Defrost,' 'full power' and 'simmer' are not accurate enough settings, so the team bypasses the control panel and varies the power externally. Cooling water protects the metal top, and holes drilled through the sides admit a nitrogen supply pipe. Otherwise it is the same as a microwave from any high-street store and, Agrawal says, entirely safe. Metal powders mixed with solid ammonium chloride are packed into pellets and placed inside the nitrogen supply tube at the oven's centre. Ceramic fibre insulation is packed around the tube before the microwave is turned on.
Microwave ovens produce high-quality nitrides of titanium, vanadium and aluminium, the group says.
Gallium is more problematic as it melts before it reaches the required reaction temperature. But Agrawal's team did manage to prepare gallium nitride in a microwave by modifying the recipe. These are the best results so far. The key to successful nitrides is a microwave-absorbing carbon paste, says Agrawal.