Who Will Do the Necessary Experiments?
J. Phase Equilib. Diffus.
Who Will Do the Necessary Experiments?
Herbert Ipser
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Last year I attended the TOFA (Thermodynamics of
Alloys) Meeting in Santos, Brazil. Quite a number of
contributions were on phase diagram optimizations using
the well-known CALPHAD method. As the CALPHAD
method is a semi-empirical method, one needs a minimum
of experimental data, both thermodynamic data as well as
phase diagram information, in order to arrive at a reliable
and consistent description of the binary or higher-order
system. If experimental enthalpies of formation are not
available, ab initio calculations may provide additional
input into the CALPHAD calculations.
Several of the presenters ended their talk with the
remark that additional experimental data would be
necessary or, at least, helpful. And several times I was tempted
to raise my hand in the discussion and ask why he or she
never tried to do these necessary experiments themselves.
Many of our younger colleagues are highly proficient in
doing CALPHAD optimizations or even ab initio
calculations, and still a considerable number are able to
determine phase equilibria experimentally using x-ray
diffraction, scanning electron microscopy, and thermal
analyses. However, the number of labs where
thermodynamic properties of metallic or ceramic systems are
measured is dwindling fast. There may be still a number of
scientists who know how to use a calorimeter (although
several of them are approaching or beyond their regular
retirement age), but how many labs do still exist where
vapor pressure or emf measurements are done, although
these are valuable sources of (partial) Gibbs energy data?
Today we still rely on extremely accurate measurements
from the middle of the last century. Just a few examples are
the measurements of heat capacities in the low temperature
range by Edgar F. Westrum at the University of Michigan,
which were necessary to calculate standard entropy values;
or the heat capacity measurements in the medium
temperature range up to about 800 K by Frederik Grønvold at
the University of Oslo; or the vapor pressure and Gibbs
energy data determined by torsion effusion mass
spectrometry in the labs of Gerd M. Rosenblatt at Princeton
University or Jimmie G. Edwards at the University of
Toledo (Ohio). All these labs, and many others, have been
closed down, some of them long ago, and the equipment
has been disassembled. But who will do such careful, but
admittedly tedious, experiments in the future?
Of course, doing thermodynamic measurements is not
really ‘‘sexy,’’ and some people may consider these
experiments awfully boring. But it is a fact that we do need
more experimental data, be it enthalpies of formation of
solid compounds or enthalpies of mixing of liquids, be it
accurate heat capacities, or be it vapor pressure or emf data
from which Gibbs energies can be derived! And from my
own experience, it is not boring at all to do thermodynamic
experiments. It is true, using a computer and appropriate
software (in many cases simply as a black box) can provide
results rather quickly, and on the other hand, it is more
tedious and time consuming to run experiments where one
has to wait for the results and needs to interpret and
compare them continuously to see if they are consistent
with earlier data within the same series of measurements.
But at the end it is equally satisfactory to have a consistent
and reliable set of results that may be valuable for future
scientific work.
Thus I would like to encourage some of our younger
colleagues to try it, to try to do thermodynamic
experiments by themselves. I am sure they might like it after all.
Herbert Ipser
Associate Editor, Journal of Phase Equilibria and
Diffusion
Institute of Inorganic Chemistry/Materials Chemistry
University of Vienna (...truncated)