not too much light transmission, e.g., providing limited clarity of vision at items behind the glass- ceramic.

[0040] It has been discovered that V205, Fe203, CoO, Cr203, NiO and Ce02 may be used to tune the characteristic of the integrated visible transmission (Tl) of the glass-ceramic material. It is desirable to employ at least one of these oxides to reach the desired value of the integrated visible transmission. Notably, the Fe203 content and the V205 content (although both are primarily employed for coloration) have a relationship to one another as concerns the integrated visible transmission (Tl) . Indeed, it has been found that the amount of Fe203 should be increased in the composition as the V205 increases in order to obtain a material with an integrated visible transmission of greater than about 0.5%.

[0041] ^"It has been found that in order to achieve the desired integrated visible transmission (Tl) of the glass-ceramic material, in addition to Fe203 and Cr203, at least one of the following oxides is highly preferably: V205, CoO, NiO and Ce02. Thus, as can be seen in FIG. 1, each of the samples includes at least one of the aforementioned oxides.

[0042] Additionally and/or alternatively, the optical

transmission (measured at about 625 nm) may be- one of:^' (i) higher than about 1%; (ii) higher than about 2%; and higher than about 3.5%. For example, an optical transmission (at about 625 nm) of greater than about 2%, and preferably greater than about 3.5%, is desirable for radiant cook-top

applications. Additionally, such characteristic would permit one to see through the ceramic material in applications where there were red LEDs behind the material.

[0043] In some embodiments, such as when certain types of electronic controls are employed in a product (e.g., IR touch controls), it may be desirable to control the optical

transmission (measured at about 950 nm) . For example, the optical transmission (measured at about 950 nm) may be one of:

(i) between about 35-75%; (ii) between about 50-70%; and (iii) between about 45-55%. In addition to providing good performance for cooktop applications in general, the preferred range of between about 50% - 70% would permit the use of infrared (IR) touch controls on a product, such as on a cooktop appliance.

[0044] Additionally and/or alternatively, the infra-red optical transmission (e.g., measured at about 1600 nm) may be one of: (i) between about 45-80%; (ii) between about 50-75%; and (iii) between about 45-60%. A preferred range of between about 50%-75% provides good heating performance in a cooktop application. In a cooktop application, it has been found that an infra-red optical transmission of less than about 50% begins to show signs of reduced ability to heat an item placed thereon, and an infra-red optical transmission of more than about 75% can begin to show signs of excessive heating of materials located in proximity of, but outside, a desired heating zone.

Color Characteristics

[0045] As discussed above, an important aspect of the

embodiments herein are their color characteristics. Indeed, for- commercial purposes it is desirable to achieve a glass- ceramic having the aforementioned functional properties as well as certain coloration, specifically in the grey family, such as brown-grey.

[0046] In this regard, reference is now made to FIG. 4, which is a graph on a Cartesian coordinate system illustrating the effect of certain coloring agents within the glass

compositions of the embodiments herein. The y-axis (ordinate) represents the hue (b*), blue-yellow component of color, while the x-axis (abscissa) represents the hue (a*) , green-red component of color. The color values on the graph may be quantified, for example, using the known illuminant D65, 10° observer test, which was used to measure color of the 4 mm thick and 5.2 mm thick samples herein. The a* and b*

coordinates are typically measured simultaneously with the L* value.

[0047] The primary contributors to variations in the color of the resultant glass-ceramic are vanadium oxide (V205), chromium oxide (Cr203), and iron oxide (Fe203) . This

combination of coloring agents permits relatively high

quantities of Cr203 and Fe203 without incurring significant cost insofar as iron and chromium are readily available at low cost.

[0048] V205, in the presence of Sn02, significantly darkens the glass during ceramming, as V205 is responsible for

absorption of light having wavelengths mainly below 700 nm. Yet, even in the presence of V205 and Sn02 it is possible to retain sufficiently high optical transmission at 650nm, 950 nm and in the infra-red optical transmission frequencies (e.g., 1600 nm) . In accordance with embodiments herein, an amount of V205 may be one of: (i) between about 0% to 0.3%; (ii) between about 0.005% to 0.2%; and (iii) between about 0.05% to 0.1%.

[0049] Chromium oxide (Cr203) has been found to be suitable for providing a darkening function of wavelengths within the visible range (e.g., between about 400-600 nm) while retaining high transmission in. the wavelengths between about 600 and 800 nm. In accordance with embodiments herein, an amount of Cr203 may be one of: (i) between about 0.01% to 0.04%; (ii) between about .0.01% to 0.02%; and (iii) between about 0.016% to 0.018%. Due to the presence of Cr203 in the composition, the glass-ceramic shows low transmission in the blue range.

[0050] Iron oxide (Fe203) leads to absorption mainly in the infra-red wavelengths; however, iron oxide is also involved in the visible wavelengths and affects the coloration of the glass-ceramic. In accordance with, embodiments herein, an amount of Fe203 may be one of: (i) between about 0.1% to 0.4%; (ii) between about 0.12% to 0.4%; (iii) between about 0.15% to 0.35%; and (iv) between about 0.16% to 0.25%.

Notably, the effect of Fe203 within the listed compositions may be adjusted by varying the vanadium oxide content. For example, at Fe203 content greater than about 0.15%,

transmission in the visible range is slightly increased

(probably because Sn02 preferentially reduces Fe203 and, as a consequence, the amount of reduced vanadium is lower) . Such lightening of the glass-ceramic may then be compensated by a greater V205 content (however remaining within the range indicated above) .

[0051] With reference still to FIG. 4, as the content of Cr203 is increased, the hue (b*) moves from negative levels (blue) to positive levels (yellow) . Comparative Example 7 (labeled ^XN7'") is depicted for illustration. As the content of Fe203 is increased, the hue (a*) moves from low positive levels (green) to higher positive levels (red), and the hue (b*) moves from negative levels (blue) to positive levels (yellow) . A number of samples are shown on the illustrated plot. A first sample (labeled "1" and corresponding to Example 1 of FIG. 1) was of a base composition within the ranges discussed above, including 0.0173% Cr203 and 0.16% Fe203. Such a composition is clearly on the blue side of the coloration scale illustrated. A second sample (labeled "2" and

corresponding to Example 2 of FIG. 1) was also of a base composition within the desired ranges, including 0.0173% Cr203 and 0.25% Fe203. The composition exhibited movement in both the yellow and red directions (i.e., towards brown) of the coloration scale illustrated. A third sample (labeled "5" and corresponding to Example 5 of FIG. 1) was also of a base composition within the desired ranges, including 0.021% Cr203 and 0.25% Fe203. The composition exhibited further movement in both the yellow and red directions of the coloration scale illustrated. A fourth sample (labeled "3" and corresponding to Example 3 of FIG. 1) was also of a base composition within the desired ranges, including 0.0173% Cr203 and 0.3% Fe203. The composition exhibited a coloration even closer to a red- brown.

[0052] Taking the above into consideration, along with one or more other characteristics discussed above, in accordance with one or more desired embodiments, the hue (a*) may be one of:

(i) between -1 to +4; (ii) between about 0 to +4; (iii) +0 to +3; and (iv) +0 to +2. Additionally and/or alternatively, the hue (b*) may be. one of: (i) between about -2 to +4; (ii) -1 to +3; and (iii) 0 to +2.

[0053] With reference to FIG. 5 a number of samples were prepared having differing compositions as compared with the samples of FIG.- 1. FIG. 6 is a table of characteristics of the glass-ceramic materials produced using the compositions of FIG. 5 after a glass ceramming process. It was found that the compositions of comparative examples 1, 2, 3, and 4 were undesirable because the level of Fe203 was too low and- yielded unacceptable values of the integrated optical transmission (Tl) . It was found that the composition of . comparative example 5 was undesirable because it did not contain any Cr203 and therefore did not yield satisfactory coloration. A similar issue existed for comparative example 7 as it also did not contain any Cr203. With reference to FIG. 4, the data point for comparative example 7 is shown (see label number 7'), which exhibits a hue (b*) significantly toward blue.

When a small amount of Cr02 is added (see Example 5 or Example 2 of FIG. 1), the color^■ shifted toward positive values of hue (b*) as shown in FIG. 4 by label number 2 or label number 5. Comparative example 6 is undesirable because it does not include at least one of the oxides (V205, CoO, NiO and Ce02) and therefore does not exhibit satisfactory integrated optical transmission (Tl) . ^■

[0054] Within the scope of the disclosed embodiments, it is contemplated that the composition of the glass-ceramic

contains, in addition to Fe203 and Gr203, at least one further coloring agent. However, it is important to keep in mind that the presence of one or more further coloring agents may have an influence on the targeted optical transmission

characteristics discussed above. Therefore, attention should be paid to possible interactions, even with relatively low levels of such further coloring agents. For example, CoO may only be tolerable in very small amounts because, CoO strongly absorbs light in. the infra-red wavelengths and in a non- negligible way at wavelengths of about 625 nm.

Variations and Embodiments [0055] Although the above discussion has been presented primary in terms of obtaining a glass-ceramic for a cooktop, skilled artisans will appreciate that the embodiments herein may be applied to many other products .

[0056] Although the above discussion has been primarily directed to glass compositions, and gla^'ss-ceramic properties, skilled artisans will appreciate that the discussion has been provided in significant detail to enable any number of methods and processes to fabricate such glass and glass-ceramic ^■materials and resultant products. -In essence, the base process steps may include the heat treatment of a vitrifiable load of raw materials under conditions which successively ensure melting, fining and then ceramming. The load is a precursor of a glass for producing the glass-ceramic materials discussed above, advantageously having the base composition specified above.

[0057] Although the disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the

principles and applications of the embodiments herein. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other

arrangements may be devised without departing from the spirit and scope of the present application.

Claims

CLAIMS :

1. A glass-ceramic of a- lithium aluminosilicate type, containing beta-spodumene as a predominant crystalline phase and exhibiting a generally brown-grey color.

2. The glass-ceramic of claim, 1, wherein a lightness L* thereof is between about 20 - 40, measured in reflection using an illuminant D65, -10° observer test.

3. The glass-ceramic of claim 1, wherein at least one of:

a green-red hue (a*) of the glass-ceramic is one of: (i) between about -1 to +4; (ii) 0 to +4; (iii) +0 to +3; and (iv) +0 to +2,

a blue-yellow hue (b*) of the glass-ceramic is one of: (i) between about -2 to +4; (ii) -1 to +3; and (iii) 0 to +2, and

said hue is measured using an illuminant D65, 10° observer test.

4. The glass-ceramic of claim 1, wherein a coefficient of thermal expansion is one of: (i) less than about 15x10-7 /°C; (ii) less than about 13x10-7 /°C; and (iii) less than about 11x10-7 /°C.

5. The glass-ceramic of claim 1, wherein a integrated visible transmission (Tl) is one of: (i) between about 0.3% to about 6%; (ii) between about 0.4%_. to about 5%; (iii) between about 0.5% to about 5%; (iv) between about 0.6% to about 4%; (v) between about 0.7% to about 3%; and (vi) between about 0.8% to about 2%, and wherein, said integrated visible transmission (Tl) is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

6. The glass-ceramic of claim 1, wherein an. optical transmission, measured at about 625 nm, is one of: (i) higher than about 1%; (ii) higher than about 2%; and higher than about 3.5%, and wherein said optical transmission is measured using an illuminant D65, 2° observer test on 4 mm thick glass- ceramic .

7. ^' The glass-ceramic of claim 1, wherein an optical transmission, measured at about 950 nm, is one of: (i) between about 35-75%; (ii) between about 50-70%; and (iii) between about 45-55%, and wherein said optical transmission is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

8. The glass-ceramic of claim 1, wherein an infra-red optical transmission, measured at about 1600 nm, is one of: (i) between about 45-80%; (ii) between about 50-75%; and (iii) between about 45-60%, and wherein said optical transmission is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

9. The glass-ceramic of claim 1, further comprising (in weight %) : 60-72% Si02, 18-23% A1203, and 2.5-4.5% Li20.

10. The glass-ceramic of claim 7, further comprising (in weight %): 0-2.5% Zr02, and 1.5-4% Ti02.

11. The glass-ceramic of claim 9, further comprising (in weight %) : 0-3% MgO, 0-3% ZnO, 0-5% BaO, 0-2% CaO, 0-1.5% K20, 0-1.5% Na20.

12. The glass-ceramic of claim 11, wherein a combined amount of CaO, K20, and Na20 is less than one of: (i) about 1.5%; (ii) about 1.25%; and (iii) about 1%.

13. The glass-ceramic of claim 9, further comprising (in weight %): 0-0.3% V205, 0.1-0.4% Fe203, 0.01-0.04% Cr203, 0- 0.05% CoO, 0-0.3% NiO, and 0-0.2% Ce02.

14. The glass-ceramic of · claim 13, comprising 0.12-0.4% Fe203.

15. The glass-ceramic of claim 9, further comprising (in weight %) : 0-0.6% Sn02.

16. A glass precursor composition, which when subject to ceramming exhibits a lithium aluminosilicate characteristic, containing beta-spodumene as a predominant crystalline phase, the glass precursor comprising, (in weight %) :

60-72% Si02, 18-23% A1203, and 2.5-4.4% Li20; and

0-0.3% V205, 0.1-0.4% Fe203, 0.01-0.04% Cr203, 0-0.05% CoO, 0-0.3% NiO, and 0-0.2% Ce02.

17. The glass precursor of claim 16, comprising 0.12- 0.4% Fe203.

18. The glass precursor of claim 16, further comprising (in weight %) : 0-2.5% Zr02, and 1.5-4% Ti02.

19. The glass precursor of claim 16, further comprising (in weight %): 0-3% MgO, 0-3% ZnO, 0-5% BaO, 0-2% CaO, 0-1.5% K20, 0-1.5% Na20.

20. The glass precursor of claim 16, further comprising (in weight %) : 0-0.6% Sn02.

21. A method, comprising:

melting a load of vitrifiable raw materials;

fining the load to obtained molten glass;

cooling the molten glass to a temperature sufficient to shape it into a desired shape; and

ceramming of the shaped glass at a maximum temperature between about 960°C to about 1060°C, to produce a lithium aluminosilicate type glass-ceramic material containing beta- spodumene as a predominant crystalline phase,

wherein the glass-ceramic exhibits a generally brown-grey color .

22. The method of claim21, wherein at least one of:

a green-red hue (a*)_of the glass-ceramic is one of: (i) between about -1 to +4; (ii) 0 to +4; (iii) +0 to +3; and (iv) +0 to +2,

a blue-yellow hue (b*) of the glass-ceramic is one of: (i) between about -2 to +4; (ii) -1 to +3; and (iii) 0 to +2, and said hue is measured in reflection using an illuminant D65, 10° observer test.

23. The method of claim 21, wherein a lightness L* of the glass-ceramic is between about 20-40 measured in reflection using an illuminant D65, 10° observer test.

24. The method of claim 21, wherein a integrated visible transmission (Tl) of the glass-ceramic is one of: (i) between about 0.3% to about 6%; (ii) between about 0.4% to about 5%; (iii) between about 0.5% to about 5%; (iv) between about 0.6% to about 4%; (v) between about 0.7% to about 3%; and (vi) between about 0.8% to about 2%, and wherein said integrated visible transmission (Tl) is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

25. The method of claim 21, wherein an optical transmission of the glass-ceramic, measured at about 625 nm, is one of: (i) higher than about 1%; (ii) higher than about 2%; and higher than about 3.5%, and wherein said optical transmission is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

26. The method of claim 21, wherein an optical transmission of the glass-ceramic, measured at about 950 nm, is one of: (i) between about 35 - 75%; (ii) between about 50 - 70%; and (iii) between about 45 - 55%, and wherein said optical transmission is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

27. The method of claim 21, wherein an infra-red optical transmission of the glass-ceramic, measured at about 1600 nm, is one of: (i) between about 45-80%; (ii) between about 50- 75%; and (iii) between about 45-60%, and wherein said optical transmission is measured using an illuminant D65, 2° observer test on 4 mm thick glass-ceramic.

28. The method of claim 21, wherein the glass comprises (in weight %) : 60-72% Si02, 18-23% A1203, and 2.5-4.5% Li20.

29. The method of claim 28, wherein the glass comprises (in weight %) : 0-2.5% Zr02, and 1.5-4% Ti02.

30. The method of claim 28, wherein the glass comprises (in weight %) : 0-3% MgO, 0-3% ZnO, 0-5% BaO, 0-2% CaO, 0-1.5% K20, 0-1.5% Na20.

31. The method of claim 28, wherein the glass comprises (in weight %) : 0-0.3% V205, 0.1-0.4% Fe203, 0.01-0.04% Cr203, 0-0.05% CoO, 0-0.3% NiO, and 0-0.2% Ce02.

32. The method of claim 31, comprising 0.12-0.4% Fe203.

33. The method of claim 28, wherein the glass comprises (in weight %) : 0-0.6% Sn02.