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Phase I occurs at low temperatures and pressures, and consists of a hexagonal close-packed array of freely rotating H 2 molecules. Upon increasing the pressure at low temperature, a transition to Phase II occurs at up to 110 GPa. [3] Phase II is a broken-symmetry structure in which the H 2 molecules are no longer able to rotate freely. [4]
However, the liquid density is very low compared to other common fuels. Once liquefied, it can be maintained as a liquid for some time in thermally insulated containers. [6] There are two spin isomers of hydrogen; whereas room temperature hydrogen is mostly orthohydrogen, liquid hydrogen consists of 99.79% parahydrogen and 0.21% orthohydrogen. [5]
At room temperature or warmer, equilibrium hydrogen gas contains about 25% of the para form and 75% of the ortho form. [31] The ortho form is an excited state, having higher energy than the para form by 1.455 kJ/mol, [32] and it converts to the para form over the course of several minutes when cooled to low temperature. [33]
The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. [1]
Celsius Fahrenheit; 1 H hydrogen (H 2) use: 20.271 K: −252.879 °C: −423.182 °F ... Values are in kelvin K and degrees Celsius °C, rounded For the equivalent in ...
All values refer to 25 °C and to the thermodynamically stable standard state at that temperature unless noted. Values from CRC refer to "100 kPa (1 bar or 0.987 standard atmospheres)". Lange indirectly defines the values to be standard atmosphere of "1 atm (101325 Pa)", although citing the same NBS and JANAF sources among others.
At room temperature, the diffusivity is very low, and the hydrogen is trapped in the HGM. The disadvantage of HGMs is that to fill and outgas hydrogen effectively the temperature must be at least 300 °C which significantly increases the operational cost of HGM in hydrogen storage. [119]
Celsius Fahrenheit Comments 1 H hydrogen (H 2) use: 13.99 K: −259.16 °C: ... unless noted. Triple point temperature values (marked "tp") are not valid at standard ...