Electrodeposition constant current

In electrogravimetry, also called electrodeposition, an element, e.g., a metal such as copper, is completely precipitated from its ionic solution on an inert cathode, e.g., platinum gauze, via electrolysis and the amount of precipitate is established gravimetrically in the newer and more selective methods one applies slow electrolysis (without stirring) or rapid electrolysis (with stirring), both procedures either with a controlled potential or with a constant current. Often such a method is preceded by an electrolytic separation using a stirred cathodic mercury pool, by means of which elements such as Fe, Ni, Co, Cu, Zn and Cd are quantitatively taken up from an acidic solution whilst other elements remain in solution. 

In these clusters tantalum atoms are bound to other tantalum atoms and are also edge bridged via halide. As our deposit was completely amorphous without any XRD peak we concluded that it did not consist of crystalline tantalum but rather of such clusters. We varied the electrode potential for deposition and tried deposition with very low constant current densities, but in no case was crystalline tantalum obtained. Thus, the electrochemical window of our liquid was surely wide enough, but for some reason the electrodeposition stopped before Ta(0) was obtained. When we studied the literature dealing with metal clusters we found that the cluster chemistry with fluoride seems to be less comprehensive. Consequently... 

The following examples are presented to illustrate some of the sources of error and some of the precautions necessary for accurate results in electrodeposition at constant current. 

In a constant-potential electrodeposition the current has fallen to 20% of its initial value in 10 min. Estimate the time required for 99.9% deposition. 

The first electrodeposition of aluminum from an ionic liquid was reported in 1994 by Carlin etal. [157], Two years later, Zhao et al. [158] smdied the aluminum deposition processes on tungsten electrodes in trimethylphenylanunonium chlo-ride/aluminum chloride with mole ratio 1 2. It was shown that the deposition of aluminum was instantaneous as a result of three-dimensional nucleation with hemispherical diffusion-controlled growth, underpotential deposition of aluminum, corresponding to several monolayers. Liao et al. investigated the constant current electrodeposition of bulk aluminum on copper substrates was in 1-methyl-... 

Jiang et al. studied the electrodeposition and surface morphology of aluminum on tungsten (W) and aluminum (Al) electrodes from 1 2 M ratio of [Emim]CI/AlCl3 ionic liquids [165,166]. They found that the deposition process of aluminum on W substrates was controlled by instantaneous nucleation with diffusion-controlled growth. It was shown that the electrodeposits obtained on both W and Al electrodes between -0.10 and -0.40 V (vs. AI(III)/A1) are dense, continuous, and well adherent. Dense aluminum deposits were also obtained on Al substrates using constant current deposition between 10 and 70 mA/cm. The current efficiency was found to be dependent on the current density varying from 85% to 100%. Liu et al. showed in similar work that the 20-pm-thick dense smooth aluminum deposition was obtained with current density 200 A/m for 2 h electrolysis [167],... 

Zinc was electrodeposited either in the potentiostatic (constant potential) mode or in the galvanostatic (constant current) mode at room temperature in an aqueous solution composed of 2.2 M ZnCl2 and 4.8 M KC1 without stirring. The electrolyte was prepared with analytical chemicals and deionized water, and deaerated with bubbling nitrogen prior to electroplating. 

The inclusion of metallic particles can be done in two different ways. The first one consists in carrying out the metal deposition during the electropolymerization process in a solution containing both the monomer and the precursor metallic salt. This leads to a dispersion of the metallic particles inside the polymer layer, but, all these particles are not accessible for the electrocatalytic reaction. The second way is to electro-deposit the metal after the electropolymerization process. This electrodeposition can be carried out at a fixed potential, at a constant current or during continuous potential cycling. 

In recent work related to the electrodeposition of PPy from an aqueous pyrrole-oxalic acid solution, the influence of the iron surface pretreatment on the corrosion properties was reported by Van Shaftinghen, Deslouis et al. [79]. The performances of PPy-coated iron samples, obtained through three different electropolymerization techniques were tested (i) electropolymerization at constant current (1 mA cm ) (denoted galstat), (ii) potentiostatic electropolymerization at IV vs. Ag/AgCl in oxalic acid for 600 s followed by addition of pyrrole into the solution (denoted one-step), (iii) potentiostatic polarization in a two-step process identical to the previous one, except that a prehminary polarization at 0 V vs. Ag/ AgCl for 600 s was carried out in the electrolyte alone (denoted two-step) (Figure 16.11). From the anodic curves of iron in oxalic acid alone, a first zone of potential ranging... 

Figure 15.15 shows the chronopotentiogram for the constant current-(l mA/cm ) mediated electrodeposition of a PPy film on AA 2024-T3 using Tiron as both mediator and dopant ion. Compared to the nonmediated electrodeposition in the presence of p-toluene sulfonic acid sodium salt (Na-pTS), both the nucleation potential (maximum potential reached in the transient) and the growth (plateau) potential have been lowered by --- 700 and 500 mV, respectively. The film deposited by Tiron mediation was uniform and complete, whereas the film deposited with Na-pTS was patchy even after two times the deposition time [57]. From measurements of film thickness, doping level and polymer density, the current efficiency for polymer deposition is estimated to be nearly 100%. Electrochemical AFM studies revealed many more nucleation sites during initial stages of electrodeposition in the presence of Tiron than in control experiments where Tiron was replaced by Na-pTS [59]. 

There have been several recent reports of corrosion studies involving polypyrrole or polypyrrole composites on iron or steel [217-226]. One study examined the influence of preparation method on the morphology, mechanical properties, and corrosion inhibition of PPy films on steel, concluding that the best mechanical properties (microhardness. Young s modulus, and elastic recovery) and the best corrosion protection were obtained for coatings electrodeposited at constant current and then thermally treated at 80°C for 1 d [219]. 

It was shown earlier that at sufficiently high frequencies, the average current density in electrodeposition at a periodically changing rate produces the same concentration distribution inside the diffusion layer as a constant current density of the same intensity. Hence, Eq. (4.76) is valid for all cases of electrodeposition at a constant and periodically changing rate at sufficiently high frequencies. 

Fig. 7.35 Schematic representation of the partial current density changes (a) and corresponding potential response (b) during the electrodeposition of two-layer of metals A and A - - B by constant current density pulse (k) up to time T and during the replacement reaction at i = 0. Partial curroit density for electrodeposition of metal A after reaching ta, id(A) partial current density for electrodeposition of metal B after reaching Ta, id(B) partial current density for electrodeposition of metal A during the replacement reaction, id(A)r partial current density for dissolution of metal B during the replacement reaction, idiss(B)r (Reprinted from Ref. [5] with kind permission from Springer)...

Fig. 7.36 Potential responses recorded during constant current density = mA cm pulse trains on a stationary glassy carbon electrode from a solution containing 0.01 M Cu (CH3COO)2 + 0.01 M Pb(CH3COO)2 +1 M HBF4. After the electrodeposition, zero current density (/ = 0) was applied (positions marked in the figure with 1-9) (Reprinted from Ref. [5] with kind permission from Springer)...

From all solutions, Fe-Ni alloy powders were electrodeposited at a constant current density corresponding to the slightly lower value (/pinflection point B (marked with ( )) on the polarization curves (see Fig. 8.14) [1, 8]. 

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