PHASE-DOPPLER DIAGNOSTIC STUDIES OF PRIMARY AND TERTIARY AEROSOLS PRODUCED BY A HIGH-EFFICIENCY NEBULIZER

Two phase-Doppler instruments (a two- and a four-beam laser light-scattering interferometer) are used for the diagnostic studies of aerosol produced by a pneumatically driven, high-efficiency nebulizer (HEN). The new nebulizer (capillary i.d. = 79 mu m) is useful in plasma spectrometries for nebulization of solutions at uptake rates of 10-1200 mu L/min. Diagnostic studies involve measurements on primary and tertiary aerosols prior to injection into a high-temperature plasma. Simultaneous measurements are conducted on droplet size and droplet velocity distributions, size-velocity correlation, span of aerosols, droplet number density, volume flux, and percent volume of aerosol droplets under 8 mu m. The four-beam interferometer (or the 2D phase-Doppler system) is used to assess the axial and radial velocity components of the primary aerosol from the HEN. A broad range of droplet velocities is observed near the nebulizer tip for the primary aerosol, but most tertiary droplets travel at nearly the same velocity, much slower than the primary droplets. The Sauter mean diameter (D-3,D-2) of the primary aerosol is found to increase both along the center line of the aerosol pathway and at the boundary of the spray. The D-3,D-2 of tertiary aerosol generated by the HEN is approximately 2-3 mu m smaller than that of a conventional pneumatic nebulizer (capillary i.d. = 422 mu m) over a wide range of solution uptake rate (10-1200 mu L/min). For the solutions tested, the D-3,D-2 of tertiary aerosol from the HEN is not affected significantly by solution viscosity and surface tension. The significance of these measurements and data for enhancing analytical performance indexes in plasma spectrochemical analysis are discussed.