Ford Motor Company Limited

Ceradyne, Inc.

Ceradyne Advanced Products, Inc.

Elaine C Beckwith

Andre Ezis

Robert M Williams

Mohinder S Chattha

Henk Van Oene

Howard D Blair

Warren B Copple

Yun-Feng Chang

Henk V Oene

A method of making a reaction bonded/hot pressed silicon nitride comprising object is disclosed. Second phase crystallites are formed prior to hot pressing. A mixture of silicon, SiO.sub.2, and 0.4-2.3 molar percent (by weight of the silicon) of oxygen carrying agents, i.e., Y.sub.2 O.sub.3 and Al.sub.2 O.sub.3, is performed and reaction nitrided to form discs or billets having at least 60% alpha Si.sub.3 N.sub.4 and a high proportion of second phase crystallites which displace substantially all silicate glass except for a controlled small quantity. The reactive amounts of Y.sub.2 O.sub.3, Al.sub.2 O.sub.3 and SiO.sub.2 are controlled to assure formation of substantially Y.sub.1 SiO.sub.2 N as the second phase crystallite. Al.sub.2 O.sub.3 is controlled in an amount of 0.4-4% by weight to ensure that the small proportion of glass serves to protect the oxynitrides against linear oxidation kinetics. The hot pressed material has no visual mottle porosity associated therewith.

Method of making reaction bonded/hot pressed Si.sub.3 N.sub.4 for use as

The invention is a method of making ultrapure silicon yttrium oxynitride by using the steps of (a) in an argon stream, heating hydrated yttrium nitrate to a substantially dehydrated point; (b) adding to such heated hydrated yttrium nitrate an amount of silicon diimide to form a suspension and continuing to heat the mixture to melting so as to react the water of hydration of said nitrate with said silicon diimide and thereby form stoichiometric amounts of silica and yttrium/nitrogen/oxygen complex; and (c) heating said silica and nitrate in an inert atmosphere to an elevated temperature and for a period of time to chemically form ultrapure silicon yttrium oxynitride. The temperature of heating the hydrated yttrium nitride can be to a range of 340.degree.-360.degree. C. which is 85-92% of the dehydration point of yttrium nitrate. The temperature to which the mass of step (c) is heated can be in the range of 1450.degree.-1600.degree. C. and the time period can be in the range of 5-6 hours.

Method of making oxynitrides

Ultrapure silicon nitride precursor is made by: (a) continuously reacting liquid silicon halide (SiCl.sub.4) with an excess of liquid ammonia (NH.sub.3) (i) in the effective absence of contaminants, (ii) at a reaction situs in an inert atmosphere to form the silicon nitride precursor as a precipitate, and (iii) with a ratio of liquid ammonia to silicon halide (equal to or greater than 21 molar) effective to solubilize any gas reaction products; (b) providing a pressure differential to simultaneously and continuously withdraw a filtered portion of the excess liquid ammonia to leave the silicon nitride precursor precipitate in the reaction situs; and (c) adding ammonia to the excess of ammonia in said reaction situs to replace the withdrawn filtered portion of the liquid ammonia. The reaction is carried out with vigorous stirring of the liquid mixture and the atmosphere over the entire mixture is regulated to contain only ammonia vapor and nitrogen. The temperature of the liquid mixture is maintained between -33.degree. C. to -69.degree. C. by employing a cooling jacket containing dry ice, a slush of dry ice and acetone, isopropanol or cellosolve, and by recycling the withdrawn liquid ammonia and re-adding it to the reaction situs either as a cooling liquid or as a heating gas.

Method of making ultrapure silicon nitride precursor

A method is disclosed of making yttrium silicon oxy compounds, comprising: (a) mixing powdered hydrated metal nitrate with silica in molar equivalent amounts to yield upon heating a desired duo metal oxy compound; (b) agitatingly heating said mixture to melt and decomposition temperatures for the nitrate (e.g., 340.degree.-370.degree. C.), the melt encapsulating the silica particles; and (c) heating the sludge to a temperature (1300.degree.-1550.degree. C.) for a period of time (2-5 hours) effective to stimulate chemical reaction between the decomposed nitrate and silica to form yttrium silicon oxide.

Method of making yttrium silicon oxy compound

A method is disclosed of making a plurality of dimensionally accurate hot pressed ceramic bodies. A plurality of Si.sub.3 N.sub.4 plates having a thickness to width ratio of 1:3 to 1:40 are stacked in a hot pressing assembly (40-41-42-43). The plates are arranged in groups of progressively decreasing number so that (a) for a plate group (10-11-12-13-14) residing in a zone of compression (15) that will experience the least movement along the pressing direction the stacked number of plates is greatest within such group, and (b) for a plate group residing in a zone of compression (22) that will experience the most movement along the pressure direction the stacked number of plates (21) within such group is the lowest, each group being separated from adjacent groups by an inert rigid spacer.

Method of fabricating hot pressed silicon nitride billets

A method of improving the quality of hot pressed Si.sub.3 N.sub.4 bodies is disclosed. Unpurified silicon powder and admixed oxygen carrying agents are compacted to form a preform. The preform is nitrided, facilitated by the presence of certain impurities, to agglomerate the mixture to an increased density no greater than 2.7 gm/cm.sup.3. The nitrided preform is immersed in one or more stages in one or more leaching solutions of effective concentration to remove the selected impurities. The treated preform is then hot pressed to full density accompanied by a substantial reduction or absence of undesirable impurities such as iron silicide, which can conventionally form during hot pressing.

Method of improving quality of hot pressed Si.sub.3 N.sub.4 bodies

A method of making a compacted body useful in the fabrication of an improved, fully densified silicon nitride ceramic is disclosed. Silicon powder, oxygen carrying agents, and a dry lubricant (an aliphatic acrylate resin) are admixed. The lubricant is selected to have a low surface energy value less than 28 dyne/cm, have a glass transition temperature of -43.degree. to -82.degree. C., and a molecular weight equal to or less than 5000. The admixture is milled to a desired average particle size no greater than 35 microns. The milled mixture is then formed into a compact which can be nitrided and hot pressed to form a fully dense silicon nitride object.

Method of preparing powder ingredients by dry milling for subsequent

Method of making a densified silicon nitride/oxynitride composite

A thermosetting coating composition which may have nonvolatile solids content as high as 60% or greater and which may be employed as an automotive topcoat. The composition, exclusive of pigments, solvent, reactive and non-reactive diluents and other non-reactive components, consists essentially of:

Coating composition of aminoplast, hydroxy polymers and vinylic monomers

A fast curing, high solids coating composition that is adapted for use as an automotive topcoat and which upon curing forms a hard, glossy, durable coating exhibiting excellent resistance to solvents and water. The coating composition contains greater than about 60 percent by weight of nonvolatile solids and, exclusive of pigments, solvents and other nonreactive components, consists essentially of:

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Riverview, MI, United States of America

Elaine C Beckwith