Analysis of the fog corrosion test of the surface anti-corrosion ability salt of lighting products

1. Corrosion mechanism The working environment of lighting products is the atmosphere and indoor environment, and the harsh conditions are in the marine climate or the seabed. Atmospheric corrosion is divided into three categories: dry atmospheric corrosion; damp atmospheric corrosion; wet atmospheric corrosion. 1. Characteristics of atmospheric corrosion Atmospheric corrosion is characterized by the corrosion process in which the metal surface is in a thin layer of electrolyte, and its corrosion mechanism conforms to the law of electrochemical corrosion: when a continuous thin layer of electrolyte is formed on the metal surface, the cathodic process of atmospheric corrosion is : O2+2H2O+4e→4OH- anode process is: Me- ne→Men+; when Fe and Zn are all immersed in reducing acid solution: the cathode is hydrogen depolarized; under the acidic water film formed by the urban polluted atmosphere: the cathode is oxygen depolarized corrosion. Under the thin liquid film: oxygen can easily reach the metal An oxide film is formed on the surface, the anode is passive, and the anode is polarized; when the liquid film thickens (wet atmosphere), there must be a diffusion process for oxygen to reach the metal surface, so the corrosion is controlled and slowed down. Corrosion mechanism: The rust layer of atmospheric corrosion is under humid conditions, the rust layer acts as a strong oxidant, and the anode in the rust layer occurs on the Fe3O4 interface of the metal: Fe-2e→ Fe2+; the cathode occurs at the interface of Fe3O4 and FeOOH: 6FeOOH+2e→ 2Fe3O4+2H2O+2OH-, the rust layer participates in the cathodic process. In the industrial atmosphere, SO2, NO2, H2S and NH3 all increase atmospheric corrosion. When the humidity is greater than 70%, a water film is formed, electrochemical corrosion occurs, and the corrosion rate increases sharply; when the humidity is less than 70%, the electrochemical corrosion rate of sulfur dioxide is very small. In particular, metals such as iron, zinc, cadmium, and nickel that are not resistant to sulfuric acid are easily corroded in the atmosphere. It is generally believed that the corrosion mechanism of SO2 is the autocatalytic process of sulfate caves. Once the rust layer generates sulfate, the rust layer has no protective ability. Therefore, carbon steel must be protected under outdoor atmospheric conditions. The methods include anti-rust paint, Zn plating, AI, etc. or adding alloying elements resistant to atmospheric corrosion, such as Cu, P, etc., so that the rust layer has a good protective effect. 2. Characteristics of seawater corrosion Seawater is about 3.5% NaCI solution, (NaCI, MgCI2, CaSO4, K2SO4, CaCO3, MgBr2) with an average conductivity of 4×10-2S.CM-1, much larger than river water and rainwater. When the salt concentration and temperature increase, the solubility of oxygen in seawater decreases. Seawater is a typical electrolyte solution, which is characterized by electrochemical corrosion. Except for active Mg and its alloys, the corrosion process of seawater is an oxygen depolarization process, and the corrosion rate is determined by Oxygen diffusion process control. For most metals such as iron, steel, zinc, etc., due to the high concentration of CI-, the blocking effect of the anode process is very small, and it is not easy to reduce it. Corrosion resistance. Due to the high conductivity and small resistive retardation of seawater, the macroscopic and microscopic cell activities of seawater corrosion are large, so the galvanic corrosion caused by the contact of dissimilar metals in seawater has a considerable destructive effect. Such as ships and bronze propellers can cause corrosion of steel ship hulls tens of meters away. 2. Corrosion resistance test and determination of anti-corrosion performance 1. Weather resistance test method , PH=3.1-3.3 copper accelerated acetic acid salt spray test: 5%NaCl solution, add 2g/L±0.2g/L CuCI2.2H2O, PH=3.1-3.32, metal material and protective layer weather resistance simulation test standard A) Test equipment requirements: The material of the test chamber is not corroded and does not affect the test results; the salt spray cannot be directly sprayed on the surface of the sample ; Condensed water from anywhere in the working space cannot drip onto the sample; the temperature fluctuation of the test chamber is±0.5℃, its uniformity is±2°C. B) Selection of test conditions: acidity of test solution: PH=7±0.2 There are four options for the composition of the test solution according to the needs: ①, 3% NaCl solution; ②, 5% NaCl solution; ③, 20% NaCl solution; ④, artificial seawater; 27g/L NaCl+6g/LMgCI2+1g/ LKCI+1g/LCaCI2C) test test temperature: 35±2°C D) Salt spray deposition volume: 1.0-2.0ml/80cm2.hE) The test period can be selected according to needs: ①, 24 hours of continuous spraying, and observe the time when corrosion begins to appear. ②. Continuous spray for 8 hours, stop for 16 hours, 24 hours as a cycle, and specify the number of test cycles according to the function of different products. ③, intermittent spray for 8 hours (the fountain stops for 5 minutes and 45 minutes), stop for 16 hours, and a cycle of 24 hours. The number of test cycles is specified according to the function of different products. 3. Determination method of paint film salt spray resistance according to GB1765 to make paint panels; test solution: 3.5% NaCI solution, PH=6.1-7.5 Test chamber working temperature: 40±2°C; spray cycle: spray every 45 minutes for 15 minutes. 4. Evaluation method of corrosion resistance test The usual evaluation methods of corrosion test results are: appearance and appearance after removing surface corrosion products; the distribution and number of pitting corrosion, cracks and bubbles are evaluated according to the properties of the base material and the coating, and the substrate is a cathode such as Ni-Cr or Cu-Ni-Cr plating on the surface of steel and aluminum alloy die castings is rated according to GB6461; the substrate is anode such as steel zinc plating and copper tin plating, etc. to be rated according to GB12335; the corrosion initiation time is the most commonly used judgment of corrosion resistance method; the corrosion resistance test results can also be judged by weight change, microscopic observation and mechanical property change. The salt spray resistance of paint film is rated according to GB1740. The evaluation standards of salt spray test and results of different products in different countries and industries are different. my country's regulations on coating salt spray test are in accordance with the attached table, and the results are judged into three categories: good, qualified and unqualified: good: no change in color or Slight darkening; neither coating nor substrate corroded. Qualified: The color is dull, and the coating has continuous uniform or non-uniform oxide film; the corrosion area of ​​the coating is less than or equal to 3%.
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