Showing papers on "Silicon carbide published in 1985"

Growth of beta-silicon carbide whiskers by the VLS process

Abstract: Beta-silicon carbide whiskers are being grown by a vapour-liquid-solid (VLS) process which produces a very high purity, high strength single crystal fibre about 6μm in diameter and 5–100 mm long. Details of the growth process are given along with a general explanantion of the effects of the major growth parameters on whisker growth morphology.

Effect of Reinforcement on the Pitting Behavior of Aluminum‐Base Metal Matrix Composites

Abstract: This paper examines the effect of graphite and silicon carbide reinforcements on the pitting behavior of graphite/aluminum (Gr/Al) and silicon carbide/aluminum (SiC/Al) metal matrix composites. Electrochemical corrosion tests were performed on both Gr/Al and SiC/Al composite specimens. Identical tests were completed on powder metallurgy processed aluminum and wrought aluminum of the same composition. The electrochemical behavio of the SiC/Al composites was essentially identical to that of the powder processed and wrought aluminum alloys; however, the pitting attack on the SiC/Al composites was distributed more uniformly across the surface, and the pits penetrated to significantly less depths. The presence of graphite in the Gr/Al composites did not cause an electropositive shift in corrosion potential as anticipated, but caused a substantial decrease in resistance to passive film breakdown. This effect is the predominant reason for the poor performance of Gr/Al composites in marine environments.

Silicon carbide filaments - Microstructure

Abstract: The microstructure of chemically vapour deposited silicon carbide filaments has been examined using transmission electron microscopy. The filament bulk consisted of heavily faulted columnar subgrains ofβ-SiC which were preferentially oriented such that {1 1 1} planes were parallel to the surface of the carbon fibre substrate. The protective coating on the filament surface was characterized by several microstructurally distinct layers, all of which consisted primarily of carbon. The first layers of the coating contained small crystallites of SiC in addition to turbostratic carbon, while the outer layers showed no evidence of SiC. Implications of the filament microstructure with respect to mechanical properties are discussed.

Creep Deformation of an Alumina Matrix Composite Reinforced with Silicon Carbide Whiskers

Abstract: Whisker-reinforced ceramic composites with enhanced fracture toughness properties are being developed. The creep behavior of such a composite was studied. The introduction of silicon carbide whiskers significantly improves the creep resistance of polycrystaline alumina.

Bonding mechanism between silicon carbide and thin foils of reactive metals

Abstract: Pressureless-sintered SiC pieces and SiC single crystals were joined with foils of reactive metals at 1500° C (1773 K) for titanium and zirconium foils or at 1000° C (1273 K) for Al/Ti/Al foils. Bend testing at various temperatures up to 1400° C (1673 K), optical and electron microscopy, and electron-probe X-ray microanalysis studies were carried out on the specimens. From the results, it was concluded that the fairly high bond strength of titanium-foil joined SiC specimens might be attributed to the formation of a Ti3SiC2 compound, since good lattice matching between SiC and Ti3SiC2 was obtained in the SiC single crystals. Also in the Al/Ti/Al-foil joined SiC, high bond strength was obtained, but it decreased steeply at 600° C (873 K) because of a retained aluminium phase. The bond strength in the zirconium-foil joined SiC was low.

Abrasive surfaced article for high temperature service

Abstract: Abrasive Surfaced Article for High Temperature Service Abstract A very thin abrasive material on a substrate is comprised of ceramic particulates contained within a metal matrix. The particulates extend fully through the matrix from the substrate surface to the machined free surface of the abrasive. In a representative 0.38 mm abrasive the particulates are sized nominally at 0.42-0.50 mm and have an aspect ratio of less than 1.9 to 1. This enables a high density of particulates, in the range 33-62 per cm2, while at the same time ensuring good bonding in that most of the particulates are fully surrounded by matrix. When the abrasive is applied to the tip of a superalloy gas turbine engine blade, about 10-50% of the matrix metal is removed after machining. This allows the machined ceramic particulates to project into space and to thus better interact with ceramic abradable seals. In the preferred practice of the invention the particulates are alumina coated silicon carbide contained in a nickel superalloy matrix.

The influence of iron on the preparation of silicon nitride from silica

Abstract: The thermodynamics of carbothermal reduction and nitriding of silica in the temperature range 1200 to 1600° C have been evaluated and may be used to determine the conditions required to form silicon nitride, silicon oxynitride or silicon carbide. The products of reaction are, however, frequently dictated by kinetic rather than thermodynamic considerations and the presence of impurities in the silica and carbon reactants is especially important. α-silicon nitride has been prepared from high purity silica and carbon but under identical conditions of temperature and nitrogen pressure the chemistry of the process changes markedly when a small amount of iron is added to the reactants. Below 1320° C iron has no effect and pure α-silicon nitride is formed but with increasing temperature the proportion of silicon carbide in the product increases. Above 1550° C silicon carbide is the stable solid phase in the Si-C-O-N system at 1 atm pressure. The process chemistry has been investigated by high-temperature reaction studies and X-ray diffraction and reaction mechanisms are proposed on the basis of microstructural observations of reactants and products.

Friction and wear properties of monolithic silicon-based ceramics

Abstract: Friction and wear properties of two forms of silicon nitride (reaction bonded and hot pressed) and two of silicon carbide (reaction sintered and sintered) are reported. The materials were slid against themselves under unlubricated conditions. Tests were run using a simulated inertial sample dynamometer. Sliding speeds ranged from 0.5 to 5.5 m sec−1 with applied loads of 225 or 450 N. Friction coefficients were found to be in the range of 0.15 to 0.8 for both types of material. Friction response was qualitatively correlated with changes in surface chemistry at the sliding interface. Wear rates were of the order of 10−14 to 10−13m3 (Nm)−1, in order-of-magnitude agreement with previous pin-on-disc results reported in the literature. Wear surfaces exhibit plastic deformation, ploughing, and oxide film formation and removal.

Silicon carbide-to-metal joint and method of making same

Abstract: A silicon carbide-to-metal joint includes a thin layer of metal adherent to the ceramic material, a compliant layer of metal overlying the thin metal layer and a brazing alloy in contact with the metal to which the ceramic material is joined. A method for preparing a silicon carbide surface for joining by metallic brazing to a metal includes the steps of applying a thin layer of metal adherent to the ceramic surface followed by application of a compliant layer of metal. Also described is an easily brazable silicon carbide article which includes a silicon carbide substrate, a thin electrically conductive adherent metal layer overlying the substrate and a compliant metal layer overlying the thin metal layer.

Thermal diffusivity of chemically vapour deposited silicon carbide reinforced with silicon carbide or carbon fibres

Abstract: The thermal diffusivity of chemically vapour deposited silicon carbide reinforced with either Nicalon SiC yarn or PAN-precursor carbon fibres was measured by the laser-flash method during various time-temperature treatments. The diffusivity was found to depend on the degree of densification, the direction of heat flow with respect to the fibre orientation, and the thermal history. Structural modifications, confirmed by X-ray diffraction, produced large permanent changes in the thermal properties of the SiC-SiC composites when heated above 1200° C, while only minor changes were seen in C-SiC composites heated above 1500° C.

Novel Passivation Dielectrics—The Boron‐ or Phosphorus‐Doped Hydrogenated Amorphaus Silicon Carbide Films

Abstract: Mesures de conductivite electrique, du seuil de claquage dielectrique et l'indice de refraction

Silicon carbide film for X-ray masks and vacuum windows

Abstract: A layered structure for use in an X-ray membrane (pellicle) mask or a vacuum window is provided in which an intermediate amorphous layer such as silicon dioxide is grown on a silicon substrate which provides a stress relief medium and surface properties which enhance and improve subsequent process layers by breaking the epitaxial nature of these later deposited layers. Upon subsequent deposition of an inorganic overcoat, such as SiC, on the intermediate amorphous layer, the overcoat produces a nearly defect-free layer with a substantially reduced stress of suitable quality for X-ray lithography mask fabrication. Furthermore, additional alternating layers of a silicon carbide film and an intermediate inorganic layer, such as silicon nitride, can be deposited to obtain an even smoother silicon carbide surface and stronger structure.

Occurrence of airborne silicon carbide fibers during industrial production of silicon carbide.

Abstract: Airborne dust from the production of silicon carbide has been analyzed for particle morphology and composition. Fibers of alpha silicon carbide were identified by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) with selected area electron diffraction techniques (SAED). Micrographs taken at high magnification revealed several stacking periods along the fiber axis, and one or more of the polytypes 2H, 4H, or 6H could be distinguished. Preliminary investigations applying SEM showed that 80% of the fibers had diameters of less than 0.5 micron and a length greater than 5 micron. Fiber concentrations were examined by the counting of stationary and personal samples in an optical phase contrast microscope. The fiber levels in the three plants investigated were low and less than 1 fiber/cc of air (10(6) fibers/m3). Dust samples from the handling of raw material, including recycled material, contained up to 5 fibers/cc (5 X 10(6) fibers/m3).

Gas turbine composite parts

Abstract: Gas turbine engine carbon-carbon composite components having multilayer coatings resulting in components resistant to oxidation at temperatures greater than 2500° F. A first multilayer coating comprises a pack derived silicon carbide coating covered with a chemical vapor deposition layer of silicon nitride. A second multilayer coating comprises a layer of pyrolytic graphite covered with a pack derived silicon carbide coating covered with a chemical vapor deposition layer of silicon nitride. The third multilayer coating comprises a layer of chemical vapor deposition applied silicon carbide covered with a pack derived silicon carbide coating covered with a chemical vapor deposition layer of silicon nitride. Carbon fibers are carbonized or graphitized, formed into woven structures which are stacked in a prepreg with impregnating resin, pyrolyzed and optionally graphitized to form an engine component, and then coated with the above-described layers to achieve an engine component highly resistant to oxidation at elevated temperatures.

29 Si and 13C magic angle spinning n.m.r. spectra of silicon carbide polymorphs

Abstract: Hexagonal and cubic silicon carbide polymorphs give distinctive 29Si and 13C magic spinning n.m.r. spectra that can be related to the number of nonequivalent lattice sites in the structure and variations in the non-nearest-neighbour environment.

Electrostatic spray coating system

Abstract: An electrostatic spray system including a spray device having a coating-charging electrode, a source of high voltage electrostatic potential, and a resistive path for safely transmitting high voltage between the electrode and the electrostatic supply. The resistive high voltage transmission path is composed of plural parallel-connected continuous silicon carbide fibers.

High strength, thermally stable magnesium aluminosilicate glass-ceramic matrix-sic fiber composites

Abstract: A silicon carbide fiber reinforced barium modified magnesium aluminosilicate matrix composite is described having high strength and thermal stability at temperatures in excess of 1200° C. The matrix material contains about 5% to about 14% magnesium oxide and about 5% to about 25% barium oxide. While any suitable ratios of fiber to matrix can be used, the composite for most applications for example, in the heat engine area, will contain approximately 20% to 50% by volume silicon carbide fibers.

Process for preparing silicon carbide whiskers

Abstract: The present invention provides a process for preparing silicon carbide whiskers. According to the process, carbon black having the following properties (a) to (c) is blended, as a carbonaceous material, with a silicon source material, and the resulting mixture is heated in a non-oxidizing atmosphere at 1,300° to 1,800° C. (a) Nitrogen adsorption specific surface area: 150 to 500 m2 /g (b) Dibutyl phthalate absorption: 120 to 200 ml/100 g. (c) Tint strength (%): equal to or below a value calculated according to the following formula: 0.3496×(nitrogen adsorption specific surface area)-0.2143×(dibutyl phthalate absorption)+101.87

Method for preparing configured silicon carbide whisker-reinforced alumina ceramic articles

Abstract: A ceramic article of alumina reinforced with silicon carbide whiskers suitable for the fabrication into articles of complex geometry are provided by pressureless sintering and hot isostatic pressing steps. In accordance with the method of the invention a mixture of 5 to 10 vol. % silicon carbide whiskers 0.5 to 5 wt. % of a sintering aid such as yttria and the balance alumina powders is ball-milled and pressureless sintered in the desired configuration in the desired configuration an inert atmosphere at a temperature of about 1800° C. to provide a self-supporting configured composite of a density of at least about 94% theoretical density. The composite is then hot isostatically pressed at a temperature and pressure adequate to provide configured articles of at least about 98% of theoretical density which is sufficient to provide the article with sufficient strength and fracture toughness for use in most structural applications such as gas turbine blades, cylinders, and other components of advanced heat engines.

Formation of a silicon‐carbide layer during CF4/H2 dry etching of Si

Abstract: Silicon specimens which had been reactive ion etched in CF4/x% H2 (0≤x≤40) have been characterized by x‐ray photoelectron emission spectroscopy. Angular rotation was used to study films deposited by the plasma process onto the Si surface. In agreement with previous studies it is found that plasma exposure of Si specimens leads to the deposition of a fluorocarbon film. An intriguing new finding was the discovery of a silicon‐carbide layer localized near the fluorocarbon‐film/Si interface. The existence of this carbide layer was found to be independent of gas composition from 0–40% H2 for a 1‐min plasma exposure.

Effect of Impurity and Carrier Concentrations on Electrical Resistivity and Thermal Conductivity of Sic Ceramics Containing BeO

Abstract: Silicon carbide ceramics with BeO as an additive exhibit unusually high electrical resistivity and thermal conductivity compared to conventional SiC ceramics. Studies concerning the effects of carrier concentration in the SiC grains on electrical properties and thermal conductivity are described. The low carrier concentration in this ceramic is responsible for the high electrical resistivity. The thermal conductivity, however, decreases gradually with increasing impurity concentration.

Silicon carbide-carbon composite molded product and process for manufacturing the same

Abstract: A molded product consisting mainly of silicon carbide and a process for mfacturing the same. This invention is to provide a product having a desired or complicated shape and a process which enables the manufacture of any such product at a drastically lower temperature than any conventional process. This object is attained by applying an organic silicon polymer having a skeleton composed mainly of carbon-silicon bonds by impregnation or adherence to a base material having a desired shape, and by burning the base material at a temperature of 700° C. to 2,000° C. in a vacuum or in a nonoxidizing gas atmosphere. The product of this invention has a fibrous, granular and/or filmy carbon structure in the matrix consisting mainly of SiC. The product of this invention is useful for a wide variety of applications, for example, for making heat-resistant structural members of electronic devices.

Cubic boron nitride compact and method of making

Abstract: The invention is a process for preparing a sintered polycrystalline compact of cubic boron nitride (CBN) with substantial intercrystalline bonding, together with the compact produced by the process. A carbon containing material, such as diamond or graphite, is added to a binder material which comprises elemental silicon. The carbon from the carbon containing material reacts with the silicon to form silicon carbide. Having silicon carbide as a constituent of the final product is preferable to having elemental silicon because the silicon carbide does not expand on cooling, and is also harder and more wear resistant than elemental silicon. In this way, the benefits of using elemental silicon in a binder system to enhance intercrystalline bonding of the CBN are realized while avoiding the disadvantages otherwise present. Another advantage is provided in the compact of this invention may be cut into precision shapes with a conventional Electric Discharge Machine (EDM).

Sintered silicon carbide molding and process for production thereof

Abstract: Sintered silicon carbide moldings produced by using as a sintering aid a composition comprising oxide(s) of at least one element selected from the group consisting of Li, Be, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Sr, Zr, Nb, Mo, Ba, Tc, Ta, W and Th in addition to known sintering aids used for the production of sintered silicon carbide moldings, such as rare earth element oxides, boron oxide and aluminum oxide, and a process for production thereof.

Method for depositing silicon carbide non-single crystal semiconductor films

Abstract: A method of forming a silicon carbide non-single crystal semiconductor, characterized in that said method comprises the step of: applying electric or light energy to a methylsilane expressed by the formula of SiH 4-n (CH 3 ) n (where n=1 to 3) or Si 2 (CH 3 ) n H 6-n (where n=1 to 5) and a silane hydride (of Si m H 2m+2 , where m=1 to 3), thereby forming a silicon carbide non-single crystal semiconductor film layer containing Si x C 1-x (where 0

Method of making porous silicon carbide bodies

Abstract: Porous silicon carbide bodies are obtained by starting with a powder of particle size falling within a single sieve mesh range fraction and consisting either entirely of carbon particles or a mixture of carbon and silicon carbide particles of the same mesh fraction is mixed or coated with 15 to 30% by weight of a binder, moulded to shape, warmed in the temperature range from 40° to 200° C. to vaporize volatile material and then coked at a temperature rising to 850° C. Then it is siliconized by raising the temperature to the range from 1650° to 1950° C. with gaseous silicon or impregnated with silicon by dipping the body into a silicon melt and convert it to carbide, with the excess silicon thereafter being removed by vaporizing out or by boiling in lye. Sieve mesh fractions in the region of a few hundred μm are preferred, and the density of the porous body after pressing but before siliconizing should lie in the neighborhood of 0.6 to 0.7 g/cm3.