Mechanochemically Induced Phase Transformation and Leaching of Decay Products from U(IV, VI) Oxide (original) (raw)
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Mechanochemical effects in U 3 O 8
Journal of Radioanalytical and Nuclear Chemistry, 2004
The effect of the mechanical treatment of U3O8 in a planetary ball mill in air or as a suspension in benzene solution of thyolilthreefluoroacetone (TTA) on the nature of the oxide and on the leaching of U and 234Th into diluted aqueous solutions of HCl, Na2EDTA and NaCl has been studied. Transformation of U3O8 to UO2, is much stronger expressed when the mechanoactivation is performed in air is established. The leaching behavior of U and Th depends significantly on the activation mode and on the leaching reagent nature. The role of mechanochemically enhanced UO2-ThO2 solid solution formation for the observed effects is discussed.
Mechanochemistry of the 5f-element compounds Part 4. Mechanochemistry of uranium (IV and VI) oxides
Journal of Radioanalytical and Nuclear Chemistry
The effect of the mechanoactivation on UO3 and U3O8 in agate or stainless steel vessels in air or in toluene is studied. UO2(OH)2 is the main product of UO3.H2O activation in steel vessel in air. The presence of toluene leads to strong amorphization and dispersity increase and, probably, to the formation of U2O5. The activation of U3O8 leads to its reduction to U3O7 which relative content in the reaction mixture depends on the mechanoactivation conditions.
Journal of Radioanalytical and Nuclear Chemistry, 2011
The structure changes and the degree of reduction of U 3 O 8 after mechanoactivation in agate and stainless steel vessels in different media are studied. Clearly expressed reduction of U(IV, VI) oxide, accompanied by oxygen release as a result of mechanochemical activation is observed. The highest degree of reduction is reached when mechanoactivation is performed in suspension with nonpolar organic solvents. The presence of acetaldehyde as a reducing agent did not cause valuable increase of the reduction process. Quantitative evaluation of the mechanochemically induced changes in the crystal structure of U 3 O 8 is done. Decrease of the crystallite sizes of both the U 3 O 8 and the reduced form, provoked by the mechanochemical treatment is observed for all the samples. No other uranium-contained compounds, formed during the mechanoactivation in the different media and mixtures were found.
Journal of Radioanalytical and Nuclear Chemistry, 2011
Method for synthesis of UO 2?x and uraniumthorium mixed oxides by using sol-gel method and mechanochemical activation is proposed. The synthesis of UO 2?x and solid solutions with equal amount of metals or enriched to one of them is performed by external gelation process, thermal decomposition of the sol-gel products in air and subsequent mechanochemical activation in air in stainless steel vessels. The crystal structures of the obtained oxides before and after the mechanochemical treatment are analysed by the use of X-ray diffraction method. Quantitative phase analysis and calculations of the size of the crystallites, lattice parameters, and densities of the oxides are performed by BRASS program for Rietveld calculation. The proposed method leads to decrease of the lattice parameters and thus to higher density of the obtained oxides with crystallites size in the range of 12-16 nm.
Application of mechanochemical activation for synthesis of uranium–lanthanoid mixed oxides
Journal of Radioanalytical and Nuclear Chemistry, 2011
The applicability of mechanochemistry to produce uranium-lanthanoid mixed oxides is presented. Phase homogeneous uranium-cerium solid solutions of the type Ce x U 1-x O 2 (x = 0.3 7 0.95) and polyphase systems containing La y U 1-y O 2?x (y = 0.12) were prepared by mechanochemical activation in air of sol-gel produced precursors. The possibility for synthesis of urania-lanthania solid solution by mechanochemical interaction of La 2 O 3 with sol-gel produced U (IV,VI) oxide is established. The crystal structures of the obtained oxides before and after the mechanochemical treatment are analysed by the use of X-ray diffraction method. The size of the crystallites (8-16 nm), lattice parameters, crystallite strains and densities of the oxides are calculated by BRASS program for Rietveld calculation.
Effects of mechanochemical treatment of ThO2 with UO3 and CеO2
Machines. Technologies. Materials. vol.I, issue 1 (8), 2018
The paper presents the effects of the mechanochemical activation of ThO 2 -UO 3 and ThO 2 -CeO 2 mixtures in air and (for ThO 2 -UO 3 ) in suspension in H 2 O or CHCl 3 . Planetary ball mill (Pulverisette 5, Fritch) with stainless steel triboreactors and milling balls from the same materials are used. Milling for 5 h of the ThO 2 -UO 3 mixture does not affect significantly the crystal structure of the ThO 2 but leads to amorphization of UO 3 , sharp decrease of its crystallites size and increase of the ionic character of the U-O bond. Storage of the activated product (2 months at room temperature) or heating (3 h, 165 o C) leads to partial relaxation of the UO 3 crystal structure. The X-ray diffraction data does not give proves for formation of ThO 2 -UO 3 solid solution. Formation of solid solution Ce 0.6 Th 0.4 O 2 accompanied with some amount of amorphisized ThO 2 , is established as a result of co-milling at the same conditions of the mixture ThO 2 -CeO 2 with a mole ratio 1. XRD-determined lattice parameter (5.
Radiation-induced decomposition of U(VI) phases to nanocrystals of UO2
Earth and Planetary Science Letters, 2005
U 6+ -phases are common alteration products, under oxidizing conditions, of uraninite and the UO 2 in spent nuclear fuel. These U 6+ -phases are subjected to a radiation field caused by the a-decay of U, or in the case of spent nuclear fuel, incorporated actinides, such as 239 Pu and 237 Np. In order to evaluate the effects of a-decay events on the stability of the U 6+ -phases, we report, for the first time, the results of ion beam irradiations (1.0 MeV Kr 2+ ) of U 6+ -phases. The heavy-particle irradiations are used to simulate the ballistic interactions of the recoil-nucleus of an a-decay event with the surrounding structure. The Kr 2+ -irradiation decomposed the U 6+ -phases to UO 2 nanocrystals at doses as low as 0.006 displacements per atom (dpa). U 6+ -phases accumulate substantial radiation doses (~1.0 displacement per atom) within 100,000 yr if the concentration of incorporated 239 Pu is as high as 1 wt.%. Similar nanocrystals of UO 2 were observed in samples from the natural fission reactors at Oklo, Gabon. Multiple cycles of radiation-induced decomposition to UO 2 followed by alteration to U 6+ -phases provide a mechanism for the remobilization of incorporated radionuclides. D
ADVANCES IN PROCESS MATERIALS FOR PRODUCTION OF UO
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article deal with the development of a nano/meso hybrid microstructure by mechanical alloying of stainless steel and titanium powders followed by hot rolled sintering resulting in improved mechanical properties. This is followed by design, fabrication and performance evaluation of a high energy mill and the preparation of nanocrystalline stainless steel powders from powders of iron and ferrochromium by mechanical alloying. On line density determination of MIM parts inside the sintering furnace using model based supervisory control system is another contribution.
High-Temperature Annealing of Natural UO2+x
MRS Proceedings, 1990
ABSTRACTFour powdered samples of natural UO2+x (uraninite) were annealed in a reducing atmosphere up to 1200°C. The initial unit cell parameters ranged from ao=0.5463 to 0.5385 nm. Small amounts of UO2.25 occur in all samples after annealing. Annealing curves show the effects of recovery of point defects in the oxygen sublattice, ordering of U4+ and U6+, vacancy migration in the cation sublattice, and second order phase transformations. The difference in the annealing behavior of UO2+x with x < 0.15 as compared to x = 0.25 between 400 and 700°C is due to ordering of U4+ and U6+. Density increased after annealing except for one sample in which a large number of cavities (1–2 μm in size) formed. Oxidation and chemical composition have a more dramatic effect on the structural state of natural UO2+x than self-irradiation caused by a-decay damage.