Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-20 GTBL042-Callister-v3 September 21, 2007 19:48

794 • Chapter 20 / Economic, Environmental, and Societal Issues

INPUTS

Energy

Raw

materials

OUTPUTS

Usable products

Water effluents

Air emissions

Solid wastes

Other impacts

Materials production

Product manufacturing

Product use

Product disposal

Figure 20.2 Schematic representation of an input/output inventory for the life-

cycle assessment of a product. (Adapted from J. L. Sullivan and S. B. Young,Advanced

Materials & Processes,Vol. 147, No. 2, p. 38, 1995. Copyright©c1995 by ASM

International. Reprinted by permission of ASM International, Materials Park, OH.)

friendly product or process will inherently be more costly than one that is envi-

ronmentally unfriendly. Engineers who use “out-of-the-box” thinking can generate

better and cheaper products/processes. Another consideration relates to how one

defines “cost”; in this regard it is essential to look at the entire life cycle and take into

account all relevant factors (including disposal and environmental impact issues).

One approach that is being implemented by industry to improve the environ-

mental performance of products is termedlife cycle analysis/assessment. With this

approach to product design, consideration is given to the cradle-to-grave environ-

mental assessment of the product, from material extraction to product manufacture

to product use, and, finally, to recycling and disposal; sometimes this approach is also

labeled “green design.” One important phase of this approach is to quantify the vari-

ous inputs (i.e., materials and energy) and outputs (i.e., wastes) for each phase of the

life cycle; this is represented schematically in Figure 20.2. In addition, an assessment

is conducted relative to the impact on both global and local environments in terms

of the effects on the ecology, human health, and resource reserves.

20.5 RECYCLING ISSUES IN MATERIALS SCIENCE

AND ENGINEERING

Important stages in the materials cycle where materials science and engineering

plays a significant role are recycling and disposal. The issues of recyclability and

disposability are important when new materials are being designed and synthesized.

Furthermore, during the materials selection process, the ultimate disposition of the

materials employed should be an important criterion. Let us conclude this chapter

by briefly discussing several of these recyclability/disposability issues.

From an environmental perspective, the ideal material should be either totally

recyclable or completely biodegradable. Recyclable means that a material, after hav-

ing completed its life cycle in one component, could be reprocessed, reenter the

materials cycle, and be reused in another component—a process that could be re-

peated an indefinite number of times. By completely biodegradable, we mean that, by