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Title: Adsorption at treated steel-paint interfaces
Author: Poon, Chun Yin Jeffrey
ISNI:       0000 0004 8501 3117
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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In this thesis, a wide range of surface sensitive techniques have been used to characterise surfaces relevant to offshore steel structures, to provide fundamental understanding of steel-paint binding that prolongs coating lifespans and corrosion inhibition. Particular steel surfaces are characterised before and after almandine garnet abrasive blasting. Significant build-up and coverage of abrasive residue (almandine and calcium carbonate) is identified on the post-treatment steel, covering up to a third of the steel surface; Given the importance of the blasting materials on the surface, almandine garnet is also characterised for its surface chemistry and behaviour. By characterising both bare steel and almandine garnet, adsorption on `real' garnet-blasted steel substrates can be modelled. A dry ice-garnet mixed stream is also investigated to see whether abrasive residue could be reduced. It is found that a quarter of the steel surface is covered with blasting residue. However, cooling and moisture-condensation leads to corrosion spots formation. The adsorption of potential paint additives and components on S355 steel and garnet are determined using solution depletion isotherms. Quantitative data such as equilibrium adsorption constants, and estimation of monolayer molecular geometries are collected. The latter is further investigated through novel surface spectroscopy. In brief, most organics are found to have higher The steel surface is shown to be likely to corrode in offshore conditions with corrosion marine aerosols in a matter of a few hours. It is these corrosion products which will be substrates for coating/paint molecules. A `salt drop' corrosion study simulates relatively short timescale aerosol exposure (mins to hours). Surface chemical-environments are characterised. The corrosion products are found to be porous, inhomogeneous in chemical environment, and evolve through time, with adsorbed/occluded marine ions. Finally, as steel corrosion products are likely to adsorb marine salts, ion adsorption on almandine garnet is investigated. Cations of sodium, magnesium, and calcium are found to specifically adsorb. Numerical model co-fitting of data from different techniques successfully obtains the adsorption equilibria and constant, and the surface site density of almandine garnet. The study highlights a general need for more complete studies, using multiple adsorption experiments, for aqueous phase adsorption investigations on minerals in the future.
Supervisor: Clarke, Stuart Matthew Sponsor: Royal Dutch Shell
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: surface chemistry ; steel ; corrosion ; marine ; garnet ; adsorption ; ions ; isotherm ; blasting ; XPS ; SEM ; TEM ; EDX ; SFG ; iron oxide ; UV-Vis ; spectroscopy ; EBSD ; surface characterisation