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0903-Z08-03.1

Densification of Monodisperse Iron Nanoparticles from a Colloidal Dispersion at Moderate Heating Rates and Temperatures Nathan B. Crane1, Emanuel Sachs2, Samuel M. Allen3 1

Sandia National Laboratories, MS 1245, PO Box 5800, Albuquerque, NM, USA 87185-1245 Department of Mechanical Engineering, MIT, Room 35-011, 77 Massachusetts Ave, Cambridge, MA, USA 3 Department of Materials Science and Engineering, Room 35-415, MIT, 77 Massachusetts Ave, Cambridge, MA, USA 2

Abstract This work reports on the densification of iron nanoparticles heated at moderate rates without applied pressure as observed by TEM imaging, gas adsorption pore size measurement, and X-ray diffraction. Despite a low packing density, the small pore size is amenable to significant densification by pressureless sintering. Carbon residues from the stabilizing ligands affect both the composition and processing of the particles. This approach is amenable to deposition on nonplanar or fragile substrates. Additionally, large areas can be processed in parallel. Introduction Nanostructured materials have unique properties that both allow and require unique processing methods. For example, Buffat [1] showed that nanoparticles melt at much lower temperatures than bulk material. Some have utilized this property to deposit materials, particularly metals at low temperatures. Typically, a liquid suspension of the particles is patterned and then quickly heated to dry the solvent and densify the particles [2-4] by melting or sintering. However, deposits produced via this method have required high intensity energy sources such as focused laser beams to approach bulk material properties such as resistivity and density [5]. Alternatively, nanoparticles may be densified by pressure-assisted sintering. The applied pressure is required to eliminate large interagglomerate pores and also helps complete densification while maintaining their nano-scale structure to create materials of superior strength and hardness. If a final nano-sized structure is not required and the interagglomerate pores can be eliminated, the particles can be densified by simple sintering without the need for applied pressure or high intensity energy sources. This work seeks to demonstrate such pressureless sintering of nanoparticles by sintering monodisperse iron nanoparticles suspensions after a controlled drying that achieves a narrow pore size distribution. Monodisperse suspensions of nanoparticles can be dried to form superlattice structures with very narrow pore size distributions [9] as required for densification by pressureless sintering. Without the need for a concentrated energy source or applied pressure, this method can be used to deposit materials on fragile or curved substrates that might not provide clear access for laser heating. This process is also amenable to controlling deposition location and geometry via differences in wetting characteristics, surface curvature, and/or magnetic fields. [10,11]

0903-Z08-03.2

Methods The nanoparticles used in this study were purchase