Anode construction

Improvements in anode construction have also been carried out to reduce the non-uniform material loss along the length of the HSCI anode, the so-called end effect phenomenon. This involves the use of hollow, centrifugally... 

Magnetite anodes exhibit a relatively low consumption rate when compared with other anode materials, namely graphite, silicon iron and lead and can be used in seawater, fresh water and soils. This low consumption rate enables a light-weight anode construction to be utilised. For example, the anode described by Linder is 800 mm in length 60 mm in diameter, 10 mm wall thickness and 6 kg in weight. 

The materials used for the anode construction have to be stable in the reducing atmosphere prevailing in the anode. Besides, these materials ought to be electronically conducting, and, finally, must have enough porosity to permit the diffusion [66,135,137]. In this region, the oxidation reaction takes place. 

For the electro winning of nickel, a tubular anode constructed from titanium with a mixed metal oxide coating is employed. In a standard design EMEW cell, the anode is approximately 50mm in diameter. The cathode is a stainless steel tube approximately 151 mm in diameter. Both the anode and cathode are fixed in the cell. A thin stainless steel starter sheet is rolled and inserted in the cell to deposit nickel. The deposited nickel cathode is removed from the cell as a tube. The stainless steel starter sheet then springs off the deposit to release the nickel cathode. 

In several runs, e.g. run 17, Table 4, stable operation of the anode was obtained at a rather low voltage. This was due to the effect of the anode construction (the inner current lead had been pressed into a hole in the anode body) and also that the temperature in this run was high, which resulted first in a relatively low electrical resistance of the ceramic anode and secondly in a more complete and faster metal-thermal reduction reaction. As a result tantalum powder was not spread over the container volume, but was concentrated on the cathode rod as a compact conglomerate which could be removed from the melt together with the cathode. In addition there was practically no Ta205 powder in the container and after the experiment it was not difficult to separate the tantalum powder from that of TajOj. The low current efficiency in this run is due to the non-optimized operating conditions of electrolysis in particular that an excess amount of electricity had been passed. 

Figure n.5. Basic cathode-electrolyte-anode construction of a fuel cell... 

Nickel layers are more homogenous and therefore more corrosion resistant compared to microcrack-prone hard chrome layers. Electroless nickel has been adopted in plastic mold making firstly because there is no need for anode construction, and secondly because of the uniform layer thicknesses of up to approximately 200 pm without edge build-up compared to electrochemical nickel. 

The other two materials which have become useful as anode materials are compounds lead dioxide and magnetite which are not oxidized any further under anodic conditions, indeed the stability of lead dioxide has been remarkable. Lead dioxide has been more widely used for anode construction than magnetite, its specific resistance is lower than many metals, it is hard and the oxygen overvoltage on it is the same as on platinum. Thus it is suitable as a substitute in many processes which initially required platinum anodes. The difficulty with both lead dioxide and magnetite anodes is their fabrication and this has delayed their development. 

Mallory produce special mercury cells, based on the wound-anode construction principle, which are particularly suitable for use at lower temperatures than those recommended for normal mercury cells. Thus Mallory types RM1438, RMI450R and RM2550R operate efficiently at a temperature 15°C lower than the standard mercury cells. 

Mallory produce special mercury cells based on the wound-anode construction principle, which are particularly suitable for use at lower temperatures than... 

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