Generation and investigation of airborne silver nanoparticles with specific size and morphology by homogeneous nucleation, coagulation and sintering

An aerosol generation facility has been characterized to produce well-defined silver nanoparticles for use as a test aerosol when evaluating instrument response to different particle morphologies within a range of sizes. The generator consists of two in-series laminar tube furnaces to produce and subsequently sinter particles, and is capable of generating spherical or agglomerated fractal-like silver particles, with corresponding projected surface (two-dimensional) fractal dimensions from 1.58 to 1.94. The morphologies of generated particles as well as size distributions at different sintering temperatures were characterized using a transmission electron microscope (TEM) and a scanning mobility particle sizer (SMPS). Mean diameters measured were significantly reduced for sintering temperatures from 100 to 300 ^{{ring operator}} C, but showed little variation for sintering temperatures above 500 ^{{ring operator}} C. TEM analysis indicated that this phenomenon was caused by sintering, followed by partial and complete coalescence of fractal-like agglomerates into spheres. Agglomerate restructuring from classical completely sintered agglomerates ( 500 ^{{ring operator}} C ) to spherical particles ( 700 ^{{ring operator}} C ) did not lead to a change in the particle mobility size distribution. The temperature at which complete sintering occurred was higher than that predicted by theory, but was in reasonable agreement with previously published experimental data. For monodisperse particles in the size range from 20 to 100 nm, a simple exponential model related sintering temperature to the diameter of coalesced spherical particles.