Mechanical alloying
Mechanical alloying is a powder preparation process in which metal or alloy powder is produced repeatedly by cold welding and fracture of powder particles through long-term intense impact and collision between powder particles and grinding ball in a high-energy ball mill, leading to the diffusion of powder atoms, so as to obtain powder. Mechanical alloying to prepare titanium and titanium alloy powder is to load titanium compound or mixed powder and development medium (usually need to add a small amount of process control agent) into high energy ball mill (argon gas protection) for grinding. In the grinding process, the powder particles are continuously grinding and gradually mixing through the continuous process of repeated welding - fracture - welding, so as to produce very fine powder particle size. The advantage of this process is that the grinding materials can be matched in any proportion, which can prepare alloy material or single metal powder.
Hydrogenation dehydrogenation method (HDH)
HDH is a process to prepare titanium powder by using the reversible properties of titanium and hydrogen. After hydrogen absorption, titanium will produce brittleness, which will be mechanically broken into titanium hydride powder and then dehydrogenated to produce titanium powder under vacuum condition at high temperature. The titanium powder produced by this process has a wide range of particle size, low cost and low requirement for raw materials, so it has become the main method of titanium powder production at home and abroad, but the titanium powder prepared by this method has a high content of O and N. In recent years, the research on the preparation of low cost and low oxygen content titanium powder is increasingly active at home and abroad.
Atomization method
Atomization method is a method of breaking liquid metal or alloy flow into tiny droplets, and then cooling and solidification in the environment to obtain metal powder. At present, titanium powder can be prepared by atomization method mainly by gas atomization method and centrifugal atomization method.
Gas atomization method
Gas atomization method is generally used to melt raw materials in a crucible, through the nozzle at the bottom of the crucible with high-speed gas to produce metal molten spray into a spray, condensed into metal powder.
Centrifugal atomization method
The centrifugal atomization method is used to make titanium powder by means of the centrifugal force generated by rotation, the metal is broken and thrown out in the form of mist droplets, and then the high purity spherical titanium powder is solidified. At present, centrifugal atomization methods mainly include rotating electrode method (REP), plasma rotating electrode method and electron beam rotating disk method (EBRD).
The titanium powder obtained by centrifugal atomization is spherical with smooth surface, relatively dense, good fluidity, narrow particle size distribution, and the particle size can be adjusted by rotating electrode speed. Compared with the powder prepared by gas atomization, the powder prepared by rotating electrode process does not have the common associated phase in atomized spherical titanium powder, and the powder particle size is more uniform. However, the titanium powder produced by this method has a high cost and is generally used in the field of aerospace.
Thermal reduction of metal
The traditional metal thermal reduction methods for preparing titanium powder mainly include TiO2 calcium thermal reduction method and TiCl4 metal thermal reduction method. TiO2 calcium thermal reduction method is to prepare titanium powder by reducing TiO2 with metal calcium at high temperature. TiCl4 metal reduction methods include magnesium reduction method (Kroll method) and sodium reduction method (Hunter method). The titanium powder prepared by magnesium reduction method is mainly the isoexternal titanium powder produced in the process of preparing sponge titanium. Due to the high content of impurities, it is rarely used in the production of titanium powder. The titanium powder prepared by sodium reduction method has high purity, especially low content of oxygen, nitrogen, iron and carbon impurities, and good fluidity. It is one of the promising methods for producing titanium powder.
Molten salt electrolysis method
Similar to other active metals the preparation of titanium powder by electrolysis must be carried out in molten salt medium. The traditional method of molten salt electrolysis is to dissolve titanium salt in molten salt. Dow-Howmet and Timet of the United States built two electrolytic production lines respectively, but they were terminated because they could not control the reverse reaction of titanium and chlorine. At present, Ginatta Company in Italy has built a large test plant in Torino city to continue the research of this process, and put forward the diaphragm free electrochlorination and fluorination.
