Current density deposits

Figure 3 presents the transients in the resistance of the PR ED films. The resistance of films deposited at higher current densities decrease more with time than those deposited at lower current densities. The same trend is seen for the DC waveform case shown in Figure 4. However, larger decreases are seen for all current densities deposited with a DC waveform. This may be due to the fact that the average current density of the PR waveform is less than that of the applied current density of the DC waveform. The PR waveform used may also produce a variety of initial microstructures that could also account for these differences.

It is very clear from the above consideration that the quantities of evolved hydrogen and hence the morphologies of electrodeposited metal will depend strongly on the applied parameters of PC regimes, such as the amplitude of the current density, deposition pulse, and pause duration. 

Coordination compounds found their application in various areas including plating, which did not lose its importance until now. Much interest in the recent investigations was shown in the problems of an applied nature, underlining the effect of plating parameters such as current density, deposition time, temperature, and pH in relation to the phase composition, structure, and quality of deposit. 

Another aim of the present work is to determine the influence of electrodeposition conditions (applied current density, deposition time, ratio of PC on-time/off-time) on the quality of deposited layers in such melting electrolytes. DC and PC techniques are used to prepare the titanium electrocoatings. 

Figure 16. Plots of thickness of CdS film deposited on stainless steel against current density. Deposition time, solution composition and temperature were constant during the deposition, a) in DMSO, b) in PC (63).

Figure 23. High current density deposit of GaP on silicon done early in investigation. Shows layer with dendritic over-growth around craters (40 mA/cm ) (69).

Electrodeposition is a well-known method to produce in situ metalhc coatings by the action of an electric current on a conductive material immersed in a solution containing a salt of the metal to be deposited. Moreover, by controlhng synthesis conditions, the electrochemical synthesis/deposition can be used to produce thin films of oxides and/or l droxides on conductive materials [12]. The composition, morphology and texture of the film coating can be controlled by tuning the experimental parameters such as the potential, current density, deposition time, and plating solution composition. In... 

The Fe, Co, and Ni deposits are extremely fine grained at high current density and pH. Electroless nickel, cobalt, and nickel—cobalt alloy plating from fluoroborate-containing baths yields a deposit of superior corrosion resistance, low stress, and excellent hardenabiUty (114). Lead is plated alone or ia combination with tin, iadium, and antimony (115). Sound iasulators are made as lead—plastic laminates by electrolyticaHy coating Pb from a fluoroborate bath to 0.5 mm on a copper-coated nylon or polypropylene film (116) (see Insulation, acoustic). Steel plates can be simultaneously electrocoated with lead and poly(tetrafluoroethylene) (117). Solder is plated ia solutioas containing Pb(Bp4)2 and Sn(Bp4)2 thus the lustrous solder-plated object is coated with a Pb—Sn alloy (118). 

Piebaked anodes aie produced by molding petroleum coke and coal tar pitch binder into blocks typically 70 cm x 125 cm x 50 cm, and baking to 1000—1200°C. Petroleum coke is used because of its low impurity (ash) content. The more noble impurities, such as iron and siUcon, deposit in the aluminum whereas less noble ones such as calcium and magnesium, accumulate as fluorides in the bath. Coal-based coke could be used, but extensive and expensive prepurification would be required. Steel stubs seated in the anode using cast iron support the anodes (via anode rods) in the electrolyte and conduct electric current into the anodes (Fig. 3). Electrical resistivity of prebaked anodes ranges from 5-6 Hm anode current density ranges from 0.65 to 1.3 A/crn. ... 

An electrorefining plant may operate with either an acid or an alkaline bath. The acid bath contains stannous sulfate, cresolsulfonic or phenolsulfonic acids (to retard the oxidation of the stannous tin in the solution), and free sulfuric acid with P-naphthol and glue as addition agents to prevent tree-like deposits on the cathode which may short-circuit the cells. The concentration of these addition agents must be carefliUy controlled. The acid electrolyte operates at room temperature with a current density of ca 86—108 A/m, cell voltage of 0.3 V, and an efficiency of 85%. Anodes (95 wt % tin) have a life of 21 d, whereas the cathode sheets have a life of 7 d. Anode slimes may be a problem if the lead content of the anodes is high the anodes are removed at frequent intervals and scmbbed with revolving bmshes to remove the slime (7). 

Other processes have been developed in which the impregnation is accompHshed in one or two steps the most promising is electro deposition directiy from nitrate solutions having pH controlled at 4—5. After electro deposition, the plaques are either cathodicaHy polarized in sodium hydroxide solution or electrochemically formed in sodium hydroxide to eliminate all traces of nitrate. The latter steps must proceed at low current densities to avoid blistering and shedding of the loaded plaques. 

Cadmium is usually plated from a cyanide bath that consists of an aqueous solution of cadmium oxide (35 g/L) and sodium cyanide (75 g/L). An additive and a brightener are used to produce smooth, fine-grain deposits. Current density ranges from 1.4 to 3.7 A/dm, depending on the concentration of cadmium cations in the electrolyte. 

Developments. Electrolytic refining requires a large capital investment, and labor costs per kilogram of copper produced are high. Most refineries have traditionally operated at current densities of about 240 A/m. Thus, a tank house area of approximately 40 m is required per ton of copper produced daily. The use of higher current densities reduces capital requirements but may impair deposition efficiency and product quaUty. 

Electrolytic plating rates ate controUed by the current density at the metal—solution interface. The current distribution on a complex part is never uniform, and this can lead to large differences in plating rate and deposit thickness over the part surface. Uniform plating of blind holes, re-entrant cavities, and long projections is especiaUy difficult. 

Electroless plating rates ate affected by the rate of reduction of the dissolved reducing agent and the dissolved metal ion which diffuse to the catalytic surface of the object being plated. When an initial continuous metal film is deposited, the whole surface is at one potential determined by the mixed potential of the system (17). The current density is the same everywhere on the surface as long as flow and diffusion are unrestricted so the metal... 

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