Impressed current anodes platinized titanium

Galvanic or impressed current anodes are used to protect these components. The anode material is determined by the electrolyte zinc and aluminum for seawater, magnesium for freshwater circuits. Platinized titanium is used for the anode material in impressed current protection. Potential-regulating systems working independently of each other should be used for the inlet and outlet feeds of heat exchangers on account of the different temperature behavior. The protection current densities depend on the material and the medium. 

Partially platinized titanium impressed current anodes were chosen because contamination of the feed water by anodic decomposition products had to be avoided. Four pure zinc reference electrodes were installed in the tank to control and regulate the potential. The supports for the anodes were of polypropylene, which can operate for short periods up to 100°C, in contrast to the usual PVC supports used in cold water. 

Figure 21-1 shows the object to be protected and the arrangement of impressed current anodes and reference electrodes. A central anode and two ring anodes of platinized titanium wire 3 mm in diameter provided with additional copper wire conductors are installed here. It is worth noting that the central anode is suspended from a float, whereas the ring anode is mounted on plastic supports. The zinc reference electrodes are also on floats near the inner side of the bell, while the 17 reference electrodes are mounted on plastic rods on the bottom of the cup and in the ring... 

Precious metals are used for impressed current anodes because they are highly efficient electrodes and can handle much higher currents than anodes fabricated from other materials. Precious metal anodes are actually platinized titanium or niobium anodes the platinum is either clad or electroplated on the substrate. 

Design of cathodic protection for marine structures in both fresh and salt water require special techniques. Galvanic systems usually employ zinc or aluminum alloy anodes. Impressed current systems frequently use high silicon, chromium bearing iron, platinized niobium, or mixed-metal oxide/titanium anodes. The structure being protected affects the design. Stationary facihties such as bulkheads and support piles require different techniques from ship hulls [55]. 

Anodes of a corrosion-resistant material such as Pt, PbSbAg, graphite, magnetite or high-silicon iron are normally used in impressed current installations. Pt is often used as a thin layer on a substrate of another material, e.g. in the form of platinized titanium. A corroding material, such as scrap steel, can also be used, but additional anode material must be supplied regularly in this case. 

For protection of structures in seawater, platinum-clad copper, 2% Ag—Pb, platinized titanium, or platinized niobium have been recommended as corrosion-resistant anodes using impressed current [10-12]. Whereas sacrificial magnesium anodes require replacement approximately every 2 years, the 2% Ag—Pb anodes are estimated to last more than 10 years, and the 90% Pt-10% Ir anodes still... 

Fig. 10.29 Cathodic protection using impressed current, (a) A circuit showing the principles the signal from the reference electrode is passed to a power-unit control where it is compared with a preset level. The resultant error signal is amplified and used to control semiconductor power devices which allow a controlled current to pass through the anodes, (b) A typical layout of components in various types of vessel, (c) Transformer/rectifier power units for marine use. (d) Platinized titanium or lead-silver alloy anodes being installed on a ship s hull. The anodes are insulated from the hull and have special insulating, backing shields which help to improve potential distribution and prevent over-protection, i.e. too negative a potential (Photographs courtesy Corrintec (UK) Ltd.)...

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