EP2595931A1

EP2595931A1 - Transparent or transparent dyed lithium aluminium silicate glass ceramic material having adapted thermal expansion and use thereof

Info

Publication number: EP2595931A1
Application number: EP11721745.5A
Authority: EP
Inventors: Friedrich Siebers; Evelin Weiss; Klaus Schoenberger
Original assignee: Schott AG
Current assignee: Schott AG
Priority date: 2010-07-23
Filing date: 2011-05-17
Publication date: 2013-05-29
Also published as: EP3878825A1; CN103003210A; DE102010032113A1; CN103003210B; WO2012010341A1; DE102010032113B4; JP5889297B2; US20130164509A1; US9446982B2; DE102010032113B9; JP2013532622A

Abstract

The invention relates to transparent or transparent dyed lithium aluminium silicate (LAS) glass ceramic material having an adapted thermal expansion, consisting of a glass ceramic material comprising high-quartz mixed crystals as the predominant crystalline phase, and a thermal expansion between room temperature and 700°C from 1.0 to 2.5 ∙ 10^-6/K, preferably from 1.3 to 1.8 ∙ 10^-6/K.

Description

Transparent or transparent colored lithium aluminum silicate glass ceramic with adapted thermal expansion and their use
The invention has a transparent or transparent colored lithium aluminum silicate glass ceramic with adapted thermal expansion consisting of a glass ceramic with high quartz mixed crystals as the predominant crystal phase and their use for the subject.
It is generally known that glasses of the system Li 2 O-Al 2 O 3 -SiO 2 can be converted into glass ceramics with high-quartz mixed crystals and / or keatite mixed crystals as main crystal phases.
A key property of these glass ceramics with high quartz mixed crystals as the main crystal phase is the manufacturability of materials which have a very low coefficient of thermal expansion in a given temperature range. In general, the thermal expansion behavior is set so that the materials in the range of their application temperatures over thermal zero expansion, usually 0 ± 0.3 • 10 -6 / K. So z. B. when used as a substrate material, wafer stages or mirror support for telescopes, the thermal expansion in the range of room temperature minimized. For applications as a transparent fireplace visor or dark colored cooking surface, the thermal zero expansion is set to the lowest possible values in a temperature range between room temperature and approx. 700 ° C.
Due to the low thermal expansion at their application temperatures, these glass ceramics have excellent temperature difference resistance and thermal shock resistance, as well as dimensional stability.
In transparent form, z. As a window for fireplaces for fire-resistant glazing, as a cooking surface with colored bottom coating and display applications is usually high transparency, preferably a light transmission (brightness Y) in the visible greater than 80% and a defined set, usually neutral hue desired.
The inherent color of transparent glass ceramic plates has various causes. In the batch raw materials for the melts, the coloring element Fe is contained as an impurity. The use of refining agents Sb 2 O 3 and CeO 2 also leads to a low intrinsic color. The described brownish yellow intrinsic coloration of the transparent glass-ceramics is based essentially on electronic transitions to color complexes which absorb in the short-wave range of visible light and in which the nucleating active component TiO 2 is involved. The most common absorbing color complex is the formation of adjacent Fe and Ti ions, between which electronic charge transfer transitions occur. Sn / Ti complexes also cause an intrinsic color. The Fe / Ti color complexes lead to a red-brown, the Sn / Ti color complexes to a yellow-brown discoloration. The formation of these color complexes already takes place during cooling of the starting glass and in particular during later ceraming of the glass ceramics. By adding coloring components, such as Nd 2 O 3 and CoO which absorb in the longer wavelength red spectral range, the intrinsic color can be reduced at the expense of a reduced light transmission. This optical overstaining is disclosed in EP1837312 A1.
For use as a cooking surface, a dark coloration of the per se transparent glass ceramic with reduction of light transmission to values below 5% is desired, which prevents the review of the technical structures under the cooking surface. On the other hand, the radiant radiators should be clearly visible even at low power and colored displays below the cooking surface. It is advantageous if, in addition to the usual red LED displays and the display with blue, green, yellow, orange, white displays or even the true color display of color screens is possible.
The large-scale production of these glass ceramics takes place in several stages. First, the crystallizable starting glass is melted from a mixture of shards and powdery vegetable raw materials at temperatures usually between 1500 and 1650 ° C. Arsenic and / or antimony oxide is typically used as the refining agent in the melt. These refining agents are compatible with the required glass-ceramic properties and lead to good bubble qualities of the melt. Even if these substances are firmly bound in the glass framework, they are disadvantageous in terms of safety and environmental protection. For example, special precautionary measures must be taken in the extraction of raw materials, the processing of raw materials and the evaporation from the melt. Recently, in particular, the use of SnO 2 is described as a harmless refining agent. In order to achieve good bubble qualities, halide compounds are preferably used as additional refining agent in addition to SnO 2 at conventional melting temperatures of up to 1700 ° C. Thus, in Japanese applications JP 11 100 229 A and JP 11 100 230 A, the use of 0.1-2% by weight of SnO 2 and 0-1% by weight of Cl is described. The addition of 0.05-1 wt% F (US 2007/0004578 A1) and 0.01-1 wt% Br (US 2008/0026927 A1) is also disclosed.
The use of SnO 2 in conjunction with high-temperature refining above 1700 ° C to achieve good bubble qualities is described in DE 199 39 787 C2.
After melting and refining, the glass usually undergoes hot forming by rolling or, more recently, floating to produce sheets. For economical production, a low melting temperature and a low processing temperature V A are desired. Furthermore, the glass must not show any devitrification during the shaping. That is, during the shaping must not form interfering crystals, which affect the strength in the starting glasses and the glass ceramics produced therefrom. Since the shaping takes place in the vicinity of the processing temperature V A (viscosity 10 4 dPas) of the glass, it must be ensured that the upper devitrification temperature of the melt is below the processing temperature in order to avoid the formation of troublesome crystals.
In a subsequent temperature process, the starting glass is transferred by controlled crystallization in the glass-ceramic article. This ceramization takes place in a two-stage temperature process in which nuclei, usually from ZrO 2 / TiO 2 mixed crystals, are initially produced by nucleation at a temperature of between 680 and 800 ° C. SnO 2 may also be involved in nucleation. Upon subsequent increase in temperature, the high-quartz mixed crystals grow on these nuclei. High crystal growth rates, as desired for efficient, fast ceramification, are achieved at temperatures of 800 to 950 ° C. At this maximum production temperature, the microstructure of the glass-ceramic is homogenized and the optical, physical and chemical properties are adjusted. If desired, the high quartz mixed crystals can subsequently be converted into keatite mixed crystals. The conversion into keatite mixed crystals takes place at a temperature increase in a temperature range of about 970 to 1250 ° C. With the conversion, the thermal expansion coefficient of the glass ceramic increases. For glass ceramics with keatite mixed crystals as the main crystal phase, for example in document EP 1 170 264 B1. Great efforts have been made here to increase the coefficient of thermal expansion to as low as possible values of approx.
Lower 1 • 10 -6 / K to allow use as a cooking surface with radiant heating. For this type of heating a temperature difference of> 650 ° C is required.
The transformation also involves crystal growth to mean crystallite sizes of 100 nm and above and associated light scattering. Glass ceramics with keatite mixed crystals as the main crystal phase are therefore no longer transparent, but translucent or opaque. When used as a cooking surface, the light scattering has a negative effect on the display ability, as the displays under the glass ceramic plate are no longer clearly visible and forms a disturbing halo.
The temperature difference resistance in the glass-ceramic is given by the following relationship:
It corresponds T is the temperature difference strength, f is a dimensionless correction factor (due to the plate geometry and the temperature distribution), μ is the Poisson's number, E is the modulus of elasticity, the thermal expansion coefficient and g is the strength for which the value must be used that arises in practical use due to surface damage.
Until now, glass ceramics with high-quartz mixed crystals as the main crystal phase have been developed in such a way that they have as low or zero thermal expansion as possible in their field of application. Common specifications are approx. 0 ± 0.15 • 10 -6 / K for cooking surfaces and approx. 0 ± 0.3 • 10 -6 / K for chimney panes (see tables 3.3 and 3.4 in the book "Low Thermal Expansion Glass Ceramics", Second Edition, Editor Hans Bach, Dieter Krause, Springer-Verlag Berlin Heidelberg 2005, ISBN 3-540-24111- 6). This is due to the fact that a high temperature difference resistance of the glass-ceramics in use can be achieved since no thermally induced stresses build up during temperature changes and adjacent regions with different temperatures build up no or only very low voltages. This is a necessity especially for cooktops with radiant heating.
But now the low thermal expansion is also associated with technical disadvantages. The low thermal expansion is a peculiarity for materials. Bonded joints with other materials, such as e.g. Metals, ceramics, glasses are hardly possible due to the high differences in the thermal expansion or require complex constructions with transition materials. The metallic or inorganic filler itself also have a too high thermal expansion. The different thermal expansion coefficients lead to high stresses, which destroy the joint usually during cooling or induce such high voltages that the strength is impaired.
In mechanically pressed from the outside compounds it comes in the temperature change to a constant working of the materials against each other, resulting in loosening and gap formation, z. B. can lead in glass ceramics with metallic frame.
For transparent glass ceramics such. As chimney windows or transparent colored glass ceramics such. B. cooking surfaces, the decoration with inorganic colors is common. Such decorative colors are z. As described in DE 197 21 737 C1. Depending on the composition, these decorative paints, which consist of an inorganic glass flux and coloring pigments, have thermal expansion coefficients between room temperature and 300 ° C of approx. 4 to 10 · 10 -6 / K. Decorating is possible only with restrictions due to these different thermal expansion coefficients. In particular, the layer thickness is at values of at most about 3 to 5 m limited if the usual minimum values for the bending tensile strength of the decorated glass ceramic above about 30 MPa to be achieved. At higher layer thicknesses, a strength-reducing crack network is formed due to the resulting high tensile stresses in the decorative layer. The adhesion of the decorative layers is reduced and there is a risk of flaking, in which most of a part of the glass ceramic substrate with mussels.
The large difference in the coefficients of thermal expansion results in decorated glass-ceramics having reduced flexural strength. The impact resistance is also lowered when the externally applied mechanical tensile load acts on the decorated side of the glass ceramic. Undecorated glass ceramics, in contrast, have values of bending tensile strength of about 130 MPa.
Higher values of the bending tensile strength can be achieved with decorated glass ceramics if they have keatite mixed crystals as the main crystal phase and thus have higher thermal expansion coefficients of approximately 1 to 2 × 10 -6 / K. DE 197 21 737 C1 shows in the exemplary embodiments the comparison between coated with the same decor colors substrates that have been converted into glass ceramics with high quartz or keatite mixed crystals as the main crystal phase. The flexural tensile strengths of the decorated keatite glass-ceramics are about a factor of 2 higher. However, glass ceramics with keatite mixed crystals as the main crystal phase have the disadvantages described. With transparent colored glass ceramics, as used for cooking surfaces, the display capability for colored light displays is insufficient. In the case of transparent glass ceramics used for chimney glasses, glass ceramics having keatite mixed crystals as the main crystal phase are unsuitable because of the high scattering of the comparatively large crystallites and consequently the lack of transparency.
For glass ceramics with high quartz mixed crystals as main crystal phase and low thermal expansion, the usable thicknesses of the decorative layer are limited for reasons of strength. However, the limited layer thicknesses limit the color opacity and thus the design ability in the design.
With transparent glass-ceramics, it is hardly possible to produce opaque decorative coatings. The decoration usually looks transparent due to lack of opacity.
Cooktops made of colored glass ceramics are black in supervision. The limited layer thickness of the decorative colors leads to a change in hue, especially in bright decor colors, because the black substrate is not completely covered. In general, color intensity and the color range, which can be represented in the design, so limited.
Since decorative inks with zero thermal expansion appear to be hardly feasible, it is desirable in this respect to increase the thermal expansion coefficient of the glass ceramic.
New developments in the field of chimney panes and also in the heating systems of cooking surfaces have led to lower demands on the glass ceramic materials with respect to the temperature difference resistance.
For chimney panes installed in modern ovens, the requirement for temperature differential resistance decreases. Thus, a cold air curtain is generated to avoid soot loading of the disc in the combustion chamber in front of the inside of the transparent glass ceramic. This reduces the temperatures to which the glass ceramic pane is exposed.
For inductively heated cooking surfaces with electronic control, the required temperature difference resistance drops to values of <600 ° C and in modern systems partially to values of <400 ° C. This is due to the principle of induction heating, which does not directly heat the glass ceramic plate itself, but the metallic pot bottom. The glass ceramic cooking surface is heated indirectly only by reheating. As cooktops with inductive heating both black-colored glass ceramics and transparent with opaque colored underside coating in use. Such transparent glass ceramics with colored underside coating and separately coated areas are known, for example, from document US Pat. No. 6,660,980 B2. Due to the design of the underside coating, colored displays are possible.
Even with gas-heated cooking surfaces are generally lower requirements for the temperature difference resistance.
In newer applications of transparent glass ceramic panes as display glasses, in glazing for fire protection as well as in security glazing in architecture or for ballistic protection, a higher thermal expansion coefficient is advantageous for the better adaptation to other materials. For example, the glass ceramic panes are installed in metallic frames or joined with plastics to form a laminate.
Due to the lower requirements on the temperature difference resistance, it is permissible to increase the thermal expansion coefficient of the glass ceramic. For some newer applications of transparent glass-ceramics, higher thermal expansion is advantageous.
It is an object of the invention to take advantage of the lower temperature difference resistance requirements associated with new glass-ceramic applications in order to exploit the advantages with regard to an improved adaptation of the thermal expansion of the glass-ceramic to other materials and decorative paints.
Due to their composition, glass ceramics should be suitable for economical and environmentally friendly production. For economic production, the starting glasses should be readily meltable and cleanable, have a high devitrification stability and be ceramizable in short times.
When used as a fireplace or cooking surface, the glass ceramic should meet all requirements, such. Chemical resistance, mechanical strength, transmittance, temperature resistance and long-term stability with respect to changes in their properties (such as thermal expansion, transmission, stress build-up). With regard to the transmission is in transparent glass ceramics, a high light transmission and low intrinsic color advantage. Transparent colored glass ceramics, which are mainly used for cooking surfaces, require a black appearance and a good display capability with different colored displays.
These objects are achieved by a lithium aluminum silicate glass-ceramic according to claim 1 and by their use according to claim 11.
The transparent or transparent colored lithium aluminum silicate glass ceramic has an adapted thermal expansion between room temperature and 700 ° C of 1.0 to 2.5 • 10 -6 / K and preferably from 1.3 to 1.8 • 10 -6 / K and consists of high quartz mixed crystals as the predominant crystal phase.
The glass ceramic according to the invention contains as main constituents the components:
Li 2 O 2.0 - <3.0
MgO 1.4-3
Al 2 O 3 19-23
SiO 2 60-69
TiO 2 0.5-6.0
ZrO 2 0 - <2.0
SnO 2 0 - 0.6.
The oxides Li 2 O, MgO, Al 2 O 3 and SiO 2 in the preferred limits given are components of the high-quartz mixed crystals. In the formation of the mixed crystals, the Li atoms and the Mg atoms together with the Al atom substitute the Si atoms. The Al atom is incorporated in the crystal framework in the position of the Si atom, and the Li or Mg atoms in the channels of the crystal structure serve for charge compensation. A minimum content of Li 2 O of 2% by weight is advantageous for a readily controllable crystallization. Higher contents from 3% by weight and above make it difficult to adjust the thermal expansion values according to the invention, since Li 2 O lowers them. For their adjustment, an MgO content of 1.4 to 3 wt.% Is required. Since MgO leads to an increase in the thermal expansion of the high-quartz mixed crystal and thus of the glass-ceramic, comparatively higher contents than usual are required.
In order to avoid higher viscosities of the starting glass and the unwanted devitrification of mullite during shaping, the Al 2 O 3 content is limited to preferably not more than 23% by weight. The SiO 2 content should be at most 69% by weight, because this component greatly increases the viscosity of the glass. For good melting of the glasses and for low molding temperatures, higher contents of SiO 2 are uneconomical. The minimum content of SiO 2 should be 60 wt.%, Because this is advantageous for the required properties, such as chemical resistance and temperature resistance.
TiO 2 , ZrO 2 and SnO 2 are required as nucleating agents and form in the nucleation mixed crystals of the three components. The crystals of high quartz crystals then grow on these nucleator crystals during crystallization.
The ZrO 2 content is limited to less than 2% by weight, since higher contents may impair the melting behavior of the batch in the glass production and the devitrification stability during forming may be impaired by the formation of ZrO 2 -containing crystals. The component TiO 2 is a very effective and important for short nucleation times component. The TiO 2 content should be at least 0.5% by weight and at most 6% by weight. The content should not exceed 6 wt.%, Because otherwise the devitrification stability is deteriorated. This also applies in particular to the component SnO 2 , which is limited to values of at most 0.6% by weight. Higher contents lead to the crystallization of Sn-containing crystal phases on the contact materials (eg Pt / Rh) during shaping and should be avoided.
The coefficient of thermal expansion should be at least 1.0 • 10 -6 / K in order to improve the advantages of adapting the thermal expansion to other materials and, in particular, decorative paints. The coefficient of thermal expansion is at most 2.5 · 10 -6 / K because otherwise the associated temperature difference resistance drops to impermissibly low values. Also stand for such high thermal expansion coefficients already industrially producible glasses such. As borosilicate glasses available.
The thermal expansion coefficient is preferably 1.3 to 1.8 · 10 -6 / K. With these values, also in terms of temperature difference resistance more demanding applications such. B. Induction cooking surfaces with fast cooking times (booster function) and chimney sight glass with a simpler structure in which the glass ceramic panes are exposed to higher temperatures operated.
The adjustment of the thermal expansion coefficient depends on two requirements. On the one hand, the coefficient of expansion in the range according to the invention will be set as high as possible in order to improve the thermal adaptation to other materials, in particular decorative colors. On the other hand, the coefficient of thermal expansion is limited by the temperature differential strength associated with the intended application. Depending on the technical design, the desired applications, in particular chimney windows and cooking surfaces with gas or induction heating, generally require values of the temperature difference between 250 and 600 ° C.
With the value of the coefficient of thermal expansion which can be set in the range according to the invention to the respective requirement, a markedly improved adaptation to other materials and decorative colors is achieved. Due to the increased thermal expansion coefficient joining with other materials such. As plastics, metals, ceramics and glasses compared to the glass ceramics with zero thermal expansion facilitates. The use of metallic and inorganic fulcrum leads to lower stresses and thus the joined compounds have higher strength values. For mechanically pressed connections z. As in glass ceramics with metallic frame, the materials work less in temperature change against each other d. H. There is less displacement and thus loosening and gap formation in the frame.
In coatings of the glass ceramic with inorganic decorative paints, the difference in the thermal expansion coefficient is reduced. This makes it possible with currently customary layer thicknesses of about 2 to 5 m to achieve higher strengths of the decorated glass ceramic articles. The building-up of the decor colors upon cooling tensions are reduced. The usually resulting crack network is thereby reduced. This means that the cracks resulting from stress relaxation are reduced in their depth with which they extend into the glass ceramic and the distances of the cracks in the decorated areas are increased. The usual crack depths can otherwise be about 30 μm, whereby the cracks penetrate into the glass-ceramic substrate. It is even possible to avoid the formation of cracks in general. Due to the improved thermal adjustments, the adhesion of the decorative layers is also improved, both after decorative firing and during use under normal mechanical loads and recurring temperature changes. In addition to improving the strength, the improved thermal adaptation of the decorative colors to the glass-ceramic substrate can also be exploited in order to increase the color covering power via increased layer thicknesses. With transparent glass-ceramics it is possible to produce decorative coatings with improved opacity (lower transmission). With cooktops made of colored glass ceramics with a black appearance, it is possible to achieve much more intense shades through the higher layer thickness. For bright decor colors, visual falsification of hue is avoided by the incompletely covered black glass-ceramic substrate. The color range that can be displayed in the design is thus extended to lighter areas and purer hues. Measured in remission, this is expressed in the CIELAB color system in higher L values. The adapted value of the thermal expansion therefore makes it possible to expand the creative possibilities in the design.
The glass ceramic consists of high quartz mixed crystals as the predominant crystal phase. Other secondary crystal phases are z. For example, the nucleating crystals formed from the nucleating agents TiO 2 , ZrO 2 and SnO 2 and crystals of the keatite mixed crystal type. The proportion of secondary crystal phases should preferably be less than 10% by weight. Otherwise, due to the high refractive index of the nucleation crystals or the larger crystallite size of the keatite mixed crystals, an interfering light scattering of the glass ceramic occurs. For keatite mixed crystals, the average crystallite size is generally at least 100 nm. The associated light scattering is noticeable in transparent glass ceramics very disturbing as white veil. For transparent colored glass ceramics, eg cooktops, the light scattering has a negative effect on the readability. Luminous displays under the glass ceramic are no longer contour sharp and have a disturbing halo.
It is therefore advantageous if the average crystallite size of the glass-ceramic with high-quartz mixed crystals as the predominant crystal phase is less than 150 nm and particularly preferably less than 70 nm.
The crystal phase content of the high-quartz mixed crystals of the glass-ceramic according to the invention is preferably 50-75% by weight. The crystal phase content should be at least 50% by weight because this is advantageous for higher bending tensile strengths of the glass-ceramic. Preferably, the crystal phase content is less than 75% by weight. At higher values, it becomes difficult to ceramize the crystallizable glasses without deformation in short times. Due to the higher heat of crystallization values which occur unevenly in the crystallization of the glass-ceramics and the higher stiffness of the glass-ceramic, longer times are required to obtain non-deforming glass-ceramic articles, such as flat plates.
The glass ceramic according to the invention preferably contains as main constituents of the composition the components (in% by weight based on oxide):
Li 2 O 2.0 - <3.0
Na 2 O + K 2 O 0 - 2
MgO 1.4-3
CaO + SrO + BaO 0 - 4
ZnO 0-3
Al 2 O 3 19-23
SiO 2 60-69
TiO 2 0.5-6.0
ZrO 2 0 - <2.0
SnO 2 0 - 0.6
TiO 2 + ZrO 2 + SnO 2 3 - 6
P 2 O 5 0-3
with the condition (in% by weight):
MgO / Li 2 O> 0.4,
and optionally a refining agent selected from the group Sb 2 O 3 , As 2 O 3 in contents of 0.1 to 2 wt.%.
In the production of glass ceramic articles, bubbles having a bubble rate of less than 5, preferably less than 3 bubbles / kg in the crystallisable starting glass or in the glass ceramic (based on bubble sizes greater than 0.1 mm) are required as good bubble qualities.
In order to improve the refining can be used in addition to the listed Hauptläutermitteln additional refining aids such as CeO 2 , sulfate, sulfide and halide compounds. Their contents are usually limited to amounts up to 1% by weight.
For the inventive setting of the thermal expansion of the glass ceramic, the MgO content is at least 40%, preferably at least 50% of the Li 2 O content, ie, the relationship MgO / Li 2 O ≥ 0.4, preferably ≥ 0.5.
The minimum amount of nucleating agents TiO 2 , ZrO 2 and SnO 2 is 3% by weight. During the ceramization they form crystal nuclei in high density during the nucleation, which serve as a substrate for the growth of the high quartz mixed crystals during crystallization. The high nucleus density leads to a high crystal density and ensures an average crystallite size which remains below the size of 150 nm, the exceeding of which is critical for disturbing light scattering. In addition, the nucleator contents are correlated with the nucleation rate and thus important for shorter ceramification times. Higher contents than the sum of 6% by weight deteriorate the devitrification stability. For improved devitrification stability, the SnO 2 content is limited to 0.6% and preferably 0.4% by weight.
As further components, ZnO and P 2 O 5 can be incorporated into the high quartz mixed crystals. The ZnO content is limited to values of at most 3% by weight during the ceramization because of the problem of the formation of undesired crystal phases, such as zinc spinel (Gahnit). The addition of P 2 O 5 can be up to 3% by weight and is preferably limited to 1.5% by weight. The addition of P 2 O 5 is favorable for the devitrification stability, higher contents have an unfavorable effect on the acid resistance of the glass ceramic.
The addition of the alkalis Na 2 O, K 2 O and the alkaline earths CaO, SrO, BaO and B 2 O 3 improves the meltability and the devitrification behavior during the shaping of the glass. However, the contents must be limited because these components are not incorporated into the crystal phases, but remain essentially in the residual glass phase of the glass ceramic. Too high contents impair the crystallization behavior during the conversion of the crystallizable starting glass into the glass ceramic, in particular at the expense of faster ceramization speeds. In addition, higher contents have an unfavorable effect on the time / temperature resistance of the glass ceramic. The sum of the alkalis Na 2 O + K 2 O is at most 2% by weight and preferably at most 1.5% by weight.
The sum of the alkaline earths CaO + SrO + BaO should amount to a maximum of 4% by weight.
The mentioned alkalis and alkaline earths accumulate, except in the residual glass phase between the crystals, also on the surface of the glass ceramic. When ceramizing, a glassy surface layer approximately 200 to 1500 nm thick which is virtually free of crystals and enriched in these elements and depleted in lithium forms. This glassy surface layer has a favorable effect on the chemical resistance of the glass ceramic.
The water content of the starting glasses for producing the cooking surfaces according to the invention is usually between 0.015 and 0.06 mol / l, depending on the choice of the batch raw materials and the process conditions in the melt. This matches with OH values of 0.16 to 0.64 mm -1 for the crystallizable starting glasses.
The glass ceramics according to the invention preferably have a composition without the refining agents arsenic and / or antimony oxide and are thus technically free from these components which are disadvantageous in terms of safety and environmental protection. As an impurity, these components are usually present at levels of less than 0.05% by weight.
The transparent lithium aluminum silicate glass ceramic according to the invention, or the article produced therefrom, preferably has a composition of the glass ceramic which, in wt.% Based on oxide, consists essentially of:
Li 2 O 2.0 - <3.0
Na 2 O + K 2 O 0.1 - 1.5
MgO 1.4 - 2.6
CaO + SrO + BaO 0 - 4
ZnO 0-3
B 2 O 3 0 - 2
Al 2 O 3 19-23
SiO 2 60-69
TiO 2 0.5 - 2.5
ZrO 2 0 - <2
P 2 O 5 0-3
SnO 2 0 - 0.6
TiO 2 + ZrO 2 + SnO 2 3 - 6
Nd 2 O 3 0-0.4
Fe 2 O 3 <0.03
under the condition:
MgO / Li 2 O> 0.5,
and optionally a refining agent selected from the group Sb 2 O 3 , As 2 O 3 in contents of 0.1 to 2 wt.%.
The term "consisting essentially of" means that the listed components should be at least 96%, typically 98% of the total composition. A variety of elements such. As F, Cl, the alkalis Rb, Cs or elements such as Hf are common impurities in the bulk used raw materials. Other compounds, e.g. those of the elements Ge, rare earths, Bi can be added in small amounts.
With these composition ranges favorable properties in terms of transmission, as well as the meltability and the devitrification stability can be achieved. For improved meltability and devitrification stability, the content of the alkalis Na 2 O + K 2 O should preferably be at least 0.1% by weight.
For improved devitrification stability, the SnO 2 content is limited to 0.6% and preferably 0.4% by weight.
For fireplace viewing windows, a good view of the combustion chamber and the flames is desired. For cooking surfaces with colored underside coating, the color of the underside coating should not be falsified by the intrinsic color or a gray cast of the glass ceramic.
For the applications of the transparent glass ceramic, therefore, a high light transmission (brightness) Y of at least 80%, preferably greater than 85%, measured at 4 mm thickness with standard light C, 2 ° is required. The terms light transmission and brightness (brightness) Y correspond to the same measured variable, measured according to DIN 5033.
A preferred embodiment of the invention is to provide a low intrinsic color in addition to the high light transmission. The transparent glass ceramic then has a yellowness index (measured according to the standard ASTM 1925/70 (77, 85)) of less than 12 at a thickness of 4 mm.
This combination of high light transmission and low intrinsic color is possible with the coordinated according to the invention low Fe 2 O 3 contents <0.03 wt.%, With the defined levels of nucleating TiO 2 , SnO 2 and ZrO 2 and by the MgO / Li 2 O ratio.
The intrinsic color is primarily attributable to the described color complexes in which the component necessary for nucleation, the Ti ion, is involved.
In order to reduce the intrinsic color, the contents of Fe 2 O 3 are limited to less than 0.03% by weight and of TiO 2 to a maximum of 2.5% by weight.
The ratio of the oxides MgO / Li 2 O is at least 0.5. It has been shown that despite the high MgO contents at the low Li 2 O contents, the intrinsic color of the transparent glass ceramic is not impaired by the high MgO contents, as usual. This negative influence of the higher MgO contents is described, for example, in US Pat. No. 4,438,210. The cause of this surprising observation is seen in the fact that because of the low Li 2 O contents, larger amounts of Mg are incorporated into the high quartz and substitute the Li there. It is believed that the component MgO is detrimental to the inherent color of transparent glass-ceramics only if it remains in the residual glass phase.
The optional addition of the overstaining agent Nd 2 O 3 in contents of up to 0.4% by weight can reduce the intrinsic color, which, however, lowers the light transmission. Other coloring components such. B. CoO may be added at levels up to about 100 ppm to adjust the color locus.
In the form of a transparent, colored lithium aluminum silicate glass ceramic, or as an article produced therefrom, it preferably has a light transmission of less than 5% and a composition of the glass ceramic which, in% by weight, based on oxide, essentially consists of:
Li 2 O 2.0 - <3.0
Na 2 O + K 2 O 0.1 - 1.5
MgO 1.4 - 2.6
CaO + SrO + BaO 0 - 4
ZnO 0-3
B 2 O 3 0 - 2
Al 2 O 3 19-23
SiO 2 60-69
TiO 2 2 - 6
ZrO 2 0 - <2
P 2 O 5 0-3
SnO 2 0 - 0.6
TiO 2 + ZrO 2 + SnO 2 3 - 6
V 2 O 5 0.01-0.06,
under the condition:
MgO / Li 2 O> 0.5,
and optionally a refining agent selected from the group Sb 2 O 3 , As 2 O 3 in contents of 0.1 to 2 wt.%.
In order to adjust the light transmittance according to the invention, which is adapted to the respective thickness of the glass-ceramic article, less than 5%, measured with standard light C, 2 °, the glass-ceramic as colorant contains 0.01-0.06% by weight of V 2 O 5 . The higher TiO 2 contents of at least 2% by weight support the color effect of V 2 O 5 . As a further color oxide, the composition contains Fe 2 O 3 in levels which exceed the usual contamination in technical batch raw materials of about 0.03 wt.% And can be up to 0.3 wt.%. At higher levels, the decorability is affected by bright colors, as they discolor.
The condition MgO / Li 2 O> 0.5 should also apply to this preferred composition range according to the invention. This ensures that the desired thermal expansion values of the invention are achieved.
As the main explanatory agent, at least one of SnO 2 , Sb 2 O 3 or As 2 O 3 is selected in an amount of 0.1 to 2% by weight. Preferably, less than 0.6 wt.% SnO 2 is used for an environmentally friendly refining and the composition is technically free from Sb 2 O 3 or As 2 O 3 . For improved devitrification stability, the SnO 2 content is preferably limited to 0.4% by weight.
For economical production, the crystallizable starting glass should be readily meltable and have a high devitrification stability. Here, the processing temperature should be less than 1320 ° C and preferably less than 1310 ° C. The upper devitrification limit should be at least 15 ° C and preferably at least 30 ° C below the processing temperature. With regard to devitrification, critical crystal phases are mullite (aluminum silicate), Baddeleyt (ZrO 2 ) and SnO 2 -contained crystal phases. With regard to the devitrification stability, accordingly, higher contents of Li 2 O, Al 2 O 3 , SiO 2 , ZrO 2 and SnO 2 are disadvantageous. In order to lower the viscosity of the molten glass, it has been found necessary to reduce the content of SiO 2 , Al 2 O 3 , ZrO 2 , while the contents of alkalis Na 2 O + K 2 O and alkaline earths CaO + SrO + BaO are selected at higher values.
Preferably, the transparent colored lithium aluminum silicate glass-ceramic has a light transmission of less than 5% and an oxide-based weight percent composition of:
Li 2 O 2.0 - <3.0
Na 2 O 0.1 - 1
K 2 O 0.1 -1
Na 2 O + K 2 O 0.2 - 1.5
MgO 1.5 - 2.6
CaO 0.1 - 1
SrO 0 - 1
BaO 0 - 3
CaO + SrO + BaO 0.2 - 4
ZnO 0-2.5
B 2 O 3 0 - 1
Al 2 O 3 19-23
SiO 2 62-67
TiO 2 2.5 - 6
ZrO 2 0 - 1.6
P 2 O 5 0-1.5
SnO 2 0.1-0.4
TiO 2 + ZrO 2 + SnO 2 4.2 - 6
V 2 O 5 0.01-0.05
Fe 2 O 3 0.05-0.3,
with the conditions:
Fe 2 O 3 / V 2 O 5 > 2
MgO / Li 2 O> 0.5,
without the refining agents arsenic and antimony oxide.
The condition MgO / Li 2 O> 0.5 ensures that the desired thermal expansion values according to the invention are achieved.
For the adjustment of the light transmission of less than 5% measured with standard light C, 2 °, adjusted to the thickness of the glass ceramic, or of the article produced therefrom, a combination of the color oxides V 2 O 5 and Fe 2 O 3 is used. The amount of Fe 2 O 3 should be at least twice as large as that of V 2 O 5 . The component Fe 2 O 3 is cheaper as a raw material and more environmentally friendly. In addition, Fe 2 O 3 supports the refining of the glass melt. Higher amounts than 0.3 wt.% Are unfavorable for decorating with bright colors, as they discolor.
0.1 to 0.4% by weight SnO 2 is preferably used for an environmentally friendly refining and the composition is technically free from Sb 2 O 3 or As 2 O 3 .
The preferred geometry for the transparent or transparent colored glass ceramic, or the article produced therefrom, is plate-shaped with thicknesses of 2.5 to 14 mm, because important applications such. As a fireplace visor, fire-resistant glazing, display screen, cooking surface, as well as security glazing with mechanical or ballistic protective effect. With lower thicknesses, the strength is impaired, higher thicknesses are less economical due to the higher material requirements. Apart from the use as safety glass, which depends on high strength, the thickness is therefore usually chosen below 6 mm.
Suitable shaping methods for the required plate-shaped geometry are rollers and floats.
The glass ceramic plate can not only be formed flat, but also three-dimensionally deformed, such. B. beveled, angled or curved plates can be used. The plates may be rectangular or in other shapes, and in addition to planar regions, three-dimensionally deformed regions such as e.g. Woks or rolled webs included. The geometric deformations of the plates are in the hot forming, such. B. by structured shaping rolls or by downstream hot forming of the starting glasses such. B. made by burners or by gravity sinking during ceramizing with supporting ceramic molds.
The transparent or transparent colored glass ceramic plate is preferably completely or partially coated with an inorganic decoration.
Preferably, an inorganic decorative ink having a comparatively low thermal expansion is used. The decor color is chosen so that the difference in thermal expansion to the glass ceramic plate, measured between room temperature and 300 ° C, is less than 4 • 10 -6 / K. This is facilitated by the inventively higher expansion of the glass-ceramic and leads to lower voltages between the decorative layer and the substrate. For the environmentally friendly decoration with inorganic colors, a composition is preferably selected which is technically free of lead, cadmium, mercury, hexavalent chromium and their compounds.
Examples of decorations are the surrounding frame in chimney panes made of transparent glass ceramic plates. For cooking surfaces, there are a variety of decorations for reasons of design or technical nature, eg. B. for cooking zone markings.
Usually, the layer thickness of the decoration after firing is limited to 2 - 5 microns in order to achieve the minimum strengths for most requirements of greater than 30 MPa. With the glass ceramic according to the invention can be in the usual layer thicknesses of the decoration of at least 3 microns higher bending tensile strengths than usual of greater than 50 MPa and even greater than 60 MPa achieve.
Due to the inventively higher thermal expansion of the glass ceramics with high quartz mixed crystals as the main crystal phase, the usable thicknesses of the decorative layer are increased. This is especially true if the usual specifications for bending tensile strength are maintained. The thickness of the decoration is greater than 5 microns, preferably greater than 6 microns, the minimum strength of 35 MPa is achieved. This allows decor layers with increased color opacity and extends the overall design possibilities in the design.
Cooking surfaces made of transparent colored glass ceramic with a black appearance in the top view can be decorated with more intense shades due to the higher layer thickness of the decor. The decor colors are more color true and are less distorted by the translucent black substrate. In general, the color range, which can be represented in the design is thus extended.
With transparent glass ceramics, the higher layer thickness makes it possible to produce decorative coatings with improved opacity.
The transparent or transparent colored lithium aluminum silicate glass-ceramic plate is preferably designed as a cooking surface, because here the advantages of the adapted thermal expansion in the decoration, as described, come particularly to bear.
If the cooking surface consists of a transparent colored lithium aluminum silicate glass-ceramic plate, it should have a light transmission of 0.5 to 2.5%. In order to prevent the annoying inspection of the technical components under the glass ceramic cooking surface, the light transmission is limited to values less than 2.5%. This limitation also ensures the desired black appearance in supervision. On the other hand, a light transmission of at least 0.5% is required for the display ability, since the luminous displays are usually installed from light emitting diodes below the hotplate. These values are independent of the thickness of the glass ceramic plate, which is usually 2.5 to 6 mm. With lower thicknesses, the strength is impaired, higher thicknesses are less economical due to the higher material requirements.
In order to enable the display with the usual red and other color displays, the transmission in the range of visible light for the entire wavelength range from 450 nm should be greater than 0.1%. This transmission value of 0.1% is undershot for commercial glass-ceramic cooking surfaces for wavelengths below 550 nm. The usual red LEDs emit at wavelengths around 630 nm. Due to the strong absorption in the range of visible light below 550 nm, which is smaller than 0.1%, however, the display capability for differently colored displays is lost. This applies especially to the display with standard blue and green LEDs.
When the cooking surface is made by roll forming, the underside is usually studded to protect it from strength-reducing injuries during manufacture. Often, the area of colored displays is smoothed with transparent organic polymer to avoid optical distortion from the pimples. On cooktops with a smooth underside, without pimples, colored displays are undistorted and lighter.
Preferably, the transmission of the cooking surface to values of:
> 0.15% at 450 nm,
> 0.15% at 500 nm,
> 0.25% at 550 nm,
2 - 12% at 630nm
and a visible light transmittance of 0.7 - 2.5% is set.
With these values, the color display capability is further improved and the different demands on the transmission process are further optimized. A particularly good coverage of the technical installations below the cooktop glass ceramic and a particularly aesthetic black appearance in incident light is achieved when the light transmission is less than 1.7%. Transmission values of the cooking surface at 630 nm from 2 to 12% correspond to the tolerance values of commercially available cooking surfaces. It is advantageous to set these common values, so that the appearance of the conventional red LED displays is unchanged even in the cooking surface according to the invention.
In addition to the color oxide V 2 O 5 in contents of 0.01 to 0.06 wt.%, Other coloring components such as chromium, manganese, cobalt, nickel, copper, selenium, rare earth, molybdenum - or sulfide compounds are used to assist the staining. Thus, for example, the addition of CoO and NiO is particularly suitable for optimizing the display with blue LEDs. The content of the coloring additives is limited to amounts of at most about 2% by weight, preferably less than 1% by weight, because these compounds generally lower the transmission in the visible and in the infrared. In addition, these largely polyvalent compounds can interfere with the coloring of the V 2 O 5 via redox reactions and make it difficult to adjust the transmission values according to the invention.
By adding reducing agents in powdery and / or liquid form to the starting mixture, the coloring effect of the V 2 O 5 can be enhanced. For this purpose, metals, carbon and / or oxidizable carbon or metal compounds such as Al or Si powder, sugar, charcoal, SiC, TiC, MgS, ZnS are suitable. Gaseous reducing agents such as forming gas are also suitable.
Preferably then less than 0.03 wt.% V 2 O 5 are needed. Since vanadium oxide is a costly raw material, it is economically advantageous to minimize the content.
Preferably, under the cooking surface according to the invention with improved color display capability, one or more differently colored displays, such as blue, green, yellow, are used instead of or in addition to the usual red displays.
arranged in orange or white. Due to the transmission curve, blue or white displays are particularly preferred. The colored displays consist of light-emitting electronic components, mostly of light-emitting diodes. There are all forms of ads, punctual as well as area possible. Due to the uniform spectral profile of the transmission in the visible, color displays or screens can be displayed for the first time.
The heating of the cooking surface is preferably carried out with gas burners or inductive. The temperature differential strength of the cooking surface associated with the thermal expansion according to the invention is less than 600 ° C. This is sufficient for the mentioned types of heating and the advantages due to the adapted thermal expansion are maintained.
The present invention will be further clarified by the following examples.
For some embodiments, Table 1 lists compositions and properties of crystallizable starting glasses for transparent glass-ceramics. The glasses 1 to 3 are glasses according to the invention and the glass 4 is a comparative glass outside the scope of the present invention. Table 2 shows compositions and properties of crystallizable starting glasses for transparent colored glass-ceramics. The glasses 5 to 11 are glasses according to the invention and the glass 12 is a comparative glass outside of the present invention. Due to typical impurities in the large-scale batch raw materials used, the compositions do not exactly add up to 100% by weight. Typical impurities, although not intentionally introduced into the composition, are F, Cl, B, P, Rb, Cs, Hf or Sr, which are usually less than 0.05% by weight. They are often introduced via the raw materials for the related components, e.g. Rb and Cs via the Na or K raw materials, or Sr over the Ba raw material.
In Table 1 and 2, the properties in the glassy state, such as: transformation temperature Tg, processing temperature V A , devitrification temperature, and the density are listed. To measure the devitrification temperature, the glasses are melted in Pt / Rh 10 crucibles. Subsequently, the crucibles are kept at different temperatures within the range of the processing temperature for 5 hours. The uppermost temperature at which the first crystals at the contact surface of the molten glass occur to the crucible wall determines the devitrification temperature.
The water content of the glasses is 0.03-0.05 mol / l, corresponding to β OH values of 0.32 to 0.53 mm -1 .
The starting glasses of Table 1 and 2 were melted from conventional raw materials in the glass industry at temperatures of about 1620 ° C, 4 hours. After melting the mixture into crucibles made of sintered silica glass, the melts were recast in Pt / Rh crucible with inner crucible made of silica glass and homogenized by stirring at temperatures of 1550 ° C, 30 minutes. After this homogenization, the glasses were refined for 2 hours at 1640 ° C. Then pieces of about 140x140x30 mm³ size were poured and cooled in a cooling oven, starting from 660 ° C to room temperature. The castings were subdivided into the sizes required for the investigations and for the ceramization.
Tables 3 and 4 show the ceramification conditions and properties of the obtained glass ceramics. The ceramizations were carried out with the following temperature programs. Up to a temperature of 680 ° C is heated with the highest heating rate, which is possible in Keramierungofen, about 20 ° C / min. The temperature range of 680 to 800 ° C is important for nucleation. The temperature increase in this area is adapted to the particular composition in such a way that light scattering by excessively large crystallites is avoided. Above 800 ° C, the crystallization of the desired high quartz mixed crystal phase takes place. In the ceramization programs 1 and 2, a hold time t KB is introduced in the area of nucleation at the temperature T KB . Likewise, the maximum temperature T max and hold time t max are individually adapted to the composition. The values are given in the tables.
Ceramization program 1:
a) rapid heating from room temperature to 680 ° C,
b) temperature increase from 680 ° C to nucleation temperature T KB at a heating rate of 5 ° C / min, holding time t KB of 30 min at T KB , further heating at 2.5 ° C / min to 800 ° C,
c) temperature increase from 800 ° C to maximum temperature T max with a heating rate of 2.5 ° C / min, holding time t max of 15 min at T max ,
d) Cooling to 600 ° C at 4 ° C / min, then rapid cooling to room temperature.
Ceramization program 2:
a) rapid heating from room temperature to 680 ° C,
b) temperature increase from 680 ° C to nucleation temperature T KB at a heating rate of 10 ° C / min, holding time t KB of 15 minutes at T KB , further heating at 10 ° C / min to 800 ° C,
c) temperature increase from 800 ° C to maximum temperature T max with a heating rate of 10 ° C / min, holding time t max of 15 min at T max ,
d) Cooling to 800 ° C at 10 ° C / min, then rapid cooling to room temperature.
Ceramization program 3:
a) rapid heating from room temperature to 680 ° C,
b) temperature increase from 680 ° C to 730 ° C at a heating rate of 10 ° C / min, further heating at 5.2 ° C / min to 800 ° C,
c) temperature increase from 800 ° C to maximum temperature T max of 920 ° C with a heating rate of 6 ° C / min, holding time t max of 6 min at T max ,
d) Cooling to 800 ° C at 4 ° C / min, then rapid cooling to room temperature.
Ceramization program 4:
a) rapid heating from room temperature to 680 ° C
b) Temperature increase from 680 ° C to 800 ° C with a heating rate of 10 ° C / min
c) temperature increase from 800 ° C to maximum temperature T max with a heating rate of 10 ° C / min, holding time t max of 15 minutes at T max
d) Cooling to 800 ° C at 10 ° C / min, then rapid cooling to room temperature.
Examples 4 and 13 in Tables 3 and 4 are comparative glass ceramics outside the invention made from the comparative crystallizable comparative glasses 4 and 12, respectively. The thermal expansion between 20 and 500 ° C and between 20 and 700 ° C and the measured by X-ray diffraction phase content of the main crystal phase, consisting of high quartz mixed crystals, and the average crystallite size shown.
The transmission measurements were carried out on polished plates of the specified thickness with standard light C, 2 °. The measurements on the transparent or transparent colored glass-ceramics (Table 3 or Table 4) show the transmission values at selected wavelengths as well as the brightness Y or light transmission according to DIN 5033.
The inherent color of the transparent glass-ceramics in Table 3 is characterized by the yellowness index according to standard ASTM 1925/70 (77, 85).
In further Examples 14 to 25 (Table 5) plates of dimensions 50 × 50 × 3 mm were prepared from the crystallizable starting glasses. The surfaces of the plates are polished.
The plates were screen-printed all over the surface in different layer thicknesses. For comparison purposes, some plates remained undecorated. In screen printing screen printing pastes were prepared from inorganic powders in a known manner. For this purpose, first a powder in an average particle size of about 2 m made of a low-melting glass with a composition according to DE 19721737 C1. This was mixed with 20% of a white or black pigment and processed with the addition of screen printing oil based on spruce oil to a screen printing paste. By varying the screen printing parameters, different layer thicknesses of the decoration were set. The decorative burn-in of the printed test samples was carried out in a laboratory oven. The ceramization of the crystallizable starting glasses was also carried out in a glass ceramic with high quartz mixed crystals as the main crystal phase. Table 5 shows the firing and ceramization programs used and the properties obtained as a function of the layer thickness.
The layer thickness was determined after firing with a profilometer with diamond tip designation Alphastep Tencor. The bending tensile strength was measured according to the double-ring method (DIN EN1288-5).
In Examples 15 to 17 and Comparative Examples 19 to 21, glasses which are crystallizable to transparent black-colored glass ceramics were decorated. Examples 14 and 18 are the undecorated reference plates. The plates are prepared in the same way. Comparative Examples 18 to 21 are made of another comparative crystallizable glass No. 13. Its composition is disclosed in DE 10 2008 050 263 A1, Table 1, Glass No. 13, and results in a glass-ceramic with a low thermal expansion of -0.14 · 10 -6 / K, outside the present invention.
The inorganic decoration contains as pigment a commercial TiO 2 white pigment. The color hiding power and color intensity of the decorated areas as a function of the layer thickness of the decoration and compared to the undecorated reference was determined by remission and measurement of the light transmission in transmitted light with standard light C / 2 °. The values are given for the Lab and CIE color systems. The advantageous effect of higher layer thicknesses can be seen from the values. In the comparative examples, the greater drop in flexural tensile strengths of the decorated panels can be seen.
Depending on the layer thickness, the resulting crack network was also evaluated for frequency (distance of the cracks) and depth of the cracks with a light microscope. Here, 5 means a very dense deep-going crack network, which suggests high tensions between the decorative layer and the glass-ceramic substrate, and 0 means no microscopically visible cracks. The decorated comparative examples have a stronger crack network.
The hiding power of the black-decorated transparent glass-ceramics, Examples 23 to 25 was carried out as a function of the layer thickness by measuring the light transmission in transmitted light in the decorated area. For comparative purposes, both bending tensile strength and light transmission were performed on undecorated comparative samples of the same thickness (Example 22). The advantageous effect of higher layer thicknesses of the decor for the color opacity is recognizable.
[Corrected in accordance with Rule 26 09.06.2011]
[Corrected in accordance with Rule 26 09.06.2011]
[Corrected in accordance with Rule 26 09.06.2011]
[Corrected in accordance with Rule 26 09.06.2011]
[Corrected in accordance with Rule 26 09.06.2011]

Claims

Transparent or transparent colored lithium aluminum silicate (LAS) glass ceramic with adapted thermal expansion consisting of a glass ceramic with high quartz mixed crystals as predominant crystal phase,

characterized,

that the glass-ceramic contains as main constituents (in% by weight based on oxide):

Li 2 O 2.0 - <3.0

MgO 1.4-3

Al 2 O 3 19-23

SiO 2 60-69

TiO 2 0.5-6.0

ZrO 2 0 - <2.0

SnO 2 0 - 0.6

and a thermal expansion between room temperature and 700 ° C of 1.0 to 2.5 • 10 -6 / K, preferably 1.3 to 1.8 • 10 -6 / K.
Transparent or transparent colored lithium aluminum silicate glass-ceramic according to claim 1,

characterized by a composition containing as main constituents the components (in% by weight based on oxide):

Li 2 O 2.0 - <3.0

Na 2 O + K 2 O 0 - 2

MgO 1.4-3

CaO + SrO + BaO 0 - 4

ZnO 0-3

Al 2 O 3 19-23

SiO 2 60-69

TiO 2 0.5-6.0

ZrO 2 0 - <2.0

SnO 2 0 - 0.6

TiO 2 + ZrO 2 + SnO 2 3 - 6

P 2 O 5 0-3

under the condition:

MgO / Li 2 O> 0.4

and optionally a refining agent selected from the group Sb 2 O 3 , As 2 O 3 in contents of 0.1 to 2 wt.%.
Transparent or transparent colored lithium aluminum silicate glass-ceramic according to one of claims 1 to 2,

characterized,

that the glass ceramic contains, except for unavoidable traces, none of the chemical refining agents arsenic oxide and / or antimony oxide.
Transparent lithium aluminum silicate glass-ceramic according to claims 1 to 3,

characterized by a light transmission greater than 80% and a composition consisting essentially of (in% by weight based on oxide),

Li 2 O 2.0 - <3.0

Na 2 O + K 2 O 0.1 - 1.5

MgO 1.4 - 2.6

CaO + SrO + BaO 0 - 4

ZnO 0-3

B 2 O 3 0 - 2

Al 2 O 3 19-23

SiO 2 60-69

TiO 2 0.5 - 2.5

ZrO 2 0 - <2

P 2 O 5 0-3

SnO 2 0 - 0.6

TiO 2 + ZrO 2 + SnO 2 3 - 6

Nd 2 O 3 0-0.4

Fe 2 O 3 <0.03

under the condition:

MgO / Li 2 O> 0.5,

and optionally a refining agent selected from the group Sb 2 O 3 , As 2 O 3 in contents of 0.1 to 2 wt.%.
Transparent colored lithium aluminum silicate glass-ceramic according to claims 1 to 3,

characterized by a light transmission of less than 5% and a composition consisting essentially of (in% by weight based on oxide)

Li 2 O 2.0 - <3.0

Na 2 O + K 2 O 0.1 - 1.5

MgO 1.4 - 2.6

CaO + SrO + BaO 0 - 4

ZnO 0-3

B 2 O 3 0 - 2

Al 2 O 3 19-23

SiO 2 60-69

TiO 2 2 - 6

ZrO 2 0 - <2

P 2 O 5 0-3

SnO 2 0 - 0.6

TiO 2 + ZrO 2 + SnO 2 3 - 6

V 2 O 5 0.01-0.06

under the condition:

MgO / Li 2 O> 0.5,

and optionally a refining agent selected from the group Sb 2 O 3 , As 2 O 3 in contents of 0.1 to 2 wt.%.
Transparent colored lithium aluminum silicate glass-ceramic according to one of the preceding claims,

characterized by good fusibility and devitrification stability of the crystallizable starting glass having a processing temperature V A of less than 1320 ° C, an upper devitrification limit of at least 15 ° C below V A , a light transmittance of less than 5% and a composition of the glass-ceramic (in% by weight based on oxide) from:

Li 2 O 2.0 - <3.0

Na 2 O 0.1 - 1

K 2 O 0.1 - 1

Na 2 O + K 2 O 0.2 - 1.5

MgO 1.5 - 2.6

CaO 0.1 - 1

SrO 0 - 1

BaO 0 - 3

CaO + SrO + BaO 0.2 - 4

ZnO 0-2.5

B 2 O 3 0 - 1

Al 2 O 3 19-23

SiO 2 62-67

TiO 2 2.5 - 6

ZrO 2 0 - 1.6

P 2 O 5 0-1.5

SnO 2 0.1-0.4

TiO 2 + ZrO 2 + SnO 2 4.2 - 6

V 2 O 5 0.01-0.05

Fe 2 O 3 0.05-0.3,

with the conditions:

Fe 2 O 3 / V 2 O 5 > 2,

MgO / Li 2 O> 0.5,

without the refining agents arsenic and antimony oxide.
Transparent or transparent colored lithium aluminum silicate glass-ceramic according to one of claims 1 to 6,

characterized,

that it is in the form of a plate.
Transparent or transparent colored lithium aluminum silicate glass-ceramic according to claim 7,

characterized,

that the plate is coated on at least one side wholly or partially with an inorganic decoration.
Transparent or transparent colored lithium aluminum silicate glass-ceramic according to claim 8,

characterized,

that the decorated plate with a layer thickness of the decoration of at least 3 microns has a bending tensile strength of greater than 50 MPa.
Transparent or transparent colored lithium aluminum silicate glass-ceramic according to one of claims 8 to 9, characterized

that the layer thickness of the decorative paint is greater than 5 m, preferably greater than 6 m, wherein the bending tensile strength of the decorated glass ceramic plate is at least 35 MPa.
Use of a transparent or transparent colored lithium aluminosilicate glass ceramic according to the preceding claims 1 to 10 as chimney panel, fire-resistant glazing, display screen, safety glazing or cooking surface with opaque colored underside coating in transparent form or use as a cooking surface in transparent colored form.
Transparent colored lithium aluminum silicate glass-ceramic according to one of the preceding claims as cooking surface,

characterized,

that the cooking surface has a visible light transmission of 0.5 to 2.5% and a transmission greater than 0.1% in the visible light range for the entire wavelength range from 450 nm.
Transparent colored lithium aluminum silicate glass ceramic as cooking surface according to claim 12, characterized by transmission values of

> 0.15% at 450 nm

> 0.15% at 500 nm

> 0.25% at 550 nm

2 - 12% at 630 nm

and a visible light transmission of 0.7 - 2.5%.
Cooking surface according to claim 11 to 13,

characterized,

that one or more differently colored displays, such as blue, green, yellow, orange or white are used instead of or in addition to the usual red displays.
Cooking surface according to claim 11 to 14, characterized by a heating by means of induction or gas and a temperature difference resistance of less than 600 ° C.