Unless you happen to follow fusion news in exceptional depth, you’re probably wondering what “Ultra-Dense Deuterium” is and why would you want to make it.
Furthermore, if you don’t have a background in chemistry or physics you may simply be wondering what deuterium is.
One thing you should be familiar with is regular hydrogen, the first element of the periodic table, a single electron bound to a proton:
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The properties of an atom are primarily determined by the number of protons and electrons it has; however, there is another component of atoms, the neutron. Atoms with the same number of protons, but different numbers of neutrons, are said to be different “isotopes” of the same element.
The most common isotope of hydrogen simply has a single proton and no neutrons. This form is sometimes referred to as “protium” but there are two other forms that exist in non-negligible quantities.
The isotope with 1 proton and 1 neutron is known as “deuterium”. On Earth, roughly 1 in every 6400 hydrogen atoms are the deuterium isotope. The most noticeable difference between deuterium and protium is the weight. Protons and neutrons each have a weight of about 1 atomic mass unit (AMU) while electrons have a negligible mass (<1/1600th that of a proton). As such, protium weights approx. 1 AMU, and deuterium weights about 2 AMU, which is why it is often referred to as “heavy hydrogen”.
Correspondingly, water that is made with deuterium instead of protium is known as “heavy water”. Because the weight of the oxygen atom in water is significantly higher than the density of the hydrogen heavy water is only around 11% higher than that of regular water. This is a sufficiently higher density that heavy ice will sink in regular water.
The third form of hydrogen, with 1 proton and 2 neutrons, is known as tritium. Unlike protium and deuterium, tritium is radioactive (with a half-life of around 12 years) and thus exists only in very small quantities on Earth. For this reason, tritium cannot be extracted from water, and can only be produced from the refinement of water that had been bombarded with neutrons, or directly produced from other nuclear reactions. The one application in which you may have encountered tritium in is exit signs or watches, where tubes of tritium gas coated in a phosphor layer glow without the need for electricity.
Now that we know what deuterium is, let’s get back to the first question. What is Ultra-Dense Deuterium?
In standard conditions, pure hydrogen (of any isotope) exists as a gas with two hydrogen atoms bound to each other, at a distance of 74 picometers (pm). All gasses can also be turned into “condensed” phases like liquid or solid. There are typically two ways to cause a gas to condense into a liquid or solid, either cool it down, apply pressure, or both.
Many other gasses, like nitrogen or carbon dioxide, can be condensed quite easily by cooling them, producing liquid nitrogen and “dry ice”, respectively. Alternatively, carbon dioxide can be turned into a liquid by heating dry ice in a sealed container, raising the pressure. Further heating and application of pressure can generate more exotic forms of matter, like the supercritical phase, which acts with properties intermediate a liquid and a gas.
Hydrogen molecules have very weak intermolecular forces, which means that it is very difficult to cause hydrogen gas to condense, requiring cooling to below 20 Kelvin. Turning hydrogen solid takes cooling to 14 kelvin, and solid hydrogen has a density of .08 grams/cm3 .
Just like applying pressure to solid carbon dioxide can turn it into a more exotic phase (the supercritical phase) it has been theorized that applying a great deal of pressure to solid hydrogen could turn it into a metallic phase, though no one has succeeded in synthesizing this metallic phase to date for prolonged periods of time. Metallic hydrogen is estimated to have a density >0.6 grams/cm3 and have several other remarkable properties, such as superconductivity, which will be discussed more in future posts.
Ultra-Dense Deuterium is another condensed form of hydrogen, and specifically the deuterium isotope, that does not require high pressures to synthesize and yet seems to have many of the remarkable properties of metallic hydrogen, with an even high density of approx. 140 kilograms/cm3, higher than that of any previously created material.