The Weihs lab travelled to Argonne National Laboratory for three days of experiments in combusion. In-situ x-ray phase contrast images were taken on combusting Al:Zr reactive ball-milled powders at beamline 32-ID-B of the Advanced Photon Source. For the first time, bubble nucleation, rapid growth, and a critical growth rate threshold necessary to cause microexplosions have been measured in pure metal or metal composite combusion.