Laboratory SWAXS combined with a low-pressure impactor for quasi-online analysis of nanoparticles generated by spark discharge

Metal nanoparticles are widely used in many different fields of science and technology. A green and sustainable synthesis process, namely electrical discharge in gases at atmospheric pressure, has recently been advanced towards a scale-up of nanoparticle and nanostructure production in order to meet the increasing market demand. Quick characterization of particles synthesized, e.g. with this method allows better knowledge of the product quality and further optimization of the synthesis process. In this work, a new analysis system, consisting of a laboratory small- and wide-angle X-ray scattering (SWAXS) camera and a single-stage multi-orifice low-pressure impactor (SS-MOLPI), has been developed as a process analysis tool (PAT) for quasi-online analysis of nanoparticles generated by electrical discharge in inert gas. The SS-MOLPI allows quick sampling of the aerosol particles directly onto a substrate, e.g. an adhesive tape which is transferred to the SWAXS equipment for quick analysis. The entire sampling and analysis process takes a few minutes, providing information on primary particle size, aggregation state, morphology and crystalline properties in a single run. It is much more affordable and quicker than SEM/TEM and XRD techniques, respectively. Different metallic and alloyed nanostructured particles generated by spark discharge in inert gas using a single generator were analyzed with this measuring system. In addition to sampling with the SS-MOLPI, the SWAXS camera may also be applied to the characterization of dispersions prepared by washing particle-loaded surface filters with a liquid like ethanol and subsequent ultrasonication. Some selected experimental results concerning this procedure are presented and discussed in comparison. The results obtained by SWAXS were also compared with those by TEM and the XRD reference database, and good agreement has been found. The unique SWAXS and SS-MOLPI assembly was found to be suitable for quasi-online analysis and quality control of nanoparticles produced in the gas phase, and in particular for process monitoring and control of the aerosol product delivered by large-scale facilities containing multiple parallel generators for the synthesis of metal nanoparticles. (C) 2015 Elsevier Ltd. All rights reserved.