What are the detection methods of stainless steel passivation film?
Stainless steel undergoes some surface changes during treatments such as pickling, polishing or grinding, and in order to protect these treated surfaces from secondary oxidation or corrosion, a passivation film is usually formed on the surface. The quality and integrity of the passivation film is critical to the corrosion resistance of stainless steel. Therefore, it is very necessary to inspect the stainless steel passivation film.
At present, the detection methods of stainless steel passivation film are mainly as follows:
1. Metallographic method.
Metallographic method is a more traditional method to judge the quality of stainless steel by observing the structure and morphology of the passivation film on the surface of stainless steel under a metallographic microscope. The specific steps are as follows:
1.The surface of the stainless steel is polished to make its surface smooth and flat;
2.The polished sample is immersed in a nitric acid solution to remove metal impurities and oxides from the surface;
3.The cleaned sample is immersed in the passivation solution to form a passivation film on its surface
4.The passivated sample is immersed again in the nitric acid solution to dissolve the passivation film on the surface;
5.The sample was observed under a metallographic microscope to observe the microstructure of its surface, including the thickness, compactness and uniformity of the film layer.
The microstructure of the passivation film can be observed by metallographic method, but the results may vary for different types of stainless steels and different passivation conditions.
2. Electrochemical methods.
The electrochemical method is another commonly used stainless-steel passivation film detection method. The method evaluates the corrosion resistance of a sample by measuring its electrochemical properties. The specific steps are as follows:
1.The stainless steel sample was used as a working electrode and immersed in the electrolyte
2.Measure the current-voltage curve or Tafel curve of the sample over a certain potential range
3.Analyze the electrochemical properties of the sample, such as corrosion current density, corrosion potential, and Tafel slope, according to the measured curves
4.The corrosion resistance of the sample is evaluated based on these parameters.
Electrochemical methods can quickly and accurately assess the quality and corrosion resistance of stainless steel passivation films, suitable for large-scale production and quality control. However, this method requires the use of electrolyte, which may have some impact on the environment.
3. Spectral analysis methods.
The spectroscopic method is a non-destructive detection method that determines the quality of a sample by analyzing its elemental composition and content. The specific steps are as follows:
1.Stainless steel surfaces are treated mechanically or chemically to expose fresh metal surfaces;
2.The treated surface is analyzed using a spectrometer to measure its elemental composition and content;
3.Based on the results of the measurements, the corrosion resistance of the sample is evaluated.
Spectroscopic analysis methods can quickly and accurately detect the elemental composition and content of sample surfaces, which is suitable for large-scale production and quality control. However, this method requires the use of chemical reagents or mechanical treatment, which may have some effect on the sample.
Fourth, surface analysis methods.
The surface analysis method is a relatively new detection method, which determines the quality of the chemical bonds and molecular structure of the surface of the sample. The specific steps are as follows:
1.The surface of the stainless steel is polished to make its surface smooth and flat;
2.Analyze the sample surface using high-resolution surface analysis instruments (e.g., infrared spectrometer, Raman spectrometer, etc.);
3.Based on the results of the measurements, the corrosion resistance of the sample is evaluated.