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The Science Of Precision Coatings

Passivation

Corrosion

Reduces Surface Corrosion

Free Iron

Arrests Free Iron Particles

Citric

Natural Process

Eco Friendly

Easy on the Environment

A NATURAL, ENVIROMENTALLY-FRIENLY PROCESS THAT PREVENTS CORROSION OF STAINLESS STEEL SURFACES

Stainless steel is inherently corrosion resistant due to its high chrome content, however, during subsequent forming and machining operations free iron and other contaminants can be introduced to its surface.  If not effectively removed, these surface contaminants compromise the naturally occurring passive layer of the stainless steel and increase the opportunity for corrosive attack of the base metal.

Citric passivation is a non-electrolytic finishing process that removes free iron and other surface contaminates to maximize the corrosion resistant nature of most stainless steels including all 300/400 series SS and high chromium content steels such as 17-4.

The result is an inert, passive oxide layer rich in chromium oxides for enhanced corrosion protection.  The passivated layer is often superior to the naturally occurring protective oxide layer.

While initially developed for the beverage industry, citric acid passivation is now commonly used in food, medical, aerospace, semiconductor and military applications to name a few.  Our process fully complies with and is certifiable to common industry specifications such as AMS 2700, ASTM A380, and ASTM A967. Periodic testing includes methods such as water immersion, copper sulfate testing, and salt spray (ASTM B 117).

 

Citric vs. Nitric Passivation Comparison

Nitric acid was long used as the only means to passivate stainless steel before studies showed that citric acid provided a safer, more effective process.  Compared to nitric acid, citric acid is organic, non-hazardous, and safe to use.  The citric passivation process emits no toxic fumes and can be disposed of at a much lower overall cost than nitric waste.

Citric passivation has also been shown to perform equally if not better than both nitric and phosphorous passivation in numerous studies.  A common method of evaluation, electron spectroscopy is used to analyze the ratio of chromium oxide to iron oxide found on passivated surfaces.  The higher the ratio of chromium to iron, the more corrosion resistant the surface.  While the nitric process resulted in an average ratio of 2.1 chrome to iron content, the citric passivation process returned an average of 2.36 chrome to iron content.  While both processes will remove excess free iron and provide superior protection, the citric process is shown to be more effective at maximizing the protective chromium oxide layer.

In another study sponsored by NASA, citric passivation was found to produce higher Fe/Cr oxide ratios than nitric while producing an oxide layer nearly 50% thicker than nitric on 316L coupons.

While most grades of stainless can be passivated using nitric acid, there are some exceptions and variations in chemistry and temperature must be tightly controlled to meet industry specifications.  There are 8 compositions of the nitric solutions depending on the grade of stainless steel and periodic testing specified.  Comparatively, citric acid solutions can passivate the same range of stainless grades with a single solution.  Variations in temperature are specified only as a means to control total immersion time.

Dowload your copy of  “Citric Passivation of Stainless Steel” by NASA engineer Chad Carl.

APPLICATION SPECIALTIES

Plastic Injection Molding

Through precise, engineered deposits, Armoloy TDC, XADC, and Nyflon 25 add incredible value to plastic injection molding applications, as well as those in the areas of extrusion and thermoforming... Read More

Machined Components

From fundamental components such as shafts, gears, and bearings, to the more complex components found in automated lines, packaging machines, and specialized machinery of every type, Armoloy Southeast can... Read More

Automation + Linear Motion

For over 20 years, Armoloy TDC has been the premier coating for the Linear Motion industry. The Armoloy TDC coating lowers the coefficient of friction of bearing steels, for smoother movement over rolling surfaces... Read More

Pumps And Compressors

For protection against the most common forms of wear including corrosive, abrasive, and erosive wear, consider coating your critical pump, valve and compressor surfaces with a protective Armoloy coating... Read More

Food Processing And Packaging

Apply Armoloy TDC and XADC to food-processing and food-packaging equipment and components for the most beneficial combination of wear resistance and corrosion resistance. The Armoloy coatings... Read More

Oil And Gas Extraction

In the field of oil and gas drilling and extraction, the Armoloy coatings are ideally suited for components operating in corrosive downhole environments. The coatings’ high corrosion and wear resistance... Read More

Aerospace

Armoloy TDC is an optimal metal surface coating for aerospace components that require improved wear and corrosion resistance, vast functional temperature range, and consistent, even deposits... Read More

Medical

Armoloy TDC and Electrolizing are precise, biocompatible, pure, metallic chromium coating for medical, surgical, laboratory and clean room environments. Highly trained coating professionals and strict... Read More

Nuclear

For over 30 years the Armoloy TDC coating has been applied to variety of nuclear industry devices including fuel cell and reactor core components. The improved wear and corrosion resistance of... Read More