Complex hydrides as solid storage materials: First safety tests

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 behavior 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 test. 80–100 ml of the material was 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 °C and the burst disk ruptured at 9 bar hydrogen overpressure the behavior 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.