Ceramics-Silikáty 58, (4) 249 - 259 (2014)

A high-temperature observation of bubble evolution by the effect of mains alternating current (50 Hz) in borosilicate glass melt at temperatures of 1100 and 1225 C was completed by measurement of the polarization curves and measurement of the mean electrode potential and potential course at electrodes fed by rectangular alternating current. The development of oxygen bubbles already starts at a current density of about 30 mA/cm-2. Above 100 mA/cm-2, fluctuations in bubble development occur and bubbles start to release from the electrode. Above 220 - 250 mA/cm-2, massive bubble evolution starts. Bubble development at 1100 C is considerably higher than at 1225 C and limits in their evolution are more noticeable. The limits in bubble development correspond to changes of potential course and of mean electrode potential. An explanation of the changes in electrode behaviour, based on an alternating transition between two mechanisms of oxygen development and/ or on alternating reduction and re-forming of oxidic layer on the electrode in the transition range, has been suggested. Start of bubble evolution at low alternating current density has also been observed in simple sodium-calcium-silicate glass melt. A relation between bubble release and platinum corrosion caused by reduced silicon has been suggested.