Development and characterization of glass matrix composites as porous coating film of a solid state reference electrode
For protection against leaching of the electrolyte reservoir of a solid state reference electrode a porous covering film was prepared and characterized. The porous covering film is based on a glass matrix composite and fired at 400 °C according to the thick-film-based structure of the reference electrode. Based on stability investigations on low sintering glasses in the range of pH 1.68 to pH 9.18 and in various concentrated potassium chloride solutions, a suitable zinc borate glass was selected. Using this glass and Al2O3 or ZrO2 oxide powders, various glass matrix composites were prepared and their sintering behavior was investigated in dependence on the amount of crystalline fraction up to 45 vol%. The shrinkage was measured by heating microscopy of powder compacts of cylindrical shape. In addition composite films on ZrO2 substrates screen-printed and at 400 °C fired were characterized in terms of their porosity by means of micro structural analysis and electrochemical deposition of copper. According to these investigations, suitable composites were selected as porous covering materials for the reference electrode and were tested therefore. The electrochemical characterization showed that the solid-state reference electrodes with porous covering films have a very good performance compared to conventional reference electrodes.