Ondrej Bošák

Chosen Electrical Properties of Montmorillonite/Polyaniline Composites

The paper deals with the electrical properties of Montmorillonite (MMT)/Polyaniline (PANI) composites. These materials show specific electrical properties as relatively high anisotropic electrical conductivity, pressure dependent electrical resistance with relatively high hysteresis. Metallographic analyse as well as the Vickers micro-hardness dsof sample surfaces is presented. All these properties predetermine this material as an interesting piezoresistor.

Monitoring of vulcanization process using measurement of electrical properties during linear increasing temperature

The article presents the possibilities of diagnostics of irreversible chemical reaction – vulcanization in case of laboratory prepared rubber mixture based on styrene – butadiene (SBR) using measurements of selected physical parameters. Our work is focused on the measurement of current rheologic parameters (torque at defined shear deformation) and selected electrical parameters (DC conductivity) during linear increasing temperature. The individual steps of vulcanization are well identified by means of measurements of rheologic parameters, while significantly affecting the value of the electrical conductivity. The value of the electrical conductivity increases with the increasing of rate of the crossbridging reactions during vulcanization. The rate of the heating affects both types of measurements. When the rate of the heating is increasing the temperature of the beginning of networking step of reactions and also the rate of vulcanization grow. The sensitivity of the both types of measurements allows a good mathematical description of the temperature dependence of the torque and the electric conductivity during the vulcanization of rubber mixtures based on SBR.

Mathematical characterization of values of rheological variables during the networking reaction of rubber mixtures based on SBR

The article presents an analysis of cross-linking reaction using measurements of time dependencies of torque at constant temperature from the range 100 up to 200 °C. The measured results obtained on sample based on styrene – butadiene (SBS) prepared in the laboratory show the behaviour which can be well described by equations of chemical reactions of first-order kinetics. It is possible mathematically describe significant constants of the kinetics of networking reaction (induction period, reaction rate coefficient) by the solution of differential equations and by mathematical approximation. Constants are exponentially dependent on the temperature of vulcanization, while dependencies are Arrhenius like. Math description allows describe the progress of the vulcanization reaction also in the temperature range outside of the monitoring interval, i.e. in the area of extremely long times required for the realization of the cross-linking reaction.

Monitoring the Influence of Chemical Composition of Electrical and Dielectric Properties of Special Glasses

Monitoring the Influence of Chemical Composition of Electrical and Dielectric Properties of Special Glasses The paper deals with the results of experimentally determined influence of the chemical composition change of pure Ge-Se-Te glasses systems with the rare earths elements additions (Pr, Er and Ho in oxide or pure metal form) on electrical and dielectric properties of the glasses. We used chalcogenide bulk glasses Ge20Se80-xTex for x ∈ (0, 5, 10, 15) prepared by systematic replacement of Se by Te. We wanted to find how electrical and dielectric properties of chosen chalcogenide glasses change with the change of content and form of rare earths. We carried out the measurements at different temperatures from 20 °C to 170 °C. Results show that the inhomogeneity and defects in the measured glasses have had an impact on the measured dielectric parameters.