Gold has been prized for thousands of years for its enduring shine, but researchers at Tulane University have finally discovered the physical mechanism behind its legendary resistance to tarnishing — and it is far more sophisticated than simple chemistry.

In a new study published in Physical Review Letters, chemical engineers Matthew Montemore and Santu Biswas showed that atoms on the two most common gold surface types spontaneously rearrange themselves into protective zigzagging hexagonal patterns. This atomic restructuring dramatically suppresses reactions with oxygen by a factor of one billion to one trillion.

"People have generally thought gold doesn't tarnish simply because it doesn't interact strongly with oxygen," said Montemore, associate professor at Tulane's School of Science and Engineering. "What we show is that for two of the most common gold surface types, the surface atoms actually rearrange themselves in a way that makes the gold much more resistant to oxidation."

Using computer simulations that predict atomic and electron behavior, the team modeled how oxygen molecules interact with gold surfaces. Without the atomic rearrangement, oxygen could break apart and react with gold much more easily. The protective reorganization essentially creates an atomic-scale barrier that keeps gold shiny indefinitely.

The discovery could lead to practical applications beyond jewelry. Gold-based catalysts are already used in industrial processes like producing vinyl acetate for plastics and cleaning carbon monoxide from car exhaust. But gold's natural resistance to breaking apart oxygen molecules — the same trait that prevents tarnishing — has limited its catalytic usefulness.

"If you can trick gold into dissociating oxygen, it can actually become a very effective catalyst for certain reactions," Montemore said. "Our work suggests a new strategy for potentially doing that by preventing or reversing these surface rearrangements."

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