Technique for measuring the particle retention of liquid filters to 10 nanometers
Gary Van Schooneveld, Don Grant – CT Associates, Inc
Industrial requirements have driven the particle retention capabilities of microfiltration and ultrafiltration processes to near or below 10 nanometers. For example, the International Technology Roadmap of Semiconductor (ITRS) has defined a critical particle size (the particle size that can result in a reduction in manufacturing yield) of 20 nm for 2013 and projects that in 2019, the critical particle size will be 10 nm. Historically, filter particle retention capabilities have been measured using optical particle counters. Current state-of-the-art optical particle counters are capable of measuring particles as small as 30-40 nm but have limited detection efficiency near the lowest detection threshold.
This paper describes a test method and instrumentation capable of measuring removal of particles as small as 10 nm in diameter from liquids. The filters are challenged with colloidal silica particles ranging from 10 to 50 nm in diameter. Challenge concentrations typically range from 1E7 to 1E11/mL ? 10nm. Filter inlet and outlet concentrations are measured using a Liquid Nanoparticle Sizer, a recently-developed instrument and measurement technique. In this technique, a very fine mist of particle-laden water is created, the water in the mist droplets is evaporated and the sizes and numbers of the remaining particles are measuring using conventional aerosol measurement instrumentation (e.g. a scanning mobility particle sizer). This technique allows very accurate resolution of particle size with up to 64 size channels per decade of size (e.g. between 10 and 100 nm).
Examples of particle retention by several filters used in ultrapure water as a function of particle size and loading will be presented.
CTA publication #116: American Filtration & Separations Society Spring Conference May 6-9, 2013 Minneapolis, MN