On the Mechanism of Anodic Chlorate Oxidation

Abstract

Anodic polarization curves were determined on smooth Pt, Pt-coated Ti, PbO2-coated graphite, and PbO2-coated Ti. Operating conditions were typical for industrial perchlorate production, i.e. 1.6 moles/liter NaC104, while NaC10~ concentration was ranging between 0.47 and 4.7 moles/liter, at 50~ p.H 6-7. For solutions containing NaC104 only, the anodic current potential alagram is rectilinear, irrespective of any presence of NaF or Na2Cr2OT. If NaC103 also is present, the diagram shows a strong inflection. For each set of conditions, current efficiency and anode potential were determined vs. current density. This allowed two separate curves for C10~-conversion rate and O2 evolution rate, respectively, to be plotted vs. anode potential. Tafel linearity for C103-conversion is thus obtained on Pt and on PbO2 under all conditions, with a slope ranging between 0.1 and 0.12. This fact supports the view that C103-is oxidized through a path involving primary discharge of C10~with formation of CIO3 radicals and that charge transfer is in most cases the rate-determining step.The over-all reaction of anodic chlorate oxidation is

Mechanism of anodic oxidation of chlorate to perchlorate on platinum electrodes

“…3). The first stage, occurring between 1.3 and 1.9V, was found to correspond to oxygen evolution and the second stage, higher than 2.2V, corresponded to perchlorate formation [5]. In the transition range from 1.9 to 2.2V, the nature of the anode surface may change strongly.…”

“…Only oxygen and perchlorate are formed at the anode during electrolysis under the conditions used in this investigation [5]. In this case the sum of the current efficiencies 1-'o2 and I'clo4 is equal to 1.…”

“…Anodic polarization curves on smooth platinum electrodes in NaC103 solutions show a strong inflection [5]. This means that the adopted method to calculate the ohmic potential drop must be used carefully.…”

“…This step is followed either by the fast combination of OH radicals, (OH)ads q-(OH)ads , (O)ads -I-H20 (5) or by the discharge of OH radicals…”

A potential method for electrochemical micromachining of titanium alloy Ti6Al4V

“…Previously, the mechanism of reaction (1) had been studied extensively [33,34]. The H + generated from reactions (1) and (2) combines with F -and NO 3 -on the surface of the mold to form etchants HF and HNO 3 .…”