A process for chemical stabilization of a uranium carbide composite material: UC.sub.x+yC with x≧1 and y>0, placed in a stabilization chamber, comprises: a rise in chamber internal temperature for oxidation of the compound based on uranium carbide between approximately 380° C. and 550° C., the chamber being fed with a neutral gas; isothermal oxidative treatment at the oxidation temperature, the chamber being placed under O.sub.2 partial pressure; controlling completion of stabilization of the compound, comprising monitoring the amount of molecular oxygen consumed and/or carbon dioxide or carbon dioxide and carbon monoxide given off, until achievement of an input set-point value for the amount of molecular oxygen, of a minimum threshold value for the amount of carbon dioxide or minimum threshold values for the carbon dioxide and carbon monoxide. A device implements the process.

The present invention relates to a method for preparation of a powder comprising at least one carbide of at least one metal, comprising the steps consisting of: (a) preparing a solution comprising at least one organic gelling agent and at least one inorganic salt of at least one metal in a solvent; (b) modifying the pH of the solution prepared in step (a) in such a way as to precipitate said at least one metal and to obtain a colloidal suspension comprising nanoparticles of oxyhydroxides of said at least one metal; (c) removing the solvent from the colloidal suspension obtained in step (b) by which means a precursor of at least one carbide of at least one metal is obtained; and (d) subjecting the precursor obtained in step (c) to a thermal treatment in order to transform same into a powder comprising at least one carbide of at least one metal. The present invention also relates to the powder thus prepared and the various uses thereof.

Hafnium carbide powder for plasma electrodes is represented by a chemical formula HfC.sub.x (where x=0.5 to 1.0). The content of carbon particles contained as impurities in the hafnium carbide powder is less than or equal to 0.03% by mass. The hafnium carbide powder preferably has an average particle size of 0.5 to 2 μm. To produce the hafnium carbide powder, a pellet made from mixed powder of hafnium oxide and carbon is first placed in a second crucible made of silicon carbide. Then, the hafnium carbide powder is formed by heating the second crucible at 1800 to 2000° C. with the second crucible arranged in a first crucible made of carbon.

The method described herein may be characterized as reacting uranium dioxide with carbon to produce uranium carbide, and, reacting the uranium carbide with a silane, a silicon halide, a siloxane, or combinations thereof, and excess hydrogen to produce uranium silicide.

The method described herein may be characterized as reacting uranium dioxide with carbon to produce uranium carbide, and, reacting the uranium carbide with a silane, a silicon halide, a siloxane, or combinations thereof, and excess hydrogen to produce uranium silicide.

The method described herein may be characterized as reacting uranium dioxide with carbon to produce uranium carbide, and, reacting the uranium carbide with a silane, a silicon halide, a siloxane, or combinations thereof, and excess hydrogen to produce uranium silicide.

The method described herein may be characterized as reacting uranium dioxide with carbon to produce uranium carbide, and, reacting the uranium carbide with a silane, a silicon halide, a siloxane, or combinations thereof, and excess hydrogen to produce uranium silicide.

Composite gel particles with an ammonium diuranate matrix phase and a phenolic resin phase incorporated within the ammonium diuranate matrix phase are produced from a first solution comprising uranyl nitrate, a phenol, and optionally formaldehyde, wherein the uranyl nitrate and the phenol are present in a ratio ranging from 2:1 to 25:1; and a second solution comprising hexamethylenetetramine and urea. The first solution and the second solution are mixed, and drops of the resulting mixture into a heated second liquid which is immiscible with the mixed solution. Heat from the second liquid causes the hexamethylenetetramine to decompose to form ammonia, which reacts with the uranyl nitrate to cause each of the drops to form an ammonium diuranate gel particle. The ammonium diuranate gel particles are collected. The ammonium diuranate gel particles include the phenolic resin phase within the ammonium diuranate matrix phase, where the phenolic resin phase is formed by reaction between the phenol and formaldehyde. The first solution may include uranyl nitrate, the phenol, and formaldehyde, and the formaldehyde and the phenol may react to form the phenolic resin phase prior to mixing the first solution and the second solution. The first solution may be free of formaldehyde, and heat from the second liquid may causes the hexamethylenetetramine to decompose to form formaldehyde in situ; so that the formaldehyde and the phenol react to form the phenolic resin phase while the ammonia reacts with the uranyl nitrate.

Composite gel particles with an ammonium diuranate matrix phase and a phenolic resin phase incorporated within the ammonium diuranate matrix phase are produced from a first solution comprising uranyl nitrate, a phenol, and optionally formaldehyde, wherein the uranyl nitrate and the phenol are present in a ratio ranging from 2:1 to 25:1; and a second solution comprising hexamethylenetetramine and urea. The first solution and the second solution are mixed, and drops of the resulting mixture into a heated second liquid which is immiscible with the mixed solution. Heat from the second liquid causes the hexamethylenetetramine to decompose to form ammonia, which reacts with the uranyl nitrate to cause each of the drops to form an ammonium diuranate gel particle. The ammonium diuranate gel particles are collected. The ammonium diuranate gel particles include the phenolic resin phase within the ammonium diuranate matrix phase, where the phenolic resin phase is formed by reaction between the phenol and formaldehyde. The first solution may include uranyl nitrate, the phenol, and formaldehyde, and the formaldehyde and the phenol may react to form the phenolic resin phase prior to mixing the first solution and the second solution. The first solution may be free of formaldehyde, and heat from the second liquid may causes the hexamethylenetetramine to decompose to form formaldehyde in situ; so that the formaldehyde and the phenol react to form the phenolic resin phase while the ammonia reacts with the uranyl nitrate.