Significance Statement
Rust formed on carbon steel exposed to marine atmospheres comes in different morphologies. There is not much studies concerning this aspect in the rust phases complex mixture formed. Researchers led by Professor Manuel Morcillo from the National Centre for Metallurgical Research in Spain published an article in peer-reviewed journal, Materials Characterization, with the aim of classifying different types of morphologies by microscopic observation of rust formed and finally identifying the common morphologies using the combined high resolution scanning electron microscopy (SEM)/micro-Raman spectroscopic technique. The authors are not aware of the existence in the scientific literature of equivalent studies using this new and powerful technique.
The research team exposed 350 panels of plain carbon steel on open-air racks, withdrawn from marine atmospheric corrosion stations of annual average chloride deposition rates ranging from 55 to 652 mg/m2day at different exposure times of 3, 6 and 12 months, after which selected specimens were subjected to laboratory characterization of the formed rust.
Both SEM images and Raman spectra were correlated. To that end, the region of interest for carrying out the Raman analysis was selected based on the previously obtained SEM image. Typical morphologies of the main rust phases formed (lepidocrocite, goethite, akaganeite and magnetite) were characterized by Raman spectroscopy.
When observing SEM images the authors noticed the following:
- Lepidocrocite forms preferentially at the outermost surface of the rust layer acquiring globular and laminar morphologies in the form of bars, worm nests, bird´s nests, feather-like, etc.
- Goethite forms in the proximity of the lepidocrocite phase presenting acicular morphologies, in the form of needles and tubular morphologies in the form of prisms.
- Magnetite and akaganeite are preferentially located in the inner strata of the rust-layer, the former like blackish toroidal growths in the form of circular rings and the latter in tubular morphologies comprising cigar-shaped crystals.
This work successfully distinguished the main rust morphologies: globular, acicular, laminar, tubular and toroidal, and the variants existing within each group. Moreover, rust phases were rigorously identified by analytical characterization.
About the author
Belén Chico received the B.S. degree in Chemical Sciences and the Ph.D degree from Complutense University of Madrid, Spain, in 1992 and 2001, respectively. She was awarded a “Marina Bueno” grant (through a CSIC/British Council agreement) to conduct research at the Swinden Technology Centre (Corus Research Development and Technology) in Rotherham, UK, in 2000-2001.
She is currently working as Technical Researcher at National Centre for Metallurgical Research (CENIM/CSIC) in Madrid, Spain. She has specialized in metallic corrosion and protection by coatings in natural environments for more than 20 years.
About the author
Dr. Daniel de la Fuente joined the National Centre for Metallurgical Research (CENIM) of the Spanish Council for Scientific Research (CSIC) in 1998 and he hold a permanent position as Tenured Scientist at this Research Centre in 2008. Since 2014 he is also heading the Department of Surface Engineering, Corrosion and Durability of this Centre.
Specialised in metallic corrosion and protection, in the research areas of corrosion in natural environments and protection by coatings, he has published several scientific publications in specialised national and foreign journals included in the Science Citation Index of ISI.
About the author
Iván Díaz received his Bacherlor’s degree in materials chemistry and his PhD, with a distinction “cum laude”, from the Complutense University in Madrid. His dissertation research work involved “marine atmospheric corrosion of Ni-advanced weathering steels”. During his PhD, he received several pre-doctorate research scholarships to complete his training at the Old Dominion University (USA) and University of Antioquia (Colombia).
Currently, he is working as postdoctoral researcher at the Nacional Centre for Metallurgical Research (CENIM-CSIC), Madrid, Spain, whose research interests are outdoor and indoor atmospheric corrosion.
About the author
Jenifer Alcántara received the Diploma of Higher Education in Technical Architecture from Polytechnic University of Madrid, Madrid, Spain, in 2011 and the Engineer’s Degree in Materials Engineering from Complutense University of Madrid, Madrid, Spain, in 2014. She did her dissertation at the National Centre for Metallurgical Research (CENIM/CSIC) on corrosion of steel in chloride-rich atmospheres.
She is currently working on her doctoral thesis on marine atmospheric corrosion of steel at the National Centre for Metallurgical Research (CENIM/CSIC).
About the author
Dr. Joaquín Simancas received his PhD degree from the Complutense University of Madrid in 1991. At present he holds a permanent position as Tenured Scientist at the National Centre for Metallurgical Research (CENIM) of the Spanish Council for Scientific Research (CSIC). He has been involved as researcher in many research projects financed by the European Union, the Spanish National R&D Plan and especially by national and foreign private companies.
He has published scientific publications in specialised national and foreign journals mainly on the topics of atmospheric corrosion and anticorrosive coatings for natural and artificial environments (accelerated corrosion tests)
About the author
Dr. Manuel Morcillo received the Ph.D degree from Complutense University of Madrid, Spain in 1974. He joined the National Centre for Metallurgical Research (CENIM) of the Spanish Council for Scientific Research (CSIC) in 1969. He is currently working as Research Professor at the Department of Surface Engineering, Corrosion and Durability of this Centre.
He has been Director of CENIM (2000-2009) and President of the International Corrosion Council (2011-2014).
His current research interests include atmospheric corrosion, with an emphasis on Weathering Steels and Marine Atmospheric Corrosion.
Journal Reference
Alcántara, J., Chico, B., Simancas, J., Diaz, I., de la Fuente, D., Morcillo. M. An attempt to classify the morphologies presented by different rust phases formed during the exposure of carbon steel to marine atmospheres, Materials Characterization 118 (2016) 65-78.
National Centre for Metallurgical Research (CENIM/CSIC), Avda. Gregorio del Amo 8, 28040 Madrid, Spain.
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