Adding Lithium to Hydgrogen Could Improve Production
In our energy deprived world scientists are trying to find out various elements, alloys and substances that can provide clean and green energy along with meeting our energy demands. This quest has led them to superconductors. Superconductor materials have no electrical resistance. This property paves way for electrons to travel through them freely. Superconductor materials also carry large amounts of electrical current for long periods of time without losing energy as heat. Scientists are of the view that metallic hydrogen can prove to be a high-temperature superconductor.
We know that hydrogen is the lightest element present in this universe and lithium is the third lightest element. We find hydrogen as gas and lithium as metal at given temperature and pressure present on the earth. In hydrogen gas, the atoms are robustly paired and each hydrogen atom contributes one electron to the bonding. In chemistry shorthand, hydrogen is called H2.
Proceedings of the National Academy of Sciences published a paper this week written by a team of scientists from Cornell University and the State University of New York. They shared that if we add small amounts of lithium to hydrogen and if we keep the pressure at about one-fourth of a pressure (on which hydrogen turns into a metal) hydrogen transforms into a metal with superconductivity properties. National Science Foundation (NSF) has provided finances for this project.
Hydrogen and lithium react with each other and form a non-metallic stable compound. This is shown as LiH and known as lithium-hydrogen compound. Jupiter and Saturn experience intense gravitational forces and pressures therefore hydrogen is found in metallic form there. Scientists are trying to create situations so that they can extract hydrogen’s electron. How? They are trying to squeeze it between the facets of a diamond anvil cell under pressures up to 3.4 million atmospheres. We know that the atmospheric pressure at sea level is one atmosphere and at the center of the earth is around 3.5 million atmospheres. Scientists have faced lots of difficulties with this method of steady pressures. They have been trying shock-wave methods. This is a kind of sophisticated computer program.
The programs theoretically compute if hydrogen can be metalized by uniting a lithium atom with varying numbers of hydrogen atoms. The programs also calculate if metallic hydrogen can be made under pressures attainable in a laboratory. The lithium and hydrogen combinations predicted by the study have not been verified in a laboratory till now.
The research team is trying out various combinations of hydrogen and lithium. One of the combinations contains one lithium atom for every six hydrogen atoms or LiH6. The complex calculations forecast that in the imaginary compound the Li atom is activated to discharge its solitary outer electron, which is then distributed over the three H2 molecules. It has already been confirmed that under pressure, the hypothetical reaction forms a stable and metallic hydrogen compound. The calculations also foresee that LiH6 could be a metal at normal pressures. However, under these conditions it is unstable and would decompose to form LiH and H2.
“The stable and metallic LiH6 compound is predicted to form around 1 million atmospheres, which is around 25 percent of the pressure required to metalize hydrogen by itself,” said Eva Zurek, lead author of the paper and an assistant professor of chemistry at The State University of New York, Buffalo.
“Interestingly, between approximately 1 and 1.6 million atmospheres, all the LiH combinations studied were stable or metastable and all were metallic,” said Roald Hoffmann, co-author, recipient of the 1981 Nobel Prize in chemistry and Cornell’s Frank H.T. Rhodes Professor of Humane Letters, Emeritus.
Another one of the hypothetical compounds studied by the team was composed of one lithium atom and two hydrogen atoms or LiH2 (see bottom right image).
“The theoretical study opens the exciting possibility that non-traditional combinations of light elements under high pressure can produce metallic hydrogen under experimentally accessible pressures and lead to the discovery of new materials and new states of matter,” said Daryl Hess, a program director in the NSF Division of Materials Research.
“Once again, these researchers have taken chemistry to a new frontier,” said Carol Bessel, a program director in the NSF Division of Chemistry. “They have described, through their theories and calculations, molecules that test our fundamental assumptions about atoms, molecules and structures. In doing so, they challenge the experimentalists to make what they have imagined in their minds a reality to be held in the hand.”
The team members believe the information gleaned from the study suggests that one may combine large amounts of hydrogen with other elements. The information may also someday assist with the design of a metallic hydrogen-based superconductor.
Neil W. Ashcroft, who is the co-author, and Cornell’s Horace White Professor of Physics, Emeritus says, “We have already been in touch with laboratory experimentalists about how LiH6 might be fabricated, starting perhaps with very finely divided forms of the common LiH compound along with extra hydrogen.”