V. P. Orlovskii

Hydroxyapatite and Hydroxyapatite-Based Ceramics

Data are summarized on the synthesis of hydroxyapatite (HA) by wet-chemical processes, solid-state reactions, and hydrothermal treatment. The conditions for HA preparation via precipitation from solutions of calcium chloride, dibasic ammonium phosphate, and aqueous ammonia are discussed at length. Detailed analysis of the fabrication and properties of calcium-phosphate-based ceramics is presented. The techniques for producing dense and porous HA ceramics are considered. The fabrication and medical applications of HA granules are discussed. Data are presented on HA-based composites.

Synthesis and Structure of Magnesium-Substituted Hydroxyapatite

Magnesium-substituted calcium phosphates with the general formula Ca10 – xMgx(PO4)6(OH)2 (x & 1) are synthesized and characterized by IR spectroscopy and x-ray diffraction. The magnesium ion is found to destabilize the structure of hydroxyapatite: increasing the Mg content from 1 to 10 at. % (in terms of metals) reduces the temperature of the hydroxyapatite–whitlockite transition.

Dielectric characteristics of biocompatible Ca10(PO4)6(OH)2 ceramics

The temperature dependence of the dielectric permittivity and losses of biocompatible Ca10(PO4)6(OH)2 ceramics were studied in a temperature range from 20 to 500°C. An approach to the interpretation of anomalies (bending points) observed in the dielectric characteristics of the ceramic samples is proposed, which takes into account features of the crystal structure of calcium hydroxyapatite and the defects formed in the course of thermal treatments.

Luminescence of Eu3+-Activated Potassium Scandium and Potassium Yttrium Phosphate Vanadates

The photoluminescence spectra of potassium rare-earth phosphate vanadates K3R1 – yEuy(PO4)x(VO4)2 – x(R = Sc, Y) were measured in the range 450–800 nm under excitation at 337 nm. The energies of the Stark components of the 7Fj(j= 0, 1, 2) multiplet were determined, and the crystal-field parameters were evaluated. The effects of the Eu3+concentration and PO43–/VO43–ratio on the luminescence of the materials studied and the concentration quenching of luminescence were analyzed. The materials with high Eu3+concentrations are shown to be potentially attractive as photo- and cathodoluminophors.

Luminescence Spectra of Eu3+-Activated Potassium Lanthanum and Potassium Gadolinium Phosphate Vanadates

The effects of the Eu3+concentration and PO4/VO4ratio on the photoluminescence (PL) of K3R1 – yEuy(PO4)x(VO4)2 – x(R = La, Gd) phosphate vanadates were studied over wide composition ranges. The energies of the Stark components of the 7Fj(j= 0, 1, 2) levels were determined, and the crystal-field parameters were evaluated. The concentration quenching of Eu3+luminescence was examined. The PL intensity was found to increase with Eu3+content up to y= 0.3. At higher Eu3+contents, the PL intensity decreases, without, however, complete luminescence quenching even at y= 1. K3Gd0.7Eu0.3(VO4)2and K3Gd0.7Eu0.3(PO4)0.3(VO4)1.7were found to exhibit the brightest photoluminescence.

Structural–Thermodynamic Model for Synergistic Exchange of Hydroxyl and Fluoride Ions in Apatites with the Participation of the Carbonate Ion

Based on crystal-chemical and thermodynamic data, a model was proposed for the synergistic participation of the carbonate ion in hydroxyl–fluoride ion exchange in the Ca channels of apatites (bony and dental tissue). The synergistic effect of the carbonate ion develops upon partial isomorphic substitution [PO4] groups and consists in equalizing the bonding energies of F– and OH– in the Ca channel.

Exoemission Analysis of Energy Levels in the Surface Layer of Biocompatible Ca10(PO4)6(OH)2

Thermostimulated exoelectron emission from sintered hydroxyapatite (HAP), Ca10(PO4)6(OH)2 , prepared by the alkoxy method was studied in the temperature range 300–800 K. The results were used to determine trap depths, the frequency factor in the Boltzmann probability of thermal release, lifetime of conduction-band electrons, and charge density at active centers in the surface layer of the material. The exoelectron emission data are correlated with earlier thermostimulated current measurements and structural studies of phase transitions in HAP. Possible lines of further research are discussed.

Thermostimulated exoelectron emission during the structural transition in Ca10(PO4)6(OH)2

Thermostimulated exoelectron emission (TSEE) from a biocompatible calcium hydroxyapatite Ca10(PO4)6(OH)2 (CHA) was studied in a temperature range from 20 to 400°C. It was established that the structural transition in CHA is manifested by a sharp increase in the exoelectron emission intensity beginning at 200°C, followed by a peak in the TSEE spectrum.

The effect of mechanical activation on the synthesis of biocompatible Ca10(PO4)6(OH)2

The effect of mechanical activation on the course of reactions involved in the synthesis of calcium hydroxyapatite Ca10(PO4)6(OH)2 was studied; the composition, crystallographic parameters, spectroscopic characteristics, and dielectric properties of the products were determined. The role of the composition of initial components on the rate of synthesis is analyzed.