It is now more than 100 years since certain detrimental effects on the
ductility of iron were first associated with the presence of hydrogen.
Not only is hydrogen embrittlement still a major industri- al problem,
but it is safe to say that in a mechanistic sense we still do not know
what hydrogen (but not nitrogen or oxygen, for example) does on an
atomic scale to induce this degradation. The same applies to other
examples of environmentally-induced fracture: what is it about the
ubiquitous chloride ion that induces premature catastrophic fracture
(stress corrosion cracking) of ordinarily ductile austenitic stainless
steels? Why, moreover, are halide ions troublesome but the nitrate or
sulfate anions not deleterious to such stainless steels? Likewise, why
are some solid metals embrit- tled catastrophically by same liquid
metals (liquid metal embrit- tlement) - copper and aluminum, for
example, are embrittled by liquid mercury. In short, despite all that we
may know about the materials science and mechanics of fracture on a
macroscopic scale, we know little about the atomistics of fracture in
the absence of environmental interactions and even less when
embrittlement phe- nomena such as those described above are involved. On
the other hand, it is interesting to note that physical chemists and
surface chemists also have interests in the same kinds of interactions
that occur on an atomic scale when metals such as nickel or platinum are
used, for example, as catalysts for chemical reactions.