Is it possible to freeze hydrogen

If frozen hydrogen is found to be a viable fuel source, scientists and engineers believe the potential power generated from liquid hydrogen would rival, if not far surpass, that of fuels currently in use.

The advantage of frozen hydrogen is in its potential energy , per pound. Scientists at NASA believe that if it could be put to practical use, launches could occur with a mere 20 percent of the fuel weight currently required to achieve orbit. This also has the potential of allowing larger, heavier payloads and saving billions of dollars.

Freezing hydrogen is no simple task. In order to achieve frozen hydrogen, the gas must be cooled to very low temperatures. Liquid hydrogen, cooled to 14 kelvins Fahrenheit, Celsius , is dropped onto liquid helium , and cooled to 4 kelvins Fahrenheit, Celsius.

The colder medium of the liquid helium causes the liquid hydrogen to freeze and float on top of the helium. By crushing Earth's lightest element with mind-boggling pressures, scientists have revealed an entirely new state of matter: phase V hydrogen. The squished hydrogen is a precursor to a state of matter first proposed in the s, called atomic solid metallic hydrogen.

When cooled to low enough temperatures, hydrogen which on Earth is usually found as a gas can become a solid; at high enough pressures, when the element solidifies, it turns into a metal. Planetary scientists think the interior of Jupiter is largely made of the stuff.

And so, in crushing hydrogen at such high pressures, the physicists also got a glimpse of the inner atmosphere of a gas giant, where pressures reach millions of Earth atmospheres. At the University of Edinburgh in Scotland, doctoral student Philip Dalladay-Simpson and his colleagues Ross Howie and Eugene Gregoryanz put a small amount of hydrogen between two diamond anvils, and dialed up the pressure to gigapascals, or 55 million pounds per square inch psi.

By comparison, Earth's atmosphere is kilopascals, or 15 pounds per square inch, at sea level. On Jupiter , the weight of the atmosphere hits 29 million psi at about 10, miles 16, kilometers below the cloud tops, and models suggest that's where hydrogen may take the form of a liquid metal.

In this case, when the pressure hit the gigapascal mark, or 47 million psi, the hydrogen became a solid, with the atoms forming layers that alternated between orderly and jumbled arrangements. This is the first time anyone has seen this form of the element at close to room temperature about degrees Kelvin, or about 80 degrees Fahrenheit , the scientists said.

Liquid hydrogen is created routinely in industry at cryogenic temperatures with pressures in the tens of atmospheres, but nobody has yet cooled the element enough to solidify it, Dalladay-Simpson said. Why does water expand when it freezes?

Why does liquid water have a density maximum? Most liquids have a quite simple behavior when they are cooled at a fixed pressure : they shrink. The liquid contracts as it is cooled; because the molecules are moving slower they are less able to overcome the attractive intermolecular forces drawing them closer to each other. Then the freezing temperature is reached, and the substance solidifies, which causes it to contract some more because crystalline solids are usually tightly packed.

Water is one of the few exceptions to this behavior.