Measuring the Particle Retention of Liquid Filters below 100 nanometers
Gary Van Schooneveld – 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 Semiconductors (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 by 2019, the critical particle size will be 10 nm. Historically, filter particle retention capabilities have been measured using polystyrene latex particles (PSL) and optical particle counters. Current state-of-the-art optical particle counters are capable of measuring PSL particles as small as 30-50 nm, but have limited detection efficiency near the lowest detection threshold.
This paper will review and discuss a number of test methods currently in use or under consideration for measuring the removal of particles below 100 nm in diameter from liquids. These methods take advantage of recently introduced optical particle counters, nebulization/aerosol sizing, and inductively coupled plasma/mass spectrometry as measurement tools. The methods also use a variety of nanoparticles such as PSL, gold, and silica as challenge materials. Critical to the success of these methods is an understanding of the particle size distribution of the filter challenge particles, and the potential interaction between the test particle and the filter membrane. The paper will present size distribution data for the various nanoparticle challenge candidates. In addition, examples of particle retention by several filters used in ultrapure water as a function of particle type, particle size, and particle loading will be presented.
CTA publication #121: American Filtration & Separations Society Fall Conference October 14-16, 2013 Cincinnati, OH