DE1158434B - Stoneware resistant to temperature changes and process for its production - Google Patents

Description

Stoneware resistant to temperature changes and the process for its production The invention relates to the production of a novel, acid-resistant and in particular, stoneware resistant to temperature changes with very dense ceramic Shards and high mechanical strength based on lithium aluminum silicate.

It is already known that ceramic bodies of the three-component system Li20 -A1203-S'02 have particularly low coefficients of thermal expansion, which to the artificial formation of the S-modifications (high-temperature modifications) of Spodumene and / or eucryptite and their intermediate products in ceramic material can be traced back.

In such masses (US Pat. No. 2,785,080) the molar ratio of Oxyde Li2O: A1203: S'02 between 1: 1: 2 (= 11.8: 40.5: 47.7 "/ o) and 1: 1: 10 (= 4.1: 13.9: 82.0%).

The primary components of these bodies are those that are difficult to dissolve Lithium salts, mostly lithium carbonate, A1203 in the form of alumina and S'02 in the form of quartz or flint, furthermore kaolin or clays as subordinate additives and called organic binders. When using Spodumene and Petalit for Manufacture of ceramic bodies may only be small amounts of clay (no more than 5%) are applied to the minimum content of Li, 0 in the ceramic masses of 4.1% and the specified optimal properties, especially with regard to To achieve thermal shock resistance.

These pronounced lean masses are therefore naturally completely non-plastic and cannot be deformed like plastic ceramic stoneware masses. Even it is an extremely porous ceramic body.

According to another embodiment, the above-mentioned starting components by thermal pretreatment initially so-called ceramic frits, d. H. strong sintered, partially melted products are produced and these after grinding and Addition of small amounts of suitable binders to ceramic bodies, usually through Casting or pressing deformed and cooked at temperatures above 1000 ° C. Man thus leads to the main offset through the finely ground frits in the Pre-sintering newly formed high-temperature modifications (= ß-modifications) of a Minerals of the class spodumene-eucryptite or their siliceous intermediate products a.

It is also known (French patent 1037 673) to manufacture ceramic body also lithium carbonate, alumina in the form of boehmite A100H and chemically precipitated silica (silica gel) and clay additives to use. The L'20 salary However, this ceramic mass should not be less than 5 to 25 percent by weight. In this context it is even expressly stated that natural lithium minerals not directly in the raw state, d. H. to ceramic masses without prior frying can be processed, since these raw materials are only too porous and mechanically little lead solid finished products.

All masses produced by this process or its variants or ceramic bodies formed therefrom have the major disadvantage that they are porous, not mechanically strong and extremely difficult to burn, because their sinter-melting interval is very narrow.

The state of the art also includes a method (U.S. Patent 2 426 395) for the production of glass or. glaze-like sintered or melted bodies that soften even at very low temperatures and using 331 / s parts Boric acid, 331 / s parts lead oxide and 9 to 15 parts lithium nitrate or carbonate or phosphate and silica are produced.

According to a variant of this process, the mineral lepidolite should also be used (Lithium mica) can be used in amounts of 10 to 601 / o.

These mixtures result in easily melting, low-viscosity glass flows, which with advantage z. B. for ceramic glazes with a low expansion coefficient be used.

The ceramic bodies conceivable according to all of these processes mentioned thus become predominant using synthetic lithium salts and other, mostly synthetic oxide components or from these raw materials ceramic frits produced by thermal pretreatment. aside from that it is known to pre-fry Li-Al-silicate base masses or not pre-fritted Adding masses of clay.

Because the proportion of plastic clays or kaolins in these masses must be kept very low (Li20 content must not be below 4 to 5%), plastic deformation into large bodies is impossible.

Furthermore, due to their increased porosity, these masses have but partly also as a result of their chemical composition, e.g. B. from essential The proportions of boric acid and red lead and similar additives are much lower Acid resistance than comparable ceramic bodies made of ordinary, mullitic Stoneware; this excludes these masses from being used in chemical-technical Processes with an acidic environment. Likewise, these masses divide with theirs Generation of toxic compounds of lead etc. are processed for use in the food industry from the start.

It is also similar to porcelain (German Auslegeschrift 1010 0'00) Body with a low coefficient of thermal expansion and high thermal shock resistance on lithium-aluminum-silicate base has become known, which is obtained when z. B. 1 mole of Li2CO3, 1 mole of A1203 and 4 to 6 moles of Si02, optionally with addition of zirconium oxide at temperatures from 1100 to 1300 ° C, pre-fritted, ground and 100 parts of this synthetic frit after adding compounds of lead, boron, Manganese, cobalt and lithium in amounts up to 4 percent by weight and kaolin and Quartz up to 3011 / o can be fired at temperatures from 1300 to 1350 ° C.

This method also works with pre-fried venison, whereby the composition of the finished products can vary from about 4 to 5 1 / a Li20 (corresponding to 1 mole of Li2CO3 to 1 mole of A1203 to 6 moles of SiO2 to 1 mole of Li2C03 to 1 mole A1203 to 4 moles of SiO2; according to this teaching, the frit offsets are up to 4 percent by weight of the metal compounds described above and up to 30 percent by weight quartz and kaolin added). Here too, additions of boric acid, red lead, etc. increase the rate Acid solubility considerable. A plastic deformation of such very emaciated Frit offsets with a kaolin addition of -30% to larger vessels is not conceivable.

After all, it is already known that naturally occurring, pneumatolytic lithium minerals such as a-spodumene, a-eucryptite and also petalite, individually or in mixtures without prior thermal pretreatment, such as annealing, Melts or frits, possibly ground in a certain grain size in combination with quartz material or quartz glass in the finest and / or granular form below Addition of considerable proportions of plastic, flux-rich, especially illitic or sericite clays to be processed into fully plastic stoneware masses.

After all previously known methods are so in the ceramic Masses of Li, 0 contents introduced, which are significantly above 2 percent by weight low coefficient of thermal expansion and therefore good resistance to temperature changes to reach. Except for the one process in which a porcelain-like body arises, only porous and mechanically little is obtained according to the known processes solid bodies which burn in ceramic furnaces due to the narrow sinter-melting interval because of the high Li, 0 content of the masses encountered considerable difficulties.

It has now surprisingly been shown that, contrary to the previous Knowledge and experience, is possible (M. Mehmel, »The meaning of lithium in ceramic masses and glazes ”, lecture hall 90 [1957], No. 4, pp. 90/91, and No. 5, p. 111/115, in particular p. 113, left column, second paragraph), masses based on lithium-aluminum-silicate with a Li20 content below 2.0 Weight percent and their coefficient of thermal expansion is extremely low and that of quartz glass. As a result, such masses show extraordinary good resistance to temperature changes.

The inventive method for producing a temperature change resistant, acid-resistant stoneware with a low coefficient of thermal expansion, dense ceramic Shards and high mechanical strength based on lithium aluminum silicate with the addition of clay is characterized in that the lithium-aluminum-silicate base material Compounds of iron, nickel, zinc and / or magnesium preferably in the Form of their titanates, chromates, aluminates and / or their oxides in amounts up to 3'0 / 0, based on the base mass, can be added individually or in mixtures, the Li, 0 content of the base mass is below 2 0/0 and the mass obtained in this way, if applicable after their deformation in a reducing atmosphere at temperatures between 1250 and is fired at 1350 ° C.

In addition, soluble salts of phosphoric acid are preferably added to the raw material with organic bases, especially aliphatic amines, e.g. B. triethanolammonium phosphate or hexylammonium phosphate, added.

In a further embodiment of the invention, the raw mass can also be added lean agent such as quartz glass, corundum, porcelain and / or ground fired stoneware according to of the present invention in granular form with grain sizes from 0.1 to 1 mm to add in a proportion of 25 percent by weight, the mass in reducing Atmosphere is cooked at 1250 to 1350 ° C.

The masses produced according to the invention have compared to the previously known masses have the following decisive advantages: 1. Due to the increased proportion of Clay minerals or by reducing the strong thixotropic properties The high lithium content that has caused the previous masses increases the plastic workability of the masses significantly improved. In particular, it is now through the invention possible to manufacture ceramic bodies exclusively with natural lithium raw materials, without the plastic deformability of the masses for larger bodies as a result of the Compared to previous habits, the proportion of these substances is greatly increased becomes insufficient. 2. The sintering-melting interval of these low-lithium Mass is considerably wider than the previously known mass, which is the burning such ceramic body greatly facilitated.

3. The compositions according to the invention are completely dense and highly mechanical Strength, which is also possible due to the comparatively low L '., O content will. It is well known that weights with a high lithium content tend to develop very easily a so-called foamy body caused by the evaporation of lithium oxide during of burning.

4. Since the lithium content of the mass has a significant influence on the price has, the masses according to the present invention because of the greatly reduced Lithium content much cheaper.

In further investigations with the manufactured according to the invention Stoneware has shown that a) ions of the same size as those of Fe2 +, Zn2 +, Ni2 +, Sn4 + and Mg2 + by replacement of the Lil - ion the structure desired in the masses of the ß-spodumen with a very low coefficient of thermal expansion even in mixtures are able to stabilize, which are far below the levels previously used of lithium oxide in ceramic masses. This partial replacement of lithium thus enables ceramic bodies with an extremely low coefficient of thermal expansion and thus good thermal shock resistance with a minimum of lithium oxide to manufacture.

b) It has also been shown that these surcharges reduce the formation of glass in the Influence broken fragments extremely favorably in such a way that once the willingness to react promoted between the starting components, but on the other hand in such a way that the in the case of lithium masses, very narrow silicate melting range due to a corresponding change in viscosity the glass phase can be widened considerably. The previous masses point against it a silicate melting range of only 5 ° C.

c) By adding sparingly soluble and / or soluble phosphates the ion exchange between lithium raw material and clay minerals, which the Dreaded colloid chemical changes in the plastic properties of the raw material causes to be largely switched off, since it is known that the lithium phosphate formed is extremely difficult to dissolve and thus the stray lithium ions blokk'ert. The plastic workability of lithium-aluminum-silicate masses is so significantly improved by this measure.

The following are some examples of that made according to the invention stoneware that is resistant to temperature changes can be specified. Example 1 32 to 40 parts by weight natural lithium aluminum silicate or mixtures of minerals such as spodumene and petalite with the approximate theoretical composition of Li203: A1203: S'02 = 1: 1: 7, are made with 65 to 70 parts by weight of clay and an addition of 1.5 Parts by weight of a mixture of 30 percent by weight MgO - A1203, 50% Fe0 - AlO3 and 20 percent by weight NiO - A1203 or PbCr4 up to a fineness of 60 to 100 #L grind and then at temperatures between 1250 and 1320 ° C. in reducing Burned atmosphere. Example 2 parts by weight of Li2C03, 20 parts by weight of A1 "03 and 70 parts by weight of SiO2 are made after adding 4 parts by weight of a mixture 30 weight percent MgTi03, 30 weight percent Mg2P207 and 40 weight percent FeP04 pre-fried at temperatures of 1050 to 1200 ° C and then to a grain size of 60 to 100 # t ground. 5'0 parts by weight of this ground frit are added 50 parts by weight of plastic clays mixed and at temperatures between 1240 and Fired at 1310 ° C in a reducing atmosphere. Example 3 32 to 35 parts by weight Lithium-aluminum-silicate with a composition of Li20: A1203: S'02 = 1: 1: 6.5 are annealed with up to 2 percent by weight, based on the base mass Mixture of 30 parts by weight of MgO, 20 parts by weight of ZnO and 30 parts by weight Fe0, e.g. B. as iron (II) oxalate, ground to 60 to 100 #L and then added grained with 10 to 20 parts by weight. Lean substances such as quartz glass, corundum, Porcelain or re-ground base material mixed together. At the same time, sound becomes one Amount corresponding to the remainder mixed to 100 parts by weight. Thereupon the mix becomes of 1 / somolar triammomium phosphate solution in amounts of 100 ml / 100 kg mass and fired in a reducing atmosphere at a temperature of 1250 to 1320 ° C.

Claims (4)

PATEN TANSPR0CHE: 1. Process for the production of a temperature shock-resistant, acid-proof stoneware with a low coefficient of thermal expansion, dense ceramic body and high mechanical strength on the basis of lithium-aluminum-silicate with the addition of clay, characterized in that the lithium-aluminum-silicate base material Compounds of iron, nickel, zinc and / or magnesium, preferably in the form of their titanates, chromates, aluminates and / or their oxides, are added individually or in mixtures in amounts of up to 3%, based on the basic mass, with the Li20 content of the base mass is below 2-14 and the mass obtained in this way, if necessary after its deformation, is fired in a reducing atmosphere at temperatures between 1250 and 1350 ° C. 2. The method according to claim 1, characterized in that that the raw mass also contains soluble salts of phosphoric acid with organic bases, in particular aliphatic amines, such as triethanolammonium phosphate or hexylammonium phosphate, can be added. 3. Method according to one or more of the previous Claims, characterized in that the raw mass lean agent in granular Form with a grain size of 0.1 to 1 mm up to 25% can be added. 4. Procedure according to claim 5, characterized by the use of quartz glass, porcelain, corundum and / or ground base as a leaning agent. Considered publications: Lecture hall 1957, pp. 111 to 114 and 90, 91; German interpretative document No. 1010 000.