orthorhombic black powder(s), a=0.8236 nm, b=0.4773nm, c=0.8523 nm; hardness 4.5 Mohs; resistivity 123μοhm· cm can be prepared by reaction of the elements; used in special alloy applications, as a flame-resistant coating material, also as 99.5 or 99.9% pure material, as a sputtering target in the fabrication of integrated circuits [HAW93] [STR93] [CER91]
(1) PREPARATION FROM THE ELEMENTS
Ti + 2 Si = TiSi2
The silicides are prepared by fusing or sintering intimate
stoichiometric mixtures of the elements (in powder form). The
reaction is carried out in sintered clay or ceramic crucibles,
placed in a Tammann furnace under a blanket of Ar. In all three
cases the reaction takes place at a relatively low temperature and
is highly exothermic; therefore, one should work with gram quantities only.
(2) ALUMINOTHERMIC METHOD
Ignition of a mixture of, for example, 200 g. of Al powder, 250 g.
of S, 180 g. of SiOa and 15 g. of TiO2 (or 40 g. of K2TiF6 ), covered
with a thin layer of Mg, yields an ingot containing, in addition to Si
and Al, small, iron-gray tetragonal pyramids of TiSi2 .
(3) ELECTROLYTIC PREPARATION
The pure, crystalline silicides ar e obtained by melt electrolysis
of a mixture of, for example, 10K2SiF6
+ TiO2 at about 900°C, using
an iron cathode; alternately, electrolysis of TiO2
dissolved in a
melt of silicate may be used.
