The following variables were considered in an investigation of the sintering of uranium dioxide: (1) sintering aids, i.e., small additions of substances that might aid the densification process, (2) soaking temperature, (3) soaking time, (4) furnace atmosphere, and (5) particle size of the uranium dioxide. The incipient sintering temperature, the effect of binders, and the effect of fabricating pressure also were determined. The data obtained in the investigation led to the following optimum conditions for obtaining dense UO2 by cold pressing and sintering: (1) preparing the UO2 as a submicron powder but not fine enough to be pyrophoric, (2) cold pressing at 20 to 30 tons per sq. in. without the use of organic binders, (3) using the following sintering schedule: (a) in H2 to 1400°C., (b) in steam or a wet inert gas from 1400° to 1500°C., (c) in steam or a wet inert gas at 1500°C. for a 1‐hour soak, and (d) cooling in H2 from 1500°C. to room temperature. By following this procedure, pellets of UO2 (3/8 in. in diameter by 1/4 in. high) were obtained that were 97 to 98% of theoretical density.
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