What are the commonly used methods for coating porosity inspection?
Commonly used methods for measuring the porosity of coatings include the paste method and the test paper method. The ointment method is more troublesome to prepare the ointment, so the test paper method is mostly used. The test paper method is to cut the filter paper
After forming a test paper of a certain size, soak it in the test solution containing the following components: potassium iron oxide 10g/1, sodium chloride 10g/1.
Then paste this test paper flatly on the coating to be tested. After 10 minutes, count the number of color points per unit area on the test piece, which is the porosity of the coating with a certain thickness. For the convenience of statistics, a transparent plexiglass to cover the color test paper for statistics. Usually, the average value , expressed in the number of holes per square centimeter.
Improved porosity test method
The direct measurement of the porosity of the locking layer by using potassium ferrite and sodium chloride has the disadvantage that the result is not clear due to the strong corrosion effect. As an improved method, the relatively low corrosive act on the pores of the lock layer, and then the porosity is displayed in the iron potassium nitride solution. The specific method is as follows.
Choose cloth paper with high fastness, and apply a gelatin aqueous solution . The formula of the solution is as follows: sodium chloride 50g/L, white gelatin 50g/L. Then let it dry. When carrying out the test, first soak the gummed paper in a solution containing 50g/L of sodium chloride, then take it out and stick it on the sample with the side coated with gelatin facing the lock layer, and let the sodium chloride electrolyte solution pass through the pores of the lock layer Work with the substrate, then keep the test paper moist. After an appropriate period of time (not too long, otherwise the pores will expand due to corrosion and the pitting state cannot be detected), take off the test paper and put it into an aqueous solution . At this time, there is iron on the test paper. Where there are ionic pitting marks , blue corrosion spots will appear due to the reaction with potassium ferrite hydride . This method of indirectly showing the porosity on the lock layer is more applicable than the direct sticker test.
