CitriSurf: The Wave of the Future

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The CitriSurf® citric acid cleaning and passivation process is based on a new technology using safe and environmentally friendly citric acid to remove the free iron from the surface of stainless steel and chromium enrich the surface.

Austenitic stainless steel surfaces can be made highly resistant to corrosion if it is properly cleaned and passivated prior to use. Organic acids have been found to be much more effective than the traditional toxic mineral acids such as nitric acid. In addition, citric acid does not pose the environmental hazards that are present with nitric and other mineral acids.

Even with austenitic stainless steel, such as the 300 series, once a corrosion site has started it only gets worse, being continuous and self-catalyzing. In corrosive environments the growth of the corrosion site will accelerate rapidly! Thus, proper cleaning and passivation of surfaces prior to use is essential to achieve maximum resistance to corrosion.

CitriSurf® solutions provide the maximum protection by providing:

• Improved removal of free iron from the surface
• Faster removal of free iron from the surface
• Low hazard chemistry
• Environmentally safe chemistry
• Lower cost
• Passivated surfaces that pass all salt spray, immersion and high humidity tests

Safe, economical cleaning and passivation lines can be set up easily with CitriSurf® solutions because of the low hazard and environmentally safe chemicals. Stainless steel is comprised of a mixture of materials, primarily iron, chromium, nickel and in some cases molybdenum and manganese along with other materials in small quantities. It is this unique blend that allows the special properties of corrosion resistance by formation of an outer oxide protective layer, or “passive” film.

There is not agreement in industry as to exactly how the passive layer works, but it is generally agreed that the outer layer after passivation consists of only oxides of chromium and iron or nickel which are highly resistant to corrosion. It is critical, therefore in passivating stainless steel that the material is very clean and absent of free iron to form the passive layer upon oxidation. Cleaning the surface of all impurities is critical to make the surface ready for oxidation (forming the passive surface).

Most companies have used and continue to use methods for cleaning and “passivating” stainless steel which utilize mineral acids such as nitric acid. Their effect is limited to surface iron, although in many cases this method redeposits contaminant iron on the surface again. Nitric acid is known to many times produce pitting corrosion. There are many problems with long term use of mineral acid applications, especially under corrosive environments.

Although not really “new”, an emerging technology that is proving to be a vast improvement over the mineral acids is the use of safer organic acids such as citric acid. These are very effective materials which complex and remove a variety of metallic ions that would otherwise adversely affect the corrosion resistance of the stainless steel. These acids are materials that work in aqueous solutions to tie up metal ions so that they are no longer effective or able to have a negative impact. After stripping the metal ions from the surface, the citric acid forms a water soluble complex with a metal ion. It will not precipitate the metal ions again like the mineral acids are known to do.

By their very nature, these products are non toxic, non-corrosive and biodegradable. Citric acid is the natural organic acid produced in oranges and other citric fruits, and is Generally Regarded As Safe (GRAS) for use in food products. It is a common material used in many food and beverages, including most of the carbonated beverages sold on the market. This means that citric acid is compatible with the environment and can usually be blended into sanitary sewage systems with environmental agency approval.

Conversely, mineral acids such as nitric acid are corrosive by nature and they represent significant personnel hazards and threaten property as well. Heated, their risk is intensified. After use, very careful handling is required. Expensive transportation may be necessary to dispose of the residues. In addition to being corrosive, nitric acid is also an oxidizer which increases risk and expense. Eliminating the waste products can expose the user to long term liability under RCRA and CERCLA.

The citric acid cleaning process has a history of excellent results in the pharmaceutical industry and the beverage industry. There is considerable technical data available and research papers are available if one is inclined to look at the background materials. In recent years excellent data is available from all industries showing the improvements of CitriSurf over nitric acid.

After many years of use, testing and data collection, it is obvious that materials such as citric acid produce superior results, at lower cost, and are safer and more environmentally friendly. The use of mineral acids exists today only because it has been accepted as the “way to do it” and Federal Specification QQ-P-35C has been the industry standard through the years. Now that QQ-P-35C has been canceled in favor of ASTM A-967, a consensus industry standard, it is certainly time to switch to the safer, higher performance citric acid system. Aerospace customers can use AMS 2700.

CitriSurf® solutions represent the state-of-the-art technology that is highly effective in stainless steel passivation. The old constraints of mineral acids such as nitric acid date back many years, and are no more effective now than when initially developed at a time when the chemistry of passivation was little understood. With current technologies available for study of the surface chemistry of stainless steel we can see that it makes sense to choose a material that eliminates the contaminants from the surface more completely and helps to produce a truly passive surface by giving the best chromium enrichment to the surface.

Contact us with your questions, or if you would like to try a sample of CitriSurf. We have the ability to completely set you up with this new citric acid based system to simplify your production and reduce your costs, no matter what the size of your operation is!

We look forward to hearing from you!!