Electronic Absorption Spectra of Niobium Species in Halide Melts

Abstract

The results of spectroscopic studies of Nb anodic dissolution, dissolution of NbCl5 and reaction of various niobium oxides with HCl in different chloride melts at 450-7500C are presented. Nb(III) species, NbCl63-, is the major product of niobium anodic dissolution at current densities up to 40 mA/cm2. Addition of NbCl5 to alkali chloride melts predominantly leads to the formation of Nb(V) species, NbCl6-. Upon increasing Nb(V) concentration NbCl6- tend to decompose to Nb(IV) and Cl2. Reaction of NbO and NbO2 with HCl proceeds via an intermediate oxygen-containing Nb(IV) complexes. Oxygen-free Nb(IV) ions, NbCl62-, were obtained by exchange reactions between metallic niobium and melts containing Bi(III), Ag(I) or Ni(II) chloro-ions. Electroreduction of Nb(III) on a tungsten working electrode below -1.45 V vs. Cl2/Cl- led to the formation of metallic niobium, no evidence of intermediate reduction products was obtained.

Local Coordination Environment of 3d and 4d Transition Metal Ions in LiCl-KCl Eutectic Mixture

“…In Figure 5, the computed coordination of Mo 3+ and Nb 3+ at 400 • C is shown along with the computationally obtained optical absorbance using the HSE-06 hybrid functional. We find that both Mo and Nb obtain an octahedral structure in the eutectic melt (MoCl 6 3− and NbCl 6 3− ) at 400 • C. This observation is in good agreement with prior experimental research on the two species in the LiCl-KCl eutectic melt [37,38].…”

“…The experimental results reported by Gabriel et al lacked a conclusive coordination state for Mo in LiCl-KCl primarily due to its high volatility. Our computational results signify the formation of a distorted octahedral complex MoCl 6 3− for Mo 3+ at 400 • C. Likewise, Nb has also been found to adopt multiple coordination states in LiCl-KCl [38], and we have chosen to focus on the predominant Nb 3+ coordination for our computational results. The octahedral NbCl 6…”