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Particle Control Methods: I
Published in R. P. Donovan, Particle Control for Semiconductor Manufacturing, 2018
Membrane filters can be considered to be porous sheets of polymeric material. The primary collection of particles is on the surface by direct interception and impaction. Collection by diffusion is of less importance in membrane filters as opposed to fibrous filters because of the very thin media. Three general types have different processes of manufacture: cast membrane, Nuclepore, and Goretex. The cast filters are formed by dissolving a polymer in a solvent and then casting the liquid on a flat surface. As the solvent evaporates, a porous structure is formed by the polymer, as shown in Figure 7-2. The Nuclepore filter is formed by irradiating a thin sheet of polycarbonate film in a nuclear reactor and then etching the radiation-damaged sites. The result is a field of round holes “drilled” through the sheet. Nuclepore filters are very useful for obtaining samples for analysis because the holes can be differentiated from the contaminant particles when viewed by a microscope. An example of a clean filter is shown in Figure 7-3. Goretex filters are made by stretching Teflon™ films and causing the formation of pores and a fiberlike structure. A photomicrograph is shown in Figure 7-4.
Sampling Aerosols by Filtration
Published in James P. Lodge, Methods of Air Sampling and Analysis, 2017
The term membrane filter was originally applied to discs of a cellulose ester gel having interconnected pores of uniform size. Paulus et al. (3) described the various applications of such filters for air sampling in the 1950’s. Gel-type membrane filters are now available in polyvinyl chloride (PVC), nylon, and other plastics. While the method of production is quite different from those used to make fibrous filters or granular beds, the flow pathways of all three types of structures are quite similar. The Nuclepore filter, a polycarbonate pore filter, is generally considered to be a membrane filter, but has a radically different structure; i.e., a series of parallel straight-through holes. It is made by exposing a thin sheet (∼10 µm) of polycarbonate plastic to a flux of neutrons in a nuclear reactor, and then chemically etching the fission fragment tracks.
Pretreatment System
Published in Tadahiro Ohmi, Ultraclean Technology Handbook, 2017
Nuclepore filter (25 mm dia., 1 μm pore size) is used. The water filtered at 3.0 kgf cm−2 forms laminar flow at the outset. Over the course of filtration, however, the filtered water assumes a droplet shape as a result of clogging of the filter. The PN value is the volume (liters) of water collected before the filtered water attains the droplet shape. Figure 19 illustrates the method.
The air quality of Palangka Raya, Central Kalimantan, Indonesia: The impacts of forest fires on visibility
Published in Journal of the Air & Waste Management Association, 2022
Muhayatun Santoso, Philip K. Hopke, Endah Damastuti, Diah Dwiana Lestiani, Syukria Kurniawati, Indah Kusmartini, Djoko Prakoso, Dyah Kumalasari, Ahmad Riadi
A dichotomous sampler Gent stacked filter unit (SFU) was set-up on the rooftop of the building about 4–5 m above ground level and about 100 m from the road. There are no tall building and there were no significant changes in the surrounding environment during the sampling period. The Gent SFU particle sampler is capable of collecting particulate matter in two fractions, PM2.5–10 and PM2.5 size (Hopke et al. 1997). The coarse fraction sample was collected on an 8 µm pore coated nucleopore filter, and the fine fraction sample was collected on a 0.4 µm pore nucleopore filter. The sampling was carried out for 24 h at least once per week from October 2011-October 2020.