Our passivation services turn reactive surfaces into passive surfaces, modifying the outer layer of the base material to create a barrier against corrosion. Our process is tightly controlled and follows the industry standards established for descaling, cleaning, and passivating the surface of small metal parts by precisely applying the “Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts” (ASTM A967M).
Why Metal Passivation?
The passivation process is a method of stopping oxidation of metals by *starting* with oxidation. Commonly applied to stainless steel parts, the chemical treatment creates an inert, protective coat that prevents rouging and reduces the rate of corrosion in the finished parts, depending on the kind of base metal and the environmental conditions.
Surface passivation strengthens and preserves the appearance of metallic parts and is also used in microelectronics to enhance silicon. The process begins with ultrasonically cleaning the parts to remove contaminants. Then the parts are immersed in an acidic bath mixed according to manufacturer instructions and industry-specified requirements for temperature and chemistry. After the set time elapses, parts are then bathed in a neutralizing solution, rinsed, and dried.
Where Passivation Is Used
Metal passivation helps to ensure that oxygen, water, or other elements that come into contact with stainless steel will not damage the integrity of the metal. The process is often used for applications where minimizing the potential for contamination and corrosion is critical to the safety and performance of small stainless steel parts. However, the process is not recommended for parts that will be used in aggressive chemical or physical environments.
Surface passivation is frequently used in the finishing of medical devices such as implants and surgical tools, as well as for aerospace components. For medical and dental applications, the process helps metal components resist corrosion, inhibit bacterial growth, and deliver optimal performance.
Our Advantages for Metal Passivation
At Metal Cutting, we are experienced and highly successful in both citric acid and nitric acid passivation. The more commonly requested option is citric acid treatment, where our process adheres to ASTM A967M and sub-clause 7.1.1.3 Citric 3. This method, which is more environmentally friendly than the nitric acid process and, we find, is just as effective, can also produce shorter cycle times. It calls for a solution of 4 to 10 weight percent of citric acid, with parts immersed for at least 20 minutes at a temperature of approximately 70-120° F (21-49° C). Our less frequently used nitric acid method adheres to ASTM A967M and sub-clause 6.1.1.2 Nitric 2, with the process utilizing a 20 to 45 volume percent solution.
Our surface passivation treatments are performed at room temperatures of about 70-90° F (21-32° C), which avoids the addition of heat and makes for an effective and safe process. In addition, by mixing the acid solution anew with each batch rather than reusing it, our process enables us to maintain the optimal solution chemistry for each batch of parts undergoing treatment and ensures that there is no contamination from other metal parts in the solution.
Both prior to treatment and after, all parts also undergo an ultrasonic deionized water rinse — first to thoroughly clean the surface and remove any contaminants, such as oil, grease, rust, scale, or other particulates, and then to halt passivation and ensure that the surface of the finished parts is neutralized. Additionally, our methods are calibrated using the ASTM A967M standard copper sulfate test, to confirm that parts are being passivated effectively. This helps to ensure that our passivation services deliver consistent, high-quality results for your small stainless steel parts.
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