E. A. Tkachenko

Preparation of MgO nanoparticles

MgO nanoparticles have been prepared via hydroxide precipitation from aqueous solutions, followed by the thermal decomposition of the hydroxide. The nanoparticles inherit the platelike shape from the hydroxide and break into isometric particles upon significant superheating. The particle size of the synthesized magnesium oxide powders varies from 30 to 75 nm, depending on the annealing temperature.

Lower Rare-Earth Molybdates

Data are summarized on rare-earth molybdates containing Mo in lower oxidation states (including 4+ and 5+) and in the form of clusters. Particular attention is given to the synthesis and structure of the lower rare-earth molybdates.

Nanoporous crystalline material CsLiB6O10

CsLiB6O10 crystals up to 60 × 40 × 20 mm in dimensions were prepared by top-seeded solution growth, and their interaction with water was studied. The crystals were found to be subject to hydration followed by hydrolysis, during which water leaches Cs from the structural channels to yield Cs2B10O16 · 8H2O as the final product. The channel dimensions are not large enough to incorporate ethanol or acetone molecules.

Chemical transformations of basic yttrium nitrates during ultrasonic-hydrothermal treatment

We studied how hydrothermal treatment per se or combined ultrasonic-hydrothermal treatment affects the micromorphology and phase composition of yttrium hydroxonitrates. We show that ultrasonication during the hydrothermal treatment of yttrium hydroxonitrate suspensions of the bulk composition Y(OH)2.53(NO3)0.47 · 0.16H2O produces yttrium oxohydroxonitrate crystals of the composition YO0.25(OH)2.25(NO3)0.25.

Yttrium oxide nanopowders from carbonate precursors

Reactions of solutions of yttrium oxide in nitric acid with a 1.67 M NH4HCO3 solution were studied by direct and back titration. When the concentration of the reacting solution was within 0.031–0.052 mol/L (as Y2O3), yttrium carbonate Y2(CO3)3 · nH2O (n ≈ 2.5) of fibrous or spherulitic morphology precipitated. When the concentration was decreased to 0.022 mol/L, a new phase of platy morphology appeared. Heating these precipitates to 650–680°C yielded yttrium oxide having coherent scattering domain sizes of 40–80 nm. Y2O3 particles retain the precursor morphology.

Evolution of yttria nanoparticle ensembles

The formation of Y2O3 nanoparticles in precipitation from acidic nitrate aqueous solutions, which was done by regulating pH at the expense of their titration with an ammonium hydroxide aqueous solution, was studied. The jellylike precipitates of a (Y2(OH)5NO3 · nH2O, n = 2, 3) precursor lose their volatile components under heating and drying in several stages. Their chemical decomposition terminates at 500–550°C with the formation of the cubic modification of yttria. Yttria particles inherit the platelike morphology of the particles of their precursor. Under further heating, Y2O3 particles lose their nonequilibrium shape due to the decomposition of plates into roundish nanoparticles with the relief of mechanical stresses. The isothermal exposure of nanoparticles formed in this way leads to their stepped agglomeration with a sequential increase in the size of particles by an order of magnitude. The sintering of Y2O3 powders with the formation of ceramics was investigated.

Synthesis of scandium orthoborate powders

Two polymorphs of scandium orthoborate, ScBO3, are synthesized by adding aqueous ammonia to aqueous solutions of scandium nitrate and boric acids and calcining the resulting precipitates. Dehydration of the precipitates reaches completion below 300°C, and further heating leads to highly exothermic crystallization near 750°C. The synthesized ScBO3 powders consist of submicron-sized particles.

Synthesis of yttrium orthoborate powders

Yttrium orthoborate YBO3 is synthesized by calcining precursors precipitated with aqueous ammonium hydroxide from yttrium nitrate or yttrium chloride solutions (with concentrations ranging from 4.8 × 10−3 to 0.0165 mol/L) and with a more than tenfold excess of boric acid. Single-phase YBO3 is obtained at pH 5–6. Higher pHs result in the formation of mixtures of yttrium orthoborate and yttrium hydroxide phases. Dehydration occurs up to 288°C as shown by differential thermal analysis. Further heating induces crystallization. Addition of surfactants (polyvinylpyrrolidone (PVP) or ammonium polyacrylate (APA)) to the starting solution in an amount of 1 wt % of the yttrium salt affects the sizes and shapes of the precipitated particles. YBO3 platelets with nanometer thicknesses are obtained. The temperature of the low-temperature ⇄ high-temperature vaterite phase transition in YBO3 is 977°C upon heating and 640°C upon cooling.