During preparation of a new hydrogen storage material, ammonia borane (AB) loaded onto mesoporous carbon, an unexpected incident was observed. As with all procedures with new materials the work is conducted on a small scale and in a laboratory fume hood. They followed the procedures that they had used for absorption of ammonia borane onto mesoporous silica without incident.
To absorb the solid AB into a scaffold material they dissolve AB in a dry aprotic polar solvent, THF. The saturated solution of AB in THF is added to the mesoporous carbon material in a round bottom flask, stirred for 10 minutes to saturate the mesoporous scaffold with AB and then the solvent is slowly removed under vacuum. At this point the sample is assumed to be prepared and ready for transfer to a sample vial for storage.
The material (1:1 mesoporous carbon:AB) was exposed to the atmosphere for close to five minutes without incident and the round bottom flask containing the material was cool to the touch as they have always noted for the silica materials. In order to transfer the material from the round bottom flask to the storage vessel a stainless steel spatula was introduced to the round bottom flask. Upon touching the stainless steel spatula against the inside of the flask, the flask became warm to touch and then a small flame was observed to arise from the round bottom flask. The flask was immediately placed under a large glass crystallizing dish to remove oxygen and the flame was extinguished. After the flame was extinguished, the flask was then placed under nitrogen atmosphere.
Dry carbon materials have been reported to develop a static charge under vacuum. It is likely that using the metal spatula provided a grounding source to release the charge. This static charge may have been responsible for the flame and any exothermic reaction. Likely residual THF ignited.
- Laboratory Equipment
In the future, this mesoporous carbon material and ammonia borane:mesoporous carbon material will be handled under anaerobic conditions (glove box) to prevent further incidents.