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.
Salt spray testing is a critical corrosion evaluation method widely used in industries such as automotive, aerospace, and electronics. To ensure accurate and repeatable test results, it is essential to prepare the salt solution correctly and use a high-quality salt spray test chamber that maintains precise testing conditions. Below are the preparation procedures for common salt spray tests, including Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS), and Copper-Accelerated Acetic Acid Salt Spray (CASS):
1. Neutral Salt Spray (NSS) Solution Preparation
Prepare sodium chloride solution: Dissolve 50g of sodium chloride (NaCl) in 1L of distilled or deionized water to achieve a concentration of 50g/L ± 5g/L. Stir until completely dissolved.
Adjust pH (if necessary): Measure the pH of the solution using a pH meter. The pH should be within 6.4–7.0. If adjustment is required:
Use sodium hydroxide (NaOH) to increase pH.
Use glacial acetic acid (CH₃COOH) to decrease pH.
Note: Even small amounts of NaOH or acetic acid can significantly alter pH, so add cautiously.
For optimal performance, ensure the solution is used in a professional salt spray test chamber that provides consistent temperature, humidity, and spray distribution.
2. Acetic Acid Salt Spray (AASS) Solution Preparation
Prepare base sodium chloride solution: Same as NSS (50g NaCl per 1L distilled/deionized water).
Adjust pH: Add glacial acetic acid to the NaCl solution while stirring. Measure the pH until it reaches 3.0–3.1.
A reliable salt spray corrosion test chamber with precise pH monitoring and spray control is crucial for AASS testing, as slight deviations can affect test validity.
3. Copper-Accelerated Acetic Acid Salt Spray (CASS) Solution Preparation
Prepare sodium chloride solution: Same as NSS (50g NaCl per 1L distilled/deionized water).
Add copper(II) chloride (CuCl₂): Dissolve 0.26g/L ± 0.02g/L of CuCl₂·2H₂O (or 0.205g/L ± 0.015g/L anhydrous CuCl₂) in the NaCl solution.
Adjust pH: Add glacial acetic acid while stirring until the pH reaches 3.0–3.1.
CASS testing requires an advanced salt spray test chamber capable of maintaining strict temperature and corrosion acceleration conditions to ensure fast and accurate results.
4. Key Considerations for Salt Spray Testing
Purity requirements:
Use high-purity NaCl (≥99.5%) with ≤0.1% sodium iodide and ≤0.5% total impurities.
Avoid NaCl with anti-caking agents, as they may act as corrosion inhibitors and affect test results.
2.Filtration: Filter the solution before use to prevent nozzle clogging in the salt spray test chamber.
3.Pre-test checks:
Verify the salt concentration and solution level before each test.
Ensure the salt spray corrosion test chamber is properly calibrated for temperature, humidity, and spray uniformity.
Why Choose a Professional Salt Spray Test Chamber?
A high-performance salt spray test chamber ensures:
✔ Precise environmental control – Maintains stable temperature, humidity, and spray conditions.
✔ Corrosion resistance – Made of high-quality PP or PVC materials to withstand long-term testing.
✔ Compliance with standards – Meets ASTM B117, ISO 9227, and other industry requirements.
✔ User-friendly operation – Automated controls for consistent and repeatable test results.
For industries requiring reliable corrosion testing, investing in a high-quality salt spray test chamber is essential to achieve accurate and repeatable results.
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