Corrosion Inhibitor Use for Titanium Alloy Plates

Titanium alloy plates corrode rapidly in reducing inorganic acids and certain organic acids due to their inability to maintain a passive oxide film. Adding corrosion inhibitors is an effective measure to reduce corrosion. Inhibitors include precious metal ions, heavy metal ions, oxidizing inorganic compounds, oxidizing organic compounds, and complexing organic inhibitors. Precious metal ions are very expensive and rarely used as corrosion inhibitors for reducing organic acids. Mineral ions like copper and iron have very significant corrosion inhibition properties, but require a critical concentration to be effective. Oxidizing inorganic compounds include nitric acid, chlorine, potassium chlorate, potassium dichromate, potassium permanganate, and hydrogen peroxide. Oxidizing organic compounds include nitro or nitroso compounds and nitrogen compounds. Unlike oxidizing organic compounds, complexing organic inhibitors can inhibit corrosion at any concentration; there is no critical concentration; the effect varies only in magnitude. grade 7 titanium alloy sheet / Titanium Hot Rolled Sheet 

Surface treatment is a very effective method for improving the corrosion resistance of titanium alloy plates. Surface treatment methods include cathodic oxidation, thermal oxidation, nitriding, and coating techniques. The effects of anodic oxidation, thermal oxidation, and a platinum coating on the crevice corrosion time of titanium alloy plates have been investigated. Data show that platinum coating has the most significant effect on improving the corrosion resistance of titanium alloy plates, even surpassing the corrosion resistance of Ti-0.15Pd.

Anodizing titanium alloy plates is typically performed in a 5%-10% (NH4)2SO4 solution with a 25V DC voltage. The thickness of the anodic oxide film can reach 300-500nm. Anodizing effectively removes iron contamination from the surface, effectively prolongs the passivation time of the titanium alloy plate, and prevents hydrogen absorption caused by iron contamination. Therefore, international standards require that all titanium equipment be anodized. To improve the anodizing effect, sodium platinate is used instead of ammonium sulfate in the anodizing solution, resulting in better corrosion resistance.

Thermal oxidation of titanium alloy plates in air can produce a thicker, more crystalline rutile thermal oxide film than the anodic oxide film, which has better corrosion resistance than the anodic oxide film. Thermal oxidation of titanium alloy plates is achieved at a temperature between 600-700°C for 10-30 minutes. Higher temperatures or longer times can have negative effects.

Palladium-containing coatings are most effective for titanium alloy plates. Palladium-containing coatings are typically palladium oxide or lead alloy coatings. The typical preparation method for palladium oxide coatings (PdO-T102) involves applying a solution of PdCl4 and TiCl3 to the titanium alloy surface and heating at 500-600°C for 10-50 minutes. This process can be repeated several times to achieve a coating thickness exceeding 1g/m². The lead alloy coating is first applied using a thin layer of electroplating or vacuum deposition, followed by surface alloying treatments such as laser remelting or ion implantation. Its adhesion and corrosion resistance are superior to those of palladium oxide coatings.