Electrode dependent Joule heating during flash processes in soda lime silicate glass
Flash sintering was initially discovered in crystalline ceramic systems like YSZ, Al2O3, SiC etc. More recently, it has been shown that also alkali-containing glasses undergo to the flash event when heated and simultaneously subjected to electric potential although the flash process in such systems is characterized by strongly inhomogeneous Joule heating, the positive electrode being overheated by hundreds of degrees.
In this work, we investigate the electrode configuration effect on the Joule heating during the flash in soda lime silicate glass. Two different electrodes are used at the anode (+), (i) a platinum plate and (ii) some molten NaNO3. We show that the highly inhomogeneous temperature profile developed with Pt anode becomes very homogeneous by using molten NaNO3. The Joule heating in glass appears therefore not only dependent on the sample temperature and composition, but it is strongly influenced by the electrode configuration. This is attributed to the fact that a highly resistive alkali depletion layer develops at the anode when Pt is used. Conversely, molten NaNO3 acts as a sodium supplier at the anode keeping the glass composition constant during the process. The effect of the anode material on the flash onset and on the luminescent effects observed during the process is investigated as well.