Chemistry in Pictures: Grainbow colors

This is a close-up photo of a piece of stainless steel from a large spring, meant to support 5000 lbs (around 2200 kg) of weight, that failed during testing. Russell Rohloff, a chemist in the materials and surface engineering group at Woodward Inc., captured the image while preparing a sample of the metal for scanning electron microscopy analysis to look at the composition and distribution of carbides in the material. Excess carbides at grain boundaries can cause metals to break more easily. After vacuum etching the sample at 3500 °C to expose the metal’s internal grain structure, Rohloff cleaned the surface with a mixture of alcohol and acetone. During the cleaning step, he accidentally contaminated it with oils from his skin—which gave the surface an iridescent rainbow sheen. Though he couldn’t use the contaminated sample, Rohloff used the image, taken at 2500x magnification under white light, in an assignment for an art appreciation class he was taking at the local community college (and got an A).

Submitted by Russell Rohloff

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