The salt spray testing machine is a widely used corrosion testing device. Its core function is to evaluate the corrosion resistance of materials by simulating and accelerating the corrosion process. Firstly, the sprayed sodium chloride (NaCl) solution forms a thin, conductive salt film on the surface of the sample. This liquid film, as an electrolyte, provides the necessary environment for electrochemical corrosion. The region with higher surface activity of the metal serves as the anode, where metal atoms lose electrons and undergo oxidation reactions, transforming into metal ions that dissolve into the electrolyte. The area with lower surface activity of the metal serves as the cathode. A reduction reaction occurs in the presence of oxygen in a salt solution. Finally, the metal ions produced at the anode (such as Fe²⁺) combine with the hydroxide ions (OH⁻) generated at the cathode to form metal hydroxides, which are further oxidized into common rust.
For example: Fe²⁺ + 2OH⁻ → Fe(OH)₂
4Fe(OH)₂ + O₂ → 2Fe₂O₃·H₂O + 2H₂O(Red rust)
Compared with the slow corrosion in nature, the salt spray test greatly accelerates the corrosion process in the following ways:
1. Constant high-concentration brine environment: Usually a 5% sodium chloride solution is used, with a concentration much higher than that of most natural environments (such as seawater), providing a large amount of corrosive chloride ions (Cl⁻). Chloride ions have strong penetrating power and can destroy the passivation film on the metal surface, allowing corrosion to continue.
2. Continuous spraying: The machine continuously atomizes salt water and sprays it into a sealed box, ensuring that all surfaces of the sample are evenly covered by the salt spray. This avoids the alternating dry and wet conditions in the natural environment and allows the corrosion reaction to proceed without interruption.
3. Heating: The temperature of the test chamber is usually kept constant at 35℃. The temperature rise accelerates the rates of all chemical reactions, including the electrochemical corrosion process, thereby significantly speeding up corrosion.
4. Oxygen supply: The surface area of the atomized droplets is extremely large, which can fully dissolve oxygen in the air. Continuous spraying ensures a steady supply of oxygen required for the cathodic corrosion reaction.
Lab salt spray testing machine is suitable for neutral salt spray tests (NSS) and corrosion tests (AASS, CASS) of various communication electronic products, electronic appliances and hardware components. Complies with standards such as CNS, ASTM, JIS, and ISO. The salt spray test is conducted on the surfaces of various materials that have undergone anti-corrosion treatments such as coating, electroplating, anodizing, and anti-rust oil to assess the corrosion resistance of the products.
It is worth noting that salt spray testing is a highly accelerated test, and its corrosion mechanism and morphology are not exactly the same as those in real outdoor environments (such as atmospheric exposure and seawater immersion). Products that pass this test do not necessarily achieve the same corrosion resistance period in all real environments. It is more suitable for relative rankings rather than absolute predictions.
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