Passivation refers to the process of metal oxidation by strong oxidizing agent or electrochemical method, so that the surface becomes inactive, that is, passivation process, is to transform the metal surface into a state that is not easy to be oxidized, and delay the corrosion rate of the metal. In addition, an active metal or alloy, in which the chemical activity is greatly reduced, and become a precious metal state phenomenon, also called passivation.

Because the surface of titanium and titanium alloy can quickly form a layer of a few nanometers to tens of nanometers thick oxide film, so that it has a very outstanding passivation performance, so it shows good corrosion resistance.

The common passivation of titanium alloys is divided into three types.

An electrochemical passivation

The surface of titanium alloy can be oxidized, and a dense oxide film can be formed on the surface by electrochemical passivation. This layer of oxide film can effectively prevent the corrosion of titanium alloy in the chemical medium and scratch during processing. There are two methods of electrochemical passivation: anodic oxidation and cathodic reduction.

At present, the most common titanium and titanium alloy products are anodized surfaces. The anodizing method forms a very thin (colorless and transparent) oxide film on the surface of titanium products (such as titanium cups and titanium chopsticks), which uses the principle of light refraction to make the human eye see various colors after refraction. The thickness of the oxide film is different, and the color seen by the human eye is different. The thinest oxide film starts from 0.01μm, thickens with 0.01μm as an increasing unit, and the thickest can reach 0.15μm, so the color of pure titanium metal products can be very rich and gorgeous, and titanium metal material is a fantastic metal material.

Second, heat treatment passivation

Heat treatment passivation is to put titanium alloy into a hot furnace, oxidize the surface at a certain time and temperature, and cold after forming a certain thickness of the oxide layer to form a dense oxide film, thereby increasing the corrosion resistance of titanium alloy.

Third, chemical treatment passivation

Chemical treatment passivation includes pickling and chemical passivation, pickling can remove oil, oxide film and impurities on the surface of titanium alloy, and create good conditions for subsequent chemical passivation. Chemical passivation refers to the treatment of the titanium alloy surface into a solution containing chemicals to produce a dense oxide film to stabilize the surface and improve the durability and corrosion resistance of the titanium alloy.

Pickling is a method used in the processing of titanium and titanium alloys.

1. Pre-treatment of pickling and passivation. If there is surface dirt before pickling passivation, it should be cleaned by mechanical cleaning, and then degreasing.

2. Process control in pickling passivation operation. A solution of nitric acid (HNO3) is generally used. As a rule of thumb, the proportion of water is 1:10 or 1:15. If the ratio is improper or the operation is improper, the operation tank will release a large amount of "yellow smoke".

3. In the case of other conditions unchanged, the longer the pickling time, the more adequate the corresponding reaction, the better the pickling effect. However, because titanium has a strong hydrophilic property, too long will lead to the hydrogen content of titanium adsorption will gradually rise, therefore, in the pickling process, 5 to 10 minutes is a more suitable time.

4 After pickling passivation washing: After pickling is completed, water needs to be washed to remove the residual pickling solution and impurities. Drying: After washing is completed, it needs to be dried to remove surface moisture.

5 Pay attention to the use and disposal of acidic solutions to avoid harm to the environment and human body.

In short, titanium alloy passivation process is a common surface treatment technology, which can effectively remove oxides, corrosion products and other impurities on the surface of titanium alloy, and improve its surface quality and material properties.