Current density range

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. ... 

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. 

Free KCN = surplus KCN over that required to complex the CuCN the titratable KCN. NaCN can be substituted on an equimolar basis with the CN content. Current density range is less and throwing power is less but NaCN costs less. 

RoUs and other relatively simple shapes make use of inert shields and thieves to avoid edge buildup and produce a more even plate thickness. For more compUcated shapes having deeper recesses thicker deposits from cyanide copper baths have been used as an undercoat to the copper sulfate deposit. Acid copper baths operate near 100% efficient over a wide current density range. The cathode efficiency is usuaUy slightly less than the anode efficiency, bringing about a slow increase in copper unless drag-out losses are high. 

Fig. 10.17 Performance of commercially-cast anodes in field trials (free-running) over wide current density range in ambient Gulf of Mexico mud. Potentials negative volts versus Ag/AgCl. Zn 310-350 Ah/lb at 40 and 80mA/ft (after Schreiber and Murray )...

Platinised titanium anodes may be operated at current densities as high as 5 400 Am however at these current densities there is the possibility that the breakdown potential of titanium may be exceeded. The normal operating current density range in seawater is 250-750 Amwhilst that in brackish waters is given as 100-300 Am with values within the range... 

Comparative tests between HSI and HSCI in seawater at 93° C and 10-8Am showed consumption rates of 8-4kg A y and 0-43 kg A y , respectively . These figures show that the consumption rate of HSI when used in seawater without the addition of chromium may approach that of steel, but because of the very deep pitting and its fragility, it is in most cases inferior to steel. However, in fresh waters HSI has a far lower corrosion rate than steel. The consumption rate of HSCI freely suspended in seawater in the current density range 10-8 to 53-8 Am increases from 0-33 kg A y at 10-8Am to 0-48 kg A" y at 53-8Am Direct burial in seawater silt or mud will also increase the consumption rate, with values of 0-7kg A y at 8-5 Am increasing to 0-94 kg A " y at 23-4 Am . 

Tests carried out in seawater over the current density range 30 to 190 Am showed the consumption rate to be dependent upon current density, increasing from 1-4 to 4g A y over the current density range studied (with the recommendation that to achieve the required life, the current density should not exceed 115 Am ) ... 

The action of platinum microelectrodes has been extensively studied Trials carried out by Peplow have shown that lead/ platinum bi-electrodes can be used in high velocity seawater at current densities up to 2 000 Am and that blister formation with corrosion under the blisters is decreased by the presence of platinum microelectrodes. The current density range in which the anode is normally operated is 200-750 Am with the maximum working current density quoted as 1 000 Am The consumption rate of theje anodes ranged from 0-0014 kg A y at 500Am , but increased to 0-003 kg... 

The current density applied to the electroactive coating has been set at 0-1 Am whilst for short-term polarisation current densities up to 0-2 Am may be applied. However, certain anode manufacturers now state that a maximum current density of 0-2 Am may be used for long-term polarisation and 0-4 Amfor short term use. The current density range is... 

Hard anodic films, 50-100/rm thick, for resistance to abrasion and wear under conditions of slow-speed sliding, can be produced in sulphuric acid electrolytes at high current density and low temperature. Current densities range from 250 to 1 000 Am , with or without superposed alternating current in 20-100g/1 sulphuric acid at —4—I- 10°C. Under these conditions, special attention must be paid to the contact points to the article under treatment, in order to avoid local overheating. 

Electrodeposition of polycrystalline mngsten disulfide (WS2) thin films on TO/glass, from an aqueous solution of tungstic acid and Na2S03 (pH 7.0-9.5), at different current densities ranging from 20 to 60 mA cm , and temperatures 40, 60, and 80 °C, has been reported [155]. Both the 2H and 3R phases of WS2 were found... 

The fact is that, on the one hand, a significant field strength, E9 is needed to provide significant current. On the other hand, once in the practical current density range between 0.1 and 10 mA/cm2, a relative insensitivity of the field to the current density is found. In fact, an inverse field of 1.3 to 1.8 nm/V is accepted in the literature as characteristic of the oxide growth, without mention of the current density used. 

Takahashi et a/.,79 in their work on the structure of the barrier layer [cf. Section IV(2)], have considered phosphate ions, which are found in the outer layer of the oxide, as immobile markers and, from the position of the boundary between the outer and the inner layer, deduced the transport number of the cation to vary between 0.73 and 0.81 in the current density range between 0.05 and 10 mA/cm 2. 

Nevertheless, the comparison (Figure 5) of the polarization curves of the same air electrodes show that the polarization at the high current density range of the most active electrode is much higher that that of the electrodes... 

Cu, In, Ga, and Se are codeposited from the solution at room temperature in a three-electrode cell configuration, where the reference electrode is a platinum pseudo-reference, the counter electrode is platinum gauze, and the working electrode is the substrate. The substrates typically used are glass, DC-sputtered with about 1 pm of Mo. In all experiments, the applied potential is -1.0V versus the Pt pseudo-reference electrode. The corresponding current density range for the deposition is 5 to 7 mA/cm2. 

If all responses to these tests are linear and typical, and all other independent variables remain within normal operating specifications, it can be assumed that the membrane and electrolyser interactions are optimised for operation within the current density range tested in Section 6.3.1. This procedure has been used successfully to diagnose and optimise operating conditions for both standard and high current density operations where unexpected performance issues have arisen. Furthermore, operators... 

The F-8934 seems attractive to any commercial plants operational in the range of 3-4 kA m-2. This membrane has already been supplied to such end-users. As a result, they have obtained a 30-40 kWh tonne-1 reduction in power consumption compared to the power consumption of the F-893 membrane. Figure 19.11 shows the current efficiency plots from two AZEC plants in the current density range just touched on. 

The macrohomogeneous model was exploited in optimization studies of the catalyst layer composition. The theory of composifion-dependent performance reproduces experimental findings very well. - The value of the mass fraction of ionomer that gives the highest voltage efficiency for a CCL with uniform composition depends on the current density range. At intermediate current densities, 0.5 A cm < jo < 1.2 A cm , the best performance is obtained with 35 wt%. The effect of fhe Nation weight fraction on performance predicted by the model is consistent with the experimental trends observed by Passalacqua et al. ... 

So, here is the summary of what we can do to help the experimenter be sure that his or her measurement reflects interfacial and not transport control.3 (1) Working at short times (microseconds up to a millisecond, say), increases iL and therefore lengthens the current density range in which diffusion-free measurements can be made. (2) Working at times > about 10 s means that natural convection tends to make 8 constant, i. e., independent of time. However, this time-independent value can still be reduced (and hence iL helpfully increased by methods already reviewed (Chapter 7),... 

Tafel s law applies also in current density ranges well below that of the limiting current at semiconductor/solution interfaces and to photoelectrochemical reactions. Its application to liquid-liquid interfacial electron transfer is also good [see Fig. 9.25(d)] (Schmickler 1995). In hydrogen evolution, it has been followed down to the picoam-pere region and up to 100 A cm-2. 

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