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: 60-70% of SiO2, 17-25% of Al2O3, 2.0-lt of Li2O, 0.5-1% of MgO, 0.5-1% of MgO, 0.5-1% of MgO, 0.5-1% of MgO, 0.5-1% of 3.2 parts of MgO, 0-3 parts of ZrO < 2 > gt; 1.3 to 4 parts by weight of ZnOgt; 3.2 to 7 parts of SnO2, and 0.1 to 1t of SnO2; 1.0% and P2O50 to 1t; 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, the raw glass, i.e., the so-called green glass, is first 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 crystal 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, the lithium 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 with a Li2O content below 3.5% and capable of competing with the glass-ceramics on the current market has been found.

[0006] Glass-ceramics with a Li2O content below 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 to be glass ceramics with low light scattering. The transmittance of transparent glass ceramics can be adjusted within a wide range by absorption characteristics (i.e., colorability) components.

[0008] When transparent glass ceramics are used for cooking surfaces, they are either volume-colored by adding colored oxides or a bottom coating is provided 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 inexpensive without imposing limitations on the use characteristics.

[0010] Good melting properties mainly include here: a processing point at a temperature below 1340 °C, preferably below 1330 °C, 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 remove 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, undesired 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, 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 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. Herein, "ppm" means "parts per million", i.e. the relative change in dimension for a temperature change of 1 K is 10 -6 . A more negative coefficient of thermal expansion is 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 stress will 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. Furthermore, 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 only 0.6 ppm / K.

[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 a radiant heating element.

[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 use, for example, as the cooking surface in a cooking appliance having an induction heating element.

[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 2.0 - 3.2.

[0025] The components SiO2 and Al2O3 together with Li2O in the glass - ceramic form the main components of the crystalline phase. 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 temperatures, 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 temperature resistance. When the SiO2 fraction is very high, exceeding 70 wt%, deep 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 temperature 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 in thermo - 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 undesired 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 undesired 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 temperature 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 in thermo - 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 shown that if the glass-ceramic contains > 21.0 - 25 wt%, preferably 21.5 - 24 wt%, particularly preferably 22.0 - 23 wt% of Al₂O₃, this 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 2.0 - 3.2 wt%. Surprisingly, it has been shown 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 according to the invention in order to achieve the thermal shock resistance required by the invention. Additionally, a Li₂O fraction of more than 2.0 wt% has a positive effect on the manufacturability of the glass-ceramic, because this 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 increased. 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 2.1 wt%, preferably 2.2 wt%, and particularly preferably 2.3 wt% of Li₂O. As the upper limit, in this embodiment, the glass-ceramic contains a maximum of 3.1 wt%, 3.0 wt% or even 2.9 wt% of Li₂O. In this embodiment, the glass-ceramic contains 2.1 - 3.1 wt%, preferably 2.2 - 3.0 wt%, particularly preferably 2.3 - 2.9 wt% of Li₂O. Glass-ceramics with particularly high thermal shock resistance can be obtained within these narrower limits.

[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. "Main crystal phase" means that the glass-ceramic contains a volume fraction of high quartz mixed crystals greater than the volume fraction of hydrothermal quartz mixed crystals. In a further aspect 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 proportion of high quartz mixed crystals and a low proportion 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 - 3 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 3 wt%. Preferably, the glass-ceramic contains a maximum of 2.5 wt%, 2.0 wt%, 1.5 wt%, 1.0 wt%, 0.7 wt%, or even only 0.4 wt% of MgO.

[0038] In an advantageous embodiment 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%, or even 0.3 wt% of MgO. MgO can also be introduced into the glass-ceramic as an impurity in the raw materials.

[0039] Furthermore, the glass-ceramic according to the invention contains >1.3 - 4 wt% of ZrO2 and 0.1 - <1.0 wt% of SnO2. ZrO2 and SnO2 mainly act as nucleating agents in the glass-ceramic and interact closely as nucleating agents. A content of >1.3 wt% of ZrO2 and 0.1 wt% of SnO2 in combination with the other components of the glass-ceramic according to the invention is advantageous to ensure sufficient nucleation for the properties according to the invention.

[0040] The amount of ZrO2 is limited to a value of 4 wt% because ZrO2 increases the viscosity of the glass melt, thus also increasing 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%, particularly preferably 1.5 wt% of ZrO2. Furthermore, it preferably contains at most 3.9 wt%, 3.8 wt%, 3.2 wt%, 3.0 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 the acceptable deterioration of fusibility and thermoforming.

[0041] In a further development of the invention, for the above reasons, the glass-ceramic contains 1.4 - 3.9 wt%, preferably 1.5 - 3.8 wt% of ZrO2.

[0042] The amount of SnO2 should not exceed <1.0 wt%. Higher contents lead to the precipitation of Sn-containing crystalline phases at the contacting materials (such as Pt / Rh) during shaping and should be avoided. Preferably, the glass-ceramic contains at most 0.8 wt%, 0.6 wt%, or even only 0.4 wt% of SnO2.

[0043] In a further embodiment of the invention, the glass-ceramic may 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 retained bubbles.

[0044] In another improved embodiment of the invention, the glass-ceramic may 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.

[0045] Furthermore, the glass-ceramic according to the invention contains >3.2 - 1 wt% of ZnO. ZnO leads, especially in combination with a large amount of Al2O3, to the formation of undesired zinc spinel crystals. Therefore, the amount of ZnO in the glass-ceramic according to the invention is limited to 7 wt%. Additionally, experience has shown that glass-ceramics with very high amounts of ZnO tend to form undesired crystals on the surface of the glass-ceramic. Therefore, the amount of ZnO is preferably limited to at most 6.5 wt%, 6.0 wt%, 5.5 wt%, or even 5.0 wt%.

[0046] The glass-ceramic according to the invention contains more ZnO than Li2O. During crystal formation, lithium and zinc are incorporated into the high-quartz mixed crystal successively. It has been shown that, due to this very high ZnO fraction, a particularly low thermal expansion of the glass-ceramic can be achieved in the glass-ceramic according to the invention. Additionally, ZnO in the glass-ceramic according to the invention reduces the processing point and the upper devitrification temperature. Therefore, the glass-ceramic preferably contains at least 3.5 wt%, 3.8 wt%, 4.0 wt%, 4.2 wt%, 4.4 wt% or even 4.6 wt% of ZnO. In these ranges, the thermal shock resistance of the glass-ceramic is particularly improved.

[0047] In a preferred embodiment, for the reasons mentioned above, the glass-ceramic contains, for example, >3.5 - 6.5 wt%, preferably 3.8 - 6.0 wt%, particularly preferably 4.0 - 5.5 wt% of ZnO.

[0048] The glass-ceramic according to the invention 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 can even be 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.

[0049] In a preferred embodiment, the glass-ceramic contains TiO2. TiO2 together with ZrO2 and SnO2 contributes to nucleation. The amount of TiO2 is limited to a maximum of 5.0 wt%. Larger amounts of TiO2 will lead to devitrification during thermoforming. Additionally, it will lead to an undesired increase in the refractive index of the residual glass phase. Preferably, the glass-ceramic contains at least 1 wt%, 1.5 wt%, 2.0 wt%, >2.5 wt% or even >3.0 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%, 3.6 wt%, or even only 3.4 wt% of TiO2. In the case of a higher TiO2 fraction, nucleation progresses faster. Thereby, the ceramization time of the glass-ceramic can be reduced. Lower fractions can stabilize the ceramization process and prevent accidental devitrification of the green glass during thermoforming.

[0050] In a preferred embodiment, for the reasons mentioned above, the glass-ceramic contains, for example, 1 - 5 wt%, preferably 2 - 4.5 wt%, particularly preferably >2.5 - 4.0 wt% of TiO2.

[0051] In a further development of the invention, the glass-ceramic contains 0 - 4.0 wt% of BaO. BaO, like Li2O, reduces the viscosity of the glass melt and thus the processing point. To improve the fusibility of the green glass, it is advantageous if the glass-ceramic contains at least 0.2 wt%, preferably at least 0.4 wt%, 0.6 wt%, 0.8 wt%, or even 1.0 wt% of BaO in combination with the above amounts of Li2O. In the glass-ceramic, BaO also makes a significant contribution to improving the devitrification characteristics during thermoforming of the green glass. BaO reduces the upper devitrification limit of the green glass and thus helps to widen the distance between the working point and the upper devitrification limit. This widens the temperature window for stable thermoforming without devitrification problems.

[0052] 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%, preferably a maximum of 3.0 wt%, particularly preferably <2.0 wt%. The less BaO the glass-ceramic contains, the faster the ceramization proceeds.

[0053] In a further development of the invention, the glass-ceramic contains 0 - 4.0 wt%, preferably 0.4 - 3.0 wt%, particularly preferably 0.8 - <2.0 wt% of BaO.

[0054] The addition of the alkalis Na2O and K2O and the alkaline earths CaO and SrO as well as B2O3 improves the fusibility and devitrification properties during the shaping of the glass. CaO can particularly be contained in the glass-ceramic in order to reduce the processing point and the upper devitrification temperature. However, since these components do not incorporate into the crystal phase but rather remain substantially in the residual glass phase of the glass-ceramic, the content is limited. An excessive content impairs the crystallization properties when the starting glass capable of crystallization transforms into the glass-ceramic, in particular the rate of rapid ceramization. In addition, a higher content acts disadvantageously on the time / temperature tolerance of the glass-ceramic. Thus, the glass-ceramic contains each of these components in an amount of 0 - 2 wt%.

[0055] In a preferred further embodiment, the glass-ceramic contains 0 - 2 wt% of Na2O and 0 - 2 wt% of K2O. The addition of K2O serves for reducing the upper devitrification temperature without significantly changing the processing point. Thus, K2O can be used for setting the distance between these temperatures without having to increase the temperature during thermoforming. This is particularly advantageous for thermoforming.

[0056] In a further development of the invention, the glass-ceramic can contain 0.2 - 1.6 wt%, or even 0.3 - 1.4 wt% of Na2O.

[0057] In a further development of the invention, the glass-ceramic can contain 0.2 - 1.6 wt%, or even 0.3 - 1.4 wt% of K2O in combination with the aforementioned amount of Na2O.

[0058] The sum of the alkalis Na2O + K2O in combination with the aforementioned amount of ZrO2 is preferably at least 0.1 wt% and at most 3 wt%. Particularly preferably, the sum is at least 0.2 wt%, or at least 0.4 wt% or at least 0.6 wt% or at least >0.8 wt% or even at least 1.0 wt%, and at most 2.5 wt% or at most 2.0 wt% or at most 1.9 wt% or at most 1.8 wt% or even at most 1.7 wt%. In these amounts, a particularly good compromise between fusibility and devitrification is achieved for the glass-ceramic according to the invention without deteriorating the ceramization rate.

[0059] If not only MgO but also K2O is present in the glass-ceramic, then advantageously the glass-ceramic preferably contains less MgO than K2O. Such a glass-ceramic contains, among other components:

[0060] MgO >0 - <1.2 wt%,

[0061] K2O is >0 - 2 wt%, and

[0062] MgO < K2O.

[0063] In a further development of this embodiment, the ratio of K2O to MgO, K2O / MgO (by weight %), is 1.1 - 10, preferably 1.5 - 8, particularly preferably 2 - 6.

[0064] Not only MgO but also K2O acts actively on the electrical conductivity of the melt. Because potassium as an ion has a stronger influence on conductivity than magnesium. At the same time, MgO has a stronger influence on the thermal expansion of the glass-ceramic than K2O. Therefore, it is advantageous for the glass-ceramic to contain more K2O than MgO.

[0065] If the glass-ceramic contains less MgO than K2O, a particularly well-coordinated compromise is provided between fusibility, in particular the viscosity matching and resistance of the melt, and the process stability of thermoforming. At the same time, the glass-ceramic has a particularly low thermal expansion and particularly good thermal shock resistance.

[0066] In a particularly preferred further development of this embodiment, for the above reasons, the ratio of MgO to K2O, i.e., the quotient of MgO / K2O, has a value of 0 > - < 1, preferably 0.01 - 0.9, particularly preferably 0.05 - 0.8 or even 0.1 - 0.5.

[0067] In the production of glass-ceramics, As2O3 and Sb2O3 are usually used as clarifying agents. However, in the glass-ceramics according to the invention, these components have surprisingly been shown to be disadvantageous for the devitrification stability. Therefore, the amounts of As2O3 and Sb2O3 are preferably limited to less than 0.1 wt% each. Particularly preferably, the glass-ceramics each contain less than 0.09 wt%, 0.08 wt%, 0.07 wt%, 0.06 wt%, or even less than 0.05 wt% of As2O3 and Sb2. Particularly preferably, except for unavoidable traces, the glass-ceramics do not contain As2O3 and Sb2O3.

[0068] However, As2O3 and Sb2O3 can occur as impurities in the glass-ceramics, especially when using blanks containing As2O3 and Sb2O3 to manufacture the glass-ceramics. This is especially the case when using cooking surface blanks from the recycling cycle. For environmental protection and sustainable development reasons, it is advantageous to use blanks from the recycling cycle 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 each. If both As2O3 and Sb2O3 are present, they are each present in the said amounts.

[0069] In a further embodiment of the present invention, it may be advantageous if the glass-ceramic contains Cl - . The addition of a certain amount of Cl - results in better bubble quality in the green glass and thus in better bubble quality in the glass-ceramic. It has been demonstrated by combination with the remaining components that the glass-ceramic contains 0.003 - 0.1 wt%, preferably 0.005 - 0.03 wt%, particularly preferably 0.007 - 0.02 wt% of Cl - is particularly advantageous. An amount below 30 ppm does not have a sufficient effect on the bubble quality. Amounts above 1000 ppm should be avoided because the added chloride fraction may react with other components in the mixture as well as with the process exhaust gases. For example, HCl may be formed here, which can lead to 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-ceramic can be adjusted, for example, by adding NaCl to the mixture - .

[0070] 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

[0071] 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

[0072] The coloring of the glass-ceramic according to the present invention by means of V2O5 as the main coloring agent is shown here by way of example as follows. In order to reduce the transmittance to the desired value, more V2O5 will be used compared to a comparable glass-ceramic with a higher Li2O content. Thus, the reduction of Li2O results in weaker absorption of V2O5 in the glass-ceramic. Similar, sometimes even opposite correlations also exist with the other components of the basic composition

[0073] 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% by weight of V2O5. Particularly preferably, it contains >0.002 to 0.08% by weight, >0.003 to 0.07% by weight, >0.004 to 0.06% by weight, >0.005 to 0.05% by weight, or even >0.01 - 0.04% by weight of V2O5. With these amounts of V2O5, for a 4 mm thickness, the light transmittance of the glass-ceramic can be adjusted within the range of 0.1% to 80%.

[0074] In a particularly preferred further embodiment of the above-described embodiment, the ratio V2O5 / Li2O is 0.005 - 0.06, preferably 0.007 - 0.055, and particularly preferably 0.01 - 0.05. Without being limited in 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 has a small grain size. It has been shown that when the ratio of V2O5 to Li2O is adjusted within the above range, particularly effective coloring can be achieved. When this ratio is set within this range, for a 4 mm thickness, 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 applied when using the glass-ceramic as a cooking surface.

[0075] The glass-ceramic can be colored particularly neutrally with MoO3. The advantage of this is that light-emitting displays with a white light color can be applied 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 4 mm thickness, 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 and distortion-free presentation.

[0076] In a particularly preferred further embodiment of the above-described embodiment, the ratio of MoO3 / Li2O is from 0.015 to 0.1, preferably from 0.02 to 0.08, particularly preferably from 0.025 to 0.07. By setting this ratio within this range, for a thickness of 4 mm, a light transmittance in the range of 0.5 - 4%, preferably 0.8 - 3.5%, particularly preferably 0.7 - 3.3%, and even more particularly preferably 1.0 - 3.0% can be achieved. With these transmittances, a white light-emitting display can be used when using the glass-ceramic as a cooking surface. At the same time, the visibility of the components present inside the cooking appliance is also significantly reduced.

[0077] Nd2O3 can likewise be used for coloring. It differs from the remaining 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 passing through the glass-ceramic can be finely adjusted. For example, a glass-ceramic containing only a small amount of Fe2O3 as a coloring component usually has a yellowish tint. This can occur, for example, when the glass-ceramic contains both TiO2 and Fe2O3 introduced through raw material impurities at the same time. If such a glass-ceramic, for example, has 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.

[0078] Preferably, the amount of Nd2O3 contained in the glass-ceramic is from 0 to 0.6% by weight. Since Nd2O3 is relatively expensive, its amount should be limited to 0.6% by weight. Particularly preferably, the glass-ceramic contains 0.005 - 0.5% by weight, 0.01 - 0.4% by weight, 0.02 - 0.3% by weight, 0.03 - 0.2% by weight, or even 0.04 - 0.1% by weight of Nd2O3.

[0079] 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. Thus, Fe2O3 does not only affect 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 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 the 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 incompatible 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.

[0080] CoO can be contained in the glass-ceramic, for example, in an amount of 0 - 0.5 wt%. Preferably, it is contained in an amount of 0.01 - 0.2 wt%, more preferably 0.02 - 0.08 wt%, and particularly preferably 0.04 - 0.06 wt%.

[0081] 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 also contains 0.05 - 0.25 wt% of Fe2O3 and especially <30 ppm of V2O5. With these amounts of CoO and preferably other colorants, the light transmittance of the glass-ceramic can be adjusted in the range of 0.1% to 80% for a thickness of 4 mm. Thus, a white display can also be achieved in the warm white spectral range.

[0082] Unlike V2O5, MoO3, or CoO, Cr2O3, NiO, CuO, and MnO are typically used for auxiliary coloring, but they are rarely used as the main coloring agent. Here, the main coloring agent refers to the coloring component that has the most significant impact on the transmittance of the glass-ceramic in the visible spectral range. They usually occur as impurities in the raw materials. These components are preferably included in the glass-ceramic in an amount of 0 to 0.5 wt%. 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%.

[0083] 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.

[0084] In addition to their 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 with the same energy input. This has a positive impact on both 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.

[0085] In a further aspect of the present 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.

[0086] Here, "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 transmittance data, the Lambert-Beer law can be used for conversion.

[0087] 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.

[0088] The chromaticity C* is determined from the L*a*b* color coordinates according to the following formula:

[0089]

[0090] 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.

[0091] A 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, this transmittance makes the flame particularly clearly visible. For example, in a cooking appliance, this transmittance makes a light-emitting display having a relatively low luminous density (such as an LCD or an OLED display) particularly clearly visible.

[0092] 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, such that the color shift caused by the inherent color of the glass-ceramic has a greater effect compared to when the path is shorter. Therefore, for a cooking surface or a fireplace viewing window with a white coating on the rear side, a relatively low chromaticity is particularly advantageous.

[0093] In a further embodiment of the present invention, a glass-ceramic having a light transmittance of 80 - 90% or a corresponding preferred range and a chromaticity C* of 2 - 6 or a corresponding preferred range, in addition to the composition according to the present invention, further comprises one or more of the following components (in wt%):

[0094] Nd2O3 0.005 - 0.1, preferably 0.01 - 0.08, particularly preferably 0.03 - 0.065,

[0095] Fe2O3 0 - 0.02, preferably 0.0025 - 0.018, particularly preferably 0.005 - 0.016,

[0096] V2O5 0 - 0.0015, preferably 0 - 0.001, particularly preferably 0 - 0.0005,

[0097] Cr2O3 0 - 0.001, preferably 0 - 0.0005, particularly preferably 0 - 0.0003,

[0098] MoO3 0 - 0.001, preferably 0 - 0.0008, particularly preferably 0 - 0.0006,

[0099] CoO 0 - 0.001, preferably 0 - 0.0005, particularly preferably 0 - 0.0001,

[0100] NiO 0 - 0.001, preferably 0 - 0.0005, particularly preferably 0 - 0.0001,

[0101] CuO 0 - 0.001, preferably 0 - 0.0007, particularly preferably 0 - 0.0002,

[0102] MnO 0 - 0.02, preferably 0 - 0.01, particularly preferably 0 - 0.006,

[0103] TiO2 1.6 - 2.5, preferably 2.0 - 2.4, particularly preferably 2.1 - 2.3,

[0104] ZrO2 > 1.3 - 2.2 or 1.4 - 2.0 or 1.4 - 1.8, or even 1.4 - 1.6,

[0105] SnO2 0.1 - 0.2, preferably 0.1 - 0.18, particularly preferably 0.1 - 0.15.

[0106] In a particularly preferred further embodiment, the glass - ceramic contains all these components present in these amounts. If these components are included in the glass - ceramic in the amounts mentioned here, then it is further preferred that the sum of Fe2O3 + V2O5 + Cr2O3 is 0 - 0.0225 wt%, preferably 0.0005 - 0.0175 wt%, particularly preferably 0.0010 - 0.0170 wt%.

[0107] These components, whether alone or in combination with each other, affect the light transmittance and chromaticity of the glass - ceramic. If the above - mentioned amounts are adhered to, the light transmittance and chromaticity can be finely adjusted within the above - mentioned ranges.

[0108] The following table contains three embodiments of the glass - ceramic according to the invention, based on oxides and in wt%:

[0109] Preferably Particularly preferably Most preferably <![CDATA[Li2O]]> 2.0-3.2 2.1-3.1 2.2-3.0 <![CDATA[Na2O]]> 0-2 0.2-1.6 0.3-1.4 <![CDATA[K2O]]> 0-2 0.2-1.6 0.3-1.4 MgO 0-3 0.05-1.5 0.1-0.7 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 0.4-3.0 0.8-<2.0 ZnO >3.2-7 >3.5-6.5 3.8-6.0 <![CDATA[Al2O3]]> 17-25 17-23 17-21 <![CDATA[SiO2]]> 60-70 61-69 62-68 <![CDATA[TiO2]]> 1-5 2-4.5 >2.5-4.0 <![CDATA[ZrO2]]> >1.3-4 1.4-3.9 1.5-3.8 <![CDATA[SnO2]]> 0.1-<1.0 0.1-0.8 0.2-0.7 <![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

[0110] 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 lighting equipment, refractory glass and safety glass, optionally for laminated composites, a carrier plate or oven lining in heat treatment or the back cover of a mobile electronic device.

[0111] The glass-ceramics according to the invention can in particular be used as a cooking surface. The cooking surface can here be provided, in whole or in part, with a decorative or functional coating on the top and / or bottom surfaces. Touch sensors for operating the cooking surface can also be provided on the bottom surface. These can be, for example, printed, adhered or pressed capacitive sensors.

[0112] Furthermore, the glass-ceramics 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. Cutouts, for example for operating gas burners, are also possible. Detailed Description of the Invention

[0113] The present invention will be further described below with reference to embodiments.

[0114] The crystallizable green glass of the embodiment is melted from the 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 low impurity content of undesired impurities. After melting the batch in a crucible made of sintered quartz glass, the melt is 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 is clarified at 1640 °C for 3 hours. Subsequently, blocks with dimensions of approximately 120×140×30 mm 3 are 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 are divided into the dimensions required for research and ceramization.

[0115] The ceramization of the samples in the green glass state is carried out in a continuous furnace by a ceramization process in the following steps:

[0116] a) Heating from room temperature to 740 °C at a heating rate of 30 K / min,

[0117] b) Holding at 740 °C for 3 minutes and 20 seconds,

[0118] c) Increasing the temperature from 740 °C to 810 °C at a heating rate of 28 K / min,

[0119] d) Holding at 810 °C for 9 minutes and 20 seconds,

[0120] e) Increasing the temperature from 810 °C to 930 °C at a heating rate of 21 K / min,

[0121] f) Holding at 930 °C for 6 minutes,

[0122] g) Cooling to room temperature at a cooling rate of 15 K / min.

[0123] The following table contains the compositions and material properties of examples according to the present invention. Different from other examples, Examples 2 and 4 are heated to 945 °C and maintained at this temperature in steps e) and f).

[0124] 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.

[0125] To measure the upper devitrification temperature (OEG), the green glass is melted in a Pt / Rh10 crucible. Then the crucible is held for 5 hours at different temperatures within the processing temperature range. The highest temperature at which the first crystals appear at the contact surface of the glass melt with the crucible wall determines the OEG.

[0126] According to the DIN ISO 7884-2 standard, a stirring viscometer is used to determine the processing point (T4) of the green glass.

[0127] When the green glass is transformed into a glass-ceramic, 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 transforms into a glass-ceramic. It is calculated based on the density of the green glass and the density of the glass-ceramic:

[0128]

[0129] Tg represents the transformation temperature of the green glass, also known as the glass transition temperature. It is determined by the dilatometric method.

[0130] In accordance with DIN 5033, the light transmittance is determined using light of standard light type D65 in 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.

[0131] According to the xy color coordinates of 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:

[0132]

[0133] The transmission spectrum is determined according to ISO 15368:2021. Table 2 exemplarily contains the spectral transmittances "T@..." for wavelengths of 470 nm, 600 nm, 630 nm, 700 nm, 950 nm, and 1600 nm.

[0134] In accordance with CIE 1932, the color coordinates in the CIExyY color space and the Lab color space are determined in transmission with an 8° observer angle and using light of standard light source D65.

[0135] All transmission measurements were performed on smooth-sided samples with a thickness of 4 mm.

[0136] Rietveld analysis was 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" from the X-ray diffraction spectra.

[0137] Example 1 2 3 4 <![CDATA[Li2O]]> 2.100 2.100 2.100 2.100 <![CDATA[Na2O]]> 0.528 0.528 0.514 0.514 <![CDATA[K2O]]> 0.720 0.720 1.150 1.150 MgO 0.304 0.304 0.216 0.216 CaO 0.200 0.200 0.240 0.240 SrO 0.014 0.014 0.010 0.010 BaO 1.380 1.380 0.820 0.820 ZnO 4.730 4.730 5.260 5.260 <![CDATA[Al2O3]]> 19.400 19.400 19.220 19.220 <![CDATA[SiO2]]> 65.600 65.600 65.400 65.400 <![CDATA[TiO2]]> 3.170 3.170 3.180 3.180 <![CDATA[ZrO2]]> 1.380 1.380 1.380 1.380 <![CDATA[SnO2]]> 0.272 0.272 0.278 0.278 <![CDATA[Fe2O3]]> 0.093 0.093 0.093 0.093 <![CDATA[V2O5]]> 0.025 0.025 0.023 0.023 <![CDATA[Cr2O3]]> 0.005 0.005 0.005 0.005 <![CDATA[MnO2]]> 0.014 0.014 0.014 0.014 <![CDATA[P2O5]]> 0.064 0.064 0.067 0.067

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

[0139] Example 5 6 7 8 9 10 11 <![CDATA[Li2O]]> 2.71 2.42 2.46 2.55 2.67 2.03 2.44 <![CDATA[Na2O]]> 0.28 0.32 0.58 0.29 0.30 0.31 0.32 <![CDATA[K2O]]> 0.32 0.31 0.30 0.21 0.21 0.21 0.34 MgO 0.42 0.42 0.32 0.32 0.32 1.66 1.83 CaO 0.62 0.41 1.02 1.03 1.03 0.72 0.56 SrO 0.01 0.01 0.01 0.01 0.01 0.01 0.01 BaO 1.72 1.51 1.71 2.52 2.53 1.48 1.58 ZnO 3.92 4.92 3.79 3.35 3.58 4.05 3.49 <![CDATA[Al2O3]]> 18.36 18.23 18.39 18.20 18.68 17.46 19.33 <![CDATA[SiO2]]> 66.52 66.40 66.20 66.30 65.50 66.98 64.98 <![CDATA[TiO2]]> 3.19 3.17 3.17 3.28 3.18 3.18 3.19 <![CDATA[ZrO2]]> 1.39 1.38 1.52 1.43 1.53 1.38 1.40 <![CDATA[SnO2]]> 0.27 0.28 0.27 0.28 0.27 0.28 0.28 <![CDATA[Fe2O3]]> 0.1180 0.1200 0.1220 0.1220 0.1220 0.1210 0.1160 <![CDATA[V2O5]]> 0.0200 0.0180 0.0180 0.0190 0.0200 0.0160 0.0170 <![CDATA[Cr2O3]]> 0.0045 0.0046 0.0043 0.0042 0.0045 0.0044 0.0047 <![CDATA[MnO2]]> 0.0175 0.0159 0.0163 0.0169 0.0179 0.0137 0.0160 <![CDATA[P2O5]]> 0.07 0.05 0.05 0.05 0.05 0.06 0.07

[0140] Continued Table 1

[0141]

[0142] Table 2: Material properties of examples according to the invention

[0143]

[0144] Continued Table 2.

Claims

1. A lithium aluminosilicate glass-ceramic, having a coefficient of thermal expansion 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, wherein The lithium aluminosilicate glass-ceramic contains 2.1 - 3.1 wt%, preferably 2.2 - 3.0 wt%, particularly preferably 2.3 - 2.9 wt% of Li2O.

3. The lithium aluminosilicate glass-ceramic according to claim 1, wherein The lithium aluminosilicate glass-ceramic contains 1 - 5 wt%, preferably 2 - 4.5 wt%, particularly preferably >2.5 - 4.0 wt% 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 - 3.9 wt%, preferably 1.5 - 3.8 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 - 4.0 wt%, preferably 0.4 - 3.0 wt%, particularly preferably 0.8 - <2.0 wt% of BaO.

6. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains >3.5 - 6.5 wt%, preferably 3.8 - 6.0 wt%, particularly preferably 4.0 - 5.5 wt% of ZnO.

7. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The amount of Na2O + K2O is preferably at least 0.1 wt% and at most 3 wt%, preferably at least 0.2 wt% or at least 0.4 wt% or at least 0.6 wt% or at least >0.8 wt% or even at least 1.0 wt%, and at most 2.5 wt% or at most 2.0 wt% or at most 1.9 wt% or at most 1.8 wt% or even at most 1.7 wt%.

8. The lithium aluminosilicate glass-ceramic according to any one of the preceding claims, characterized in that, The lithium aluminosilicate glass-ceramic contains less MgO than K2O, preferably MgO is >0 - <1.2 wt%, and K2O is >0 - 2 wt%, and MgO < K2O.

9. 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.

10. 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.

11. 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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