Metal hydrides are chemical compounds formed when hydrogen gas reacts with metals. The most useful metal hydrides react near room temperature at hydrogen pressures a few times greater than the earth's atmosphere (e.g., 5 bar, 73 psia). Metal hydrides are certainly the safest way to store flammable hydrogen gas. If you would like to know more about metal hydrides, continue down this page. If not, just "store" above for information about specifying and ordering SOLID-H™ products.

Typical metal hydrides are powders whose particles are only a few millionths of a meter (microns) across. When these metal powders absorb hydrogen to form hydrides, heat is released. Conversely, when hydrogen is released from a hydride, heat is absorbed. The process is illustrated below.



The upper portion of the illustration shows the absorption process. Hydrogen gas molecules (H2) stick to the metal surface and break down into hydrogen atoms (H). The hydrogen atoms* then penetrate into the interior of the metal crystal to form a new solid substance called a "metal hydride". The metal atoms are usually stretched apart to accomodate the hydrogen atoms. The physical arrangement (structure) of the metal atoms may also change as the hydride forms.

The lower portion of the illustration shows the desorption process. Hydrogen atoms* migrate to the surface of the metal hydride, combine into hydrogen molecules (H2) and flow away as hydrogen gas. The metal atoms contract to form the original metal crystal structure.

*Note: It is not exactly correct to say "hydrogen atoms migrate". A hydrogen atom consists of a proton and an electron. As metallic substances absorb and release hydrogen, protons move among the metal atoms through a "sea of electrons" that include electrons from the metal and from hydrogen. If the proton is not closely associated with any particular electron it is not, strictly speaking, a "hydrogen atom". Anyway, you get the idea.