(1) Preparation of Alloys by the Use of Heat The optimum methods sometimes involve metal hydrides rather
than pure metals. The procedure is useful mainly in the case
of metals that form stable hydrides (alkali and alkaline earth
metals, Ti to Th, V to Ta, Pd). The hydrides are readily reduced
to powders and the contact of the latter with the other components
of the alloy is much better than it would be otherwise. The
thermal decomposition of the hydrides proceeds so easily that
the formation of alloys is not only not slower than in the case
of pure metals, but is faster due to the small particle size of
the material. In addition, the hydrogen liberated from the hydride
may reduce the oxide impurities. One disadvantage inherent in the
use of hydrides is that the commercial materials are usually less
pure than the corresponding metals. (2) Alloy Synthesis under Pressure Special methods are required when one of the constituent metals
of the alloy has a very low boiling point (Zn, Cd, Hg; see also
p. 1789) while the other constituent has a high melting point
(platinum metals and other transition metals; see Table 4, p. 1776).
In this case, if the pressure is atmospheric pressure, one metal
tends to vaporize before the other liquefies. Nowotny et al. have
designed a special furnace which allows heating such metal combinations in a protective gas at high pressures.
