When we leave the lab we make sure that everything is in its standby state and we set up an automated outgas (or “morning initialization” as we call it). This usually means that the cells are clean and ready to use for the next day. However, one Friday morning we came in to find that the water cooling system had broken; water was not being pumped through the cells and was boiling in the pipes, causing the cells to heat up and outgas into the chamber. Having failed to restart the water cooler we crashed the cell temperatures to prevent them from being damaged. When we took the machine apart (it needed restocking with gallium and indium anyway) we found the aluminium shutter looking like this.
The sizable blob of aluminium which had accumulated on the shutter had clearly reacted with the outgassed material from the cells and now looked pretty disgusting!
The first step in the cleaning process was to remove as much of the aluminium as possible with a craft knife. After this the shutter looked significantly better but still not quite good enough to be used again. The remaining aluminium had to be etched away, so the shutter was placed in a beaker of room temperature HCl. The reaction was very quick and after ten minutes the shutter looked like this. Nice and clean and ready to be put back into the system!