Physicists at the University of Pennsylvania have experimentally discovered a fundamental principal about how solid materials melt. Their studies have shown explicitly that melting begins at defects within the crystalline structure of solid matter, beginning along the cracks, grain boundaries and dislocations that are present in the otherwise orderly array of atoms. Their findings, which will appear today in the journal Science, answer longstanding fundamental questions about melting and will likely influence research in physics, chemistry, materials science and engineering, as well as studies of biological importance.
"Melting is one of the most fundamental phenomena in physics and is one of the phase transitions most frequently seen in daily life," said Arjun Yodh, a professor in Penn’s Department of Astronomy and Physics. "Yet major details about the mechanisms that drive the melting of an ice cube are missing. Superficially, the principle is straightforward. As a solid heats up, molecules within the ice acquire more energy and jiggle around more, driving the transition from a solid to a liquid. This is true in part, but reality is richer and more complex."
In the Science paper, the Penn physicists show direct evidence for a leading theory of melting, the notion that the start of melting – premelting – occurs at imperfections in the orderly structure of solid crystals. Premelting occurs in areas where the alignment of atoms is not perfect, especially at the boundaries within crystals where the patterns of atoms shift much like imperfections in the grain of a piece of wood.
Greg Lester | EurekAlert!
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