Study On "DC/AC" Impedance Detection For Rapidly Evaluating Corrosion Resistance Of Organic Coating And A Combined Microprobe For Imaging Local Impedance On Metal

Development of electrochemical methods for studying corrosion and protection has always been a focus in the field of corrosion science,especially explore of nondestructive and rapid detection for evaluation of protective performance of organic coatings in industrial sites,and the local ac impedance measurement with higher spatial resolution.The first part of this thesis focuses on the use of multiple circlic potentials polarization to optimize electrochemical sensor and to develop a rapid evaluation of corrosion resistance of organic coatings/metal systems under different conditions.The measured data is compared with that from AC impedance and salt spray measurements.The second part of the thesis is to combine DC and AC impedance methods to quickly evaluate the protective performance of the coating in industrial field.The third part of the work is to develop a composite microprobe that is able to in situ measure the potential distribution and local AC impedance of the metal surface.The main research contents and progress are listed as follows:(1)The electrochemical sensor is optimized and more suitable test parameters are designed for rapidly evaluating corrosion resistance of organically coated metals.The detection and evaluation of the protective performance of organic coatings are carried out by using the multi-circlic potential polarization method,and the results are compared with the data from AC impedance and salt spray.It is demonstrated that the multiple circlic potentials polarization technique is able to be applied to the rapid detection and evaluation of the protective performance of organic coatings in industrial field.(2)Combining DC impedance method and AC impedance method to quickly evaluate the protective performance of modified polyurethane and epoxy modified acrylic coatings.The results show that the low-frequency impedance modulus method(Z0.01Hz)has good applicability as a method to quickly evaluate the protective performance of coatings.Through the breakpoint frequency method,it is found that the characteristic frequency(fb)has a negative correlation with Z0.01Hz which can also be used as a rapid evaluation method of coating protection performance;Through the specific frequency method,it is found that there is a strong correlation between θ1～10Hz and Z0.01Hz,and the coating protection performance can be quickly evaluated through 01-10Hz.The obtained DC impedance value also has a strong correlation with Z0.01Hz,which further illustrates the applicability and reliability of this technology.The development of combined method based on "DC+AC" impedance realizes mutual corroboration and complementarity between DC data and AC data,and the test results are more reliable and have better application prospects.(3)A scanning combined microprobe has been successfully fabricated to in situ measure concurrently the potential distribution and local AC impedance of the metal surface.The combined microprobe assisted by the scanning electrochemical workstation was used to test the potential in micro area and local AC impedance of different metals.It is shown that there is a good consistency between the results from the two tests under the same conditions,indicating that the scanning combined microprobe can be used as a new technique for studying localized corrosion of metals.