Chapter 15 Introduction to Nonferrous Metals 333 Mining Effects Large mining activities can disrupt the landscape for miles around. Unwanted leaks from ore-roasting ovens put sulfur dioxide (SO2) into the atmosphere, where it forms acid fog and rain. Trees are stunted, if not killed, for miles around ore-roasting ovens. Rainwater leaching through sulfur-bearing tailings will destroy aquatic life, especially fish, in nearby streams. Gas masks, fume hood ventilators, and exhaust scrubbing equipment are important not only for safety, but for the operators’ long-term health. Almost any mining operation will disrupt the overburden, plus the surface and subsurface water, in order to reach the ore seam. All of these changes must be considered in the planning and operation of any mine. Most mines today do not generate pollutants with as much carelessness as in the past, at least in the United States. SUSTAINABLE METALLURGY SUSTAINABLE METALLURGY 15.4.2 Corrosion of Nonferrous Alloys Suppose two different pieces of meta l are connected electrically and placed in a conductive surrounding. A voltage occurs, driving a current, which is to say, electrons move from one metal to the other. One of the metal pieces will corrode, and the electron flow, or current, between the metals will reduce corrosion in the second metal. The chemical reaction of oxidizing metal releases electrons. When a metal part is made more electronegative by receiving electrons, the rate of corrosion of that part is reduced. The more rapidly corroding metal is said to undergo galvanic corrosion. Zinc on galvanized steel corrodes and protects the steel underneath from oxidation, as explained in Chapters 5 and 9. As shown in Figure 15-13, zinc is the second-most electronegative metal, and ease of processing makes it an excellent choice for protecting steel. The more electronegative a metal is, the more it will protect a less electronegative metal. The greater the difference in electronegativity, the more protection provided. Galvanic corrosion is most evident when metals of widely different electronegativity are exposed in a conductive solution, such as moist earth, unclean water, or a processing solution. For example, an aluminum component on a steel fixture in a tank for cleaning production parts will corrode more rapidly than expected. 15.5 Processing Used in Nonferrous Metallurgy Desirable properties of nonfer rous metals include electrical conductivity, low density, formability, or corrosion resistance, often in preference to high strength. For applications in moving vehicles, toughness and high yield strength per pound (lb-force/lb-mass or mPa/kg) are more important than high yield strength alone. The processing in nonferrous metallurgy aims to maximize these different properties. Differences between individual metals are discussed in the following chapters. The methods of fabrication of nonferrous metal parts are very similar to the methods used for steel. Casting, bulk deformation, forming, heat-treating, joining, and finishing are all done with nonferrous metals using equipment similar to that Copyright Goodheart-Willcox Co., Inc.