Influencing factors different current densities

The great influence of concentration, current density, and especially of temperature is again emphasized in the researches of Bunge. The various conditions which were followed by the individual investigators explain sufficiently the frequent differences occurring in the results. The repetition of an electrolytic experiment is only possible when an exact statement of all the factors is given. This requirement is, however, entirely omitted in the published experiments above mentioned. 

Two other factors should be considered in comparing results obtained by different methods surface diffusion of the metal atoms in the upd layer and their diffusion into the substrate, sometimes referred to as surface alloy formation [161]. Steady state of these processes is generally not achieved when deposition is conducted at high current density. A study of the influence of the current density on the EQCM response could help to understand the role of these processes in the early stages of deposition. In any event, it seems to be preferable to use galvanostatic conditions in these experiments rather than cyclic voltammetry. 

The nature of the electrodes is of great importance for the course of electrolytic processes. The material is not only decisive for the effect, as already fully discussed, but the nature of the surface and the previous treatment of the electrodes can decidedly influence the course of the electrolysis. In the first place it is obvious that the size of the surface wetted by the electrolyte is codeterminative for the potential and current density, and even on this account its smoothness or roughness form decisive factors but its form, and the mutual position of both electrodes, must also lie taken into consideration, for on these depend the distribution of the lines of force on the surface. In general, the data on the current densities and of the potentials refer to mean values actually both are usually unlike at different points of the surface, since the number of the discharging current linos in an uneven one. 

Electro-deposition of Cobalt.1—Although nickel has been very largely used for commercial electroplating purposes, there would appear to be a useful field for a cobalt electroplate industry. The earlier literature on the subject is full of contradictions,2 but this is readily understood when it is remembered what an important influence upon the nature of deposited metals is exerted by different factors such as temperature, current density, chemical composition of the solution employed, etc. 

The electrolysis products of different carboxylates have been compared with the ionization potentials of the intermediate radicals. From this it appeared that alkyl radicals with gas-phase ionization potentials smaller than 8 eV mainly lead to carbenium ions. Accordingly, a-substituents such as carboxy, cyano or hydrogen support the radical pathway, whilst alkyl, cycloalkyl, chloro, bromo, amino, alkoxy, hydroxy, acyloxy or aryl more or less favor the route to carbenium ions. Besides electronic effects, the oxidation seems also to be influenced by steric factors. Bulky substituents diminish the extent of coupling. The main experimental factors that affect the yield in the Kolbe electrolysis are the current density, the pH of the electrolyte, ionic additives, the solvent and the anode material. 

Potentiodynamic polarization determines Eap for positive scans, whereas negative scans yield E, . If they are different, the polarization curve shows a hysteresis. In many cases, this difference gets smaller with decreasing scan rates, indicating that the critical potentials are influenced by the composition of the pit electrolyte as well as kinetic factors like pit nucleation and pit growth. The ASTM standard G61 applies 10mVmin [11]. Potentiostatic tests depend less on the experimental conditions and thus are more reliable but time consuming. Usually a potential is applied and the current density is followed for some time. If the current decreases continuously, E < np will hold, whereas it increases when E exceeds np-If pits are formed at > np and then the potential is stepped to less positive values, the current density will drop continuously when E < rp is reached. For some systems, both critical potentials are... 

The critical current density Jc (T, B) obtained by applying optimal microstructural pinning of the flux lines in conductors of different composition and at different temperatures is shown in Fig. 4.2-6. Two factors of influence may be applied to obtain a higher critical current density Jc (T, B) through effects of the intrinsic properties either a decrease in temperature of application, e.g., from 4.2 to 1.8 K, or an increase of Bc2 by alloying as shown for (Nb, Ta, Ti)3Sn in both Table 4.2-8 and Fig. 4.2-6. It should be noted that the intrinsic properties are affected only marginally by differences in processing of the conductors. 

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