Community Research and Development Information Service - CORDIS

No chrome conversion coatings

There are a number of reasons why surfaces undergo treatments. They include improving their aesthetics, enhancing their resistance to weathering and impact as well as strengthening their durability. The drawbacks are that they are expensive and have a detrimental impact on the environment.
No chrome conversion coatings
Cerium salts are either red-yellowish or white in colour and have a wide variety of applications within the manufacturing industry. They can be used in steels, stainless steels, alloys such as magnesium, glass and even in petroleum cracking.

As a rare element it is now being used in the development of conversion coatings for aluminum and its alloy products. Conversion coating is a process whereby an additive (such as cerium salts) is added to combine with the original metal to enhance one of its features.

Usually in conversion coating either the chromating or phosphochromating method is used. The former is done in order to improve the metals' corrosive resistance while the latter enhances the products' ability to adhere to films of paint. In both cases the use of chrome - a toxic environmental pollutant is used.

Andalusian researchers have now developed methodologies that provide far better results, both in its material corrosion resistance factors and in its environmental pollution reduction. Using cerium salts, the process now takes a maximum two hours, avoids the use of chrome altogether and improves its resistance value by a factor of 1500.

Chrome is eliminated altogether through the use of lanthanide salts. Thermal activation may be obtained through an immersion process of Cerium nitrates Ce(NO3)3 or Cerium chlorides (CeCl3) operating at temperatures between 298-363 Kalvin.

Because Cerium salts have a rapid reaction time under heat, the entire production time is vastly reduced. This, and given the fact that the process provides a far superior product than chrome-based methods conducted at room temperature, make for a highly attractive procedure.

A prototype is available for demonstration and partners in coating industries are sought.
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