What are the factors affecting the results of salt spray test?

Date：2022-09-14 17:49:07Views：847

The results of salt spray test will be affected by various factors. The salt spray test of products is mainly used to assess the corrosion resistance of products or metal materials. Generally, the concentration of salt solution, the angle of sample placement, the pH value of salt solution, the test temperature and humidity, the amount of salt spray sedimentation, and the spray method can all affect the salt spray test. The main factors affecting the results of the salt spray test are described in detail below, hoping to be helpful to everyone.

1. Test temperature and humidity

Temperature and relative humidity affect the corrosion of salt spray. The critical relative humidity for metal corrosion is about 70%. When the relative humidity reaches or exceeds this critical humidity, the salt will deliquescence to form an electrolyte with good conductivity. When the relative humidity decreases, the concentration of salt solution will increase until crystalline salt is precipitated, and the corrosion rate will decrease accordingly.

The higher the test temperature, the faster the salt spray corrosion. IEC 60355:1971 AN APPRAISALOFTH PROBLEMSOF ACCELERATEDTESTINGFORATMOSPHERIC CORROSION standard of the International Electrotechnical Commission points out that "when the temperature rises by 10 ℃, the corrosion rate increases by 2-3 times, and the conductivity of the electrolyte increases by 10-20%". This is because the temperature increases, the molecular motion intensifies, and the chemical reaction speed accelerates. For the neutral salt spray test, most scholars believe that the test temperature of 35 ℃ is appropriate. If the test temperature is too high, the salt spray corrosion mechanism is quite different from the actual situation.

2. Concentration of salt solution

The influence of salt solution concentration on corrosion rate is related to the type of materials and coatings. When the concentration is below 5%, the corrosion rate of steel, nickel and brass increases with the increase of concentration; When the concentration is greater than 5%, the corrosion rate of these metals decreases with the increase of concentration. This phenomenon can be explained by the oxygen content in the salt solution, which is related to the salt concentration. In the low concentration range, the oxygen content increases with the increase of salt concentration. However, when the salt concentration increases to 5%, the oxygen content reaches relative saturation. If the salt concentration continues to increase, the oxygen content will decrease accordingly. When the oxygen content decreases, the oxygen depolarization capacity also decreases, that is, the corrosion is weakened. However, for zinc, cadmium, copper and other metals, the corrosion rate always increases with the increase of salt solution concentration.

3. Sample placement angle

The angle of sample placement has obvious influence on the results of salt spray test. The settling direction of the salt spray is close to the vertical direction. When the sample is placed horizontally, its projection area is large, and the amount of salt spray on the sample surface is also large, so the corrosion is serious. The results show that when the steel plate is at a 45 degree angle with the horizontal line, the corrosion loss weight per square meter is 250g, and when the steel plate plane is parallel to the vertical line, the corrosion loss weight per square meter is 140g. The GB/T2423.17-93 standard stipulates that "the placement method of flat sample should make the test surface form a 30 degree angle with the vertical direction."

4. PH value of salt solution

The pH value of salt solution is one of the main factors affecting the results of salt spray test. The lower the pH value, the higher the concentration of hydrogen ions in the solution, and the stronger the acidity, the stronger the corrosivity. The salt spray test of electroplated parts such as Fe/Zn, Fe/Cd, Fe/Cu/Ni/Cr shows that the corrosivity of acetate spray test (ASS) with pH 3.0 of salt solution is 1.5~2.0 times more severe than that of neutral salt spray test (NSS) with pH 6.5~7.2. Due to the influence of environmental factors, the pH value of salt solution will change.

5. Salt mist sedimentation and spray mode

The finer the salt spray particles, the larger the surface area formed, the more oxygen absorbed, and the stronger the corrosivity. More than 90% of the salt spray particles in nature have a diameter of less than 1 μ m. Research results show that the oxygen absorbed on the surface of the salt spray particles with a diameter of 1 μ m is relatively balanced with the oxygen dissolved in the particles. No matter how small the salt spray particles are, the amount of oxygen absorbed will not increase.

The traditional spray methods include air pressure spray method and spray tower method. The obvious disadvantage is that the uniformity of salt spray sedimentation is poor and the diameter of salt spray particles is large. The ultrasonic atomization method uses the principle of ultrasonic atomization to directly atomize the salt solution into salt fog and diffuses it into the test area, which solves the problem of poor uniformity of salt fog sedimentation, and the diameter of salt fog particles is smaller. Different spraying methods will also affect the pH value of salt solution.

The above is related to the analysis of factors that affect the results of salt spray test in wound core detection small knitting, and I hope it will be helpful to you. Our company has a team of professional engineers and industry elites, and has built three standardized laboratories with an area of more than 1800 square meters, which can undertake a variety of test projects such as electronic component test verification, IC authenticity identification, product design material selection, failure analysis, functional testing, factory incoming material inspection and tape weaving.