Preparation of Transparent MgAl2O4 Spinel by Pulsed Electric Current Sintering Using Two-step Heating Method

Transparent MgAl2O4 ceramics were fabricated by pulsed electric current sintering (PECS) employing two-step sintering mode. First, nanoscale MgAl2O4 powders were produced by solution combustion synthesis from hydrated nitrate compounds and urea. Subsequently, the synthesized powders were sintered by PECS with a heating rate of 100oC/min under an applied pressure of 100 MPa. The sintering process was conducted according to two-step heating profile. At the first step, the temperature increased to 1050, 1100, and 1150oC, followed by a dwell time of 60 min. The second-step sintering was carried out at 1300, 1350, and 1400oC for 20 min. The transparent ceramics sintered at 1050oC/ 60 min – 1400oC/ 20 min exhibited transmittance over 80% in infrared range. In addition, transparent samples presented a Vickers hardness up to 30 GPa for sintering mode of 1150oC/ 60 min – 1400oC/ 20 min.

Simple Fabrication and Carrier Type Modification of Semi-Conductive C/Al2O3 Composites by Powder Mixtures and Pulsed Electric Current Sintering

Semi-conductive C/Al2O3 ceramic composites were successfully fabricated by a pretty simple approach, combining a powder mixture process and pulsed electric current sintering. In order to obtain homogeneous distribution of carbon contents, popular polymers were used as carbon fillers to mix with Al2O3 powder by a wet ball milling step. The sintering was conducted by pulsed electric current sintering without any special requirement of the reductive environment like in conventional sintering. Density of bulk bodies, states of carbon contents after sintering and the electrical properties were analyzed in this study. Although the density of sintered bodies and their electrical properties were not superior, those characteristics of C/Al2O3 ceramic composites in this study were still comparatively high among semi-conductive ceramics. Especially, the carrier type of semi-conductive C/Al2O3 composites could be modified easily by adding polycarboxylic acid (PCA) in the powder mixture as a dispersant.

Intensification of Polysaccharides Extraction from Plant Raw Materials under the Influence of Electric Current

The article presents the results of the studies of the intensification of the processes of extraction of water-soluble polysaccharides from plant raw materials – medicinal hyssop (Hyssopus officialis L.) under the action of an electric current. The effect of direct, alternating, and pulsed electric currents on the degree of polysaccharides extraction was studied in comparison with the traditional pharmacopoeiсal method. It is shown that the energy consumption for the extraction process, intensified by a pulsed electric current, is significantly lower compared to extraction by convection heating. At the same time, the use of electric current makes it possible to reduce the limiting processing temperature from 70 °С to 40 °C, this will allow in the future to obtain not only aqueous, but also aqueous-alcoholic and alcoholic extracts, and, consequently, to extract biologically active non-soluble in water substances.