DE1227821B - Process for the production of a porcelain-like mass of high thermal shock resistance - Google Patents

Description

Process for the production of a porcelain-like mass of high thermal shock resistance It is known that ceramic bodies are resistant to temperature changes does not meet all practical requirements and with increasing density and increasing Thermal expansion of the body gets worse and worse. These more or less minor Resistance to temperature changes and thus a strong decrease in strength is presumably based largely due to the different coefficients of expansion in the porcelain mass existing individual phases. Also as particularly resistant to temperature changes known types of materials, such as. B. porcelains with a high clay substance content, porcelains With a high mullite content, codierite and lithium aluminum silicates, have a mechanical Strength that does not go beyond that of technical porcelain. When used their strength decreases by 20 to 60 0/0 with a change in temperature. Although with magnesium aluminum silicates and lithium aluminum silicates reduce the strength due to the low thermal expansion is slightly less due to thermal cycling, this is what causes the short one here Sintering interval large scatter ranges of the material properties, which is an uncertainty factor in application technology.

For many purposes, however, is both high thermal shock resistance and mechanical strength as well as a dense body of a porcelain-like Mass desirable.

So far, the efforts of the ceramic industry to produce objects which are resistant to temperature changes from masses which have at least one crystal phase and one glass phase have not yet brought the desired success. Attempts have been made to solve this problem by selecting a crystal phase which has a low coefficient of expansion. In general, the expansion coefficients of the various phases in porcelain-like masses have not been given any significant importance, and the importance of coordinating the expansion coefficients of the phases, in particular the glass phase, has not been recognized to its full extent. This repeatedly led to unsatisfactory results, since the glass phase generally has a lower coefficient of expansion, namely between 0.25-10-0 and 10-10-0 per degree Celsius, while the substances for the crystal phase, on the other hand, usually have a higher coefficient Coefficients of expansion, for example the quartz modifications between 3 - 10-s and 60-10-0 and mullite between 2.9.10-6 and 6.10-6, have. Among other things, it was proposed to use materials that are resistant to temperature changes that have the lowest possible coefficient of expansion.

The problems identified above can be solved by removing stresses between the individual phases by standardizing the phase relationships and Alignment of their expansion properties are largely prevented. According to the invention the way is now proposed, according to which a glass phase to bind the crystal phase is used whose coefficient of expansion corresponds to the relatively high coefficient of expansion . Is adapted to the crystal phase.

The invention now relates to a method for producing a new, porcelain-like - possibly glazed mass of high thermal shock resistance and mechanical strength with dense cullet from a crystal and a glass phase and is characterized in that 45 to 85% of such crystal phase constituents are used and 55 to 15% of such glass phase components are mixed that the coefficient of expansion of the two phases is as identical as possible, with aluminum oxide or as the crystal phase a mixture or mixed crystals of aluminum oxide with zirconium oxide and / or thorium oxide and / or chromium oxide with a grain size below 20 #t, preferably below 8 @u, and as glass phase 13 to 281 / o A1203, 51 to 71% Si02, 1.5 to 9.50 / 0 Ca0, 1 to 5% Mg0, 1.5 to 5% Na20 and 4.5 to 9% K20 are used, whereupon the approach in a known manner pours or forms, dries and the molding, if necessary after a pre-firing, burns at a temperature between 1300 and 1500 ° C and optionally Glazed before or after the smooth firing.

The composition according to the invention is produced according to the methods shown in FIG in the ceramic industry generally used methods by firing the raw mass after pouring or molding and dry new of the molding. The burning area : from 1300: to 1500 ° C is remarkably wide. Are in such a burnt mass then z. B. the corundum crystals good thermal conductivity in a very elastic Glass phase embedded stress-free. The uniform crystals are so, dense - matted so that the: .glass phase is no longer noticeable. ...

Between the portion of the glass phase. and the firing temperature some connection. The higher the content of A1203 or the other crystalline Oxyde, the higher the firing temperature should be. For example, is included a - A1203 content - .. from- 54 to 66% the firing temperature at about 1400 ° C. It can be fired in one fire but also in two fires, whereby the glaze may apply in the context of the second fire.

The mechanical strength as well as the resistance to temperature changes the ceramic mass can still be treated with heat after the bake increase further, an increase of up to 30% is achieved.

This tempering is based on heating above the transformation point the glass phase of about 780 ° C. It is assumed that this is due to ion diffusion some healing of the micro-notches contained in the ceramic object and fine cracks occurs, which leads to a reduction in tensile and compressive stresses leads. Similar favorable results are obtained by lengthening the cooling period after burning <. One. further increase in mechanical strength .der Mass is achieved by applying a matching glaze. -. -. , ..

The mass according to the invention has a mechanical strength of around two to three times that of conventional technical porcelain:: # 7 Tensile strength '::''h600' to '2 ° 50Ö kg / ciü2' Di ück # strength: `--.- 17 000 'to 3Ö 000 kg / cm2 `` Flexural Strength '':. f300 to 3 Ö00 kg / tin2 ` -Even though. the deformability of the green mass is quite good, it can be useful for the production of moldings-more difficult -shape and large dimensions to add organic and / or inorganic plasticizers, as they are common in the ceramic industry: a part of the inorganic .Plasticizers, e.g. bentonite, clay or the like, can enter the Al 203-Ger hold of the glass phase.

Width - exists -: a; certain connection between .the A1203 salary on the one hand: - and the combination of alkali and alkaline earth oxides in the glass phase on the other hand. If the alumina content is high, the ratio of alkali to alkaline earth oxide must also be shifted in favor of the alkaline earth oxides. It is believed that the in the interstices of the silicon tetrahedron network have a certain amount of cations Cause devitrification, which depends on the valency and the ionic radius of the cations. This devitrification causes good matting of the crystals within the body structure.

The homogeneity of the cullet structure can be checked by using a Corresponding glacial fragments-improve: -.-- - As starting materials-for the The corresponding oxides and / or silicates can be used in the glass phase. It However, substances are also suitable which, under the Breniibondüngen, the oxides deliver, e.g. B. Hydroxides, carbonates, nitrates, etc.

The following examples illustrate the invention:. Example 1 A raw mixture of the composition 12.0% orthoclase, 4.01 / o albite, 2.5% calcium carbonate, 1.5% magnesium carbonate, 22.0% kaolinite with 58% aluminum oxide and water was made in a drum mill with flint stones as above Milled for a long time until the particle size distribution was 220/0 10 to 20 g, 310/0 5 to 10 #t, 20% 1.6 to 5 t, and 27% <1.6 R. After the grinding process, the porcelain slip was pressed into filter presses and some of the water was removed again. The filter cakes were, depending on the shaping process, on the vacuum extrusion press. drawn ... or as.-casting slip: prepared by adding 100 parts by weight of the filter cake with 30 to 40 parts by weight of water, and 0.2 to. 0.4 parts by weight of "Formsil" (as an electrolyte) were liquefied. From. the so: prepared: mass produced raw moldings -were. at. in the air or in drying cabinets -dried between 25 and 80 ° C and then annealed with SK 022 to 011: a. Annealed and unannealed briquettes - were coated with a raw glaze. their composition of the Seger formula -. 0.20 K20 ..0.45 Ca0, 0.35 -MgÖ, 1.0 Al 203 , 830 8; 0 S102, corresponded, .coated and. After drying again at SK 13 bis. 15 burned smooth. It is also possible; only, . the raw blanks without glowing - the same. for SK 13 to 15-smooth fired new. Body produced in this way are dense porcelain-like materials with a volume weight. of 2.9 kg / dme and a flexural strength of 2300 kg / cm2.

Samples made of this material were heated to 1000 ° C. and then quenched to 20 ° C in a few seconds; so their flexural strength increased to -29.00 kg / cm2 ;. -This- corresponds to an increase in strength of .26%:. -It was. a raw mixture of the composition 7.0% orthoclase, 4.5% albite, 3.5% calcium carbonate, 2; 0% magnesium carbonate, 3rd, 0% kaolinite with 80% aluminum oxide and water in a drum mill .e ground with flint stones until the grain size distribution is 39 0/0 5 his. & R, 41% 1; 6 to -5 g and 201 / o <1.611. Pressing the filter cake; the shaping process, ie. .Pulling .or grating; Drying and glowing of the bricks corresponded to the example, .1 ... .both. .annealed. as well as unannealed briquettes were with - a raw glaze; - Their composition of the Segerform.el 0.10K20, 0; 50 Ca0; 0.40 Mg0; -1.4 A1203.6; 0 S102, coated and burned smooth after drying again for SK-1.6 to 18: With this mass it is also possible to burn-out the moldings directly without prior annealing. Man. received - a porcelain-like, dense - material with a density of 3; 3 kg / dm3 and a flexural strength of 2800 kg / cm ?. When quenching from .. 1000 ° C to 20- ° C , the flexural strength increased: to: 3030 kg / cm2; that is an increase in strength of 8%; - - -Beispie1--3 According to the instructions of Example-1, an approach to 12.0.e% 0, Orthoclase,. 4.0-9 / o. Albit; 3.5% calcium carbonate, 2.0% magnesium carbonate, 20.5% kaolinite with 40% zirconium oxide and 18% aluminum oxide produced as the crystal phase and treated as usual. A ceramic mass resistant to temperature changes was obtained with a density of 3.9 kg / dm3 and a flexural strength of 2500 kg / em2.

Example 4 As in Example 1, a batch with 7.0% orthoclase, 4.5% albite, 3.5% calcium carbonate, 2.0% magnesium carbonate, 3.0% kaolinite with 77.5 % Aluminum oxide and 2.5% chromium oxide mixed as a crystal phase and specified above Way further processed. The body obtained had a density of 3.3 kg / dm3 and a flexural strength of 3000 kg / cm2.

Claims (3)

Claims: 1. A method for producing a porcelain-like, ceramic, optionally glazed mass of high thermal shock resistance and mechanical strength with a dense body consisting of a crystal and a glass phase, d a - characterized in that 45 to 85% of such crystal phase constituents are used and 55 to 15% of such glass phase components are mixed that the coefficient of expansion of the two phases is as identical as possible, with aluminum oxide or as the crystal phase a mixture or mixed crystals of aluminum oxide with zirconium oxide and / or thorium oxide and / or chromium oxide with a grain size below 20%, preferably below 8 g ,, and as glass phase 13 to 28% A1203, 51 to 71% SiO2, 1.5 to 9.5% Ca0, 1 to 5% Mg0, 1.5% to 51% Na 2 O and 4.5 to 9% K 2 O is used, whereupon the approach in Pours known per se or forms, dries and the molding, if necessary after a pre-firing, burns at a temperature between 1300 and 1500 ° C and optionally Glazed before or after the final firing. 2. The method according to claim 1, characterized in that that one for the glass phase constituents silicates, hydroxide compounds and / or Salts, which decompose to the oxides under the firing conditions, are used. 3. Process according to claim 1 or 2, characterized in that the burned-out Mass of a heat treatment at a temperature above the transformation point of the Glass phase undergoes.