The characteristics and behavior of depleted uranium tetrafl uoride obtained by different methods in the process of solid-phase conversion into uranium oxides using mechano-activated crystalline and x-ray amorphous silica in oxygen-containing and inert media in the absence of mixing of the components are compared. It is found that the reactivity of depleted uranium tetrafl uoride obtained by the reduction of depleted uranium hexafl uoride by unsaturated organic halogen derivatives and hydrogen in a fl uorohydrogen fl ame is actually no different, and the solid-phase reaction products UO 2 and U 3 O 8 inherit the morphological features of the initial uranium tetrafl uoride.A significant amount of depleted uranium hexafluoride has been accumulated over more than a half-century of development of nuclear power and its storage in steel containers on open sites is an environmental hazard. An alternative method of storage is to convert the uranium hexafluoride into safer forms -uranium tetrafluoride or oxides.As part of a Ministry of Education and Science Project (No. 13.G25.31.0051), the Mendeleev Russian University of Chemical Technology has developed a process for converting depleted uranium tetrafluoride obtained by reducing depleted uranium hexafluoride by unsaturated organic halogen derivatives (OTFU-1) into uranium oxides by means of mechano-activated silica. The conversion process gives a high yield of monophase uranium oxides and high-purity silicon tetrafluoride.While studying the regularities of the solid-phase interaction in the system OTFU-1-silicon in the absence of mixing of the components, it was found that the nature of the silicon largely determines the temperature interval of the precipitation of silicon tetrafluoride [1,2]. In terms of the effectiveness of the influence on the conversion of uranium hexafluoride into uranium oxide (rate and yield of the reaction), the forms of silicon studied form the following sequence: quartz -cristobalite -x-ray amorphous silica. It was also found that owing to the Hedvall effect -the polymorphic transition of quartz into metastable β-cristobalite -the mechano-activation of quartz, including in the presence of stimulating additives, makes it possible to lower by 150-200°C the temperature of the solid-phase conversion of OTFU-1 into uranium oxides [2][3][4][5]. The solid products obtained were comprised of multiphase nanostructured uranium oxides, which inherited the morphological features of the reagents [2].American researchers also observed the inheritance of the morphology of one of the components of the systemdepleted uranium tetrafluoride -by uranium oxide [6]: U 3 O 8 particles -the products of the conversion of depleted uranium tetrafluoride (obtained by the hydrogen reduction of depleted hexafluoride) with the participation of diatomaceous earth (x-ray amorphous silica) inherited the morphological features of the initial depleted uranium tetrafluoride (spherical particles with diameter 1-10 μm). Complete conversion was attained at temperature 150°C higher t...
It is shown that the method of synthesis of precursors by spraying hot highly concentrated with respect to zirconium solutions into concentrated solutions of ammonia permits obtaining in combination with mechanical working under optimal conditions nanopowders of partially stabilized zirconium dioxide (PSZD), from which a ceramic with high mechanical strength (800 MPa) can be obtained even by consolidating powder by semidry pressing. The effect of the synthesis temperature of hydroxides on the characteristics of the powders and ceramic is studied.Materials based on zirconium dioxide partially stabilized (PSZD) by yttrium, magnesium, and calcium oxides are used to fabricate high-density, high-strength ceramic, refractories, and special-purpose composites -solid electrolytes for high-temperature fuel elements, parts for electrochemical generators and hydroabrasive cutting tools, end seals and valves in pumps for pumping corrosive liquids, milling bodies for "clean" mills, frameworks for dental prostheses, and other applications.Considering the multistage structure of ceramic technology, where each preceding stage influences the subsequent stages, as well as numerous and often contradictory requirements for powders for ceramic with high mechanical strength (chemical purity, high dispersity, low agglomeration, nearly spherical particle shape, activity with respect to sintering, and others), precursors must be obtained by methods that give the required powder quality already at the initial stages of the technological scheme, especially when the powders are consolidated by semidry pressing and sintering (SDPS). The problem of obtaining high-quality articles from PSZD can be solved by using nanodispersed powders.Of the large number of known methods of obtaining zirconium hydroxides the most suitable one for obtaining nanopowders of precursors is, in our opinion, spraying a heated highly concentrated solution into water solutions of bases, as developed by E. S. Lukin and colleagues in 1980 at the D. I. Mendeleev Russian Chemical Technology University [1]. The use of the spraying method in combination with mechanical activation of a precursor makes it possible to obtain PSZD powders with particle size of several tens of nanometers [2]. Ceramic with bending strength s b to 2500 MPa has been obtained from such powders using additional pressing in a hydrostat and sintering in a gasostat at temperature 1400 -1500°C [2].The objective of the present work is to determine the possibility of fabricating ceramic with high mechanical strength by the SDPS method from precursors obtained by spraying solutions [1].Chemically pure ZrOCl 2 × 8H 2 O (OKhTs) was used as the initial zirconium compound. Chemically pure YCl 3 × 6H 2 O was used as the compound of the stabilizing element (3% 3 Y 2 O 3 ).The PSZD precursors -highly dispersed mixed zirconium-yttrium hydroxides -were obtained by spraying a
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