Hoechst Aktiengesellschaft

Friedrich Hessel

Andreas Roosen

Katharina Seitz

Gerhard Wegner

Wolfgang Meyer

Helmut Rinno

Christian May

Jurgen Heinrich

Christine Kostler

Cornelia Boberski

Klaus Alberti

Wolfgang Bocker

Gunter Riedel

Hartmut Kruner

Ottmar Rosenfelder

Hans-Michael Guther

Wolfgang Sigmund

Frank Schroder

Katherina Seitz

Christine Koestler

Petra Dotsch

Matthias Steiner

Frank Schroeder

Jurgen Rudolph

Hans-Michael Guether

In the process for producing a homogeneous and finely crystalline silicon nitride ceramic, ceramic powder is milled, mixed with shaping aids, the mixture is shaped into parts and the shaped parts are subsequently sintered in a nitrogen atmosphere. According to the invention, sintering is carried out in a multistage process at temperatures T.sub.max in the range from 1700.degree. to 1900.degree. C. using gas pressures in the range from 0.3 to 50 MPa. In a first temperature stage, a temperature from 0.9 to 0.96.multidot.T.sub.max is maintained over a time period from 10 to 50 minutes at an N.sub.2 pressure from 0.2 to 1.2 MPa, while in a second temperature stage a temperature from 0.97 to 0.985.multidot.T.sub.max is maintained over a time period from 20 to 80 minutes at an N.sub.2 pressure from 3 to 6 MPa. Then the temperature is increased to T.sub.max and the pressure is increased to from 7 to 50 MPa.

Process for producing densely sintered silicon nitride components

A composition of inorganic powders comprises inorganic powder, dispersant and binder. The dispersant and/or binder used is a block copolymer of the units methacrylic acid and alkyl methacrylate in which the alkyl radical can comprise from 1 to 8 carbon atoms. The individual blocks of alkyl methacrylate possess an average molecular weight of at least 4000 and the total block copolymer has an average molecular weight of up to 150,000, in each case expressed as number average (M.sub.n).

Inorganic powder composition containing polymeric auxiliaries and use

A process is disclosed for reducing the microbe count in microbially-contaminated aqueous multi-phase composition containing synthetic resin, such as polymer dispersions and formulations that contain polymeric binders. The process uses dielectric heating, preferably immediately before transfer of the multi-phase composition to containers.

Process for reducing the microbe count in aqueous multi-phase

A water sensitive ceramic powder, in particular aluminum nitride, is provided with a hydrophobic coating. The coated powder is dispersed in water with addition of a binder and a nonionic surfactant from the group comprising ethylene oxide adducts with an HLB value of from 10 to 14. Subsequently the aqueous slip is converted into a free flowing granulated powder. The nonionic surfactant, which is added in an amount sufficient to give a monomolecular layer, makes possible a good dispersion of the hydrophobically coated powder in water.

Process for converting water sensitive ceramic powders into a free

The invention relates to a casting composition comprising a ceramic powder, an organic solvent, binder, plasticizer and a dispersant, which composition is suitable for producing green ceramic sheets by the tape casting process. The dispersant present in the casting composition of the invention is a polyvinyl alcohol/fatty acid ester having a degree of conversion in the range from 50 to 100%. The invention also relates to the use of such a casting composition for producing ceramic green sheets and a process for producing ceramic substrates using a green sheet thus produced.

Casting composition for producing green ceramic sheets containing

A method of processing water-sensitive ceramic powders, particularly carbothermically produced aluminum nitride, whereby the ceramic powder is deagglomerated in a dry milling step with addition of an alkylamine which is liquid at room temperature is disclosed. The alkylamine is added in an amount sufficient to produce a monomolecular layer on the surface of the ceramic powder. The deagglomerated powder subsequently is vigorously stirred with a concentrated aqueous solution or dispersion of binder and rapidly and gently dried, preferably by freeze drying. Aluminum nitride powder prepared by this process can be further processed into shaped parts with a high thermal conductivity.

Process for converting water-sensitive ceramic powders into a

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Mainz, Germany

Friedrich Hessel