Elektroschmelzwerk Kempten Gmbh

Electroschmelzwerk Kempten Gmbh

Alfred Lipp

Klaus Reinmuth

Klaus Hunold

Karl A Schwetz

Jochen Kriegesmann

Peter Arnold

Eckhart Bechler

Heinrich Knoch

Detlef Steinmann

Detlef Von Struensee

Johannes Napholcz

Hubert Thaler

Karl-Alexander Schwetz

Gunter Wiebke

Dietrich Lange

Alfred Graf Von Matuschka

Helmut Kunst

Karlheinz G Schmitt-Thomas

Peter Sindlhauser

Max Mohr

George Vogt

Wolfgang Grellner

Walter Fichtl

Georg Bachmann

Pressure-sintered polycrystalline mixed materials, with a base of boron nitride, oxides and carbides, are provided in which the hexagonal boron nitride fraction is about 30 to about 85% by weight, the oxide fraction (ZrO.sub.2, MgO) is about 10 to about 50% by weight, and the carbide fraction (SiC, TiC, ZrC) is about 5 to about 20% by weight. These mixed materials have a density of at least 94% of the theoretical density and can be produced by hot-pressing powder mixtures composed of hexagonal boron nitride, the selected oxides and carbides at temperatures in the range of from 1500.degree. C. to 1800.degree. C. under a die pressure of 7 to 20 MPa or by isostatically hot-pressing, in a vacuum tight closed case, at temperatures in the range from about 1400.degree. C. to about 1700.degree. C. under a pressure of about 100 to about 300 MPa in a high-pressure autoclave using an inert gas as the pressure transfer medium. These mixed materials are resistant to liquid metals, wear resistant and thermal shock resistant and, owing to these properties, are suitable for use as detachment or break rings in the horizontal continuous casting of steel and non-ferrous metals.

Pressure-sintered polycpystalline mixed materials with a base of

The invention relates to polycrystalline sintered articles comprising at least 50% by weight of crystalline silicon nitride phase of which at least 90% by weight is in the .beta.-form, and at least one secondary crystalline intergranular silicate phase, and having a density of at least 99% of the theoretically possible density, a modulus of elasticity at room temperature of less than 300 kN/mm.sup.2, a short-term bending strength at room temperatue, measured according to the 4-point method, of at least 600 N/mm.sup.2 which, up to 1200.degree. C., decreases by less than 50%, and a long-term bending strength, measured according to the 4-point method, which is characterized by a numerical value of more than 40 at 1200.degree. C. for the crack growth resistance parameter n. These polycrystalline sintered articles are manufactured, by sintering with or without the use of pressure, a mixture of silicon nitride powder, crystalline silicates of natural or synthetic origin having melting points in the range of from 1350.degree. C. to 1950.degree. C. as sintering additives and metal carbides having melting points at least from 1500.degree. C. as nucleus formers.

Polycrystalline sintered articles based on silicon nitride and sintering

The invention is a molded body of polycrystalline aluminum nitride having a density of at least 99.8% TD and comprising:

Dense molded bodies of polycrystalline aluminum nitride and process for

Polycrystalline sintered bodies are provided consisting of at least 66% by weight of a crystalline Si.sub.3 N.sub.4 phase, of which at least 90% by weight is in the beta-modification, and of up to 34% by weight of secondary intergranular grain boundary phases of oxide, carbide and/or nitride. At least 25% by weight of the secondary grain boundary phases consists of a quasi-ternary crystalline compound in the E.sub.1 --E.sub.2 --E.sub.3 triangle of the Ga.sub.2 O.sub.3 --La.sub.2 O.sub.3 -Al.sub.2 O.sub.3 ternary system called 'Gala', the 'Gala' compound being prepared from gallium oxide, lanthanum oxide and aluminum oxide prior to producing the sintered bodies. The polycrystalline sintered bodies are produced by sintering with and without application of pressure from silicon nitride powders having a portion of impurities not exceeding 4.0% by weight, sintering additives of oxides and optionally other refractory admixtures of carbides and/or nitrides. Powders of a quasi-ternary crystalline compound (Gala compound) are employed as at least one sintering additive prepared, prior to mixing with the remaining components and to sintering, from gallium oxide, lanthanum oxide and aluminum oxide by heating to temperatures from 1500.degree. C. to 1850.degree. C. When using at least 70% by weight of silicon nitride powder, there can be used up to 30% by weight of a crystalline 'Gala' compound alone or mixed with other admixtures of oxides, carbides or nitrides, but altogether at least 1% by weight of a crystalline 'Gala' compound must be present. The sintered bodies are especially tough and very hard and can be used for the machining of iron materials at high cutting speeds.

Polycrystalline sintered bodies on a base of silicon nitride with high

The invention is an improved theroelement which comprises a graphite/boron carbide thermocouple, the arms of which are constructed as a tube and a rod, arranged concentrically inside the tube, which are electrically connected at one end. One of the arms of the thermocouple consists essentially of boron carbide formed from self bonding boron carbide by pressureless sintering. Prefabricated sleeves of high-purity, boron-oxide-free hexagonal boron nitride are used between the arms of the thermocouple as spacers. Only the end of the arm of the thermocouple constructed as a rod is secured in an electrically conductive connecting piece and the arm is freely mobile in the direction towards the cold junction. As the material for the arm of the thermocouple constructed as a rod, there can be used, for example, boron carbide having a coarse-grained structure and a density of from 60 to 80% TD, which has been manufactured from boron carbide powder having bimodal particle size distribution by means of extrusion, followed by pressureless sintering at from 2000.degree. to 2250.degree. C. The thermoelement can also be manufactured in one operation by means of pressureless sintering of the boron carbide powder in situ. Such a thermoelement comprises, for example, a flexible graphite cord for the arm of the thermocouple constructed as a rod, a boron-nitride envelope and a boron-carbide casing, the envelope and casing having been formed from powders sintered in situ without pressure.

Thermoelement comprising a graphite/boron carbide thermocouple

The invention is a process for the manufacture of shaped articles of reaction-bonded silicon nitride in which pre-shaped articles of silicon powder are heated in a first stage under a nitrogen gas pressure of at least 6 MPa at a heating rate of not more than 50.degree. C. per hour to a reaction temperature below the melting point of silicon, the article is maintained at the reaction temperature for at least 0.5 hours and subsequently, in a second stage, heating the article at a heating rate of at least 500.degree. C. per hour to a temperature above the melting point of silicon and maintaining the article at that temperature for from 1 to 7 hours. The process can nitridate both pre-shaped articles consisting of silicon powder and, optionally, up to 15% by weight Si.sub.3 N.sub.4 powder and those containing up to 10% by weight of a sintering aid such as Y.sub.2 O.sub.3. In the former case, porous shaped articles having a density of from 87 to 91% TD and, in the latter case, dense shaped articles having a density of more than 98% TD, are obtained. In all cases, in a total nitridation time of less than 15 hours, a conversion of at least 95% of the silicon originally present into silicon nitride is achieved, which, in the finished shaped article, is substantially in the .beta.-modification.

Process for the manufacture of shaped articles from reaction-bonded

The invention is a ceramically-bonded large-area neutron absorber articles of low density having a space filling of

Ceramic bonded neutron absorber plates of boron carbide and free carbon

The invention is a polycrystalline sintered body based on lanthanum hexaboride and having a density of at least 95% of the theoretical density. The sintered body comprises lanthanum hexaboride, boron carbide and amorphous carbon, the content of B.sub.4 C+C being from 0.1 to 10% by weight and the total amount of La+B+C being at least 99.0% by weight, in each case calculated on the total weight. The sintered bodies have a homogeneous microstructure with mean grain sizes&lt;10 .mu.m, in which, in addition to the crystalline lanthanum hexaboride phase, boron carbide and carbon are detectable as separate, finely divided phases. The sintered bodies can be manufactured by pressureless sintering at temperatures of from 2150.degree. to 2200.degree. C. from powder mixtures comprising lanthanum hexaboride and, in addition, mixtures of a carbon-containing material and a boron component.

Polycrystalline sintered bodies based on lanthanum hexaboride, and a

The invention is a shaped article of boron nitride having a density of at least 95% of the theoretical density which consists of polycrystalline hexagonal boron nitride in the form of a homogeneous isotropic microstructure and which has been manufactured from pure boron nitride powder without the concomitant use of sintering aids by isostatic hot-pressing in a vacuum-tight casing at temperatures of from about 1200.degree. to 1500.degree. C. under a pressure of from about 50 to 300 MPa. Boron nitride powders having a free boric oxide content of not more than 1.0% by weight and having a specific surface area of from 5 to 30 m.sup.2 /g are used as starting material. The powders either are filled into prefabricated casings consisting of steel or glass and densified by vibration or are preshaped to form green bodies having pores open to the surface and then placed in prefabricated casings or coated with a material which forms a vacuum-tight casing. The powders or the preshaped green bodies in the vacuum-tight casings are then subjected to an isostatic hot-pressing process in a high-pressure zone using an inert gas such as argon or nitrogen, as the pressure-transfer medium.

Dense shaped articles consisting of polycrystalline hexagonal 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 is substantially pore-free shaped articles consisting essentially of polycrystalline silicon nitride and polycrystalline silicon carbide in the form of a homogeneous microstructure having grain sizes of not more than 10 .mu.m manufactured from mixtures of Si.sub.3 N.sub.4 powder and SiC powder in a weight ratio of from 5:95 to 95:5 without the concomitant use of sintering aids by isostatic hot pressing in a vacuum-sealed casing at temperatures of from 1800.degree. to 2200.degree. C. and a pressure of from 100 to 400 MPa.

Substantially pore-free shaped articles of polycrystalline silicon

The invention is refractory, electrically conductive, mixed materials based on hexagonal boron nitride and at least one electrically conductive component such as titanium boride and zirconium boride, and having a density of at least about 95% of the theoretical density and nondirection-dependent properties, which have been manufactured from powder mixtures that are practically free of oxygen and metal and comprise

Refractory, electrically conductive, mixed materials containing boron

The invention relates to dense shaped articles of polycrystalline .alpha.-silicon carbide containing from 0.1 to 0.4%, by weight, of aluminum and optionally, a small amount of nitrogen and/or phosphorus, having a homogeneous virtually single-phase microstructure. The additional constituents are substantially in the form of a solid solution in the .alpha.-SiC lattice. The shaped articles are distinguished by flexural strength of at least 600 N/mm.sup.2 up to 1450.degree. C. and low subcritical crack propagation under mechanical stress. The fracture mechanism is trans granular up to at least 1450.degree. C. The shaped articles are manufactured by simultaneously shaping and hot pressing pulverulent .alpha.-silicon carbide containing a small amount of an aluminum-containing additive, such as aluminum powder, aluminum nitride and/or aluminum phosphide, at temperatures between 1850.degree. C. and 2300.degree. C. under a pressure of at least 100 bar (10 MPa).

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Bad Worishofen, Germany

Alfred Lipp