Effect of Thermal Treatment on the Structure and Properties of Hydroxyapatite

X-ray diffraction analysis and transmission electron microscopy were used to demonstrate that hydroxyapatite produced by the precipitation method is a powder composed of anisometric particles with longitudinal size of 70–100 nm and transverse size of 7–9 nm. The particles are constituted by crystallites with longitudinal sizes of 22–24 nm and transverse sizes of 8–10 nm. At a temperature of 600°C, the crystallite sizes grow, and the volume porosity and specific surface area decrease. Synthetic hydroxyapatite has a low thermal stability as compared with hydroxyapatite of biological origin.     

Highly selective substitutions in 2,3-dichloropyrazine. A novel general approach to aloisines

A highly efficient synthesis of the potent CDKs (cyclin-dependent kinases) inhibitors, aloisines (substituted 5H-pyrrolo[2,3-b]pyrazines) is presented. The method is based on highly selective monosubstitution of a single chlorine atom in 2,3-dichloropyrazine with lithiated ketones, esters, and nitriles followed by co-cyclization of the resulting intermediates with primary amines or hydrazines.     

Growth Rate anisotropy of the K2(S,Cr)O4 Mixed Crystals Grown from Aqueous Solution

The ratio of growth rates of the K₂(S,Cr)O₄ crystals in the [100] and [001] directions (the anisometry coefficient) is proportional to the initial effective supersaturation of the solutions from which the crystals were grown. The values of the factors of asymmetry and excess of distribution of the crystal anisometry coefficient are affected by the composition of solution. The change in the values of these factors is caused by the change in the value of the initial supersaturation of solution according to the specific features of the solubility diagram.     

Electron-fractographic investigation of the brittle fracture of polyethylene

The results are presented of an electron-microscope investigation of the brittle fracture of linear polyethylene at the temperature of liquid nitrogen. It is shown that the physical nature of the structural details of the microrelief of the fracture surface is conditioned by local plastic deformation of the stratified lamellar structures in a thin layer adjacent to the fracture surface preceding and accompanying fracture. The possibility of local self-heating is discussed and a possible mechanism of plastic deformation of the crystal platelets at low temperatures is proposed.Mekhanika Polimerov, Vol. 3, No. 2, pp. 286–290, 1967