Chemistry in Pictures: Losing pressure | Chemical & Engineering News

Issue Date: March 15, 2018 | Web Date: March 16, 2018

Chemistry in Pictures: Losing pressure

Department: Education
Keywords: coatings, micrographs
Credit: Bob Pearce
A micrograph of a hole in a tin-plated can caused by a breach in the coating that led to corrosion.
Credit: Bob Pearce

This micrograph shows a leak caused by corrosion on the inside of a tin-plated aerosol can. Bob Pearce, R&D director for NCH Corp., wanted to test the shelf life of a coil cleaner for air conditioners. He and a colleague loaded the cleaner, which is a water-based solution containing sodium hydroxide, into a pressurized can and heated it continuously for 90 days in an oven to accelerate the breakdown of the can. After 30 days, the container’s pressure began to drop, indicating a leak, and it began to deteriorate visibly. At the trial’s end, the researchers inspected the can with a microscope and found that a breach in the coating had allowed the sodium hydroxide in the cleaner to seep underneath and corrode the can’s wall.

The largest hole is less than .5 mm.

Submitted by Bob Pearce

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