Micom Laboratories is pleased to announce that it now offers ISO 9227 testing as part of its corrosion test services.
Corrosion is the deterioration of a metal due to chemical interactions with its environment. The production of metals involves adding energy in the system and because of that, the metal has a strong driving force to convert to a more chemically-stable form which is a low energy oxide state. This return to a low energy oxide state is what we call corrosion. The latter is something we hope to avoid like death and taxes. Ultimately, we have to learn to deal with it. However, there are substantial barriers that can be used to inhibit the return to its oxidized, more stable, state. While corrosion is typically associated with metals, all material types are susceptible to this oxidation mechanism.
ISO 9227 uses a Salt Spray fog as a technique to assess a coated sample’s resistance to corrosion. By producing an attack to coated specimens, it is possible to determine if the protecting coating is suitable.
There are various types of corrosion reactions. The one used in this type of test is called oxygen-concentration cell corrosion. The concentration of oxygen in the middle of a drop of water is a lot less than the concentration of oxygen at the edge of the drop. The oxygen deficient part in the middle becomes the anode and more acidic while the oxygen rich area becomes the cathode and more alkaline thus precipitating out iron hydroxide in the form of red rust. By adding sodium chloride at a concentration of 50 g/L, the corroded metal ions stay in the solution. The corrosive effect is consequently enhanced since these metal ions act as conductors (electrolytes). Furthermore, the salt increases the solubility of different metal ions and it helps extent the life span of each electrochemical cell since more metal can be in solution. A higher temperature is also used to accelerate the speed of the reaction.
There are three distinct test method in ISO 9227: the neutral salt spray (NSS), the acetic acid salt spray (AASS), and copper-accelerated acetic acid salt spray (CASS). The choice of the test for your product(s) should be based on the type of material/coating. Indeed, AASS and CASS are mostly used for electrodeposited copper/nickel/chromium coatings, nickel/chromium coatings, and sometimes anodic coatings on aluminum whereas the NSS test, offering neutral salt spray conditions with a pH ranging between pH 6.5 to 7.2, applies for metals and their alloys, most metallic coatings, anodic oxide coatings, organic coatings, and metallic materials. The AASS and CASS methods are much more corrosive than the ordinary salt spray method (NSS) and are very useful in enhancing electroplated parts quality. For a better comparison of these tests, please see ASTM B117 vs AASS or CASS.
Micom Laboratories is a third party industrial material testing laboratory accredited by the Standards Council of Canada, CGSB, ISTA and many other organizations.
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