Thesis-1997-Wallace.pdf (4.96 MB)
Cathodic precipitation of ceramic precursor materials
thesis
posted on 2012-11-23, 12:59 authored by Andrew WallaceAn electrochemical technique has been developed for the production of precursors to
ceramic films on hydrogen sorbing metal substrates. It involves the electrolysis of
aqueous metal salt solutions which yields hydrogen at the cathode, resulting in local
generation of base (hydroxide ions) around this electrode. Such conditions promote
the precipitation of metallic hydroxides from a suitable electrolyte. If the local alkaline
environment is not disrupted by convective or other forces, then a solid phase
accumulates near the cathode, and forms an adherent gel-like structure on its surface.
In order to maintain deposition, it is essential that gaseous hydrogen evolution is
minimised, and preferably eliminated. This can be achieved by use of a hydrogen
sorbing cathode material, such as palladium. The electrode, and adherent film (or, in
appropriate circumstances, the deposit alone) can then undergo a subsequent
calcination treatment to yield the ceramic layer. It is possible to generate both porous
and compact structures by this method, depending on the potential programme
employed during deposition. Research has been conducted into the understanding of mechanisms involved in
porosity control of films deposited during different potential regimes, with view to
establishing routes to layers of predetermined physical structure. In-situ optical
methods were employed to complement the electrochemical techniques, providing
valuable insight into the initial mechanisms of film formation and the subsequent
thickening processes.
The utility of the precipitation process was illustrated by the fabrication of films which
demonstrated a variable conductivity over a range of humidities appropriate to sensing
application. Investigation into the use of a bipolar palladium electrode as an aid to generating thick
film deposits was carried out. The device comprised a palladium plate, operated as a
bipolar electrode in aqueous electrolyte. Under suitable conditions, the negative face
of this electrode can be made to generate and absorb hydrogen, whilst simultaneously,
the positive face oxidises hydrogen transported across the bipolar substrate by
diffusion. Thus the cathode face is a non-gassing electrode on which thick deposits of
metal hydroxide can be grown.
This line of research lead to the realisation of a self-feeding hydrogen anode at the
electrode's positive face. Further research was undertaken to assess the
electrochemical properties of this anode. The effective operating window for
hydrogen oxidation was investigated, and the effect of prolonged potential cycling,
elevated temperature and bipolar plate thickness on this region was also considered.
History
School
- Science
Department
- Chemistry
Publisher
© Andrew WallacePublication date
1997Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en