Slush hydrogen is a combination of

liquid hydrogen Liquid hydrogen () is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecule, molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point (thermodynamics), critical point of 33 Kelvins, ...

and solid hydrogen at the

triple point In thermodynamics, the triple point of a substance is the temperature and pressure at which the three Phase (matter), phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at ...

with a lower temperature and a higher density than

. It is commonly formed by repeating a freeze-thaw process. This is most easily done by bringing liquid hydrogen near its boiling point and then reducing pressure using a vacuum pump. The decrease in pressure causes the liquid hydrogen to vaporize/boil - which removes latent heat, and ultimately decreases the temperature of the liquid hydrogen. Solid hydrogen is formed on the surface of the boiling liquid (between the gas/liquid interface) as the liquid is cooled and reaches its triple point. The vacuum pump is stopped, causing an increase of pressure, the solid hydrogen formed on the surface partially melts and begins to sink. The solid hydrogen is agitated in the liquid and the process is repeated. The resulting hydrogen slush has an increased density of 16–20% when compared to liquid hydrogen. It is proposed as a rocket fuel in place of liquid hydrogen in order to use smaller fuel tanks and thus reduce the dry weight of the vehicle.

Production

The continuous freeze technique used for slush hydrogen involves pulling a continuous vacuum over triple point liquid and using a solid hydrogen mechanical ice-breaker to disrupt the surface of the freezing hydrogen.A.S. Rapial and D.E. Daney (May 1969)
1966 – Preparation and characterization of slush hydrogen and nitrogen gels
Cryogenics Division. Institute for Basic Standards National Bureau of Standards, Boulder, Colorado (report for NASA). Retrieved on 2012-12-29. *Fuel density: 0.085 g/cm³ *

Melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

: −259 °C *

Boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envi ...

: −253 °C

References

{{reflist, 2 Hydrogen physics Hydrogen technologies Hydrogen storage Liquid fuels Rocket fuels Coolants Cryogenics

Production

See also

References