Now that we are familiar with hydrogen, we will cover it’s only stable isotope, Deuterium on our list of cryogenic:
- Krypton (119.73 K)
- Methane (111.67 K)
- Oxygen (90.188 K)
- Argon (87.302 K)
- Fluorine (85.037 K)
- Carbon Monoxide (81.64 K)
- Nitrogen (77.355 K)
- Neon (27.104 K)
- Deuterium (23.31 K)
- Hydrogen (20.369 K)
- Helium (4.222 K)
Introduction and Discovery
Deuterium, also known as heavy hydrogen, is one of two stable isotope of hydrogen. Deuterium comes from the Greek deuteros meaning “second” referring to the two particles (proton + neutron) in the nucleus. Deuterium accounts for 0.0156% of the hydrogen in the oceans or one in 6420 hydrogen atoms. Deuterium was created during the Big Bang and accounts for 0.0013% of the Universe.
Deuterium was discovered by Harold Urey in 1931. He predicted that their would be a difference between the vapor pressure of pure hydrogen and it’s heavier isotopes. He developed a method to isolate the heavier isotope through the distillation of liquid hydrogen. This lead to Urey receiving the Nobel Prize in Chemistry in 1934 “for his discovery of heavy hydrogen”.
Similarly to hydrogen, deuterium also has 2 spin isomers denoted as orthodeuterium and paradeuterium. Contrary to hydrogen and tritium, the lower-energy, even-J states are denoted “ortho” for deuterium, while the higher-energy, odd-J states are denoted “para.” This is due to the ortho-para compositions at room temperature are different for deuterium than they are for hydrogen because deuterium has nuclear spin of +1 whereas hydrogen has a nuclear spin of +1/2.
Uses and Production
Deuterium is used as fuel in nuclear fusion reactors like the National Ignition Facility (NIF) and ITER (in development). Deuterium is also used in NMR spectroscopy, as a stable isotope tracer, nuclear weapons, and medicine for deuterated drugs. Research grade deuterium gas costs $1,112 for 500 standard liters which equates to $12.38 per gram! This price can be reduced to $1/L for larger orders of research grade deuterium. Due to the military applications, the deuterium market is very secretive and little information is available to the public. After a discussion with a Linde representative, I was able to learn that the deuterium market has rapidly grown over the last 10 years because of it’s use in the manufacturing of semiconductors and fiber optics. Linde is the largest producer of deuterium in the world producing millions of liters a years.
Due to the small differences in molecular mass, it is energy intensive and expensive to separate the isotopes of hydrogen.
Deuterium can be separate from the other hydrogen isotopes through several processes including chemical exchange, thermal diffusion, cryogenic distillation, electrolysis, and permeation.The most common method for producing deuterium is through electrolysis of heavy water, D2O, which is widely used in heavy water reactors. Until it’s closure in 1997, the Bruce Heavy Water plant in Ontario, Canada was the largest producer of D2O utilizing the Girdler Sulfide process. This is an isotopic exchange process between H2S and H2O: H2O + HDS ⇌ HDO + H2S. After several iteration this process is able to enrich the water to 15-20% D2O where it can then be purified using distillation or electrolysis. This process takes 340,000 kg of feed water to produce 1 kg of heavy water.
Canada is the largest producer and consumer of heavy water where it is used to cool their CANDU reactors. The price of heavy water is $300 per kg (2001).
Surface of State
Only the equation of state for normal deuterium is included in REFPROP. The variation in thermophysical properties between orthodeuterium and paradeuterium were not significant enough to warrant separate equation to be include in REFPROP.
Though the rectilinear diameter has a slight change in the curvature, the critical isotherm exhibits correct thermodynamic behavior.
Extrapolating to extreme pressures and densities shows the equations behaves theoretically correct at the high extremes.
The Cv vs. T plot for deuterium behaves similar to traditional fluids with saturated vapor line crossing the saturated liquid line.
The deuterium equation was complete in 2013 and is a 21 term, Helmholtz explicit equation of state.
Tritium is the heaviest of the hydrogen isotopes having 2 neutrons. Tritium is highly radioactive having a half-life of 12.3 years. Tritium is very rare in nature accounting for only 3 in 10^18 atoms of hydrogen. The radioactive decay causes phosphors to glow making it useful for self-power lighting in devices like watches, exit signs, firearm sights, etc. Tritium is also used in nuclear weapons and as fuel for fusion reactors like ITER and NIF. Tritium costs a staggering $30,000 per gram. The commercial demand is 400 grams per year. Pure tritium is produced by cryogenically distilling enriched deuterium gas streams that have been electrolyzed from the heavy water CANDU reactors.
There are only a handful of vapor pressure and density experimental measurements for tritium. The available information on the critical and triple point properties are discussed below:
A Helmholtz explicit equation of state does not exist for tritium.