Gte Laboratories Incorporated

Sophia R Su

Samuel Natansohn

Leo F Fitzpatrick

Paulette I Onorato

Scott J Butler

Elizabeth A Trickett

Sheldon I Lieberman

Daniel W Oblas

Sheryl A Robillard

Margaret O'Connor

A method for producing a superconducting copper oxide based helical resonator coil exhibiting improved quality factor, Q. A copper oxide based superconductor powder is mixed with a binder melt at about 45-65% solids by volume. The binder is an RCOOR' ester wax with R and R' each a long chain hydrocarbon group of at least 6 carbons. The ester wax has a melting point of about 40.degree.-100.degree. C. and a viscosity of about 94-2000 centipoise at its melting point. The binder/powder mixture is extruded and wrapped around a mandrel to form a helical coil. The coil is embedded in a setter powder and heated in an oxidizing atmosphere at up to about 2.degree. C./min to about 450.degree.-650.degree. C., and held for a time sufficient to remove the binder. The coil is then heated in the oxidizing atmosphere at up to about 3.degree. C./min to at least about 920.degree. C., and held at about 920.degree.-990.degree. C. for a time sufficient to achieve a density of at least about 93% of theoretical density. The densified coil is cooled in the oxidizing atmosphere at below about 2.degree. C./min to at or below about 550.degree. C., and annealed at about 450-550.degree. C. in flowing oxygen for a time sufficient to convert the crystal structure of the coil to at least 50 v/o high T.sub.c phase superconducting perovskite crystal. The geometry of the extruded, wrapped helical coil is selected to produce, after subsequent densification, a helical resonator coil about 3-17 mm in inner diameter, of a total length n .lambda./2, wherein n is an integer and .lambda. is the operating wavelength of the helical resonator coil.

Fabrication of high T.sub.C superconducting helical resonator coils

A process for producing a high critical temperature bismuth strontium calcium copper oxide superconducting material. An intimate mixture is formed of two superconducting materials. The first material is bismuth strontium calcium copper oxide or (bismuth, lead) strontium calcium copper oxide, and has a bulk critical temperature below about 90K. The second material is a seeding powder of bismuth strontium calcium copper oxide or (bismuth, lead) strontium calcium copper oxide, and includes at least 20 volume percent 2223 phase. The amount of seeding material added to the mixture is selected to result in an amount of 2223 phase in the mixture of about 2-50 weight percent. The mixture is annealed in an oxidizing atmosphere at a temperature of at least about 845.degree. C. and below the melting temperature of the 2223 phase, for a time sufficient to increase the amount of 2223 phase in the mixture. In an alternate embodiment, one or both of the superconducting materials in the mixture are provided by drying, calcining, and annealing a precursor mixture of a Sr(NO.sub.3).sub.2 solution, a Ca(NO.sub.3).sub.2, solution, a Cu(NO.sub.3).sub.2 solution, a Bi.sub.2 O.sub.3 powder, and a PbO powder.

Formation of the high TC 2223 phase in BI-SR-CA-CU-O by seeding

A superconducting copper oxide based wire exhibiting improved critical current density and method. A superconductor powder and a binder melt are mixed at a solids loading of at least 90% by weight. The binder is an ester wax with no more than about 0.25 weight percent extrusion-aiding additives. The ester wax has the general formula RCOOR' with R and R' being hydrocarbon chains of at least 6 carbons. The ester wax melting point is 40.degree.-100.degree. C.; its melt viscosity is 94-2000 centipoise. The mixture is shaped and heated in an oxidizing atmosphere at up to 120.degree. C./hr to 500.degree.-600.degree. C., and held at that temperature for a time sufficient to remove the binder and achieve a wire density of at least 50% of theoretical. The green wire is heated at 50.degree.-130.degree. C./hr to at least 920.degree. C., and held at 920.degree.-990.degree. C. to achieve 90% of theoretical density, then annealed in oxygen. The wire may be textured during the heating process or by seeding. About 3-12 w/o silver may be included in a superconducting rare earth barium copper oxide based wire. The superconducting copper oxide based wire exhibits a density of at least about 99% of theoretical density, a critical temperature at dc zero resistance of at least about 90 K, and a critical current density of at least about 1000 A/cm.sup.2.

Process for producing superconducting wires

A method of making fully dense, crack-free silicon nitride articles using polysilanes as a binder. Polysilane is dissolved in a solvent and a silicon nitride composition including a densification aid is added to form a homogeneous mixture. The mixture is dried to form a powder, and molded at a temperature less than 100.degree. C. to form a molded article. Alternatively, the slurry is poured into a mold and vacuum filtered to form a cake, then isostatically pressed at a temperature of approximately 90.degree. C. The molded article or pressed cake is heated at a rate of approximately 5.degree. C./min to about 900.degree. C. in a nonoxidizing atmosphere and held at about 900.degree. C. for a time sufficient to decompose the polysilane. The article is sintered in a nonoxidizing atmosphere at a temperature of about 1685.degree.-1900.degree. C. to form a silicon nitride article free of cracks and having a density greater than 3.5 g/cc.

SI.sub.3 N.sub.4 process using polysilane as a binder

A process for making a densified silicon nitride article utilizing polysilanes or polysilazanes as a binder is described. The process involves blending of a silicon nitride composition with a polysilane or a polysilazane to form a mixture. The mixture is molded into an article. The article is then pyrolyzed in a non-oxidizing atmosphere and at a temperature sufficient to form a pyrolyzed article comprising amorphous silicon nitride and silicon carbide. The article is then sintered at a temperature equal to or greater than 1400.degree. C. to form a densified silicon nitride article.

SI3N4 process using polysilane or polysilazane as a binder

A method of making high purity, dense silica of large particles size is described. Tetraethylorthosilicate is mixed with ethanol and is added to a dilute acid solution having a pH of about 2.25. The resulting solution is digested for about 5 hours, then 2N ammonium hydroxide is added to form a gel at a pH of 8.5. The gel is screened through an 18-20 mesh screen, vacuum baked, calcined in an oxygen atmosphere and finally heated to about 1200.degree. C. in air to form a large particle size, high purity, dense silica.

Method of making high purity dense silica of large particle size

A method of making large particle size, high purity, dense silica is described. Tetraethylorthosilicate ethanol solution is added to a 2N ammonium hydroxide solution containing silicic acid having an average particle size of about 15 micrometers to form a precipitate followed by a digestion of the precipitate in the solution. The precipitate is filtered through a screen having 45 micrometer openings and dried to form a dried powder. The dried powder is then calcined in an oxygen atmosphere followed by densifying it by heating at a temperature of about 1200.degree. C. in air to form a large particle size, high purity, dense silica.

Method of making large particle size, high purity dense silica

A composition for injection molding a ceramic powder to make ceramic shapes is described. The composition comprises a ceramic powder and a binder system. The binder system comprises a distilled thermosetting polycarbosilane containing from about 0.4 to about 0.7 weight percent of a cross-linking inhibitor, a surfactant, and with or without a lubricant. The cross-linking inhibitor is selected from the group consisting of p-benzoquinone, benzophenone, and mixtures thereof.

Method of modifying thermal properties of polycarbosilane

A process for making a homogeneous yttria-alumina doped silicon nitride article is described. A uniform coating of yttria and alumina is applied to the surface of silicon nitride particles by a chemical application of the nitrates of yttrium and aluminum followed by drying and a subsequent conversion of the nitrates to the corresponding oxides. The resulting powder is formed into an article and pressureless sintered to a density greater than 98% of theoretical at temperatures less than 1700.degree. C.

Doped silicon nitride article

A process for making a homogeneous yttria-alumina doped silicon nitride article is described. A uniform coating of yttria and alumina is applied to the surface of silicon nitride particles by a chemical application of the hydroxides of yttrium and aluminum followed by drying and a subsequent conversion of the hydroxides to the corresponding oxides. The resulting powder is formed into an article and pressureless sintered to a density greater than 99% of theoretical.

Process for making a homogeneous doped silicon nitride article

A high purity aluminum nitride is made by precipitating (CH.sub.3).sub.3 Al:NH.sub.3, washing it with hexane and pyrolyzing it to AlN. The precipitation is obtained by reacting a hexane solution of trimethyl aluminum with high purity anhydrous NH.sub.3(g), or by reaction Al(CH.sub.3).sub.3(g) and NH.sub.3(g) in a hexane solution, or by reacting Al(CH.sub.3).sub.3(g ) with NH.sub.3(1). The resulitng AlN is very pure and a density of 91.3% of theoretical has been achieved by pressing and sintering a pellet made from it as compared to a 89% theoretical density obtained by pressing and sintering a pellet made from commercial AlN powder.

Process of making high purity aluminum nitride

A silicate optical glass article is made by forming a gel from a hydrolyzed silicon alkoxide. The resulting gel is molded, cured, dried, solvents removed, heated to form a dense glass having near net shape dimensions thereby reducing expensive polishing steps to obtain the desired final dimensions and surface quality.

Process for molding optical components of silicate glass to a near net

A stabilized graphite intercalation product can be formed by sequential intercalation of graphite. Graphite is initially intercalated with an alkali metal (M). The unstable alkali metal intercalation compound is then intercalated with an organic acid (R) to form a room temperature stable, graphite intercalation containing a metal charge transfer salt of the type M.sup.+ R.sup.-.

Graphite intercalates containing metal-charge transfer salts

A method and apparatus for intercalating small graphite flakes with a metal halide. Graphite and a metal halide are placed in two chambers 12, 14 of a rotary vapor transport reactor assembly 10 and heated. The reactor is charged with a halogen gas and rotated by motor 24 during synthesis to produce a homogenous and uniform intercalated product.

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Weston, MA, United States of America

Sophia R Su