Experimental study of gas-dynamically induced nanoparticle synthesis by use of adapted sampling probes

A new process for the synthesis of nanoparticles in the gas-phase is experimentally investigated. The gas-dynamically induced nanoparticle synthesis uses the initiation of the chemical reaction by gasdynamic shock and the quenching of high temperature gas by accelerating the flow from subsonic flow speed to supersonic speed. Therefore, the design of the reactor consists of two Laval nozzles. The process provides high heating and cooling rates, an adjustable reaction time and a particle synthesis at constant thermodynamic conditions to obtain non-aggregated nanoparticles. In order to analyze the synthesized SiO₂ particles during their growth, samples are taken in the reaction volume and downstream of the quenching. The particles from the reaction chamber were extracted with the help of a specially designed water-cooled probe. The geometry of the probe is optimized by CFD simulations. The particles downstream the quenching are extracted by a heated and isolated probe. The particles are collected on TEM grids. The experimental investigations show that the synthesized particles are spherical and non-aggregated in the reaction chamber and after quenching. The possibility to synthesize a non-aggregated product in the novel process is thus demonstrated. The mean particle size is defined by the process conditions and varies from 25 to 37 nm after quenching.