Patent Number: 053207866
Section: description

The present invention is more particularly described in the following examples which are intended as illustrative only, since numerous modifications and variations will be apparent to those skilled in the art. EXAMPLE A A cold pressed uranium dicarbide pellet was prepared as follows. Uranium dioxide was converted to uranium dicarbide as the initial material by reaction of uranium dioxide with graphite at temperatures above about 1800.degree. C. in accordance with the chemical equation: EQU UO.sub.(2+y) + (2+y+x)C .fwdarw. UC.sub.x + (2+y)CO. UO.sub.2 powder and graphite powder were hand blended and then placed into a ball mill for about 16 hours. The mixture was then sieved through a fine 250 mesh. The mixture of fine particles was then pressed into 1.91 centimeter (cm) diameter briquettes. The briquettes were placed onto graphite trays and entered into a high temperature oven for reaction by carbothermic reduction. The reduction process included drawing a vacuum of 5 .times. 10.sup.-5 Torr in the furnace and heating at temperatures between 1875.degree. C. and 2150.degree. C. for about 4 hours. The furnace was held at the elevated temperature for at least four hours to allow sufficient time for carbon to remove the oxygen as CO and form the particular carbide depending upon the amount of carbon added. The furnace was then rapidly cooled to room temperature. The resultant UC.sub.x briquettes were crushed and then passed through a 16-mesh screen. A binder (0.3 percent by weight polyethylene glycol) and a lubricant (0.3 percent by weight stearic acid) were added in powder form to the crushed material to hold the particles together after subsequent pressing and to protect the die press from the abrasive uranium dicarbide particles. About 2.0 grams (g) of the UC.sub.x powder, including the binder and lubricant additives, was placed into a die cavity and about 110 MPa pressure was applied to form the initial cold pressed uranium dicarbide pellet. EXAMPLE 1 Pellets having an initial composition of UC.sub.1.95 were placed on tantalum, tungsten and graphite trays respectively. The pellets were then heated to 2100.degree. C. under an argon atmosphere for 12 hours to sinter the compositions. The pellets were then analyzed to determine the density as a function of theoretical density and to determine final pellet composition. Pellets sintered upon the tantalum or tungsten trays had a density of above 97 percent theoretical density and a composition of UC.sub.1.88. In comparison, pellets sintered upon a graphite tray had a density of about 75 percent theoretical density and a composition of UC.sub.1.95. The results of this example demonstrate the advantages of sintering uranium dicarbide compositions while in contact with carbon accepting materials such as tantalum and tungsten whereby high theoretical densities are obtained. Although, the present invention has been described with reference to specific details, it is not intended that such details should be regarded as limitations upon the scope of the invention, except as and to the extent that they are included in the accompanying claims. EXAMPLE 2 Discs having an initial diameter of 1.0 inch, a thickness of 0.150 inches, and a composition of UC.sub.1.95 were placed between two tungsten plates. The discs were then heated to 2100.degree. C. under an argon atmosphere for 12 hours to sinter to high density. The discs were then analyzed to determine the density as a function of theoretical density and to determine final disc composition. The discs sintered without cracking to a density above 97 percent theoretical density and a composition near UC.sub.1.88. The results of this example demonstrate the flexibility of this technique to fabricate high density large diameter discs.