S. S. Balabanov

Self-propagating high-temperature synthesis of Y2O3 powders from Y(NO3)3x(CH3COO)3(1 − x) · nH2O

We have studied the self-propagating high-temperature synthesis (SHS) of yttrium oxide from Y(NO3)3x(CH3COO)3(1 − x) · nH2O (0.3 ≤ x ≤ 0.7) acetate nitrates, calculated their standard enthalpies of formation using the method of valence states of atoms in a chemical compound, and compared calculated and experimentally determined yttrium oxide SHS temperatures. Using thermogravimetry and differential scanning calorimetry data and thermodynamic analysis, we have determined the optimal range of yttrium acetate nitrate compositions for the SHS of Y2O3 powder.

Effect of magnesium aluminum isopropoxide hydrolysis conditions on the properties of magnesium aluminate spinel powders

We have studied the influence of the conditions of hydrolysis of the magnesium aluminum double alkoxide MgAl2(OPri)8 and the heating rate and calcination temperature of aluminum magnesium hydroxides on the particle size and morphology of magnesium aluminate spinel powders. Conditions of the two-step process have been identified that make it possible to reproducibly prepare MgAl2O4 nanopowders with controlled properties. We have obtained MgAl2O4 powders ranging in specific surface area from 2 to 160 m2/g.

Synthesis and Properties of Yttrium Hydroxyacetate Sols

We report a process for the preparation of yttrium hydroxyacetate sols by sonicating yttria nanopowder in aqueous acetic acid. The dependences of the rheological characteristics and electrokinetic potential of the sols on the pH of the medium and the concentration of chloride and sulfate anions are used to identify the mechanism underlying the coagulation stability of the sols. The thermal decomposition of the yttrium hydroxyacetate xerogel obtained by drying the sol is analyzed in detail.

Obtaining Nanodisperse Powders of Neodymium-Activated Yttrium Aluminum Garnet by Self-Propagating High-Temperature Synthesis Method

Nanosized slightly agglomerated powders of neodymium-activated yttrium aluminum garnet (YAG:Nd) were obtained by a self-propagating high-temperature synthesis method. An increase in content of reducing substituents in metal-organic complexes as compared to oxidizing substituents leads to an increase in average size of the forming grains from 23 to 70 nm; thereupon, a decrease in powder agglomeration degree is observed. Firing of x-ray amorphous powders results in formation of polycrystalline YAG:Nd without forming intermediate phases.

Preparation of weakly agglomerated yttrium aluminum garnet powders by burning a mixture of yttrium aluminum hydroxynitrates, urea, and acetic acid

We have optimized the composition of a mixture of aluminum yttrium hydroxynitrates, urea, and acetic acid for the self-propagating high-temperature synthesis of yttrium aluminum garnet (YAG) powder. The powder prepared in this way offers a low degree of agglomeration, and the ceramic produced from it has a low carbon content. A technique has been proposed for carbon determination in YAG ceramics through gas chromatographic analysis of the gaseous products of carbide hydrolysis after the dissolution of the ceramic in pyrophosphoric acid.

Effect of Ligand Environment on the Physicochemical Properties of Aluminum Alkoxide Mixtures

This work examines the effect of ligand environment on the physicochemical properties of aluminum alkoxides containing different numbers of primary, secondary, and tertiary alkoxy groups. It is shown that aluminum alkoxides containing equal numbers of alkoxy groups differing in electronegativity are always crystalline. At other ratios, crystallization is kinetically hindered or impossible. Hydrolysis of aluminum alkoxides by atmospheric moisture leads to the formation of amorphous alcohol-containing products, which dissolve in water in the presence of nitric acid to form aluminum hydroxide sol. The hydrolysis products convert to α-Al2O3 starting at 1190°C, without γ-Al2O3 formation, as distinct from the products obtained via alkoxide hydrolysis by water in liquid phase.

Self-propagating high-temperature synthesis of Lu2O3 powders for optical ceramics

A technique has been developed for the self-propagating high-temperature synthesis of lutetium oxide (Lu2O3) powders using citric acid, glycine, and lutetium acetate as fuels. We have carried out thermodynamic analysis of synthesis conditions and examined the effect of the nature of the fuel on the properties of the resultant powders. Using vacuum sintering at a temperature of 1780°C and powders prepared with glycine as a fuel and containing 25 mol % yttrium oxide and 5 mol % lanthanum oxide as sintering aids, we have obtained transparent lutetium oxide-based ceramics.

Effect of the Composition of Starting Yttrium Aluminum Hydroxide Sols on the Properties of Yttrium Aluminum Garnet Powders

A technique has been developed for the synthesis of yttrium aluminum garnet sols aggregationstable in water as a dispersion medium. Depending on the type of precursor used, the temperature of yttrium aluminum garnet formation varies from 900°C to 1100°C. We have obtained yttrium aluminum garnet nanopowders with an average particle size from 40 to 300 nm, depending on the aluminum yttrium hydroxide hydrosol synthesis procedure and annealing temperature.

Transparent Ceramics Prepared from Ultrapure Magnesium Aluminate Spinel Nanopowders by Spark Plasma Sintering

We have studied the properties of transparent magnesium aluminate spinel ceramics prepared by spark plasma sintering (SPS) of ultrapure nanopowders. The starting powders, of ≃ 99.98% purity, ranging in specific surface area from 30 to 160 m2/g, were prepared through the hydrolysis of alcoholic solutions of magnesium aluminum alkoxide complexes, followed by calcination at temperatures from 900 to 1100°C. SPS was carried out at 1450°C, with the holding time at the highest temperature not longer than 15 min. The transparent ceramic samples thus prepared have a transmission of up to 73% in the visible and IR spectral regions (λ = 2.5–5.0 µm). The crystallite size in the ceramics is 0.2–0.4 µm, and their microhardness is HV0.1 = 14.8–16.2 GPa.