Degussa Aktiengesellschaft

Dieter Binder

Peter K Kleinschmit

Klaus Zetzmann

Gerhard Birtigh

Hans Hoffmeister

Roland Reuter

Thermally split zirconium silicate is produced such that the crystalline zirconium dioxide embedded in an amorphous silica phase exhibits an average grain or particle size (d.sub.50 value) in a range of 0.5 .mu.m to 3.0 .mu.m and a specific surface (BET) in a range of 3 to 15 m.sup.2 /g. The zirconium dioxide produced by this method is particularly suited for the production of zirconium silicate pigments with improved color characteristics. The thermally split zirconium silicate is also particularly well suited for processes used in the obtention of zirconium dioxide. The method of producing the thermally split zirconium silicate includes melting zirconium silicate in an induction melting furnace and cooling off a free falling stream of melt by blowing on it with a gas and/or spraying it with water.

Thermally split zirconium silicate, method of its production and use

A method is disclosed for the semi-continuous melting of ceramic material by means of inductive melting in high-frequency and medium-frequency induction melting furnaces whose melting coil surrounds a sintering crust crucible and contains a run-out channel. In the method, melt is periodically run out and material to be melted is supplied to the crucible so as to replace the material removed preferably so as to maintain a constant level. An intensively cooled channel is used as a run-out device. For the melt broaching, the melt nose is grasped from below by way of an automatically controllable broaching lance of a broaching device and raised. The broaching lance is then advanced between the bottom of the channel and the solidified melt until the sintering crust is pierced. The method permits a reliable and economic management of the process and the maintenance of the quality of the melted products. A device for periodic melt broaching as well as an induction melting furnace equipped with an intensively coolable run-out channel provides apparatus for carrying out the above method.

Method and apparatus for the semi-continuous melting and discharging of

A method is disclosed for the semi-continuous melting of ceramic material by means of inductive melting in high-frequency and medium-frequency induction melting furnaces whose melting coil surrounds a sintering crust crucible and contains a run-out channel. In tile method, melt is periodically run out and material to be melted is supplied to the crucible so as to replace the material removed preferably so as to maintain a constant level. An intensively cooled channel is used as a run-out device. For the melt broaching, the melt nose is grasped from below by way of an automatically controllable broaching lance of a broaching device and raised. The broaching lance is then advanced between the bottom of the channel and the solidified melt until the sintering crust is pierced. The method permits a reliable and economic management of the process and the maintenance of the quality of the melted products. A device for periodic melt broaching as well as an induction melting furnace equipped with an intensively coolable run-out channel provides apparatus for carrying out the above method.

Thermally split zirconium silicate is produced such that the crystalline zirconium dioxide embedded in an amorphous silica phase exhibits an average grain or particle size (d.sub.50 value) in a range of 0.5 .mu.m to 3.0 .mu.m and a specific surface area (BET) in a range of 3 to 15 m.sup.2 /g when the silica is removed by leaching. The zirconium dioxide produced by this method is particularly suited for the production of zirconium silicate pigments with improved color characteristics. The thermally split zirconium silicate is also particularly well suited for processes used in the obtention of zirconium dioxide. The method of producing the thermally split zirconium silicate includes melting zirconium silicate in an induction melting furnace and cooling off a free falling stream of melt by blowing on it with a gas and/or spraying it with water.

A monoclinic zirconium dioxide with an SiO.sub.2 content below 1.0% by weight is provided which is characterized by dendrite-shaped particles with an average grain size (d.sub.50 value) in a range of 0.5 .mu.m to 3.0 .mu.m and a specific surface (BET) in a range of 3 to 15 m.sup.2 /g. This zirconium dioxide is produced by thermally splitting zirconium silicate in a high-frequency- or medium-frequency induction melting furnace with sintering crust crucible, quenching the melt by blowing on a stream of melt with air and/or spraying it with water and leaching out the thermally split zirconium silicate with concentrated alkali lye at 100.degree. 200.degree. C. The zirconium dioxide of the invention provides a material with improved suitability for the production of zirconium silicate pigments of the host lattice type and inclusion type so as to provide for more color-intensive pigments.

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Alzenau, Germany

Dieter Binder