Vladimir Fedorovich Komarov

Electron microscopy of biomaterials based on hydroxyapatite

Three types of biomaterials based on hydroxyapatite are synthesized and investigated. Hydroxyapatite nanocrystals or microcrystals precipitated from low-temperature aqueous solutions serve as the initial material used for preparing spherical porous granules approximately 300–500 μm in diameter. Sintering of hydroxyapatite crystals at a temperature of 870°C for 2 h or at 1000°C (for 3 h) + 1200°C (for 2 h) brings about the formation of solid ceramics with different internal structures. According to the electron microscopic data, the ceramic material prepared at 870°C is formed by agglomerated hydroxyapatite nanocrystals, whereas the ceramics sintered at 1200°C (with a bending strength of the order of 100 MPa) are composed of crystal blocks as large as 2 μm. It is established that all the biomaterials have a single-phase composition and consist of the hydroxyapatite with a structure retained up to a temperature of 1200°C.

Study of synthetic hydroxyapatite by the method of high-resolution transmission electron microscopy: morphology and growth direction

AbstractHydroxyapatite crystals grown from aqueous solutions have been studied by the methods of high-resolution electron microscopy and transmission electron diffraction. Processing of the experimental electron micrographs with the use of the Digital Micrograph program and the study of the corresponding Fourier trans-forms showed that the submicron microcrystals grow mainly along the [0001] direction. The (0001) and the

Adsorption inhibition of the growth of CaSO4 · 2H2O crystals in aqueous solutions

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Method for producing a suspension of hydroxylapatite

planes are perpendicular and parallel to the long edge of the crystals, respectively. The good accord between the experimental electron-microscopy images and the electron microscopy images calculated by the EMS program was attained only for crystals with the thicknesses ranging from one to five lattice periods. This allows us to state that hydroxyapatite grows from aqueous solutions in the form of very thin (with the thickness of the order of several lattice parameters) platelike crystals.

Method for producing nano-sized crystalline hydroxyapatite

Growth of needlelike gypsum crystals from highly supersaturated aqueous solutions has been studied by the methods of the optical and electron microscopies. The average growth rates of the end faces and their fluctuations are determined. It is shown that the fluctuations in the growth rates of end faces are described by the Fokker-Planck equation and that the end faces of gypsum crystals grow by the layer mechanism with the layer nucleation in the vicinity of one of the crystal vertices.

Two-dimensional crystalline hydroxyapatite

The growth of gypsum CaSO4 · 2H2O crystals in aqueous solutions has been investigated, both on individual crystals and on crystals in a homogeneous suspension in the supersaturation range 1–20 and the temperature range 291–303 K. The dependence of the crystal growth rates on supersaturation is described by an S-shaped curve, which is due (i) to the specific features of CaSO4 self-adsorption on the surface of growing gypsum crystals and (ii) to the multistage character of dehydration of Ca2+ and SO42− ions at the transition from the solution to the solid. At solution supersaturations of ∼20, at which the adsorption layer is close to saturation, the growth rate weakly depends on supersaturation, approaching the limit value Gjp. A model of the crystal hydrate growth in the kinetic mode is constructed which reveals the conditions at which the growth rate reaches the limit value Gjp and does not change with a further increase in supersaturation.