Photographer: Glenn Woodell; Glenn's Web site
Summary Author: Glenn Woodell
This example of environmental wear on anodized aluminum demonstrates the electrochemical nature of corrosion. Moisture in the air or from rain combined with the molecules in the metal, or in the moisture source, forms an electrochemical cell, complete with an anode and a cathode. The anodic region is where the corrosion is centered, while the cathodic region is the oppositely charged area surrounding the anode. The radius of this charge is what actually protects, to an extent, the surrounding area from further corrosion. This causes the surface of the aluminum to have what appears to be regularly spaced corrosion. (See black & white detail.) However, rather than being regularly spaced, there's a minimum distance below which further corrosion is not being allowed to initiate. The aluminum shown above is part of the decorative facade on the front of a 50-year old building. This area was never in direct sunlight. Areas receiving direct sunlight at least part of the time had much less corrosion. Photo taken on May 3, 2012.
Photo details: Camera Maker: SAMSUNG; Camera Model: SGH-i937; Focal Length: 4.03mm; Aperture: f/2.6; Exposure Time: 0.0058 s (1/172); ISO equiv: 6400; Exposure Bias: none; Metering Mode: Center Weight; Exposure: aperture priority (semi-auto); White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB; Software: Adobe Photoshop CS5.1 Windows.
