Zinc and its alloys are among the most widely utilised metallic coatings for the sacrificial
protection of steel. Although excellent in this mode of protection, these coatings are often less
durable when subjected to environments of combined wear and corrosion due to their intrinsic
relative softness and ductility. A possible and fast growing way of improving the durability of
these coating is by the codeposition of inert particles into the zinc and zinc-alloy matrix. The
main aim of this research was therefore to improve the durability of zinc and zinc-nickel
coatings by the incorporation of inert particles via electrolytic codeposition methods.
The first five chapters of this thesis comprise literature review on the electrodeposition of zinc,
its alloys and composite electrodeposition in general. A major part of which was dedicated to
the review of various conventional methods and parameters such as current density, agitation,
temperature, solution composition, bath additives and pH usually investigated in
The experimental work was principally based on DC electrodeposition and was aimed at
understanding the deposition behaviour of zinc and zinc-nickel electrodeposition baths,
conditions which influence them and solution compatibility to the introduction of silica
particles. A systematic study on the deposition behaviour of both zinc/silica and zinc-nickel/silica
composite baths was carried out with particular interest on the rate of particle incorporation
and the influence of particles on zinc-nickel alloy deposition. The complimentary codeposition
behaviour of the nickel and silica particles was observed. The influence of bath additives such
as N,N Dimethyldodecylamine (NND) and sodium nitrate on the rate of silica incorporation
was also studied. Both additives were found to improve the rate of particle incorporation for
the zinc/silica. The morphologies and compositions of the coatings were analysed with the use
of SEM and FEGSEM. Corrosion performance studies were carried out in a neutral salt spray chamber and linear
polarisation resistance methods used to determine barrier corrosion properties of the coatings.
Anodic polarisation studies were also carried out. The results show an improvement in the
corrosion performance of these coatings with the addition of silica particles
Reciprocating wear tests were used to determine the wear behaviour of the coatings in terms
of weight loss. Improvement in wear resistance was not observed in the zinc/silica coatings
probably due to the high content of silica in the coatings. Lower silica contents may be
required for the desired improvements. However, there were obvious improvements in the
wear behaviour of the zinc-nickel/silica coatings due to the presence of the silica particles.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.