According to this method, the porosity of paint coatings and other non-metallic coatings on various metal products can be determined by the precipitation of organic dyes into the pores, which are formed due to the anodic treatment of the product ( The voltage is 8~24 volts direct current). At this time, indicator solutions of various organic dyes can be used as electrolytes.
When measuring the porosity of paint coatings on aluminum and aluminum alloys, use P-naphthol orange indicator solution. The voltage is 5~10 volts; the test time is 5~10 seconds. A brown amorphous dense precipitate was deposited in the pores. In the determination of the porosity of paint coatings and anode coatings on steel and its alloys, an indicator solution of acid fuchsin can be used. The voltage is 8~24 volts, and the test time is 10~20 seconds. There are blue crystalline scale-like precipitates in the fine pores. When determining the porosity of the anode coating on 9 and its alloys, the blunt salt of alizarin sulfonate can be used as an indicator solution. A red amorphous precipitate settled out in the pores.
The test can be summarized as follows: the painted article (metal plate) to be tested is suspended in a bath containing a suitable indicator solution as an anode; an aluminum sheet is used as a cathode. Then turn on the power supply with a voltage of 8-24 volts; when it has been adjusted to a constant current (this can be judged by the microammeter connected to the circuit), take the sample well out of the solution and rinse it with water. Where there are pores, a very large colored precipitate is formed. (Related instrument: conductivity meter)
If the painted board cannot be placed in the solution, the test can be carried out as follows. Several pieces of glass tubes with a diameter of about 50 mm and a ground edge are placed on the painted iron plate. Stick the glass tube on the surface of the test plate by means of paraffin or adhesive plastic. Then connect the iron plate to the anode of the power supply, and put an aluminum piece in the glass tube as a bright pole well to inject the indicator solution. Its porosity can be measured by the intensity of the current and the precipitation of the dye in the pores.
