Method of making carbide, nitride and boride powders
First Claim
1. A method of making metal carbide, nitride, or boride product powders and mixtures thereof by direct reduction of metal compounds comprising the steps of(a) forming a reactant mixture comprising one or more metal compounds, a source of carbon sufficient to reduce the metal compound to form metal, a source of carbon, nitrogen, or boron or mixtures thereof sufficient to react with substantially all of the metal formed by reduction, a small amount of gas or source of a gas selected from hydrogen or helium and mixtures thereof, and a heat exchange gas being substantially inert with respect to the product powders which gas may be selected from helium, argon, nitrogen and hydrogen, a source of a coating metal being added to said reactant mixture, said coating metal being vaporizable at the temperature to which the mixture is heated and having a vapor pressure higher than the product powders,(b) heating the reactant mixture to temperatures that cause the solid reactants to vaporize and above which the metal compounds are reduced,(c) passing the heated reactant mixture through a converging-diverging nozzle designed to reduce the temperature of the mixture to a temperature and for a time sufficient for further product species to form and for nuclei to form and grow by condensation to form the product powders, and such that after substantially all of the product powders have condensed from the reactant mixture in the nozzle the coating metals condense on the surface of the product powders,(d) exhausting the reactant mixture and product powders from the nozzle into an expansion chamber in a manner to reduce the total enthalpy of the mixture and powders to quickly lower the temperature of the powders sufficiently that the rate of undesired reactions is insignificant, and(e) recovering product powders with a metal coating.
1 Assignment
0 Petitions
Accused Products
Abstract
A method of making metal carbide, nitride, or boride powders and mixtures thereof by direct reduction of metal compounds comprises (a) forming a reactant mixture, (b) heating the reactant mixture to temperatures that cause solid reactants to vaporize and above which the metal precursor compounds are reduced, (c) passing the heated reactant mixture through a converging-diverging nozzle designed to reduce the temperature of the mixture to a temperature and for a time sufficient for further product species to form and for nuclei to form and grow by condensation to form the product powders, and (d) exhausting the mixture and product powders from the nozzle into an expansion chamber.
94 Citations
32 Claims
-
1. A method of making metal carbide, nitride, or boride product powders and mixtures thereof by direct reduction of metal compounds comprising the steps of
(a) forming a reactant mixture comprising one or more metal compounds, a source of carbon sufficient to reduce the metal compound to form metal, a source of carbon, nitrogen, or boron or mixtures thereof sufficient to react with substantially all of the metal formed by reduction, a small amount of gas or source of a gas selected from hydrogen or helium and mixtures thereof, and a heat exchange gas being substantially inert with respect to the product powders which gas may be selected from helium, argon, nitrogen and hydrogen, a source of a coating metal being added to said reactant mixture, said coating metal being vaporizable at the temperature to which the mixture is heated and having a vapor pressure higher than the product powders, (b) heating the reactant mixture to temperatures that cause the solid reactants to vaporize and above which the metal compounds are reduced, (c) passing the heated reactant mixture through a converging-diverging nozzle designed to reduce the temperature of the mixture to a temperature and for a time sufficient for further product species to form and for nuclei to form and grow by condensation to form the product powders, and such that after substantially all of the product powders have condensed from the reactant mixture in the nozzle the coating metals condense on the surface of the product powders, (d) exhausting the reactant mixture and product powders from the nozzle into an expansion chamber in a manner to reduce the total enthalpy of the mixture and powders to quickly lower the temperature of the powders sufficiently that the rate of undesired reactions is insignificant, and (e) recovering product powders with a metal coating.
-
8. A method of making metal carbide, nitride or boride powders and mixtures thereof by direct reduction of metal oxide compounds comprising the steps for
(a) forming a reactant mixture comprising one or more metal oxide compounds, a source of carbon comprising a gaseous hydrocarbon sufficient to reduce the metal compound to form metal, and a source of carbon, nitrogen or boron or mixtures thereof sufficient to react with substantially all of the metal formed by reduction, a small amount of gas or source of a gas selection from hydrogen or helium and mixtures thereof, and a heat exchange gas being substantially inert with respect to the product powders which gas may be selected from helium, argon, nitrogen and hydrogen, (b) heating the reactant mixture to temperatures that cause the solid reactants to vaporize and above which the metal compounds are reduced, (c) passing the heated reactant mixture through a converging-diverging nozzle designed to reduce the temperature of the mixture to a temperature and for a time sufficient for products to form and for nuclei to form and grow by condensation to form the product powders, (d) exhausting the reactant mixture and product powders from the nozzle into an expansion chamber in a manner to reduce the total enthalpy of the mixture and product powders to quickly lower the temperature of the product powders sufficiently that the rate of undesired reactions is insignificant, and (e) recovering product powders.
-
9. A method of making metal carbide product powders by direct reduction of metal oxides comprising the steps for
(a) forming a reactant mixture comprising one or more metal oxides, a source of carbon sufficient to reduce the metal oxide to form metal, a source of carbon comprising a gaseous hydrocarbon sufficient to react with substantially all of the metal formed by reduction, a small amount of gas or source of a gas selected from hydrogen or helium and mixtures thereof, and a heat exchange gas being substantially inert with respect to the product powders which gas may be selected from helium, argon, nitrogen and hydrogen, (b) heating the reactant mixture to temperatures that cause the solid reactants to vaporize and above which the metal oxides are reduced and above which the formation of carbides are favored, (c) passing the heated reactant mixture through a converging-diverging nozzle designated to reduce the temperature of the mixture to a temperature and for a time sufficient for additional carbides to form and for nuclei to form and grow by condensation to form the product metal carbide powders, (d) exhausting the mixture and metal carbide product powders from the nozzle into an expension chamber maintained at a pressure below the exhaust pressure of the nozzle and mixing with co-flowing steams of heat exchange gas in a manner to reduce the total enthalpy of the mixture and metal carbide powders to quickly lower the temperature of the metal carbide powders sufficiently that the rate of oxide formation is insignificant, and (e) electrostatically recovering metal carbide powders.
Specification