Automated Impedance Measurements in Electrochemical Cells
Abstract In this paper a system is described for impedance measurements in electrochemical cells, integrated by a fast potentiostat, signal generator, digital transient recorder and a computer interface. The treatment of the signal is made by obtaining the correlation between the response cell signal with the in-phase and in-quadrature signals, as is made in the frequency response analysis systems, but the quadrature component being numerically generated. This allows one to obtain the d.c. first and second harmonic cell responses in a single experiment, as well as the a.c. phase selective response by programming the reference signal phase angle. The results obtained with a dummy cell showed the validity of the procedure since the deviation of the measured results from the theoretical data is low. The C/E curve of the interface 1 M KCI/Hg at 25°C is concordant with that previously reported in the literature. Moreover, the system has been tested with the reduction of Cd(II) ion.
The anodic dissolution of molybdenum in alkaline solutions — electrochemical measurements
Abstract The anodic dissolution of molybdenum has been investigated in sodium hydroxide solutions using a rotating disc electrode. Log i — E curves in the potential range −500 mV to +300 mV (vs. 1 M NaOH/Hg/HgO) show a Tafel region followed by a region in which the current varies only slowly with potential. Impedance spectra give evidence for an impedance with one relaxation process and a diffusional impedance. This is considered to be due to the film/solution interface. Current-voltage curves and impedance measurements are discussed in terms of the oxide films present on the electrode surface as determined by X-ray photo-electron spectroscopy measurements. A different type of impedance spectrum is seen as each new molybdenum species is formed.
Intensification of Bubble Disintegration and Dispersion by Mechanical Stirring in Gas Injection Refining
Water model experiments were performed for establishing highly efficient gas injection refining processes. Mechanical stirring was applied to disintegrate the injected bubbles and to disperse them widely in the bath. The bubble disintegration and dispersion were investigated by changing rotation mode (direction of rotation), rotation speed, blade size of the impeller and gas flow rate. Forward rotation of the impeller induced a stable tangential flow and could not disperse bubbles in the bath due to formation of a vortex around the impeller shaft. The tangential flow could be suppressed by forward–interrupt rotation, which could reduce the vortex formation to some degree. However, forward–interrupt rotation could not disperse the bubbles widely in the bath. Forward–reverse rotation could prevent the vortex formation completely and create a strong shear stress field, which intensified the bubble disintegration and dispersion in the bath. Higher impeller rotation speed and larger blade length in forward–reverse rotation could enhance the bubble disintegration and make the dispersed bubbles smaller. The bubble dispersion zone became wider with larger blade length. The bubble size tended to be larger at higher gas flow rates. However, its dependence on the gas flow rate became smaller at higher impeller rotation speed.