A Gas Diluter for Measuring Nanometer-Sized Particles in Oxygen or Hydrogen

Abstract

A laminar flow diluter tube was designed and tested. The tube dilutes reactive gas aerosols in nitrogen using molecular diffusion. No turbulent mixing of the gases occurs in the tube. The gases are diluted without substantially changing the particle concentration of the sample. The diluted gas can then be measured using an inert gas particle counter. A numerical model predicted the molecular diffusion and particle transport behavior of the tube. Experimental tests confirmed the predictions. The tube diluted sample hydrogen to a concentration of 6.5 percent and oxygen to a concentration of 17 percent. The same tube transported particles smaller than 10 nm with greater than 78 percent efficiency. Therefore, the diluter can be used with particle counters designed for nanometer-size sensitivity. The laminar flow diluter can be used to measure contaminant particle concentrations in filtered reactive gases. Such filtered gases are typically used in microcircuit fabrication.