CORROSION–Vol. 53, No. 11 835
CORROSION SCIENCE SECTION
Submitted for publication February 1996; in revised form,
January 1997. Presented originally at the 1st NACE Latin
American Region Corrosion Congress.
* Centro de Estudios de Corrosión, Universidad del Zulia,
Maracaibo, Vanezuela.
** División de Corrosión, Centro Nacional de Investigaciones
Científicas, La Habana, Cuba.
Evaluation of Steel
Corrosion Products in Tropical Climates
A. Rincón, O.T. de Rincón,* C. Haces, N.R. Furet, and F. Corvo**
ABSTRACT
Phase variations occurring in corrosion products obtained in
steels exposed to different zones of tropical climate in Cuba
and Venezuela were determined to establish their relation-
ship to corrosion phenomena. Steel corrosion products were
obtained at four test stations in both countries with marine,
industrial, and rural characteristics. Phase composition was
determined using x-ray diffraction (XRD), infrared (IR) spec-
troscopy, and Mössbauer spectroscopy. In the rural climate
of both countries, the predominant phase was lepidocrocite
(-FeOOH), which was in agreement with reported corrosion
rates. In the marine environments, corrosion products varied
in composition. In Adicora, Venezuela, akaganeite (-FeOOH)
was found, but in Cuba, this phase was nonexistent. Results
were discussed in light of the contamination present and
meteorological parameters recorded in the test zones.
KEY WORDS: akaganeite, atmospheric corrosion, corrosion
products, goethite, industrial environments, lepidocrocite,
magnetite, marine environments, phases, rural
environments, tropical climates
INTRODUCTION
Factors influencing the acceleration of corrosion in a
tropical climate include time of wetness, contamina-
tion, and temperature.
1
The physical-chemical
properties of rust and the phase composition of the
oxide layer give information about its protective
properties
2
and allow recommendation of the most
appropriate anticorrosive measures to reduce effects
resulting from corrosion.
3
The main phases of iron corrosion products re-
ported in the literature are the oxyhydroxides of iron
-FeOOH (goethite), -FeOOH (akaganeite), -FeOOH
(lepidocrocite) and Fe
3
O
4
(magnetite).
4-5
The presence
of akaganeite and magnetite in a marine climate was
determined by Singh, et al.
6
Raman and Kiban found
only magnetite, and not the phase, in field tests in
Louisiana and Texas climates.
7
This result was cor-
roborated in field tests along the northwestern coast
of Cuba, where there is a strong influence of marine
aerosol.
8
Leidheiser and Music studied atmospheric corro-
sion products of steel and determined the formation
of -Fe
2
O
3
(maghemite),
9-10
while Johnson, et al.,
found hydrated maghemites together with goethite in
the initial stages of the corrosion process.
11
Obviously, there are no uniform criteria regard-
ing formation of the different phases that constitute
rust, perhaps because the various analytical tech-
niques used prevent appropriate comparison. The
objective of the present paper was to determine
phase composition of the corrosion products of steel
exposed in the tropical climates of Venezuela and
Cuba, using x-ray diffraction (XRD), infrared (IR)
spectroscopy, and Mössbauer spectroscopy.
Misawa, et al., found truly differentiated layers of
corrosion products in low-alloy steel but intermixed
amorphous and crystalline phases in carbon steels.
12
Okada, et al., examined the cross section of rust
0010-9312/97/000191/$5.00+$0.50/0
© 1997, NACE International