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研究了恒电流库仑滴定精密测定UO_2芯块中铀(Ⅳ)、铀(Ⅵ)和铀总量及氧铀比的分析方法。采用磷酸(加入少许氢氟酸)270±5℃的恒温搅拌回流溶样新技术,使样品溶解快而完全。用亚铁将铀(Ⅵ)还原为铀(Ⅳ),精确称量并加入略过量的重铬酸钾标准物质使铀(Ⅳ)氧化,过量的重铬酸钾由电解产生的铁(Ⅱ)进行恒电流库仑滴定。根据氧化铀(Ⅳ)所消耗的重铬酸钾的量计算铀总量。采用270±5℃磷酸在氮气气氛条件下的恒温搅拌回流溶样新技术,使样品溶解快而完全,并能保持铀的价态不变。除不加亚铁将铀(Ⅵ)还原为铀(Ⅳ)外,其它利用同测定铀总量的原理来测定铀(Ⅳ)含量。根据测定的铀总量和铀(Ⅳ)含量结果计算铀(Ⅵ)和氧铀比。测定铀总量的不确定度优于0.035％;测定铀(Ⅳ)的不确定度优于0.025％;测定铀(Ⅵ)的不确定度优于9.03％;测定氧铀比的不确定度优于0.0001 O/U单位。该方法适用于UO_2芯块和粉末及U_3O_8中铀(Ⅳ)、铀(Ⅵ)、铀总量和氧铀比的精密测定。
The analytical method of constant current coulometric titration for uranium (Ⅳ), uranium (Ⅵ), uranium and uranium ratio in UO 2 pellets was studied. Using phosphoric acid (adding a little hydrofluoric acid) 270 ± 5 ℃ constant temperature reflux sampling new technology, the sample dissolved quickly and completely. The uranium (Ⅵ) is reduced to uranium (Ⅳ) by ferrous iron, the uranium (Ⅳ) is precisely weighed and a slight excess of potassium dichromate is added, and the excess iron (Ⅱ) produced by electrolysis of potassium dichromate is oxidized. Constant current coulometric titration. The total amount of uranium is calculated from the amount of potassium dichromate consumed by uranium (Ⅳ) oxide. Using 270 ± 5 ℃ phosphoric acid in a nitrogen atmosphere at constant temperature stirring reflux reflow new technology, the sample dissolved quickly and completely, and can keep the uranium valence unchanged. In addition to not adding uranium (Ⅵ) to uranium (Ⅵ), the other with the determination of uranium (Ⅳ) by the same principle. Uranium (Ⅵ) and oxy-uranium ratios were calculated from the results of the total uranium and uranium (Ⅳ) contents determined. Uncertainty in the determination of total uranium is better than 0.035%, Uncertainty in determination of uranium (Ⅳ) is better than 0.025%, Uncertainty in determination of uranium (Ⅵ) is better than 9.03%, Uncertainty in determination of uranium-uranium ratio At 0.0001 O / U units. The method is suitable for the precise determination of uranium (Ⅳ), uranium (Ⅵ), total uranium and uranium ratio in UO_2 pellets and powders and U_3O_8.