Electrochemical investigation of the growth of anodic films on iron and ferrous alloys.

UKZN ResearchSpace

Show simple item record

dc.contributor.advisor Brookes, H.
dc.creator Graham, Fiona Jane.
dc.date.accessioned 2012-01-23T07:28:53Z
dc.date.available 2012-01-23T07:28:53Z
dc.date.created 1994
dc.date.issued 1994
dc.identifier.uri http://hdl.handle.net/10413/4875
dc.description Thesis (Ph.D.)-University of Natal, 1994. en
dc.description.abstract An electrochemical investigation of the corrosion of iron and Fe18Cr based stainless steel alloys was undertaken with particular emphasis on the nucleation and growth of surface films. Chronoamperometry was shown to be a sensitive technique to investigate the initial stages of film formation and growth. In a variety of acidic (pH < 7), alkaline and alkaline cyanide electrolytes, providing dissolution of the substrate metal could occur rising current transients, similar to those reported in electrocrystallisation studies, were observed when the electrode was stepped to the appropriate potential. This indicated that at these potentials the surface film formed via the nucleation and growth of discrete nuclei. A significant aspect of this study was visual evidence of this nucleation and subsequent growth of the film provided by scanning electron microscopy which supported the electrochemical data and interpretation thereof. Existing electrocrystallisation models were used to evaluate the experimental rising current transients. While these models gave an indication as to the prevailing nucleation and growth mechanism, they were found to be inadequate in describing anodic oxide formation on an oxidising substrate. A qualitative model was proposed. In acidic electrolytes, rising chronoamperometric transients were observed for Fe, Cr and Fe18Cr at passive potentials and for FexCr (x = 16,18, 20,23% Cr) and alloys 444, 4732, 4733, 304L and 316L at transpassive potentials. The transients were shown to be sensitive to variations of potential, temperature, electrolyte and alloy composition. A systematic investigation of the influence of temperature (20 0 C - 1200 C) on the chronoamperometric, cyclic voltammetric and rotating ring - disc electrode behaviour of Fe in O.5M and 1.0M NaOH was also undertaken. In alkaline electrolytes, the formation of a duplex surface film was proposed, with x-ray photoelectron spectroscopy indicating that the protective base layer consisted of FeO while Fez03 and FeOOH constituted the upper layer. Base layer formation was favoured with increasing temperature and increasing hydroxide ion concentration of the electrolyte. Addition of OAM NaCN to O.5M and 1.0M NaOH had a marked effect on the electrochemistry of the system, with CN- inhibiting surface film formation, particularly of the upper layer. A mechanism for the oxidation of Fe in alkaline and alkaline cyanide electrolytes was proposed. en
dc.language.iso en en
dc.subject Metals--Anodic oxidation. en
dc.subject Steel alloys--Corrosion. en
dc.subject Iron--Corrosion. en
dc.subject Electrochemistry. en
dc.subject Theses--Chemistry. en
dc.title Electrochemical investigation of the growth of anodic films on iron and ferrous alloys. en
dc.type Thesis en

Files in this item

This item appears in the following Collection(s)

Show simple item record

Search UKZN ResearchSpace


Advanced Search

Browse

My Account