Bayer Aktiengesellschaft

Toda Kogyo Corporation

Gerhard Franz

Benno Laubach

Ulrike Pitzer

Lothar Schonfelder

Wolfgang Krumbe

Ulrike Wickel

Franz Hund

Jakob Rademachers

Heinrich Heine

Gerd Passing

Ralf Riedel

Werner Fuhr

Hendrik Kathrein

Karl-Heinz Van Bonn

Bernd Holle

Karlheinz Turban

Gunter Petzow

Cobalt coated, needle shaped berthollide iron oxide pigments are disclosed which have a core of the composition (Fe.sub.x.sup.2+, Fe.sub.2.sup.3+)O.sub.3+x wherein 0.3&lt;x&lt;0.75, optionally also including an intermediate coating of Zn-containing benhollide between the core and the cobalt coating. The pigments are prepared by first coating the core with berthollide and a soluble zinc compound, followed by coating with a cobalt compound.

Low coercive iron oxide pigments and a process for their preparation

The process of preparing silicon nitride is improved by reacting silicon-oxygen compounds and a carbon-containing material in an ammonia or ammonia/nitrogen atmosphere at 1300.degree. to 1600.degree. C.

Process for the preparation of silicon nitride

Silicon nitride powder having a total oxygen content of less than 1.8% by weight and an isoelectric point in 0.001M aqueous KNO.sub.3 solution of below pH 4 is prepared by calcining Si.sub.3 N.sub.4 powder having an oxygen content of 0.4% by weight or less in an oxygen containing atmosphere at temperatures between 700.degree. and 1200.degree. C. for 15 to 90 minutes or by grinding such as Si.sub.3 N.sub.4 powder in water, lower alcohol or a water/alcohol mixture for 15 to 120 minutes.

Silicon nitride powders of low isoelectric point and processes for their

The present invention relates to an SiC powder suitable for the production of SiC sintered ceramics with compounds applied to its surface, these compounds being boron nitride and carbon; processes for production of the SiC powders; and the use of these powders to produce SiC sintered mouldings.

SI C powder, a process for its production and its use

Si.sub.3 N.sub.4 powders having a total oxygen content of less than 1.8% by weight with the proportion of surface oxygen content of more than 65% of the total oxygen content, and having a fluorine content of less than 35 ppm are prepared by annealing Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in an oxygen-containing atmosphere at temperatures of 700.degree. C. to 1200.degree. C. for 15 to 90 minutes or by grinding Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in water, alcohol or aqueous alcohol 15 to 120 minutes.

Silicon nitride powders with improved surface properties and processes

Si.sub.3 N.sub.4 powder wherein the total oxygen content of the powder is 0.4% by weight or less is produced by preparing an amorphous Si.sub.3 N.sub.4 intermediate by reacting a Si-containing compound with an N-containing compound and the intermediate is then crystallized wherein 'P', multiplication product of

Silicon nitride powder of low oxygen content

Sinterable Si.sub.3 N.sub.4 powder containing Si.sub.3 N.sub.4 particles and sintering additives wherein Si.sub.3 N.sub.4 particles have an average particle size of less than 1 .mu.m, contain no particle having a diameter greater than 100 .mu.m, have a total content of metallic impurities less than 1000 ppm and an iron content of less than 200 ppm, and wherein the sintering additives are uniformly distributed throughout the powder is prepared by co-grinding pulverulent sintering additive and Si.sub.3 N.sub.4 containing less than 1000 ppm metallic impurities in a spiral jet mill.

Sinterable SI.sub.3 N.sub.4 powders containing sintering additives and a

Carbides, nitrides or carbonitrides of elements from the main groups III and IV and sub-groups III, IV, V and VI of the periodic system of elements are prepared by

Process for the preparation of finely divided carbides and nitrides from

Sinterable Si.sub.3 N.sub.4 powder having an average particle size of less than 1 .mu.m, wherein no individual particle has a diameter greater than 100 .mu.m, the total content of metallic impurities of the powder is less than 1000 ppm and the iron content is less than 200 ppm is produced by grinding agglomerated Si.sub.3 N.sub.4 in a spiral jet mill.

Sinterable Si.sub.3 N.sub.4 powder and a process for its preparation

An improved process for preparation of silicon nitride powder having a low carbon content comprises treating silicon nitride powder with an atmosphere containing chlorine gas at temperatures from 600.degree. to 1050.degree. C. and then with an atmosphere containing gaseous oxygen.

Process for the preparation of silicon nitride low in carbon content

A process for the production of an anisometric yellow-brown zinc ferrite pigment comprising homogeneously mixing zinc oxide having a specific BET surface of more than 2 m.sup.2 /g with needle-shaped .alpha.-FeOOH obtained from an iron salt solution by mixing with alkali and subsequently oxidizing in a nucleation and pigment growth stage, the FeOOH having a specific BET surface of about 15 to 25 m.sup.2 /g, an average needle width of about 0.025 to 0.125 .mu.m and an average needle length of about 0.2 to 0.6 .mu.m, annealing the mixture at a temperature of about 700.degree. to 1000.degree. C., cooling and grinding.

Process for the production of yellow-brown zinc ferrite pigments

In the production of an .alpha.-iron oxide pigment by the hydrothermal treatment of a trivalent iron-containing solution or suspension, the improvement which comprises adding to the solution or suspension prior to the hydrothermal treatment active .alpha.-iron oxide seeds with lamellar or disc-like crystal form and a specific surface of at least 10 m.sup.2 /g, whereby the resulting pigment is lamellar with an Fe.sub.2 O.sub.3 content of at least 88%, an average particle diameter of from 0.5 to 20 .mu.m, an average ratio of diameter to thickness of from 20 to 100, and an almost normally distributed particle size distribution, the relative standard deviation of which, based on the average value of the normal distribution, is less than 0.3. The product has superior coloring properties and is used as a precursor compound for the production of lamellar magnetic pigments with superior magnetic properties.

Lamellar iron oxide pigments, a process for the production thereof and

Synthetic, hexagonal, lamellar iron oxide particles, suitable as corrosion-inhibiting or decorative colored pigments, containing about 0.1 to 12% by weight of at least one oxide of an element of the IVth, Vth or VIth Main and Secondary Groups and of the IInd Secondary Group of the Periodic System of Elements.

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Krefeld, Germany

Gerhard Franz