A. G. Veresov

Study of electrochemical lithium incorporation to whisker structure based on barium-vanadium bronze BaV8O21-δ

Both nanobands and macroscopic (up to 3mm-long) filamentous conducting BaV8O21-δ crystals are prepared for the first time by hydrothermal processing of polymerized gels. They show stable electrochemical characteristics acceptable for their usage in newly elaborated secondary cells (batteries).

Comparative analysis of the bioactivity of materials

Bioactive materials are characterized by a high rate of formation of a carbonate-containing hydroxyapatite contact layer at the implant-bone interface and by a moderate resorption capacity in weakly acidic media. In vitro tests simulating the precipitation of hydroxyapatite from interstitial tissue fluid at the surface of a material are performed to evaluate the bioactivity of a broad range of materials. The data indicate that the silicon-containing material is characterized by the highest bioactivity in the series of calcium hydroxyapatites.

On calcium phosphate bio-cements

The prospect of clinical applications of bio-cements in bone implantation and tissue substitution implies strict requirements as regards material reliability and robustness. We suggest a technique to enhance the mechanical properties of bio-cements based on α-Ca3(PO4)2. Various types of mechanical testing, including compressive deformation analysis, proved that the most robust bio-cement might be fabricated of α-TCP and 1% chitosan. The kinetics of transformation in experiments was considered in order to define the best selection of substance ratios and terms of stabilization. It is essential to increase the ultimate strength and other properties so that they are close to those of cortical bone and this was achieved with the additives chitosan and hydroxyapatite nanoparticles.

Chemical and morphological modifications of filamentary crystals of the Ba6Mn24O48 manganite with a tunnel structure

Filamentary crystals of the Ba6Mn24O48 manganite with a tunnel structure are synthesized in the protonated form for the first time. The protonated form of the whiskers is characterized by the formation of labile Mn-OH bonds, an increased value of the average oxidation number of manganese, and an anisotropic compression of the lattice in the direction perpendicular to the direction of the structural tunnels. These processes are accompanied by substantial changes in the micromorphology of whiskers, specifically by the splitting of the whiskers into 20-to 50-nm-thick nanofibers.

On the phase decomposition of Bi2Sr2CaCu2O8

One of the ways to increase pinning force in superconductors is to create small precipitates of secondary phases in the bulk matrix. The samples of superconductor Bi 2.18 Sr 3-x Ca x Cu 2 O 5 with different compositions have been decomposed according to the phase diagram of the BiO 1.5 -SrO-CaO-CuO system. The study showed that microstructure of samples and critical parameters were changed.

Biocompatible Ceramics for Implants Based on Calcium Phosphates

Hydroxyapatite (HAp), tricalcium phosphate (TCP) and calcium pyrophosphate (CPP) are known to be among calcium phosphates used in clinical medicine due to their biocompatibility. HAp and other complex calcium phosphate salts are the end-products of the biological mineralization process. Calcium pyrophosphate Ca 2 P 2 O 7 (β-CPP) is one of the intermediate products involved in this process. The biological response with respect to new bone formation is quite similar for CPP and HAp. Sintered CPP has better biological responses, and, thus, a great potential as a biodegradable bone substitute. The rate of biodegradation depends on: (i) material texture (porosity type and level), (ii) quality of biodegradation phase (phase composition, grain size, properties of grain boundaries). Several sources for CPP phase in ceramics can be assumed. CPP phase may come from frit (CaO-P 2 O 5 , Ca/P=0.2-0.75) used as a sintering additive. Ceramics can be fabricated from powder of CPP with Na 4 P 2 O 7 as sintering additive, via interaction between H3PO4 or (NH4)2HPO4 and porous HAp at high temperature after soaking it in the former solutions. The aim of the present work was focused on fabrication of multiphase ceramics with enhanced resorptivity due to presence of CPP phase and investigation of processes leading to formation of the multiphase ceramics based on HAp and CPP originated from CaHPO 4 . Ceramic materials have been made from mixtures of powders of stoihiometric HAp (Ca/P=1.67) and monetite (CaHPO 4 , Ca/P=1). Powders of HAp and monetite were synthesized by means of wet chemical precipitation from aqueous solutions of Ca(NO 3 ) 2 *4H 2 O and (NH 4 ) 2 HPO 4 at 60 °C and pH=9 for HAp and pH=4-5 for monetite. Component ratio HAp:monetite was varied from 0:100 to 100:0 % with a step of 20%. Powders of raw materials and the mixtures were tested by means of XRD, TG, DTG, SEM, dilatometry. Linear shrinkage, density and microstructure of samples of ceramic materials sintered at 900, 1000, 1100°C with isothermal holding during 6 hours were tested. Complicated consequence of phase transformations took place during heating the the mixtures from 20 to 1200 C. The CPP (Ca/P=1, converted from CaHPO 4 at 400-500°C ) reacts with HAp (Ca/P=1.67) causing additional weight loss in the region of 600-1050°C due to solid state reaction leading to TCP (Ca/P=1.55) formation. Linear shrinkage of HAp at 1100°C after 6 hours was found to be about 21%; for Ca 2 P 2 O 7 formed from monetite, and for the mixtures - less than 11%. Resulted ceramics with the phase composition of HAp, CPP and TCP, i.e. with a different content of degradable phase and different ratio of CPP/TCP, can be treated as a biocompatible bioactive material with a tunable rate and limit of biodegradation.