Research On Measurements Of Alumina Concentration By A Rotating Disc Electrode In Aluminum Electrolytes

Rotating disk electrode(RDE) is one of the few convection electrode system which could get the rigorous solution of drodynamic equations and convection-diffusion equations in the steady state. This type of electrode is easy to establish a uniform, steady state,so it is widely used in electrochemical studies of both aqueous and non-aqueous solvent at ambient temperatures.However,In spite of the significant advantages avaible with RDE technique,there is relatively few applications reported in the high temperature molten salt electrolytes.Therefore,this paper tries to design a rotating disk electrode,which is suitable for high temperature studies in cryolite-based molten salt electrolytes, evaluate its measure performance at room temperature and at high temperature,and research on measuring alumina concentration in aluminum electrolyte using the rotating disk electrode technology.A critical task in the design of an RDE for use in high temperature cryolite electrolytes is finding a suitable combination of electrode and insulator materials.In this paper, high-purity graphite was selected as the disk electrode material,and hot boron nitride was selected as insulating gap material.while the Inconel 310S was used as rotation shaft material,a asynchronous AC motor of 500watts was used as the device that drives disc electrode rotating.The rotational speed of RDE could be regulated by a variable-frequency drive,and the rotation rates could be adjusted continuously between 0 and 1450 rpm.The measurement performance of RDE designed in this paper was evaluated in 0.1mol/L aqueous solution system of NaCl at room temperature as well as in (2.2NaF+AlF3)-5wt% CaF2-5wt% LiF-lwt% Al2O3 molten salt system. In 0.1mol/L NaCl solution research system,using RDE as the work electrode, platinum electrode as the auxiliary electrode and calomel electrode as the reference electrode, the Steady-state polarization curves of the cathode were measured by linear sweep voltammetry under different rotational speeds. It was found that the limit current value of RDE increased with the rotational speeds rising,and relationship between id and ω1/2 is a straight line through the origin,which is id=4.1ω1/2 and just fits the Levich equation very well.This proved that the measurement performance of rotating disk electrode in aqueous solution at room temperature should be excellent.And in cryolite-based melts system with cryolite ratio(CR) of 2.2, using RDE as anode, graphite crucible as cathode,and platinum electrode as the reference electrode, the critical currents of the anode were measured by the linear sweep voltammetry under different rotational speeds. Experiment showed that the critical current value increased with the rotational speeds increasing.And the relationship between ic and ω1/2 is ic=0.254ω/2, which fits the the Levich equation as well,So the RDE should be fine for use in high temperature molten salt.When researching the alumina concentration by RDE in (2.2NaF·AlF3)-5wt%CaF2-5wt%LiF-Al2O3 melten salt system, linear sweep voltammetry curves were measured under the different concentrations of alumina,which was lwt%,2wt%,3wt% and 4wt%,respectively.It was found that the critical current density(ccd) increased with the alumina concentration increasing,and the relationship between ccd and alumina concentration is a linear function of what is ic=0.218Al2O3wt%+3.345,which is a straight line through the origin.