Atmospheric corrosion of zinc

Table 4.34 Atmospheric corrosion of zinc in various part of the UK...

Other factors of importance in atmospheric corrosion of zinc are (i) the distance from the ground (ii) orientation of the samples (iii) wind or rain shielding (iv) distance to the local contaminant sources (v) wind, radiation (vi) condensation and drying rate (vii) amount of contaminants and nature of corrosion products and (viii) seasonal variation of factors also should be considered. This shows the complexity of the problem of determining the atmospheric corrosion rates to a high degree of certainty. This uncertainty is exemplified by the observed corrosion rate of 0.6-3.8 pm/yr at 26 sites in rural area in Spain.95 The corrosion rate of 8.5 pm/yr observed on the zinc coating in an under-vehicle situation is comparable to severe marine atmospheric conditions.96... 

Muster et al. [64] studied the effects of salt concentration, droplet size, and droplet shape on atmospheric corrosion of zinc. Small droplets (1-10 pL) of sea water and... 

Fig. 10.20 Influence of NaCI deposition and SO2 on atmospheric corrosion of zinc at 90% RH and 25 °C [68],...

In a separate study, the effects of NaCl and SO2 air pollutants on the corrosion of zinc were investigated by Qu et at. [68]. Influence of NaCl deposition and SO2 on atmospheric corrosion of zinc at 90% RH and 25 °C is shown in Fig. 10.20 [68]. The corrosion rate decreases with time due to the large amounts of deposit buildup onto the zinc surface. NaCl increases the initial corrosion of zinc in air in the presence and absence of SO2. Presence of only SO2 slowly increases the initial corrosion rate. The synergistic corrosion effect was observed in the presence of both contaminants. 

G. A. El-Mahdy, Advanced laboratory study on the atmospheric corrosion of zinc under thin electrolyte layers. Corrosion 59 (2003) 505—510. 

I.S. Cole, N.S. Azmat, A. Kanta, M. Venkatraman, What really controls the atmospheric corrosion of zinc Effect of marine aerosols on atmospheric corrosion of zinc, Int. Mater. Rev. 54 (2009) 117-133. 

H. Muster, A. Bradbury, A. Trinchi, I.S. Cole, T. Markley, D. Lau, S. Dligatch, A. Bendavid, P. Martin, The atmospheric corrosion of zinc the effects of salt concentration, droplet size and droplet shape, Electrochim. Acta 56 (2011) 1866-1873. 

L. Veleva, M. Acosta, E. Meraz, Atmospheric corrosion of zinc induced by runoff, Corros. Sci. 51 (2009) 2055-2062. 

Atmospheric corrosion of zinc is roughly proportional to the time of wetness in a particular location, a point emphasized by Mikhailovskii et al. (1986) for areas of the former Soviet Union, provided the nature and quantity of environmental pollution do not change a high relative humidity, which can cause condensation, increases corrosion. Rain obviously increases time of wetness, but it can have an indirect beneficial effect by removing corrosive materials. In practice, time of wetness is often taken as the time when relative humidity (RH) exceeds 80% and the temperature is above 0°C. Thin layers of solutions (except acids) are more corrosive than bulk solutions (Mansfield and Tsai, 1979). The general consensus is that the significance of atmospheric humidity in the corrosion of zinc is related to the conditions that may cause condensation of moisture on the metal surface and to the frequency and duration of the moisture contact. 

Sulfur dioxide is the most important individual contaminant to be considered in atmospheric corrosion of zinc. At relative humidities of about 70% or above, it usually controls the corrosion rate. Figure 2.12 shows the linear relationship for zinc and contrasts it with the way in which the unit influence of sulfur dioxide on steel decreases with concentration (although the total amount of corrosion on steel is of course much more). 

Table 2.19 Recommended Reference Data on the Rate of Atmospheric Corrosion of Zinc in the Soviet Union...

The tropics here means the region between latitudes approximately 30°N and 30 S, that is, comprising somewhat more territory than the geographical tropics (23 N and 23°S). A great variety of climatic conditions can be found in the tropics, and the atmospheric corrosion of zinc varies accordingly. Distinctions are therefore made between dry tropical atmospheres (deserts), moist tropical atmospheres (tropical rain forests), and tropical marine atmospheres (near the coast). 

Bottcher, H. J. (1982). Zur atmospharischen Korrosion von Zink und Zinkiiberziigen (Atmospheric corrosion of zinc and zinc coatings). Werkst. Veredll.,4(3), 109-113 (in German). 

Cramer, S. D., Carter, J. P., Linstrom, P. J., and Flinn, D. R. (1987). Environmental effects in the atmospheric corrosion of zinc. Symposium on the Degradation of Metals in the Atmosphere, ASTM STP 965. American Society for Testing and Materials, Philadelphia, pp. 229-247. 

Goodwin, F. E. (1991). The effect of environmental acidification on atmospheric corrosion of zinc. 16th Int. Galv. Conf., EGGA, London, pp. GHl/l-12. 

Hippensteel, C. L., and Borgmann, C. W. (1930). Outdoor atmosphere corrosion of zinc and cadmium electrodeposited coatings on iron and steel. Trans. Am. Electro-chem. Soc., 58, 23-41. 

Linder, M. (1988). The Influence of Environmental Acidification on the Atmospheric Corrosion of Zinc. Swedish Corrosion Institute, Stockholm, Report to ILZRO... 

Schikorr, G. (1961a). Relation between the atmospheric corrosion of zinc and nickel and the sulfur dioxide content of the air. Metall, 15, 981-987 (in German). 

Strekalov, P., and Benikshtis, G. (I%5). Atmospheric corrosion of zinc and cadmium coatings on steel and the changeover from accelerated to actual testing conditions. Korroz. Met. Splavov. Sb. (2), 264-278 (in Russian). 

The atmospheric corrosion of zinc involves the following partial reactions ... 

The protection mechanism is similar to that of metallic zinc coatings zinc is less noble than steel and protects the substrate by forming a galvanic corrosion cell, in which zinc is the anode. This mechanism is particularly active in presence of defects in the coating that provide an electrolyte path to the substrate surface. In addition, the atmospheric corrosion of zinc yields voluminous solid corrosion products (oxides, carbonates, etc.) that are capable of blocking pores or small defects in the coating, thereby reinforcing its barrier effect. 

In the atmospheric corrosion of zinc, the most important atmospheric con-taminent to be considered is sulfur dioxide. At relative humidities of about 70% or above, it usually controls the corrosion rate. 

Goodwin, F. E The Effect of Environmental Acidification on Atmospheric Corrosion of Zinc," 16th International Galvanizing Conference, European General Galvanizers Association, London, 1991, pp. GHl/1-12. 

Influence ofNOi on Atmospheric Corrosion OF Zinc Exposed in a Climate Chamber... 

Zinc-coated steels are widely used in automotive and construction industries, and in manufacturing electronic equipment. Therefore, these materials are exposed to a wide variety of outer and irmer atmospheres. The general picture of the atmospheric corrosion of zinc has... 

Influence of NO2 on Atmospheric Corrosion of Zinc Exposed in a Climate... 91... 

In the past decade, Odnevall and Leygraf [23-25] made a 90-day, systematic study of atmospheric corrosion of zinc exposed to different atmospheres. They proposed a sequence of formation of corrosion products for the various atmospheres. In most cases, all main corrosion products can be detected after one month of atmospheric exposure. In aggressive environments (marine and industrial) the formation of sulfur and chlorine compounds occurs very fast (often in a single day). While the process advances, these compoimds generally increase in amount, although some can disappear as a result of their transformation into other components, depending on the atmosphere. 

Very little information has been published on the atmospheric corrosion of zinc over long time periods (10-20 years) [27, 28]. In a long-term study in Spain, the characteristics of corrosion products formed on zinc panels (after 13-16 years) in various types of atmospheres in Spain (rural, urban, industrial, mild marine and severe marine) were studied [28], and the authors found a linearly increasing amount of zinc corrosion with time at the different test sites, except the marine atmospheres, where the zinc deviated from the usual behavior... 

In this work, the role of NO2 in the atmospheric corrosion of zinc was analyzed from a detailed characterization of corrosion products. Laboratory tests with exposru e parameters close to the conditions observed in real atmospheres were performed, with the aim of simulating close-to-reality corrosion mechanisms. Low-pollutant concentrations and shortterm exposmes were carried out. For these reasons, XPS were used for the analysis of very thin corrosion layers formed. 

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