Page 170 - Materials Chemistry, Second Edition

CHAPTER 3

METALS

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 for applications ranging from aircraft bodies to hip replacements
and 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, feldspar, mica, 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 com-
paction of small grains deposited as sediment in a riverbed or sea. Common
examples include shale, limestone, sandstone, and dolomite. Metals such as copper,
iron, zinc, lead, nickel, molybdenum, and gold may all be found together within
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