Lithium aluminosilicate glass ceramics

Abstract

The invention relates to a lithium aluminosilicate glass ceramic having a coefficient of thermal expansion in the range of 20 DEG C to 700 DEG C of-0.5 to 1.9 ppm / K and to the use thereof. The glass ceramic contains the following components in percentage by weight on the basis of oxides: 60 to 70 percent of SiO2, 17 to 25 percent of Al2O3, 1.0 to 1t of Li2O, 0.1 to 0.5 percent of Na2O, 0.1 to 0.5 percent of Na2O, 0.1 to 0.5 percent of Na2O, 0.1 to 0.5 percent of Na2O, 3.0, 0 to 1t of MgO; 1, ZrO2gt; 1.3 to 3.0 parts of K2O, 0 to 3.0 parts of TiO2 gt; 3.0 to 5.0% of SnO2 and 0.1 to 1t of SnO2; 1.

Description

Technical Field

[0001] The present invention relates to a lithium aluminosilicate glass-ceramic suitable for use as a cooking surface of a cooking appliance and to its use. Background Art

[0002] Glass-ceramic cooking surfaces and the glass-ceramics used therefor have been known for many years. For this purpose, lithium aluminosilicate (LAS) glass-ceramics are used, which contain high quartz mixed crystals (HQMK) especially for transparent materials or hydrothermal quartz mixed crystals (KMK) especially for translucent or opaque materials as the main crystal phase. To manufacture such glass-ceramics, first a raw glass, i.e., a so-called green glass, is manufactured by conventional methods for glass manufacture. The green glass is converted into a glass-ceramic by a heat treatment process, i.e., ceramization.

[0003] The basic property of these materials used as cooking surfaces is that they have a very low thermal expansion in the temperature range from room temperature to 700 °C. The low thermal expansion in turn results in high thermal shock resistance. The thermal expansion is composed of a crystalline phase with negative thermal expansion and an amorphous residual glass phase with positive thermal expansion. In the glass-ceramics used hitherto, the lithium content is usually more than 3.6% to 5.0% by weight.

[0004] Due to the rising raw material price of lithium, it is economically advantageous to minimize the lithium content in the glass-ceramic. However, since lithium is one of the three main components in lithium aluminosilicate glass-ceramics, it cannot be reduced arbitrarily. The content of Li2O directly affects the key properties of the glass-ceramic, such as the viscosity important for manufacturability in the melt or the thermal expansion important for use as a cooking surface.

[0005] The price trend of lithium is not a new issue. The price of lithium has been rising continuously for the past 20 years. Nevertheless, due to the long-term demand, most of the glass-ceramics used for cooking surfaces on the market contain about 3.8% by weight of Li2O. So far, in practice, no glass-ceramic containing less than 3.5% of Li2O and capable of competing with the glass-ceramics currently on the market has been found.

[0006] Glass-ceramics with a Li2O content of less than 3.5% by weight are known from the following documents: WO 2012 / 010341A1, EP3502069 A1, US2017050880, US2020189965, US2020140322, US2021387899, WO2021 / 224412A1. However, these glass-ceramics have various disadvantages, such as reduced thermal shock resistance or poor fusibility of the green glass.

[0007] Here, transparent glass ceramics are generally understood as glass ceramics with low light scattering. The transmittance of transparent glass ceramics can be adjusted within a wide range by absorption characteristics (i.e., coloring components).

[0008] When transparent glass ceramics are used for cooking surfaces, they are either volume-colored by adding colored oxides or provided with a bottom coating to visually hide the technical devices located below the cooking surface. Various colored oxides can be used for the volume coloring of glass ceramics. These especially include V2O5, CoO, Fe2O3, Cr2O3, Nd2O3, NiO, CuO, MnO, and MoO3. Each of these colored oxides has a different effect on the absorption of glass ceramics in the visible and infrared spectral ranges. The coloring of glass ceramics is especially described in the following documents: WO 11089220 A1, US 8765619, DE 102008050263B4, DE 102009013127B4. Summary of the Invention

[0009] The object of the present invention is to provide a lithium aluminosilicate glass ceramic that has good green glass melting characteristics and is cost-effective without imposing limitations on the usage characteristics.

[0010] Good melting performance mainly includes here: a processing point at a temperature below 1340 °C, preferably below 1330 °C, and particularly preferably below 1320 °C. The processing point is the temperature at which the green glass has a viscosity of 10 4 dPa*s. The thermoforming of the green glass occurs near this temperature. The higher the temperature during thermoforming, the more complicated it is to discharge the heat introduced into the forming machine by the glass. In the case of temperatures above 1340 °C, this can only be achieved by reducing the glass production volume to reduce the heat. However, this is economically disadvantageous.

[0011] During the thermoforming process, when the temperature is below the upper devitrification temperature, undesirable spontaneous crystallization may occur. To prevent this, the upper devitrification temperature should be at least 15 K lower than the processing point, preferably at least 20 K, and particularly preferably at least 30 K.

[0012] In particular, the glass ceramic should meet all the requirements for use in combination with all types of heating elements as a cooking surface. These heating elements especially include radiant heating elements, induction heating elements, and gas heating elements. This especially requires a sufficiently high thermal shock resistance and high long-term temperature resistance characteristics.

[0013] The object of the present invention is achieved by the subject matter of the independent claims. Preferred embodiments and improvements are derived from the dependent claims.

[0014] The lithium aluminosilicate glass-ceramic according to the invention has a coefficient of thermal expansion in the range from 20 °C to 700 °C of from -0.5 to 1.9 ppm / K. The glass-ceramic contains the following components in the amounts indicated in % by weight, based on oxides:

[0015]

[0016]

[0017] The glass-ceramic having the corresponding coefficient of thermal expansion has both high thermal shock resistance and high long-term thermal stability. Thereby it is suitable as a cooking surface for use in conjunction with all types of heating elements. The coefficient of expansion is at least -0.5 ppm / K. Here, "ppm" means "parts per million", i.e. the relative change in dimension for a temperature change of 1 K is 10 -6 −6. A more negative coefficient of thermal expansion is also to be avoided. In the case of negative expansion, i.e. shrinkage, tensile stresses are generated in the surface of the glass-ceramic during heating. When the value is less than -0.5 ppm / K, the stresses reduce the mechanical strength of the cooking surface at the typical operating temperatures of the cooking appliance. A coefficient of thermal expansion above 1.9 ppm / K is also to be avoided. When the expansion exceeds 1.9 ppm / K, a sufficiently high thermal shock resistance cannot be ensured, so that the glass-ceramic cannot be used in cooking appliances having radiant heating elements.

[0018] In a further embodiment of the invention, the coefficient of thermal expansion is at least -0.4 ppm / K, -0.2 ppm / K, 0.0 ppm / K, 0.2 ppm / K, 0.4 ppm / K, 0.6 ppm / K, 0.8 ppm / K, or even 0.9 ppm / K. In addition, the coefficient of thermal expansion is preferably at most 1.7 ppm / K, 1.5 ppm / K, 1.3 ppm / K, 1.1 ppm / K, 1.0 ppm / K, 0.8 ppm / K, or even at most 0.6 ppm / K only.

[0019] In a preferred embodiment of the invention, the coefficient of thermal expansion of the glass-ceramic is from -0.5 to 1.0 ppm / K, preferably from -0.1 to 0.8 ppm / K, particularly preferably from 0 to 0.6 ppm / K. Such a glass-ceramic is particularly suitable for the cooking surface of a cooking appliance having radiant heating elements.

[0020] In a further preferred embodiment of the invention, the coefficient of thermal expansion of the glass-ceramic is from 0.5 to 1.9 ppm / K, preferably from -0.7 to 1.7 ppm / K, particularly preferably from 0.9 to 1.5 ppm / K. Such a glass-ceramic is suitable for the cooking surface in a cooking appliance having, for example, induction heating elements.

[0021] The glass-ceramic according to the invention contains the following components in % by weight:

[0022] SiO2 60 - 70,

[0023] Al2O3 17 - 25, and

[0024] Li2O 1.0 - <3.0.

[0025] The components SiO2 and Al2O3 together with Li2O form the main components of the crystalline phase in the glass - ceramic. At the same time, they essentially determine the glass - forming properties and the viscosity of the green glass.

[0026] The SiO2 content of the glass - ceramic according to the invention should be at most 70 wt%, because this component greatly increases the viscosity of the glass, especially the processing point. For good glass melting and low forming temperature, a higher SiO2 content is uneconomical. The minimum content of SiO2 should be 60 wt%, because this is advantageous for the required properties such as chemical resistance and heat resistance. When the SiO2 fraction is very high, exceeding 70 wt%, deep - seated quartz crystals are formed during the ceramization process. This leads to a sharp increase in thermal expansion.

[0027] Preferably, the glass - ceramic contains at least 61 wt%, 62 wt%, 63 wt%, 64 wt%, or even 65 wt% of SiO2. The more SiO2 the glass - ceramic contains, the better its heat resistance and chemical resistance. In addition, it preferably contains at most 69 wt%, 68 wt%, 67 wt%, or even only 66 wt% of SiO2. The less SiO2 the glass - ceramic contains, the better the fusibility and processability of the green glass during hot forming.

[0028] The Al2O3 content of the glass - ceramic according to the invention is in the range of 17 to 25 weight - percent. A higher Al2O3 fraction leads to devitrification problems and the formation of unwanted mullite. Therefore, it should not exceed 25 wt%. An Al2O3 content below 17 wt% is not conducive to the formation of high - quartz mixed crystals and promotes the formation of unwanted crystalline phases.

[0029] Preferably, the glass - ceramic contains at least 18 wt%, 19 wt%, or even 20 wt% of Al2O3. The more Al2O3 the glass - ceramic contains, the better its heat resistance. In addition, it preferably contains at most 24 wt%, 23 wt%, 22 wt%, or even only 21 wt% of Al2O3. The less Al2O3 the glass - ceramic contains, the better the fusibility and processability of the green glass during hot forming.

[0030] It has been shown that if the glass - ceramic contains 17 - <19.0 wt%, preferably 17.5 - 18.9 wt%, particularly preferably 18 - 18.8 wt% of Al2O3, it is particularly advantageous for the fusibility of the green glass.

[0031] It has been proven that if the glass-ceramic contains >21.0 - 25 wt%, preferably 21.5 - 24 wt%, particularly preferably 22.0 - 23 wt% of Al2O3, it is particularly advantageous for the heat resistance of the glass-ceramic.

[0032] The Li2O content of the glass-ceramic according to the invention is in the range of 1.0 - <3.0 wt%. Surprisingly, it has been proven that when the Li2O content is within this range in combination with the remaining components within the above ranges, a glass-ceramic with high thermal shock resistance and good fusibility can be achieved. Since Li2O has a great influence on the thermal expansion of the glass-ceramic, Li2O is selected within the above range to be combined with the remaining components of the glass-ceramic of the invention to achieve the required thermal shock resistance of the invention. In addition, an Li2O fraction above 1.0 wt% has a positive effect on the manufacturability of the glass-ceramic because it reduces the electrical resistance of the glass melt, reduces the viscosity, and thus also reduces the processing point. By reducing the viscosity of the glass melt, the clarification efficiency can also be improved. The improved clarification results in fewer production rejects due to the formation of bubbles in the green glass.

[0033] In a preferred embodiment, the glass-ceramic contains at least 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, or even 1.8 wt% of Li2O. As an upper limit, the glass-ceramic preferably contains at most 2.9 wt%, 2.8 wt%, 2.7 wt%, 2.6 wt%, 2.5 wt%, 2.4 wt%, 2.3 wt%, or even 2.2 wt% of Li2O. Particularly preferably, the glass-ceramic contains 1.2 - 2.8 wt% or 1.4 - 2.6 wt% or 1.6 - 2.4 wt% or even 1.8 - 2.2 wt% of Li2O. Glass-ceramics with particularly high thermal shock resistance can be obtained within these narrower ranges.

[0034] For cost reasons, natural mineral raw materials (such as spodumene or petalite) or alternatively synthetically produced Li2CO3 are usually used as the source of lithium. However, natural mineral raw materials contain impurities that may, for example, have an undesirable effect on the optical properties of the glass-ceramic. In addition, the amount of impurities in natural raw materials may vary with each delivery, making it difficult to adjust the required properties of the glass-ceramic. For this reason, it is also advantageous to minimize the amount of Li2O in the glass-ceramic.

[0035] In a preferred embodiment, the glass-ceramic contains high-quartz mixed crystals as the main crystal phase. The "main crystal phase" means that the volume fraction of high-quartz mixed crystals contained in the glass-ceramic is greater than the volume fraction of hydrothermal quartz mixed crystals. In a further embodiment of this embodiment, the glass-ceramic contains <10 vol%, preferably <5 vol%, particularly preferably <3 vol% of hydrothermal quartz mixed crystals. Here, vol% refers to the volume of the glass-ceramic, preferably the volume of the crystal phase. The volume fraction is determined from the X-ray diffraction spectrum using Rietveld analysis.

[0036] Hydrothermal quartz mixed crystals generally have a higher thermal expansion than high-quartz mixed crystals. Therefore, the coexistence of a high fraction of high-quartz mixed crystals and a low fraction of hydrothermal quartz mixed crystals is particularly advantageous for the thermal expansion coefficient of the glass-ceramic. It thus improves the thermal shock resistance of the glass-ceramic.

[0037] In addition to the above amounts of SiO2, Al2O3, and Li2O, the glass-ceramic according to the invention also contains 0 - <1 wt% of MgO. Since MgO causes an increase in the thermal expansion of the glass-ceramic, the amount of MgO in the glass-ceramic is limited to a maximum of <1 wt%. Preferably, the glass-ceramic contains a maximum of 0.9 wt%, 0.8 wt%, 0.7 wt%, 0.6 wt%, or even only 0.5 wt% of MgO.

[0038] In an advantageous design of the invention, it is preferred that the glass-ceramic contains a small amount of MgO. A small amount of MgO can be used to lower the processing point and the upper devitrification temperature. The glass-ceramic preferably may contain at least 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, or even 0.4 wt% of MgO. MgO can also be introduced into the glass-ceramic as an impurity in the raw materials.

[0039] In a further embodiment of the invention, the glass-ceramic contains 0.05 - 0.9 wt%, or 0.1 - 0.8 wt%, 0.2 - 0.7, or even 0.3 - 0.6 wt% of MgO.

[0040] The glass-ceramic according to the invention contains 0 - 3.0 wt% of K2O. In the glass-ceramic according to the invention, K2O acts to improve the fusibility and devitrification characteristics during the glass forming process. K2O can additionally increase the electrical conductivity of the melt. This contributes to the energy coupling of the electric heater in the melting bath. However, since it does not incorporate into the crystal phase but remains substantially in the residual glass phase of the glass-ceramic, the content is limited to 3.0 wt%. An excessive content will damage the crystallization behavior during the conversion of the starting glass that can crystallize into a glass-ceramic, particularly damaging the rapid ceramization rate. In addition, a higher content acts unfavorably on the time / temperature tolerance of the glass-ceramic.

[0041] These properties can be further improved if the amount of K2O in the glass-ceramic is at least 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or even 1.1 wt%, and at most 2.6 wt%, 2.3 wt%, 2.0 wt%, 1.8 wt%, or even 1.6 wt%.

[0042] In a further embodiment of the invention, the glass-ceramic contains 0.1 - 2.6 wt% or 0.3 - 2.3 wt% or 0.6 - 2.0 wt%, or even 0.9 - 1.6 wt% of K2O.

[0043] In a further embodiment of the invention, the glass-ceramic contains more MgO than K2O. Surprisingly, it has been shown that glass-ceramics containing more MgO than K2O have a low processing temperature and an upper devitrification temperature, but have no disadvantages with respect to the ceramization rate.

[0044] In addition, the glass-ceramic according to the invention contains > 1.3 - 3.0 wt% of ZrO2. ZrO2 acts mainly as a nucleating agent in the glass-ceramic and interacts closely with SnO2 as a nucleating agent. A content of > 1.3 wt% - 3.0 wt% of ZrO2 in combination with the specified amounts of SnO2 and TiO2 according to the invention is conducive to improving nucleation.

[0045] The amount of ZrO2 is limited to a value of 3.0 wt% because ZrO2 increases the viscosity of the glass melt and thus also the processing point. Additionally, ZrO2 may cause devitrification during the thermoforming process. Here, this may lead to the formation of undesired baddeleyite. Preferably, the glass-ceramic contains at least 1.4 wt%, 1.5 wt%, 1.6 wt%, or even > 1.7 wt% of ZrO2. Furthermore, it preferably contains at most 2.6 wt%, 2.3 wt% or even only 2.0 wt% of ZrO2. With these amounts, a particularly good compromise can be achieved between the positive contribution to nucleation and an acceptable deterioration of fusibility and thermoforming.

[0046] In a further embodiment of the invention, for the above reasons, the glass-ceramic contains 1.4 - 2.6 wt%, preferably 1.5 - 2.3 wt%, particularly preferably 1.6 - 2.0 wt% of ZrO2.

[0047] In addition, the glass-ceramics according to the invention contain > 3.0 - 5.0 wt% of TiO₂. TiO₂, together with SnO₂ and ZrO₂, contributes to nucleation. The amount of TiO₂ is limited to a maximum of 5.0 wt%. Larger amounts of TiO₂ would lead to devitrification during thermoforming. Additionally, it would lead to an undesired increase in the refractive index of the residual glass phase. Preferably, the glass-ceramics contain at least 3.1 wt%, 3.2 wt%, or even 3.3 wt% of TiO₂. At the same time, it preferably contains a maximum of 4.5 wt%, 4.2 wt%, 4.0 wt%, 3.8 wt%, or even only 3.6 wt% of TiO₂. In the case of a higher TiO₂ fraction, nucleation progresses faster. Thereby, the ceramization time of the glass-ceramics can be reduced. Lower fractions can stabilize the ceramization process and prevent accidental devitrification of the green glass during thermoforming.

[0048] In a further embodiment of the invention, the glass-ceramics can contain, for example, 3.1 - 4.5 wt%, preferably 3.2 - 4.2 wt%, particularly preferably 3.3 - 4.0% of TiO₂ for the reasons mentioned above.

[0049] The glass-ceramics according to the invention contain 0.1 - < 1.0 wt% of SnO₂. 0.1 wt% of SnO₂ in combination with the other components of the glass-ceramics according to the invention is advantageous to ensure sufficient nucleation for the properties according to the invention. However, the amount should not exceed < 1.0 wt%. Higher contents lead to the precipitation of Sn-containing crystalline phases at the contact material (e.g., Pt / Rh) during forming and should be avoided. Preferably, the glass-ceramics contain a maximum of 0.8 wt%, 0.6 wt%, or even only 0.4 wt% of SnO₂.

[0050] In a further embodiment of the invention, the glass-ceramics can contain 0.1 - 0.8 wt%, preferably 0.2 - 0.7, particularly preferably 0.3 - 0.6 wt% of SnO₂. SnO₂ in these amounts can support the clarification of the green glass. Glass-ceramics with these amounts of SnO₂ are notable for particularly few defects caused by trapped air bubbles.

[0051] In another improvement of the invention, the glass-ceramics can contain 0 - 0.8 wt%, preferably 0.1 - 0.6 wt%, particularly preferably 0.2 - 0.4 wt% of CeO₂. CeO₂ in combination with SnO₂ can also support clarification and improve the bubble quality.

[0052] In a further embodiment of the present invention, Na2O is added to improve the solubility and devitrification characteristics of the glass during the forming process. Na2O can additionally improve the electrical conductivity of the melt. This helps to couple energy by electrical heating in the melting tank. However, since it is not incorporated into the crystalline phase, but is essentially retained in the residual glass phase of the glass ceramic, the content should be limited. Excessive content damages the crystallization behavior when the crystallizable starting glass is converted into glass ceramics, especially the rapid ceramicization rate. In addition, the higher content has an unfavorable effect on the time / temperature tolerance of the glass ceramics. Therefore, the glass ceramics preferably contain 0-<1% by weight or 0.05-0.9% by weight or 0.1-0.8% by weight, or even 0.2-0.7% by weight of Na2O.

[0053] In a further development of the invention, the glass ceramic preferably contains more MgO than Na 2 O. If the glass ceramic contains more MgO than Na 2 O, both better melting properties and faster ceramization can be achieved.

[0054] In a further development of the invention, the glass ceramic preferably contains more K2O than Na2O. The ratio of K2O to Na2O allows fine-tuning of the solubility and the thermal expansion. Na2O improves melting and, in the present composition, reduces the viscosity of the glass melt more than K2O, but also increases the thermal expansion of the glass ceramic more.

[0055] In a further development of the invention, the ratio of K2O to Na2O K2O / Na2O (in wt. %) is in the range of >2-20, preferably 3-15, particularly preferably 4-10. In this range, particularly well-meltable green glass can be produced without negatively influencing the thermal expansion of the glass ceramic.

[0056] As2O3 and Sb2O3 are usually used as fining agents in the production of glass ceramics. However, in the glass ceramics according to the invention, these components have surprisingly been shown to be detrimental to the devitrification stability. Therefore, in a further embodiment of the invention, the amount of As2O3 and Sb2O3 is preferably limited to a maximum of 0.1% by weight, respectively. Particularly preferably, the glass ceramics each contain less than 0.09% by weight, 0.08% by weight, 0.07% by weight, 0.06% by weight, or even less than 0.05% by weight of As2O3 and Sb2. Particularly preferably, the glass ceramics contain no As2O3 and Sb2O3 except for unavoidable traces.

[0057] However, As2O3 and Sb2O3 can occur as impurities in glass ceramics, especially when using batches containing As2O3 and Sb2O3 to manufacture glass ceramics. This is especially the case when using cooking surface batches from the recycling loop. For environmental protection and sustainability reasons, it is advantageous to use batches from the recycling loop as raw materials. Therefore, the glass ceramics preferably contain at least 0.01 wt%, 0.02 wt%, 0.03 wt%, or even at least 0.04 wt% of As2O3 and / or Sb2O3, respectively. If both As2O3 and Sb2O3 are present, they are each present in the stated amounts.

[0058] In a further embodiment of the invention, it may be advantageous for the glass ceramics to contain Cl - . It has been found that adding a certain amount of Cl - results in better bubble quality in the green glass and thus better bubble quality in the glass ceramics. It has been shown that in combination with the remaining components, the glass ceramics contain 0.003 - 0.1 wt%, preferably 0.005 - 0.03 wt%, particularly preferably 0.007 - 0.02 wt% of Cl - is particularly advantageous. Amounts below 30 ppm do not have a sufficient effect on the bubble quality. Amounts above 1000 ppm should be avoided because the added chloride part may react with other components in the mixture and with the process exhaust gases. For example, HCl may be formed here, which can cause corrosive damage to the tank. In addition, the evaporation of alkali metal chlorides and alkaline earth metal chlorides is also undesirable. The amount of Cl in the glass ceramics can be adjusted, for example, by adding NaCl to the mixture. - amount.

[0059] In a further embodiment of the invention, the glass ceramics contain 1.0 - 4.0 wt% of BaO. Like Li2O, BaO reduces the viscosity of the glass melt and thus the processing point. To improve the fusibility of the green glass, it is advantageous for the glass ceramics to contain at least 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, or even 1.8 wt% of BaO when combined with the specified amount of Li2O according to the invention. In the glass ceramics, BaO also makes a significant contribution to improving the devitrification characteristics during the hot forming of the green glass.

[0060] However, it has been shown that BaO has a negative impact on the formation of the crystalline phase during the ceramization process. To avoid the need for a long ceramization time, the amount of BaO is therefore preferably limited to a maximum of 4.0 wt%, 3.6 wt%, 3.3 wt%, 3.0 wt%, or even 2.7 wt%. The less BaO the glass ceramics contain, the faster the ceramization proceeds.

[0061] In a further embodiment of the present invention, the glass-ceramic contains 1.0-4.0 wt% or 1.2-3.6 wt% or 1.4-3.3 wt% or even 1.6-3.0 wt% of BaO.

[0062] In another improved embodiment of the present invention, the glass-ceramic contains more BaO than Li2O. This has a positive effect on reducing the viscosity of the glass melt and the devitrification resistance of the green glass.

[0063] In a further embodiment of the present invention, the glass-ceramic contains 1.0-6.0 wt% of ZnO. ZnO can cause the formation of undesirable zinc spinel crystals, especially in combination with a large amount of Al2O3. Therefore, the amount in the glass-ceramic according to the present invention is limited to 6.0 wt%. Additionally, experience shows that glass-ceramics with very high amounts of ZnO tend to form undesirable crystals on the surface of the glass-ceramic. Therefore, the amount of ZnO is preferably limited to a maximum of 5.5 wt%, 5.0 wt%, 4.5 wt%, 4.0 wt%, 3.5 wt%, or even 3.0 wt%.

[0064] ZnO reduces the processing point and the upper devitrification temperature. Therefore, the glass-ceramic preferably contains at least 1.5 wt%, 2.0 wt%, 2.2 wt%, or even at least 2.5 wt% of ZnO. The thermal shock resistance of the glass-ceramic is particularly improved within these ranges.

[0065] In a preferred embodiment, for the above reasons, the glass-ceramic contains 1.0-6.0 wt%, preferably 1.5-4.5 wt%, particularly preferably 2.0-3.0 wt% of ZnO.

[0066] The addition of alkaline earth metals CaO, SrO, and B2O3 improves the fusibility and devitrification characteristics during glass forming. CaO can be contained in the glass-ceramic in particular to reduce the processing point and the upper devitrification temperature. However, since these components do not incorporate into the crystal phase but remain essentially in the residual glass phase of the glass-ceramic, the content is limited. Excessive content impairs the crystallization characteristics when the starting glass that can crystallize transforms into the glass-ceramic, especially the rapid ceramization rate. In addition, a higher content has an adverse effect on the time / temperature tolerance of the glass-ceramic. Therefore, the glass-ceramic contains each of these components in an amount of 0-2 wt%.

[0067] In a further embodiment of the present invention, the glass-ceramic contains 0 - <1 wt% of P2O5. P2O5 acts positively on the devitrification stability of the green glass. However, larger amounts will reduce the ceramization rate and act negatively on the acid resistance of the glass-ceramic. Therefore, the amount of P2O5 is limited to a maximum of <1 wt%, preferably a maximum of 0.9 wt%, particularly preferably a maximum of 0.8 wt%. To improve the devitrification stability, it is advantageous if the glass-ceramic contains at least 0.01 wt%, preferably at least 0.05 wt%, particularly preferably at least 0.1 wt% of P2O5.

[0068] In addition to these components, in a further embodiment of the present invention, the glass-ceramic may also contain coloring components. As coloring components, for example, V2O5, CoO, Fe2O3, Cr2O3, Nd2O3, NiO, CuO, MnO or MoO3 may be included singly or in combination. The specific choice of the type and amount of the coloring component depends on the optical properties to be achieved.

[0069] The coloring of the glass-ceramic is a complex, non-linear process. Many of the components contained in the glass-ceramic can affect the degree to which the coloring component absorbs light. Therefore, those skilled in the art will adjust the amount of the coloring component according to the respective basic composition of the glass-ceramic to obtain the desired optical properties.

[0070] The coloring of the glass-ceramic according to the present invention by means of V2O5 as the main coloring agent is shown here as an example as follows. To reduce the transmittance to the desired value, more V2O5 will be used compared to a comparable glass-ceramic with a higher Li2O content. Therefore, the reduction of Li2O weakens the absorption of V2O5 in the glass-ceramic. Similar, sometimes even opposite correlations also exist with the other components of the basic composition.

[0071] Even small amounts of V2O5 can generally cause very intense coloring in the glass-ceramic. The glass-ceramic colored with V2O5 has a relatively low transmittance in the blue and green spectral ranges, while having a relatively high transmittance in the red spectral range. The glass-ceramic preferably contains 0 to 0.1 wt% of V2O5. Particularly preferably, it contains >0.002 to 0.08 wt%, >0.003 to 0.07 wt%, >0.004 to 0.06 wt%, >0.005 to 0.05 wt%, or even >0.01 - 0.04 wt% of V2O5. With these amounts of V2O5, for a thickness of 4 mm, the light transmittance of the glass-ceramic can be adjusted in the range of 0.1% to 80%.

[0072] In a particularly preferred further embodiment of the above-described embodiments, the ratio V2O5 / Li2O is 0.005 - 0.06, preferably 0.007 - 0.055, and particularly preferably 0.01 - 0.05. Without limitation of generality, it is assumed that the coloring effect of V2O5 depends on the microstructure of the glass-ceramic. The glass-ceramic according to the invention has a relatively low crystalline phase fraction due to the low Li2O content and, at the same time, a small grain size. It has been shown that particularly effective coloring can be achieved when the ratio of V2O5 to Li2O is adjusted within the above range. When this ratio is set within this range, for a thickness of 4 mm, the spectral transmittance at a wavelength of 630 nm can reach within the range of 0.5 - 15%, preferably within the range of 1 - 13%, and particularly preferably within the range of 2 - 10%. In the case of these transmittances, commercially available red light-emitting displays can be used when the glass-ceramic is used as a cooking surface.

[0073] By means of MoO3, the glass-ceramic can be colored particularly neutrally. The advantage of this is that light-emitting displays with a white light color can be used in cooking appliances without changing the color of the light of the display when passing through the glass-ceramic. The glass-ceramic preferably contains 0 to 0.5% by weight of MoO3. Particularly preferably, it contains >0.002 to 0.4% by weight, >0.003 to 0.3% by weight, >0.004 to 0.2% by weight, >0.005 to 0.15% by weight, or even >0.01 to 0.1% by weight of MoO3. With these amounts of MoO3, for a thickness of 4 mm, the light transmittance of the glass-ceramic can be adjusted within the range of 0.1% to 80%. At the same time, a white light-emitting display can achieve a colorless distortion presentation.

[0074] In a particularly preferred further embodiment of the above-described embodiments, the ratio MoO3 / Li2O is 0.015 - 0.1, preferably 0.02 - 0.08, and particularly preferably 0.025 - 0.07. By setting this ratio within this range, for a thickness of 4 mm, a light transmittance within the range of 0.5 - 4%, preferably 0.8 - 3.5%, particularly preferably 0.7 - 3.3%, and more particularly preferably 1.0 - 3.0% can be achieved. With these transmittances, white light-emitting displays can be used when the glass-ceramic is used as a cooking surface. At the same time, the visibility of the components present in the interior of the cooking appliance is also greatly reduced.

[0075] Nd2O3 can also be used for coloring. It differs from the other colorants in that it produces relatively narrow absorption bands in the glass-ceramic. These absorption bands are mainly located in the green spectral range. With a small amount of Nd2O3, the color coordinates of the transmitted light through the glass-ceramic can be finely adjusted. For example, glass-ceramics containing only a small amount of Fe2O3 as a coloring component usually have a yellowish tint. This may occur, for example, when TiO2 and Fe2O3 introduced through raw material impurities are present in the glass-ceramic at the same time. If such a glass-ceramic has, for example, a white bottom coating, these bottom coatings have a clearly perceptible yellowish tint. In such a glass-ceramic, the addition of Nd2O3 can be used to reduce or eliminate the yellowish tint without significantly reducing the light transmittance. This makes it possible to produce a cooking surface with a white appearance.

[0076] Preferably, the glass-ceramic contains Nd2O3 in an amount of 0 - 0.6 wt%. Since Nd2O3 is relatively expensive, its amount should be limited to 0.6 wt%. Particularly preferably, the glass-ceramic contains 0.005 - 0.5 wt%, 0.01 - 0.4 wt%, 0.02 - 0.3 wt%, 0.03 - 0.2 wt%, or even 0.04 - 0.1 wt% of Nd2O3.

[0077] Fe2O3 affects not only the transmittance in the visible spectral range but also the transmittance of near-infrared light with wavelengths up to about 3 μm. Therefore, Fe2O3 not only affects the achievability of a specific color or the presentability of a color display. The absorption of near-infrared light determines how much heat energy the glass melt in the trough can absorb. This determines how much of the heating power of the radiant heating element can pass through the glass-ceramic. This also determines whether and which infrared sensors can be used in the stove. For example, these sensors can be designed as optical touch sensors or infrared receivers for wireless data transmission. At the same time, Fe2O3 is also often contained as an impurity in the raw materials used for production. A higher content of Fe2O3 in the glass-ceramic makes it possible to use raw materials with a higher impurity content but lower cost. All of these must be considered when selecting an appropriate amount of Fe2O3. The amount of Fe2O3 should preferably be 0 - 0.4 wt%. Glass-ceramics containing more than 0.4 wt% of Fe2O3 are not compatible with commercially available radiant heating elements for cooking appliances due to the low transmittance of near-infrared light. Preferably, the glass-ceramic contains 0.005 - 0.3 wt%, 0.01 - 0.25 wt%, 0.02 - 0.2 wt%, or even 0.04 - 0.18 wt% of Fe2O3. Such glass-ceramics can be produced at low cost and are at the same time compatible with radiant heating elements and optical sensors for cooking appliances. Fe2O3 is usually contained as an impurity in the raw materials used for glass production, such as spodumene.

[0078] CoO can be included in the glass-ceramic, for example, in an amount of 0 - 0.5 wt%. Preferably, it is included in an amount of 0.01 - 0.2 wt%, more preferably 0.02 - 0.08 wt%, and particularly preferably 0.04 - 0.06 wt%.

[0079] Preferably, the glass-ceramic colored with 0.02 - 0.1 wt% of CoO additionally contains 0.02 - 0.1 wt% of Cr2O3. The glass-ceramic particularly preferably further contains 0.05 - 0.25 wt% of Fe2O3 and especially <30 ppm of V2O5. With these amounts of CoO and preferably other colorants, for a thickness of 4 mm, the light transmittance of the glass-ceramic can be adjusted within the range of 0.1% to 80%. Thus, white display can also be achieved within the warm white spectral range.

[0080] Different from V2O5, MoO3 or CoO, Cr2O3, NiO, CuO and MnO are usually used for auxiliary coloring, but they are rarely used as main colorants. Here, the main colorant refers to the coloring component that has the most important influence on the transmittance of the glass-ceramic in the visible spectral range. They usually appear as impurities in the raw materials. These components are preferably included in the glass-ceramic in an amount of 0 to 0.5 wt% respectively. Particularly preferably, they are included in the glass-ceramic in an amount of 0.001 - 0.4 wt%, 0.002 - 0.3 wt%, 0.004 - 0.2 wt%, 0.006 - 0.1 wt%, 0.008 - 0.08 wt%, or even 0.01 - 0.05 wt%.

[0081] In a preferred embodiment, the glass-ceramic contains 0 to 0.1 wt% of V2O5 or 0 to 0.5 wt% of MoO3 or 0 to 0.6 wt% of Nd2O3 or 0 to 0.4 wt% of Fe2O3 or 0 to 0.5 wt% of CoO or 0 to 0.5 wt% of Cr2O3 or 0 to 0.5 wt% of NiO or 0 to 0.5 wt% of CuO or 0 to 0.5 wt% of MnO or a combination of these components.

[0082] In addition to the coloring effect, these components can also have a positive impact on the glass quality. This is especially the case for components that absorb in the infrared spectral range in the glass melt. Due to the absorption of infrared light, the heat introduced into the melting tank by the heating device can be more effectively absorbed by the glass melt. This causes the temperature of the glass melt to rise under the same energy input. This has a positive impact on the melting of raw materials that are difficult to melt and the reduction of bubbles during clarification. This is especially the case for the above amounts of Fe2O3, CoO and NiO.

[0083] In a further embodiment of the invention, for a thickness of 4 mm, the glass-ceramic has a light transmittance of 80 - 90% or 81 - 89% or 82 - 88% or even 83 - 87%. For a thickness of 4 mm, the glass-ceramic having such a light transmittance preferably has a transmission chromaticity C* in the range of 0 - 6, preferably 1.5 - 5, particularly preferably 3.0 - 4.6.

[0084] Herein, "for a thickness of 4 mm" means that the corresponding property is either determined on a sample with a material thickness of 4 mm or determined for different material thicknesses and converted to a material thickness of 4 mm. For the transmittance data, the Lambert-Beer law can be used for conversion.

[0085] In accordance with the provisions of DIN 5033, the light transmittance is determined using standard light type D65 in the wavelength range of 380 - 780 nm. This value corresponds to the luminance Y in the CIExyY color space.

[0086] The chromaticity C* is determined from the L*a*b* color coordinates according to the following formula:

[0087]

[0088] The color coordinates a* and b* are determined from the transmission spectrum of the glass-ceramic in a known manner using standard light of standard light type D65.

[0089] The glass-ceramic having a light transmittance of 80 - 90% for a thickness of 4 mm is particularly suitable for use as a fireplace viewing window or a cooking plate. In a fireplace, such transmittance makes the flame particularly clearly visible. For example, in a cooking appliance, such transmittance makes a light-emitting display with a relatively low luminous density (such as an LCD or OLED display) particularly clearly visible.

[0090] A chromaticity C* of 0 - 6 causes only a very slight change in the color of light when passing through the glass-ceramic. For example, this enables the glass-ceramic to have a white coating, and when viewed through the glass-ceramic, the white coating still produces a white impression. For example, when used as a cooking surface or a fireplace viewing window, this is particularly important. The glass-ceramic in these applications usually has a thickness of 4 mm. The light reflected by the rear coating thus travels an optical path of 8 mm, making the color shift caused by the inherent color of the glass-ceramic have a greater effect compared to a shorter path. Therefore, a relatively low chromaticity is particularly advantageous for a cooking surface or a fireplace viewing window with a white coating on the rear side.

[0091] In a further embodiment of the invention, the glass-ceramic having a light transmittance of 80 - 90% or a corresponding preferred range and having a chromaticity C* of 2 - 6 or a corresponding preferred range, in addition to the composition according to the invention, further comprises one or more of the following components (in wt%):

[0092] Nd2O3 is 0.005 - 0.1, preferably 0.01 - 0.08, particularly preferably 0.03 - 0.065,

[0093] Fe2O3 is 0 - 0.02, preferably 0.0025 - 0.018, particularly preferably 0.005 - 0.016,

[0094] V2O5 is 0 - 0.0015, preferably 0 - 0.001, particularly preferably 0 - 0.0005,

[0095] Cr2O3 is 0 - 0.001, preferably 0 - 0.0005, particularly preferably 0 - 0.0003,

[0096] MoO3 is 0 - 0.001, preferably 0 - 0.0008, particularly preferably 0 - 0.0006,

[0097] CoO is 0 - 0.001, preferably 0 - 0.0005, particularly preferably 0 - 0.0001,

[0098] NiO is 0 - 0.001, preferably 0 - 0.0005, particularly preferably 0 - 0.0001,

[0099] CuO is 0 - 0.001, preferably 0 - 0.0007, particularly preferably 0 - 0.0002,

[0100] MnO is 0 - 0.02, preferably 0 - 0.01, particularly preferably 0 - 0.006,

[0101] TiO2 is > 3.0 - 3.5, preferably > 3.0 - 3.4, particularly preferably > 3.0 - 3.3,

[0102] ZrO2 is > 1.3 - 2.2 or 1.4 - 2.0 or 1.4 - 1.8, or even 1.4 - 1.6,

[0103] SnO2 is 0.1 - 0.2, preferably 0.11 - 0.18, particularly preferably 0.12 - 0.15.

[0104] In a particularly preferred further embodiment, the glass - ceramic contains all these components in these amounts. If these components are included in the glass - ceramic in the amounts mentioned here, then further preferably, the sum of Fe2O3 + V2O5 + Cr2O3 is 0 - 0.0225 wt%, preferably 0.0005 - 0.0175 wt%, particularly preferably 0.0010 - 0.0170 wt%.

[0105] These components, either alone or in combination with each other, affect the light transmittance and chromaticity of the glass-ceramic. If the above amounts are adhered to, fine adjustment of the light transmittance and chromaticity can be carried out within the above ranges.

[0106] The following table contains three modifications of the glass-ceramic according to the invention, based on oxides and in % by weight:

[0107] Preferably Particularly preferably Even more particularly preferably <![CDATA[Li2O]]> 1.0-<3.0 1.2- 2.8 1.6-2.4 <![CDATA[Na2O]]> 0-<1 0.05-0.9 <![CDATA[K2O]]> 0-3.0 0.1-2.6 0.3-2.3 MgO 0-<1 0.05-0.9 0.2-0.7 CaO 0-2 0.2-1.6 0.3-1.4 SrO 0-2 0.2-1.6 0.3-1.4 BaO 0-4.0 1.6-3.6 1.8-3.0 ZnO 0-6.0 1.5-4.5 2.0-3.0 <![CDATA[Al2O3]]> 17-25 17-23 17-21 <![CDATA[SiO2]]> 60-70 61-69 62-68 <![CDATA[TiO2]]> >3.0-5.0 3.1-4.5 3.2-4.2 <![CDATA[ZrO2]]> >1.3-3.0 1.4-2.6 1.5-2.3 <![CDATA[SnO2]]> 0.1-<1.0 0.15-0.8 0.2-0.6 <![CDATA[Fe2O3]]> 0-0.4 0.005-0.3 0.01-0.25 <![CDATA[V2O5]]> 0-0.1 0-0.1 0-0.1 <![CDATA[MoO3]]> 0-0.5 0-0.5 0-0.5 <![CDATA[Cr2O3]]> 0-0.5 0-0.5 0-0.5 <![CDATA[Nd2O3]]> 0-0.6 0-0.6 0-0.6 CoO 0-0.5 0-0.5 0-0.5 NiO 0-0.5 0-0.5 0-0.5 CuO 0-0.5 0-0.5 0-0.5 <![CDATA[MnO2]]> 0-0.5 0-0.5 0-0.5 <![CDATA[P2O5]]> 0-5 0.01-4 0.05-3

[0108] The uses of the glass-ceramic according to the invention are as a cooking surface, a fireplace viewing window, a grill or frying surface, a lid for a combustion element in a gas grill, an oven viewing window (especially a viewing window of a pyrolysis furnace), a workbench or tabletop in a kitchen or laboratory, a lid for a lighting device, fireproof glass and safety glass, optionally for laminated composites, a carrier plate or oven lining in heat treatment or a rear cover of a mobile electronic device.

[0109] The glass-ceramic according to the invention can in particular be used as a cooking surface. The cooking surface can here be provided entirely or partly with a decorative or functional coating on the top and / or bottom surfaces. A touch sensor for operating the cooking surface can also be provided on the bottom surface. This can for example be a printed, adhered or pressed capacitive sensor.

[0110] Furthermore, the glass-ceramic can also be present in the form of a three-dimensionally shaped plate. This means that the plate can be angled or curved, or for example contain regions shaped in the form of a wok. A cut-out for operating a gas burner is also possible, for example. Detailed Description

[0111] The present invention will be further described below with reference to embodiments.

[0112] The crystallizable green glass of the example was melted from technical batch raw materials commonly used in the glass industry at a temperature of 1680 °C for 4 hours. This choice can meet the requirements for economical raw materials and the requirements for unwanted impurities with low impurity content. After melting the batch in a crucible made of sintered quartz glass, the melt was poured into a Pt / Rh crucible having an inner crucible made of quartz glass and homogenized by stirring at a temperature of 1600 °C for 90 minutes. After homogenization, the glass was clarified at 1640 °C for 3 hours. Subsequently, blocks with dimensions of approximately 120×140×30 mm 3 were cast and cooled in a cooling furnace starting from 640 - 670 °C to room temperature at 30 K / h (depending on the viscosity of the glass) to reduce stress. The cast blocks were divided into the dimensions required for research and ceramization.

[0113] The ceramization of the samples in the green glass state was carried out in a continuous furnace by a ceramization method in the following steps:

[0114] a) Heat from room temperature to 740 °C at a heating rate of 30 K / min,

[0115] b) Hold at 740 °C for 3 minutes and 20 seconds,

[0116] c) Increase the temperature from 740 °C to 810 °C at a heating rate of 28 K / min,

[0117] d) Hold at 810 °C for 9 minutes and 20 seconds,

[0118] e) Increase the temperature from 810 °C to 930 °C at a heating rate of 21 K / min,

[0119] f) Hold at 930 °C for 6 minutes,

[0120] g) Cool to room temperature at a cooling rate of 15 K / min.

[0121] The following table contains the compositions and material properties of examples according to the present invention.

[0122] In the case of a heating rate of 2 K / min, the coefficient of thermal expansion (CTE) of the rod-shaped sample is determined dynamically by means of a push-rod dilatometer.

[0123] To measure the upper devitrification temperature (OEG), the green glass is melted in a Pt / Rh10 crucible. Then the crucible is held at different temperatures within the processing temperature range for 5 hours. The highest temperature at which the first crystals appear at the contact surface between the glass melt and the crucible wall determines the OEG.

[0124] According to the DIN ISO 7884-2 standard, a stirring viscometer is used to determine the processing point (T4) of the green glass.

[0125] When the green glass is transformed into glass-ceramics, the density increases because the density of the crystalline phase is higher than that of the amorphous glass. The shrinkage rate represents the linear change in length when the green glass is transformed into glass-ceramics. It is calculated based on the density of the green glass and the density of the glass-ceramics:

[0126]

[0127] Tg represents the transformation temperature of the green glass, also known as the glass transition temperature. It is determined by the dilatometry method.

[0128] In accordance with the provisions of DIN 5033, the light transmittance is determined using standard light type D65 within the wavelength range of 380 - 780 nm. This value corresponds to the luminance Y in the CIExyY color space. This value is a measure of the human eye's brightness perception.

[0129] According to the xy color coordinates in the CIExyY color space, the distance d to the color coordinates (0.3127 / 0.3290) of the standard light of standard light type D65 is determined as follows:

[0130]

[0131] The transmission spectrum is determined according to ISO 15368:2021. Table 2 exemplarily includes the spectral transmittances “T@...” for wavelengths 470 nm, 600 nm, 630 nm, 700 nm, 950 nm, and 1600 nm.

[0132] According to the provisions of CIE 1932, the color coordinates in the CIExyY color space and the Lab color space are determined in transmission with an 8° observer angle of view and using the light of standard light source D65.

[0133] All transmission measurements are performed on a sample with a thickness of 4 mm and smooth surfaces on both sides.

[0134] Rietveld analysis is used to determine the volume fraction “XRD fraction HQMK” or “KMK” and the grain size of the crystalline phase “XRD grain size HQMK” or “KMK” according to the X-ray diffraction spectrum.

[0135] Example 1 2 3 4 5 6 7 8 9 <![CDATA[Li2O]]> 2.991 2.890 1.880 2.780 2.600 2.610 2.921 2.590 2.870 <![CDATA[Na2O]]> 0.467 0.288 0.463 0.274 0.384 0.410 0.151 0.289 0.394 <![CDATA[K2O]]> 0.512 1.120 0.505 0.452 0.279 0.276 0.800 0.359 0.287 MgO 0.199 0.198 0.200 0.198 0.100 0.099 0.095 0.052 0.102 CaO 0.511 0.569 0.786 0.813 0.775 0.916 0.250 0.810 0.710 SrO 0.015 0.009 0.009 0.017 0.019 0.000 0.016 0.018 0.023 BaO 1.490 0.810 0.910 1.720 2.020 2.050 1.651 1.900 2.500 ZnO 2.511 2.990 3.890 2.510 2.240 2.510 2.701 2.010 2.030 <![CDATA[Al2O3]]> 20.735 20.910 19.840 21.330 21.462 21.400 21.429 21.400 21.440 <![CDATA[SiO2]]> 65.517 65.200 66.400 64.799 65.006 64.600 64.826 65.500 64.600 <![CDATA[TiO2]]> 3.011 3.160 3.160 3.180 3.190 3.180 3.181 3.180 3.180 <![CDATA[ZrO2]]> 1.502 1.384 1.388 1.396 1.399 1.390 1.391 1.390 1.390 <![CDATA[SnO2]]> 0.281 0.274 0.262 0.279 0.281 0.282 0.264 0.278 0.285 <![CDATA[Fe2O3]]> 0.091 0.095 0.091 0.091 0.090 0.094 0.116 0.094 0.093 <![CDATA[V2O5]]> 0.025 0.023 0.023 0.026 0.027 0.029 0.061 0.026 0.026 <![CDATA[Cr2O3]]> 0.004 0.005 0.005 0.004 0.003 0.005 0.005 0.005 0.004 <![CDATA[MnO2]]> 0.019 0.019 0.012 0.017 0.016 0.018 0.019 0.017 0.019 <![CDATA[P2O5]]> 0.074 0.077 0.065 0.072 0.067 0.070 0.076 0.073 0.077

[0136] Table 1: Composition of examples according to the present invention

[0137] Example 10 11 12 13 14 15 16 17 18 <![CDATA[Li2O]]> 2.780 2.860 1.290 1.870 1.900 1.670 1.690 1.910 1.890 <![CDATA[Na2O]]> 0.288 0.288 0.520 0.400 0.387 0.380 0.384 0.501 0.281 <![CDATA[K2O]]> 0.314 0.319 0.500 0.410 0.408 0.410 0.410 0.506 0.313 MgO 0.098 0.094 0.600 0.775 0.770 0.711 0.708 0.799 0.620 CaO 0.769 0.709 1.020 0.916 0.910 1.020 1.010 1.420 0.813 SrO 0.018 0.023 0.019 0.024 0.024 0.024 0.024 0.014 0.024 BaO 1.940 2.500 1.880 2.500 2.480 2.520 2.510 1.430 2.520 ZnO 2.030 2.000 3.380 2.180 2.190 2.470 2.490 2.720 2.480 <![CDATA[Al2O3]]> 21.340 21.180 19.710 20.500 20.390 20.070 19.990 19.500 20.080 <![CDATA[SiO2]]> 65.300 64.900 66.000 65.400 65.500 65.600 65.700 66.200 65.900 <![CDATA[TiO2]]> 3.160 3.170 3.180 3.180 3.180 3.210 3.220 3.170 3.190 <![CDATA[ZrO2]]> 1.401 1.392 1.390 1.390 1.401 1.400 1.401 1.390 1.400 <![CDATA[SnO2]]> 0.280 0.275 0.273 0.278 0.275 0.277 0.275 0.281 0.277 <![CDATA[Fe2O3]]> 0.116 0.120 0.094 0.094 0.092 0.091 0.091 0.093 0.091 <![CDATA[V2O5]]> 0.052 0.056 0.027 0.028 0.028 0.028 0.029 0.024 0.030 <![CDATA[Cr2O3]]> 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 <![CDATA[MnO2]]> 0.018 0.019 0.009 0.013 0.013 0.012 0.011 0.013 0.012 <![CDATA[P2O5]]> 0.073 0.074 0.057 0.064 0.062 0.062 0.062 0.062 0.058

[0138] Continued Table 1: Composition of examples according to the present invention

[0139] Example 19 20 21 22 23 24 25 26 <![CDATA[Li2O]]> 1.860 1.910 1.900 2.190 2.190 1.900 2.470 2.180 <![CDATA[Na2O]]> 0.477 0.269 0.154 0.158 0.153 0.200 0.280 0.395 <![CDATA[K2O]]> 0.507 0.408 0.419 1.500 1.100 0.222 0.570 0.491 MgO 0.796 0.134 0.940 0.197 0.620 0.727 0.502 0.190 CaO 1.410 1.210 1.692 0.812 0.820 0.910 0.880 0.910 SrO 0.014 0.025 0.013 0.021 0.016 0.023 0.023 0.024 BaO 1.440 2.620 1.390 2.030 1.520 2.530 2.390 2.520 ZnO 2.720 2.200 2.870 2.880 2.530 2.010 1.930 2.000 <![CDATA[Al2O3]]> 19.560 21.120 19.370 20.890 21.380 20.530 20.600 21.370 <![CDATA[SiO2]]> 66.000 65.000 66.100 64.200 64.500 65.800 65.400 64.800 <![CDATA[TiO2]]> 3.180 3.150 3.200 3.180 3.190 3.240 3.070 3.180 <![CDATA[ZrO2]]> 1.430 1.398 1.393 1.391 1.387 1.403 1.358 1.403 <![CDATA[SnO2]]> 0.266 0.274 0.261 0.269 0.268 0.271 0.265 0.275 <![CDATA[Fe2O3]]> 0.090 0.118 0.118 0.116 0.118 0.091 0.087 0.090 <![CDATA[V2O5]]> 0.000 0.056 0.064 0.067 0.064 0.029 0.028 0.029 <![CDATA[MoO3]]> 0.102 0.000 0.000 0.000 0.000 0.000 0.000 0.000 <![CDATA[Cr2O3]]> 0.005 0.003 0.000 0.004 0.003 0.005 0.005 0.005 <![CDATA[MnO2]]> 0.013 0.013 0.013 0.015 0.014 0.013 0.016 0.014 <![CDATA[P2O5]]> 0.062 0.060 0.062 0.073 0.068 0.061 0.070 0.065

[0140] Continued Table 1: Composition of examples according to the present invention

[0141] Example 27 28 29 30 31 <![CDATA[Li2O]]> 2.790 2.790 2.580 2.590 2.990 <![CDATA[Na2O]]> 0.490 0.483 0.496 0.494 0.930 <![CDATA[K2O]]> 1.070 1.070 1.080 1.080 0.560 MgO 0.502 0.529 0.199 0.204 0.990 CaO 0.889 0.838 1.230 1.220 0.650 SrO 0.023 0.020 0.024 0.024 0.025 BaO 2.220 1.870 2.350 2.350 2.320 ZnO 1.750 1.750 1.780 1.810 1.740 <![CDATA[Al2O3]]> 20.230 20.770 20.660 20.710 20.930 <![CDATA[SiO2]]> 64.900 64.800 64.600 64.400 63.700 <![CDATA[TiO2]]> 3.170 3.180 3.170 3.130 3.150 <![CDATA[ZrO2]]> 1.400 1.400 1.390 1.437 1.410 <![CDATA[SnO2]]> 0.281 0.276 0.275 0.278 0.290 <![CDATA[Fe2O3]]> 0.090 0.090 0.092 0.090 0.097 <![CDATA[V2O5]]> 0.028 0.026 0.026 0.000 0.001 <![CDATA[MoO3]]> 0.000 0.000 0.000 0.106 0.110 <![CDATA[Cr2O3]]> 0.005 0.005 0.005 0.004 0.002 <![CDATA[MnO2]]> 0.019 0.019 0.018 0.017 0.022 <![CDATA[P2O5]]> 0.075 0.073 0.073 0.073 0.060

[0142] Continued Table 1: Composition of examples according to the present invention

[0143] Example 32 33 34 35 36 <![CDATA[Li2O]]> 2.71 2.42 2.46 2.55 2.67 <![CDATA[Na2O]]> 0.28 0.32 0.58 0.29 0.30 <![CDATA[K2O]]> 0.32 0.31 0.30 0.21 0.21 MgO 0.42 0.42 0.32 0.32 0.32 CaO 0.62 0.41 1.02 1.03 1.03 SrO 0.01 0.01 0.01 0.01 0.01 BaO 1.72 1.51 1.71 2.52 2.53 ZnO 3.92 4.92 3.79 3.35 3.58 <![CDATA[Al2O3]]> 18.36 18.23 18.39 18.20 18.68 <![CDATA[SiO2]]> 66.52 66.40 66.20 66.30 65.50 <![CDATA[TiO2]]> 3.19 3.17 3.17 3.28 3.18 <![CDATA[ZrO2]]> 1.39 1.38 1.52 1.43 1.53 <![CDATA[SnO2]]> 0.27 0.28 0.27 0.28 0.27 <![CDATA[Fe2O3]]> 0.118 0.120 0.122 0.122 0.122 <![CDATA[V2O5]]> 0.020 0.018 0.018 0.019 0.020 <![CDATA[Cr2O3]]> 0.005 0.005 0.004 0.004 0.005 <![CDATA[MnO2]]> 0.018 0.016 0.016 0.017 0.018 <![CDATA[P2O5]]> 0.07 0.05 0.05 0.05 0.05

[0144] Continued Table 1: Composition of examples according to the present invention

[0145] Table 2: Material properties of examples according to the present invention

[0146]

[0147] Continued Table 2: Material Properties of Examples According to the Invention

[0148] Continued Table 2: Material Properties of Examples According to the Invention

[0149] Continued Table 2: Material Properties of Examples According to the Invention

[0150] Continued Table 2: Material Properties of Examples According to the Invention

[0151] Continued Table 2: Material Properties of Examples According to the Invention.

Claims

1. A lithium aluminosilicate glass-ceramic, having a thermal expansion coefficient in the range of -0.5 to 1.9 ppm / K from 20 °C to 700 °C, and comprising, on an oxide basis, a composition by weight %:

2. The lithium aluminosilicate glass-ceramic according to claim 1, characterized in that, The lithium aluminosilicate glass-ceramic contains 1.2 - 2.8 wt% or 1.4 - 2.6 wt% or 1.6 - 2.4 wt% or even 1.8 - 2.2 wt% of Li2O.

3. The lithium aluminosilicate glass-ceramic according to claim 1, characterized in that, The lithium aluminosilicate glass-ceramic contains 3.1 - 4.5 wt%, preferably 3.2 - 4.2 wt%, particularly preferably 3.3 - 4.0% of TiO2.

4. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 1.4 - 2.6 wt%, preferably 1.5 - 2.3 wt%, particularly preferably 1.6 - 2.0 wt% of ZrO2.

5. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 0.05 - 0.9 wt% or 0.1 - 0.8 wt%, 0.2 - 0.7, or even 0.3 - 0.6 wt% of MgO.

6. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 0.1 - 2.6 wt% or 0.3 - 2.3 wt% or 0.6 - 2.0 wt%, or even 0.9 - 1.6 wt% of K2O.

7. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains more MgO than K2O.

8. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 0 - <1 wt% or 0.05 - 0.9 wt% or 0.1 - 0.8 wt%, or even 0.2 - 0.7 wt% of Na2O.

9. The lithium aluminosilicate glass-ceramic according to the preceding claim, characterized in that, The lithium aluminosilicate glass-ceramic contains more MgO than Na2O.

10. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains more K2O than Na2O.

11. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains less than 0.1 wt% of As2O3 and less than 0.1 wt% of Sb2O3.

12. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 1.0 - 6.0 wt%, preferably 1.5 - 4.5 wt%, particularly preferably 2.0 - 3.0 wt% of ZnO.

13. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 1.0 - 4.0 wt% or 1.2 - 3.6 wt% or 1.4 - 3.3 wt% or even 1.6 - 3.0 wt% of BaO.

14. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains 0 to 0.1 wt% of V2O5 or 0 to 0.5 wt% of MoO3 or 0 to 0.6 wt% of Nd2O3 or 0 to 0.4 wt% of Fe2O3 or 0 to 0.5 wt% of CoO or 0 to 0.5 wt% of Cr2O3 or 0 to 0.5 wt% of NiO or 0 to 0.5 wt% of CuO or 0 to 0.5 wt% of MnO or a combination of these components.

15. Use of the glass-ceramic according to any one of the preceding claims as: a cooking surface; a fireplace viewing window; a grill or frying surface; a lid for a combustion element in a gas grill; an oven viewing window, in particular a viewing window of a pyrolysis oven; a workbench or tabletop in a kitchen or laboratory; a lid for a lighting device; a refractory glass and a safety glass; an optional laminated composite material; a carrier plate in heat treatment or an oven lining or a rear cover of a mobile electronic device.

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