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|Section2= |Section3= |Section4= |Section7= |Section8= }} Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is a yellow-orange powder. ==Production and use== There are three methods to generate uranium trioxide. As noted below, two are used industrially in the reprocessing of nuclear fuel and uranium enrichment. # U3O8 can be oxidized at 500 °C with oxygen. Note that above 750 °C even in 5 atm O2 UO3 decomposes into U3O8. # Uranyl nitrate, UO2(NO3)2·6H2O can be heated to yield UO3. This occurs during the reprocessing of nuclear fuel. Fuel rods are dissolved in HNO3 to separate uranyl nitrate from plutonium and the fission products (the PUREX method). The pure uranyl nitrate is converted to solid UO3 by heating at 400 °C. After reduction with hydrogen (with other inert gas present) to uranium dioxide, the uranium can be used in new MOX fuel rods. # Ammonium diuranate or sodium diuranate (Na2U2O7·6H2O) may be decomposed. Sodium diuranate, also known as yellowcake, is converted to uranium trioxide in the enrichment of uranium. Uranium dioxide and uranium tetrafluoride are intermediates in the process which ends in uranium hexafluoride. Uranium trioxide is shipped between processing facilities in the form of a gel, most often from mines to conversion plants. When used for conversion, all uranium oxides are often called reprocessed uranium(RepU).〔http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Transport/Transport-of-Radioactive-Materials/〕 Cameco Corporation, which operates at the world's largest uranium refinery at Blind River, Ontario, produces high-purity uranium trioxide. It has been reported that the corrosion of uranium in a silica rich aqueous solution forms both uranium dioxide and uranium trioxide.〔Trueman ER, Black S, Read D, Hodson ME (2003) "Alteration of Depleted Uranium Metal" ''Goldschmidt Conference Abstracts,'' p. A493 (abstract )〕 In pure water, schoepite (UO2)8O2(OH)12·12(H2O) is formed〔(Schoepite ). Webmineral.com. Retrieved on 2011-07-19.〕 in the first week and then after four months studtite (UO2)O2·4(H2O) was produced. Reports on the corrosion of uranium metal have been published by the Royal Society.〔Ander L, Smith B (2002) "(Annexe F: Groundwater transport modelling )" ''The health hazards of depleted uranium munitions, part II'' (London: The Royal Society)〕〔Smith B (2002) "(Annexe G: Corrosion of DU and DU alloys: a brief discussion and review )" ''The health hazards of depleted uranium munitions, part II'' (London: The Royal Society)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「uranium trioxide」の詳細全文を読む スポンサード リンク
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