Complex Hydrides as Solid Storage Materials - First Safety Tests-Paper

Hydrogen technology requires efficient and safe hydrogen storage systems. For this purpose, storage
in solid materials, such as high capacity complex hydrides, is studied intensely. Independent from the
actual material to be used eventually, any tank design will combine nanoscale powders of highly
reactive material with pressurized hydrogen gas and so far, little is known about the behaviour of these
mixtures in case of incidents. For a first evaluation of a complex hydride in case of a tank failure,
NaAlH4 (doped with Ti) was investigated in a small scale tank failure tests. 80-100 ml of the material
were filled into a heat exchanger tube, and sealed under argon atmosphere with a burst disk.
Subsequently, the NaAlH4 was partially desorbed by heating. When the powder temperature reached
130 øC and the burst disk ruptured at 9 bar hydrogen overpressure the behaviour of the expelled
powder was monitored using a high speed camera, an IR camera as well as sound level meters.
Expulsion of the hydrogen storage material into (dry) ambient atmosphere yields a dust cloud of finely
dispersed powder which does not ignite spontaneously. Similar experiments including an external
source of ignition (spark / water reacting with NaAlH4) yield a flame of reacting powder. The intensity
will be compared to the reaction of an equivalent amount of pure hydrogen.
KEYWORDS:
solid state hydrogen tank, safety test, complex hydride, NaAlH4