Page 42 - Materials Science and Engineering An Introduction

14 • Chapter 1 / Introduction

Whenever a new material is developed, its potential for harmful and toxicological
interactions with humans and animals must be considered. Small nanoparticles have ex-
ceedingly large surface area–to–volume ratios, which can lead to high chemical reactivi-
ties. Although the safety of nanomaterials is relatively unexplored, there are concerns
that they may be absorbed into the body through the skin, lungs, and digestive tract
at relatively high rates, and that some, if present in sufficient concentrations, will pose
health risks—such as damage to DNA or promotion of lung cancer.

1.6 MODERN MATERIALS’ NEEDS
In spite of the tremendous progress that has been made in the discipline of materials
science and engineering within the past few years, technological challenges remain, in-
cluding the development of even more sophisticated and specialized materials, as well
as consideration of the environmental impact of materials production. Some comment
is appropriate relative to these issues so as to round out this perspective.
Nuclear energy holds some promise, but the solutions to the many problems that
remain necessarily involve materials, such as fuels, containment structures, and facilities
for the disposal of radioactive waste.
Significant quantities of energy are involved in transportation. Reducing the weight of
transportation vehicles (automobiles, aircraft, trains, etc.), as well as increasing engine op-
erating temperatures, will enhance fuel efficiency. New high-strength, low-density struc-
tural materials remain to be developed, as well as materials that have higher-temperature
capabilities, for use in engine components.
Furthermore, there is a recognized need to find new and economical sources of
energy and to use present resources more efficiently. Materials will undoubtedly play
a significant role in these developments. For example, the direct conversion of solar
power into electrical energy has been demonstrated. Solar cells employ some rather
complex and expensive materials. To ensure a viable technology, materials that are
highly efficient in this conversion process yet less costly must be developed.
The hydrogen fuel cell is another very attractive and feasible energy-conversion
technology that has the advantage of being nonpolluting. It is just beginning to be im-
plemented in batteries for electronic devices and holds promise as a power plant for
automobiles. New materials still need to be developed for more efficient fuel cells and
also for better catalysts to be used in the production of hydrogen.
Furthermore, environmental quality depends on our ability to control air and
water pollution. Pollution control techniques employ various materials. In addition,
materials processing and refinement methods need to be improved so that they pro-
duce less environmental degradation—that is, less pollution and less despoilage of the
landscape from the mining of raw materials. Also, in some materials manufacturing
processes, toxic substances are produced, and the ecological impact of their disposal
must be considered.
Many materials that we use are derived from resources that are nonrenewable—that
is, not capable of being regenerated, including most polymers, for which the prime raw
material is oil, and some metals. These nonrenewable resources are gradually becoming
depleted, which necessitates (1) the discovery of additional reserves, (2) the development
of new materials having comparable properties with less adverse environmental impact,
and/or (3) increased recycling efforts and the development of new recycling technologies.
As a consequence of the economics of not only production but also environmental im-
pact and ecological factors, it is becoming increasingly important to consider the “cradle-
to-grave” life cycle of materials relative to the overall manufacturing process.
The roles that materials scientists and engineers play relative to these, as well as
other environmental and societal issues, are discussed in more detail in Chapter 22.