Open zinc anodes

Nickel—2iiic batteries containing a vibrating zinc anode lias been reported (83). In this system zinc oxide active material is added to the electrol 1 e as a slurry. During charge the anode substrates are vibrated and the zinc is electroplated onto the surface in a unifomi mamier. Tlie stationary positive electrodes (nickel) are encased in a thin, open plastic netting which constitutes the entire separator system. 

Batteries. The shelf life of dry batteries (qv) is increased from 50 to 80% by the use of a few grams of zinc chromate or dichromate near the zinc anode. This polarizes the anode on open circuit but does not interfere with current deUvery. 

Table 1. Open-circuit voltages of battery systems with zinc anodes...

The galvanic cell pictured in Figure 7.1 is not at equilibrium. If switch S is closed, electrons will spontaneously flow from the zinc (anode) to the copper (cathode) electrode. This flow will continue imtil the reactants and products attain their equilibrium concentrations. If switch S is opened before the cell reaches equilibrium, the electron flow will be interrupted. The voltmeter would register a positive voltage, which is a measure of the degree to which the redox reaction drives electrons from the anode to the cathode. Since this voltage is a type of energy that has the potential to do work, it is referred to as a redox potential or cell potential, denoted as... 

This reaction, which takes place at open circuit, or as a side reaction during discharge of the battery, is detrimental in two ways it consumes one of the active materials in the cell, and it produces a gas that can build up pressure and eventually rupture the cell. This is the purpose of adding HgO to the zinc anode. In contact with metallic zinc, it is reduced to mercury, which amalgamates the zinc. The exchange... 

Direct Oxidation. The zinc anode of a zinc/air battery can be oxidized directly by oxygen which enters the cell and dissolves in and diffuses through the electrolyte. Measurements of the effect of direct oxidation on cell capacity have been predicted experimentally, using advanced microcalorimetry techniques to predict direct oxidation effects on DA675 type cells (cells open, not sealed). This research indicates a capacity loss of less than 1.5% of rated capacity per year at 25 C and less than 5% per year at 37.5°C. 

Magnesium and zinc are the predominantly used galvanic anodes for the cathodic protection of pipelines [13—16]. The corrosion potential difference of magnesium with respect to steel is 1 V, which Umits the length of the pipeline that can be protected by one anode. Economic considerations have led to the use of aluminum and its alloys as anodes. However, aluminum passivates easily, decreasing current output. To avoid passivation, aluminum is alloyed with tin, indium, mercury, or gallium. The electrochemical properties of these alloys, such as theoretical and actual output, consumption rate, efficiency, and open circuit (corrosion) potential, are given in Table 15.1. 

Figure 2 - Effect of the Frame on the Morphology of the Zinc Deposit. A) Cathode and Anode Frame Opening are the Same Size, B) Cathode is Slightly Larger than the Anode Frame Opening, and C) Cathode is Much Larger than the Anode Frame Opening...

Temperature is of particular importance to the performance of anodes, especially when anodes are buried. Anodes may often be used to protect pipelines containing hot products. Thus temperature effects must be considered. Figure 10.14 illustrates the effect of temperature on different anodes in hot saline mud. Al-Zn-In anodes experience greatly reduced capacity in open seawater at temperatures above 70 C (down to 1200Ah/kg at 100°C) and in seabed muds in excess of 50 C (900 Ah/kg at 80°C). At elevated temperatures passivation of both aluminium alloys and pure zinc can occur". Considerable improvement in performance (capacity, and to a lesser extent operating potential) has been claimed for a range of modified Al-Zn-In anode materials... 

The use of high teinpeiature spraying gives a very porous, open coating made up of small droplets of zinc metal. The coating has excellent adhesion to the concrete. The zinc coating looks similar to concrete and there is no need for extra protective or cosmetic coatings. The system is w ell established in the USA and trial sacrificial anode systems were described above. 

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