DE1238376B - Ceramic materials resistant to temperature changes - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C04b

German class: 80 b -12/05

Number: 1238 376

File number: R 37085 VI b / 80 b

Filing date: January 29, 1964

Opened on: April 6, 1967

The invention relates to the production of ceramic materials with previously unattained thermal shock resistance, very low thermal expansion and high mechanical strength based on aluminum-silicon-titanium.

The ceramic materials previously known to be resistant to temperature changes, e.g. B. chemical porcelain with a high mullite content, cordierite or lithium aluminum silicate ceramic can withstand a temperature drop from 320 to 20 ⁰ C at most. Although the magnesium-aluminum-silicates and lithium-aluminum-silicates have a relatively low thermal expansion, products made from them have so far remained of no importance, because the range of their thermal properties is very large due to the short firing interval and thus represents an uncertainty factor in application technology . In addition, these known compositions which are resistant to temperature changes have a relatively low melting point (<1460 ° C.) which also stands in the way of use at high temperatures. _;

Furthermore, it was already known that the expansion coefficient and thus also the resistance to temperature changes of the fired shaped body can be influenced favorably _{by adding TiO 2 to ceramic masses.} According to the Journal of the Amer. Cerium. Soc, 1953, pp. 349 to 356, presented test _{results which were achieved with Al 2} O ₃ · SiO ₂ · TiO ₂ masses, but which only contained up to 10 percent by weight of TiO ₂ , ie at most 0.21 mol of TiO ₂ 1 mole of Al ₂ O ₃ . ^

It has now been found that certain compositions of matter in the Al ₂ O ₃ - SiO ₂ - TiO _{2 material system} have extremely good thermal shock resistance, very low thermal expansion and high mechanical strength. These properties occur in a wide range of the three-component system, so that the chemical composition and the firing temperature to be used can be varied as desired, especially since the compositions according to the invention also have a large firing interval. Such compositions of matter also make it possible to use a sufficient plastic fraction in the form of kaolinite as the starting material. Because of the very high melting temperatures of the substances composed according to the invention, which are in the range from 1600 to over 1800 ^° C., such compositions can also be used with advantage for products which are to be exposed to very high temperatures. According to the invention, the compositions are particularly suitable

Ceramic materials resistant to temperature changes

Applicant:

Rosenthal Aktiengesellschaft, Selb

Named as inventor:
Peter Bock, Bayreuth

in the range of 1 mol Al ₂ O ₃ , 0.05 to 1.5 mol SiO ₂ and 0.5 to 1.5 mol TiO ₂ ; preferably a 1: 1: 1 molar ratio can be used. In this area of the three-component system, the thermal expansion is extremely low and, depending on the composition, is minus 1.5 · 10 ~ ^β to plus 1.5 · 10 ~ ^e per I ⁰ C.

These ceramic materials are so resistant to temperature changes that they can withstand ^{a drop in temperature from 1000 to 20 ° C.}

Depending on the composition of such materials can be densely fired preferably at 1400-1600 ⁰ C. It has been shown that it is possible to lower the firing temperature of the basic compositions by adding small amounts of oxides without the high thermal shock resistance being noticeably changed. The alkaline earth oxides, zinc oxide and lithium oxide are particularly suitable for this purpose. Furthermore, highly refractory oxides such as thorium oxide, zirconium oxide, yttrium oxide or the oxides of the rare earths (especially the cerite and ytter earths) as well as highly refractory carbides, nitrides, borides and / or sulfides can be added to the basic materials according to the invention, whereby the temperature of use of the products to be manufactured ( High temperature substances) is increased without the thermal shock resistance achieved according to the invention suffering. With the same advantage, part of the SiO ₂ content can also be replaced by B ₂ O ₃ or by P ₂ O ₅ .

Furthermore, according to the invention, during the firing process in the temperature range from 1000 to 1300 ^° C., the TiO ₂ contained in the compositions can be reduced in a hydrogen-containing furnace atmosphere. The reduced titanium content obtained in this way is optionally converted into mixed ceramics containing titanium nitride or titanium carbide by post-treatment in a nitrogen or carbon-containing atmosphere in the same temperature range. Who is responsible for the hydrogen treatment or

709 548/360

The burnout that follows the treatment is carried out in a neutral or slightly reducing atmosphere. Man receives a material with excellent thermal and mechanical resistance.

In addition to the oxides, compounds from which the corresponding oxides are formed in the fire can of course also be used as starting materials. The SiO ₂ content and part of the aluminum oxide is preferably introduced as kaolinite. For ceramic masses, the starting mixture is ground in a ball mill in a manner known per se for 12 to 48 hours, depending on the composition, the weight ratio of the grist to grinding balls to water being 1: 1: 0.5 to 1. The prepared mass is dewatered on a filter press and shaped into bodies by pressing, extrusion, pulling, turning or casting, optionally with the addition of an organic binder and / or an organic lubricant that burns out without residue in the subsequent firing process. Moldings obtained in this way are then burned smooth by the methods customary in ceramics. Although the glow firing that normally precedes the burnout is not required, it can be advantageous in the production of complex or thick-walled molded bodies. For the purpose of regulating the reaction conditions and the shrinkage, part of the starting mixture can be pre-burned or pre-fritted and then mixed in again in a finely ground state.

The ceramic materials composed according to the invention or the bodies produced therefrom apart from the very good resistance to thermal shock, the low thermal expansion and the high mechanical strength also good thermal conductivity and after an oxidizing fire also good thermal conductivity good electrical insulation. There is thus the possibility of their use in the field of chemical technology, high temperature technology, electrical engineering, laboratory equipment technology and household goods, z. B. in the manufacture of cookware.

The invention is explained below using exemplary embodiments which, however, do not limit the subject matter of the invention in any way.

Examples

1. The starting mixture consists of 1 mole of Al ₂ O ₃ , 1 mole of SiO ₂ and 1.0 mole of TiO ₂ and is composed of

49.6 parts by weight of kaolinite,

19.6 parts by weight of aluminum oxide,

30.8 parts by weight of titanium dioxide.

The preparation and the firing process carried out by the customary methods in the ceramic, wherein the fineness of grinding <60 μ and the firing temperature should be 1500 ⁰ C (Sk 18). The ceramic material obtained therefrom has an average coefficient of expansion of minus 0.1 · 10 ~ ⁶ per 1 ° C up to 1000 ° C.

2. The starting mixture consists of 1 mol of Al ₂ O ₃ , 0.1 mol of SiO ₂ and 0.9 mol of TiO ₂ and is composed of

7.1 parts by weight kaolinite,
53.3 parts by weight of aluminum oxide,
39.6 parts by weight of titanium dioxide.

; The preparation is carried out according to Example 1, while the firing temperature is 1530 ° C (Sk 20). The material obtained from this has a mean expansion coefficient of plus 0.9 · 10 ~ ^e per I ⁰ C up to 1000 ^ C.

3. The starting mixture consists of 1 mol Al ₂ O ₃ , 0.5 mol SiO ₂ , 1 mol, OMoI TiO ₂ and 0.1 mol Li ₂ O and is made up of

28.2 parts by weight of kaolinite,

33.5 parts by weight of aluminum oxide,

35.0 parts by weight of titanium dioxide,

3.3 parts by weight of lithium carbonate.

The preparation takes place according to example 1,

while the firing temperature is 141O ⁰ C (Sk 14).

The material obtained therefrom has to 1000 ⁰ C has an average coefficient of expansion minus 0.8 10 ~ ^e Jei ⁰ C.

4. The starting mixture consists of 1 mole of Al ₂ O ₃ , 0.5 mole of SiO ₂ and 1 mole of TiO ₂ and is composed of

27.0 parts by weight kaolinite,

18.1 parts by weight of aluminum oxide,

21.3 parts by weight of aluminum hydroxide,

33.6 parts by weight of titanium dioxide.

The preparation is carried out according to Example 1, while the firing temperature is 151O ⁰ C (~ Skl9). The material obtained therefrom has to 1000 ⁰ C has an average expansion coefficient of 0.4 x 10- minus _β per I ⁰ C.

All ceramic materials composed according to the invention are in their hitherto known ones Properties in terms of thermal shock resistance, low thermal expansion and mechanical Strength superior and also have the technological advantage that

a) Their starting mixtures are proportionate due to their chemical composition high plastic content, for example up to more than 50% kaolinite, and that

b) the prepared masses of the compositions according to the invention have a large burning interval have, so that it is possible to produce dense ceramic materials from it.

Claims (6)

Patent claims: 1. Ceramic materials resistant to thermal shock, characterized in that their compositions are in the range of 1 mol Al ₂ O ₃ , 0.05 mol to 1.5 mol SiO ₂ and 0.5 to 1.5 mol TiO ₂ . 2. Thermal shock resistant ceramic materials according to claim 1, characterized in that the molar ratio of Al ₂ O ₃ to SiO ₂ to TiO ₂ = 1: 1: 1. 3. Thermal shock resistant ceramic materials according to claim 1 and 2, characterized in that SiO ₂ is partly replaced by B ₂ O ₃ and / or P ₂ O ₅ . 4. Thermal shock resistant ceramic materials according to claim 1 to 3, characterized in that that small amounts of alkaline earth oxides, zinc oxide and / or lithium oxide are added as fluxes are. 5. Thermal shock resistant ceramic Stof ^ fe according to claim 1 to 4, characterized in that that highly refractory oxides, especially thorium, zirconium and / or yttrium oxide, oxides of 5 6 rare earths (cent or ytter earths), highly corresponding part of the Al ₂ O ₃ as kaolinite in Refractory carbides, nitrides, borides and / or the mass is introduced. Sulphides are added. 6. Thermal shock resistant ceramic materials. Considered publications: Fe according to claims 1 to 5, characterized in that 5 German Auslegeschriften No. 1158 434.1 010 000; that the SiO ₂ proportion wholly or partially and a Journal of the Amer. Cerium. Soc, 1953, pp. 349 to 356. 709 548/360 3.67 © Bundesdruckerei Berlin