Throwing out the textbook: Salt surprises chemists

December 19, 2013

Washington, D.C.--Table salt, sodium chloride, is one of the first chemical compounds that schoolchildren learn. New research from a team including Carnegie's Alexander Goncharov shows that under certain high-pressure conditions, plain old salt can take on some surprising forms that violate standard chemistry predictions and may hold the key to answering questions about planet formation. Their work is published December 20 in Science.

The team, which also included Carnegie's Elissaios Stavrou and Maddury Somayazulu, among others, combined new computational methods and structure-prediction algorithms with high-pressure experiments to study the range of changes that simple sodium chloride undergoes under pressure. They predict some unanticipated reaction results under high pressure that could help geochemists scientists reconcile ongoing mysteries involving minerals found in planetary cores.

The team first used advanced algorithms to identify an array of possible stable structural outcomes from compressing rock salt. They then attempted to verify these predictions, using a diamond anvil to put salt mixed with molecular chlorine or metallic sodium under high pressured.

"We discovered that the standard chemistry textbook rules broke down," Goncharov said.

The well-understood rock salt, NaCl, turned into stable compounds of Na3Cl, Na2Cl, Na3Cl2 and NaCl7, all of which have highly unusual chemical bonding and electronic properties.

"If this simple system is capable of turning into such a diverse array of compounds under high-pressure conditions, then others likely are, too," Goncharov added. "This could help answer outstanding questions about early planet cores, as well as to create new materials with practical uses."

The research team also included lead author Weiwei Zhang of China Agricultural University; Artem Oganov, Qiang Zhu, Eddine Boulfelfel, and Andriy Lyakhov of State University of New York Stony Brook; Vitali Prakapenka of the University of Chicago; and Zuzana Konopkova of Photon Science DESY.
This work was supported by the National Science Foundation, DARPA, the government of the Russian Federation, China's Foreign Talents Introduction and Academic Exchange Program, German BMBF, the Young Teachers Development Project in China Agricultural University, the Army Research Office, and EFREE a BES-EFRC center at Carnegie.

Calculations were performed on XSEDE facilities and on the cluster of the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the DOE-BES. X-ray diffraction experiments were performed at GeoSoilEnviroCARS (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory and Petra III, DESY, Hamburg, Germany. GeoSoilEnviroCARS is supported by the National Science Foundation - Earth Sciences and Department of Energy - Geosciences. Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences. PETRA III at DESY is a member of the Helmholtz Association (HGF).

The Carnegie Institution for Science is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

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