Precious metal-coated titanium anodes

Cathodic Protection Systems. Metal anodes using either platinum [7440-06 ] metal or precious metal oxide coatings on titanium, niobium [7440-03-17, or tantalum [7440-25-7] substrates are extensively used for impressed current cathodic protection systems. A prime appHcation is the use of platinum-coated titanium anodes for protection of the hulls of marine vessels. The controUed feature of these systems has created an attractive alternative... 

The dimensionally stable anode in this system is composed of an electrically conductive substrate of titanium, having a coating of a defect solid solution containing mixed crystals of precious metal oxides. These substitutional solid solutions are both electrically conductive, electrocatalytic, and dimensionally stable. Within the aforementioned solid-solution host structures the valve metals include titanium, tantalum, niobium, and... 

Dimensionally Stable Anodes— These anodes are composed of a base metal such as titanium, coated with a precious metal oxide (e.g., ruthenium dioxide). Such anodes can be used instead of Pt or carbon for oxygen evolution counter electrodes in an organic electrosynthesis. They have also found some applications for organic oxidation reactions [61]. 

The other factor that is important to process economics is the high oxygen evolution overpotential that increases the cell voltage. More recently, anodes of titanium coated with precious metals, metaUic oxides, and/or their alloys are manufactured. These types of electrodes are referred to as dimensionally stable anodes (DSAs) or inert anodes. The advantages of the DSA-type anodes include higher purity deposit, lower anode overpotential, and high corrosion resistance. 

The type of electrolytic cell commonly used in these marine and offshore applications is a tube within a tube , (but there are a variety of configurations.) A tube within a tube type cell consists of one anode, one cathode, and one bipolar tube with the necessary ancillary hardware to facilitate assembly-see Fig. 1. The outer anode and cathode are manufactured firom seamless titanium pipe. The anode surface is coated with proprietary precious metal oxides, primarily ruthenium and iridium. Seawater enters one end of the cell and passes between the cathode, the anode and bipolar tube annular spaces. When direct current is applied to the cell, sodium hypochlorite results. One cell can produce up to 5.5 kg/day and a maximum of 12 cells can be connected in series for a capacity of 65 kg/day per train. Multiple trains can operate in parallel to produce the required capacity. 

For horizontal surfaces, anodes without overlay can be recessed in the concrete surface. Nonuniform current distribution is a fundamental concern in these systems. Anodes in the form of a titanium mesh, with proprietary surface coatings of precious metals are commonly used in concrete structures, in conjunction with cementitious overlays. These systems are applicable to both horizontal and vertical surfaces and generally provide uniform current distribution. 

One of the most successful commercial anodes is the expanded titanium mesh with an activated precious or mixed metal oxide coating. This also comes in the form of an expanded titanium mesh, strips and other configurations. It is fixed onto the surface, usually with plastic fixings and a cementitious overlay applied. 

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