Analysis of the temperature-frequency effect on dielectric losses in a grain medium

The aim of the study is to determine the influence of the thermal effect on dielectric losses in grain mass subject to bruising during drying and storage on the example of wheat across a wide external electric field frequency range. The study of the electrophysical characteristics of a dispersed medium comprising mechanically activated wheat grains takes into account the effect of the degree of breakage on the dielectric parameters of the studied medium. The studies were carried out on experimental samples having different degrees of mechanical activation of particles, which ranged in size from from 50 to 1000 μm. Variations in the dielectric loss tangent were studied using the dielectric method across a wide temperature-frequency range. Studies of variations in dielectric properties were carried out for wheat sam-ples subjected to grinding according to the mechanical activation method at temperatures varying from 20°C to 255°C with a constant heating rate of 0.7 deg / min. During the course of the experiment, the frequency of the external electric field was varied from 25 Hz to 1∙106 Hz. Dielectric constant and dielectric loss tangent calculations were carried out using data on electrical capacity and conductivity obtained using an E7-20 immittance meter and a measuring cell in the form of a flat capacitor. An analysis of variations in these dielectric characteristics was also performed. The obtained stable correlation of the dielectric loss tangent with the frequency of external electric impact and the degree of heating of the samples was most pronounced for finely dispersed samples (particle size 50 μm). Variations in dielectric characteristics are most significant when the frequency decreases to 100 Hz and below. The study of variations in the main dielectric parameters can be used to prevent self-heating and ignition of the grain mass during storage, as well as for selecting the most efficient energy-saving drying mode.

ВПЛИВ МЕХАНІЧНОЇ АКТИВАЦІЇ НА РОЗМІРНІ ХАРАКТЕРИСТИКИ ТА ФОРМУ ЧАСТИНОК ГЛИНОПОРОШКІВ РІЗНОГО ТИПУ

Purpose. Determination of the influence of the process of preliminary mechanical activation on the dimensional characteristics and shape of particles of different types of clay powders.Methodology. Clay powders of montmorillonite and palygorskite type were chosen as the objects of research in this work. The process of mechanical activation of clay powders was carried out using a laboratory ball mill. For microanalysis of sample particles, the method of optical polarizing microscopy was used. Morphometric analysis of clay powder particles was performed by image analysis using the ImageJ software. At the same time, the area and perimeter were determined, and the equivalent diameter and also the shape index of the particles of the samples were calculated. The experimental data were statistically processed using the Statistica and Excel software packages.Results. The paper investigates the effect of the process of mechanical activation on the dimensional characteristics and shape of particles of montmorillonite and palygorskite type clay powders. It was found that the decrease in the average values of the equivalent particle diameter in the process of mechanical action (~14–15%) is realized mainly due to the destruction of their largest aggregates. Moreover, the intensity of this process is noticeably higher for clay of the montmorillonite type. It is shown that for both studied samples, the process of mechanical activation leads to an increase in the average values of the particle shape index (~ by 9–10%) and an increase in the uniformity of their distribution by this index.Scientific novelty. Using a detailed morphometric analysis of particles of various types of clay powders, the regularities of the influence of the mechanical activation process on the quantitative statistical characteristics of their distribution over the equivalent diameter and shape index have been established.Practical value. The results obtained will make it possible to reasonably approach the choice of pretreatment methods for clay powders intended for the production of polymer filled nanocomposite materials.

Сверхизлучение и синтез наночастиц металла в полистирольном композите с многоспиновыми комплексами Eu при быстром одноосном сдавливании

Composites of heterospin molecular magnet [EuIII(SQ)3bipy] in a polystyrene (PS) matrix have been synthesized. This complex [EuIII(SQ)3bipy] contains four paramagnetic centers - the Eu3+ ion and three SQ ligands (SQ—3,6-di-tert-butyl benzoquinone radical anion); bipy (bipyridyl) is diamagnetic. It has been established that intensive mechanical activation of [EuIII(SQ)3bipy]/PS samples leads to an reological explosion, as a result of which radio frequency superradiance, the appearance of free electrons and the formation of Eu metal nanoparticles are observed. The duration of this process is 10 ns.

Solid-phase synthesis of ytterbium zirconate using mechanical activation

Nanocrystalline ytterbium zirconate Yb4Zr3O12 was prepared by the solid-phase method using mechanical activation of stoichiometric mixture of zirconium and ytterbium oxides. Mechanical activation was carried out in an AGO-2 centrifugal-planetary mill at a centrifugal factor of 40 g for 10 min. The processes occurring during the calcination of the mechanically activated mixture of ytterbium and zirconium oxides in the range from 600 to 1300 °C were investigated using X-ray phase analysis, IR spectroscopy, and complex thermal analysis.