Chemical properties of titanium rods and titanium electrodes
Titanium is a very corrosion-resistant metal. Thermodynamic data for titanium indicate that titanium is an extremely thermodynamically unstable metal. If titanium can dissolve to form Ti2, its standard electrode potential will be very negative (-1.63V), and its surface will always be covered with a passivation oxide film. This causes the stable potential of titanium to be steadily biased toward positive values. For example, the stable potential of titanium in seawater at 25°C is about 0.09V. In chemistry handbooks and textbooks, a series of standard electrode potentials corresponding to titanium electrode reactions can be obtained. It is worth pointing out that in fact these data are not directly measured, but can often only be calculated based on thermodynamic data. Moreover, due to different data sources, several different electrode reactions may be represented simultaneously, resulting in different data. Strange.
Electrode potential data for titanium electrode reactions show that its surface is very active and is usually always covered with an oxide film naturally occurring in the air. Therefore, the excellent corrosion resistance of titanium comes from the fact that there is always a stable, highly adhesive and protective oxide film on the surface of titanium. In fact, it is the stability of this natural oxide film that determines the stability of titanium. Corrosion resistance, including titanium and titanium alloy titanium rods, titanium wires, titanium plates, etc., all have strong corrosion resistance. Of course, the corrosion resistance of each brand is different. We have mentioned it in previous content on the website. Okay, I won't say much today. Theoretically, 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 and cannot protect it. If this ratio is too large, the compressive stress in the oxide film will increase accordingly, which can easily cause the oxide film to rupture and lose its protective effect. The P/B ratio of titanium changes with the composition and structure of the oxide film, ranging from 1 to 2.5. From this basic point of analysis, the titanium oxide film can have relatively good protective performance.
When the titanium surface is exposed to the atmosphere or aqueous solution, a new oxide film will automatically form immediately. For example, the thickness of the atmospheric oxide film at room temperature is 1.2~1.6nm, and it thickens with time, and naturally thickens to 5nm after 70 days. After 545 days, it gradually increased to 8~9nm. Artificially strengthening oxidation conditions (such as heating, using oxidants or anodizing, etc.) can accelerate the growth of the surface oxide film and obtain a thicker oxide film, thus improving the corrosion resistance of titanium. Therefore, the oxide film produced by anodizing and thermal oxidation will significantly improve the corrosion resistance of titanium. Now our customers have used our titanium rods and wires to make many similar products, which shows that this is a feasible method.
The oxide film of titanium (including thermal oxidation film or anodic oxide film) is usually not a single structure, and the composition and structure of its oxide change with the formation conditions. Generally, the interface between the oxide film and the environment may be TiO2, but the interface between the oxide film and the metal may be dominated by TiO. That is to say, under normal circumstances, the surface of the titanium rods we produce is TiO2, and the interface between the metal and the oxide film is TiO. Of course, this includes titanium plates and titanium alloy forgings, and the surface of titanium alloy rods is more complex. But whether it is pure titanium rods, titanium alloy rods, or titanium alloy wires, there are transition layers with different valence states in the middle, and even non-stoichiometric oxides. This means that the oxide film of titanium material has a multi-layer structure. As for the process of forming this oxide film, it cannot simply be understood as a direct reaction between titanium and oxygen (or oxygen in the air). Various mechanisms have been proposed by many researchers. Workers in the former Soviet Union believed that hydride was generated first, and then a passivating oxide film was formed on the hydride.
