Platinized Titanium Anodes

5 Things We Need to Know About Platinized Titanium Anodes

1st, Combining Platinum and Titanium for Outstanding Corrosion Prevention

Platinized titanium anodes synergistically combine the favorable electrochemical features of platinum (Pt) with the corrosion resistance and other characteristics of titanium. They are anodes normally produced by the electrochemical deposition of a very thin layer of platinum metal or the oxides of platinum onto a titanium substrate. These anodes operate as inert anodes with high durability and are preferred because they remain insoluble in common electrolytes.

platinized-titanium-anodes
platinized titanium anodes

Platinum is a precious metal known for its unique favorable attributes, including:

*High resistance to corrosion
*Resistance to oxidation
*High electrical conductivity
*Ability to act as catalyst
*High chemical stability
*Capability to produce an excellent finish

The low consumption rate backed by high electrical conductivity makes platinum a preferred anode substance. But because of its high cost, only a thin layer of platinum is typically plated on different corrosion resistant materials such as tantalum (Ta), niobium (Nb) or titanium (Ti) to take advantage of these favorable features.

By electroplating the platinum metal on titanium, a composite metallic coating can also be produced on the substrate.This composite consists of titanium metal, platinum, oxides of titanium and metallic compounds of titanium and platinum. The process of heat treating the composite coating produces changes in chemical composition and morphology that improves its electrochemical properties.

The adoption of platinum plated and platinum cladded anodes has provided additional novel options and choices to designers of impressed current cathodic protection (ICCP) systems, because the additional benefits offered by anodes made of composites of platinum on titanium are game changers in the corrosion protection industry, thus enabling their widespread adoption.

Galvanic materials generally used in anodes, such as magnesium and zinc, are not preferred materials because they are bulky, expensive to maintain and must be replaced frequently.

2nd Chemical Behavior of Platinum and Titanium

Platinum is preferred on an anode’s outer surface because it is highly resistant to corrosion and can ensure current flow in most electrolyte media without leading to the formation of an insulating layer on itself. Because it doesn’t corrode, it doesn’t produce corrosion products and hence the consumption rate is very low.

Platinum is inert in fused salts and acids, whereas it is dissolved in aqua regia. There is no risk of hydrogen embrittlement. It is one of the few rare metals that perfectly resist chlorides of seawater.

Titanium shows reasonably good resistance to a marine environment (seawater in particular). It does not react with concentrated (80%) solutions of metallic chlorides. However, it is susceptible to attack by hydrofluoric acid (HF)and hot hydrochloric acid (HCl) of higher concentrations. Even hydrogen peroxide and hot nitric acid can attack titanium. Oxidizing agents normally do not attack titanium because it readily forms a protective oxide coating. However, non-oxidizing substances such as sulfuric acid (above 5% concentration) and phosphoric acid (above 30%) can attack titanium.

3rd Advantages of Platinized Titanium Anodes

Platinum has the advantages of electrochemical inertness, mechanical strength, workability and favorable electrical conductivity. However, it is prohibitively expensive. Development of platinum on titanium materials has opened up the feasibility of using these for anode materials for metal finishing and cathodic protection systems in critical applications.

When used for anodes in aqueous media such as seawater, the titanium forms a stable layer of insulating oxide film on the surface that is stable below a certain breakdown voltage, thus preventing a current flow between the aqueous media and the anode. In the marine environment, the oxide formed on titanium is able to withstand 12 volts, beyond which the insulating barrier breaks down and current flow starts the corrosion process. As an example, the US submarine Seawolf has an automatic corrosion protection system based on platinum plated anode. The use of platinum on titanium anodes has enabled a CP system with reasonable current density and low cost, which protects the nuclear-powered submarine from deterioration on a long-term basis.

New ways to produce titanium anodes at a commercial scale and thin films of platinum on titanium anodes by vapor depositing, rolling and plating have ensured superior and durable anodes at a reasonable cost.

These anodes allow moderate current densities without affecting the base metal. Platinum layers need not be free of pores to ensure effective performance. Low resistance maintained between the electrode and aqueous media (e.g., seawater) ensures the formation of a durable oxide film on titanium so as long as the voltage is maintained within a safe range. These anodes can be lightweight and a convenient size and shape, and ensure stability of operational voltage due to a low platinum consumption rate per ampere-hour.

In hard chrome plating applications, platinum on titanium anodes are environmentally friendly because they are lead-free. They maintain their geometrical shape for almost three years, ensure low downtime and pose a lower employee health risk because there is no lead chromate to be disposed of. Energy losses are lower with platinum-titanium anodes compared to lead anodes.

While lead anodes must be rods and sheets, platinum on titanium anodes can be made in T or U shapes, cylinders or plates, based upon the geometrical shapes of the parts to be plated.

The consumption rate of platinum on platinized titanium anodes is low and proportionate to the current flow. In the case of deep well groundbed applications (for land-based oil and gas wells) the platinized titanium anodes are an easily manageable, non-brittle alternative to magnetite or graphite anodes, because they come with small diameter hole, thus also saving the deep drilling expense.

Overall benefits of using platinized titanium anodes include:

*A low consumption rate that conserves precious platinum
*Favorable dimensional stability
*Corrosion resistance ensures durability with easy maintainability
*Light weight, as well as favorable current distribution in electroplating

4th Disadvantages of Platinized Titanium Anodes

As a substrate for platinized anodes, titanium has the disadvantage of lower electrical conductivity compared to niobium or copper. A low breakdown voltage also is an important limitation for applications that involve a chloride medium. A lower operating voltage of 8 volts reduces the current density. Platinum on titanium substrate anodes are used in applications where lower electrical conductivity and breakdown potential are not a concern. For better electrical conductivity, copper-cored platinized titanium anodes are sometimes used.

Applications for platinized titanium anodes are limited to those electrolytes that do not react with titanium. They cannot be used in chromium baths that contain fluorides.

5th Platinum Film Durability

Manufacturing of platinized titanium anodes has evolved and improved over the last two decades. Although the electrodeposition technique for coating platinum continues to be popular, the difficulty in achieving an adherent coating on titanium has been overcome by our SAGAMMO.

According to some studies, platinum coat thickness generally varies from one to five microns, and in special applications of cathodic protection, (the thickness) could go up to 20 microns. For the cathodic protection of onshore bridge decks, a copper cored titanium with 2.5 micron platinum sheath has been developed. The studies have further concluded that in a concentrated NaCl solution, the platinum consumption could be less than 0.1 micrograms per ampere-hour, whereas in seawater (ten percent saturation) it could go up up to one microgram per ampere-hour.

For the cathodic protection systems of power station condensers using a mixture of river and sea water, the platinum consumption rate shoots up due to the simultaneous evolution of oxygen along with chlorine, and with brackish water, due to the presence of dissolved solids the consumption of platinum rose to tens of micrograms per ampere-hour.

In the case of nickel electroplating, the presence of brightening agents could affect platinum consumption rates, whereas sugar content in the brine feedstock in the steel vessels accentuated the rate of platinum consumption.

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