Callister - An introduction - 8th edition

876 • Chapter 22 / Economic, Environmental, and Societal Issues in Materials Science
Synthesis
and
processing
Raw
materials
Engineered
materials
Recycle/reuse
Product design,
manufacture,
assembly
Waste
Applications
Agriculture • Construction
Environmental • Defense
Information/Communications
Transportation • Energy • Health
Extraction/Production
Figure 22.1 Schematic representation of the total materials cycle. (Adapted from M. Cohen,
Advanced Materials & Processes, Vol. 147, No. 3, p. 70, 1995. Copyright © 1995 by ASM
International. Reprinted by permission of ASM International, Materials Park, OH.)
It has been estimated that worldwide, about 15 billion tons of raw materials are
extracted from the earth every year; some of these are renewable and some are not.
Over time, it is becoming more apparent that the earth is virtually a closed system
relative to its constituent materials and that its resources are finite. In addition, as
our societies mature and populations increase, the available resources become
scarcer, and greater attention must be paid to more effective use of these resources
relative to the materials cycle.
Furthermore, energy must be supplied at each cycle stage; in the United States
it has been estimated that approximately one-half of the energy consumed by
manufacturing industries goes to produce and fabricate materials. Energy is a resource
that, to some degree, is limited in supply, and measures must be taken to
conserve and more effectively use it in the production, application, and disposal
of materials.
Finally, there are interactions with and impacts on the natural environment at
all stages of the materials cycle. The condition of the earth’s atmosphere, water, and
land depends to a large extent on how carefully we traverse the materials cycle.
Some ecological damage and landscape spoilage undoubtedly result during the extraction
of raw materials. Pollutants may be generated that are expelled into the air
and water during synthesis and processing; in addition, any toxic chemicals that are
produced need to be disposed of or discarded. The final product, device, or appliance
should be designed so that during its lifetime, any impact on the environment
is minimal; furthermore, at the end of its life, provision should be made for recycling
its component materials, or at least for their disposal with little ecological
impact (i.e., it should be biodegradable).
Recycling of used products rather than disposing of them as waste is a desirable
approach for several reasons. First of all, using recycled material obviates the
need to extract raw materials from the earth and thus conserves natural resources