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Eur. J. Mass Spectrom. 4, 197 - 202 (1998) |
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Mass spectrometric study of thermal decomposition process of niobium clusters Nb3Cl8 and Nb6Cl14 | ||
V.I. Tsirelnikov |
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ABSTRACT: | ||
The thermal decomposition process of solid niobium clusters Nb3Cl8 (NbCl2.67) and Nb6Cl14 (NbCl2.33) was studied by effusion methods with mass spectral registration of the vapour composition and pressure and their dependence on temperature. It is shown that the NbCl2.67 cluster decomposes to the NbCl2.33 cluster with formation of niobium tetrachloride in the gas phase. The process is monovariant. The NbCl2.33 cluster decomposes to niobium dichloride. The process is bivariant because the homogeneity region is formed on the basis of the NbCl2.33 crystal lattice. The composition of the vapour phase changes with an Nb : Cl atomic ratio which decreases during the process. At the beginning of the process the vapour consists of niobium tetrachloride and at the end the vapour is only niobium trichloride. The enthalpy of thermal decomposition of NbCl2.67 (1.67 Nb3Cl8 (s) = 0.67 Nb6Cl14 (s) + NbCl4 (g)) which is DrH°(700K) = 287.4 ± 3.8 kJ mol1 and the formation enthalpy of NbCl2.33, which is DfH°(Nb6Cl14, 298K) = 479 ± 10 kJ mol1, were calculated from experimental data. | ||
Keywords: Niobium chloride clusters, thermal decomposition, thermodynamics. |
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