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Factors affecting the corrosion rate of salt spray tester
It is widely recognized that the concentration of sodium chloride plays a crucial role in determining the quality of metal corrosion during neutral salt spray testing. The corrosion rate in a salt spray tester, under specific temperature conditions, is primarily influenced by two key factors: the concentration of the salt solution and the amount of dissolved oxygen within it. When the oxygen level in the solution is sufficient to support electrochemical reactions, the corrosion rate is mainly governed by the salt concentration. However, once the salt concentration exceeds 5%, the dissolved oxygen content begins to decrease as the concentration increases, which may no longer be enough to sustain the electrochemical process. In such cases, the corrosion rate becomes limited by the available oxygen. Therefore, the optimal corrosion rate is typically achieved at around a 5% sodium chloride solution, which is why this concentration is commonly used as the standard in salt spray testing.
The above discussion highlights that the concentration of the salt solution is a critical factor affecting the accuracy of test results. To minimize its impact, regular monitoring of the solution's concentration is essential. One effective method for measuring this is through density testing. At 25°C, a 5% sodium chloride solution has a density ranging between 1.029 and 1.041 g/mL. This can be quickly and accurately measured using a hydrometer, ensuring consistency and reliability in the testing process.
Note: The test samples discussed here are primarily anti-corrosion coatings, such as paint films. Other types of samples should be considered for reference only.