Livermore scientists unveil melting point of iron

Two scientists at Lawrence Livermore National Laboratory have discovered that iron in Earth-core conditions melts at a pressure of 225 GPa (or 32 million pounds per square inch) or about 5,100 kelvins (8,720 degrees Fahrenheit).

Determining the melting point of iron is essential to determine the temperatures at core boundaries and the crystal structure of the Earth’s solid inner core. To date, the properties of iron at high pressure have been investigated experimentally through laser-heated diamond anvil cells, shock compression techniques and theoretical calculations.

However, those techniques have not produced a consensus on the melt line or the high-pressure, high-temperature phase of iron in the inner core. Previous reports differed in structure and by more than 2,000 degrees Kelvin (3,600 degrees Fahrenheit) at these conditions.

Using LLNL’s two-stage gas gun — which is capable of generating pressures as high as 400 GPa (58 million psi) in the iron sample, a pressure that exceeds the center of the Earth (361 GPa) — physicists Jeffrey Nguyen and Neil Holmes show in the Jan. 22 edition of Nature that a shocked sample of iron crosses the melt line at a pressure between those of the core-mantle boundary and the inner-outer core boundary.

“By determining the melting point of iron, we can estimate the temperature at the core boundaries,” Nguyen said. “This information provides us with another tool to study the temperature of the Earth’s core.”

Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy’s National Nuclear Security Administration.