Government of the United States of America, As Represented by the Secretary of Commerce

Joseph J Ritter

Taki Negas

Robert D Shull

Richard A Keller

Michel Lamotte

Harry J Dewey

Samuel M Freund

Robert S Roth

A process for producing bismuth telluride including dissolving tellurium to form a first solution; heating the first solution to approximately 70.degree. C.; stirring the first solution; slowly and quantatively adding an amount of bismuth trioxide (Bi.sub.2 O.sub.3) to produce a Bi/Te second solution wherein the ratio of Bi: Te=2:3; cooling the second solution to approximately 25.degree. C.; preparing a solution of concentrated aqueous ammonia and distilled water; adding the solution of aqueous ammonia and distilled water dropwise to the second solution at approximately 25.degree. C. to form a third solution; rapidly stirring the third solution to produce a precipitate therefrom; separating the precipitate from the third solution by centrifugation; washing the separated precipitate in distilled water; drying the washed precipitate in air to produce a Bi.sub.2 Te.sub.3 O.sub.9.xH.sub.2 O, where x=1, precursor powder; heating predetermined quantities of the dried precursor powder to 250.degree. C.-275.degree. C., and exposing the heated precursor powder to flowing hydrogen at 1 atmosphere pressure for a period in the range of 3 to 12 hours to produce a final black powder of bismuth telluride.

Process for the chemical preparation of bismuth telluride

A chemical process for producing bulk quantities of an iron-silica gel composite in which particle size, form, and magnetic state of the iron can be selected. The process involves polymerizing an ethanolic solution of tetraethylorthosilicate, ferric nitrate and water at low temperature under the influence of an HF catalyst. The chemical and magnetic states of the iron in the resultant composite are modified in situ by exposure to suitable oxidizing or reducing agents at temperatures under 400.degree. C. Iron-containing particles of less than 200 .ANG. diameter, homogeneously dispersed in silica matrices may be prepared in paramagnetic, superparamagnetic, ferrimagnetic and ferromagnetic states.

Process for the controlled preparation of a composite of ultrafine

A co-precipitation synthesis of precursors to bismuth-containing ceramic superconducting materials is disclosed in which bismuth and at least one other approrpiate metal are dissolved in a non-aqueous acidic solvent, which are then recovered as a homogeneous dry powder. The mixed metal salts are co-precipitated from aqueous solution in the form of the corresponding homogeneous hydroxycarbonate precursor mixture by reaction with either sodium carbonate or potassium carbonate. The homogeneous precursor may be then converted to the BiCuSrCuO.sub.x ceramic by calcining the mixed hydroxycarbonate to a powder, compressing said powder into a green compact, sintering said green compact at a temperature of at least 750.degree. C., and cooling the ceramic material so produced at a controlled rate, preferably about 50.degree. C./minute.

Co-precipitation synthesis of precursors to bismuth-containing

A method of forming a ceramic monolith comprises exposing a pre-formed metal substrate to a NaCl filtered continuous wave laser beam of about 50 to 100 W power and about 80 to 315 W/cm.sup.2 power density in an atmosphere of a gas desired to react with the metal, allowing for the gas to diffuse into the metal substrate at a temperature effective to permit reaction thereof to form the ceramic monolith, and cooling the monolith.

Process for the fabrication of ceramic monoliths by laser-assisted

Refractory borides or carbides are prepared by contacting an alkali-metal ducible metal chloride or silicon tetrachloride with boron trichloride or carbon tetrachloride in an inert solvent in the presence of an alkali metal, the metal chloride or silicon tetrachloride and the boron trichloride or carbon tetrachloride being present in an amount about stoichiometrically equivalent to the boride or carbide to be prepared and the alkali metal being present in an amount about stoichiometrically equivalent to the amount of chloride in the metal chloride or silicon tetrachloride and the boron trichloride or carbon tetrachloride, until all chloride present has reacted with the alkali metal to form alkali metal chloride, separating the inert solvent to leave a solid residue containing a metal boride, silicon carbide or metal carbide precursor together with the alkali metal chloride, and calcining the residue while separating the alkali metal chloride until the precursor is converted to the refractory boride or carbide.

Process for preparing refractory borides and carbides

A process for producing any desired Ba/Ti mixture to be formulated as an amorphous solid which crystallizes at very low temperatures to yield a desired phase or phases is disclosed. The process yields products free of undesirable impurities and allows macroscopic production of certain phases in the baria-titania system, having exceptional high frequency dielectric properties, that were previously unattainable through solid-state high temperature production techniques.

Process of synthesizing mixed BaO-TiO.sub.2 based powders for ceramic

An isotopic starting material consisting of a mixture of chlorine-35 and chlorine-37 isotopic species of an isotopic compound having the formula CYClX, wherein Y is O or S and X is Cl or F, such as thiophosgene, is selectively isotopically enriched by means of a laser-induced photochemical reaction between selected chlorine isotopic species in the starting material and a dialkoxyethylene, such as diethoxyethylene. The method is carried out by irradiating with laser radiation, a gaseous mixture at a reduced pressure of the isotopic starting material and the dialkoxyethylene, until a stable reaction product is formed. The wavelength of the radiation is selected so as to selectively excite at least one but less than all of the chlorine isotopic species in the starting material, thereby causing the excited species to preferentially react with the dialkoxyethylene. The resulting reaction product is readily separable from the reaction mixture thereby leaving unreacted isotopic starting material selectively enriched in the unexcited chlorine isotopic species.

Photochemical method for chlorine isotopic enrichment

A boron trichloride starting material containing both boron-10 isotopes and oron-11 isotopes is selectively enriched in one or the other of these isotopes by a laser-induced photochemical method involving the reaction of laser-excited boron trichloride with either H.sub.2 S or D.sub.2 S. The method is carried out by subjecting a low pressure gaseous mixture of boron trichloride starting material and the sulfide to infrared radiation from a carbon dioxide TE laser. The wave length of the radiation is selected so as to selectively excite one or the other of boron-10 BCl.sub.3 molecules or boron-11 BCl.sub.3 molecules, thereby making them preferentially more reactive with the sulfide. The laser-induced reaction produces both a boron-containing solid phase reaction product and a gaseous phase containing mostly unreacted BCl.sub.3 and small amounts of sulfhydroboranes. Pure boron trichloride selectively enriched in one of the isotopes is recovered as the primary product of the method from the gaseous phase by a multi-step recovery procedure. Pure boron trichloride enriched in the other isotope is recovered as a secondary product of the method by the subsequent chlorination of the solid phase reaction product followed by separation of BCl.sub.3 from the mixture of gaseous products resulting from the chlorination.

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Mt. Airy, MD, United States of America

Joseph J Ritter