Cathodic protection optimization

R.A. Adey, J. Baynham. Design and Optimization of Cathodic Protection Systems using Computer Simulation. CORROSION 2000, Paper 723. Houston, Texas. NACE International, 2000. 

With durable anodes, such as the DSA , current is applied from an external power supply to achieve cathodic protection. However, it is necessary to optimize the electrode geometry of this system to realize uniform current distribution. Cathodic protection is widely used to protect pipelines, buried steel structures, steel reinforcement in concrete, and chemical process equipment. 

Cathodic protection by impressed current involves the use of a rectifier connected to a power line. Contrary to sacrificial anodes, which operate at a fixed potential, the use of a rectifier permits to adjust the voltage (or the current) to the particular requirements of a protection scheme. This not only allows one to optimize the electrochemical conditions for protection, but the method is also well suited to protect large surfaces. On the other hand, protection by impressed current needs more maintenance than the use of sacrificial anodes. In order to protect buried structures by impressed currents one uses consumable anodes such as scrap iron or, more often, non-consumable anodes made of iron-silicon alloy, graphite or of titanium coated with noble-metal oxides. 

Adoption of the concept of kinetic criteria allows a simple optimization of protective installation working parameters. In many cases it is unnecessary to fully retard the corrosion of a protected metal structure. Deep cathodic polarization is an expensive process. It requires the application of high power equipment, developed anodic systems, and is connected with high operation costs. For practical reasons, partial protection is sufficient in most cases, ensuring a decrease of the corrosion rate to such a level at which the assumed lifetime of the structure is attained. Evaluation of the effectiveness of cathodic protection based on a criterion taking into account the degree of decrease of corrosion process rates can become in the near future a new, important application element in the anticorrosion protection technology. 

Newly developed alloys have improved properties in many aspects over traditional compositions for interconnect applications. The remaining issues that were discussed in the previous sections, however, require further materials modification and optimization for satisfactory durability and lifetime performance. One approach that has proven to be effective is surface modification of metallic interconnects by application of a protection layer to improve surface and electrical stability, to modify compatibility with adjacent components, and also to mitigate or prevent Cr volatility. It is particularly important on the cathode side due to the oxidizing environment and the susceptibility of SOFC cathodes to chromium poisoning. 

Due to the relatively high mobility of holes compared with the mobility of electrons in organic materials, holes are often the major charge carriers in OLED devices. To better balance holes and electrons, one approach is to use low WF metals, such as Ca or Ba, protected by a stable metal, such as Al or Ag, overcoated to increase the electron injection efficiency. The problem with such an approach is that the long-term stability of the device is poor due to its tendency to create detrimental quenching sites at areas near the EML-cathode interface. Another approach is to lower the electron injection barrier by introducing a cathode interfacial material (CIM) layer between the cathode material and the organic layer. The optimized thickness of the CIM layer is usually about 0.3-1.0 nm. The function of the CIM is to lower... 

The first standalone photo water-splitting device having a practical conversion efficiency was described by Kainthla and Khan (1987). Their cell is shown in Fig. 10.26. Both electrodes were simultaneously irradiated. The calculated optimal match between materials of the two electrodes was found in theory to be p-InP as cathode and n-GaAs, the latter protected from electrochemical oxidation by a film of Mn02. The InP was duly decorated with platinum to catalyze H recombination the Mn02 allowed photo 02 evolution on its surface with a stability unchanged over prolonged periods. 

In order to realize the sol-gel method as a competitive technique in manufacturing of electrolyte layers for SOFC applications, further optimizations of fabrication procedures are required in the future work. For example, surface treatment of the substrates and proper thermal treatment of all layers are proposed to avoid delamination of the cathode. Deposition of a Ceo 8Gdo.20i 90 barrier layer will protect the electrolyte from the diffusion of Strontium and efficiently avoid formation of isolating zirconate layers. 

Using multilayer ceramic technology, the thickness of the fuel cell is reduced, in part by the use of ceramics fluidic channels and inherent insu-lative characteristics (Figure 6-2). The fuel channels are incorporated inside the ceramic substrates. This allows the fuel to be protected from contaminates as well as allow for sealing due to ceramics ability to be hermetic when designs require complete sealing. This quality provides a mechanical structure which can effectively supply fuel to the MEA as well as seal off the MEA to optimize efficiency and prevent contamination. In addition, the ceramic separator plates are coated with metals which allow for the interconnection between the cathode and anode sides of the MEA for purposes... 

When an optimal combination of Ketjen black carbon and CUCI2 is used as the cathode, limited overdischarge-overcharge protection can be achieved. These batteries can also deliver extra capacity when needed. The discharge-charge as well as the overdischarge-overcharge characteristics of such a battery are shown in Fig. 34.33c. Possible cell reactions are as follows ... 

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