Nanostructured powders: a new class of materials for forming high performance particulate coatings

Abstract

ABSTRACTNanostructured powders, with particle sizes in the range 1 to 100 nm, have shown great promise in the forming of advanced films and coatings for a variety of applications including tribological, high surface area supports for catalysts, chemical gas sensors, and optoelectronics. This paper is a summary of two major classes of powder synthesis techniques: (1) precipitation from aqueous salt solutions, and (2) condensation from vapor phase. The solution approach leads to powder particles that are spherical shells consisting of nanograins. The powder is milled with melting point lowering compounds and reagglomerated to make it suitable for thermal spraying. In contrast, the vapor condensation approach yields powder particles that are discrete, and loosely agglomerated. In a variation of the process, the heated clusters or nanoparticles are allowed to sinter on a heated substrate, forming porous or dense coatings. Films/coatings with thicknesses between 0.5 μm and 20.0 μm at rates in excess of 1 μm/min. are formed by thein situdeposition process. The synthesis techniques, powder and coating characteristics, and applications of the technologies, are described in this paper.