Platinized Titanium / Niobium
The first published results on the use of platinized titanium as anode were in 1958. Further development of the anode material has resulted in the use of superior substrates other than titanium. Its use has gone through several phases; however, it is recognized for its superior anodic properties.
Platinum is an excellent anode material due to its high conductivity and low consumption rate. However, because of its high cost, it is not economical to use platinum by itself. Platinum is made practical for use by cladding or electroplating a thin layer of platinum over a lower cost substrate. This also extends the effective anode surface area. The substrate must also have the ability to form an insulating oxide film under anodic conditions. The two substrate materials most commonly used are titanium and niobium.
Titanium and niobium both form insulating oxide films when exposed to anodic conditions. Titanium is less expensive; however, it has a much lower breakdown potential than niobium. The titanium oxide is reported to break down at anodic potentials in the 10V range. The niobium film is resistant to breakdown up to 80V. Niobium is also a much better electrical conductor than titanium. Niobium is normally used with a copper core. This reduces the cost and also provides a much better electrical conductivity.
Platinum coated anodes are available as rod, wire, sheet, tube, strip, and mesh. Rod and wire sizes normally range from 0.031 inches to 1″. Platinum thicknesses range from 25 micro-inches to 1000 micro-inches.
Connection to platinum coated anodes depends upon the anode shape. Wire type anodes normally use a soldered connection. Rod anodes generally have a drilled, threaded connection to the substrate material.
The mechanism of deterioration of a platinum based anode is consumption of the platinum coating. Rate of consumption is controlled by many factors, primarily environment and current density. The consumption rate of platinum in seawater is approximately 8 mg/A-yr. In fresh and brackish waters, consumption is 2 to 3 times greater at low current densities (10 A/sq. ft). At high current densities, consumption is much higher.
The use of platinum is now primarily limited to water environments. Its predominant use is probably in fresh water tank applications; with secondary applications such as condenser water boxes, reinforced concrete, process equipment, docks, etc. Anode manufacturers indicate that platinum can be successfully used underground, both in surface beds and deep anode beds. However, most operators experience has been negative. There have been numerous reports of anode failures when installed underground. The primary failure mechanism is felt to be excessive consumption in small areas and loss of substrate oxide. This could be a result of non-uniform electrolyte resistivities and/or non-linear current distribution in the anode conductor core. Platinum has performed well in water applications. It is probably the most widely used impressed anode material in fresh water applications such as storage tanks and condensers.