A GAS DILUTER FOR MEASURING NANOMETER-SIZED PARTICLES IN OXYGEN OR HYDROGEN

A laminar flow diluter tube was designed and tested. The tube dilutes reactive gas aerosols in nitrogen using molecular diffusion. No turbul ent mixing of the gases occurs in the tube. The gases are diluted with out substantially changing the particle concentration of the sample. T he diluted gas can then be measured using an inert gas particle counte r. A numerical model predicted the molecular diffusion and particle tr ansport behavior of the tube. Experimental tests confirmed the predict ions. The tube diluted sample hydrogen to a concentration of 6.5 perce nt and oxygen to a concentration of 17 percent. The same tube transpor ted particles smaller than 10 nm with greater than 78 percent efficien cy. 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 ga ses. Such filtered gases are typically, used in microcircuit fabricati on.