New processes, new technologies, and new applications for titanium
Titanium and titanium alloys possess numerous excellent properties.
1. High strength. Titanium alloys exhibit exceptionally high strength, with tensile strengths ranging from 686 to 1176 MPa, while their density is approximately 60% that of steel, resulting in a very high specific strength.
2. High hardness. The hardness of titanium alloys (annealed state) is HRC 32–38.
3. Low elastic modulus. The elastic modulus of titanium alloys (annealed state) is 1.078×10^(−1) to 1.176×10 MPa, approximately half that of steel and stainless steel.
4. Excellent high-temperature and low-temperature performance. At high temperatures, titanium alloys maintain good mechanical properties, with heat resistance far exceeding that of aluminum alloys, and a wide operating temperature range. Currently, new heat-resistant titanium alloys can operate at temperatures ranging from 550 °C to 600°C. At low temperatures, the strength of titanium alloys increases compared to room temperature, and they exhibit good toughness. Low-temperature titanium alloys can maintain good toughness even at –253°C.
5. Titanium has strong corrosion resistance. At temperatures below 550°C in air, titanium rapidly forms a thin, dense titanium oxide film on its surface. Therefore, in oxidizing media such as air, seawater, nitric acid, sulfuric acid, and strong alkalis, its corrosion resistance surpasses that of most stainless steels.
New processes, technologies, and applications of titanium
Methods for preparing titanium:
Although titanium is relatively abundant in nature, it is dispersed and difficult to extract, making it a rare metal. Currently, the preparation of titanium is divided into two main categories: thermal reduction method and molten salt electrolysis method.
Thermal Reduction Method for Producing Titanium
The thermal reduction method involves using strong reducing agents such as Li, Na, Mg, Ca, and their hydrides at a certain temperature to reduce titanium from its compounds, such as TiCl₄, TiO₂, and K₂TiF₆. Depending on the type of titanium compound, the thermal reduction method for producing titanium can be divided into three categories:
① The redox method for titanium chlorides, such as the Kroll method, Hunter method, Armstrong method, and EMR method;
② The redox method for titanium oxides, such as the OS method, PRP process, and MHR method;
③ The redox method for titanates.
Currently, only the Kroll method and Hunter method have been successfully applied in industrial production. The Kroll process uses magnesium metal to replace titanium from chlorides, while the Hunter process uses sodium metal to replace titanium from chlorides. Additionally, the Armstrong process developed by the Chicago International Titanium Powder Company in the United States has a preparation method similar to the Hunter process, also using sodium as a reducing agent to purify metallic titanium. The United States has already begun using this method for pre-production in factories.
Melted Salt Electrolysis Method for Producing Titanium
In 1959, Kroll predicted that within the next 5 to 10 years, melted salt electrolysis would replace the Kroll method as the mainstream method for producing titanium. Over the years, research institutions and laboratories both domestically and internationally have developed over a dozen new technologies for producing titanium using the melted salt electrolysis method. These can be categorized into the following three types based on raw materials:
① Electrolysis of titanates;
② Electrolysis of titanium chlorides;
③ Electrolysis of titanium oxides, including the FFC Cambridge method, MER process, USTB method, QIT process, SOM method, and ionic liquid electrolysis method, among others.
New applications of titanium
Since the 1940s, the applications of titanium have developed rapidly, and it has been widely used in aircraft, rockets, missiles, artificial satellites, spacecraft, naval vessels, the military industry, medicine, and the petrochemical industries. Recent research has found that the human body contains a certain amount of titanium, which stimulates phagocytes and enhances immune function. Therefore, many laboratories are currently focusing on the development and application of bio-titanium.