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Production and sintering of reaction bonded silicon nitride composites containing silicon carbide whiskers or silicon nitride powders
Molybdenum disilicide matrix composite Petrovic, J.J., Carter, D.H. and Gac, F.D. (United States Department of Energy, Washington, DC, USA) US Pat 4 927 792 (22 May 1990) Molybdenum disilicide is reinforced with single crystal silicon carbide whiskers. Each whisker is 1-5 ~tm long and 0.1-0.5 ~m in diameter and has an aspect ratio of between 5:1 and 15:1. Chemically treated glass fibres for reinforcing polymers Dana, D.E. and Morris, S.J. (PPG Industries, lnc, Pittsburgh, PA, USA) US Pat 4 927 869 (22 May 1990) An aqueous chemical treatment for fibrous inorganic oxide surfaces comprises 1-30 weight % of two film-forming polymers, an acryloxy alkyltrialkoxy silane coupling agent, a polyester polymer curing agent, a fibre lubricant, a silylated polyazamide if the lubricant is a cationic lubricant, and water in such an amount that 1-30 weight % of the aqueous solution is solids.
PROCESSES Production process of silicon carbide short fibres Abe, S., Ikai, T. and Ogawa, M. (Toyota Jidosha Kabushiki Kaisha, Aichi, Japan) US Pat 4 917 866 (17 April 1990) Metallic silicon is oxidized to silicon monoxide in the form of ultrafine particles or gas. This is carbonized in a carbon-containing reducing atmosphere at between 1300 and 1800°C to produce silicon carbide fibres. Reservoir feed method of making ceramic composite structures and structures made thereby Weinstein, J.G., Kantner, R.C. and Newkirk, M.S. (Lanxide Technology Company, Newark, DE, USA) US Pat 4 918 034 (17April 1990) A source of a first parent metal and a permeable mass of filler are orientated such that the formation of an oxidation reaction product will occur in the direction of and into the filler wherein the mass of metal is insufficient to completely embed the mass of filler. A reservoir of a second parent metal with a different composition to the first is connected to the first source. The apparatus is heated to a temperature below the melting point of the oxidation reaction product but above the melting point of the metal and brought into contact with an oxidant. The oxidation reaction front propagates through the filler body. The source of the first metal is replenished at temperature so that the oxidation reaction continues until all the filler is embedded in a polycrystalline oxidation reaction product, giving a self-supporting ceramic composite structure. Production and sintering of reaction bonded silicon nitride composites containing silicon carbide whiskers or silicon nitride powders Huang, J.-L. (Champion Spark Plug Company, Toledo, OH, USA) US Pat 4 919 868 (24 April 1990) Powdered silicon with an average particle size not greater than 5 ttm is mixed with a suitable amount of a sintering aid and 10-35% silicon carbide whiskers and/or 15-50% silicon
nitride. The suitable amount of the sintering aid is 3-7% each of MgO and CeO 2, 2-8% of Y203, 6% o f Y 2 0 3 and 2% of A]20 3, 2-8% of MgO, BeO, HfO2 or ZrO2, or 1-5% CaO. The mixture is pressed and heated at a controlled rate in a nitrogen atmosphere at about 1 atmosphere pressure until a predetermined temperature is reached so that the reaction between the pressed body and the nitrogen is complete; the body is then rapidly heated to a temperature at which the sintering aid reacts to form a glass. The resulting body has a density that is between 65 and 85% of the theoretical density.
Forming glass fibres from sol-gel compositions Lin, C.-C. and Milliron, R.C. (PPG Industries, lnc, Pittsburgh, PA, USA) US Pat4 919 871 (24 April 1990) An alkoxide compound of general formula M(OR)x is hydrolysed to form a liquid sol of sufficient concentration and viscosity for fibre forming. The sol is passed through an orifice to form the fibre which is then passed through an atmosphere containing a sufficient concentration of ammonia such that the fibre may be wound without self-sticking. Production of fibre composites Winkler, M., Ittemann, P. and Matthies, H.G. (BASF Aktiengesellschaft, Ludwigshafen, FRG) US Pat 4 919 978 (24 April 1990) Parallel reinforcing fibres in the form of a woven fabric in which the fibres are held together by thermoplastic filament yarns are impregnated with a solution containing 0-50% of a thermoplastic polymer in an organic solvent. The solvent is evaporated and the fibres are made up. Method of making short fibre reinforced glass and glass-ceramic matrix composites Allaire, R.A. and Gadkaree, K.P. (Coming Incorporated, Coming, NY, USA) US Pat 4 921 518 (1 May 1990) Continuous lengths of fibres are impregnated with glass, and at least partially consolidated by partially wetting or coating the fibres with glass and forming a fibre/glass matrix system. After cutting, lengths of this short fibrereinforced composite are heated as a batch to form a molten material with short fibres suspended therein. A gob of this material is then moulded to a desired shape to form a fibre-reinforced glass component with a random distribution of short fibres in it. Method of reinforcing utility poles Skiff, R.A. (Visalia, CA, USA) US Pat 4 921 555 (1 May 1990) Any decomposed or damaged material is removed from the area to be repaired and the edges above and below the area to be repaired are coated with an uncured resin. A porous reinforcing material is used to cover the outer surface of the pole between these two resin rings and a resin-impervious material is wrapped around the area so that it at least extends to the two rings. A liquid curable resin is then injected beneath this material and allowed to cure. Poly(arylene sulphide) composites Johnson, T.W. and Brady, D.G. (Phillips Petroleum Company, Bartlesville, OK, USA) US Pat 4 921 558 (1 May 1990) A poly(arylene sulphide) resin matrix with
long carbon fibre reinforcements and a crackinhibiting agent in the matrix is formed by first mixing particles of a poly(arylene sulphide) and the crack-inhibiting agent with a liquid carrier to form an aqueous slurry. This slurry is agitated and at least one roving of carbon fibres is pulled through the slurry to form an impregnated wet roving which is then partially dried, pulled through a die at a sufficient temperature to soften the poly(arylene sulphide) particles and consolidated by applying sufficient pressure to fuse the particles together. The crack-inhibiting agent is selected from polyethylene, polpropylene and copolymers of polyethylene or polypropylene and up to 10 weight % of other monomers based on the total copolymer weight. The slurry contains 20-501.1 parts by weight of poly(arylene sulphide) for every one of the crack-inhibiting agent and the average particle size in the slurry is 2-50 ~m.
Method for preparing reinforced thermoset articles Pennington, D.W. and McLemore, J.K. (The Dow Chemical Company, Midland. MI, USA) US Pat 4 921 658 (1 May 1990) A dilute aqueous slurry of 19-79% of solid, heat fusible organic polymer particles, 10-80% of reinforcing fibres and 1-10% of a latex binder of a substantially water-insoluble organic polymer is prepared and flocculated during agitation with a polymeric flocculant with a charge opposite to the bound charge of the latex binder. The solids are collected in the form of a mat, dewatered, dried and then densified and consolidated by heat and pressure to prcduce a composite. This composite is permitted to loft to a predetermined shape, impregnated with a thermoset resin composition and cured. Process for coating carbon fibres with a carbide Bouix, J., Viala, J.C., Vincent, H., Vincent, C., Ponthenier, J.L. and Dazord, J. (Centre National de la Recherche Scientifique (CNRS). Paris, France) US Pat 4 921 725 (I May 1990) One or more multi-filament strands of carbon are placed in a reaction chamber and exposed to a carbon-free gas mixture containing hydrogen and a volatile compound which is capable of reacting with the carbon to form a carbide passivation overlayer on each filament. The pressure is maintained at about atmospheric pressure and the strands are heated to a desired reaction temperature, below the temperature at which the gas phase reacts to form brittle crystals on the surface of the filaments, to form a carbide overlayer. The time of exposure is controlled to prevent carbon diffusing through the overlayer and further reacting, so that each filament substantially retains its original characteristics. Method of making ceramic composites Lesher, H.D.. Kennedy, C.R., White, D.R. and Urquhart, A.W. (Lanxide Technology Company, LP, Newark, DE, USA) US Pat 4 921 818 (1 May 1990) A permeable mass of filler with a coating of a silicon source on at least part of the filler (this coating has a different composition to the primary mass of the filler and has doping properties) and a parent metal are placed relative to each other such that the oxidation reaction product of the parent metal occurs towards and into the filler mass. The whole is
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PROCESSES Production process of silicon carbide short fibres Abe, S., Ikai, T. and Ogawa, M. (Toyota Jidosha Kabushiki Kaisha, Aichi, Japan) US Pat 4 917 866 (17 April 1990) Metallic silicon is oxidized to silicon monoxide in the form of ultrafine particles or gas. This is carbonized in a carbon-containing reducing atmosphere at between 1300 and 1800°C to produce silicon carbide fibres. Reservoir feed method of making ceramic composite structures and structures made thereby Weinstein, J.G., Kantner, R.C. and Newkirk, M.S. (Lanxide Technology Company, Newark, DE, USA) US Pat 4 918 034 (17April 1990) A source of a first parent metal and a permeable mass of filler are orientated such that the formation of an oxidation reaction product will occur in the direction of and into the filler wherein the mass of metal is insufficient to completely embed the mass of filler. A reservoir of a second parent metal with a different composition to the first is connected to the first source. The apparatus is heated to a temperature below the melting point of the oxidation reaction product but above the melting point of the metal and brought into contact with an oxidant. The oxidation reaction front propagates through the filler body. The source of the first metal is replenished at temperature so that the oxidation reaction continues until all the filler is embedded in a polycrystalline oxidation reaction product, giving a self-supporting ceramic composite structure. Production and sintering of reaction bonded silicon nitride composites containing silicon carbide whiskers or silicon nitride powders Huang, J.-L. (Champion Spark Plug Company, Toledo, OH, USA) US Pat 4 919 868 (24 April 1990) Powdered silicon with an average particle size not greater than 5 ttm is mixed with a suitable amount of a sintering aid and 10-35% silicon carbide whiskers and/or 15-50% silicon
nitride. The suitable amount of the sintering aid is 3-7% each of MgO and CeO 2, 2-8% of Y203, 6% o f Y 2 0 3 and 2% of A]20 3, 2-8% of MgO, BeO, HfO2 or ZrO2, or 1-5% CaO. The mixture is pressed and heated at a controlled rate in a nitrogen atmosphere at about 1 atmosphere pressure until a predetermined temperature is reached so that the reaction between the pressed body and the nitrogen is complete; the body is then rapidly heated to a temperature at which the sintering aid reacts to form a glass. The resulting body has a density that is between 65 and 85% of the theoretical density.
Forming glass fibres from sol-gel compositions Lin, C.-C. and Milliron, R.C. (PPG Industries, lnc, Pittsburgh, PA, USA) US Pat4 919 871 (24 April 1990) An alkoxide compound of general formula M(OR)x is hydrolysed to form a liquid sol of sufficient concentration and viscosity for fibre forming. The sol is passed through an orifice to form the fibre which is then passed through an atmosphere containing a sufficient concentration of ammonia such that the fibre may be wound without self-sticking. Production of fibre composites Winkler, M., Ittemann, P. and Matthies, H.G. (BASF Aktiengesellschaft, Ludwigshafen, FRG) US Pat 4 919 978 (24 April 1990) Parallel reinforcing fibres in the form of a woven fabric in which the fibres are held together by thermoplastic filament yarns are impregnated with a solution containing 0-50% of a thermoplastic polymer in an organic solvent. The solvent is evaporated and the fibres are made up. Method of making short fibre reinforced glass and glass-ceramic matrix composites Allaire, R.A. and Gadkaree, K.P. (Coming Incorporated, Coming, NY, USA) US Pat 4 921 518 (1 May 1990) Continuous lengths of fibres are impregnated with glass, and at least partially consolidated by partially wetting or coating the fibres with glass and forming a fibre/glass matrix system. After cutting, lengths of this short fibrereinforced composite are heated as a batch to form a molten material with short fibres suspended therein. A gob of this material is then moulded to a desired shape to form a fibre-reinforced glass component with a random distribution of short fibres in it. Method of reinforcing utility poles Skiff, R.A. (Visalia, CA, USA) US Pat 4 921 555 (1 May 1990) Any decomposed or damaged material is removed from the area to be repaired and the edges above and below the area to be repaired are coated with an uncured resin. A porous reinforcing material is used to cover the outer surface of the pole between these two resin rings and a resin-impervious material is wrapped around the area so that it at least extends to the two rings. A liquid curable resin is then injected beneath this material and allowed to cure. Poly(arylene sulphide) composites Johnson, T.W. and Brady, D.G. (Phillips Petroleum Company, Bartlesville, OK, USA) US Pat 4 921 558 (1 May 1990) A poly(arylene sulphide) resin matrix with
long carbon fibre reinforcements and a crackinhibiting agent in the matrix is formed by first mixing particles of a poly(arylene sulphide) and the crack-inhibiting agent with a liquid carrier to form an aqueous slurry. This slurry is agitated and at least one roving of carbon fibres is pulled through the slurry to form an impregnated wet roving which is then partially dried, pulled through a die at a sufficient temperature to soften the poly(arylene sulphide) particles and consolidated by applying sufficient pressure to fuse the particles together. The crack-inhibiting agent is selected from polyethylene, polpropylene and copolymers of polyethylene or polypropylene and up to 10 weight % of other monomers based on the total copolymer weight. The slurry contains 20-501.1 parts by weight of poly(arylene sulphide) for every one of the crack-inhibiting agent and the average particle size in the slurry is 2-50 ~m.
Method for preparing reinforced thermoset articles Pennington, D.W. and McLemore, J.K. (The Dow Chemical Company, Midland. MI, USA) US Pat 4 921 658 (1 May 1990) A dilute aqueous slurry of 19-79% of solid, heat fusible organic polymer particles, 10-80% of reinforcing fibres and 1-10% of a latex binder of a substantially water-insoluble organic polymer is prepared and flocculated during agitation with a polymeric flocculant with a charge opposite to the bound charge of the latex binder. The solids are collected in the form of a mat, dewatered, dried and then densified and consolidated by heat and pressure to prcduce a composite. This composite is permitted to loft to a predetermined shape, impregnated with a thermoset resin composition and cured. Process for coating carbon fibres with a carbide Bouix, J., Viala, J.C., Vincent, H., Vincent, C., Ponthenier, J.L. and Dazord, J. (Centre National de la Recherche Scientifique (CNRS). Paris, France) US Pat 4 921 725 (I May 1990) One or more multi-filament strands of carbon are placed in a reaction chamber and exposed to a carbon-free gas mixture containing hydrogen and a volatile compound which is capable of reacting with the carbon to form a carbide passivation overlayer on each filament. The pressure is maintained at about atmospheric pressure and the strands are heated to a desired reaction temperature, below the temperature at which the gas phase reacts to form brittle crystals on the surface of the filaments, to form a carbide overlayer. The time of exposure is controlled to prevent carbon diffusing through the overlayer and further reacting, so that each filament substantially retains its original characteristics. Method of making ceramic composites Lesher, H.D.. Kennedy, C.R., White, D.R. and Urquhart, A.W. (Lanxide Technology Company, LP, Newark, DE, USA) US Pat 4 921 818 (1 May 1990) A permeable mass of filler with a coating of a silicon source on at least part of the filler (this coating has a different composition to the primary mass of the filler and has doping properties) and a parent metal are placed relative to each other such that the oxidation reaction product of the parent metal occurs towards and into the filler mass. The whole is
COMPOSITES. MARCH 1992
137