Corrosion of titanium

Titanium is a thermodynamically unstable metal with a negative passivation potential and a standard electrode potential of -1.63V. Therefore, it is easy to form an oxide film with passivation properties in the atmosphere and aqueous solution, which has good corrosion resistance.

1. Corrosion resistance of titanium in different media
It is very important to study the corrosion resistance of medical materials. On the one hand, some metal ions or corrosion products of the implanted materials penetrate into the tissues of organisms, which can cause physiological reactions of different degrees. On the other hand, due to the presence of body fluids, the properties of some materials may be severely reduced, resulting in rapid damage or even failure. The human environment is relatively complex, which is more likely to cause the dissolution of trace elements and change the stability of the oxide layer. Slight friction can cause the passivation film formed on the surface of titanium to suffer different degrees of damage, such as in an oxygen-poor environment, the stability of the oxide layer is weakened, and it can not be repaired immediately when damaged or a new oxide layer is formed, which is more likely to cause corrosion. This situation is almost impossible to avoid in the repeated movement of the human body and the use of instruments. Plastic deformation will change the microstructure of the material, which will affect the corrosion properties of the material. The influence of different degree of plastic deformation on the corrosion properties of materials is very different. In the process of plastic deformation, due to the concentration of internal stress resulting in the interface and grain defects, plastic deformation will weaken the corrosion resistance of the material.

2. Corrosion mechanism of titanium
Titanium is a transition element of the IVB group, which is chemically active and has great affinity with oxygen. In any oxygen-containing medium, the surface of titanium is easy to generate a dense passivation film, which is extremely thin, and its thickness is usually a few nanometers to tens of nanometers. The existence of titanium alloy passivation film reduces the surface active dissolution area and slows down the dissolution rate, thus resisting the damage caused by dissolution. In addition, the passivation film can also be automatically repaired, and when damaged, a new protective film can be quickly formed. Therefore, the corrosion resistance of titanium is good. The corrosion forms of titanium implanted in organisms can be divided into pore corrosion, stress corrosion, crevice corrosion, galvanic corrosion and wear corrosion.