| 摘要 |
Sols of uranous oxide coated with thoria or of thoria coated with uranic oxide are prepared by heating and agitating (e.g. by boiling under reflux) a solution of salts of the respective metals in the presence of a hydrolytic agent slowly liberating ammonia under the process conditions whereby consecutive hydrolysis takes place, and thereafter removing electrolytes from the sol. The sols may thereafter be clad with silica by mixing with a silica sol and adjusting the pH. Suitable hydrolytic agents are urea, ammonium carbamate, potassium cyanate, hexamethylene tetramine, acetamide and formamide, which are preferably used in amount equal to or slightly in excess of the amount required for hydrolysis. Electrolyte-removal generally involves flocculation followed by centrifuging or decantation, redispersion in deionized water and removal of remaining ions in the resultant sol, e.g. by passage through a mixed ion exchange resin bed. For the production of uranous oxide/thoria sols, it is necessary to start with a solution of pH 0.1-0.4, to interrupt the heating after deposition of uranous oxide (about pH 2.8) and to continue heating thereafter until a pH of 3.0-5.0 is reached. For thoria/uranic oxide, the initial solution has a pH of below 2 and heating is terminated when both oxides have formed, at a pH of 4.5-5.0. The sols produced in examples have sizes ranging from 10-150 mm to 40-400 mm . Starting materials are Th(NO3)4 and UO2(NO3)2, and ThCl4 and UCl4. In an example of silica cladding, the final sol is stabilized with NaOH to a pH of 8.
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