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Instructions,
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SOURCES OF POWDERS FOR INHALATION CHALLENGES Both the Vilnius aerosol generator (VAG) and the Wright dust feeder (WDF) produce a dust aerosol from powdered material that is caused to be suspended in air. The VAG uses mechanical impact on a membrane and air flow to get the dust airborne. The WDF scrapes a dust cake and aspirates the scraped material to get the dust airborne. Overviews of dry dispersal techniques have been presented by, among others, Hinds (1980), and Corn and Esmen (1976). This note deals with sources of such powdered material. Hidy (1984) tabulated experimental results from A. Anderson that lists particle types, their radius limits and their "dispersibility," as determined by pouring them into a 2.5m-high tube and measuring the fraction suspended after 6 seconds. The finest particles tended to remain airborne, as would be expected. The powders listed were: lycopodium spores, wood charcoal dust, aluminum powder, talc, carbon black, potato starch, graphite dust, pulverized slate, cement, prepared chalk, silica dust, and porcelain dust. Some dispersed powders mentioned in Willeke (1980) were: fly ash, clay, copper, ferric oxide (iron oxide), ferric sulfate, aluminosilicate, titanium dioxide (titania), calcium carbonate, metallic silicon, latex spheres, lycopodium spores, methylene blue dye, silicon dioxide (silica), talc, thorium dioxide (thoria), uranium dioxide (urania). Hinds (1999) listed silica and urania powders as appropriate for use in the WDF but reported difficulties with using soft or very fine powders such as carbon black, zinc oxide and iron oxide. In a more general comment, he noted that AC test dust ("Arizona road dust," mostly silica), has been widely used for testing air cleaners and is available from General Motors' AC Spark Plug Division in Flint, Michigan, the fine grade having 39% of its mass in particles smaller than 5æm. In their chapter, "Aerosol Generation," Corn and Esmen (1976) in Dennis (1976) tabulated over a hundred particle types suitable for dry dispersal. Commercial sources of powders include: Duke Standards, 2463 Faber Place, Palo Alto, CA 94303, phone 800 334 3883. [Wide variety of powders.] Bangs Laboratories, Inc. 979 Keystone Way, Carmel, IN 46032, phone 317 844 7176. [Mostly latex spheres.] Handy & Harman, 850 Third Avenue, New York, New York 10022, phone 212 752 3400. [Metal powders, such as silver.] Particle Technology, Inc., P.O. Box 924, Hanover, Maryland 21076, phone 410 859 5800. [Metallic oxide powders.] References M. Corn and N. A. Esmen, "Aerosol Generation," in R. Dennis (Ed.), Handbook on Aerosols, TID-26608, USERDA, Oak Ridge, TN, 1976. G. M. Hidy, Aerosols, Academic Press, Orlando, FL, 1984. W. C. Hinds, "Dry - Dispersion Aerosol Generators," in Willeke, K. (Ed.), Generation of Aerosols, Ann Arbor Science, Ann Arbor, MI, 1980. Douglas W. Cooper, Ph.D. |