Lithium aluminum silicate glass ceramics

Abstract

The lithium aluminum silicate glass ceramics according to the present invention exhibit a coefficient of thermal expansion of -0.5 to 1.9 ppm / K in the temperature range 20°C to 700°C and their use. The glass ceramics contain the following components in the indicated amounts, expressed in weight percent on an oxide basis: SiO2 60-70, Al2O3 17-25, Li2O 1 to <2.9, MgO 0 to <1, Na2O >0.05 to <0.5, K2O >0.05 to <0.6.

Description

[Technical Field]

[0001] The present invention relates to lithium aluminum silicate glass-ceramics suitable for use as cooktops in cooking appliances and their uses.

[0002] Background of the Invention Glass-ceramic cooktops and the glass-ceramics used therein have been known for a long time. These include lithium aluminum silicate (LAS) glass-ceramics, which contain either high-quartz solid solution (HQMK) for transparent materials or keatite solid solution (KMK) for translucent or opaque materials as the predominant crystalline phase. To produce such glass-ceramics, a starting glass, known as a green glass, is first prepared by methods conventionally used in glassmaking. This green glass is then converted into a glass-ceramic by a heat treatment known as ceramization.

[0003] An essential characteristic of these materials used as cooktops is their very low coefficient of thermal expansion in the temperature range from room temperature to 700°C. This low coefficient of thermal expansion results in high thermal shock resistance. The coefficient of thermal expansion is set by the combination of a crystalline phase with a negative coefficient of thermal expansion and a residual amorphous glass phase with a positive coefficient of thermal expansion. For this reason, conventional glass-ceramics typically use lithium percentages of more than 3.6% by weight and up to 5.0% by weight.

[0004] Due to the rising cost of lithium as a raw material, it is advantageous for economic reasons to minimize the proportion of lithium in glass-ceramics. However, lithium is one of the three main components of lithium aluminum silicate glass-ceramics, so it cannot simply be reduced at will. The proportion of Li2O directly affects key properties of glass-ceramics, such as their viscosity when melted, which is important for manufacturability, and their coefficient of thermal expansion, which is important for use as cooktops.

[0005] The trend in lithium prices is not a new issue. For the past 20 years, the price of lithium has been steadily increasing. Despite this long-standing need, most commercially available glass-ceramics for cooktops contain approximately 3.8% Li2O by weight. To date, it is virtually impossible to find glass-ceramics containing less than 3.5% Li2O that can compete with currently available glass-ceramics.

[0006] Glass-ceramics with a proportion of LiO of less than 3.5% by weight are known from WO 2012 / 010341, EP 3502069, US 2017050880, US 2020189965, US 2020140322, US 2021387899, and WO 2021 / 224412. However, these glass-ceramics have various drawbacks, such as reduced thermal shock resistance and poor melting properties of the green glass.

[0007] In this context, transparent glass-ceramics are understood, as is customary, to mean glass-ceramics with low light scattering, the transmittance of which can be adjusted over a wide range by the addition of absorbing, i.e. coloring, components.

[0008] When transparent glass-ceramics are used for cooktops, they are volume-colored by adding coloring oxides or by applying an undercoat to visually conceal the technical equipment underneath. Various coloring oxides can be used for volume-coloring glass-ceramics. These include, among others, V2O5, CoO, Fe2O3, Cr2O3, Nd2O3, NiO, CuO, MnO, and MoO3. Each of these coloring oxides has a different effect on the absorption of glass-ceramics in the visible and infrared spectral ranges. The coloring of glass-ceramics is described, inter alia, in WO 11089220, U.S. Pat. No. 8765619, DE 102008050263, and DE 102009013127.

[0009] Problem to be solved by the invention The object of the present invention is to provide a lithium aluminum silicate glass ceramic which has the good melting properties of green glass without any limitations in terms of use properties and is inexpensive.

[0010] Good melting properties include, in particular, a processing point of less than 1340° C., advantageously less than 1330° C., particularly preferably less than 1320° C. The processing point is when the green glass is 10 4 dPa * This is the temperature at which the glass has a viscosity of 1000 psi. Hot forming of green glass is carried out around this temperature. The higher the temperature during hot forming, the more complicated it becomes to dissipate the heat introduced into the forming machine by the glass. At temperatures above 1340 °C, this can only be achieved by reducing the heat output by reducing the glass throughput, which is economically unfavorable.

[0011] If the temperature falls below the upper devitrification temperature during hot forming, undesirable spontaneous crystallization may occur. To avoid this, the upper devitrification temperature should be at least 15 K, preferably at least 20 K, and particularly preferably at least 30 K lower than the processing point.

[0012] Glass-ceramics are particularly desirable for use as cooktops with all types of heating elements, including radiant, induction, and gas heating elements, which require a sufficiently high thermal shock resistance as well as a high long-term heat resistance.

[0013] Summary of the Invention The problem of the present invention is solved by the subject matter of the independent claims. Preferred embodiments and developments can be found in the dependent claims.

[0014] The lithium aluminum silicate glass ceramic according to the present invention has a thermal expansion coefficient of -0.5 to 1.9 ppm / K in the range of 20° C. to 700° C. The glass ceramic contains the following components in the indicated amounts, expressed in weight percent on an oxide basis: SiO260~70 Al2O317~25 Li2O 1~<2.9 MgO 0~<1 Na2O >0.05~<0.5 K2O >0.05~<0.6

[0015] Glass-ceramics with an appropriate thermal expansion coefficient combine high thermal shock resistance with high long-term thermal stability, making them suitable for use as cooktops with any type of heating element. The thermal expansion coefficient is at least -0.5 ppm / K, where "ppm" stands for "parts per million," i.e., 10 parts per million for a temperature change of 1 K. -6This refers to the relative magnitude change in the coefficient of thermal expansion. Shifting the coefficient of thermal expansion towards more negative values ​​is to be avoided. A negative coefficient of thermal expansion, i.e., contraction, generates tensile stresses on the surface of the glass-ceramic during heating. At values ​​below -0.5 ppm / K, these stresses can reduce the mechanical strength of the cooktop at typical operating temperatures of the cooking appliance. A coefficient of thermal expansion above 1.9 ppm / K is also to be avoided. A coefficient of thermal expansion above 1.9 ppm / K does not ensure sufficient thermal shock resistance for the use of glass-ceramics in cooking appliances with radiant heating elements.

[0016] In one development of the invention, the thermal expansion coefficient 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 thermal expansion coefficient is advantageously 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.

[0017] In a preferred embodiment of the invention, the glass-ceramics have a thermal expansion coefficient of -0.5 to 1.0 ppm / K, advantageously -0.1 to 0.8 ppm / K, particularly preferably -0 to 0.6 ppm / K. Such glass-ceramics are particularly suitable for cooktops of cooking appliances equipped with radiant heating elements.

[0018] In a further preferred embodiment of the invention, the glass-ceramics have a thermal expansion coefficient of 0.5 to 1.9 ppm / K, advantageously -0.7 to 1.7 ppm / K, particularly preferably 0.9 to 1.5 ppm / K. Such glass-ceramics are suitable, for example, for cooktops of cooking appliances with induction heating elements.

[0019] The glass ceramic according to the invention comprises the following components in % by weight: SiO260~70, Al2O317~25 and Li2O 1~<2.9.

[0020] The elements SiO2 and Al2O3 form the main crystalline phase together with Li2O in glass-ceramics. At the same time, they largely determine the glass-forming properties and viscosity of the green glass.

[0021] The SiO2 content of the glass ceramics according to the present invention should be a maximum of 70% by weight, since this component significantly increases the viscosity of the glass, especially the processing point. Higher SiO2 contents are uneconomical for achieving good glass melting and low forming temperatures. The minimum SiO2 content should be 60% by weight, since this is advantageous for desired properties, such as chemical and heat resistance. If the SiO2 proportion is too high, exceeding 70% by weight, low quartz crystals may form during ceramization, which leads to a significant increase in the thermal expansion coefficient.

[0022] Advantageously, the glass-ceramic contains at least 61%, 62%, 63%, 64%, or even 65% by weight of SiO2. The more SiO2 contained in the glass-ceramic, the better its heat and chemical resistance. Furthermore, the glass-ceramic advantageously contains 69%, 68%, 67%, or even only 66% or less by weight of SiO2. The less SiO2 contained in the glass-ceramic, the better the meltability and processability of the green glass in hot forming.

[0023] The Al2O3 content of the glass-ceramics according to the present invention is in the range of 17-25 wt. Higher Al2O3 proportions lead to problems of devitrification and undesired mullite formation. Therefore, it should not exceed 25 wt. An Al2O3 content below 17 wt. % is detrimental to the formation of a high-quartz solid solution and promotes the formation of undesired crystalline phases.

[0024] Advantageously, the glass-ceramic contains at least 18%, 19%, or even 20% Al2O3 by weight. The more Al2O3 contained in the glass-ceramic, the better its heat resistance. Furthermore, the glass-ceramic advantageously contains 24%, 23%, 22%, or even only 21% Al2O3 by weight or less. The less Al2O3 contained in the glass-ceramic, the better the meltability and processability of the green glass in hot forming.

[0025] It has proven particularly advantageous for the meltability of the green glass if the glass ceramic comprises 17 to <19.0% by weight, advantageously 17.5 to 18.9% by weight, particularly preferably 18 to 18.8% by weight, of Al2O3.

[0026] It has proven particularly advantageous for the heat resistance of the glass-ceramics if they contain >21.0-25% by weight, advantageously 21.5-24% by weight, particularly preferably 22.0-23% by weight, of Al2O3.

[0027] In one development of the invention, the ratio of SiO to AlO in weight percent in the glass ceramic, SiO / AlO, is less than 3.5, preferably less than 3.3, particularly preferably less than 3.15, and greater than 2.4, preferably greater than 3.0, particularly preferably greater than 3.1. In this range, a particularly favorable compromise exists between the meltability of the batch raw materials and the devitrification stability during hot forming.

[0028] The Li2O content of the glass ceramics according to the present invention is in the range of 1 to <2.9% by weight. Surprisingly, it has been found that a Li2O content in this range, combined with the remaining components within the stated limits, allows for the production of glass ceramics with high thermal shock resistance and good melting properties. Because Li2O significantly influences the thermal expansion coefficient of the glass ceramic, Li2O is selected within the above-mentioned limits in combination with the remaining components of the glass ceramics according to the present invention, thereby achieving the thermal shock resistance required for the present invention. Furthermore, a Li2O content of more than 1% by weight reduces the electrical resistance and viscosity of the glass melt, thereby lowering the processing point, thus favorably affecting the manufacturability of the glass ceramics. The reduced viscosity of the glass melt also improves the efficiency of the fining process. This improved fining process reduces production waste due to bubble formation in the green glass.

[0029] In a preferred embodiment, the glass ceramic contains 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or even 1.8 wt.% LiO. As an upper limit, the glass ceramic advantageously contains 2.8, 2.7, 2.6, or even 2.5 wt.% LiO. Particularly preferably, the glass ceramic contains 1.1 to 2.8 wt.%, or 1.2 to 2.7 wt.%, or 1.3 to 2.6 wt.%, or 1.4 to 2.5 wt.% LiO. Within these narrow limits, glass ceramics with particularly high thermal shock resistance can be obtained in combination with other components.

[0030] Lithium sources are typically natural mineral sources such as spodumene and petalite, or synthetically produced Li2CO3. However, natural mineral sources contain impurities that can have undesirable effects on, for example, the optical properties of glass-ceramics. Furthermore, the amount of impurities in natural materials can vary from source to source, making it difficult to determine the desired properties of the glass-ceramics. For these reasons, it is advantageous to minimize the amount of Li2O in glass-ceramics.

[0031] In a preferred embodiment, the glass ceramic comprises a high-quartz solid solution as the predominant crystalline phase. "Predominant crystalline phase" means that the glass ceramic comprises a large volume fraction of the high-quartz solid solution. In one development of this embodiment, the glass ceramic comprises <10 vol.%, preferably <5 vol.%, particularly preferably <3 vol.% of the high-quartz solid solution. Here, these volume percentage data are relative to the volume of the glass ceramic, preferably the volume of the crystalline phase. The volume fraction is determined by Rietveld refinement from the X-ray diffraction spectrum.

[0032] High-quartz solid solutions generally have a high thermal expansion coefficient. Therefore, a high proportion of high-quartz solid solution and a low proportion of keatite solid solution are particularly advantageous for the thermal expansion coefficient of the glass-ceramic, thereby improving the thermal shock resistance of the glass-ceramic.

[0033] In addition to the aforementioned amounts of SiO2, Al2O3, and Li2O, the glass-ceramics according to the invention contain 0 to <1 wt.% MgO. Since MgO leads to an increase in the thermal expansion coefficient of the glass-ceramics, the amount of MgO in the glass-ceramics is limited to <1 wt.%. Advantageously, the glass-ceramics contain <0.8 wt.%, <0.7 wt.%, <0.6 wt.%, <0.5 wt.%, <0.4 wt.%, or even only <0.3 wt.% MgO.

[0034] In an advantageous embodiment of the present invention, it may be preferable for the glass ceramic to contain a small amount of MgO. This small amount can be used to lower the processing point and the upper devitrification temperature. The glass ceramic preferably contains at least 0.05 wt. %, particularly preferably at least 0.1 wt. % MgO. MgO may also be introduced into the glass ceramic as an impurity in the raw materials.

[0035] In a particularly preferred embodiment, the glass-ceramic may contain 0 to <0.8 wt. %, 0 to <0.6 wt. %, 0 to <0.5 wt. %, 0.05 to <0.4 wt. %, or 0.1 to <0.3 wt. % MgO for the reasons stated above.

[0036] The addition of alkali metals Na2O and K2O improves meltability and devitrification behavior during glass forming. Both components increase the electrical conductivity of the melt, facilitating the coupling of energy through an electric heater in the melting bath. However, their content is limited because these components are not incorporated into the crystalline phase but remain essentially in the residual glass phase of the glass-ceramic. Excessively high contents impair the crystallization behavior during the conversion of the crystallizable starting glass to the glass-ceramic, particularly at the expense of a high ceramization rate. Furthermore, high contents have an unfavorable effect on the long-term durability / heat resistance of the glass-ceramic. Therefore, the glass-ceramic according to the present invention contains >0.05 to <0.5 wt.% Na2O and >0.05 to <0.6 wt.% K2O.

[0037] In a preferred development, the glass ceramic comprises 0.1 to 0.4% by weight, advantageously 0.2 to 0.3% by weight, of Na O. In a further preferred development, the glass ceramic comprises 0.1 to 0.5% by weight, advantageously 0.2 to 0.4% by weight, of K O.

[0038] In one development of the invention, the sum of the alkali metals NaO+KO in combination with the remaining components of the glass ceramic is advantageously at least 0.2% by weight and not more than 1% by weight. Particularly preferably, the sum is at least 0.3% by weight, or at least 0.4% by weight, or at least 0.5% by weight, and not more than 1.0% by weight, or not more than 0.9% by weight, or not more than 0.8% by weight, or not more than 0.7% by weight, or even not more than 0.6% by weight. With these amounts, a particularly good compromise between improved meltability and devitrification can be achieved in the glass ceramic according to the invention, without impairing the ceramization rate.

[0039] In one development of the invention, the glass ceramic comprises less MgO than K2O and / or less MgO than Na2O.

[0040] Both MgO and K2O and Na2O have a positive effect on the electrical conductivity of the melt. However, potassium and sodium ions are more mobile than magnesium, and therefore have a stronger effect on conductivity. At the same time, MgO has a stronger effect on the thermal expansion coefficient of glass-ceramics than K2O and Na2O. Therefore, it is advantageous for glass-ceramics to contain more K2O and / or more Na2O than MgO.

[0041] The ratio of K2O to Na2O, K2O / Na2O, can be used to fine-tune the meltability and thermal expansion. Na2O improves meltability more than K2O in this composition and somewhat reduces the viscosity of the glass melt, but somewhat increases the thermal expansion of the glass-ceramic.

[0042] In a first preferred embodiment of the invention, the ratio of K2O to Na2O in wt. % K2O / Na2O is in the range of 0.1 to 2, advantageously 0.5 to 1.5, particularly preferably 0.7 to 1.3, which provides a particularly good balance of the above-mentioned properties.

[0043] In a second preferred embodiment of the present invention, the ratio of KO to NaO in weight percent is in the range of 0.1 to <1, advantageously 0.2 to 0.9, particularly preferably 0.3 to 0.8. This embodiment exhibits improved meltability and viscosity, which can be particularly advantageous if the glass-ceramic contains the remaining components in combinations that tend to be somewhat difficult to melt or to exhibit somewhat high viscosities.

[0044] In a third preferred embodiment of the present invention, the ratio of K2O to Na2O in weight percent ranges from 1 to 2, advantageously from 1.1 to 1.9, particularly preferably from 1.2 to 1.8. This embodiment exhibits improved thermal expansion, which can be particularly advantageous if the glass-ceramic contains the remaining components in combinations that tend to exhibit somewhat higher thermal expansion.

[0045] In one development of the invention, the glass ceramic contains >1.7 to 6.0 wt. % ZnO. ZnO, especially in combination with large amounts of Al2O3, can lead to the undesired formation of gahnite crystals. Therefore, the amount in the glass ceramic according to the invention is limited to 6.0 wt. %. Furthermore, it has been found empirically that glass ceramics with very large amounts of ZnO tend to form undesired crystals on the surface of the glass ceramic. Therefore, the amount of ZnO is advantageously limited to an amount of 5.5 wt. %, 5.0 wt. %, 4.5 wt. %, or even 4.0 wt. % or less.

[0046] ZnO lowers the working point and upper devitrification temperature in the glass ceramics according to the invention. Therefore, advantageously, the glass ceramics contain at least >1.7 wt.%, 2.0 wt.%, 2.5 wt.%, or even at least 3.0 wt.% ZnO. The thermal shock resistance of the glass ceramics is particularly improved with a ZnO content in these ranges.

[0047] In a preferred embodiment, the glass-ceramic contains >1.7-6.0 wt. %, or 2.0-5.5 wt. %, or 2.5-5.0 wt. %, or even 3.0-4.0 wt. % ZnO for the reasons stated above.

[0048] Surprisingly, it has been found that the invention can be further developed by selecting the amounts of Li2O and ZnO so that they differ by ±0.5% by weight, or ±0.3% by weight, or even ±0.2% by weight. Glass-ceramics that fulfill this condition are characterized by good meltability and at the same time stable hot forming without undesirable devitrification problems.

[0049] In one development of the invention, the glass ceramic contains 0 to 4 wt. % BaO. BaO, like Li2O, causes a decrease in the viscosity of the glass melt and thus a decrease in the processing point. To improve the meltability of the green glass, it is advantageous for the glass ceramic to contain at least 0.1 wt. % BaO in combination with the above-mentioned amount of Li2O, advantageously at least 0.3 wt. %, 0.6 wt. %, 0.9 wt. %, or even 1 wt. % BaO. In the glass ceramic, BaO also significantly contributes to improving the devitrification behavior of the green glass during hot forming.

[0050] However, it has been found that BaO can have a negative effect on the formation of crystalline phases during ceramization. Therefore, to avoid the need for long ceramization times, the amount of BaO is limited to a maximum of 4 wt. %, advantageously a maximum of 3.5 wt. %, particularly preferably 3.0 wt. %, or even a maximum of 2.7 wt. The less BaO contained in the glass-ceramic, the faster the ceramization.

[0051] In one development of the invention, the glass ceramic contains 0.1 to <1.0 wt. % SnO2. 0.1 wt. % SnO2 is advantageous in combination with other components of the glass ceramic according to the invention to ensure sufficient nucleation for the properties according to the invention. However, amounts of <1.0 wt. % should not be exceeded. Higher contents lead to the crystallization of Sn-containing crystalline phases on contact materials (e.g., Pt / Rh) during molding and should be avoided. Preferably, the glass ceramic contains 0.1 to <1.0 wt. % SnO2, preferably 0.15 to 0.8 wt. %, particularly preferably 0.2 to 0.6 wt. % SnO2.

[0052] In one development of the invention, the glass-ceramics can contain 0.1 to 0.8 wt. %, preferably 0.2 to 0.7 wt. %, and particularly preferably 0.3 to 0.6 wt. % SnO2. In these amounts, SnO2 can assist in the fining process of green glass. Glass-ceramics with these amounts of SnO2 are characterized by a particularly low number of defects due to trapped gas bubbles.

[0053] In a further development of the invention, the glass-ceramic may contain 0 to 0.8 wt. %, preferably 0.1 to 0.6 wt. %, particularly preferably 0.2 to 0.4 wt. % CeO2, which in combination with SnO2 can likewise aid the fining process and improve bubble quality.

[0054] In one development of the invention, the glass ceramic contains TiO2. TiO2, together with SnO2, contributes to nucleation. The amount of TiO2 is limited to a value of <4.2 wt.% in combination with the components of the glass ceramic according to the invention. Higher amounts of TiO2 can lead to devitrification during hot forming. This can also lead to an undesirable increase in the refractive index of the residual glass phase. Advantageously, the glass ceramic contains at least 1 wt.%, 1.5 wt.%, 2.0 wt.%, >2.5 wt.%, or even >3.0 wt.% TiO2. At the same time, it advantageously contains 4.1 wt.%, 4.0 wt.%, 3.8 wt.%, 3.6 wt.%, or even only 3.4 wt.% or less TiO2. A higher TiO2 proportion accelerates nucleation. As a result, the ceramization time of the glass ceramic can be shortened. A lower TiO2 proportion stabilizes the ceramization process and prevents unintended devitrification during hot forming of the green glass.

[0055] In a preferred embodiment, the glass ceramic may contain 1.0 to <4.2 wt. %, preferably 2.0 to 4.1 wt. %, particularly preferably >3.0 to 4.0 wt. % TiO2 for the reasons mentioned above.

[0056] In a further development of the invention, the glass-ceramic according to the invention contains 1.0 to 4.0 wt. % ZrO2. ZrO2 and SnO2 act particularly as nucleating agents in the glass-ceramic and interact closely with each other. A ZrO2 content of 1.0 wt. % is advantageous for improving nucleation, especially in combination with SnO2 and TiO2.

[0057] Because ZrO2 also increases the viscosity of the glass melt, i.e., the processing point, the amount of ZrO2 is limited to a value of 4.0 wt.%. Furthermore, ZrO2 can cause devitrification during hot forming, which can lead to the undesirable formation of baddeleyite. Advantageously, the glass-ceramic contains at least >1.3 wt.%, particularly preferably >1.7 wt.%, of ZrO2. Furthermore, it advantageously contains 3.9 wt.%, 3.8 wt.%, 3.2 wt.%, 3.0 wt.%, or even only 2.0 wt.% or less of ZrO2. At these amounts, a particularly good compromise can be achieved between a positive contribution to nucleation and still acceptable deterioration in meltability and hot forming.

[0058] In one development of the invention, the glass ceramic contains, for the reasons stated above, 1.0 to 4.0 wt. % ZrO2, advantageously >1.3 to 3.9 wt. %, particularly preferably >1.7 to 3.8 wt. %.

[0059] As2O3 and Sb2O3 are often used as fining agents in the production of glass ceramics. However, it has been surprisingly found that these components are detrimental to devitrification stability in the glass ceramics according to the present invention. Therefore, in one development of the present invention, the amount of As2O3 and Sb2O3 is advantageously limited to less than 0.1 wt. % each. Particularly preferably, the glass ceramic contains less than 0.09 wt. %, less than 0.08 wt. %, less than 0.07 wt. %, less than 0.06 wt. %, or even less than 0.05 wt. % As2O3 and Sb2O3, respectively. It is particularly preferred that the glass ceramic does not contain As2O3 and Sb2O3, except in unavoidable trace amounts.

[0060] However, As2O3 and Sb2O3 can occur as impurities in glass ceramics, especially when cullet containing As2O3 and Sb2O3 is used in the production of glass ceramics. This is particularly true when cullet from cooktops from the recycling cycle is used. For environmental protection and sustainability reasons, it is advantageous to use cullet from the recycling cycle as raw material. Therefore, advantageously, the glass ceramic contains at least 0.01 wt.%, 0.02 wt.%, 0.03 wt.%, or even at least 0.04 wt.% of As2O3 and / or Sb2O3, respectively. When As2O3 and Sb2O3 are included together, they can each be present in the amounts mentioned.

[0061] However, As2O3 and Sb2O3 contribute to the refinement of green glass, thereby improving the bubble quality. To this end, in further developments of the invention, the glass ceramics can contain 0.1 to 1.8 wt.%, 0.2 to 1.7 wt.%, 0.3 to 1.6 wt.%, or even 0.4 to 1.5 wt.% As2O3. Alternatively, the glass ceramics can contain 0.5 to 2.1 wt.%, 0.6 to 2.0 wt.%, 0.7 to 1.9 wt.%, 0.8 to 1.8 wt.%, 0.9 to 1.7 wt.%, or even 1.0 to 1.6 wt.% As2O3.

[0062] The addition of alkaline earth metals CaO and SrO, as well as BO, improves meltability and devitrification behavior during glass forming. CaO, in particular, can be included in glass-ceramics to lower the processing temperature and upper devitrification temperature limits. However, there are limits to their content, since these components are not incorporated into the crystalline phase but remain essentially in the residual glass phase of the glass-ceramic. Excessive content impairs the crystallization behavior during the conversion of the crystallizable starting glass to the glass-ceramic, particularly at the expense of high ceramization rates. Furthermore, high content adversely affects the long-term durability / heat resistance of the glass-ceramic. Therefore, glass-ceramics can contain 0-2 wt. % of each of these components.

[0063] In one development of the invention, the glass-ceramic contains 0 to <1 wt. % P2O5. P2O5 has a positive effect on the devitrification stability of the green glass. However, higher amounts reduce the ceramization rate and adversely affect the acid resistance of the glass-ceramic. Therefore, the amount of P2O5 is limited to a maximum of <1 wt. %, advantageously a maximum of 0.9 wt. %, particularly preferably a maximum of 0.8 wt. %. To improve the devitrification stability, it may be advantageous for the glass-ceramic to contain at least 0.01 wt. %, preferably at least 0.05 wt. %, particularly preferably at least 0.1 wt. % P2O5.

[0064] In one development of the invention, the glass ceramic is - It may be advantageous to include Cl. - It has been found that the addition of a certain amount of Cl improves the bubble quality of the green glass and thus the glass-ceramics. In combination with other components, the glass-ceramics contain 0.003 to 0.1 wt. %, preferably 0.005 to 0.03 wt. %, and particularly preferably 0.007 to 0.02 wt. % Cl. -It has been found to be particularly advantageous to include chlorides. Amounts below 30 ppm do not have a significant effect on foam quality. Amounts above 1000 ppm should be avoided, since some of the added chlorides may react with other components of the batch and with process waste gases. This can lead, for example, to the formation of HCl, which can cause corrosive damage to the bath. Furthermore, evaporation of alkali metal chlorides and alkaline earth metal chlorides is undesirable. Cl in glass ceramics - The amount of can be adjusted, for example, by adding NaCl to the batch.

[0065] In addition to these components, the glass-ceramics can also contain coloring components in one development of the invention, such as V2O5, CoO, Fe2O3, Cr2O3, Nd2O3, NiO, CuO, MnO, or MoO3, either individually or in combination. The exact choice of type and amount of coloring component depends on the optical properties to be achieved.

[0066] The coloring of glass-ceramics is a complex and nonlinear process. Many components in glass-ceramics can affect the intensity of the coloring component's light absorption. Therefore, a skilled artisan can adjust the amount of coloring component to the respective base composition of the glass-ceramic to achieve the desired optical properties.

[0067] Regarding the coloring of glass-ceramics according to the invention using V2O5 as the main colorant, for example, the following can be shown: To reduce the transmittance to the desired value, more V2O5 is used than in comparable glass-ceramics with a higher Li2O content. Thus, the reduction in Li2O results in less V2O5 absorption in the glass-ceramics. Similar, and sometimes opposite, correlations exist with other components of the base composition.

[0068] V2O5 generally colors glass-ceramics very strongly even in small amounts. Glass-ceramics colored with V2O5 have relatively low transmittance in the blue and green spectral ranges and relatively high transmittance in the red spectral range. Advantageously, the glass-ceramics contain 0 to 0.1 wt.% V2O5. Particularly preferred are >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 to 0.04 wt.% V2O5. These V2O5 amounts allow the light transmittance of the glass-ceramics at a thickness of 4 mm to be set in the range of 0.1 to 80%.

[0069] In a particularly preferred development of the aforementioned embodiment, the ratio V2O5 / Li2O is between 0.005 and 0.06, preferably between 0.007 and 0.055, and particularly preferably between 0.01 and 0.05. Without limiting generality, it is assumed that the coloring effect of V2O5 depends on the microstructure of the glass-ceramic. Due to the low Li2O content, the glass-ceramic according to the present invention has a relatively low proportion of crystalline phases and simultaneously small crystallite sizes. It has been found that particularly effective coloring is possible when the ratio of V2O5 to Li2O falls within the above-mentioned limits. With this ratio, a spectral transmittance at a wavelength of 630 nm at a thickness of 4 mm can be achieved in the range of 0.5 to 15%, advantageously between 1 and 13%, and particularly preferably between 2 and 10%. These transmittances allow the use of commercially available red-light displays when the glass-ceramic is used as a cooktop.

[0070] MoO3 can be used to color glass ceramics, particularly to achieve neutral color tones. This has the advantage that white light displays can be used in cooking appliances without the display light changing color as it passes through the glass ceramic. Advantageously, the glass ceramic contains 0 to 0.5 wt.% MoO3. Particularly preferred are >0.002 to 0.4 wt.%, >0.003 to 0.3 wt.%, >0.004 to 0.2 wt.%, >0.005 to 0.15 wt.%, or even >0.01 to 0.1 wt.% MoO3. These amounts of MoO3 allow the light transmittance of the glass ceramic at a thickness of 4 mm to be set in the range of 0.1 to 80%. At the same time, accurate color display of the white light display is possible.

[0071] In a particularly preferred development of the aforementioned embodiment, the MoO3 / Li2O ratio is 0.015 to 0.1, advantageously 0.02 to 0.08, and particularly preferably 0.025 to 0.07. This ratio range allows for a light transmittance at a thickness of 4 mm of 0.5 to 4%, advantageously 0.8 to 3.5%, particularly preferably 0.7 to 3.3%, and very particularly preferably 1.0 to 3.0%. These transmittances allow for the use of white light displays when the glass ceramic is used as a cooktop. At the same time, the visibility of the interior components of the cooking appliance is significantly reduced.

[0072] Nd2O3 can also be used for coloring. Unlike other colorants, it produces relatively narrow absorption bands in glass-ceramics. These absorption bands are primarily in the green spectral range. Small amounts of Nd2O3 can be used to precisely control the color of light transmitted through the glass-ceramics. For example, glass-ceramics containing only small amounts of Fe2O3 as a coloring component often have a yellowish tint. This can occur, for example, in glass-ceramics containing both TiO2 and Fe2O3 impurities. If such glass-ceramics are coated with a white undercoat, the undercoat will have a noticeable yellowish tint. Adding Nd2O3 to such glass-ceramics can reduce or eliminate the yellow tint without significantly reducing light transmittance. As a result, it is possible to produce cooktops with a white appearance.

[0073] Advantageously, Nd2O3 is contained in the glass-ceramics in an amount of 0 to 0.6 wt. %. Since Nd2O3 is relatively expensive, it is desirable to limit its amount to 0.6 wt. Particularly preferably, the glass-ceramics contain 0.005 to 0.5 wt. %, 0.01 to 0.4 wt. %, 0.02 to 0.3 wt. %, 0.03 to 0.2 wt. %, or even 0.04 to 0.1 wt. % Nd2O3.

[0074] Fe2O3 affects transmittance not only in the visible spectral range but also in the near-infrared range up to wavelengths of approximately 3 μm. Therefore, Fe2O3 not only influences the realization of specific colors and the displayability of color displays. Absorption in the near-infrared range determines how much heat energy the glass melt can absorb in the vessel, which in turn determines how much heat output from radiant heating elements can pass through the glass-ceramic. This also determines whether and what infrared sensors can be used in stovetops. Such sensors can be designed, for example, as optical touch sensors or infrared receivers for wireless data transmission. At the same time, Fe2O3 is often present as an impurity in the raw materials used in production. A higher amount of Fe2O3 in glass-ceramics allows the use of less expensive raw materials with higher impurity concentrations. All of these factors must be taken into consideration when selecting the appropriate amount of Fe2O3. The amount of Fe2O3 is preferably between 0 and 0.4 wt.%. Glass-ceramics containing more than 0.4 wt.% Fe2O3 have low transmittance in the near-infrared range and are therefore not compatible with radiant heating elements used in commercial cooking appliances. Advantageously, the glass-ceramics contain 0.005-0.3 wt.%, 0.01-0.25 wt.%, 0.02-0.2 wt.%, or even 0.04-0.18 wt.% Fe2O3. Such glass-ceramics are inexpensive to produce and are compatible with radiant heating elements used in cooking appliances and optical sensors. Fe2O3 is often present as an impurity in raw materials used in glass production, such as spodumene.

[0075] CoO may be present in the glass ceramic in an amount of, for example, 0 to 0.5% by weight, advantageously in an amount of 0.01 to 0.2% by weight, preferably 0.02 to 0.08% by weight, particularly preferably 0.04 to 0.06% by weight.

[0076] Advantageously, glass-ceramics colored with 0.02-0.1 wt. % CoO further contain 0.02-0.1 wt. % Cr2O3. Particularly preferred are 0.05-0.25 wt. % Fe2O3, especially <30 ppm V2O5. These amounts of CoO, preferably in combination with other colorants, allow the light transmittance of the glass-ceramics at a thickness of 4 mm to be set in the range of 0.1-80%. Furthermore, this allows for the realization of white displays in the warm white spectral range.

[0077] Unlike V2O5, MoO3, or CoO, Cr2O3, NiO, CuO, and MnO are usually used for secondary coloring and rarely as primary colorants. Primary colorants are understood to be coloring components that have the greatest influence on the transmittance of the glass-ceramics in the visible spectral range. They often occur as impurities in the raw materials. These components are advantageously contained in the glass-ceramics in amounts of 0 to 0.5% by weight each. Particularly preferred are amounts of 0.001 to 0.4%, 0.002 to 0.3%, 0.004 to 0.2%, 0.006 to 0.1%, 0.008 to 0.08%, or even 0.01 to 0.05% by weight.

[0078] In a preferred embodiment, the glass-ceramic comprises 0-0.1 wt.% V2O5 or 0-0.5 wt.% MoO3 or 0-0.6 wt.% Nd2O3 or 0-0.4 wt.% Fe2O3 or 0-0.5 wt.% CoO or 0-0.5 wt.% Cr2O3 or 0-0.5 wt.% NiO or 0-0.5 wt.% CuO or 0-0.5 wt.% MnO or a combination of these components.

[0079] In addition to their coloring effect, these components can also have a positive effect on the quality of the glass. This is especially true for components that absorb in the infrared spectral range in the glass melt. Absorption in the infrared range allows the heat introduced into the melting vessel by the heating device to be absorbed more efficiently by the glass melt. This allows the glass melt temperature to be increased with the same energy input. This can have a positive effect on the melting of difficult-to-melt raw materials and on the reduction of bubbles during the fining process. This is especially true for Fe2O3, CoO, and NiO in the amounts mentioned above.

[0080] In one development of the invention, the glass ceramic has a light transmittance of 80 to 90%, or 81 to 89%, or 82 to 88%, or even 83 to 87% at a thickness of 4 mm. Glass ceramics with such a light transmittance advantageously have a chroma C in the range of 0 to 6, preferably 1.5 to 5, particularly preferably 3.0 to 4.6 at a thickness of 4 mm. * It has.

[0081] "At 4 mm thickness" means that the corresponding property is measured on a 4 mm material sample, or measured at another material thickness and converted to a 4 mm material thickness. For transmittance data, the conversion can be performed using the Beer-Lambert law.

[0082] The light transmittance is measured in the wavelength range of 380 to 780 nm using light of standard illuminant D65 in accordance with the specifications of DIN 5033. This value corresponds to the luminance Y in the CIExyY color space.

[0083] Saturation C * L * a * b * It is determined from the color coordinates according to the following formula:

number

[0084] Color coordinates a * and b *is determined in a known manner from the transmission spectrum of the glass-ceramic using standard illuminant D65.

[0085] With a light transmission of 80-90% at a thickness of 4 mm, glass-ceramics are particularly suitable for use as fireplace viewing windows or cooktops. In fireplaces, this transmittance allows for particularly good visibility of the fire. In cooking appliances, this transmittance allows for particularly good visibility of relatively low-brightness optical displays, such as LCD or OLED displays.

[0086] Saturation C * A chromaticity of 0 to 6 ensures that the color of light changes only slightly when passing through the glass-ceramic. As a result, it is possible to apply a white coating to the glass-ceramic, which still gives the impression of white when viewed through the glass-ceramic. This is particularly important when used as a cooktop or fireplace viewing window, for example. Glass-ceramics for such applications are often 4 mm thick. Therefore, light reflected by the backside coating travels an 8 mm optical path, meaning that color shifts due to the inherent color of the glass-ceramic have a greater effect than if the optical path were shorter. Therefore, a correspondingly low chromaticity is particularly advantageous for cooktops or fireplace viewing windows with a white backside coating.

[0087] In one development of the invention, the light transmittance is in the range of 80 to 90% or a correspondingly preferred range and the saturation C is in the range of 2 to 6 or a correspondingly preferred range. * and the glass ceramics having the composition according to the invention contain, in addition to the composition according to the invention, one or more of the following components, expressed in % by weight: Nd2O3 0.005 to 0.1, preferably 0.01 to 0.08, particularly preferably 0.03 to 0.065, Fe2O3 0 to 0.02, preferably 0.0025 to 0.018, particularly preferably 0.005 to 0.016, V2O50 to 0.0015, preferably 0 to 0.001, particularly preferably 0 to 0.0005, Cr2O3 0 to 0.001, preferably 0 to 0.0005, particularly preferably 0 to 0.0003, MoO3 0 to 0.001, preferably 0 to 0.0008, particularly preferably 0 to 0.0006, CoO 0 to 0.001, preferably 0 to 0.0005, particularly preferably 0 to 0.0001, NiO 0 to 0.001, preferably 0 to 0.0005, particularly preferably 0 to 0.0001, CuO 0 to 0.001, preferably 0 to 0.0007, particularly preferably 0 to 0.0002, MnO 0 to 0.02, preferably 0 to 0.01, particularly preferably 0 to 0.006, TiO2 1.6 to 2.5, preferably 2.0 to 2.4, particularly preferably 2.1 to 2.3, ZrO20~2.2, or 0.1~2.0, or 0.2~1.8, or even 0.3~1.6, SnO2 is 0.05 to 0.2, preferably 0.08 to 0.18, and particularly preferably 0.1 to 0.15.

[0088] In a particularly preferred development, the glass-ceramic comprises all of these components in these amounts. If these components are present in the glass-ceramic in the amounts stated here, it may be further preferred if the sum of Fe2O3 + V2O5 + Cr2O3 is 0 to 0.0225 wt.-%, preferably 0.0005 to 0.0175 wt.-%, particularly preferably 0.0010 to 0.0170 wt.-%.

[0089] These components, either alone or in combination with one another, affect the light transmittance and color saturation of the glass-ceramics, which can be fine-tuned within the above limits if the above amounts are observed.

[0090] The following table contains three further developments of the glass-ceramics according to the invention in % by weight on an oxide basis: [Table 1]

[0091] The glass ceramics according to the invention are used as cooktops, fireplace sight glasses, grill or roasting tops, covers for combustion elements of gas grills, oven sight glasses, in particular oven sight glasses for pyrolysis furnaces, kitchen or laboratory workbenches or table tops, covers for lighting devices, in fire glazing and as safety glass, optionally in laminated composites, as carrier plates or as linings for furnaces in thermal processes or as back covers for portable electronic devices.

[0092] The glass ceramics according to the invention can be used in particular as cooktops. In this case, the cooktops can be provided with a decorative or functional coating on all or part of the top and / or bottom surface. Touch sensors for operating the cooktop can also be provided on the bottom surface. These can be, for example, printed, glued or pressure-bonded capacitive sensors.

[0093] Furthermore, glass-ceramics can be in the form of three-dimensionally shaped plates, i.e., they can be angled, curved, or contain areas shaped like a wok, for example, or recesses for operating a gas burner.

[0094] The present invention will now be further illustrated by the following examples.

[0095] The crystallizable green glass of the example was melted at 1680°C for 4 hours from industrial batch raw materials commonly used in the glass industry. This choice allows for both economical raw materials and a low content of undesirable impurities. After melting the batch in a sintered silica glass crucible, the melt was poured into a Pt / Rh crucible with a silica glass inner crucible and homogenized by stirring at 1600°C for 90 minutes. After this homogenization, the glass was fined at 1640°C for 3 hours. It was then poured into a glass tube measuring approximately 120 x 140 x 30 mm. 3Pieces of this size were produced and cooled to room temperature in a cooling furnace at 30 K / h, starting from 640-670 °C depending on the viscosity of the glass, to relieve stress. The cast pieces were divided into those required for testing and those required for ceramization.

[0096] Ceramization of the samples in the green glass state was carried out in a continuous furnace in a ceramization process having the following steps: a) heating from room temperature to 740°C at a heating rate of 30 K / min; b) holding at 740°C for 3 minutes and 20 seconds; c) heating from 740°C to 810°C at a heating rate of 28 K / min; d) holding at 810°C for 9 minutes and 20 seconds; e) heating from 810°C to 930°C at a heating rate of 21 K / min; f) holding at 930°C for 6 minutes; g) Cooling to room temperature at a cooling rate of 15 K / min.

[0097] The following table contains the compositions and material properties of examples according to the invention. Example 24 differs from the other examples in that it was heated to a temperature of 915°C in step e) and held at this temperature in step f). Example 25 differs from the other examples in that it was heated to a temperature of 905°C in step e) and held at this temperature in step f).

[0098] The coefficient of thermal expansion CTE was measured dynamically on bar samples using a shear rod dilatometer at a heating rate of 2 K / min.

[0099] To measure the upper limit of devitrification temperature (OEG), green glass was melted in a Pt / Rh10 crucible. The crucible was then held at various temperatures within the processing temperature range for 5 hours. The highest temperature at which the first crystals appear at the interface between the glass melt and the crucible wall determines the OEG.

[0100] The working point (T4) of the green glass was measured using a stirring viscometer in accordance with DIN ISO 7884-2.

[0101] When green glass transforms into glass-ceramics, the density increases because the crystalline phase is denser than the amorphous glass. The shrinkage ratio indicates the linear change in length as the green glass transforms into glass-ceramics. The shrinkage ratio is calculated from the density of the green glass and the density of the glass-ceramic as follows:

number

[0102] Tg denotes the transformation temperature of the green glass, also known as the glass transition temperature, which is measured by dilatometry.

[0103] Light transmittance is measured in the wavelength range of 380-780 nm using standard illuminant D65 according to DIN 5033. This value corresponds to the luminance Y in the CIExyY color space. This value is a measure of the luminance perception of the human eye.

[0104] The distance d from the xy color coordinates in the CIExyY color space to the color position of the standard illuminant D65 (0.3127 / 0.3290) was calculated as follows:

number

[0105] The transmission spectra were measured in accordance with ISO 15368:2021. Table 2 lists examples of the spectral transmittance "T@···" at wavelengths of 470 nm, 600 nm, 630 nm, 700 nm, 950 nm, and 1600 nm.

[0106] The color coordinates in the CIExyY color space and Lab color space were determined according to the specifications of CIE 1932 using an 8° observer and transmitted light of standard illuminant D65.

[0107] All transmittance measurements were performed on 4 mm thick samples that were smooth on both sides.

[0108] The volume fraction "XRD fraction HQMK" or "KMK" and the crystallite diameter of the crystalline phase "XRD crystallite diameter HQMK" or "KMK" were determined from the X-ray diffraction spectrum by Rietveld analysis.

[0109] [Table 2-1] [Table 2-2] [Table 2-3] [Table 2-4]

[0110] [Table 3-1] [Table 3-2] [Table 3-3] [Table 3-4] [Table 3-5]

Claims

1. Lithium aluminum silicate glass ceramics, wherein the lithium aluminum silicate glass ceramics are The coefficient of thermal expansion in the range of 20°C to 700°C is -0.5 to 1.9 ppm / K. In terms of oxide-based weight percentages, the following: Yes ２ 60~70 Al ２ O ３ 17-25 Li ２ O 1~<2.9 MgO 0 to <1 Na ２ O>0.05~<0.5 K ２ O >0.05~<0.6 Having a composition including, Lithium aluminum silicate glass ceramics.

2. 1.1–2.8% by weight, or 1.2–2.7% by weight, or 1.3–2.6% by weight, or 1.4–2.5% by weight of Li ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing O.

3. The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing 1.7 to 6.0% by weight, or 2.0 to 5.5% by weight, or 2.5 to 5.0% by weight, or 3.0 to 4.0% by weight of ZnO.

4. Li ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized in that the difference between O and ZnO is ±0.5% by weight, ±0.3% by weight, or even ±0.2% by weight.

5. 1.0 to <4.2 wt%, preferably 2.0 to 4.1 wt%, particularly preferably >3.0 to 4.0 wt% of TiO ２ The lithium aluminum silicate glass ceramics according to claim 1, characterized by containing

6. SiO in glass ceramics, in units of weight percentage. ２ and Al ２ O ３ The ratio of SiO ２ / Al ２ O ３ The lithium aluminum silicate glass ceramic according to claim 1, characterized in that the value is less than 3.5, preferably less than 3.3, particularly preferably less than 3.15, and greater than 2.4, preferably greater than 3.0, particularly preferably greater than 3.

1.

7. 0.1 to <1.0 wt% SnO ２ Advantageously, 0.15 to 0.8% by weight, particularly preferably 0.2 to 0.6% by weight of SnO ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing the following.

8. The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing 0 to <0.8% by weight, 0 to <0.6% by weight, 0 to <0.5% by weight, 0.05 to <0.4% by weight, or 0.1 to <0.3% by weight of MgO.

9. The aforementioned glass ceramics are K ２ It contains less MgO than O, and / or Na ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing less MgO than O.

10. K in weight percentage ２ O / Na ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized in that the ratio of O is in the range of 0.1 to 2, preferably 0.5 to 1.5, particularly preferably 0.7 to 1.3, or 0.1 to < 1, preferably 0.2 to 0.9, particularly preferably 0.3 to 0.8, or 1 to 2, preferably 1.1 to 1.9, particularly preferably 1.2 to 1.

8.

11. 1.0–4.0% by weight, preferably >1.3–3.9% by weight, and especially preferably >1.7–3.8% by weight of ZrO ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing the following.

12. Na ２ O+K ２ The lithium aluminum silicate glass ceramic according to claim 1, characterized in that the amount of O is at least 0.2% by weight, and 1% by weight or less, preferably at least 0.3% by weight, or at least 0.4% by weight, or at least 0.5% by weight, and 1.0% by weight or less, or 0.9% by weight or less, or 0.8% by weight or less, or 0.7% by weight or less, or 0.6% by weight or less.

13. Less than 0.1% by weight of As ２ O ３ and less than 0.1% by weight of Sb ２ O ３ The lithium aluminum silicate glass ceramic according to claim 1, characterized by containing the following.

14. 0-0.1% by weight of V ２ O ５ Or 0-0.5% by weight of MoO ３ , or 0-0.6% by weight of Nd ２ O ３ , or 0-0.4% by weight of Fe ２ O ３ , or 0-0.5% by weight of CoO, or 0-0.5% by weight of Cr ２ O ３ The lithium aluminum silicate glass ceramic according to claim 1, characterized by comprising 0 to 0.5 wt% NiO, 0 to 0.5 wt% CuO, 0 to 0.5 wt% MnO, or a combination thereof.

15. Use of the glass ceramics according to any one of claims 1 to 14 as a cooktop, fireplace viewing window, grill top or roast top, cover for combustion element of gas grill, oven viewing window, especially oven viewing window of pyrolysis furnace, kitchen or laboratory workbench or tabletop, cover for lighting fixture, in fire glazing, and as safety glass, optionally in laminated composite materials, as a carrier plate, or as a furnace lining in a thermal process, or as a back cover for portable electronic devices.