Electronic Absorption Spectra of Niobium Species in Halide Melts

摘要

The results of spectroscopic studies of Nb anodic dissolution,dissolution of NbCl_5 and reaction of various niobium oxides withHCl in different chloride melts at 450-750°C are presented.Nb(Ⅲ) species, NbCl_6~(3-), is the major product of niobium anodicdissolution at current densities up to 40 mA/cm~2. Addition ofNbCl_5 to alkali chloride melts predominantly leads to the formationof Nb(Ⅴ) species, NbCl_6~-. Upon increasing Nb(Ⅴ) concentrationNbCl_6~- tend to decompose to Nb(Ⅳ) and Cl_2. Reaction of NbO andNbO_2 with HCl proceeds via an intermediate oxygen-containingNb(Ⅳ) complexes. Oxygen-free Nb(Ⅳ) ions, NbCl_6~(2-), wereobtained by exchange reactions between metallic niobium andmelts containing Bi(Ⅲ), Ag(Ⅰ) or Ni(Ⅱ) chloro-ions.Electroreduction of Nb(Ⅲ) on a tungsten working electrode below-1.45 V vs. Cl_2/Cl~- led to the formation of metallic niobium, noevidence of intermediate reduction products was obtained.