Determination of Coating Porosity by Paste Method

       The porosity of the coating is determined by the paste coating method. The paste containing the corresponding test solution is applied to the surface of the treated sample, and the test solution in the test paste interacts with the metal at the bottom of the pores to generate a characteristic color. spots, and finally the porosity of the coating was evaluated by the number of colored spots on the paste layer. This method is suitable for porosity inspection of cathodic coatings on steel, iron, copper-zinc, aluminum and their alloy substrates.



     Paste method test paste:

     No. 1 mud paste: Dissolve 0.1g~0.2g of a-a1 biphenylpyridine or o-phenanthroline in 10mL of hydrochloric acid solution with a concentration of 0.1mL/L~0.2mL/L, add 10g~15g of titanium dioxide powder after dissolving , mix well into a paste for later use. This paste is valid for 14 days.

     No. 2 mud paste: heat water acetic acid in a water bath, and prepare an acetic acid solution (solution 1) with a mass fraction of 20% diphenyl-p-diaminocarbazide. Add 15g~30g of titanium dioxide powder to every 10mL of this solution. Dissolve 10 g of ammonium persulfate in 100 mL of concentrated ammonia water to prepare an ammoniacal solution of ammonium persulfate with a mass fraction of 10% (solution 2), which should be fully stirred during preparation. Finally, the solution 1, the solution 2 and the glycerin are prepared into a paste in a volume ratio of 1:1:0.5. This paste is valid for 2 to 3 days.

    No. 3 mud paste: add 5g~15g ammonium persulfate and 5mL~20mL concentrated ammonia water to 100mL distilled water to make an ammoniacal solution of ammonium sulfate, and mix the same volume and mass fraction of 2% cadmium reagent (II) aqueous solution, and then each Add 12g~15g of titanium dioxide powder to 10mL of the mixture to prepare a paste. This paste is valid for 3 to 4 days.

    No. 4 mud paste: Dissolve 0.05g of diphenylthio-p-diaminocarbazide in 10mL of ethanol, add 20g~30g of titanium dioxide powder after dissolving, stir well, and then add twice the volume of sodium hydroxide with a concentration of 0.5mL/L The solution is prepared into a paste for later use. This paste is valid for 3 to 4 days.

    No. 5 mud paste: add 15g~20g titanium dioxide powder and hydrogen peroxide equivalent to 1/2 volume of the aluminum reagent solution (relative density is 0.14~0.15) per 10mL solution in the aluminum reagent aqueous solution with a mass fraction of 2%. Stir to form a paste. This paste is valid for 3 to 4 days.