Marian Kubliha

Order and disorder and their influences on optical absorption of glasses in the gap region

The exponential increase of the absorption coefficient near the absorption edge is usually explained by existence of the density-of-states tails. Among the quoted theoretical models which are widely used to explain the manifestations of the Urbach rule in semiconductors, are the Sumi–Toyozava and the Dow–Redfield models and ab initio (from begining) theory. Our barrier-cluster-heating model assumes the different creating mechanism of exponential tails. The energy by optical transition is provided to electrons except from photons also from vibration of microregion. It deals about the replenishment of absented photons energy, which is smaller as gap width. Absented energy needed for the transition by light absorption is acumulated in certain microregions of material in the form of vibrational energy. At absorption sufficiently big package of accumulated energy can be used. Energy of emptied microarea is filled by phonons from surrounding of microarea (as result of temperature status of surrounding), resp. p...

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.

The Influence of Carbon Fillers on Thermal Transport in Polyurethane

The paper is devoted to the study of thermal, as well as mechanical properties of polyurethane samples (PU) filled by carbon black (CB), graphite (G) and MWCNT(CNT). Thermal conductivity k(W.m-1.K-1), specific heat capacity cp(J.kg-1.K-1) and thermal diffusivity a(mm2.s-1) were measured by the impulse method. An increase of all the above mentioned thermal parameters after addition of fillers under investigation was observed. The dc electrical conductivity drastically increases from PUPU+CBPU+GPU+CNT.