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.

С использованием прямого и обратного титрования исследовано взаимодействие растворов оксида иттрия в азотной кислоте с 1.67 М раствором NH4HCO3. При концентрации исходного раствора 0.031–0.052 моль/л (в расчете на Y2O3) в осадок выпадает карбонат иттрия Y2(CO3)3 · nH2O (n 2.5) волокнистой или сферолитной морфологии. При уменьшении концентрации до 0.022 моль/л образуется новая фаза пластинчатой морфологии. Нагревание осадков до 650–680°С приводит к образованию оксида иттрия с размером областей когерентного рассеяния 40–80 нм. Частицы Y2O3 сохраняют морфологию прекурсоров.

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.

Получены наночастицы MgO методом осаждения из водных растворов с последующим термическим разложением гидроксида. Наночастицы MgO наследуют пластинчатую форму частиц гидроксида и превращаются в изометрические частицы при значительном перегреве. Нанопорошки оксида магния имеют с размеры от 30 до75 нм в зависимости от температуры отжига.

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.

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.

Two polymorphs of scandium orthoborate, ScBO 3 , 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 ScBO 3 powders consist of submicron-sized particles.

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 (NO 3 ) 0.47 · 0.16H 2 O produces yttrium oxohydroxonitrate crystals of the composition YO 0.25 (OH) 2.25 (NO 3 ) 0.25 .

Differential thermal analysis and visual polythermal analysis are used to study phase equilibria in the BaO-BaB2O4 system. The following compounds are formed in the system: Ba5B4O11 (which melts peritectically at 1170 +/- 10 degrees C), Ba3B2O6 (which melts congruently at 1390 +/- 10 degrees C), and Ba4B2O7 (which decomposes in the solid state at 1190 +/- 10 degrees C).

Indium orthoborate InBO3 was synthesized through calcining the precipitate after reacting ammonium hydroxide with an aqueous solution of indium nitrate and metaboric acid. The dehydration leads to amorphism. Subsequent heating induces crystallization with a strong exotherm at ca. 700 degrees C. Broadening of the X-ray diffraction reflections from InBO3 shows grain sizes of 70-95 nm.

Conditions are optimized for top-seeded solution growth of bulk indium orthoborate, InBO3 , crystals using the Na2O–BaO–B2O3 flux system. InBO3 has a hexagonal unit cell and is isostructural with calcite; a= 4.812 Å, c = 15.47 Å, microhardness of 11 ± 0.70 GPa. InBO3 crystals are essentially insoluble in common organic and inorganic solvents.

The interaction of rare-earth molybdates of composition LnMoO(4) (Ln = La, Nd, Gd, Dy, Er) with sulfur is studied. Gadolinium molybdate yields a single-phase product. Its unit cell parameters were calculated from indexing of its X-ray diffraction pattern. The thermal stability of the interaction products of LnMoO(4) with sulfur is studied.

Spontaneous NaBa4(BO3)(3) crystals were grown from BaO-B2O3-Na2O fluxed melts. The compound melts at 1260degreesC. It was structurally studied using X-ray diffraction (R = 0.035 for 606 reflections). The crystals are cubic with a = 15.783 Angstrom, Z = 16, space group 1a3d. The structure is a framework built of face- and edge-sharing barium octatopes and hexatopes. The Na and B atoms reside in framework voids. The borate anions exist as isolated triangles. The Na atoms are oxygen six-coordinated. Phase equilibria along the Ba3B2O6-NaBaBO3 stable join were studied.

Mechanical properties and the grain size of alloy D16ch and 1163 used for the sheeting of aircraft fuselages after 21% and 74% deformation and different kinds of heat treatment are studied. The effect of the modes of intermediate, preliminary, and final annealing operations on the grain size is determined. Recommendations are given for providing a small grain size.