Cadmium reference solution

The quantitative results quoted above all refer to zinc surface. It is likely that the behaviour of cadmium would be similar in view of the fact that the equivalent weight of cadmium is double that of zinc, it is even more important that the passivation solution shall not attack and dissolve the metal to any appreciable extent. 

FIGURE 3-15 Stripping potentiograms for a solution containing 100 pg L-1 tin, cadmium, and lead 80 s accumulation at — 1.40 V Original (a) and differential (b) displays. (Reproduced with permission from reference 22.). 

The methodology most practiced is referred to here as codeposition, where a single solution contains precursors for all the elements being deposited and is reduced at a fixed potential or current density. The earliest report appears to be that by Gobrecht et al., which was published in 1963 [45]. Two anodes were used in the study, one of Se and one of Cd (or Ag), to form selenite and cadmium ions, respectively. CdSe was then formed by co-reduction of both species at the cathode. Reports of the formation of GaP in 1968 [46] and ZnSe in 1975 [47] via codeposition were subsequently published, and both involved molten salt electrolysis. 

The clean trough is filled by the liquid on the surface of which the films will be prepared. This liquid is referred to as the subphase. Usually the subphase is either pure water or a dilute aqueous solution of an inorganic salt, typically with a divalent cation, such as cadmium. The nature of the cation and its concentration, as well as the pLI and temperature of the subphase, were found to play an important role in the structure and stability of the films. 

The properties of the dual-film electrode were characterized by in situ Fourier transform infrared (FTIR) reflection absorption spectroscopy [3]. The FTIR spectrometer used was a Shimadzu FTIR-8100M equipped with a wide-band mercury cadmium teluride (MCT) detector cooled with liquid nitrogen. In situ FTIR measurements were carried out in a spectroelectro-chemical cell in which the dual-film electrode was pushed against an IR transparent silicon window to form a thin layer of solution. A total of 100 interferometric scans was accumulated with the electrode polarized at a given potential. The potential was then shifted to the cathodic side, and a new spectrum with the same number of scans was assembled. The reference electrode used in this experiment was an Ag I AgCl I saturated KCl electrode. The IR spectra are represented as AR/R in the normalized form, where AR=R-R(E ), and R and R(E ) are the reflected intensity measured at a desired potential and a base potential, respectively. 

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