Saturday, January 9, 2016

What To Consider When Choosing The Diffusion Coatings

By Dennis Campbell


Semiconductors and PV manufacturers are faced with significant corrosion challenges. They target to produce metallic components that can withstand extreme conditions such as varying pH levels, extremely high and low temperature, high pressure, and exposure to different environmental elements that significantly affects their physical properties. More often, the solution often involves diffusion coatings to give the base metal physiochemical and structural properties making them suitable to operate under extreme physical conditions.

The top choice coating materials include the steel alloy, aluminum, alloy, chromium and titanium alloys, and silicon. Most of these are able to stand varying pH levels, extreme temperatures, and other physical conditions, offering a protective cover to iron materials, nickel, cobalt, steel and carbon among other metals.

The process targets to give the base metal physiochemical and physical properties that enable them to build resistance against oxidation, erosion, and corrosion. It offers the solution to critical components of machines and structures. The gas turbine components, including vanes, blades, valves, and power generation components are just a few examples.

Through the diffusion process, the base metal gains physiochemical properties the enable them remain operational under extreme pH or temperature conditions. The gas turbine components such as the gate valves, vanes and blades and the power generation parts are for instance coated for this reason.

However, not every coat works in the same way under the same conditions. Silicon has different properties from aluminum under the same conditions. As such, depending on the environment on which the base metal will be exposed, there are factors to consider when selecting the right coating material. Most alloys tend to leach metal ions which affect the process yield; however, silicon does not leach and has higher corrosion resistance properties. It is appropriate for highly sensitive processes.

Compatibility is perhaps the most important factor to consider. No single coating or alloy is able to withstand corrosive attack from all types of acids and bases. Your choice of the coating material should be guided with all potential chemical exposures, including air and water.

Whether the operating environment includes fluids that are basic or acidic, you have to go the extra mile to consider the concentration of the fluids. High concentration level translates to a high rate of corrosion and vice versa. Other factors like fluid velocity and the fluid type also affect the rate of corrosion.

In addition to this, the longer the metal is exposed to the corrosive element the higher the rate of corrosion. The nature of exposure, such as cyclical exposure, also increases the corrosion rate. Cyclical exposure involves periodic wetting and drying the metal without rinsing.

When dealing with acids and bases, pH level must be given a special consideration. Low pH (acidic conditions) does not have a significant impact on silicon. Basic condition (high pH) level on the other hands is likely to dissolve silicon coat. In regards to temperature, the rate of corrosion is high when the temperature is high for aluminum and stainless steel given that the passive film that prevents corrosion is dissolved as temperature increases.




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