In addition to oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium, titanium ranks ninth in the earth's reserves. Its reserves are about 0.44%~0.57%, which is a relatively abundant element. In its pure state, titanium is silvery white in color, has metallic luster, and has a very high melting point. It is a relatively insoluble metal. Titanium has two isomers: α-Ti and β-Ti. α-Ti has a close-packed hexagonal structure and can only remain stable below 882°C. When it exceeds 882°C, α-Ti will transform into β-Ti. Ti and β-Ti have a body-centered cubic structure and can remain stable between 882°C and 1678°C.
Titanium has been receiving widespread attention since its discovery. Scientists have never stopped researching and exploring it. Now we have a deeper understanding of the properties of titanium. Titanium and titanium alloys have many advantages, such as high density and high specific strength. , corrosion resistance and high-temperature resistance, good mechanical properties, lightweight, etc. They have developed rapidly with these excellent properties and have been widely used in various industries, such as the chemical industry, aerospace, medical materials, electronics industry, and other fields. Compared with other metals, titanium also has excellent biocompatibility and is very close to the elastic modulus of the human femoral head. Therefore, the use of titanium in the preparation of biomaterials is of great help in the treatment of certain human diseases.
Although titanium and titanium alloys have advantages that other metals cannot match, with the progress of society and the development of science, their own properties can no longer meet the needs of human production and life. How to modify them to overcome the limitations of their use It has become an urgent problem to be solved. Compared with traditional materials, nanomaterials have superior properties. Therefore, people think of applying nanotechnology to titanium and titanium alloys to make it more widely used. Nowadays, the cost of directly preparing nanomaterials is high, the output is small, and the standards for equipment and materials are strict. However, surface nanotechnology has relatively low requirements for equipment and other hardware conditions, low cost, and simple and mature operating technology. To a certain extent, it can meet production needs, so titanium and titanium alloys are directly surface nanometered to enhance or improve their performance and enhance their application value.
There are many methods for surface modification of titanium and titanium alloys, such as sol-gel method, hydrothermal method, template method, anodizing method and electrochemical deposition method. Among these many methods, anodizing treatment on titanium and titanium alloys is a simple and effective surface treatment method. Compared with other methods, this method is simple to operate and low-cost. So here is a summary of this surface treatment Give a brief description of the method.
Anodizing is an electrochemical method that produces an oxide film on metal or alloy. After preparing the plating solution in advance, the test piece is placed in it. By setting the voltage or current, the surface of the test piece is anodized to produce an oxide film. , and for metals such as titanium and its alloys, a group of TiO 2 nanotubes with controllable length and diameter can be obtained by adjusting the concentration of the electrolyte, the size of the voltage and current, and the length of the reaction time, thereby achieving experimental results. The surface of the part is nanosized. These tubes grow from the surface of the specimen base and are closely combined with the base. The experimental principle of using anodization to prepare TiO 2 nanotubes on the surface of titanium and titanium alloys is summarized. There are two important reactions:
Ti+2H 2O＝TiO 2+4H ++4e (this process actually includes 2H 2O→O 2+4e+4H +Ti+O 2→TiO 2)
TiO 2+6F -+4H +＝[TiF 6] 2-+2H 2O
By observing the reaction formula, we can see that it mainly includes two reaction processes: one is the formation process of TiO 2, and the other is the dissolution process of TiO 2. The formation of TiO 2 is carried out in an electrochemical environment, while the process of dissolving TiO 2 is a chemical reaction. Through the cycle of these two reactions, nanotubes are finally produced. The current also plays a key role in the anodizing reaction. If divided according to current and time, the production of TiO 2 nanotubes can also be divided into three stages, as shown in the current density-time curve of the anodizing process in Figure 1.
Figure 1 Current density-time curve during the anodization process
In the first stage, the TiO oxide layer is formed, and the reaction has just started. The resistance is small and a huge current is generated. A TiO film is formed on the surface of Ti. We call this film a barrier layer; the second stage is generated by the first stage. The barrier layer of the TiO film begins to dissolve. When the barrier layer reaches a certain thickness, the current in the circuit slowly returns to a stable state. At this time, the TiO film partially dissolves and produces many small holes; in the third stage, TiO nanotubes are formed, and from the second stage The micropores formed in this stage cause the uneven surface potential of the specimen. The electric field is mostly concentrated in the low recesses of the holes, which accelerates the oxidation in this area. The Ti 4 produced by the oxidation reaction moves the oxide layer as the reaction continues. , causing the oxide layer to dissolve, while the oxide layer at the top of the nanopore dissolves slowly, and the oxide layer caused by the electric potential at the bottom of the hole dissolves quickly, so the originally generated small micropores continue to dissolve and extend to gradually produce nanotubes. As the reaction time increases, With the increase, the dissolution reaction speeds at the bottom of the hole and the top of the hole gradually become consistent, and the length of the nanotube remains unchanged.
The development of science and technology continues to advance, and the level of social civilization continues to improve. With the advancement of science and technology, the application fields of titanium and titanium alloys are expanding day by day, and people's requirements for material properties are further improved. Titanium and titanium alloys will move towards high-temperature resistance and higher strength. , more excellent plasticity, better wear resistance, and titanium alloys with comprehensive properties will also be produced. Titanium alloy surface treatment technology will develop in a more advanced direction. Titanium alloys that have undergone surface nano-treatment have surface resistance The friction performance, acid resistance, and corrosion resistance will also be further improved. In the new era, titanium and titanium alloys will definitely achieve greater development.
