Scientists have known for centuries that gold does not rust the way iron and other common metals do, but the exact cause has been debated for just as long.
A study published in Physical Review Letters by two researchers at Tulane University now points to a specific atomic process as the primary explanation.
Santu Biswas, a postdoctoral fellow, and Matthew Montemore, an associate professor of chemical engineering at the university, used computer simulations to study how oxygen interacts with gold surfaces at the atomic level.
The prevailing explanation had been that gold holds tightly to its electrons, making it difficult for oxygen to bond with its surface. Montemore said the new research shows that while this is true, it does not fully account for just how resistant gold actually is to oxidation.
Gold atoms rebuild their own surface within seconds
The more significant factor, the researchers found, is what happens the moment a new gold surface is created. When gold is cut or broken, the exposed atoms do not stay in their original positions.
Within seconds, they shift from a square-shaped arrangement into a denser, hexagonal pattern. This natural rearrangement, called surface reconstruction, produces a herringbone-like structure detectable under specialized microscopes.
Biswas said the team’s main question was not simply whether gold is hard to oxidize, but why it is so much harder than expected.
Their simulations showed that oxygen molecules can break apart and bind to gold surfaces far more easily in the brief period before reconstruction takes place.
Once the atoms settle into the new pattern, the surface becomes dramatically more resistant. The researchers calculated that this rearrangement reduces oxygen reactions by a factor of one billion to one trillion.
Why gold does not rust, confirmed by atomic data
This two-part protection, electron retention combined with surface reconstruction, explains why gold objects do not rust or tarnish even after hundreds of years.
The findings also open a new direction in industrial chemistry. Gold-based catalysts are used in producing vinyl acetate, a compound used in plastics, and researchers are examining gold for removing carbon monoxide from vehicle exhaust and manufacturing propylene oxide.
The limitation has always been that gold resists oxygen too well to be broadly useful in such reactions. Montemore said that finding a way to make gold interact with oxygen more readily could make it a far more effective industrial catalyst. Disrupting or preventing surface reconstruction is one potential path toward that goal.
Breaking reconstruction could make gold a better catalyst
Biswas noted that placing an absorbent material on the gold surface is one method that could achieve this by stopping the rearrangement from occurring.
Current methods for improving gold catalysts involve combining it with other metals or using very small gold particles. Targeting surface geometry directly could serve as a separate and more precise approach.
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