Measurement of Concentration Profiles of Cu2+ Ion and H+ Ion near a Plane Vertical Cathode by Two‐Wavelength Holographic Interferometry

Abstract

A technique of two-wavelength holographic interferometry was applied to simultaneously measure the concentration profiles of Cu 2~ ion and H + ion near a plane vertical cathode placed in an unstirred aqueous solution containing CuSO4 and excess H2SO4. It was revealed that the measured concentration profiles of Cu 2+ ion and H + ion are approximated with the parabolic equations of horizontal distance from cathode surface and that the concentration gradient of Cu 2+ ion at the cathode surface is larger in CuSO4-H2SO4 solution than in CuSO4 solution at the same cathodic current density and vertical distance. The following matters were also clarified: (i) the nondimensional rate of ionic mass transfer is shown as a function of Ray]eigh number based on the boundary layer theory, and (ii) the effect of the addition of excess H2SO4 is expressed by a parameter f which is the ratio of Rayleigh numbers in CuSO4-H2SO4 solution and in CuSO4 solution under the conditions of the uniform distribution of cathodic current density and an excess of H2SO4.The measurement of cathodic concentration profile of ion is important for elucidating not only the ionic mass transfer itself, but also the effect of supporting electrolyte (1, 2). The optical methods such as Jamin (3), Mach-Zehnder (4), and holographic interferometry (5, 6) are effective for the measurement in the single-component aqueous solutions because of the proportionality between the ionic concentration and the refractive index of the solution.In the industrial electrolysis, such as the electrolytic refining of copper, for example, an excess of sulfuric acid is added. In the multicomponent aqueous solutions, the above proportionality no longer holds and the measurement of concentration profiles of ions becomes more difficult.An experimental technique using an image sensor of one-dimensional photodiode array was developed in order to measure the concentration profile of Cu ~+ ion in aqueous CuSO4-H2SO4 solution (7). In this measurement of the light absorbance distribution, however, a noise caused by the light diffraction near the cathode surface was superimposed on the output signal, and the concentration of Cu 24 ion on the cathode surface was estimated by extrapolating the profile toward the cathode surface. The estimation of the concentration of H + ion on the cathode surface was tried by subtracting the light absorbance due to Cu 2+ ion from the refractive index of the solution measured by the conventional holographic interferometry (5). Due to the error of the measurements and the extrapolation, however, the precision and accuracy of the estimated H + ion concentration was relatively poor.It is the intent of the present work to carry out the simultaneous measurement of concentration profiles of Cu 2+ ion and H + ion in the cathodic boundary layer by using a technique of two-wavelength holographic interferometry which is based on the dispersion effect of refractive index of the solution. The problem due to diffraction pattern appearing near the cathode surface can be avo...

Model Based Analysis of Forced and Natural Convection Effects in an Electrochemical Cell

“…He studied the transient behaviour of the natural convection at a constant current density [12]. Later, he focused on ___________________________________ *Corresponding Author: brni@zhaw.ch the ionic mass transfer in CuSO4-H2SO4 solutions whereas the electric field and electrochemical reaction were solved as well [4][5][6]10]. The results show a good agreement with the conducted experiments.…”

“…Wagner analysed the steady state ionic mass transfer due to natural convection along the vertical electrode [1], which leads to the limiting current density based on the boundary-layer theory. Ever since, numerous theoretical and experimental papers have been published on velocity profile of natural convection [2][3], concentration profile [4][5][6] and current density distribution [7][8][9]. Most of these studies focus on the cathode, with fewer focusing on the anode.…”

Ionic mass transfer during electrochemical dissolution of Li metal in PC electrolyte solution

“…(4) describing natural convective mass transfer in aqueous electrolytic solutions (Fig. 7) [17][18][19][20][21][22],…”

Numerical simulation of transient natural convection induced by electrochemical reactions confined between vertical plane Cu electrodes

“…Wagner analyzed the steady state ionic mass transfer rate followed by natural convection along a vertical cathode immersed in semiinfinite stagnant electrolyte media by applying the similarity principle [1,2]. Since then, numerous theoretical and experimental studies have been accumulated on the velocity profile of natural convection [3,4], the concentration profile in the diffusion layer [5][6][7], and the current density distribution along a vertical plane electrode surface [8][9][10]. Most of these studies have concerned only the cathodic boundary layer and few ones have however, been focused on the anodic boundary layer [11][12][13].…”