Ruthenium dioxide thick film pH electrodes
PH sensitive electrodes have been fabricated using thick film screen printing techniques. Powdered ruthenium dioxide hydrate was incorporated in a printable paste by mixing with an uncured polymer precursor. This paste was printed onto alumina tiles which had been previously patterned with conductive tracking which enabled connection to measurement circuitry. The liquid polymer was cured to a resistant solid using either temperature or ultraviolet light treatments. Large numbers of electrodes were fabricated in this way, using ruthenium dioxide with varying levels of hydration. Printed electrodes were tested for pH response using a number of fixed pH buffers. A commercial silver/silver chloride reference electrode was used to complete the potentiometric measurement cell. The response of electrodes was found to be comparable to that of commercial electrodes based upon a pH sensitive glass bulb. Electrodes were tested after prolonged soaking in various solutions, both acidic and alkali. Some types of printed electrode showed signs of chemical attack and failure after storage in acidic media. Charge was passed through electrodes to investigate the possible perturbation of electrochemical equilibria within the oxide. Electrodes were characterised by microscope examination of used and unused samples. The hydration level of the oxide powders used was investigated using thermogravimetric analysis techniques. The electrochemical mechanisms underlying the potentiometric pH response are speculated upon. The experimental evidence could indicate that an ion exchange mechanism involving hydroxide groups on the oxide surface is responsible for pH sensitivity. Results are discussed with respect to this and other mechanisms.