V. A. Klyuev

The effect of mechanical activation on the heat capacity of powdered tungsten

We have studied the heat capacity (Cp) of a mechanically activated tungsten powder. It is established that the mechanical processing leads to an increase in Cp of the metal powder at low temperatures and modifies the character of the temperature dependence of this parameter. The dependences of Cp and its heating-induced variation on the treatment duration have been determined. It is concluded that the observed effects are related to the accumulation of defects in the metal grain volume during mechanical activation and their annealing in the course of heating.

Thermal activation currents of biocompatible nanocrystalline calcium hydroxyapatite Ca10(PO4)6(OH)2

Nanocrystalline stoiochiometric calcium hydroxyapatite, Ca10(PO4)6(OH)2 (NCHA), a counterpart of the inorganic osseous tissue component, is synthesized under biomimetic conditions. Methods of physico-chemical analysis (XRD, IRS, derivatography, DSC, ESCA, SEM, TEM) are used to identify the products of synthesis. The temperature dependence of thermally stimulated currents (TSCs) of NCHA is studied in the temperature range of 300–600 K and the effect of the dispersion degree on TSCs is analyzed.

Effect of mechanical activation on the thermal stability of polytetrafluoroethylene powder

It was found that processing in a planetary activator leading to amorphization of the structure of polytetrafluoroethylene powder was not accompanied by a noticeable decrease in its thermal stability. It was established that the temperature at the onset of melting drops slightly, the melting rate increases, and the enthalpy of the endoeffect declines noticeably heating.

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.

On Diagnostics of Double Electric Layer in the Zone of Metal–Polymer Adhesion Contact Using the Positron-Annihilation-Probe Method

Application of the positron-annihilation-probe technique for nondestructive diagnostics of the double electric layer (DEL) at the polymer–metal interface and, hence, of the electric component of polymer adhesion to the metal is described. Separated curves of angular correlation of positron-annihilation radiation (ACPAR) for metal, polymer, and metal with a polymer layer allow detecting the presence of a strong electric field of a DEL at the nickel–epoxy-resin interface. The value of the DEL potential is determined to be 15 keV. The method of a positron-annihilation probe allows identifying the presence of a DEL on the internal interfaces of materials and estimating its energy parameters so as to correctly reflect the value of the contribution of the electrostatic component to the interphase interaction.

The influence of methylcellulose (MC) on solubility of calcium hydroxyapatite (HA) crystals in HA/MC nanocomposites

The influence of methylcellulose ([C6H7O2(OH)3–x(OCH3)x]n, MC) on the morphology and solubility of calcium hydroxyapatite (Ca10(PO4)6(OH)2, GA) nanocrystals (NCs) in GA/MC organomineral nanocomposites (OMCs) is studied. GA/MC OMCs with the MC content of 0.5, 1, 2, 5, 10 and 20 wt % are synthesized in the Ca(OH)2–H3PO4–[C6H7O2(OH)3–x(OCH3)x]n–H2O system under biomimetic conditions (37°C). The composition and structural features of OMCs, as well as crystallographic characteristics, size, and morphology of GA NC in OMCs, are determined via chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (IRS), thermal analysis (DTA and DTG), scanning (SEM) and transmission (TEM) electron microscopy, and electron diffraction (ED). It is shown that the growth in the MC concentration in OMCs leads to the change in the GA NC morphology and the increase in their solubility (for Ca2+ and PO43- ions).

The influence of mechanical activation on the adsorption properties of powdered tungsten

Mechanical activation in a planetary ball mill activator changes the adsorption properties of powdered tungsten. The activation leads to changes in both the adsorption energy and the concentration of active adsorption sites on the surface, thus resulting in a change in the adsorption capacity. The character and degree of the change in the adsorption properties depends nonlinearly on the duration of the mechanical effect.

Effect of the mechanical activation of fillers on the parameters of thermostimulated current in polymer composites

The influence of the mechanical activation of powdered fillers on the character of thermoactivation processes in polymer composites involving these fillers has been studied. It is demonstrated that thermostimulated current spectroscopy is a promising method for investigating the interaction of fillers with polymer matrices in electret compositions.

Exoelectron Emission and Critical Phenomena in CuCl Crystals

The temperature dependence of thermostimulated exoelectron emission (TSEE) and the specific heat cp of CuCl single crystals were studied in a broad temperature range. It is suggested that the TSEE peaks observed in the region of 375 and 420°C are due to the polytype formation and the structural transition from a sphalerite to wurtzite polymorph; the peak at 170°C is assigned to Cu2+ ions present in the CuCl crystals studied.

Interaction of Hydrogen with Silicon during Mechanical Activation

Mechanical activation of silicon powder under hydrogen was investigated using an AGO-2U centrifugal planetary activator. An IR spectroscopic study revealed that there was direct chemical interaction between hydrogen and silicon with the formation of hydrides.