Corrosion science and engineering: some recent developments

Abstract

The changes that have occured and advances that have been achieved in corrosion science and engineering over the past two decades can be attributed to a number of factors. These include fundamental advances in the science of corrosion and new mechanistic insights, more sophisticated experimental equipment, particularly in the areas of the surface analysis and electron optical techniques, pressure from new service conditions and industrial requirements and the greatly increased availability and power of computers. While most aspects of materials science and engineering have benefited from similar trends, corrosion science and engineering, particularly in the UK, received the added impetus and stimulus of the publication in 1971 of the DTI Hoar Report on Corrosion. This estimated that corrosion cost the UK about £1300m(about 3.5% of the then GDP), of which about £350m could be saved by improved selection of existing materials and wider use of existing techniques for corrosion prevention and control. The corresponding figures in 1993 would be about £11bn and £2.5bn respectively. Rather than reviewing advances in the whole, very broad field of corrosion science and engineering, which is clearly beyond the scope of a single paper, this paper presents a highly selective perspective of some of the developments in three specific areas: passivityy, environmental cracking and organic coatings. In each case the paper presents a broad summary of the major developments and then highlights specific advances for more detailed discussion. Thus, in the field of passivity, the use of percolation theory and computer modelling to explain the observed compositional thresholds for active-passive transitions in FeCr alloys is discussed in some detail. Specific developments in environmental cracking include the film-induced cleavage model for the mechanism of transgranular stress corrosion crack propagation and the role of crack-tip chemistry and electrochemistry in determining susceptibility to cracking. In the case of organic coatings, there is emphasis on the potential of electropolymerization as a non-toxic alternative to chromates for improved adhesion and performance. The picture that emerge from this selective review of developments since the establishment of the Department of Materials Engineering at the University of Cape Town is one of incremental fundamental and practical advances in a relatively mature discipline.