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[ link to www.livescience.com (secure)] Scientists may finally understand the mysterious transition behind a century-old chemistry experiment. The details of this transformation, in which adding electrons to a bright blue ammonia solution morphs it into a lustrous, metallic bronze, have long eluded scientists.
The new study reveals the subtle details of this change, and shows that this transformation is gradual, rather than sudden. "What we've done successfully is that we've pretty much understood how these solutions behave at a wide range of concentrations using a microjet technique," said study co-author Ryan McMullen, a doctoral student in chemistry at the University of Southern California. This technique, which involves shooting hair-thin streams of the solution through a vacuum, has not been used on the lustrous liquid before.
But how do some nonmetals transform into metals? In a new study, researchers answered that question by adding metals to liquid ammonia.
The result was an expected reaction: The liquid ammonia pulled electrons from the metal. Those electrons then became trapped between the ammonia molecules, creating the so-called solvated electrons the researchers hoped to study. At low concentrations, the result was a blue, non-metallic liquid. As the solvated, or trapped, electrons piled up, though, the solution transitioned to shiny bronze.
The next challenge was to investigate how the solvated electrons behaved at different concentrations. This involved shooting a microjet of the solution — about the width of a human hair — through a beam of synchrotron X-rays, which are high-energy X-ray beams. The X-rays excited the solvated electrons, causing them to hop out of their liquid cage of ammonia molecules. The researchers could then measure how much energy it took to release the solvated electrons.
"When you increase the concentration to the metallic range then you see, this wonderful pattern emerges that is very, very characteristic of a metal," McMullen said.
The results were interesting because they showed that the metal-like liquid created by combining alkali metals and ammonia actually is a metal on a fundamental physical level, he said.
"It is a genuine metal, it's not something that just looks like one," McMullen said.
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