When we see a jumbo jet at the airport, we sometimes wonder how such a
huge, heavy plane can fly high in the sky. To the extent that we think
in a static way, it is certainly not understandable. In such a manner,
dynamics yields behavior quite different from statics. When we want to
prepare an iron nitride, for example, one of the most orthodox ways is
to put iron in a nitrogen atmosphere under pressures higher than the
dissociation pressure of the iron nitride at temperatures sufficiently
high to let the nitrogen penetrate into the bulk iron. This is the way
thermodynamics tells us to proceed, which requires an elaborate,
expensive high-pressure apparatus, sophisticated techniques, and great
efforts. However, if we flow ammonia over the iron, even under low
pressures, we can easily prepare the nitride-provided the hydrogen
pressure is sufficiently low. Since the nitrogen desorption rate is the
determining step of the ammonia decomposition on the iron surface, the
virtual pressure of nitrogen at the surface can reach an extremely high
level (as is generally accepted) because, in such a dynamic system, the
driving force of the ammonia decomposition reaction pushes the nitrogen
into the bulk iron to form the nitride. Thus, dynamics is an approach
considerably different from statics.