- Sep 29, 2018 -
The main operating conditions of trivalent chromium passivation are related to the PH, passivation temperature and passivation time of the passivation solution. Through these processes, iridescent films of iridescent colors and other different colors can be obtained in the zinc plating layer and the zinc alloy plating layer. 1, PH value. The pH of the trivalent chromium passivation is mostly under acidic conditions, and the pH mainly affects the dissolution of zinc and the rate of redissolution of the passivation film. The low pH and the faster dissolution rate of zinc are beneficial to the formation of the passivation film in this sense, but the dissolution of the already formed passivation film is also accelerated when the pH is low. Some studies have also shown that PH is also related to the color of the passivation film. Therefore, the appropriate pH should be chosen in order to get the best passivation film, generally between 1.5 and 2.5.
2. Passivation temperature. When the passivation temperature is low, the formation speed of the colloidal precipitate of the galvanized layer is slow, and the time required for the passivation film of the same thickness is long; when the temperature is high, the film formation speed is fast, and the dissolution speed of the film is also fast. Moreover, the high temperature also increases the decomposition of the oxide, and at the same time increases the cost due to the temperature rise. Therefore, room temperature operation is generally used, and the specific temperature varies depending on the system used, and the working temperature can be 10 to 70 °C.
3. Passivation time. There is a certain relationship between passivation time and temperature. Generally, at the same temperature, the passivation time is long, and the obtained passivation film is thick, but it is not absolute. The passivation time varies from 10 to 60 s.