Showing papers on "Silicon carbide published in 1972"

Silicon carbide coated graphite members and process for producing the same

Abstract: A preferred process for producing coated isotropic graphite members comprises: A. HEAT TREATING THE ISOTROPIC GRAPHITE MEMBER TO A TEMPERATURE FROM ABOUT 1700*C to 2400*C in a halogen atmosphere comprising chlorine or fluorine to reduce the impurity ash content to the range of the order to 2 to 10 ppm, B. MACHINING THE HEAT TREATED ISOTROPIC GRAPHITE MEMBER TO A PREDETERMINED SHAPE AND SURFACE CONDITION, C. ULTRASONICALLY CLEANING THE MACHINED GRAPHITE BODY IN A LIQUID CLEANING FLUID TO REMOVE LOOSE SURFACE PARTICLES, D. DEPOSITING A LAYER OF SILICON ON THE CLEAN GRAPHITE BODY BY A GAS PHASE REACTION AT A TEMPERATURE ABOVE 1000*C but below the melting point of silicon, E. HEATING THE GRAPHITE MEMBER WITH THE APPLIED LAYER OF SILICON TO A TEMPERATURE TO CAUSE THE SILICON TO MELT AND PENETRATE THE PORES OF THE GRAPHITE AND CAUSE THE SILICON TO REACT COMPLETELY IN SITU WITH THE GRAPHITE TO FORM A LAYER OF SILICON CARBIDE PENETRATING TO A DEPTH OF AT LEAST ABOUT 5 MILS, AND F. DEPOSITING BY A GAS PHASE REACTION A SEALING LAYER OF SILICON CARBIDE OVER THE UNDERLYING, PREVIOUSLY REACTED SILICON CARBIDE LAYER.

Field Emission from Carbon Fibres: A New Electron Source

Abstract: IN certain electron beam devices, field electron emitting sources possess distinct advantages over thermionic emitters1. Much effort has been expended to exploit these advantages in instruments such as scanning electron microscopes2, microwave amplifiers1,3, and X-ray generators1,4. The preferred emitter material in nearly all these devices has been tungsten, which operates only under ultra high vacuum conditions; it is primarily for this reason that field electron emitters have not been widely adopted commercially. Consequently attempts have been made to find materials which will operate in the region 10−6 to 10−8 torr5–7. As field electron emitters silicon carbide “whiskers” were less sensitive to vacuum conditions than tungsten8, but a number of practical difficulties—the material varied considerably from sample to sample, it was not easy to make a reliable ohmic contact to the crystal and the etching technique (similar to that of Smith9) was somewhat variable in its results—made reproducible operation difficult.

Low‐Temperature Solid‐State Phase Transformations in 2H Silicon Carbide

Abstract: Study of the phase transformations taking place in 2H SiC single crystals at temperatures as low as 400 C. Some crystals transformed to a structure with one-dimensional disorder along the crystal c axis. Others transformed to a faulted cubic/6H structure. The transformation is time and temperature dependent, and is greatly enhanced by dislocations. The transformation takes place by means of a slip process perpendicular to the c axis. Cubic SiC crystals were observed to undergo a solid-state transformation above 1400 C.

Hot pressed silicon carbide

Abstract: A dense silicon carbide having improved properties is disclosed which is prepared by the addition of a carbonaceous additive to a boron doped silicon carbide and hot pressing the mixture at a sufficient temperature and pressure whereby a dense substantially nonporous ceramic is formed.

Growth mechanism of polycrystalline β‐SiC layers on silicon substrate

Abstract: The surface of monocrystalline silicon was chemically converted with hydrocarbon to polycrystalline β‐silicon carbide, and the growth mechanism was investigated by means of 14C tracer method. It is shown that the growth of the silicon carbide layer is due to diffusion of silicon through the SiC layer so that the Si–SiC conversion is taking place at the surface of the sample. Dependence of layer thickness on carbidizing time and on hydrocarbon concentration in the carrier gas hydrogen was measured.

Defects in silicon carbide

Abstract: Defects in various forms of SiC, both single crystal and polycrystalline, have been examined using transmission electron microscopy. Dislocations were not as common as stacking faults, which were observed in all materials examined. The mechanism of formation of stacking faults is discussed and two types of both intrinsic and extrinsic faults are shown possible. The stacking-fault energy of SiC was measured to be 1.9 ergs/cm2 by the extended node method.

Dense composite ceramic bodies and method for their production

Abstract: Hard, dense composite ceramic bodies of titanium diboride, boron carbide, silicon carbide and silicon, having a wide variety of utilities, are produced by forming a mixture of titanium diboride, boron carbide and a temporary binder into a desired shape to obtain a coherent green body which is siliconized by heating it in contact with silicon to a temperature above the melting point of silicon, whereupon the molten silicon infiltrates the body and reacts with some of the boron carbide therein to produce silicon carbide in situ.

Sintered silicon carbide

Abstract: A DENSE SILICON CARBIDE PRODUCT IS DESCRIBED. THE PRODUCT HAS A FLEXURAL STRENGTH ABOVE 100,000 P.S.I. AT ROOM TEMPERATURE, ABOVE 80,000 P.S.I. AT 1200*C., ABOVE 60,000 P.S.I. AT 1375*C. AND ABOVE 45,000 P.S.I AT 1500*C. THE PRODUCT HAS A GRAIN SIZE OF LESS THAN 5 MICRONS AND ESENTIALLY ALL OF THE SILICON CARBIDE IS IN THE ALPHA FORM. THE PRODUCT HAS A DENSITY IN EXCESS OF 99% OF THEORETICAL DENSITY AND CONTAINS ABOUT .5% TO 5% ALUMINUM. A PREFERRED PROCESS FOR PREPARING THE PRODUCT IS ALSO DESCRIBED.

Silicon carbide junction thermistor

Abstract: A high impedance, junction thermistor for sensing temperatures from about -200*C. to above 1,400*C. is provided with a semiconductor body of silicon carbide. The silicon carbide semiconductor body has at least first and second impurity regions forming a PN junction therebetween. The temperature is sensed by the impedance response across the PN junction.

Injection of a ceramic into a mould

Abstract: A method of producing an injection moulded silicon carbide article comprises charging a chamber with a mix of alpha silicon carbide, graphite and a binder thereof, injecting the mix from the chamber into a mould, removing the mix from the mould, reheating the moulded mix so as to remove the binder and finally heating the finished moulded mix in a vacuum or inert atmosphere in the presence of molten silicon so as to absorb the silicon which reacts with the graphite to form beta silicon carbide and so obtain final densification of the finished moulded article.

Acicular silicon carbide dispersion in pyrolytic graphite matrix for use in biomedical implants

Abstract: Prosthetic devices for implanting into a living body composed of a composite of a pyrolytic graphite matrix containing codeposited silicon carbide. The pyrolytic graphite matrix comprises crystallite layers of pyrolytic graphite while the silicon carbide is in the form of crystalline aciculae. The silicon carbide aciculae are embedded within the pyrolytic graphite crystallites and oriented so that the longitudinal axes are substantially aligned with the c-direction of the crystallites. The composites of the implant may have a plurality of pores on the surface. These pores can serve as sites for tissue and bone growth, thus improving the attachment of the implant.

Silicon carbide surfaced filaments with titanium carbide coating

Abstract: A composite filament suitable for use as a reinforcement in titanium or nickel matrices comprises a filamentary substrate having a silicon carbide surface layer and a thin, adherent outer layer consisting essentially of titanium carbide.

Dense silicon carbide ceramic and method of making same

Abstract: A dense silicon carbide ceramic is disclosed which is composed of a silicon carbide matrix filled with a boron carbide-silicon carbide composition. The silicon carbide ceramic is prepared by performing a porous silicon carbide body, infiltrating the pores of the body with a boron carbide-silicon carbide melt at a sufficient temperature, and directionally cooling the filled body to advance the solidification front through the body whereby a dense substantially nonporous ceramic is formed.

Method of manufacturing silicon carbide crystals

Abstract: A method of manufacturing silicon carbide crystals in which a core of silicon dioxide is embedded in a mass of granular silicon carbide, or materials which form silicon carbide on heating this mass being heated to a temperature at which silicon dioxide volatilizes, i.e. above about 1500°C, and the silicon carbide coheres. This leaves a cavity, formerly occupied by the silicon dioxide which is surrounded by silicon carbide. Heating is then continued at a temperature, above about 2500°C, at which silicon carbide crystals are formed on the walls of the cavity.

Thermal expansion at elevated temperatures III. A hemispherical laminar composite of pyrolytic graphite, silicon carbide and its constituents between 300 and 800 K

Abstract: Attention is drawn to attempts which have been made to calculate thermal and elastic properties of particle-, fibre- and laminar-reinforced composite materials from corresponding properties of their constituents. The results of measurements of the linear coefficients of thermal expansion of small (similar 0?5 mm) hollow hemispherical specimens of pyrolytic graphite, silicon carbide and triplet hemispherical composite specimens of these components over the approximate temperature range 300 to 800 K are then reported. In conclusion it is shown how dilatation in composite structures such as these is amenable to the application of classical elasticity theory, and how agreement between the results of such calculations and observation provides evidence for the absence of layer separation resulting from constrained expansion.

Method for descaling steel

Abstract: Steel is descaled by spraying a mixture of a solid such as aluminum oxide and silicon carbide, water and a gas such as air under specified conditions onto the steel.

Cutting and welding using a CO2 laser

Abstract: Of all the types of lasers now available, the CO 2 laser is particularly suitable for materials working. It has a very high efficiency (15–20%) and a high out-put power (up to several kW). When the laser light is focused by means of a lens or a mirror, a c.w. power density of more than 10 9 W cm -2 can be attained. The laser need not be used in vacuum. The CO 2 laser is a suitable cutting tool for numerous materials. These include metals such as titanium or steel; combustible materials such as paper, textiles and wood; and plastics. The CO 2 laser can also cut hard and brittle materials such as aluminum oxide and silicon carbide. If metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width, however, is determined by the size of the laser spot. Another important field of application is the growth of single crystals. Experiments are reported in which the CO 2 laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. A comparative study of laser and electron beam techniques is included.

Silicon carbide lamp mounted on a ceramic of poor thermal conductivity

Abstract: A boron-doped silicon carbide light-emitting diode chip is mounted, such as on a support member of porous ceramic or other material of similarly low thermal conductivity, so as to operate at a temperature of at least 150 DEG C. Such a construction increases the amount of light produced by the boron-doped silicon carbide diode, due to increased operating temperature. A cover is placed over the diode to prevent convection cooling, thus further increasing the operating temperature and hence the light output. Instead of boron doping, the silicon carbide diode can be doped with other materials that produce similarly deep acceptor levels.

Interfacial characteristics of silicon carbide-coated boron-reinforced aluminium matrix composites

Abstract: The fibre-matrix interfacial region has been examined in BORSIC®-aluminium. The structure of this interface and that of the silicon carbide-boron interface have been revealed by transmission electron microscopy. Observations of composite fracture surfaces have indicated the considerable strength of the fibre-matrix interface and have shown that interfacial failure is seldom a mode of composite fracture.

The preparation of difluoro(trifluorosilyl)borane

Abstract: The reaction of SiF4 with solid silicon or silicon carbide at 1200°–1850° forms gaseous species which, on condensation with BF3 at –196°, yield SiF3BF2 in addition to known silicon boron fluorides.

Method for producing whiskers

Abstract: 1. A METHOD OF GROWIN CARBIDE WHISKERS OF SILICON AND OF BORON COMPRISING THE STEPS OF PREPARING AN INTERDISPERSION OF MATERISLS REACTABLE TO FORM CARBIDE WHISKERS IN TH PRESENCE OF A SUITABLE CATALYST, ALL MATERIALS INCLUDING CATALYST BEING IN THE FORM OF GRANULES RANGING IN SIZE FROM 1/200U TO 5U, SAID INTERDISPERSION INCLUDING CARBON IN THE FORM OF A MEMBER OF THE GROUP CONSISTING OF GRAPHITE, CARBON BLACK, CHARCOAL AND A CARBOHYDRATE THERMALLY DECOMPOSABLE TO CARBON AT SUFFICIENTLY HIGH TEMPERATURE, SAID CATALYST BEING SELECTED FROM THE GROUP CONSISTING OF NI AND COMPOUNDS THEREOF REDUCIBLE TO NI WHEN EXPOSED OF H2 AT HIGH TEMPERATURE WHEN BORON CARBIDE IS TO BE FORMED, AND SAID CATALYST BEING SELECTED FROSM THE GROUP CONSISTING OF NI, PD, CO AND FE COMPOUND REDUCIBLE TO NI, PD, CO, OR FE IN THE PRESENCE OF H2 AT HIGH TEMPERATURE, WO3 AND MIO2, WHEN SILICON CARBIDE IS TO BE FORMED, SAID CATALYST FOR PREPARING WHISKERS OF EITHER BORON OR SILICON CARBIDE BEING PRESENT IN QUANTITY FROM 1X10**-3 TO 2 ATOMIC PERCENT, AND AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF SI AND B OF WHICH A CARBIDE IS TO BE FORMED, SAID ELEMENT BEING PRESENT IN BOTH THE ELEMENTARY AND AN OXIDE FORM, AND EXPOSING SAID INTERDISPERSION TO HYDROGEN AT ELEVATED TEMPERATURE FOR A PEROD OF TIME SUFFICIENT TO ACHIEVE THE DESIRED GROWTH. D R A W I N G

High Temperature Oxidation of Silicon Carbide

Abstract: : Thermogravimetric measurements were made for the oxidation of hot pressed silicon carbide at an oxygen pressure of 150 torr and at temperatures from 1300C to 1600C. Oxidized samples were then analyzed using X-ray, metallograph, and electron probe techniques. The oxidation rate was found to increase with temperature. The products of oxidation were a carbon oxide and a protective layer of silica. The silica was primarily amorphous with some tridymite or alpha-cristobalite.

Zirconium diffusion barrier in titanium-silicon carbide composite materials

Abstract: A composite article, comprising silicon carbide-containing reinforcing filaments in a titanium or titanium alloy matrix, is found to have increased strength when the filaments are initially provided with a thin coating of zirconium. The zirconium acts as a barrier to interdiffusion of titanium and silicon carbide and prevents weakening of the composite structure which would otherwise result from such interdiffusion.