CLUSTERS OF IMMISCIBLE METALS - IRON LITHIUM NANOSCALE BIMETALLIC PARTICLE SYNTHESIS AND BEHAVIOR UNDER THERMAL AND OXIDATIVE TREATMENTS

Iron and lithium atoms have been trapped in cold, frozen pentane. Upon warming, atom agglomeration took place to form Fe-Li clusters/particles that incorporated some fragments of the organic solvent. At room temperature very small alpha-Fe crystallites embedded in a matrix of nanocrystalline Li were obtained. Particle sizes averaged 21 nm with alpha-Fe crystallite regions of about 2.8-3.8 nm. This ultrafine powder (140 m2/g surface area) was pyrophoric. Upon allowing slow air exposure, particle growth took place and surface area dropped. However, alpha-Fe crystallites remained. Rapid air exposure caused intense heating to a dull red heat due to oxidation. Surprisingly, alpha-Fe particles remained as dominant and were encapsulated and protected from further oxidation by a Li2O/LiOH/Fe2O3 coating. Heat treatment of the fresh Fe-Li powder caused phase separation of Fe and Li, with alpha-Fe crystallite growth. Air oxidation again formed a protective outer layer of Li2O/LiOH/Fe2O3. By choice of proper temperature and time of heating the alpha-Fe crystallite sizes could be controlled. However, upon longer term heating at 470-degrees-C, significant amounts of Fe3C formed due to alpha-Fe crystallites reacting with carbonaceous fragments from the pentane solvent. Heating to even higher temperature then caused Fe3C decomposition to larger alpha-Fe crystallites and carbonaceous species. Characterization methods included Mossbauer, X-ray powder diffraction, surface area measurements, electron microscopy, elemental analyses, X-ray photoelectron spectroscopy, and differential scanning calorimetry. These results demonstrate, for the first time, that normally immiscible metals can be forced to form metastable clusters by using low-temperature, kinetic growth control methods. Also, the isolation of encapsulated, protected alpha-Fe and Fe3C nanoscale particles is a significant finding vis-a-vis new magnetic materials.