FODOR et al.: KEGGIN TRIHETEROPOLYACIDS
157
The endothermic reactions from 470–738°C in DTA curves correspond to the crys-
talline phase transformation of the oxides: at ~480°C WO3 changes its geometry from
tetragonal to rhombic, at ~600°C one can observe the melting of V2O5 and in
the 720–740°C temperature range, the tetragonal MoO3 and WO3 becomes rhombic [28].
The crystalline phase formed at 400°C is a mixture of metal oxides in stoichiometric
ratios 10WO3+V2O5 and 10MoO3+V2O5, results obtained by comparing the obtained and
the calculated calcinations residue.
Conclusions
The triheteropolyacids synthesis method suggested in the present paper increases the
efficiency comparatively to the classical method. The obtained compounds were char-
acterized by elemental analysis, IR spectra and thermal behaviour over 20–800°C tem-
perature range and their determinate formula is:
H5[AsW10V2O40]⋅16H2O, respectively, H5[AsMo10V2O40]⋅13H2O.
The crystalline phase formed at 400°C is a mixture of metal oxides in stoichio-
metric ratios, results that allow us to propose an alternative method for the synthesis
of a mixture of two oxides with a known composition, a method which consists of
calcinations of the compounds at ~400°C.
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