S. V. Kutsev

TiO2 nanoparticles in opal crystals

We have studied the effect of the size factor on the phase composition of fine-particle TiO2 using three-dimensional opal crystals as a system of nanoreactors for sol-gel synthesis of TiO2 · nH2O. The results indicate that the stability region of the thermodynamically metastable TiO2 polymorphs can be extended to higher temperatures.

Ni, Co, Cu, Ni-Co, and Ni-Cu nanoparticles in opal matrices and mesoporous silica gels

NiCo solid solutions and Ni-Cu bimetallic particles have been prepared in opal-matrix nanocomposites by reacting Ni, Co, and Cu double salts and oxides with supercritical (SC) isopropanol. According to X-ray diffraction and transmission electron microscopy data, the nanocomposites have an X-ray amorphous opal matrix and contain crystalline nanoparticles of individual metals, solid solutions, or bimetallic materials of various morphologies in the opal pores. Mesoporous silica gel matrix composites remain X-ray amorphous after treatment in SC alcohols because of the small particle size of the metallic phase, or form solid solutions between Ni and Co silicates. The phase composition of the composites can be controlled by varying experimental conditions.

Hydroxyapatite-Calcium Carbonate Ceramic Composite Materials

Hydroxyapatite/calcium carbonate (CC) composite powders containing up to 50 wt % CO32−, have been prepared via precipitation from aqueous solutions. According to chemical analysis data, the CO32− content of the powders coincides with the intended one over the entire composition range studied. With increasing CO32− content, the specific surface area of the powders decreases because of the formation and growth of large needlelike CC crystals up to 1.5 μm in size. The addition of low-melting-point alkali carbonates to the starting powder mixture reduces the sintering temperature of the powders to below 720°C, thereby preventing the thermal decomposition of CC. The highest bending strength, up to 76 MPa, is offered by the materials with the lowest CC content, about 20 wt %, and an average crystal size of 100 nm. The solubility of the composites gradually increases with CC content. In vitro experiments with a human fibroblast model (MTT test) demonstrate that the composites have zero cytotoxicity.

Phase transformations during the synthesis and sintering of Y2 − xYbxO3 nanopowders

The formation of an Y2O3-Yb2O3 solid solution (8 mol % Yb2O3) during the thermal decomposition of (Y,Yb)2(CO3)3 · 2H2O mixed carbonates obtained by coprecipitation from a nitrate solution has been studied by X-ray diffraction, thermal analysis, and optical microscopy. The results demonstrate that the formation of a cubic yttria-based solid solution begins in the range 470–500°C and reaches completion at temperatures above 1100°C. The unit-cell parameter a of the cubic solid solution and the X-ray density of the corresponding ceramic are 10.5910 Å and 5.349 g/cm3, which corresponds to the intended chemical composition of the isovalent substitutional solid solution: Y1.84Yb0.16O3.

High-temperature hydroxyapatite-titanium interaction

Hydroxyapatite-titanium interaction has been studied in the temperature range 700 to 1200°C with a view to designing biocompatible dispersion-hardened hydroxyapatite-matrix materials for bone implants. The sequence of phase transformations in hydroxyapatite-titanium powder mixtures during heating in air has been identified using IR spectroscopy, differential thermal analysis, and X-ray diffraction. It is shown that hydroxyapatite decomposition can be inhibited via heat treatment in an atmosphere containing carbon monoxide.

Influence of ripening time on the properties of hydroxyapatite-calcium carbonate powders

Abstract80 wt % hydroxyapatite + 20 wt % calcium carbonate composite powders have been synthesized through precipitation from aqueous solutions. Increasing the ripening time of the precipitate in the mother liquor leads to partial calcium carbonate dissolution and the formation of carbonate-substituted hydroxyapatite and improves its crystallinity. In addition, the specific surface area of the powders increases from 83.2 to 238.7 m2/g. The powders ripened for 14 and 21 days show the best sinterability.

Nanocrystalline hydroxyapatite ceramics

The possibility of using high pressures in uniaxial pressing and rolling of nanopowders is investigated. Obtainment of a nanocrystalline hydroxyapatite ceramic intended for use in medicine is studied. The sintering temperature is reduced by approximately 600°C, and a ceramic with a grain size of less than 50 nm and high values of microhardness (up to 5.7 GPa) after annealing at 750°C is obtained. A substantial collective recrystallization of crystallite powder is overcome.

Influence of anions stabilizing the sols in synthesis of powders of highly dispersed titanium dioxide and three-dimensional nanocomposites based on SiO2/TiO2

This paper reports on the results of investigations into the influence of anions (Cl−, SO42−,NO3−), which stabilize the sol-gel synthesis of highly dispersed titanium dioxide, on the crystallization and phase transition of TiO2 upon dehydration. The effect of the size factor on the phase composition of TiO2 in SiO2/TiO2 nanocomposites has been investigated using a three-dimensional opal matrix as a set of nanoreactors for the sol-gel synthesis of TiO2 · nH2O. It has been shown that there is a possibility of extending the region of the existence of a thermodynamically metastable modification of TiO2 (anatase) to the temperature of 1100°C due to the changes in the conditions of the sol-gel synthesis of TiO2 · nH2O.

Magnesium-substituted calcium phosphate cements with (Ca + Mg)/P = 2

The introduction of magnesium ions into bone calcium phosphate cements (CPCs) increases the strength and biodegradation rate of the materials. Cement powders with the (Ca + Mg)/P ratio of 2 and the degree of magnesium substitution for calcium of 0, 10, 20, and 40 wt % were used in the study. Sodium phosphate-based solutions were used as the cement fluids. Depending on the magnesium content, CPCs based on magnesium-substituted apatite and whitlockite phases were obtained. The phase composition, setting time, strength, and microstructure of the cements were determined. An increase in the acidity of the cement liquid was found to give cements with a greater content of amorphous phase and more homogeneous structure, resulting in higher strength.

Colloidal and transparent opal-matrix nanocomposites filled with europium-doped silica sols

Three-dimensional ordered opal-matrix composites filled with europium-doped silica sols have been produced using methods of colloid chemistry. According to elemental analysis data, the Eu concentration in the nanocomposites was ∼30 ppm. A uniform europium distribution over the tetrahedral and octahedral pores of the 3D opal matrix was ensured by repeatedly filling the opal pores with silica sols doped with europium salts or europium oxide. Varying high-temperature annealing conditions, one can control the microstructure of 3D ordered nanocomposites, producing opaline and transparent photonic crystals. The microstructure of opal photonic crystals has the form of an ordered fcc lattice of amorphous silica spheres, whose tetrahedral and octahedral pores are filled with mesoporous europium-doped glass. Partial sintering of the silica spheres and mesoporous glass in transparent photonic crystals results in a periodic arrangement of quantum dots enriched in Eu-doped silica.