Cordierite-containing ceramic material, a process for its production, and its use

Abstract

Cordierite-containing ceramic material with a classic porcelain appearance, comprising the following components in mass % SiO2 48 to 55.5 Al2O3 32 to 37 MgOsowie 7.5 to 11.5 K2O 1.5 to 3.0 and / or Na2O 0.5 to 0.8 and / or Fe2O3 up to 0.6 and which is a composition of 55 - 75% by mass cordierite, 8 - 16 mass-% mullite, 10-20% corundum as well as a residue of 100% of an X-ray amorphous phase, and which is characterized by a porosity of less than 0.05%, and which is is provided with a glaze containing the following components, which are listed in mass % SiO2 52 to 63 Al2O3 16 to 30 MgO 5.6 to 12 Na2O 0.9 to 1.9 K2O 0.7 to 1.7 B2O3 2.5 to 5.0.

Description

[0001] The invention relates to a cordierite-containing ceramic material, a method for its production, and its use.

[0002] Ceramics are used in many areas of technology as hard and durable components. Furthermore, porcelain ceramics are used in the home, among other things, as tableware, especially as cookware and eating utensils. These include vessels, plates, pots, pans, etc., for storage, preparation, serving, and consumption, made from materials such as plastic, cardboard, metal, ceramic, glass, wood, stone, and others. Such porcelain items consist of a wide variety of different materials. These specialized products each fulfill only specific tasks. This means that different products are required in the chain of food storage, preparation, consumption, and waste disposal. For example, it is well known that vessels made of metal or porous ceramic are not suitable for microwave heating. For cooking, steaming, and frying, metals (stainless steel, aluminum, copper, enameled iron) are preferred due to their heat resistance.But here too, attempts are being made to improve performance characteristics with various coatings made of heat-resistant organic materials (Teflon, silicone) or, more recently, with so-called white ceramic coatings.

[0003] In the realm of dining, classic porcelain and related products such as bone china and vitreous china are still preferred for cultural and hygienic reasons. It is therefore evident that the transfer of food from one item to another occurs.

[0004] From DE 196 17 147 A1 it is further known to provide porcelain or ceramic with electrically conductive layers in order to heat the porcelain or ceramic by means of induction devices in order to heat food or to keep it warm.

[0005] On the other hand, ceramic and glass-ceramic products are known for their low coefficient of thermal expansion, which allows for the preparation of food to a limited extent. Classic ceramics (also porcelain, bone china, vitreous china, stoneware, earthenware) have a coefficient of thermal expansion of 5.0 to 7.0 × 10⁻⁶. -6 K -1 However, their resistance to temperature changes is only sufficient, at best with appropriate optimization, for use in a classic oven, allowing food to be cooked in so-called casserole dishes at temperatures up to approximately 250 °C. Ceramics with lower coefficients of thermal expansion exist based on cordierite and lithium silicates.

[0006] US 4 295 892 A discloses a ceramic cordierite composite body with a coefficient of thermal expansion in the temperature range of 25 to 1000°C of not more than 2.2 · 10 -6 K -1WO 00 / 30995 A1 discloses a sintered ceramic article containing, as a crystalline phase, 65-95% cordierite and 5-35% mullite, spinel and / or sapphirine, as well as 32-51% SiO2, 35-49% Al2O3 and 7-16% MgO. The coefficient of thermal expansion in the range of 25 to 1000°C is less than about 1.5 × 10⁻⁶. -6 K -1 .

[0007] US 2014 / 370 232 A1 discloses cordierite-containing ceramic composite bodies containing an aluminum oxide component between 34.9 and 71.8 wt.%, silicon dioxide between 28.2 and 52.0 wt.% and magnesium oxide between 5.0 and 13.8 wt.%.

[0008] DE 10 2011 005 817 A discloses a solar absorber module containing cordierite, wherein the cordierite contains 30 wt.% to 60 wt.% aluminium oxide, 30 wt.% to 60 wt.% silicon oxide and 1 wt.% to 10 wt.% magnesium oxide.

[0009] However, the products currently available on the market are only partially suitable. Some ceramics have a relatively low coefficient of thermal expansion of 1.0 to 1.5 × 10⁻⁶. -6 K -1 They are porous, have opaque glazes, and therefore do not meet the appearance and basic properties of porcelain (DE 20 2010 014 638 U1). Various other porcelain-like products achieve average coefficients of thermal expansion of 3.1 × 10 -6 K -1Currently available products are intended for cooking and baking in the kitchen only and tend to develop cracks in the glaze or even the base material under high temperature fluctuations. The instructions for use advise particular caution.

[0010] From DE 1 621 026 B a glaze for ceramic shards with a low linear coefficient of thermal expansion of 1.5 to 2.0 · 10 -6 K -1 well-known. This glaze is opaque and has a matte appearance.

[0011] In summary, it can be stated that no products exist on the market that universally meet all requirements for microwave, gas flame, oven tube, also with grill, ceramic hob and induction hob in the kitchen and for eating.

[0012] The invention therefore aims to provide a material, in particular a porcelain-like material, that avoids the disadvantages of the prior art and is suitable for broad application both as a technical material and for household use, such as in the kitchen and tableware sector. Furthermore, it should be producible using conventional methods.

[0013] The invention also aims to provide a ceramic material that is not only break-resistant but also highly resistant to temperature changes, so that it can be quenched from high temperatures to room temperature with water without being destroyed.

[0014] Furthermore, the invention aims to provide such a ceramic material which can also be produced with a short firing time, e.g. by means of a so-called rapid firing, in order to reduce energy consumption during firing.

[0015] Furthermore, the invention also aims to provide such a material, in particular a tableware, which has a glaze with such low roughness that it forms a macroscopically shiny surface.

[0016] This goal is now achieved through a ceramic material which consists of more than 50% cordierite and which, in its fired state, contains the following components in mass % (fired): SiO2 48 to 55.5 Al2O3 32 to 37 MgO 7.5 to 11.5 as well as usual accessories.

[0017] Such a ceramic is formed in particular from cordierite, mullite, corundum, and a residue of X-ray amorphous components. The amount of cordierite is at least 55%, preferably at least 60%, and particularly at least 62%. Typical upper limits for cordierite porcelain are 75% by weight, particularly a maximum of 70% by weight, expediently a maximum of 69%, with a maximum of 68% being preferred.

[0018] The mullite content is typically at least 8% by mass, preferably at least 9%, with the upper limit for mullite being 16% by mass, particularly 15% by mass. Mullite limits of 14% are preferred.

[0019] Typical amounts of corundum are at least 10% by mass, particularly at least 11%, with at least 12% being preferred. The maximum corundum content is at most 20% by mass, with at most 19%, particularly 18%, being especially preferred.

[0020] The remaining components of the ceramic are formed by a non-crystalline X-ray amorphous structure, which constitutes the remaining portion of the 100 wt%. This is typically at least 1 wt%, particularly at least 3%, with at least 5%, and particularly 6%, being preferred. The maximum amount of X-ray amorphous phase is 18 wt%, with maximum amounts of 16% or 15% being common. Maximum amounts of 13%, and particularly 12%, are preferred, with maximum amounts of 11% or 10% being especially preferred.

[0021] The total number of all crystalline and non-crystalline phases in the ceramic according to the invention amounts to 100% by mass.

[0022] The ceramic according to the invention contains SiO2 in an amount of at least 48% by mass. Advantageously, however, the minimum amount is 49.5% or 50%, with 50.5% or 51% being particularly preferred. The maximum amount of SiO2 is 55.5% or 55%. Particularly preferred maximum amounts are 54.5% or 54%.

[0023] The Al₂O₃ content is at least 32%. The maximum Al₂O₃ content is at most 37% by mass, with maximum amounts of 36.5% and 36% having proven advantageous. Particularly preferred maximum amounts are 35.5%. The MgO content in the ceramic according to the invention is at least 7.5% by mass, with minimum amounts of 7.8% and 8% being suitable. Minimum amounts of 8.5% are particularly preferred. The maximum amount of MgO in the ceramic according to the invention is 11.5% by mass, in particular 11%, with maximum amounts of 10.5% and 10% having proven advantageous. Maximum amounts of 9.8% and 9.5% are particularly preferred, with a most preferred maximum amount of MgO being 9.2%.

[0024] The total alkali oxide content is typically a maximum of 3.8% by mass, in particular a maximum of 3.5% or 3.2%, with a maximum content of 3%, in particular 2.8%, being preferred. Typical alkali oxides are Li₂O, Na₂O, and K₂O. The typical minimum content of such alkali oxides is at least 1% by mass, in particular at least 1.5%, with at least 1.8% or 2% having proven to be common. In individual cases, such alkali elements can readily exceed 2%, in particular at least 2.1% or 2.2% by mass. The pure content of K₂O + Na₂O is typically at least 2%, in particular at least 2.2%, with maximum contents of 3.8%, in particular 3.5%, having proven advantageous. Further maximum contents of these two oxides are typically a maximum of 3%.

[0025] The ceramic according to the invention also contains conventional impurities which, together with the components described above, constitute 100% of the total porcelain content. Typical impurities are CaO, Li₂O, and a small number of trace elements and impurities such as oxides of Ti, Mn, Co, Cr, Sr, V, Zn, and iron.

[0026] Furthermore, impurities such as calcium oxide may be present in amounts of at least 0.1%, particularly 0.2% up to a maximum of 3%, with a maximum content of 2.8% or 2.5% being typical. If iron oxide is present as an impurity, its maximum content is usually no more than 0.6% by mass. Typical impurities range from 0.4% to 0.6% by mass.

[0027] The ceramic material according to the invention has a coefficient of thermal expansion of 20°C - 400°C < 2.5×10 -6 K -1a value of less than 2.3, and particularly less than 2.2, is especially preferred. Thermal expansion coefficients with values ​​less than 2.15 are particularly preferred.

[0028] Furthermore, the fired ceramic material according to the invention exhibits an extremely low porosity of less than 0.05%. Typically, the porosity is < 0.04%, and particularly < 0.03%. A porosity of < 0.02%, and especially < 0.015%, is particularly preferred. Due to the low porosity, the water absorption is less than 0.05% by mass. Typically, it is < 0.04%, and particularly < 0.03%.

[0029] Surprisingly, it has been found that the fired ceramic material according to the invention exhibits exceptionally high thermal shock resistance, such that it can be quenched in hot water to room temperature without any cracking occurring. The thermal shock resistance is > 280 °C, particularly > 300 °C, typically > 350 °C, with > 380 °C and > 400 °C being especially preferred.

[0030] The ceramic according to the invention is provided with a glaze of the following composition. SiO2 52 to 63% by mass (burned) Al2O3 16 to 30% by mass (burned) MgO 5.6 to 12% by mass (burned) B2O3 2.5 to 5.0% by mass (burned) Na2O + K2O 2.0 to 3.8% by mass (burned)

[0031] The glaze also contains the same common additives as previously described for the ceramic base. All components together make up 100% by mass.

[0032] As previously mentioned, the glaze has at least the same, but preferably a lower, coefficient of thermal expansion than the ceramic base. The SiO₂ content of the glaze is at least 52 wt%, with at least 54 wt% or 55 wt% being particularly preferred. Minimum SiO₂ contents of 57 wt% are especially preferred. The maximum SiO₂ content is at most 63 wt%, with 62 wt% or 61 wt% being preferred. A maximum of 60 wt%, and particularly 59 wt%, is especially preferred.

[0033] The proportion of Al₂O₃ in the total amount of the glaze is at least 16% by weight, with at least 18% or 19% by weight being preferred. The maximum Al₂O₃ content is not more than 30% by weight, and in particular not more than 29% by weight.

[0034] The MgO content in the glaze is at least 5.6 wt%, with 9 wt% being preferred. Typical maximum MgO contents are 12 wt%, particularly 11 wt%, with a maximum content of 10 wt% being preferred.

[0035] The B₂O₃ content is at least 2.5% by mass. The maximum B₂O₃ content is at most 5% by mass, with a maximum of 4% by mass, and in particular 3.5% by mass, being preferred. Maximum contents of 3% by mass and 2.8% by mass have proven to be particularly advantageous.

[0036] The compositions may optionally contain further alkali oxides, calcium oxides and trace elements in an amount of less than 1% by mass, as described, for example, for the ceramic base material according to the invention.

[0037] The invention also relates to a method for producing such a porcelain with a classic porcelain appearance by forming a mass with the composition previously specified for porcelain. Such a composition is typically obtained by using feldspar, calcined clay, talc, kaolin, and optionally chamotte.

[0038] If necessary, a pre-calcined additive can be added to such a mixture as a nucleating agent for cordierite formation. Such nucleating agents are obtained by calcining a mass of 60 to 70% by mass kaolin and 30 to 40% by mass talc.

[0039] Such a base mass is obtained by mixing 6 to 10 wt% feldspar, 4.5 to 10 wt% alumina, 20 to 33 wt% talc, 30 to 55 wt%, optionally up to 60 wt% kaolin, and optionally 5 to 12 wt% kaolin chamotte. If a nucleate is added, its content is at least 0.5 wt%, in particular at least 1 wt% and at most 5 wt%, in particular at most 4 wt%.

[0040] A crude product produced in this way is first dried under normal conditions and then pre-burned in a conventional oven. Such pre-burning is carried out at temperatures between 700 and 1100°C, particularly between 800 and 1000°C, with temperatures between 850 and 950°C being especially preferred. The pre-burning takes place over a period of 3 to 5 hours, particularly 3.5 to 4.5 hours.

[0041] In a conventional procedure, the pre-fired raw product obtained in this way is subsequently coated with the glaze described above. Such a glaze is typically obtained from a mixture of the ceramic material pre-fired and ground according to the invention, a borosilicate glass, kaolin, calcined alumina, and talc. Typical compositions of such a material are: pre-burned material 50 to 55% by mass borosilicate glass 20 to 25% by mass kaolin 3 to 11% by mass Calcined clay 2 to 4% by mass Talc OOS and possibly others. 12 to 16% by mass pre-burned additive as a germ 0.2 to 0.8 mass % contains.

[0042] The pre-fired material contained in the glaze is obtained by pre-milling the ceramic base mass according to the invention after firing. Typical milling processes are, for example, first carried out using a conventional mill such as a ball mill, and the resulting material is then further milled in a vibratory mill. In principle, the finely milled, pre-fired material used has few upper and lower grain sizes and exhibits a steep particle size distribution. The typically used milled particles have a mean particle size d 50 The particle size is preferably between 3 and 5 µm, with particle sizes between 3.2 µm and 4.3 µm being preferred. Due to the steep or narrow particle size distribution, the particles exhibit a sieve residue >20 µm of less than 1%, with <0.1% or <0.01% being preferred. Particles with a size of <1 µm are typically present in less than 15%, and in particular in less than 12% or 11%.

[0043] The borosilicate glass contains 70-83%, in particular 75-83% SiO2, 7-15%, in particular 9-14% B2O3, 2-8%, in particular 3-5% Na2O + K2O, 1.7%, in particular 1.5-3% Al2O3 and possibly small amounts of alkaline earth oxides as impurities.

[0044] The final ceramic firing, especially the one with glaze, is usually carried out in an industrial rapid-firing tunnel kiln. Using such a kiln, it is possible to fire ceramics at a maximum temperature of 1400°C for a maximum of 8 hours, and in particular, a maximum of 6.5 or 5 hours, including the total time spent in the kiln (dwell time).

[0045] A ceramic obtained in this way and coated with a glaze according to the invention exhibits low surface roughness.

[0046] The arithmetic mean RA of the absolute values ​​of all profile values ​​(depth) of the roughness profile is at most 0.13, usually at most 0.1, with 0.095 being preferred. The roughness depth R z, i.e., the arithmetic mean of successive individual measurement sections at a maximum of 1.00, in particular at most 0.95, with 0.90 being particularly preferred. The usual standard deviation δ is at most 0.2, in particular 0.18, with 0.17 being particularly preferred. Such a roughness is a measure of a high porcelain appearance or gloss.

[0047] The cordierite-containing ceramic material according to the invention typically has the following parameters: - general porcelain appearance - Whiteness > 70% - Transparency visually recognizable - Gloss exhibits low opacity - Breaking strength > 850 kg / cm² 2 - Coefficient of thermal expansion at 20-400 °C < 2.6 · · 10 -6 K -1 , especially < 2.35 · · 10 -6 K -1 , - Temperature cycling resistance > 280 °C, in particular > 300 °C, usually > 350 °C, with > 380 °C and > 400 °C being particularly preferred - Water absorption < 0.05%, especially < 0.03%, - Chemical resistance according to DIN EN ISO 11885

[0048] In an advantageous application of the material according to the invention, it has an electrically conductive layer, e.g. in the form of an induction pattern. This makes it possible to heat or keep the cordierite-containing material warm using an induction device without the material being destroyed by cracking after a relatively short time.

[0049] In a suitable embodiment, a pre-fired material with the following components in mass-% is used to produce cordierite tableware with a classic porcelain appearance. Feldspar AKW 900 / 12 6 to 10 Calcined clay 5 to 10 Talc OOS 20 to 30 Kaolin Grolleg 30 to 40 Kaolin SSP 16 to 20 Kaolin chamotte AK45 5 to 12 Possibly mixed with a pre-burned additive as a nucleation for cordierite formation of 0.5 to 5% by mass, the composition of which includes the components kaolin 60 to 70% by mass talc 30 to 40% by mass and contains further trace amounts of Ca, Ti, Se, P below 1% by mass.

[0050] The material is formed into a molded piece using a shaping process, dried, and smoothed. It is then annealed in a rapid-firing kiln at 900 °C for a total residence time of 4 hours and subsequently coated with a glaze whose composition includes at least the following components: the pre-burned material 50 to 55% by mass Borosilicate glass (e.g. Duran glass 3.3 Schott) 20 to 25% by mass Kaolin SSP 1 to 5% by mass Kaolin Grolleg 2 to 6% by mass Calcined clay 2 to 4% by mass Talc OOS 12 to 16% by mass Pre-burned additive containing germs. 0.2 to 0.8 mass %

[0051] The ceramic firing is advantageously carried out in an industrial rapid firing tunnel kiln at a maximum temperature of 1400°C in 6 hours cold / cold.

[0052] For use with cordierite-containing ceramic material in an induction cooktop, an induction pattern can advantageously be applied to the underside or inside of the cookware. This pattern is then fired on by rapid firing at a maximum temperature of 860°C for a firing time of 180 minutes.

[0053] The invention is explained in more detail by the following examples. 1. The combustion conditions

[0054] The firing conditions for the glaze firing are determined by the use of a modern, energy-efficient, 70-meter-long, operational rapid-firing tunnel kiln, in which classic porcelain is fired in a mixture with the cordierite-containing ceramic material according to the invention. The essential parameters are a short firing time of 6 hours cold / cold, at a maximum temperature of 1400 °C, and a reducing gas atmosphere. Under certain conditions, the material tends to so-called seepage or self-glazing, which can lead to adhesion problems when in contact with the firing aids. Therefore, an engobed firing aid is used. 2. Mass composition, production and processing

[0055] Based on the known chemical composition of pure cordierite 2MgO × 2Al2O3 × 5SiO2 or Mg2Al3 (AlSi5O 18Soapstone or talc are used as MgO suppliers, and otherwise feldspar, kaolin and burnt alumina are used as basic raw materials.

[0056] The composition according to the invention includes the following components: Feldspar AKW 900 / 12 6 to 10% by mass Calcined clay 5 to 15% by mass Talc OOS 20 to 30% by mass Kaolin Grolleg 30 to 40% by mass Kaolin SSP 16 to 20% by mass Kaolin chamotte AK45 5 to 12% by mass

[0057] The resulting chemical composition is: SiO2 50 to 54% by mass Al2O3 31 to 37% by mass Fe2O3 0.4 to 0.6 mass % MgO 8 to 11% by mass K2O 1.5 to 3.0 mass % Na2O 0.5 to 0.8 mass %

[0058] Furthermore, to achieve a specifically low coefficient of thermal expansion of < 2.4 · · 10 µm at temperatures between 20 and 400°C, a specific value is used. -6 K -1 According to the invention, an additive is added as a nucleation for cordierite formation in the amount of 0.5 to 5%. Its composition consists of a pre-calcified mixture of Kaolin: 60 to 70% by mass Talc: 30 to 40% by mass and other trace components (Ca, Ti, Se, P below 1 mass-%).

[0059] The production of this mass according to the above-mentioned mixing process is carried out by adding water and, if necessary, a liquefier to create a suitable base mass. For this purpose, the raw materials are milled with water in a drum mill for 6 hours to homogenize the mass. After sieving (160 µm), the mass remains in a settling tank to degas. The parameters to be achieved are... Density: 1720 to 1750 g / 1 Viscosity: Dispensing time of 50 ml: 40-80 sec Thixotropy factor: 0,7 Shard formation in 10 minutes: 3 to 4 mm

[0060] The material is used, for example, in die casting as a shaping process for the production of the desired tableware. Alternatively, isostatic pressing can be used. After demolding, drying, and finishing, the items are cold-annealed in a single layer at 900 °C for 4 hours in a rapid-firing furnace. 3. Glaze composition, production and application

[0061] The coefficient of thermal expansion of the glaze is slightly lower than that of the cordierite-containing ceramic material according to the invention, because only in this way is the strength and thermal shock resistance of the cordierite-containing ceramic material not negatively affected. Tests with articles where this condition was not met show that hairline cracks appear in the glaze after thermal shocks.

[0062] According to the invention, the following glaze composition and selective preparation were developed which meets this requirement and achieves a thermal expansion coefficient of 2.14 · · 10 µm at 20 - 400°C. -6 K -1 exhibits: A mass is pre-fired under analogous firing conditions and selectively pre-ground together with borosilicate glass (Duranglas 3.3 from Schott) in a drum mill using alubit balls of a specific diameter. Further components are then added and the mixture is ground further for blending and fine grinding down to a D50 particle size of 4.5 to 5.5 µm.

[0063] The composition of the glaze contains the following components: pre-burned mass, as described in point 2 50 to 55% by mass Borosilicate glass (Duran glass 3.3 Schott) 20 to 25% by mass Kaolin SSP 1 to 5% by mass Kaolin Grolleg 2 to 6% by mass Calcined clay 2 to 4% by mass Talc OOS 12 to 16% by mass pre-burned germination agent 0.2 to 0.8 mass %

[0064] The nucleating agent is identical to the one used in the mass.

[0065] This offset results in the following chemical composition: SiO2 55.0 to 61.0 mass % Al2O3 23.0 to 27.0 mass % MgO 9.3 to 11.3% by mass Na2O 0.6 to 1.6 mass % K2O 1.0 to 2% by mass B2O3 2.3 to 3.9% by mass

[0066] The glazing process is carried out by dipping or spraying. 4. The design-oriented product development

[0067] According to the invention, a product range was developed that meets, on the one hand, the formal functional requirements, such as aesthetics, product size, intended use, stackability, and, on the other hand, in particular, the alternating thermal requirements.

[0068] The following contributes to the latter: - the design, which absorbs mechanical forces caused by temperature differences and ultimately compensates for them through flexural strength; furthermore, the handle design such that it is ensured that, on the one hand, the body of the article is exposed to high temperatures, but on the other hand, the handle elements are heated to only hand-warm temperatures if possible; - Design of the ceramic shard, in particular the shard thickness of only 3.5 to 5 mm, because this allows the heat exchange from the hot outside to the cold inside to be completed more quickly, given the relatively poor thermal conductivity of the ceramic material. 5. Fitting the induction pattern

[0069] Optionally, for use on an induction cooktop, an induction pattern is applied to the underside or on the inside of the base of the item. These induction patterns can, for example, be designed as simple silver-containing decals. Thus, the cookware according to the invention, with the optional induction pattern, ensures universal applicability, including in microwaves, on electric hot plates, gas burners, or ceramic hobs.

[0070] To accommodate all applications, the base and stand were designed to provide adequate protection for the image. Applying the induction image to the inside significantly increases the efficiency of heat transfer, thus saving time and energy.

[0071] Furthermore, the electrical power consumption must be adapted to the respective size and shape of the article.

[0072] According to the invention, the induction image is baked on in a rapid-firing decorative tunnel kiln at a maximum temperature of 860 °C and a firing cycle of only 180 minutes.

[0073] The invention is explained in more detail below using an exemplary embodiment.

[0074] The raw materials listed in the following table are given in mass % for the mass composition, the nucleating agent, and the glaze composition, and are pre-fired and then ground to < 30 µm: Feldspar AKW 900 / 12 Mass composition 7 Glaze composition - Calcined clay 5 3 Talc OOS 26 14 Kaolin Grolleg 33 4 Kaolin SSP 18 2,2 Kaolin chamotte AS 45 10 - smooth shards - 52 Boron glass 3.3 - 24 Germ-forming cells 1 0, 8 In total 100 100 D50 (µm) Germ-forming cells: 5,0 4,5 Talc OOS 33 33 Kaolin SSP 65 65 TiO2 1 1 Ca3(PO4)2 1 1

[0075] The properties achieved after firing at a maximum temperature of 1400 °C for 6 hours have been demonstrated as follows: Whiteness content: 72 % Water absorption: 0, 05 % Flexural strength: 850 kg / cm 2 Temperature cycling resistance: Coefficient of thermal expansion ΔT 295 °C of mass 20-400 °C: 2,14 · 10 -6 K -1 Coefficient of thermal expansion of the glaze 20-400 °C: 2,1 · 10 -6 K -1

Claims

[1] Cordierite-containing ceramic material with classic porcelain appearance, comprising the following components in mass % SiO2 48 to 55.5 Al2O3 32 to 37 MgOsowie 7.5 to 11.5 K2O 1.5 to 3.0 and / or Na2O 0.5 to 0.8 and / or Fe2O3 up to 0.6 and which is a composition of 55 - 75% by mass cordierite, 8 - 16 mass-% mullite, 10-20% corundum as well as a residue of 100% of an X-ray amorphous phase, and which is characterized by a porosity of less than 0.05%, and which is is provided with a glaze containing the following components, which are listed in mass % SiO2 52 to 63 Al2O3 16 to 30 MgO 5.6 to 12 Na2O 0.9 to 1.9 K2O 0.7 to 1.7 B2O3 2.5 to 5.

0. [2] Cordierite-containing ceramic material according to claim 1, characterized by that this has a coefficient of thermal expansion at 20°C - 400°C < 2.5 · 10 -6 K -1 exhibits. [3] Cordierite-containing ceramic material according to claim 2, characterized by that the glaze has the same or a lower coefficient of thermal expansion than the material. [4] Cordierite-containing ceramic material according to any one of the preceding claims, characterized by that it has a water absorption of < 0.05 mass-%. [5] Method for producing a cordierite-containing ceramic material with a classic porcelain appearance, characterized by , that - a pre-burned material with the components in mass % Feldspar AKW 900 / 12 6 to 10 Calcined clay 4.5 to 10 Talc OOS 20 to 33 kaolin 30 to 55 Kaolin fireclay AK45 5 to 12 is mixed with a pre-burned additive as a nucleation for cordierite formation of 0.5 to 5 mass%, the composition of which consists of the components Kaolin 60 to 70% by mass Talc 30 to 40% by mass and further trace amounts of Ca, Ti, Se, P below 1% by mass contains and the material thus mixed with the additive is subjected to a shaping process with the addition of water and liquefier, - and the demolded, dried and plastered material is annealed in a rapid-firing annealing furnace at 700-1100°C for a period of 3 to 5 hours, - the material is then coated with a glaze, the composition of which consists of the components pre-burned material 50 to 55% by mass Borosilicate glass 20 to 25% by mass kaolin 3 to 11% by mass Calcined clay 2 to 4% by mass Talc OOS 12 to 16% by mass contains. [6] Method according to claim 5, characterized by , that an induction image is applied to the underside or inside of the cookware and is baked on by rapid firing at a maximum of 860°C and a firing time of 180 min. [7] Use of a cordierite-containing ceramic material according to one of claims 1-4 or of a cordierite-containing ceramic material produced according to the method of claims 5 or 6 as a technical component or as tableware.