Method of investigation of the heterogeneous nucleation in the laminar flow chamber is developed. This method give the relationships between the main process parameters: the critical embryo radius, radius of the seed particle, supersaturation ratio, temperature and contact angle. The efficiency of this approach is demonstrated for the heterogeneous nucleation of sulfur vapor on tungsten oxide nanoparticles. The installation consists of three main parts: the generator of seed aerosol particles of tungsten oxide, the laminar flow chamber and the diffusion spectrometer of aerosol (DSA). The sulfur vapor was generated inside the chamber with the concentration below of the homogeneous nucleation limit. Clean air was used as a carrier gas. Number concentration and size distribution of aerosol particles at the outlet of reactor were measured by DSA. The comparison of the outlet and inlet spectra gives the threshold diameter from which heterogeneous nucleation was started. The approximate location of the heterogeneous nucleation region was determined experimentally using the method of selective filtration of nanoparticles. The temperature radial and axial profiles inside the chamber were measured by a chromel-alumel thermocouple. The rate of sulfur evaporation in the saturation zone and the axial profile of wall vapor deposition rate were measured experimentally. The difference between these two quantities gave the vapor concentration n averaged over the tube cross section vs the axial coordinate Z. Based on function n(Z) the radial profiles of sulfur vapor concentration were determined solving the mass transfer equation. The supersaturation profiles were calculated from the concentration and temperature profiles. Based on these experimental data and theoretical approach it were determined the parameters of sulfur critical embryo nucleus (size, contact angle) which formed on the surface of the seed particle. Contact angle of sulfur critical embryo on the surface of tungsten oxide seed particle is Θ ～ 41 °.It is shown experimentally that the presented method allows to generate a two-component nanopowder with a particle size from a few to tens of nanometers.
展开▼
