Titanium is a very corrosion-resistant metal. 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. In this way, the stable potential of titanium is stably biased toward a positive value. For example, the stable potential of titanium in seawater at 25 ° C is about + 0.09V. In chemistry handbooks and textbooks, standard electrode potentials are obtained that correspond to a series of titanium electrode reactions. It is worth pointing out that, in fact, these data are not directly measured, but often can only be calculated from thermodynamic data, and because of different data sources, several different electrode reactions that may be represented at the same time, different data are not Strange.
The electrode potential data of the electrode reaction of hafnium titanium shows that its surface is very active, and it is always always covered with an oxide film naturally generated in the air. Therefore, the excellent corrosion resistance of titanium stems from the fact that a stable, highly adherent, and particularly well-protected oxide film always exists on the titanium surface. In fact, the stability of this natural oxide film determines the titanium Corrosion resistance, including titanium and titanium alloy titanium rods, titanium wires, titanium plates, etc. have strong corrosion resistance, of course, the corrosion resistance of various brands is different, we said in the previous content of the website Yes, not much to say 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 correspondingly, which will easily cause the oxide film to rupture and fail to provide protection. The P / B ratio of titanium is between 1 and 2.5 with the composition and structure of the oxide film. From this basic point of analysis, the titanium oxide film can have better protection performance.
When the surface of titanium is exposed to the atmosphere or an aqueous solution, a new oxide film is automatically generated immediately. For example, the thickness of the oxide film at room temperature is 1.2 ~ 1.6nm, and it increases with time, and naturally thickens to 5nm after 70 days After 545 days, it gradually increased to 8-9nm. Artificially enhanced oxidation conditions (such as heating, oxidizing or anodizing) 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 oxidation film formed by anodization 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, showing that this works.
The oxide film (including thermal oxide film or anodic oxide film) of hafnium titanium is usually not a single structure, and the composition and structure of the oxide vary with the generation 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 TiO-based. That is to say, under normal conditions, the titanium rod we produce is TiO2, and the interface between the metal and the oxide film is TiO. Of course, including titanium wire, titanium plate, and titanium forgings are the same. The surface of titanium alloy rods is more complicated. However, no matter whether it is a pure titanium rod, a titanium alloy rod, or a titanium alloy wire, there are transition layers of different valence states, or even non-chemically equivalent oxides, which indicates that the oxide film of titanium material has a multilayer structure. As for the formation of this oxide film, it cannot be simply understood as the direct reaction between titanium and oxygen (or oxygen in the air). Many researchers have proposed various mechanisms. Workers in the former Soviet Union believed that hydrides were formed first, and then passive oxide films were formed on the hydrides.
