Showing papers on "Silicon carbide published in 1974"

Dense polycrystalline silicon carbide

Abstract: A dense silicon carbide material having improved electrically conducting properties is disclosed which is prepared by forming a homogeneous dispersion of silicon carbide, a sufficient amount of boron nitride, and optionally a boron containing additive and hot pressing the dispersion at a sufficient temperature and pressure whereby a dense substantially nonporous ceramic is formed. The silicon carbide material can be machined by electrical discharge machining or by electrochemical machining.

Silicon carbide diffusion furnace components

Abstract: Process tube, paddle, and boat for a semi-conductor diffusion furnace composed of a matrix of high purity sintered silicon carbide which is made impervious to gases by impregnation thereof with silicon metal which is 99.9% pure. The process tube, paddle and boat provide the ultra pure environment needed for semi-conductor production and are highly resistant to the degradative effect of a great number of high temperature heating cycles.

Silicon carbide resistance igniter

Abstract: A monolithic ceramic resistance igniter of simple configuration is composed essentially of polycrystalline silicon carbide adapted for use in gas and liquid fuel burning systems. As a result of the combination of its sintered silicon carbide composition, its microstructure, controlled density and large cross-sectional area, the igniter possesses an unusually high degree of physical ruggedness. The igniter will attain a temperature of about 1,000*C in well under 20 seconds drawing a maximum of 6 amps at 132 volts, with a room temperature resistivity of 0.10 to 1.70 ohm centimeters and a resistivity at about 1000*C of from 0.06 to 0.26 ohm centimeter. The igniter also has a physical construction such that a high percentage of its hot surface area radiates directly to the environment.

Metal material for sliding surfaces

Abstract: In a metal material having a surface adapted to slide on a surface having a nickel-silicon carbide composite electroplated layer and subjected to a treatment for causing silicon carbide particles to project outward beyond the surface, the surface of the metal material is provided with porous hard chrome plating, whereby a lubricant may be deposited and retained in the porous plated layer.

Investigation of silicon carbide single crystals doped with scandium

Abstract: Doping processes of silicon carbide crystals with scandium are investigated. It is shown that the scandium solubility in SiC is limited within the 1800 to 2600°C temperature range and amounts to (2 to 3) × 1017 cm−3. On doping silicon carbide crystals with scandium the VLS growth mechanism is possible. The luminescence spectra of the crystals are studied. It is found that nitrogen actively affects the luminescence intensity of silicon carbide doped with scandium. The depth of the radiative recombination centre in SiC (Sc) which is acceptor like is found to be 0.24 eV. [Russian Text Ignored].

Process for preparing layers of silicon carbide on a silicon substrate

Abstract: In a process for producing an epitaxial layer of hexagonal silicon carbide on a silicon monocrystal substrate by simultaneous reduction or thermal decomposition of a gas mixture containing silicon halides and organosilanes, or mixtures thereof, hydrocarbons, and H 2 on said substrate, the improvement consisting of having water or a water-forming compound present in the gas mixture, which leads to especially pure silicon carbide, useful, e.g. as material for light emitting diodes.

Method of fabricating titanium alloy matrix composite materials

Abstract: Fiber-reinforced titanium alloy composite materials and their manufacture are disclosed. Beta-titaium alloy foils are alternated with arrays or silicon carbide coated boron fibers and consolidated at a pressure of at least 22 ksi within the temperature range of 1250°-1275° F.

Method of fabricating silicon carbide articles

Abstract: A method is provided for fabricating silicon carbide articles which comprises hot pressing a homogeneous mixture of carbonaceous particles and silicon carbide powder. The presence of the carbon limits grain growth so that a silicon carbide product having greatly improved physical properties is obtained. The method is suitable for fabricating structural elements, e.g., structural components in the hot sections of air breathing propulsion systems.

The fabrication of ceramic-coated carbon fibre duplex elements

Abstract: Attempts have been made to fabricate a bicomponent composite reinforcing element comprised of a central core of carbon fibre filaments surrounded by a cylindrical silicon carbide sheath. Such fibres are particularly attractive for composite reinforcement since they are potentially capable of exhibiting “duplex” type behaviour, thereby providing a possible means of minimizing anisotropy effects and increasing composite fracture toughness and ductility. Furthermore these elements should provide additional advantages such as eventually enabling multi-filament tows of high strength, low modulus carbon fibre to be formed into large compound fibres which combine high specific strength with a significantly improved overall Young's modulus arising from the stiffness of the ceramic sheath, which should also exhibit a high resistance to chemical attack. Methods of consolidating the multi-filament tow prior to coating have been investigated and suitable preliminary treatments evolved; tows have been coated with silicon carbide using a conventional vapour phase deposition technique to form elements basically conforming to “duplex” requirements. Initial tensile tests upon these elements are reasonably encouraging and reveal none of the side effects encountered previously with boron coatings; it is anticpated that much stronger silicon carbide tubes may be fabricated eventually by this technique using more closely controlled reaction conditions.

Chemical vapor deposition in the systems silicon-carbon and silicon-carbon-nitrogen

Abstract: This report relates to the chemical vapor deposition and morphology of the systems Si + β -SiC, Si + Si 3 N 4 , and Si + β -SiC + Si 3 N 4 , which were produced from the following mixtures at temperatures ranging from 1100 to 1300 °C: SiCl 4 + CCl 4 + H 2 , SiCl 4 + N 2 + H 2 , and SiCl 4 + CCl0 4 + N 2 + H 2 . The solid phases form an unoriented, extremely fine-grained but dense mixture. These solid phases do not reveal any coherent or semicoherent intergrowth. The unoriented growth is a consequence of the permanent carbidization or nitridation of the free silicon surface and covering of the resultant crystals of silicon carbide and/or silicon nitride. At ⩽ 1200 °C Si 3 N 4 becomes amorphous and at ⩾ 1300 °C α-Si 3 N 4 is deposited in addition. In the neighbourhood of 1300 °C β-Si 3 N 4 formation cannot be excluded with certainty. As the CCl 4 concentration in the vapor phase increases, the nitridation is suppressed by the carbidization.

Ceramic electrical resistance igniter

Abstract: A ceramic resistance gas igniter comprised of 10 to 60% by weight of silicon carbide and 40 to 90% by weight of silicon nitride, slicon oxynitride, or silicon aluminum oxynitride, and having a density preferably greater than 95% of the theoretical density of the composite. As a result of the combination of high density and composition, the igniters have moduli of rupture in excess of 80,000 p.s.i., a resistivity range of from 0.1 to 104 ohm centimeters, and superior resistance to corrosive gases.

Coated nuclear fuel particles and process for making the same

Abstract: An improved nuclear fuel particle comprises (a) a generally spherical low density kernel of a fissile element having a void volume of at least 40 percent of the physical volume of the kernel in order to accommodate fission gases generated during the use of the fuel particle, (b) the kernel is coated over its entire surface with an extremely thin carbon buffer layer to provide for fission recoil, and (c) thin pyrolytic carbon, (d) silicon carbide and (e) outer pyrolytic carbon layers are superimposed thereon to hermetically seal the kernel to prevent escape of generated fission gases, the pyrolytic carbon and silicon carbide layers being of sufficient strength to resist rupture of the pressure of the contained fission gases even at high reactor temperatures of the order of 1000° C-1300° C and a burn up of 50 percent or more FIMA. Such particles can be embedded in graphitic bodies to provide fuel elements having a greatly increased fuel loading per unit volume of particle and fuel element. Processes for producing such improved fuel particles are also disclosed.

Strength and Microstructure of Dense, Hot-Pressed Silicon Carbide

Abstract: The microstructural and strength characteristics of dense SiC, hot-pressed from submicron SiC powders with small additions of boron, are shown to be strongly dependent on the control exercised over oxygen content during pressing. Uniform, equiaxed grain structures of SiC are obtained if sufficient oxygen is present to allow detectable particles of SiO2, whereas uniform, elongated grain structures of β SiC are obtained if excess carbon is utilized to reduce oxygen content to undetectable limits. At intermediate oxygen levels, free silicon was formed and large, tabular α-SiC grains in a fine-grained β-SiC matrix were obtained.

Method of improving impact resistance of ceramic bodies, and improved bodies

Abstract: A method of improving the impact resistance of bodies of polycrystalline ceramic such as alumina, silicon nitride and silicon carbide, and bodies produced by the method. The body is provided with a layer of a low elastic modulus polycrystalline ceramic material which has microcracks therein, formed by such factors as thermalexpansion coefficient anisotropy, differences in thermalexpansion coefficients between phases of the material, and by changes in volume during phase transformations in the material. The layer can be applied by preforming the layer and then applying, or by hot pressing the material of the layer onto the body.

Methods of treating silicious materials to form silicon carbide for use in refining ferrous material

Abstract: A method is provided for treating oxygen bearing silicious materials, particularly those containing ferrous metal to produce silicon carbide and metallic iron comprising the steps of mixing a silicious material with at least a stoichiometric amount of carbon to combine with the oxygen bearing silicon compounds in the material to form silicon carbide and to reduce the oxygen compounds of iron to the metallic state, heating the mixture in a non-oxidizing atmosphere to a temperature in excess of 2500*F., holding the temperature until there is no further reaction between silicon and carbon, comminuting the resulting product to free any metallic iron formed, separating the metallic iron magnetically and collecting the non-magnetic residue as silicon carbide.

Manufacture of lead dioxide/titanium composite electrodes

Abstract: A method of producing lead dioxide/titanium composite electrodes by anodic deposition of lead dioxide on a titanium surface, in which an intermediate layer of a carbide or boride of an element of sub-group 4 or 5 and/or silicide of an element of sub-group 4, 5 or 6 of the periodic table of the elements and/or silicon carbide, is applied to the titanium surface before depositing the lead dioxide.

Semiconductor indicating instrument

Abstract: A semiconductor indicating instrument or display device employing a silicon carbide crystal having a first ohmic contact with an n-type region and at least one second ohmic contact with a p-type region. Another region is disposed between the regions of opposite types of conductivity. The silicon carbide crystal also has an additional region with structure defects which are clusters with a concentration of 10 19 cm - 3 to 10 22 cm - 3 , that region adjoining the second ohmic contact and having a thickness greater than that of the p-type region by at least 0.05 mu.

Electrically conducting material containing silicon carbide in a matrix of silicon nitride

Abstract: An electrically conducting material is produced by nitriding a mixture of silicon and a component capable of being converted to an electrically conducting phase under the conditions of the nitriding, thereby to produce a material comprising silicon nitride and the electrically conducting phase. The material produced has a low resistivity, which is retained over a wide temperature range.

Method and apparatus for making elongated Si and SiC structures

Abstract: Method for making elongated structures such as furnace tubes having at least one flat side from vapor deposited silicon or silicon carbide using a graphite mandrel having a plurality of elongated edge-mated elements held in place by end collars to which an electrical power source is connected. Rectangular tubes can be sawed apart to produce flat plates if desired.

Apparatus for making abrasive articles

Abstract: Depositing abrasive particles, such as diamonds, silicon carbide, titanium carbide, aluminum oxide, or mixtures thereof, in a matrix of electrochemically deposited metals on the outer periphery and/or the adjacent marginal side portions of metal (or non-metals) blanks or wheels.

Method for producing a semi-conductor body

Abstract: A method for producing a semi-conductor body is disclosed. The batch for the body is silicon carbide and reactive alumina. The batch is first dry ball milled with from 1/2 to 2% fatty acid and pressed into a shape. The shape is then fired either in air below 2300°F. or in an inert gas atmosphere to a temperature from about 2000° to 3000°F., and for a time sufficiently long to produce a semi-conductor body having a specified apparent porosity. An impregnation step is also disclosed to achieve the specified apparent porosity.

Cylindrical Erbium Oxide Radiator Structures for Thermophotovoltaic Generators.

Abstract: : Results of an experimental investigation are reported which cover the fabrication and evaluation of slip-casted and hot pressed erbium oxide cylinders and silicon carbide structures coated with erbium oxide. Suitable erbium oxide cylindrical structures will be used as radiating mantles in thermophotovoltaic converter systems. The pure erbium oxide cylindrical mantles were found to be deficient in thermal shock resistance which resulted in cracking of the mantles and extremely low thermal cycle life. The erbium oxide coated silicon carbide structures provided satisfactory thermal cycling capability up to 1500C but their spectral emission showed a large content of background radiation which manifested itself in an increased amount of undesirable interband emission. Higher optical density of the erbium oxide coating, to provide reduction of unwanted background radiation, is necessary to make these structures of practical use.