Reductive/expansion synthesis of zero valent submicron and nanometal particles

Upon rapid heating to a high temperature (~800 °C), mixtures of nitrate compounds and urea created nano and submicron metal particles. The process (reductive/expansion synthesis, RES) results in atomic scale mixing. The product formed from mixed-nitrate (Fe + Ni) salts and urea created true metallic alloy. Unlike other product-from-powder synthesis processes, this process produced only zero valent metal. Initial work suggests this method is a scalable and efficient means for making metallic nanoparticles. Although this is primarily a phenomenological report, a preliminary model is presented: Initially, nitrates decompose to oxide; thus in the absence of urea metal oxide particles form, as in the case of combustion synthesis. In the case of urea/nitrate mixtures, there is a “convolution” of decomposition processes. Urea decomposes to yield reducing gases, leading to the formation of metal rather than oxide. Rapid “expansion” of gas leads to “shattering,” resulting in highly dispersed particles.