Campbell, Alan Gordon

2013-06-26T14:01:10Z

2013-06-26T14:01:10Z

1987

'I"he most important aspect of the metal-glass interface in a solid-connected glass pH electrode is the stability of electric potential at the interface. The development of this potential is a function of the behaviour of charge carriers near the glass surface and of any electrode process which takes place. The mechanism of conduction in the soda-lime-silica glass system, to which some pH-sensitive glass belongs, is reviewed briefly. Solid electrolytes in general, and the theory applying to contacts to them, 'are examined, with a view to their relevance to the problem of the glass-metal system. The importance of electrochemical effects in solid'systems is emphasised. Chemical and electrochemical phenomena at glass surfaces and interfaces are also reviewed. In order to investigate their applicability to sensors, contacts of aluminium, copper, silver, tungsten trioxide and sodium tungsten bronze were used in metal-glassmetal structures. These had the form of two- and thiee-electrode electrochemical cells, on which AC and galvanostatic measurements were made. The complex admittance graphs obtained from the AC data are generally of the form of a circular arc whose centre is situated below the real axis, and which approaches the origin at the low-frequency end, indicating the absence of conduction across the interface under conditions of zero bias. Nonblocking behaviour of all the contacts has been inferred from the galvanostatic data when the conditions of zero-bias are relaxed; after the passage of any amount of current, the potential tends to approach its starting point after the current has been switched off. Evidence of a kinetically-limited electrochemical reaction has been found in the case of evaporated aluminium contacts, and less strongly in the cases of silver and copper. Sodium tungsten bronze appears to achieve a steady potential difference when in contact with glass, and so seems the most likely candidate for application as a back electrode for a practical sensor. Suggestions are made for further research to test the applicability of the results to sensors, and to extend the investigation of electrode processes at glass surfaces.

378729

http://hdl.handle.net/1842/7289

eng

University of Edinburgh

Chemistry,

Physical

and

theoretical

Electrical processes at metallic contacts to sodium ion conducting glass

PhD Doctor of Philosophy