Elektroschmelzwerk Kempten Gmbh

Wacker-chemie Gmbh

Ceradyne, Inc.

Electroschmelzwerk Kempten Gmbh

Elektroschmelzwerk Kempton, Gmbh

Karl A Schwetz

Alfred Lipp

Klaus Reinmuth

Klaus Hunold

Hubert Thaler

Biljana Mikijelj

Georg P Victor

Armin Kayser

Jochen Kriegesmann

Jochen Greim

Dietrich Lange

Peter Matje

Michael Fundus

Eckhart Bechler

Heinrich Knoch

Georg Vogt

Anton Katheininger

Franz Isemann

Karlheinz G Schmitt-Thomas

George Vogt

This disclosure describes sintered bodies comprising about 90 wt % to about 99 wt % of boron carbide, having a B:C atomic ratio ranging from 3.8 to 4.5:1; 0 to 1 wt % free carbon; 0 to 1 wt % BN or AlN, remainder an oxide binder phase; said sintered body having a uniform microstructure composed of substantially equiaxed grains of said boron carbide; the oxide binder phase comprising at least a rare earth aluminate and optionally AlOor other ternary or binary phases of rare earth oxide-alumina systems; the binder phase being present in form of pockets at the multiple grain junctions and the density of no more than 2.6 g/cm. Also described is a manufacturing process for the above described substantially pore-free, sintered boron carbide materials with high strength and fracture toughness, which can be used for production of large-area parts. This is achieved by liquid phase low temperature-low pressure hot pressing of boron carbide in an argon atmosphere.

Lightweight boron carbide materials with improved mechanical properties and process for their manufacture

Shaped body based on polycrystalline SiC and having a density of greater than 90% of its theoretical density and an adherent graphite layer on its surface, wherein the graphite layer is crystalline, has a thickness of 0.1-100 &mgr;m and has been produced by thermal surface decomposition of the SiC after it has been sintered to closed porosity.

Graphite-coated shaped body made of sintered silicon carbide

The invention relates to bearing materials of porous SiC having a trimodal pore composition and also a process for their production. The porous bearing material of pressureless-sintered SiC having from 3 to 10% by volume of independent closed pores having a trimodal pore composition consisting of micropores (M), fiber-shaped macropores (F) and spherical macropores (S), where the amounts in the pore system F-M-S (FIG. 1) are fixed by the trapezoidal area having the corner points

Bearing material of porous SIC having a trimodal pore composition

The invention relates to a process for producing green compacts by the slip-casting process, injection-molding process or extrusion process from sinterable mixtures based on a starting powder mixture containing silicon nitride, and, if appropriate, aluminum nitride and/or alumina and other oxides as sinter aids. The dispersant and binder used is a magnesium chloride hydrate as a mixture with magnesium oxide and water and, after molding, the mixtures are hardened at temperatures from 30.degree. to 60.degree. C. In addition, ceramic fibers, such as silicon carbide, can also be processed as fillers. The green compacts thus produced are sufficiently stable, so that they can be worked mechanically.

Process for producing green compacts by molding sinterable ceramic

The invention is a process for the manufacture of sinterable silicon carbide and/or boron carbide powders having a maximum particle size of 1 .mu.m and finer. The process is carried out by wet grinding in aqueous suspension using mills charged with a grinding medium and with the addition of antioxidants in the presence of surfactants and subsequent wet chemical treatment with an aqueous potassium hydroxide solution. The wet grinding can be carried out, for example, with the addition of hydroquinone in the presence of quaternary ammonium salts and the wet chemical treatment with a 5-50% by weight aqueous potassium hydroxide solution under normal pressure at temperatures in the range of from room temperature to the boiling temperature of the reaction mixture or under elevated pressure at temperatures of up to 300.degree. C.

Process for the manufacture of sinterable silicon carbide and/or boron

The invention relates to polycrystalline sintered compact based on europium hexaboride having a density of at least 85% of the theoretical density. The compacts comprise EuB.sub.6, from about 0.1 to 10% by weight of B.sub.4 C and, optionally, amorphous carbon, and have a total of Eu+B+C of at least 98.5% by weight. They have a homogeneous microstructure with mean grain sizes of less than 20 .mu.m, in which, in addition to the crystalline phase EuB.sub.6-x C.sub.x, in which x has values of from 0 to 0.25, B.sub.4 C can be detected as a separate, finely divided, crystalline phase. The sintered compacts can be manufactured from powder mixtures comprising europium hexaboride of stoichiometric composition and additions of boron carbide and/or mixtures of a carbon-containing material and a boron component by means of hot pressing in graphite moulds, by means of isostatic hot pressing in casings that can be sealed so that they are gas-impermeable, or by means of pressureless sintering.

Polycrystalline sintered compacts based on europium hexaboride and

The invention is substantially pore-free shaped articles which consist essentially of polycrystalline .alpha.- or .beta.-silicon carbide in the form of a single-phase homogeneous microstructure having grain sizes not exceeding 8 .mu.m, and which are manufactured from SiC powder, without the concomitant use of sintering aides, by isostatic hot-pressing in a vacuum-tight casing at temperatures of from about 1900.degree. C. to 2300.degree. C. and at pressures of from about 100 to 400 MPa. The SiC starting materials have .alpha.- and/or .beta.-SiC powders having a total content of metallic impurities not exceeding 0.1% by weight and a particle size of 4 .mu.m and finer.

Shaped polycrystalline silicon carbide articles and isostatic

The invention provides substantially pore-free sintered polycrystalline articles comprising .alpha.-silicon carbide, boron carbide and free carbon, the quantitative proportions of which, in percent by weight, are defined by the trapezoidal area having, in the ternary system B/Si/C of FIG. 1 the corner points

Substantially pore-free sintered polycrystalline articles of

There are provided shaped articles of polycrystalline silicon carbide having densities of at least 97% and improved mechanical properties particularly at high temperatures, said articles consisting of

Dense sintered shaped articles of polycrystalline .alpha.-silicon

A method of producing dense shaped articles of pure boron carbide that optionally contain 0.1 to 8% by weight of free carbon in the form of graphite is disclosed involving the steps of homogeneously mixing boron carbide in submicron powder form with small quantities of a carbon containing additive, forming the powder mixture into a shaped green body and then sintering the body in a controlled atmosphere and in the absence of external pressure at a temperature of about 2100.degree.-2200.degree. C. The shaped articles thus obtained are polycrystalline and, insofar as they correspond to the stoichiometric composition B.sub.4 C, single-phase; they have an average grain size of not more than 10 .mu.m, a density of at least 90% of the theoretical density of boron carbide and a flexural strength of at least 300 N/mm.sup.2. The fracture mode of the sintered articles is completely transcrystalline.

Process for the production of dense sintered shaped articles of

A process for the production of oxygen free copper castings and moldings, which contain 0.05 to 0.2% by weight of boron as micro-alloy element, by deoxidation of oxygen containing copper melts by means of calcium hexaboride, comprising introducing 0.3-1% by weight of a CaB.sub.6 into the copper melt, the CaB.sub.6 containing at least 3% C calculated on the weight of the CaB.sub.6, subsequently subjecting the cooled melt, if desired while molding the same, to a solution annealing operation and following up with a storage for an extended time.

Process for the production of oxygen-free copper casting and moldings

Process for the manufacture of hexagonal boron nitride which comprises causing a starting material containing an alkali metal boride or an alkaline earth metal boride, preferably a hexa- or dodecaboride, to react with nitrogen at temperatures of at least 900.degree. C and, if desired, up to 2500.degree. C, in the presence of impurities or additives of other boron compounds or compounds of the alkaline earth metals or of carbon compounds. Boron nitride has many uses in various fields, among them, electronics and crucible melting for most non-metallic melts.

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Sulzberg, Germany

Karl A Schwetz