The effect of polar and nonpolar liquid process control agents (PCA) on properties of metal rich Al/CuO thermites prepared by Arrested Reactive Milling was studied. Acetonitrile and hexane, and their mixtures were used as PCA. Milling in nonpolar hexane results in fully dense, micron-sized composite particles of 100 nm-scale CuO inclusions in an Al matrix. Using polar acetonitrile results in a mixture of nano-sized, largely unagglomerated Al and CuO particles. Porous composites, agglomerated to different degrees, formed in hexane-acetonitrile mixtures. In particular, micron-sized porous spherical composite particles formed in a mixture with 25% acetonitrile. Such spherical composites may result from interaction of suspended powder particles with stressed droplets of a Pickering emulsion forming when immiscible liquids serve as PCA. Despite dramatic changes in the powder morphology, all composites were reactive. Systematic differences, discussed in the text, were observed in their ignition temperatures and oxidation kinetics. (C) 2019 Elsevier B.V. All rights reserved.