Spontaneous room temperature extrusion of Pb nano-whiskers from leaded brass surfaces
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Spontaneous room temperature extrusion of Pb nano-whiskers from leaded brass surfaces Z.M. Suna) Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104; and National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560, Japan
M.W. Barsoumb) Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104 (Received 27 December 2004; accepted 2 February 2005)
We report that lightly abrading the surface of a commercial leaded brass results in the room temperature spontaneous growth of Pb whiskers and hillocks. The aspect ratios and submicron diameters of the whiskers that form render them easily dispersible in the atmosphere, with potentially serious health effects, especially for people that deal with leaded brass on a daily basis.
Brasses, Cu–Zn alloys, are extensively used both in industry and in consumer products. Lead (Pb), usually with 1–2 wt%, is added to some brasses to improve their machinability1 and/or corrosion resistance.2 Because of its good machinability, electrical and thermal conductivity, corrosion resistance, and mechanical properties leaded brass is widely used in electronic equipment, construction, plumbing, and common mechanical parts, such as gears and watch or clock parts. The supply of brass mill products in the United States reached 1.4 million tons in 2003, followed by 1.1 millions tons both in Japan and in Germany.3 Whereas the annual brass supply in the United States increased by 1.3 times in the past 20 years, the Pb used in brass (≈15,000 tons) increased by more than 5 times.3 This is an indication of the increased use of leaded brass—the industry standard for “freemachining” copper alloys1—in the brass family. Lead is one of the oldest known and most widely studied occupational and environmental toxins and its harmful effects on human health4–12 have long been a concern. For example, the leaching of Pb into potable water is a problem that is currently being addressed at least in the U.S. and Europe.13 Most relevant to this work, biological and environmental monitoring has Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2005.0149 J. Mater. Res., Vol. 20, No. 5, May 2005
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shown that Pb exposure levels were high in three brass and bronze industries, in which the highest Pb levels were observed in a foundry where a scrap grinding operation was performed and the Pb limits were exceeded.6 Interestingly, the environmental concentrations and levels of other metals in that same study were within reasonable limits. The room temperature spontaneous growth of Pb whiskers from commercial leaded brass was discovered by accident, when a leaded brass, with a Cu–38Zn–2Pb composition (ASTM-C37700) was used as a support for another experiment. The brass in question was machined into small cylinders and exposed to the atmosphere for an unknown time, but no less than a
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