What are the reasons for the accuracy of the salt spray corrosion test chamber?

The salt spray test is a test method for assessing the salt spray resistance of the coating film. Whether the correct data can be obtained through the test is very important for the salt spray test. If the test data is out of alignment, it will not only make the test meaningless, but also mislead the production unit and the user, causing unnecessary losses. Here are some reasons for analyzing the accuracy of the salt spray corrosion test chamber?

First, test temperature and humidity

Test temperature and humidity will affect the corrosion of salt spray, for example: neutral salt spray test: tank temperature 35 ° C, saturated barrel 47 ° C, acid test: tank temperature 50 ° C, saturated barrel 63 ° C, the humidity inside the box At about 95% RH, the critical relative humidity of metal corrosion is about 70%. When the relative humidity reaches or exceeds this critical humidity, the salt will deliquesce to form an electrolyte with good electrical conductivity. When the relative humidity is lowered, the concentration of the salt solution will increase until the crystalline salt is precipitated, and the corrosion rate is correspondingly lowered.

Second, the pH of the salt solution

The pH value of the salt solution is one of the main factors affecting the salt spray test results. The lower the pH value, the higher the hydrogen ion concentration in the solution, and the stronger the acidity, the stronger the corrosion. The pH value of the salt liquid will be affected by environmental factors. For this reason, the salt spray test standard at home and abroad has specified the pH range of the salt liquid, and the method of stabilizing the pH value of the salt solution during the test is proposed to reduce The risk of inaccurate experimental results due to changes in the pH of the saline solution.

Third, salt spray settlement and spray method

The finer the salt spray particles in the salt spray corrosion test chamber, the larger the surface area formed, and the more oxygen is adsorbed, the stronger the corrosion. More than 90% of the salt spray particles in nature have a diameter of less than 1 micron. The results show that the amount of oxygen adsorbed on the surface of the salt spray particles with a diameter of 1 micrometer is relatively balanced with the amount of dissolved oxygen inside the particles. The salt spray particles are smaller and the amount of oxygen adsorbed does not increase any more.

Fourth, the concentration of the salt solution

The effect of the concentration of the salt solution on the corrosion rate is related to the type of material and the cover layer. When the concentration is below 5%, the corrosion rate of steel, nickel and brass increases with the increase of concentration; when the concentration is more than 5%, the corrosion rate of these metals decreases with the increase of concentration. The above phenomenon can be explained by the oxygen content in the salt solution. The oxygen content in the salt solution is related to the concentration of the salt. In the low concentration range, the oxygen content increases with the increase of the salt concentration, but when the salt concentration is increased to At 5%, the oxygen content reaches a relative saturation, and if the salt concentration continues to increase, the oxygen content decreases accordingly. As the oxygen content decreases, the depolarization ability of oxygen also decreases, that is, the corrosion effect is weakened. However, for metals such as zinc, cadmium and copper, the corrosion rate always increases with the concentration of the salt solution.

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