Anode types

Table 10.2 gives electrochemical properties for various generic anode types. It will be apparent that the driving voltages that are available from sacrificial anodes are substantially less than those available from power sources. At best an anode will produce 1 V to steel whereas an impressed current power source may produce up to 100 V. 

Fig. 10.20 Typical anode shapes and fixing methods, (t ) Offshore stand-off anode (ft)Sland-off anode - types of bowed core (c) Stand-off anode, clamp fixings (d) Typical tank fixing for shipping (e) Bracelet anode assembly...

The extent of inhibition afforded to metals other than mild steel depends on the metal and the inhibitor see The Nature of the Metal, and Dissimilar Metals in Contact). The cathodic type of inhibitor is perhaps less susceptible than the anodic type to the nature of the metal. However, cathodic inhibitors are usually less efficient (although performing quite satisfactorily in many systems) in terms of reduction in corrosion rate, than are anodic inhibitors. The latter, when used in adequate concentrations, can often achieve 100% protection. 

Figure 1.6. Schematic diagram of the basic principle of the 3DAP using a multi-anode type position-sensitive detector. (Reproduced by permission of Hono 1999.)...

In a 1999 letter to Nature (Perry Murray etal., 1999), from North Western University, Illinois, the authors record the first laboratory achievement of useful oxidation rates for direct methane electrochemical oxidation, using an IT/SOFC. The cathode structures were porous lanthanum strontium manganite (LSM) on porous ( 203)0.15 (Ce02)o,85 or YDC. The anodes were cermets, porous YSZ with nickel in the pores. The laboratory operating temperatures were in the range 500-700 °C. The account of the North Western work, reporting on new anode types, continues on pp. 921-924 of Williams (2002). 

Sacrificial-anode-type cathodic protection systems provide cathodic current by galvanic corrosion. The current is generated by metallically connecting the structure to be protected to a metal/alloy that is electrochemically more active than the material to be protected. Both the structure and the anode must be in contact with the electrolyte. Current discharges from the expendable anode through the electrolyte and onto the structure to be protected. The anode corrodes in the process... 

Sacrificial-anode-type cathodic protection systems have a number of advantages ... 

Sacrificial-anode-type systems also have disadvantages that limit their application ... 

FIGURE 19.4 (See color insert.) Schematic view showing sacrificial-anode-type cathodic protection installation for an underground steel pipeline (a) in soil and (b) in seawater [5]. 

Anode size and shape will be selected. The most frequently used sacrificial anode types and shapes are shown in Figure 19.14. 

Anodes should be selected in standard size according to information from an accepted anode supplier. As soon as the actual anode type, material, and size are selected, the anode parameters below can be defined from the supplier documentation and/or calculations [12] ... 

Based on the selected anode type with weight the required number of anodes, An, will... 

For the selected anode type, the number of anodes to deliver the total current will be calculated for initial current / and total current Ij-p. 

FIGURE 19.14 Anode types (a) standoff, (b) flush-mounted, and (c) bracelet [5]. 

R = defined by the anode type and size (see Table 19.3), D,d=outer and inner pipe diameter (m)... 

Table 7.2 Impressed current anode types and characteristics (see Notes 1-8) from haba 83/02 (2000). Courtesy of the Highways Agency... 

Anode type Long term Long term Supplier s Suitable Suitable for Dimensional Other Typical... 

The standard states that the maximnm snstained current density between the anode and the concrete should not exceed 108mA/m which is correct for the anode types described but is exceeded in the manufactnrers data sheets for many probe anode designs (see Section 7.3.6) which allow far higher current densities. 

Anode types are similar to those used for ECE. The sprayed cellulose is used by the owners of the patented system with a steel or coated titanium mesh. The steel is more likely to be used here as the treatment time is shorter and the steel is less likely to be completely consumed. 

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