V. P. Sirotinkin

Preparation of octacalcium phosphate from calcium carbonate powder

We have studied a process for the preparation of apatite precursors through calcium carbonate conversion into dicalcium phosphate dihydrate, which is then hydrolyzed to octacalcium phosphate. The process enables the preparation of both phase-pure octacalcium phosphate and calcium phosphate mixtures with variable dicalcium phosphate dihydrate : octacalcium phosphate and hydroxyapatite : octacalcium phosphate ratios.

Structural changes during the hydrolysis of dicalcium phosphate dihydrate to octacalcium phosphate and hydroxyapatite

Powders prepared through dicalcium phosphate dihydrate (DCPD) hydrolysis to octacalcium phosphate (OCP) and hydroxyapatite (HA) in an aqueous sodium acetate solution have been characterized by X-ray diffraction. The lattice parameters of the synthesized OCP and HA phases have been determined as functions of holding time at synthesis temperatures of 37 and 60°C. The structure of the HA obtained through hydrolysis at 60°C has been refined, and the distortion of the elements of the crystal lattice of this compound has been assessed in terms of Baur indices. A model has been proposed for the heterogeneous nucleation and growth of the OCP phase on DCPD crystals, in which the structure of these compounds is represented as made up of groups similar in structure to Posner regions.

Phase composition of Al2O3 nanopowders prepared by plasma synthesis and heat-treated

We present X-ray diffraction data for Al2O3 nanopowders prepared by oxidizing aluminum powder in an air plasma, followed by size separation via centrifugation and heat treatment.

Structure of hydroxyapatite powders prepared through dicalcium phosphate dihydrate hydrolysis

We have studied the structure of hydroxyapatite (HA) powders prepared by hydrolyzing dicalcium phosphate dihydrate (DCPD) in an aqueous sodium acetate solution at a temperature of 60°C for 16 h or a longer time. The results demonstrate that the HA in the powders has a distorted structure. The Baur’s distortion index for the PO4 tetrahedra is DI(TO) ≃ 0.03, whereas hydroxyapatite single crystals have DI(TO) ≃ 0.005. The powders are similar in structural parameters to calcium-deficient HAs: they have Ca/P ≃ 1.6 and an imperfect substructure (crystallite size of ≃30 nm) and contain sodium impurities. The structural features of the HA powders are analyzed in the context of their ability to biodegrade (dissolve).

X-Ray diffraction study of the microstructure of C60 fullerite powder after grinding in a planetary ball mill

The profiles of diffraction peaks of C60 fullerite were used to follow changes in the microstructure of C60 powder during grinding in a planetary ball mill at a rotation rate of 500 rpm and milling time of 8 h. The results demonstrate that grinding for just 1 h leads to a significant decrease in crystallite size. With increasing milling time, the average crystallite size varies little, whereas the lattice strain increases considerably.

Microstructure analysis of tungsten nanopowders by Williamson-Hall method using diffractometer with high-speed detector

Microstructural characteristics of tungsten nanopowders were determined by the Williams-Hall method from the experimental data obtained using an Ultima IV diffractometer with high-speed detector. The effect of the change in the slit size limiting the divergence of the incident beam on the tungsten diffraction peak profiles was investigated. It was shown that insignificant changes in the profile characteristics affect only slightly the results of microstructural analysis.

Evolution of the calcium hydroxyapatite crystal structure under plasma deposition and subsequent reducing treatment

The structure of hydroxyapatite plasma coatings on a titanium substrate has been investigated by the X-ray Rietveld method. The hydroxyapatite crystal structure in plasma-deposited samples is characterized by strong distortions of its main element (tetrahedral PO4 cluster) and coordination calcium polyhedra, as well as calcium deficit in the Ca2 site; however, these features do not change the main motif of the hydroxyapatite structure. The bond distortions in PO4 clusters are estimated by the Bauer method. It is shown that hydrothermal treatment leads to the almost complete recovery of the hydroxyapatite structure.

Effect of Deuterium Plasma Irradiation on V–Ga Alloys

Indentation tests are used to investigate the effect of high-power nanosecond deuterium ion pulses (~100 keV, ~1010 W/cm2) and dense deuterium plasma (~100 eV, ~107 W/cm2) generated by a Plasma Focus machine on the mechanical properties of vanadium-based alloys such as V–5Ti–5Cr, V–5Ga–5Cr, V–5Ga, and V–5Ga–0.1Ce. It is established that the V–Ga–Cr alloys have a higher resistance to embrittlement during radiation-thermal exposure than that of V–Ti–Cr alloys. X-ray diffraction analysis shows that the structure of solid solution is retained in all investigated alloys after pulsed ion and plasma irradiation. No signs of solid solution decomposition and the precipitation of second phases are found. It is established that pulsed ion-plasma irradiation suppresses the rolling texture that is typical of the alloys in the initial state and decreases the lattice parameter of the alloys, which in the case of the V–Ga alloy can be explained by the escape of gallium from the recast surface layer. Doping with a rare earth element (cerium) increases the radiation resistance of the V–Ga alloy, which results in the stability of the mechanical properties and the lattice parameter after irradiation.

X-ray investigation of the powders of tricalcium phosphate exposed to processing in planetary mill

Using the Rietveld X-ray method, the powders of tricalcium phosphate (α-TCP) were analyzed after their treatment in a planetary mill in various liquids (butanol, isobutyl alcohol, acetone, and ethanol). No features of the decomposition of α-TCP were detected and the parameters of its atomic-crystal structure did not change significantly. The reduction of the coherent scattering domains (DS) (d ~ 800 Å) was a major contribution to X-ray line broadening, while its value did not depend on physical properties of liquids. Particles dispersed during their processing in the mill owing to their brittle destruction by chipping. After 60 min of powder processing in butanol, mean particle size decreased by a factor of five (from 9.7 to 2 μm). After annealing at 1300°C, the fluorohydroxyapatite phase was detected in powders, whose formation was assisted by the impurities from fluorine-containing structural elements of the mill.

Formation of composite scaffolds based on chitosan and calcium phosphate

Composite materials based on chitosan and calcium phosphates with the structure and properties close to those of natural human tissues were developed. The possibility of formation of biological apatite, i.e., octacalcium phosphate, was demonstrated. The increase in the strength characteristics was caused by crystallization of the octacalcium phosphate phase on the surface of the material pore space. The materials resemble the extracellular matrix of the body in their structure and composition and can find wide use in the regenerative medicine as a scaffold for osteogenic factors.