The Ibero-American Map of Atmospheric Corrosiveness (MICAT) project was set up in 1988 sponsored by the International Ibero-American programme “Science and Technology for Development (CYTED)” and ended in 1994 after six years of activities. Fourteen countries were involved in this project: Argentina, Brazil, Chile, Colombia, Costa Rica, Cuba, Ecuador, Mexico, Panama, Peru, Portugal, Spain, Uruguay, and Venezuela. Research was conducted both at laboratories and in a network of 75 atmospheric exposure test sites throughout the Ibero-American region, thus considering a broad spectrum of climatological and pollution conditions. Although with its own peculiarities, the project basically followed the outline of the ISOCORRAG and ICP/UNECE projects, with the aim of a desirable link between the three projects. This paper summarizes the results obtained in the MICAT project for mild steel, zinc, copper, and aluminum specimens exposed for one year in different rural, urban, and marine atmospheres in the Ibero-American region. Complementary morphological and chemical studies were carried out using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and fourier transform infrared Spectroscopy (FTIR) techniques, in order to correlate climatic and atmospheric conditions and properties of the corrosion products.
During the 2nd Ibero-American Congress on Corrosion and Protection held in Maracaibo (Venezuela) in September 1986, a round-table was organized to discuss the idea of an Ibero-American Map of Atmospheric Corrosion (MICAT). Representatives of the countries present at the meeting expressed their interest in participating in such a project.
Moves were then made to include this proposal in the Ibero-American Programme Science and Technology for Development (CYTED). A year later, in January 1988, the Technical and Managing Council of CYTED, gathered in Havana (Cuba), decided to approve the inclusion of the MICAT study into the CYTED Programme.
The primary aims of the MICAT study were [ To improve knowledge of the process of atmospheric corrosion in various climatic regions of Iberoamerica. By means of statistical treatment of the results to obtain mathematical expressions of the estimation of atmospheric corrosion as a function of climatic and pollution parameters. No less important was the objective of promoting international cooperation. In this respect, the building of bridges of understanding and the establishing of Ibero-American research groups have been achievements of deep and lasting significance, taking advantage of existing synergies and above all sharing knowledge and providing training for other countries less developed in the study of atmospheric corrosion. This research project was the first time in Ibero-America that 14 countries had worked together towards a common goal in the field of corrosion.
The MICAT project was officially launched in Caracas in August 1988 and came to an end in Lisbon in December 1994, with meetings in Rio de Janeiro (1989), San Jose Costa Rica (1990), Marambio Argentine Antarctic Base (1991), Madrid (1992), and Santiago de Chile (1993).
Research was carried out in laboratories in the 14 participating countries (Argentina, Brazil, Colombia, Costa Rica, Chile, Ecuador, Mexico, Panama, Peru, Portugal, Spain, Uruguay, and Venezuela) and in a network of 72 atmospheric testing stations covering a broad spectrum of climatological and pollution conditions. Some 70 working groups comprising a total of 130 researchers took part in the project. The countries, organizations responsible, and contact persons are listed in Table
Organizations participating in the MICAT Project.
Country | Institution, organization | Contact person |
---|---|---|
Argentina | Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas (CITEFA) | B. M. Rosales |
Brazil | Centro de Pesquisas de Energía Elétrica (CEPEL) | M. Marrocos |
Chile | Universidad de Chile Instituto de Investigaciones y Ensayes de Materiales (IDIEM) | G. Joseph |
Colombia | Universidad de Antioquia | A. Valencia |
Costa Rica | Instituto Tecnológico de Costa Rica (ITCR) | J. F. Álvarez |
Cuba | Centro de Investigaciones Químicas (CIQ) | A. Cabezas |
Ecuador | Escuela Superior Politécnica del Litoral (ESPOL) | J. Peña |
Mexico | Instituto de Investigaciones Eléctricas (IIE) | J. Uruchurtu |
Panama | Universidad de Panamá | A. F. de Bósquez |
Peru | Instituto de Investigación Tecnológica Industrial de Normas Técnicas (ITINTEC) | G. Salas |
Portugal | Instituto Nacional de Engenharia e Tecnología Industrial (INETI) | E. M. Almeida |
Instituto Superior Técnico (IST) | M. G. S. Ferreira | |
Spain | Centro Nacional de Investigaciones Metalúrgicas (CENIM/CSIC) | M. Morcillo |
Uruguay | Universidad de la República Oriental del Uruguay (UROU) | S. Rivero |
Venezuela | Universidad Nacional Experimental Francisco Miranda (UNEFM) | M. R. Prato |
Universidad del Zulia | O. T. de Rincón |
The publication of preliminary results [
This paper summarises the MICAT project’s main contributions to knowledge of atmospheric corrosion.
Although with its own peculiarities, the project basically followed the outline of the ISOCORRAG [
Figure
List of MICAT test sites.
Country | Code | Test site |
---|---|---|
Argentina | 1 | Camet |
2 | V. Martelli | |
3 | Iguazú | |
4 | San Juan | |
5 | Jubani | |
6 | La Plata | |
Brazil | 7 | Caratinga |
8 | Ipatinga | |
9 | Arraial do Cabo | |
10 | Cubatao | |
11 | Ubatuba | |
12 | São Paulo | |
13 | Río de Janeiro | |
14 | Belem | |
15 | Fortaleza | |
16 | Brasilia | |
17 | P. Afonso | |
18 | Porto Velho | |
Colombia | 19 | Isla Naval |
20 | San Pedro | |
21 | Cotové | |
Costa Rica | 22 | Puntarenas |
23 | Limón | |
24 | Arenal | |
25 | Sabanilla | |
Cuba | 26 | Ciq |
27 | Cojímar | |
28 | Bauta | |
Chile | 29 | Cerrillos |
30 | Valparaíso | |
31 | Idiem | |
32 | Petrox | |
33 | Marsh | |
34 | Isla de Pascua | |
Ecuador | 35 | Guayaquil |
36 | Riobamba | |
37 | Salinas | |
38 | Esmeraldas | |
39 | San Cristóbal | |
Mexico | 48 | México |
49 | Cuernavaca | |
50 | Potosí | |
51 | Acapulco | |
Panama | 52 | Panamá |
53 | Colón | |
54 | Veraguas | |
Peru | 55 | Piura |
56 | Villa Salvador | |
57 | San Borja | |
58 | Arequipa | |
59 | Cuzco | |
60 | Pucallpa | |
Portugal | 62 | Leixões |
63 | Sines | |
64 | Pego | |
Spain | 40 | León |
41 | El Pardo | |
42 | Barcelona, S | |
43 | Tortosa | |
44 | Granada | |
45 | Lagoas | |
46 | Labastida | |
47 | Artíes | |
Uruguay | 65 | Trinidad |
66 | Prado | |
67 | Melo | |
68 | Artigas | |
69 | Punta del Este | |
Venezuela | 70 | El Tablazo |
71 | Punto Fijo | |
72 | Coro | |
73 | Matanzas | |
74 | Barcelona, V | |
75 | Puerto Cabello |
MICAT network of atmospheric corrosion stations.
The atmosphere at each test site is characterized from meteorological and atmospheric pollution data (ISO 9223 [
The materials investigated are structural metals, in the form of flat plate specimens, with the following features: steel (unalloyed, low carbon), zinc (98.5% min), copper (99.5% min), and aluminum (99.5% min). The test specimens are usually 10 × 15 cm2 and cut out from 1 mm thick sheets.
The exposure sequences include three one-year exposures, one two-year exposure, one three-year exposure, and one four-year exposure. In this paper only one-year exposures have been considered.
Four specimens of each material are exposed in each sequence, three of which are used to determine weight losses according ISO 9226 [
The identification techniques used were basically the following: X-ray diffraction (XRD), infrared spectroscopy (IR), and Mössbauer Spectroscopy (only for the steel). In certain cases elemental information was also obtained by energy dispersive spectroscopy (EDS). The techniques used are complementary. The integration of all of them has permitted a more precise identification of the corrosion compounds formed.
This information was obtained from observation with the scanning electron microscope (SEM) of both the outer surface of the layer of corrosion products and cross-sections. In some cases elemental information was also obtained by EDS, as well as X-ray mappings of certain chemical elements of interest (mainly S and Cl).
In particular, attention is paid to the atmospheric corrosion of four reference metals: unalloyed carbon steel, zinc, copper, and aluminium.
The MICAT project gathered highly varied and complementary information that allowed an in-depth insight into the atmospheric corrosion mechanisms of these four metals. This data included atmospheric aggressivity factors (meteorological parameters, time of wetness (TOW), sulphur dioxide, and chloride deposition rates), the attack experienced by the materials in different atmospheres, the nature of the corrosion products formed on the metallic surface, the morphology of the corrosion films and products, and the morphology of the attack experienced by the base metals.
In order to address this analysis in a systematic way, reference was essentially made to international standard ISO 9223 [
Classification of MICAT test sites according to ISO 9223 [
Type of atmosphere |
Denomination (ISO 9223) [ | Deposition rate | |
Cl− (mg·m−2·d−1) | SO2 (mg·m−2·d−1) | ||
Rural atmospheres | S0P0 | S ≤ 3 | P ≤ 10 |
Urban and industrial atmospheres | S0P1 | S ≤ 3 | 10 < P ≤ 35 |
S0P2 | S ≤ 3 | 35 < P ≤ 80 | |
Marine atmospheres* | S1P0 | 3 < S ≤ 60 | P ≤ 10 |
S2P0 | 60 < S ≤ 300 | P ≤ 10 | |
S3P0 | 300 < S ≤ 1500 | P ≤ 10 | |
Mixed atmospheres | S1P1 | 3 < S ≤ 60 | 10 < P ≤ 35 |
S1P2 | 3 < S ≤ 60 | 35 < P ≤ 80 | |
S2P1 | 60 < S ≤ 300 | 10 < P ≤ 35 | |
S2P2 | 60 < S ≤ 300 | 35 < P ≤ 80 |
Classification of the test sites, according to ISO 9223 [
According to Kucera and Mattsson [
In a dry, clean atmosphere the steel surface becomes coated with a 20–50 Å thick oxide film that practically prevents further oxidation.
The initiation of corrosion on a clean metal surface in nonpolluted atmospheres is a very slow process, even in atmospheres saturated with water vapour. In this case, initiation may occur at surface inclusions such as MnS, which dissolve when the surface becomes wet [
During the initiation period, anodic spots surrounded by cathodic areas are formed.
In the presence of an electrolyte film on the metal surface, conditions are created for propagation of the corrosion process.
The following equations may in principle describe the reactions taking place in the corrosion cells [
The main cathodic reaction is considered to be reduction of oxygen dissolved in the electrolyte film:
Electrochemical studies by Stratmann and Müller [
As soon as ferric corrosion products have been formed, another cathodic process may take place:
Misawa et al. [
(a) Rusting starts with the formation of
(b) The
It is known that fresh rain dissolving impurities including SO2 in the atmosphere often shows a low pH value, such as pH 4. Such a low pH water layer dissolves
Stratmann et al. [
As proposed by Evans [
Once the reducible FeOOH has been used up, the O2 reduction reaction becomes the cathodic reaction as in (
The metal dissolution rate is determined by the diffusion limited current density of the O2 reduction reaction on the pore surfaces. Because the pores in the rust layer are filled with electrolyte, the corrosion rate is quite slow during stage 2, as the diffusion rate is lower in the electrolyte than in the gas phase.
Electrochemical studies by Stratmann and Müller [
During drying-out, the rate of the diffusion limited O2 reduction reaction is extremely fast due to thinning of the electrolyte film on the inner surface of the rust layer. Accordingly, the corrosion rate is very high, O2 reduction again being the cathodic reaction.
In addition to this, O2 can reoxidise the reduced Fe2+ formed in stage 1
In the third stage, the reduced layer of
Misawa [
The atmospheric corrosion process is stimulated by SO2, which is adsorbed and oxidised in the rust layer to
When the surface becomes wetted by rain, dew, or moisture adsorption, the sulphate nests in combination with the surrounding area form corrosion cells. The electrolyte is mostly very concentrated and has low water activity. Anodes are located inside the sulphate nests.
The sulphate nest becomes enclosed within a semipermeable membrane of hydroxide formed through oxidative hydrolysis of the iron ions. Diffusion causes transfer of sulfate ions into the nest. This will stabilise the existence of the nest.
Hydrolysis of the ferrous sulphate formed in these nests controls their propagation. The osmotic pressure can cause them to burst, thus increasing the corrosion rate. The nests are covered by a membrane containing FeOOH. The higher the amorphous FeOOH content, the greater the stability of this membrane and the more unlikely it is to burst due to the effect of osmotic pressure and the repeated wetting and drying of the rust layer.
In atmospheres polluted with chlorides the corrosion of carbon steel proceeds in local cells which resemble the sulphate nests mentioned above [
In marine atmospheres, in addition to
Sea chlorides from natural airborne salinity together with SO2 play an important role in determining the magnitude of atmospheric steel corrosion. However, the scientific literature contains relatively little information on atmospheric corrosion in this type of mixed atmospheres.
The diversity of industrial environments, with the possible presence of other pollutants that may influence the corrosion process, has given rise to several papers on the effect of both pollutants (SO2 and chlorides), acting together. Thus, Ericsson [
Table
MICAT test sites characteristics. Data for mild steel.
Type of atmosphere | Id. | Name | Deposition rate | Time of wetness | 1st-year corrosion rate ( | Atmospheric corrosivity | Corrosion products | |
(Table | (Table | (mg·m−2·d−1) | (TOW) | (ISO 9223) [ | (see Table | |||
Cl− | SO2 | |||||||
S0P0 | 60 | Cuzco | (*) | (*) | 1,4 | C2 | — | |
47 | Artíes | 1,7 | 9,0 | 3,9 | C2 | L, G | ||
4 | San Juan | (*) | (*) | 4,9 | C2 | — | ||
3 | Iguazú | (*) | (*) | 5,7 | C2 | L | ||
65 | Trinidad | 1,5 | 0,7 | 6,7 | C2 | — | ||
36 | Riobamba | 1,1 | 1,2 | 8,4 | C2 | L | ||
44 | Granada | (*) | 6,2 | 8,5 | C2 | L, G | ||
16 | Brasilia | (*) | (*) | 12,9 | C2 | L | ||
49 | Cuernavaca | (*) | 7,9 | 13,4 | C2 | L, G | ||
61 | Pucallpa | (*) | (*) | 14,3 | C2 | L, G | ||
2 | V. Martelli | (*) | 9,0 | 14,7 | C2 | L | ||
59 | Arequipa | (*) | (*) | 15,4 | C2 | L | ||
20 | San Pedro | (*) | 0,6 | 17,0 | C2 | L, G | ||
14 | Belem | (*) | (*) | 19,4 | C2 | L, G | ||
21 | Cotové | (*) | 0,3 | 19,6 | C2 | L, G | ||
43 | Tortosa | (*) | 5,3 | 20,2 | C2 | L, G | ||
40 | León | (*) | (*) | 20,8 | C2 | L, G | ||
35 | Guayaquil | 1,5 | 3,0 | 22,6 | C2 | L | ||
6 | La Plata | (*) | 6,9 | 28,1 | C3 | — | ||
S0P1 | 48 | México | (*) | 13.6 | 9.7 | C2 | — | |
50 | S. L. Potosí | (*) | 18.9 | 31.1 | C3 | — | ||
S0P2 | 12 | São Paulo | (*) | 57.8 | 20.6 | C2 | L, G | |
S1P0 | 67 | Melo | 3,8 | 0,7 | 12,8 | C2 | — | |
41 | El Pardo | 3,9 | 6,4 | 11,3 | C2 | L, G | ||
7 | Caratinga | 5,8 | 1,3 | 11,1 | C2 | L, G, Mg | ||
64 | Pego | 6,0 | 7,9 | 28,5 | C3 | L, G | ||
55 | Chiriquí | 8,7 | 8,2 | 23,0 | C2 | G, L, Mg | ||
46 | Labastida | 9,8 | 3,6 | 15,0 | C2 | L, G, | ||
25 | Sabanilla | 11,3 | 4,9 | 16,6 | C2 | L, G | ||
73 | Matanzas | 15,9 | 9,3 | 23,0 | C2 | — | ||
24 | Arenal | 16,7 | 9,2 | 69,3 | C4 | L, G, M | ||
74 | Barcelona,V | 21,8 | 1,5 | 18,5 | C2 | L, G | ||
51 | Acapulco | 23,8 | 9,6 | 22,1 | C2 | L, G, M | ||
39 | S. Cristóbal | 25,0 | 1,1 | — | 34,5 | C3 | — | |
72 | Coro | 27,5 | 6,5 | 14,8 | C2 | — | ||
71 | Punto Fijo | 31,0 | 5,0 | 21,4 | C2 | L, G | ||
22 | Puntarenas | 33,4 | 7,1 | 61,6 | C4 | L, G, Mg | ||
37 | Salinas | 47,3 | 2,3 | 55,4 | C4 | — | ||
1 | Camet | 55,1 | (*) | 49,5 | C3 | L, G | ||
S2P0 | 70 | El Tablazo | 63,3 | 6,0 | 29,3 | C3 | L, G | |
75 | P. Cabello | — | (*) | 37,3 | C3 | L, G, A | ||
11 | Ubatuba | 113 | 2,6 | 302,0 | C5 | L, G, A, M | ||
69 | P. del Este | 144 | 4,0 | 53,0 | C4 | — | ||
23 | Limón | 220 | 3,5 | 371,5 | >C5 | L, G, M | ||
9 | A. do Cabo | 229 | 6,7 | 165,4 | C5 | G, M, L, Mg | ||
S3P0 | 15 | Fortaleza | >300 | (*) | 118.3 | C5 | — | |
S1P1 | 42 | Barcelona, S | 4,4 | 16,7 | 17,4 | C2 | L, G | |
54 | Veraguas | 14,8 | 16,5 | 20,0 | C2 | L, G, Mg | ||
52 | Panamá | 9,8 | 21,7 | 27,6 | C3 | L, G, Mg | ||
26 | Ciq | 12,0 | 31,6 | 30,4 | C3 | G, L | ||
58 | San Borja | 20,0 | 29,0 | 30,8 | C3 | L, G | ||
66 | Prado | 10,8 | 12,1 | 33,3 | C3 | — | ||
28 | Bauta | 6,4 | 16,4 | 33,8 | C3 | L, G | ||
57 | V. Salvador | 38,0 | 18,0 | 35,1 | C3 | L, M | ||
30 | Valparaíso | 10,0 | 23,6 | 35,5 | C3 | — | ||
29 | Cerrillos | 4,5 | 20,0 | 36,3 | C3 | L, G | ||
8 | Ipatinga | 6,8 | 23,0 | 49,4 | C3 | L, G | ||
S1P2 | 45 | Lagoas | 16,7 | 39,5 | 28,2 | C3 | L, G | |
53 | Colón | 16,8 | 47,4 | 108,1 | C5 | G, L | ||
13 | Río Janeiro | 16,4 | 43,5 | 110,5 | C5 | L, G | ||
10 | Cubatão | 8,1 | 54,5 | 158,9 | C5 | L, G, M | ||
32 | Petrox | 12,8 | 65,2 | 167,2 | C5 | — | ||
S2P1 | 19 | Isla Naval | 60,7 | 10,3 | 33,5 | C3 | L, G, A | |
27 | Cojímar | 104 | 22,5 | 193,2 | C5 | M, L, G | ||
63 | Sines | 203 | 27,0 | 365,0 | >C5 | L, G, A, M, Mg | ||
S2P2 | 62 | Leixões | 97,6 | 69,2 | 72,4 | C4 | L, G, M |
(*) apparently nonpolluted.
(—) not available.
Steel corrosion products identified in the MICAT project.
Code | Name | Composition |
---|---|---|
Hydroxides | ||
L | Lepidocrocite | |
G | Goethite | |
A | Akaganeite | |
Oxides | ||
M | Magnetite | Fe3O4 |
Mg | Maghemite |
There follows a summary of mild steel behaviour in the MICAT project testing station network covering different types of atmospheres according to ISO 9223 (Table
S0P0 rural atmospheres, with very low chloride and SO2 pollution, showed significantly different time of wetness (TOW) and environmental characteristics, such as soil particulate pollution and background pollution. As a consequence of these differences, a relatively wide range of steel corrosion rates could be observed, from 1.4 to 28.2 An extremely low first-year corrosion rate of steel (Ave. 1.4
The low atmospheric corrosion of steel in this Peruvian city was evident by inspecting the surface of steel exposed to the atmosphere for one year (Figure
Appearance of the mild steel surface after one year of outdoor exposure in Cuzco.
Different hypotheses were put forward to try to explain this singular behaviour: very short TOW, steel composition, and low atmospheric pollution. From the results obtained, it seems that the atmosphere of Cuzco is almost unpolluted, which may account for the extremely low corrosion rates found. Some authors [
The scarce data obtained in the MICAT project for steel samples exposed in urban atmospheres (SO2 ≤ 60 mg·m−2·d−1 of SO2), only 3 test sites, yields results which are not significantly different to those obtained in rural atmospheres. However, it was confirmed by Mössbauer spectroscopy that the
In S1P0 marine atmospheres (low chloride deposition rates) mild steel presented corrosivity categories from C2 to C4, and the corrosion surface layer exhibited a morphology characterized by cotton balls of acicular iron corrosion products (Figure In S2P0 marine atmospheres, corrosion product layers exhibited more open structures (Figure
SEM micrographs of corrosion product layers formed on mild steel in pure marine atmospheres: (a) Puntarenas (S1P0) and (b) Arraial do Cabo (S2P0).
They showed different corrosivity categories (from C2 to > C5), depending on their SO2 and Cl− pollution levels. Most of iron corrosion products were identified: L, G, A, M, Mg (Table The cracking effect in the corrosion product layer seems to increase with SO2 pollution and TOW while the contribution of chloride ions into the open structures seems to play a detrimental effect on atmospheric corrosion resistance.
A prerequisite for atmospheric corrosion to occur is that a moisture layer be present on the zinc surface. This layer acts as a solvent for atmospheric constituents and a medium for electrochemical reactions. The atmospheric corrosion of zinc is influenced principally by the time of wetness and the presence of atmospheric constituents such as CO2, SOx, and Cl−. When the moisture layer evaporates, a film of corrosion products precipitates.
Unlike in the atmospheric corrosion of iron, the corrosion products formed on zinc include the respective characteristic anion of the environment where the metal is exposed:
As other metals zinc corrodes in the atmosphere in a discontinuous process, electrochemical in nature, each time the metallic surface is wet. Quintana et al. [
A ZnO (zincite) film is the first thin layer to form from the reaction of zinc with atmospheric oxygen [
Carbonates are formed as a result of the reaction of zinc hydroxide with atmospheric CO2. Although several compounds have been detected, the most common are ZnCO3 (smithsonite) and Zn5(CO3)2(OH)6 (hydrozincite). However, hydrozincite is sometimes difficult to detect by XRD.
SO2 concentration in the atmosphere is a major factor in controlling the rate of corrosion of zinc; the zinc corrosion film has been shown to strongly absorb SO2 during dry deposition. Likewise, deposition of acidic condensates produces a fall in pH and the rate of zinc attack again increases [
Chloride in marine atmospheres also increases the atmospheric corrosion of zinc. There is also a linear relationship between the corrosion rate and salinity [
When SO2 is also present in marine atmospheres, Svenson and Johansson [
Table
MICAT test sites characteristics. Data for zinc.
Type of atmosphere (Table | Id. | Name | Deposition rate | Time of wetness | 1st-year corrosion rate ( | Atmospheric corrosivity | Corrosion products | |
(Table | (mg·m−2·d−1) | (TOW) | (ISO 9223) [ | (see Table | ||||
Cl− | SO2 | |||||||
S0P0 | 44 | Granada | (*) | 6,2 | 0,11 | C2 | Z, H | |
35 | Guayaquil | 1,5 | 3,0 | 0,21 | C2 | Z | ||
4 | San Juan | (*) | (*) | 0,21 | C2 | Z, H | ||
59 | Arequipa | (*) | (*) | 0,23 | C2 | Z, H | ||
43 | Tortosa | (*) | 5,3 | 0,25 | C2 | Z, H | ||
47 | Artíes | 1,7 | 9,0 | 0,28 | C2 | Z, H | ||
40 | León | (*) | (*) | 0,37 | C2 | Z, H | ||
60 | Cuzco | (*) | (*) | 0,40 | C2 | Z, H | ||
65 | Trinidad | 1,5 | 0,7 | 0,55 | C2 | — | ||
6 | La Plata | (*) | 6,9 | 0,91 | C3 | H, Z | ||
61 | Pucallpa | (*) | (*) | 1,01 | C3 | Z, H | ||
2 | V. Martelli | (*) | 9,0 | 1,19 | C3 | Z, H | ||
14 | Belem | (*) | (*) | 1,10 | C3 | — | ||
49 | Cuernavaca | (*) | 7,9 | 1,36 | C3 | — | ||
3 | Iguazú | (*) | (*) | 1,36 | C3 | — | ||
16 | Brasilia | (*) | (*) | 1,78 | C3 | Z, H | ||
20 | San Pedro | (*) | 0,6 | 3,29 | C4 | Z | ||
21 | Cotové | (*) | 0,3 | 3,30 | C4 | Z | ||
S0P1 | 48 | México | (*) | 13.6 | 0,82 | C3 | Z, H | |
50 | S.L. Potosí | (*) | 18.9 | 1.77 | C3 | Z | ||
S0P2 | 12 | São Paulo | (*) | 57.8 | 1.21 | C3 | Z, HZC, H | |
S1P0 | 67 | Melo | 3,8 | 0,7 | 0,69 | C2 | — | |
41 | El Pardo | 3,9 | 6,4 | 0,19 | C2 | Z, H | ||
7 | Caratinga | 5,8 | 1,3 | 0,67 | C2 | Z | ||
64 | Pego | 6,0 | 7,9 | 1,15 | C3 | Z | ||
46 | Labastida | 9,8 | 3,6 | 0,31 | C2 | Z, H | ||
25 | Sabanilla | 11,3 | 4,9 | — | — | H, ZC | ||
73 | Matanzas | 15,9 | 9,3 | 2,73 | C4 | — | ||
74 | Barcelona,V | 21,8 | 1,5 | 2,01 | C3 | — | ||
51 | Acapulco | 23,8 | 9,6 | 1,79 | C3 | S, Z, H | ||
72 | Coro | 27,5 | 6,5 | 0,30 | C2 | — | ||
71 | Punto Fijo | 31,0 | 5,0 | 0,57 | C2 | — | ||
22 | Puntarenas | 33,4 | 7,1 | — | — | H, HZC | ||
1 | Camet | 55,1 | (*) | 1,63 | C3 | — | ||
S2P0 | 70 | El Tablazo | 63,3 | 6,0 | — | — | — | |
11 | Ubatuba | 113 | 2,6 | 7,07 | C5 | S, H | ||
69 | P. del Este | 144 | 4,0 | 2,89 | C4 | — | ||
23 | Limón | 220 | 3,5 | — | — | H, S, HZC | ||
75 | P. Cabello | — | (*) | 4,34 | C5 | — | ||
9 | A. do Cabo | 229 | 6,7 | 4,87 | C5 | Z, S | ||
S3P0 | 15 | Fortaleza | >300 | (*) | 5,46 | C5 | — | |
S1P1 | 42 | Barcelona, S | 4,4 | 16,7 | 0,56 | C2 | Z,H | |
52 | Panamá | 9,8 | 21,7 | 1,06 | C3 | — | ||
66 | Prado | 10,8 | 12,1 | 1,10 | C3 | — | ||
26 | Ciq | 12,0 | 31,6 | 1,20 | C3 | S, ZC | ||
28 | Bauta | 6,4 | 16,4 | 1,22 | C3 | H, S | ||
8 | Ipatinga | 6,8 | 23,0 | 1,23 | C3 | Z | ||
58 | San Borja | 20,0 | 29,0 | 1,61 | C3 | Z, H | ||
56 | Piura | (*) | (*) | 1,63 | C3 | — | ||
29 | Cerrillos | 4,5 | 20,0 | 1,77 | C3 | Z | ||
57 | V. Salvador | 38,0 | 18,0 | 2,46 | C4 | Z, H | ||
S1P2 | 45 | Lagoas | 16,7 | 39,5 | 0,45 | C2 | Z, H | |
10 | Cubatão | 8,1 | 54,5 | 1,25 | C3 | H | ||
13 | Río Janeiro | 16,4 | 43,5 | 1,47 | C3 | H | ||
31 | Idiem | 16,8 | 43.3 | 3,93 | C4 | Z | ||
32 | Petrox | 12,8 | 65,2 | 8,58 | >C5 | Z | ||
S2P1 | 63 | Sines | 203 | 27,0 | 4,03 | C4 | H, BZC, S | |
19 | Isla Naval | 60,7 | 10,3 | 5,89 | C5 | S | ||
27 | Cojímar | 104 | 22,5 | 7,09 | C5 | S, ZC, H | ||
S2P2 | 62 | Leixões | 97,6 | 69,2 | 2,51 | C4 | H,S,ZH |
(*) apparently olluted.
(—) not available.
Zinc corrosion products identified in the MICAT project.
Code | Name | Composition |
---|---|---|
Oxides | ||
Z | Zincite | ZnO |
Hydroxides | ||
ZH | Zinc hydroxide | Zn(OH)2 |
Carbonates | ||
ZC | Smithsonite | ZnCO3 |
H | Hydrozincite | Zn5(CO3)2 (OH)6 |
HZC | Hydrated zinc carbonate | 4ZnO·CO2·4H2O |
BZC | Basic zinc carbonate | Zn4CO3(OH)6 |
Chlorides | ||
S | Simonkolleite | Zn5(OH)8 Cl2·H2O |
There follows an analysis of zinc behaviour in the MICAT project testing station network covering different types of atmospheres according to ISO 9223 (Table
Zinc displays a wide range of first-year corrosion rate values: 0.11–3.30 Zincite (ZnO) and hydrozincite [Zn5(CO3)2(OH)6] are the detected corrosion products on zinc surfaces exposed in rural atmospheres. The zinc surface corrosion layers show isolated white products (zincite) on a generalized and relatively uniform clear grey layer (hydrozincite) (Figure Pitting corrosion is observed (Figure
Morphology of corrosion product layers formed on zinc in unpolluted atmospheres: (a) Villa Martelli (surface view) and (b) La Plata (cross-section view).
In Sao Paulo (57.8 mg·m−2·d−1 of SO2) the characteristic morphology and nature of corrosion products, rounded agglomerates of smithsonite, are observed (Figure
Morphology of corrosion product layers formed on zinc exposed in the SO2-polluted atmosphere of Sao Paulo (a) and marine atmosphere of Puerto Cabello (b).
In low SO2 polluted (≤10 mg·m−2·d−1 of SO2) marine atmospheres corrosion of zinc is a direct function of the chloride pollution level and TOW. S1P0 atmospheres showed zinc corrosion rates of 0.19–2.73 Simonkolleite shows a similar structure to hydrozincite, differing only in its interlayer structure content [ S2P0 atmospheres showed significantly higher zinc corrosion rates (2.89–7.07
Marine atmospheres with SO2 deposition rates in excess of 10 mg·m−2·d−1 of SO2 never display any evidence of residual zinc sulphates on the surface of the corrosion product layers because even if they form they are always washed off by rainfall. When Cl− < 60 mg·m−2·d−1 of Cl−, the corrosion products do not display any evidence of simonkolleite. Zinc corrosion rates vary between 0.45 (C2) and 8.58 (C5)
Several stages may be identified in the evolution of the visual appearance of exposed copper from its initial state to its final patination. Prior to exposure to an outdoor atmosphere, new freshly cleaned copper is a salmon-pink colour, but after just a few weeks of exposure it turns a dull-brown shade.
At room temperature, copper in contact with clean air instantaneously becomes coated with a thin invisible film of cuprous oxide (cuprite) through a direct oxidation mechanism [
Copper corrosion in the atmosphere follows an electrochemical mechanism whereby the metal dissolves anodically forming cuprous and cupric ions:
With increased exposure time these spots increase in surface coverage and cause the specimens to change from their metallic colour to more familiar “copper” colours due to a thin surface oxide. After a few months the copper surface develops a uniform primary protective film of cuprite (Cu2O), which has a matt brown colour and continues to darken with exposure (blackening).
In the following corrosion stages, which can last up to 20 y depending on the environmental conditions, a green-blue patina with a layered structure corresponding to brochantite (mainly rural and urban atmospheres) or atacamite (marine atmospheres) is formed. In the latter case the time to formation is considerably shorter. During this stage, although the copper looks brown, there is an initial “incubation period” in which brochantite forms on the cuprite surface as isolated islands that gradually join together.
Dissolution of SO2 in the moisture layer leads to the formation of sulphite (
(a) Brochantite formation at discrete isolated clamps of crystals on the cuprite base layer formed in an urban atmosphere (cross-section view) [
Posnjakite [Cu4SO4(OH)6·H2O] is formed initially but is then either dissolved or converted to brochantite [Cu4SO4(OH)6] the most common sulphate-containing phase in copper patinas [
With exposure time a continuous brochantite layer forms and hides the underlying cuprite layer, giving the specimens a green appearance (Figure
In chloride environments (marine) the initial corrosion product phase to be formed is cuprite, with paratacamite [Cu2Cl(OH)3], an isomorphic compound of atacamite, appears as a secondary phase growing on the cuprite. Atacamite also appears after longer exposures. Both atacamite and paratacamite present a green-blue colouring characteristic of the copper patinas formed in marine atmospheres (Figure
Once the patina is established it remains stable, and copper corrosion occurs at an ever diminishing rate. Patinated copper typically consists of (a) the underlying copper metal, (b) a thin layer (5–20
When environmental SO2 reaches a competitive level with the chloride aerosol the patina formed is a complex mixture of basic cupric chlorides (paratacamite and atacamite) and basic cupric sulphates (antlerite and brochantite).
Table
MICAT test sites characteristics. Data for copper.
Type of atmosphere | Id. | Name | Deposition rate | T °C | RH % | Time of wetness | 1st-year corrosion rate | Atmospheric corrosivity | Corrosion products | |
(Table | (Table | (mg·m−2·d−1) | (TOW) | ( | (ISO 9223) [ | (see Table | ||||
Cl− | SO2 | |||||||||
S0P0 | 60 | Cuzco | (*) | (*) | 12.2 | 67 | 0,09 | C1 | — | |
4 | San Juan | (*) | (*) | 18.8 | 50 | 0,17 | C2 | Cu | ||
59 | Arequipa | (*) | (*) | 15.6 | 34 | 0,20 | C2 | — | ||
44 | Granada | (*) | 6,2 | 15.6 | 59 | 0,22 | C2 | Cu | ||
49 | Cuernavaca | (*) | 7,9 | 21.0 | 56 | 0,30 | C2 | — | ||
36 | Riobamba | 1,1 | 1,2 | — | — | 0,43 | C2 | — | ||
61 | Pucallpa | (*) | (*) | 26.1 | 81 | 0,56 | C2 | — | ||
47 | Artíes | 1,7 | 9,0 | 7.8 | 72 | 0,62 | C3 | Cu, Br, Po | ||
14 | Belem | (*) | (*) | 26.4 | 86 | 0,64 | C3 | Cu, At, Ca | ||
35 | Guayaquil | 1,5 | 3,0 | 25.9 | 76 | 0,71 | C3 | — | ||
21 | Cotové | (*) | 0,3 | 27.0 | 76 | 0,73 | C3 | Cu | ||
3 | Iguazú | (*) | (*) | 21.2 | 75 | 0,77 | C3 | Cu | ||
2 | V. Martelli | (*) | 9,0 | 16.9 | 74 | 0,79 | C3 | Cu, Po, Br, At | ||
40 | León | (*) | (*) | 11.2 | 65 | 0,81 | C3 | Cu | ||
43 | Tortosa | (*) | 5,3 | 17.4 | 63 | 0,81 | C3 | Cu | ||
65 | Trinidad | 1,5 | 0,7 | 16.7 | 74 | 0,83 | C3 | — | ||
20 | San Pedro | (*) | 0,6 | 11.5 | 90 | 1,05 | C3 | Cu | ||
16 | Brasilia | (*) | (*) | 20.4 | 68 | 1,12 | C3 | Cu, Po | ||
6 | La Plata | (*) | 6,9 | 16.8 | 77 | 1,57 | C4 | Cu | ||
17 | P. Alfonso | (*) | (*) | 25.9 | 77 | — | 1.86 | C4 | — | |
18 | Porto Velho | (*) | (*) | 26.6 | 90 | — | 1.94 | C4 | — | |
S0P1 | 48 | México | (*) | 12.0 | 15.4 | 64 | 0.12 | C3 | Cu | |
50 | S. L. Potosí | (*) | 18.9 | 18.0 | 58 | 0.54 | C2 | Cu | ||
S0P2 | 12 | São Paulo | (*) | 57.8 | 19.6 | 75 | 0.56 | C4 | Cu, Br, Ca | |
S1P0 | 67 | Melo | 3,8 | 0,7 | 17.4 | 80 | 1,27 | C3 | — | |
41 | El Pardo | 3,9 | 6,4 | 15.0 | 55 | 0,81 | C3 | Cu, Po | ||
7 | Caratinga | 5,8 | 1,3 | 21.2 | 74 | 0,99 | C3 | Cu, Po | ||
64 | Pego | 6,0 | 7,9 | 16.9 | 70 | 1,43 | C4 | Cu, Po | ||
46 | Labastida | 9,8 | 3,6 | 12.0 | 73 | 0,95 | C3 | Cu | ||
25 | Sabanilla | 11,3 | 4,9 | 19.9 | 83 | 1,23 | C3 | Cu | ||
73 | Matanzas | 15,9 | 9,3 | 27.7 | 75 | 0,95 | C3 | — | ||
74 | Barcelona,V | 21,8 | 1,5 | 26.7 | 78 | 0,35 | C2 | — | ||
51 | Acapulco | 23,8 | 9,6 | 24.6 | 80 | 1,23 | C3 | Cu, At | ||
39 | S. Cristóbal | 25,0 | 1,1 | 27.5 | 74 | — | 1,52 | C4 | — | |
72 | Coro | 27,5 | 6,5 | 26.5 | 77 | 2,35 | C4 | — | ||
71 | Punto Fijo | 31,0 | 5,0 | 27.6 | 76 | 3,19 | C5 | — | ||
22 | Puntarenas | 33,4 | 7,1 | 28.0 | 80 | 2,98 | C5 | Cu, At | ||
37 | Salinas | 47,3 | 2,3 | 23.3 | 80 | 2,33 | C4 | — | ||
1 | Camet | 55,1 | (*) | 14.1 | 79 | 2,23 | C4 | Cu | ||
S2P0 | 11 | Ubatuba | 113 | 2,6 | 22.1 | 80 | 3,29 | C5 | Cu, At | |
69 | P. del Este | 144 | 4,0 | 16.5 | 78 | 2,51 | C4 | — | ||
23 | Limón | 220 | 3,5 | 25.4 | 88 | 3,68 | C5 | Cu, At | ||
9 | A. do Cabo | 229 | 6,7 | 24.5 | 78 | 4,12 | C5 | Cu, At | ||
75 | P. Cabello | — | (*) | 26.7 | 82 | 4,50 | C5 | — | ||
70 | El Tablazo | 63,3 | 6,0 | 27.7 | 77 | 5,80 | >C5 | — | ||
S3P0 | 15 | Fortaleza | >300 | (*) | 26.4 | 74 | 3,80 | C5 | Cu, Co, At, Po | |
S1P1 | 42 | Barcelona, S | 4,4 | 16,7 | 16.1 | 61 | 0,71 | C3 | Cu, Po | |
29 | Cerrillos | 4,5 | 20,0 | 14.2 | 71 | 0,73 | C3 | Cu | ||
30 | Valparaíso | 10,0 | 23,6 | 14.0 | 82 | 0,87 | C3 | — | ||
8 | Ipatinga | 6,8 | 23,0 | 23.2 | 90 | 1,21 | C3 | Cu | ||
52 | Panamá | 9,8 | 21,7 | 26.9 | 71 | 1,24 | C3 | — | ||
66 | Prado | 10,8 | 12,1 | 17.0 | 76 | 1,38 | C4 | — | ||
26 | Ciq | 12,0 | 31,6 | 25.2 | 79 | 1,45 | C4 | Cu | ||
58 | San Borja | 20,0 | 29,0 | 19.4 | 84 | 1,62 | C4 | Cu | ||
28 | Bauta | 6,4 | 16,4 | 24.0 | 81 | 1,80 | C4 | Cu, At, An, Br, Po | ||
57 | V. Salvador | 38,0 | 18,0 | 19.6 | 84 | 1,98 | C4 | Cu | ||
S1P2 | 45 | Lagoas | 16,7 | 39,5 | 15.9 | 70 | 1,23 | C3 | Cu | |
10 | Cubatao | 8,1 | 54,5 | 22.7 | 74 | 2,86 | C5 | Cu, Br, Ca | ||
31 | Idiem | 16,8 | 43,3 | 12.2 | 82 | 4,79 | C5 | Cu | ||
32 | Petrox | 12,8 | 65,2 | 12.2 | 82 | 5,35 | C5 | Cu, Br | ||
13 | Río Janeiro | 16,4 | 43,5 | 21.4 | 80 | 7,01 | >C5 | Cu, Br | ||
S2P1 | 63 | Sines | 203 | 27,0 | 18.4 | 61 | 3.61 | C5 | Cu, At, La | |
19 | Isla Naval | 60,7 | 10,3 | 27.8 | 86 | 4.72 | C5 | Cu | ||
27 | Cojímar | 104 | 22,5 | 25.1 | 79 | 4.89 | C5 | Cu, At | ||
S2P2 | 62 | Leixões | 97,6 | 69,2 | 17.0 | 59 | 4.32 | C5 | Cu, Pa, At, Sc, Cc |
(*) apparently nonpolluted.
(—) not available.
Copper corrosion products identified in the MICAT project.
Code | Name | Composition |
---|---|---|
Oxides | ||
Cu | Cuprite | Cu2O |
Sulphates | ||
Sc | Copper (II) sulphate | CuSO4·H2O |
An | Antlerite | Cu3(SO4)(OH)4 |
Br | Brochantite | Cu4(SO4)(OH)6 |
La | Langite | Cu4(SO4)(OH)6·2H2O |
Po | Posnjakite | Cu4(SO4)(OH)6·2H2O |
Chlorides | ||
Cc | Copper (II) chloride | CuCl(OH) |
At | Atacamite | Cu2Cl(OH)3 |
Pa | Paratacamite | Cu2Cl(OH)3 |
Sulphides | ||
Ca | Chalcocite | Cu2S |
Co | Covellite | CuS |
There follows an analysis of copper behaviour in the MICAT project testing station network covering different types of atmospheres according to ISO 9223 (Table
From a preliminary analysis of Table To consider this question, an analysis was made of the annual average temperatures (T) and relative humidities (RH) recorded at the test sites. To this end, Figure
First-year copper corrosion rate versus temperature (a) and relative humidity (b) in rural atmospheres.
According to Barton [ Sao Paulo is a highly polluted Ibero-American city with a heavy road traffic. Volatil organic compounds (VOC) in the Sao Paulo atmosphere, mainly carboxylic acids, were measured by Souza et al. [ It is well known that copper is corroded in presence of organic acids [ The appearance of cuprous sulphide (chalcocite, Cu2S) in the first year of exposure in the Sao Paulo atmosphere, which in subsequent years is transformed into cupric sulphur (covellite, CuS), seems to indicate the presence in this atmosphere of considerable amounts of sulphide ions, and the conversion in time of brocantite into antlerite. The first transformation confirms the research of Vernon and Whitby [
A critical threshold for atmospheric salinity, ~20 mg·m−2·d−1 of Cl−, seems to differentiate copper behavior in these types of atmospheres. Below the threshold, copper behaves as in rural atmospheres with corrosion rates of <2 In Figure Copper hydroxysulfates are frequently detected in the corrosion product layers, accompanying the basic copper chlorides typical of these types of atmospheres.
First-year copper corrosion rate versus Cl− deposition rate in marine (S1P0, S2P0, and S3P0) atmospheres. In the graph, the average value of corrosion rate in rural atmospheres (O) is shown.
The presence of both pollutants (Cl− and SO2) leads to the abundant formation of basic salts, both sulfates (brochantite) and chlorides (atacamite), which noticeably compact the corrosion product layers. Copper corrosion also accelerates in these types of atmospheres after a critical threshold of 20 mg·m−2·d−1 of Cl−, increasing with Cl− and SO2 contents in the atmosphere. Basic chlorides and sulfates coexist in the atmospheric corrosion products. The threshold of 20 mg·m−2·d−1 of Cl− defines what will be the main constituent of the patinas; below this value the predominant phase is basic sulfates and above it basic chlorides.
Unlike other metals, whose corrosion causes a general loss of thickness of the material, aluminium corrosion tends to be localised, with the formation of numerous cavities (pits) spread across the entire surface, leaving large areas of the metal between them intact. In this case the concept of mean penetration becomes meaningless, and it is preferable to express corrosion as mass loss per unit of surface area.
All studies agree that upon its initial exposure aluminium quickly forms a thin film of aluminium oxide. Under continued exposure this film may grow and be transformed into various other atmospheric products,
As with other metals, the atmospheric corrosion of aluminium is strongly influenced by the presence or absence of moisture. A crucial consequence of the existence of a water layer on the metal surface is that it provides a medium for the mobilisation of aluminium cations and also for deposited anions.
At the bottom of the pit the environment is acid, and aluminium acts anodically, oxidising according to the reaction:
Al3+ ions, which are practically insoluble in water, combine with oxyhydryl ions from the dissociation of water to form aluminium hydroxide [Al(OH)3]:
There is agreement that the normal corrosion reaction consists of combining with water to form aluminium hydroxide (which constitutes the corrosion product and covers the pit in the form of voluminous bulges) and hydrogen [
The formation of pits on the surface is the most common type of corrosion found in aluminium alloys exposed to the atmosphere, above all in marine atmospheres. In the case of certain highly aggressive industrial atmospheres there are references which indicate the possibility of generalised attack.
The effect of the relative humidity (RH) of the air is of little consideration when aluminium is exposed to pure atmospheres. In fact, the corrosion of aluminium and its alloys depends primordially on the atmosphere being contaminated (in general by sulphur dioxide or chlorides), and only in such cases does the time of wetness intervene decisively in the corrosion process.
Little is known about the influence of temperature on the atmospheric corrosion of aluminium. According to Mikhailovskii et al. [
From an analysis of the available information [
Chloride ions are a significant cause of aluminium surface degradation in atmospheric exposure [
Table
MICAT test sites characteristics. Data for aluminium.
Type of atmosphere | Id. | Name | Deposition rate | Time of wetness | 1st year corrosion rate ( | Atmospheric corrosivity | Corrosion products | |
(Table | (Table | (mg | (TOW) | (ISO 9223) [ | (see Table | |||
Cl− | SO2 | |||||||
S0P0 | 59 | Arequipa | (*) | (*) | 0,01 | C1 | — | |
65 | Trinidad | 1,5 | 0,7 | 0,01 | C1 | — | ||
60 | Cuzco | (*) | (*) | 0,02 | C1 | N | ||
35 | Guayaquil | 1,5 | 3,0 | 0.03 | C1 | N | ||
61 | Pucallpa | (*) | (*) | 0.03 | C1 | N | ||
44 | Granada | (*) | 6,2 | 0.04 | C1 | N | ||
4 | San Juan | (*) | (*) | 0,08 | C1 | N | ||
43 | Tortosa | (*) | 5,3 | 0,08 | C1 | N | ||
47 | Artíes | 1,7 | 9,0 | 0,11 | C1 | N | ||
2 | V. Martelli | (*) | 9,0 | 0,12 | C1 | N | ||
40 | León | (*) | (*) | 0,13 | C1 | N | ||
21 | Cotové | (*) | 0,3 | 0,14 | C1 | — | ||
6 | La Plata | (*) | 6,9 | 0,15 | C1 | N | ||
3 | Iguazú | (*) | (*) | 0,20 | C1 | N | ||
20 | S. Pedro | (*) | 0,6 | 0,20 | C1 | — | ||
14 | Belem | (*) | (*) | 0,22 | C1 | N | ||
49 | Cuernavaca | (*) | 7,9 | 0,24 | C1 | — | ||
16 | Brasilia | (*) | (*) | 0,27 | C1 | N | ||
S0P1 | 48 | México | (*) | 12 | 0,12 | C1 | — | |
50 | S.L. Potosí | (*) | 18.9 | 0.54 | C2 | — | ||
S0P2 | 12 | São Paulo | (*) | 57.8 | 0.56 | C2 | N | |
S1P0 | 67 | Melo | 3,8 | 0,7 | 0,06 | C1 | — | |
41 | El Pardo | 3,9 | 6,4 | 0,07 | C1 | N | ||
7 | Caratinga | 5,8 | 1,3 | 0,17 | C1 | N | ||
64 | Pego | 6,0 | 7,9 | 0,35 | C2 | N | ||
46 | Labastida | 9,8 | 3,6 | 0,18 | C1 | N | ||
25 | Sabanilla | 11,3 | 4,9 | 0,14 | C1 | N | ||
73 | Matanzas | 15,9 | 9,3 | 0,28 | C1 | — | ||
74 | Barcelona,V | 21,8 | 1,5 | 0,16 | C1 | — | ||
39 | S.Cristóbal | 25,0 | 1,1 | — | 0,52 | C2 | N | |
72 | Coro | 27,5 | 6,5 | 0,75 | C3 | — | ||
71 | Punto Fijo | 31,0 | 5,0 | 0,49 | C2 | — | ||
51 | Acapulco | 23,8 | 9,6 | 1,63 | C3 | — | ||
22 | Puntarenas | 33,4 | 7,1 | 1,93 | C3 | A | ||
37 | Salinas | 47,3 | 2,3 | 1,12 | C3 | — | ||
1 | Camet | 55,1 | (*) | 0,57 | C2 | N | ||
S2P0 | 11 | Ubatuba | 113 | 2,6 | 1,17 | C3 | A | |
69 | P. del Este | 144 | 4,0 | 1,68 | C3 | — | ||
23 | Limón | 220 | 3,5 | 0,86 | C3 | A | ||
9 | A. do Cabo | 229 | 6,7 | 1,68 | C3 | A | ||
75 | P. Cabello | — | (*) | 1,64 | C3 | — | ||
S3P0 | 15 | Fortaleza | >300 | (*) | 1.58 | C3 | A | |
S1P1 | 66 | Prado | 10,8 | 12,1 | 0,27 | C1 | — | |
8 | Ipatinga | 6,8 | 23,0 | 0,39 | C2 | A | ||
52 | Panamá | 9,8 | 21,7 | 0,43 | C2 | — | ||
42 | Barcelona, S | 4,4 | 16,7 | 0,68 | C3 | N | ||
29 | Cerrillos | 4,5 | 20,0 | 0,68 | C3 | N | ||
28 | Bauta | 6,4 | 16,4 | 0,99 | C3 | N | ||
26 | Ciq | 12,0 | 31,6 | 1,11 | C3 | N | ||
58 | San Borja | 20,0 | 29,0 | 1,32 | C3 | N | ||
57 | V. Salvador | 38,0 | 18,0 | 1,57 | C3 | N | ||
30 | Valparaíso | 10 | 23.6 | 3.56 | C4 | — | ||
S1P2 | 45 | Lagoas | 16,7 | 39,5 | 0,33 | C2 | N | |
13 | Río Janeiro | 16,4 | 43,5 | 0,74 | C3 | A | ||
10 | Cubatão | 8,1 | 54,5 | 0,78 | C3 | A | ||
31 | Idiem | 16,8 | 43.3 | 5,21 | C5 | — | ||
32 | Petrox | 12,8 | 65,2 | 5,43 | C5 | — | ||
S2P1 | 19 | Isla Naval | 60,7 | 10,3 | 1.67 | C3 | N | |
27 | Cojímar | 104 | 22,5 | 3.01 | C4 | N | ||
63 | Sines | 203 | 27,0 | 3.79 | C4 | A, Sb | ||
S2P2 | 62 | Leixões | 97,6 | 69,2 | 4.09 | C4 | A, Sb, Ca |
(*) apparently nonpolluted.
(—) not available
(N) not detected any corrosion product.
Aluminium corrosion products identified in the MICAT project.
Code | Name | Composition |
---|---|---|
Oxides | ||
A | Alumina | |
Sulphates | ||
Sb | Aluminium basic sulphate | Alx(SO4)y(OH)z |
Chlorides | ||
Ca | Aluminium chloride | AlCl3·6H2O |
There follows an analysis of aluminium behaviour in the MICAT project testing station network covering different types of atmospheres according to ISO 9223 (Table
In unpolluted rural atmospheres aluminium does not present significant attack, only some soiling by dust particles (Figure
(a) Soiling of aluminium surface by dust particles. (b) Pitting of aluminium surface caused by sea-borne chlorides. Great formation of corrosion products (c) and strong pitting (d) caused by severe attack of aluminium in SO2-polluted marine atmospheres.
Unfortunately, the MICAT project involved a very small number of testing stations of this type: only two atmospheres corresponding to category S0P1 (Mexico City and San Luis Potosí) and one atmosphere corresponding to category S0P2 (Sao Paulo). With so few stations it is risky to make generalisations about aluminium behaviour in these atmospheres. Bearing this in mind, an indication is given of the most relevant findings, supplemented with other published information. Aluminium attack in these two types of atmospheres, although significant, is only low (<0.6 g·m−2·y−1), which may indicate that SO2 in the atmosphere does not have a significant effect on the atmospheric corrosion of aluminium at concentrations below 60 mg·m−2·d−1 of SO2, confirming the experience of Rozenfeld [ As in the rural atmospheres, the presence of very small amounts of corrosion products, aggravated by their location at isolated points on the surface, hinders their identification by the analytical techniques used in this research.
In pure marine atmospheres there seems to be a critical threshold for atmospheric salinity, around 20 mg·m−2·d−1 Cl−, which differentiates the corrosion behavior of aluminium. Below this threshold aluminium behaves in a similar way as in rural atmospheres, that is, practical absence of attack. Above it, aluminium undergoes pitting from the first year of exposure (Figure
Aluminium corrosion in mixed atmospheres (polluted by Cl− and SO2) depends both on the chloride concentration and the SO2 pollution level in the atmosphere. Aluminium attack can increase considerably Figures
The 72 Ibero-American Atmospheric testing stations, covering a broad spectrum of climatological and pollution conditions, were divided into subgroups according the classification of atmospheric aggressiveness (ISO 9223 [
In each of these subgroups and for each of the reference metals (low carbon steel, zinc, copper, and aluminium) the corrosion extent for the first year of exposure and the nature of the corrosion products formed were evaluated. Generalizations were made based on observed trends.
The authors wish to express their gratitude to the Programa Ibero-Americano de Ciencia y Tecnología para el Desarrollo (CYTED) for financial support granted for the international coordination of MICAT project.