PdO-TiO2 and RuO2-Ti02 coatings can significantly improve the corrosion resistance of TC4 titanium alloy, especially the crevice corrosion resistance. The usual method is to apply a solution containing chlorinated fertilizer and titanium trichloride to the surface of the titanium alloy by brushing, and then thermally oxidize it at 500-700°C for tens of minutes after drying, and finally transform it into an oxide coating. The above operation is repeated several times until the weight gain of the coating reaches 1g/m2. The mass ratio of PdO and TiO2 in the coating is usually 7:3. The TC4 titanium alloy with this coating can form very light adhesion, and its technical know-how lies in the preparation of the solution. The acid solution corrodes the surface of the TC4 titanium alloy and generates a hydride layer, which is oxidized and decomposed by high temperature, which is the key to obtain excellent adhesion of the oxide coating.
The corrosion rate of pure titanium with PdO-TiO coating and pure titanium in 70% hydrochloric acid, sulfuric acid and phosphoric acid can be seen: PdO-Ti02 coating can significantly improve the candle resistance of titanium in hydrochloric acid, sulfuric acid and phosphoric acid towels. Especially for phosphoric acid, the corrosion rate of the coating is stable, and almost increases with the increase of the acid content. The crevice corrosion resistance of the coating is also shown in table form. For the boiling sodium chloride solution, under the condition of 3 kinds of NaCl mass fractions (each mass fraction is adjusted to 3 pH values), using the opposite test method, the coating sample does not have crevice corrosion. Even in a 12% sodium chloride solution, a mass fraction of 47% is not a cause of crevice corrosion. Crevice corrosion occurs only in 42% boiling magnesium chloride solution. For industrial pure titanium, crevice corrosion can be seen in all the above solutions.
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