Sorption Concentration of Radiocesium on NaX Zeolite Modified with Cu2[Fe(CN)6]

Sorption of ¹³⁷Cs on NaX zeolite modified with Cu₂[Fe(CN)₆] was studied under dynamic conditions.     

The influence of the nature and features of carrier on activity and efficiency of catalyst in reaction of nitrous oxide decomposition

Data of activity of rhodium catalysts prepared on different carriers in reactions of nitrous oxide decomposition is presented; this data gave the possibility to choose the most promising carrier for the elaboration of the catalyst of nitrous oxide decomposition and to use it in high energy plants such as micro rocket engines of space shuttles management systems.     

Fine sructure of Na5Lu9F32 nanocrystallites formed at the initial stages of crystallization

X-ray diffraction investigations have demonstrated that the initial stages of the formation and growth of Na₅Lu₉F₃₂ nanocrystallites from a powder mixture of lutetium fluoride, ammonium fluoride, and sodium fluoride during the solid-phase synthesis are accompanied by complex structural transformations, among which a cyclic transformation of the type single-phase → two-phase → single-phase state can be distinguished. It is shown that the two-phase state consists of two isomorphous phases with a small misfit of the lattice parameters. The isomorphous phases have common extended interphase boundaries, along which a continuous change of the lattice parameters occurs as one phase transforms into the other. A long-term annealing of the two-phase state leads to the final single-phase state, which is characterized by the growth of nanocrystallites to the scale of microcrystallites.     

Specific features of the effect of dopants on the phase formation of YBO3 and ScBO3 during synthesis from the amorphous precursor state

The effect of dopants on the structural states of the YBO₃ and ScBO₃ borates during sequential isothermal annealings of the amorphous precursor state and the batch from a mixture of micropowders of initial rare-earth metal oxides of the same composition has been investigated using X-ray diffraction. It has been demonstrated that, in both cases, the phase sequences of rare-earth metal borates differ substantially from each other. Possible factors responsible for the strong effect of dopants on the structural sequences during the synthesis of the YBO₃ and ScBO₃ borates from the amorphous precursor state have been analyzed.     

Structural infection and anomalous phase sequences in complex oxides prepared from nanodispersed components

The complex oxides prepared by solid-phase synthesis from nanoscopic components are studied using X-ray diffraction. It is demonstrated that the use of nanoscopic components in the solid-phase synthesis of lutetium borate LuBO₃ and europium molybdate Eu₂(MoO₄)₃ leads to anomalous sequences of phase transformations in these compounds: the vaterite ⇒ calcite ⇔ vaterite sequence for LuBO₃ and the β ⇒ α ⇔ β sequence for Eu₂(MoO₄)₃ are observed instead of the previously known sequences, namely, the calcite ⇔ vaterite sequence for LuBO₃ and the α ⇔ β sequence for Eu₂(MoO₄)₃. The revealed anomalous sequences do not depend on the procedure used for preparing reactants and are determined by the nanoscopic sizes of the initial components. It is found that microscopic additions of a number of simple oxides can suppress the kinetics of solid-phase synthesis of particular complex oxides and initiate the formation of new phases in the synthesis of other complex oxides (the so-called structural infection effect).

     

“Isomorphous” phases in nanodispersed powders of rare-earth oxides

Using x-ray diffraction, a structural state consisting of two “isomorphous” phases was revealed in nanocrystalline powders of simple oxides Re ₂O₃ (Re = Eu, Gd, La, Lu) and Y₃Ga₅O₁₂ prepared by solvent thermolysis from simple-oxide solutions followed by annealing of obtained precursors at elevated temperatures. A model is proposed explaining such two-phase states in terms of the excess energy of nanograin surface layers which causes the formation of a surface phase isomorphous to the core phase having a smaller lattice parameter. Analogous two-phase states were also obtained in microcrystalline LuBO₃ and Eu₂(MoO₄)₃ powders subjected to long-term grinding.     

Anomalous structural states of rare-earth oxides in solid-phase synthesis during continuous heating

The kinetics of solid-phase synthesis of complex rare-earth (RE) oxides from an amorphous precursor state during continuous heating is studied by X-ray diffraction. Using the synthesis of RE borates (ReBO₃) as an example, it is shown that a continuous heating of such precursors stimulates the formation of new phases which are unknown in an equilibrium state of one rare-earth element but known for other rare-earth borates. It is established that the regime of continuous heating during solid-phase synthesis of garnets (Re ₃ M ₅O₁₂) exhibiting the only crystal phase state for all rare-earth atoms results in an accelerated growth of crystallites and that the higher the heating rate the higher the growth rate.     

Stable tetragonal HTSC Fe-doped 1-2-3 phase with oxygen excess

Mössbauer study was performed on the YBa₂Cu_2.95Fe_0.05O _y compound prepared in three different states: orthorhombic phase with y7, tetragonal non-superconducting phase with oxygen deficiency, and a new tretragonal superconducting phase with oxygen excess (y>7). The new synthesis method was used for preparation of the Fe-doped YBa₂Cu₃O _y (named 1-2-3) compound. The comparison of Mössbauer spectra of three different states allowed us to identify the oxygen environments of the Fe atoms in the Cu1 positions.     

Structure of precursors of complex oxides of rare-earth elements prepared by solvent thermolysis

X-ray diffraction and electron microscopy were used to study the structural states of precursors of borates LuBO₃, YBO₃, and EuBO₃, garnets Lu₃Al₅O₁₂ and Y₃Al₅O₁₂, and perovskites LuAlO₃ and LaAlO₃ prepared by solvent thermolysis from a nitric-acid solution or an ammonium nitrate melt solution of simple oxides and nitrates of rare-earth elements. The precursors are mainly found to be amorphous. In some cases, small amounts of non-reacted initial oxides and nitrates are observed to be in an amorphous matrix.     

Catalytic properties of molybdena-alumina catalysts pretreated at high temperatures

The dependence of the catalytic properties of molybdena-alumina catalysts reduced in hydrogen on the degree of reduction were followed in a model catalytic reaction of deuterium exchange in benzene. The reaction rate constant and the multiplicity factor decrease as the degree of reduction and the degree of dehydroxylation of the catalyst's surface increase.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1204–1207, July, 1994.