Ceramics-Silikáty 32, (3) 233 - 240 (1988)

Meranim jednosmernej a striedavej elektrickej vodivosti a kapacity bola zistená dvojstupňovosť uvoľňovania fyzikálne viazanej vody z elektroporcelánovej zmesi. Prvý stupeň predstavuje únik slabo viazanej molekulárnej vody a je charakterizovaný aktivačnou energiou 0.474 eV. Druhý stupeň, plynule navazujúci na prvý, je spojený so zánikom tenkých vrstiev vody na povrchu kryštálkov kaolinitu a s transportom iónov H⁺, OH⁻.

Measurement of DC and AC electrical conductivity and capacity of compact specimens prepared by vacuum pressing of a porcelain raw material mix containing approximately 50 % kaolin, 25 % quartz and 25 % feldspar showed the endothermal process of releasing the physically bound water was actually a two-stage one. The results are in agreement with the findings obtained by means of differential thermal analysis (DTA) and derivation thermogravimetry (DTG). The effect of both stages of releasing of physically bound water was also discernible in measurements of sound velocity CL and internal friction b by the dynamic mechanical analysis method (DMA). The two-stage character of liberation of physically bound water is indicative of two types of bonds by which water is held to electrically non-compensated defects on the surface of kaolinite crystals or other clay minerals. The first stage represents the releasing of weakly bound molecular water from the surface of pores and capillaries. This water is released from the very beginning of heating, attaining the highest intensity at 40 to 50 °C. The process is characterized by an activation energy of 0.474 eV which corresponds to the energy of releasing molecular water bound by capillary forces or surface tension. The second stage of liberation is linked directly to the first stage and shows the highest intensity at 100-105 °C.