14693-80-2Relevant articles and documents
The equilibrium phase diagrams for the tantalum-tantalum bromide and tantalum-tantalum iodide systems
McCarley, Robert E.,Boatman, James C.
, p. 1486 - 1491 (1965)
The tantalum-tantalum bromide and the essential features of the tantalum-tantalum iodide system have been elucidated. In the bromide system four phases of composition lower than TaBr5 were established, viz., TaBr4, TaBr2.5, TaBr2.5, and TaBr2.33. By comparison the iodide system is very simple as evidenced by only the two lower phases TaI4 and TaI2.33. In the bromide system a eutectic occurs at 267° and the composition TaBr4.87. The TaBr4 melts incongruently at 392° to form liquid of composition near TaBr4.85 and the next lower solid TaBr2.83. Equilibrations of TaBr4 at a series of temperatures above 400° established that TaBr2.83 melts incongruently within the interval 447-453° to form bromine-rich liquid and the phase TaBr2.5. Similarly it was determined that TaBr2.5 melts incongruently to form TaBr2.33 in the interval 671-680°. Exact location of the melting temperatures for the bromides with Br/Ta 2.33 was the lowest phase in the system was established by equilibrations of the higher halides with tantalum at temperatures up to 750°; a melting point for TaBr2.33 was not observed. In the iodide system the melting point of TaI5 occurred at 382°, with a eutectic at 365° and the composition TaI4.87. Decomposition of TaI4 into iodine-rich liquid and TaI2.33 occurred in the interval 395-402° at a very low rate. Equilibrations of TaI2.33 and Ta up to 815° provided no evidence for any new phases. Both TaBr2.33 and TaI2.33 provide aqueous solutions of the ions Ta6Br122+ and Ta6I122+. Hence these compounds are formulated correctly as (Ta6Br12)Br2 and (Ta6I12)I2. The chemical properties and stoichiometry of the phases TaBr2.5 and TaBr2.83 suggest that they should be formulated as (Ta6Br12)Br3 and (Ta6Br12)Br5, respectively.
