Environmental Effects on Metallic Corrosion Products Formed in Short-Term Atmospheric Exposures

Abstract

The Bureau of Mines has measured short-and long-term atmospheric corrosion damage on five metals and two metal-coated steel products at four sites in the east and northeast United States as part of the National Acid Precipitation Assessment Program to evaluate the effects of acid deposition on materials. The composition of the corrosion product on carbon steel, weathering steel, copper, zinc, and galvanized steel is relatively unchanged in 1-and 3-month exposures over a wide variety of environmental conditions. Spalling and runoff losses are observed on all metals. Massive reorganization of the corrosion film by a mechanism of cyclic dissolution and precipitation was observed on carbon steel, Cor-Ten A, zinc, and galvanized steel. Loss of corrosion product from zinc in runoff was a function of both dissolution in rain water and neutralization by hydrogen ion loading, with dissolution contributing the greater portion of the loss.The corrosion of metallic materials in the atmosphere has been studied extensively (1).The majority of the work in this area has been to determine the performance of materials and to evaluate mitigation techniques in environments of interest.With only a few exceptions (see for example references 2, 3), attempts have not been made in studies conducted in the United States to fully characterize the environment and to determine the relationships between components of the environment and the performance of the material of interest (see reference 4 for a recent assessment of this area). Adherent corrosion products are often characterized, but no attempts have been made, except in laboratory studies (5), to quantitatively relate the corrosion film chemistry to environmental parameters.In 1981, a field study was initiated by the Bureau of Mines to determine the effects of the environment, including acid deposition, on the corrosion of a number of commonly used metallic materials of construction.This study, which is fully described in a recent paper (6_), is being conducted at field sites where continuous air This chapter not subject to U.S.

Corrosion Mechanisms for Zinc Exposed to the Atmosphere

“…The composition of the surface film produced by atmospheric corrosion of zinc is not constant with depth (15). An O/Zn ratio consistent with ZnO occurs in the outer 15 nm of the surface layer, and a trend toward concentration ratios consistent with ZnCO~ or Zn(OH)~ deeper into the film.…”

“…Flinh and co-workers (15) have described in some detail the morphology of corrosion films on zinc exposed to the atmosphere. Under conditions of slow corrosion the film is uniform, somewhat nodular, and fine grained.…”

“…In the presence of water, the oxide is promptly transformed to zinc hydroxide, probably in several different crystal structures (16,19). For exposures of a few months, zinc hydroxides are the principal constituents of the corrosion film produced by atmospheric exposure (15). Although several different forms of zinc hydroxide have been described in the scientific literature (Table I), the only one known to occur naturally as a mineral is wulfingite [designated e-Zn(OH)2], an orthorhombic crystal with unit cube dimensions of a = 8.490, b = 5.162, and c = 4.917 A and a density of 3.5 g/cm 3 (34).…”

What really controls the atmospheric corrosion of zinc? Effect of marine aerosols on atmospheric corrosion of zinc

“…Compact oxides with low porosity and few cracks act as effective barriers, while porous, cracked or incomplete oxides are ineffective. Flinn et al 68 observed that oxides which develop slowly during atmospheric exposure of zinc are uniform, nodular and fine grained, while those that develop at a faster rate undergo massive dissolution and precipitation, and therefore do not act as effective barriers. Sandberg et al 61 studied the polarisation resistance of hot dipped galvanised steel and pure zinc exposed to the atmosphere in a marine environment for a period of one year.…”

Acid rain damage to carbonate stone: A quantitative assessment based on the aqueous geochemistry of rainfall runoff from stone

“…These supplemental data include an array of meteorological, climatological, air pollution, and rainfall chemistry measurements. The character of the general environment in which the rock samples were exposed has been given by Flinn et al (1986).…”