Joint Electroreduction of Chromium and Boron Ions and Electrochemical Synthesis of Chromium Borides in Halide–Oxide Melts
2020
The electroreduction of oxygen-containing chromium ions
$${\text{CrO}}_{{\text{4}}}^{{{\text{2}}-}}$$
and
$${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$
and their joint electroreduction with fluoroborate ion
$${\text{BF}}_{{\text{4}}}^{ - }$$
in the equimolar KCl–NaCl melt at 1073 K are studied by cyclic voltammetry. The electroreduction of
$${\text{CrO}}_{{\text{4}}}^{{{\text{2}}-}}$$
and
$${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$
proceeds via two steps to form chromium oxide Cr2O3 in the first step. In the second step, Cr2O3 also precipitates in the case of the electroreduction of
$${\text{CrO}}_{{\text{4}}}^{{{\text{2}}-}}$$
, and a mixture of Cr2O3 and metallic chromium is formed due to the electroreduction of
$${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$
. Against the background of the KCl–NaCl melt, fluoroborate ion can interact with the
$${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$
ion to form chromium (
$${\text{Cr}}{{{\text{O}}}_{{\text{2}}}}{\text{F}}_{{\text{4}}}^{{{\text{2}}-}}$$
) and boron (
$${\text{BOF}}_{{\text{2}}}^{-},$$
BOF) oxyfluoride complexes. The possibility that electrochemical synthesis of chromium boride phases occurs in a halide–oxide melt is shown by the joint electroreduction of chromium and boron oxyfluoride complexes.
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