Hn. Mcmurray et al., NOVEL THICK-FILM PH SENSORS BASED ON RUTHENIUM DIOXIDE GLASS COMPOSITES, Sensors and actuators. B, Chemical, 28(1), 1995, pp. 9-15
Potentiometric pH electrodes are described, which consist of 30 mu m f
ilms of a ruthenium dioxide-glass composite, prepared by sintering mix
tures of powdered lead borosilicate glass and ruthenium dioxide hydrat
e onto Pyrex substrates at 900 degrees C. Electrical contact is made e
ither at a point remote from the solution-contacting portion of the el
ectrode or via a platinum wire contact immediately underlying the acti
ve area. Composite electrodes with an RuO2:lead borosilicate glass rat
io of 1:1 show a near-Nernstian dependence of potential upon pH in aqu
eous buffer between pH 2 and 12, a maximum hysteresis of 30 mV and a r
esponse time of approximately 90 s. Response rates appear to be limite
d by the diffusion of protons through the porous composite and decreas
e with decreasing RuO2:glass ratio. The composite electrodes are compl
etely indifferent to changes in the concentration of dissolved oxygen,
but show a small response to chloride ions. Changes in electrode char
acteristics with aging are reported, of which the most significant is
a -65 mV drift in E(o).