Experimente und Überlegungen zum Chemischen Transport von TaS2 mit Schwefel. Die Gasmolekel TaS5

Experiments and Conclusions on the Chemical Transport of TaS₂ with Sulfur. The Gas Molecule TaS₅ The transport rate was determined experimentally in cylindrical ampouls for the unexpected transport of TaS₂ with sulfur which proceeds to the high or low temperature zone depending on temperature and pressure. The transport must obviously be due to the existence of an unknown gaseous polysulfide TaS_x. The gas transport which is governed essentially by thermal convection was evalueted by NaCl/S_x. On this base the transport rate of TaS₂ was transformed into the pressure difference ΔP(TaS_x) = P(TaS_x)T₂ – P(TaS_x)T₁. These experimental data were compared to the calculated values ΔP′(TaS_x) = Δλ(TaS₂) × 0.5 [ΣP₁(S₁) + ΣP₂(S₁)]; λ corresponds to the solubility of TaS₂ in the gas phase (based on the sulfur content). In this way we found that the transport proceeds via TaS_5,g less likely via TaS_6,g: The change in transport direction in the temperature gradient originates from the transition endothermic/exothermic reaction with increasing temperature. Although the TaS₅ pressure is small, it is sufficient for the transport of considerable amounts of TaS₂ due to the multiplicative character of the transport process.