Microstructure and thermal conductivity of surfactant-free NiO nanostructures

High purity, nanometer sized surfactant-free nickel oxide (NiO) particles were produced in gram scale using a solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), gas pycnometry and gas adsorption analysis (BET). The average particle size of the as-synthesized NiO increases significantly with the preheating temperature of the furnace, while the specific surface area decreases. A BET specific surface area of similar to 100 m(2)/g was obtained for NiO nanoparticles with size as small as 3 nm synthesized at 300 degrees C. The thermal conductivity (kappa) of pressed pellets of the synthesized NiO nanoparticles obtained using spark plasma sintering (SPS) and uniaxial hot pressing is drastically decreased (similar to 60%) compared to that of NiO single crystal. This strong reduction in kappa with particle size suggests the suitability of the synthesized surfactant-free NiO nanoparticles for use as nanoinclusions when designing high performance materials for waste heat recovery. (C) 2012 Elsevier Inc. All rights reserved.