Characterisation of Potential Replacements for Nickel Compounds used in Decorative Chromium Plating
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AuthorsHingley, Stacey Louise
MetadataShow full item record
AbstractThe electroplating industries use soluble nickel salts in numerous applications. Over the past few years this has become problematic due to the reclassification of these salts from a harmful substance to now a toxic substance. The introduction of the legislation REACH (Registration, Evaluation, Authorisation & restriction of CHemicals) has meant the electroplating industry has had to use less harmful chemicals where possible, thus meaning companies are investing in research to find an alternative to the nickel deposit. In this study, alternative deposits under investigation as a potential replacement to the nickel deposit under the decorative chromium deposit has been characterised in terms of the appearance, surface topography and corrosion resistance by using spectrophotometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), linear polarisation, electrochemical impedance spectroscopy (EIS) and accelerated corrosion salt spray methods. Spectrophotometry identified that a white Cu-Sn alloy gave a bluer appearance in comparison to the nickel deposit, when the chromium deposit was plated on top this modified the colour slightly giving the white Cu-Sn alloy with chromium a similar appearance to the nickel and chromium deposit. The yellow Cu-Sn alloy was yellow in colour with a visibly dull appearance, but when chromium was plated on top of the yellow Cu-Sn alloy the colour was improved but still remained dull. The SEM and AFM results identified that the white Cu-Sn alloy deposit had similar nodulated topography to the nickel deposit and when the chromium was plated on top the topography changed only slightly. While the yellow Cu-Sn alloy deposits showed a more crystalline structure and increased roughness in comparison to the nickel deposit, the chromium deposit plated on top did not change the structure of the underlying deposit but it did reduce the roughness slightly. Electrochemical corrosion tests showed the white Cu-Sn alloy to have a higher polarisation resistance compared to the nickel deposit, thus suggesting it would provide similar corrosion protection to the nickel deposit. The yellow Cu-Sn alloy proved to have a faster corrosion rate in comparison to the nickel deposit. Accelerated corrosion tests proved the white Cu-Sn alloy to be more corrosive than the nickel despite the electrochemical test results, it was concluded that the white Cu-Sn alloy deposit was porous and therefore provided less corrosion protection to the substrate in comparison to the nickel deposit. The yellow Cu-Sn alloy had a lower corrosion protection than the nickel deposit and when combined as a duplex Cu-Sn alloy with the white Cu-Sn alloy deposit there was no improvement in corrosion performance. The plated chromium deposit did improve the corrosion protection for most deposits but none of the alternatives could match the corrosion protection offered by the standard nickel with chromium deposit. This study concluded that the white Cu-Sn alloy with chromium deposit was found to be a potential alternative to the nickel with chromium deposit for applications where appearance is primary, no alternative could be found to match the corrosion protection provided by the standard nickel and chromium process.
PublisherUniversity of Wolverhampton
TypeThesis or dissertation
DescriptionA thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy.