Titanium is a very corrosion-resistant metal. The thermodynamic data of titanium indicate that titanium is a thermodynamically unstable metal. If titanium can dissolve to form Ti2 +, its standard electrode potential is very negative (-1.63V), and its surface is always covered with a passive oxide film. This steadily shifts the stable potential of titanium to a positive value. For example, the stable potential of titanium in seawater at 25 ° C is about + 0.09V. In the chemistry manuals and textbooks, standard electrode potentials corresponding to a series of titanium electrode reactions can be obtained. It is worth noting that in fact these data are not directly measured, but often can only be calculated from thermodynamic data, and due to different data sources, several different electrode reactions may be represented at the same time, and different data is not Strange.
The electrode potential data of titanium electrode reaction shows that its surface is very active, and it is usually covered with an oxide film that naturally occurs in air. Therefore, the excellent corrosion resistance of titanium stems from the fact that there is always a stable, strongly adherent, and particularly protective oxide film on the titanium surface. In fact, the stability of this natural oxide film determines titanium Corrosion resistance, including titanium rods, titanium wires, titanium plates, etc. of titanium and titanium alloys have strong corrosion resistance. Of course, the corrosion resistance of various brands is different. We mentioned in the previous content of the website However, I wo n’t say much today. In theory, the P / B ratio of the protective oxide film must be greater than 1, if it is less than 1, the oxide film cannot completely cover the metal surface, so it is impossible to play a protective role. If this ratio is too large, the compressive stress in the oxide film will increase accordingly, which will easily cause the oxide film to rupture and will not play a protective role. The P / B ratio of titanium varies between 1 and 2.5 with the composition and structure of the oxide film. From this basic point of analysis, the oxide film of titanium can have better protection performance.
When the surface of titanium is exposed to the atmosphere or aqueous solution, a new oxide film will be automatically generated immediately. For example, the thickness of the oxide film in the atmosphere at room temperature is 1.2 ~ 1.6nm, and it will thicken with the extension of time. After 545 days, it gradually increased to 8 ~ 9nm. Artificially strengthening the oxidation conditions (such as heating, using an oxidizer or anodizing, etc.) can accelerate the growth of the surface oxide film and obtain a relatively thick oxide film, thereby improving the corrosion resistance of titanium. Therefore, the oxide film generated by anodic oxidation and thermal oxidation will significantly improve the corrosion resistance of titanium. Now our customers have made many similar products with our titanium rods and titanium wires, which shows that this is the way to work.
Titanium oxide film (including thermal oxide film or anodic oxide film) is usually not a single structure, and its oxide composition and structure change with the production conditions. In general, the interface between the oxide film and the environment may be TiO2, but the interface between the oxide film and the metal may be mainly TiO2. That is to say, under normal conditions, the most surface of the titanium rod we produce is TiO2, and the interface between the metal and the oxide film is TiO2. Of course, including titanium plates, titanium alloy forgings are the same, the surface of titanium alloy rods is more complicated. However, whether it is a pure titanium rod, a titanium alloy rod, or a titanium alloy wire, there are transition layers of different valence states in the middle, or even non-chemically equivalent oxides, which means that the oxide film of the titanium material has a multilayer structure. As for the formation process of this oxide film, it cannot be simply understood that titanium reacts directly with oxygen (or oxygen in the air). Many researchers have proposed a variety of different mechanisms. Workers in the former Soviet Union believe that hydride is first generated, and then a passive oxide film is formed on the hydride.