Electron Transport in Nanosystems
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Of all the 115 elements listed in the Periodic Table, 70% exhibit metallic character. Since the discovery of copper and bronze by early civilizations, the study of metals (i.e., metallurgy) contributed to most of the early investigations related to materials science. Whereas iron-based alloys have long been exploited for a variety of applications, there is a constant search for new metallic compositions that have increasing structural durability, but also possess sufficiently less density. The recent exploitation of titanium-based alloys results from this effort, and has resulted in very useful materials that are used for applications ranging from aircraft bodies to golf clubs. Indeed, there are many yet undiscovered metallic compositions that will undoubtedly prove invaluable for future applications. In Chapter 2, you learned how individual atoms pack in crystal lattices. Moreover, the nature of metallic bonding was described, which is responsible for characteristic physical properties of these materials. This chapter will continue this discussion, focusing on the relationship between specific metallic lattice structures and their impact on overall physical properties. 3.1. MINING AND PROCESSING OF METALS Before we examine the structures and properties of metallic classes in further detail, it is useful to consider the natural sources of the metals, generally as oxide and/or silicate-based mineral formations. If the mineral deposit contains an economically recoverable amount of a metal, it is referred to as an ore. The waste material of the rock formation is known as gangue, which must be separated from the desired portion of the ore through a variety of processing steps. There are three main types of rocks, grouped according to their form of origin. Igneous rocks are those formed from the solidification of molten mass following volcanic activity. Common examples include granite, feldsar, and quartz; metals such as the alkali and alkaline earths, gold, platinum, and chromium are isolated from these formations. Sedimentary rocks are those formed through compaction of small grains deposited as sediment in a riverbed or sea. Common examples include limestone, sandstone, and dolomite. Metals such as copper, iron, zinc, lead, nickel, molybdenum, and gold may all be found together within sulfur-based sedimentary deposits. Metamorphic rocks are those formations that have changed composition 87
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3.1. Mining and Processing of Metals
and morphology over time through the influence of temperature and pressure. Examples of these rocks include marble, slate, and gneiss, and yield similar metals as igneous formations. Most metals are obtained through physical and chemical modification of ores that contain a sufficiently high concentration of the desired metal. Table 3.1 lists some metals, regions of their primary occurrence, and some applications for the metallic materials. Quite often, the processing steps used to isolate and purify metals from ores have a significant impact on the overall microstructure, which will affec
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