Hoechst Ceramtec Aktiengesellschaft

Gisbert Schulze

Helmut Stuhler

Paul Girmscheid, Deceased

To prepare a ceramic molded article based on silicate or based on alumina, a ceramic starting material containing clay, kaolin, steatite and/or alumina is mixed with a silicate-containing flux, the mixture is made into a molded article and the molded article is heated and dense-sintered. At least some of the flux used is composed of a preferably alkali metal-free glass frit whose beginning of softening is above 850.degree. C. Advantageously, an alkali metal-free boron silicate glass is used in amounts of 0.1-20% by weight of the starting mixture. This process makes it possible to prepare, inter alia, ceramic molded articles comprising a glass phase and a crystalline portion substantially containing Al.sub.2 O.sub.3, in which the glass phase content is 22-34% by weight and comprises 50-68% by weight of SiO.sub.2, 12-22% of Al.sub.2 O.sub.3, 0.1-4.5% of Fe.sub.2 O.sub.3, 0.1-13% of TiO.sub.2, 0.1-23% of CaO, 0.1-9% of MgO, 0-7% of Na.sub.2 O, 0-11% of K.sub.2 O, 0-9% of BaO and 0-23% of B.sub.2 O.sub.3 and the crystalline portion comprises 1-25% of SiO.sub.2, 70-80% of Al.sub.2 O.sub.3, 0.1-1% of Fe.sub.2 O.sub.3, 0.1-3% of TiO.sub.2, 0.1-5% of CaO, 0.1-2% of MgO, 0-1.5% of Na.sub.2 O, 0-2.5% of K.sub.2 O, 0-2% of Bao and 0-5% of B.sub.2 O.sub.3.

Process for the preparation of a silicate-bound material

For producing moldings composed of cordierite, a batch, which gives the composition of cordierite and contains clay and/or kaolin as well as soapstone and/or talc and also water and an organic aid, is subjected to shear mixing. For this purpose, the batch is placed between 2 bodies, which are at a small distance and move relative to one another, and at the same time the batch is subjected to a shear stress. Preferably, the batch is filled into the gap formed by 2 almost touching cylindrical shear rollers which rotate at different speeds or run in opposite directions. The batch is then deformed to give a molding, and the molding is fired until the cordierite phase is formed. Cordierite bodies of very low coefficients of thermal expansion (for example at most 1.1.times.10.sup.-6 /.degree.C. in all three spatial directions) can be obtained.

Growing community of inventors

Lauf, Germany

Gisbert Schulze