Iron Swells Up When Squeezed with Hydrogen
Pennisi, Elizabeth, Science News
Intense pressure usually makes a material shrink. But when three geophysicists recently subjected iron and hydrogen to a pressure of 35,000 atmospheres, their sample expanded by 17 percent.
This phenomenon, reported in the July 26 SCIENCE, also expands current thinking about the composition of the Earth's core. The discovery that iron hydride can exist under very high pressure adds weight to the suggestion that its presence may account for the lower-than-expected density of the core, say John V. Badding, Russell J. Hemley and H.K. Mao of the Carnegie Institution of Washington (D.C.).
From calculations of the thermodynamics required for the formation and stability of iron hydride within the Earth, the researchers conclude that the compound could result from water reacting with iron in the core. "There could be a large amount of hydrogen in the core," Hemley told SCIENCE NEWS.
"They have given us a totally new class of observations," comments geophysicist Raymond Jeanloz at the University of California, Berkeley. "If we can show there is hydrogen down there, then it has some serious implications for the earliest history and atmosphere of the Earth."
For their experiments, the researches first placed a small sample of iron into a diamond anvil cell, then filled the cell with hydrogen gas and squeezed the sealed sample between the tips of the anvil's two diamonds until the iron suddenly expanded. "It puffed up like a sponge absorbing water," says Hemley. At the same time, the sample's smooth surface became rough and grainy. …