Metallic hydrogen is a state of hydrogen predicted to form under ultra-high pressure. If achieved, some researchers predict it could function as a room-temperature superconductor—a material capable of conducting electricity with zero resistance at temperatures above 0 °C. But because the pressure required to make metallic hydrogen is so enormous—much greater the pressure experienced by materials in the center of the earth—researchers have had little luck in producing it.

In hopes of getting a better idea of how metallic hydrogen behaves, researchers are becoming increasingly interested in hydrogen-rich compounds that might have properties similar to those seen in pure hydrogen. These compounds might undergo similar phase changes as metallic hydrogen, but at more accessible pressures.

One of the most promising candidates of study is silane, which contains an atom of silicon bound to four atoms of hydrogen. Previous studies have suggested that pure silane metalizes at pressures far lower than those required to produce metallic hydrogen. The goal of the reported research was to study the properties of alloys composed of hydrogen and silane together.

For the study, co-author Wendy Mao and her colleagues studied two different silane-containing samples: one containing equal parts hydrogen and silane, another containing an abundance of hydrogen in a five-to-one ratio.

Using a device called a diamond anvil cell, the samples were squeezed at up to 6 gigapascals—60,000 times the earth’s atmospheric pressure at sea level— at 300 K (27 °C, 80°F).

The alloys solidified at much lower pressures than would be required for hydrogen alone, with the hydrogen-rich alloy forming a solid containing more than 99% hydrogen. The researchers also found that even though the amount of silane in the hydrogen-rich sample was minimal, it had a significant effect on hydrogen-hydrogen interactions.

According to Shibing Wang, a SIMES graduate student and the lead author on the paper, the finding is significant because it could contribute to a better understanding of the properties of atoms in hydrogen alloys, which are commonly used in hydrogen storage and could have implications for hydrogen fuel storage.

The study was funded through SIMES by the Department of Energy.

Resources

• Shibing Wang, Ho-kwang Mao, Xiao-Jia Chen, and Wendy L. Mao (2009) High pressure chemistry in the H₂-SiH₄ system. PNAS doi: 10.1073/pnas.0907729106