Rhenium is a rare and refractory metal with high melting point, high strength, good plasticity and excellent mechanical stability. Its melting point is second only to tungsten, as high as 3180℃. Rhenium has no brittle critical transition temperature. It has good creep resistance under all conditions and is suitable for ultra-high temperature and strong thermal shock working environment. Its room temperature tensile strength exceeds 1172 MPa, and it can still remain above 48 MPa at 2200°C, far exceeding other metals. Rhenium has very good thermal shock resistance at high temperatures. At a high temperature of 2200℃, engine nozzles made of rhenium can withstand 100,000 thermal fatigue cycles without failure. In addition, rhenium has very good wear resistance and corrosion resistance, and its wear resistance is second only to metal osmium. It can maintain relatively good chemical inertness for most fuels except oxygen, and will not be corroded by hot hydrogen. The permeability to hydrogen is also very low. Because of its series of excellent properties, rhenium and its alloys are widely used in petrochemical, electronic industry, aerospace and other industries, becoming one of the most important new materials in the modern high-tech field.

1.Application status of rhenium and rhenium alloys

1.1 Petrochemical industry

The biggest use of rhenium is as a catalyst in the petrochemical industry (approximately more than 60% of the total rhenium). Because of the electronic structure of rhenium, 5 electrons in the unsaturated 4d layer are easy to release, and 2 electrons in the 6s layer are easy to participate. Covalent bond is formed by the action, coupled with the characteristics of large lattice parameters, so rhenium and its compounds have excellent catalytic activity. The earlier catalyst system used in platinum reformers for the production of high-octane gasoline is Pt- Re, the consumption of rhenium used accounted for more than 70% of the world's rhenium consumption at that time. Since the United States Global Petroleum Products Corporation developed the continuous catalytic regeneration (CCR) platinum reconnection process, Pt-Rc is no longer used as a catalyst in this process, and the application of rhenium has declined. However, there have been reports recently that the platinum used in the CCR process. The effectiveness of tin catalyst is not ideal, Rt. The Re catalytic system was re-applied. In addition, rhenium is used to produce unleaded gasoline and a catalyst for car exhaust purification; NH is used. Re04/C is used as a catalyst for the dehydrogenation of cyclohexane and ethanol; Re207 is used to convert S02 to S03
And a good catalyst for converting HN02 to HN03. In addition, the surface of metals and alloys coated with rhenium and rhenium alloy composite materials can also be used for anticorrosion and corrosion resistance in the petrochemical industry, especially to prevent corrosion by hydrochloric acid. The method of electrolytic plating rhenium on copper, brass and nickel and the method of vapor deposition of rhenium on tungsten wire by decomposition of rhenium halide have been developed.

1.2 Aerospace
Rhenium is one of the most refractory metals. Rhenium and its alloy forming parts are mainly used for aerospace components, various solid propulsion heat-sensitive components, anti-oxidation coatings, etc. A series of high-temperature, corrosion-resistant, and wear-resistant alloys can be made from rhenium and other metals. For example, Re25-W was used as a material for nuclear reactors in space stations; Re-Pt was used as a structural material for atomic energy reactors, which can resist high temperatures at 1000°C. Corrosion; Re. Mo alloy still has high mechanical strength up to 3000℃, and can be used to make supersonic aircraft and missiles with high temperature and high temperature.
Strength parts. Since the 1980s, Ultramet, a subsidiary of NASA, has begun to study the liquid rocket engine combustor with metal rhenium as the substrate and high temperature and oxidation resistant metal iridium as the coating, and it has been successfully prepared and applied to satellite attitude control engines. . Ultramet also deposits a metal rhenium coating on the graphite substrate by CVD method, which is used to make the gas rudder of the rocket engine. Experiments show that metal rhenium can be very good with graphite or C. The combination of C matrix, compared with other hard metal carbides, rhenium and graphite or C. The combination of C is plastic and has good thermal compatibility, so its melting point is higher than that of other hard metal carbides, and it is chemically inert in the presence of exhaust gas. Because metal rhenium also has resistance to hot hydrogen corrosion and low hydrogen permeability, it is used to make heat exchanger parts of solar rockets. Through this heat exchanger part, the heat energy of solar radiation is transferred to hydrogen gas, and then the hydrogen gas is sucked into the rhenium tube. This generates thrust, and its maximum operating temperature can reach 2500°C. In recent years, the amount of rhenium used in superalloys has exceeded the amount used in catalysts, and its superalloy has become its most important application field.

1.3 Metallurgical industry
Rhenium can be used as an alloy additive in the metallurgical industry. Adding rhenium to the alloy can greatly improve the properties of the alloy, especially as an additive of tungsten or molybdenum, it can increase the strength of tungsten and molybdenum alloys, overcome the tendency of embrittlement of these metals after recrystallization, and improve the formability and weldability of the metal. Tungsten and molybdenum alloys have better robustness and stability. The tensile strength of molybdenum-rhenium alloy is more than 2 times greater than that of pure molybdenum, without delamination, and its processing performance is better than pure molybdenum. Molybdenum rhenium alloy is non-magnetic and can be used to seal metal and glass, as a high-temperature thermocouple protective sleeve and parts of high-temperature furnaces. Adding rhenium to tungsten alloy can improve its high-temperature performance and high-temperature ductility. W-Re alloy is harder than pure tungsten, its tensile strength is as high as 3260 MPa2, and its wear resistance is several times larger than pure tungsten. It is easy to weld and has a processing temperature range. Wider. Adding rhenium to platinum and rhodium alloys can improve wear resistance without reducing its corrosion resistance. These alloys can also be used as thermocouple materials.

1.4 Electronic materials and high temperature materials
Rhenium and tungsten rhenium alloys have good corrosion resistance, arc ablation resistance, "water cycle" erosion resistance, high hardness, and high thermionic emission performance. It is a good electrical contact material, even if it is partially oxidized It does not affect its electrical conductivity, and is especially suitable for environments with high temperature and high humidity. Rhenium's high temperature resistance is widely used in heating elements, thermocouples, special metal wires and components in electronic tubes. In this field, the most prominent application of rhenium is the manufacture of ultra-high temperature emitters. Made by Tokyo Tungsten Corporation, Japan
It is used as a high-temperature emitter that is coated with a layer of rhenium-based niobium, tantalum alloy and molybdenum composite material system on the tungsten single crystal oriented functional material substrate as the base material, which increases the thermionic discharge effect by 20% and also greatly increases the current density , Improved thermoelectric emission performance. W-Re and W-Th. Re alloy is used as an electronic tube component, which can improve the strength of the electronic tube component, and it can be used as a heater wire to avoid damage even after recrystallization and carburization. Due to its low vapor pressure, rhenium can be used as a nickel matrix cathode instead of nickel. The alloy or coating material composed of rhenium and tungsten, molybdenum or platinum group metals is widely used in the electronics industry because of its high melting point, high resistance and good stability to the environment. Tungsten wire doped with 3%---20% Re or H4Re04 coated tungsten wire is not as brittle as tungsten wire, but can also increase its elongation and resistance. It has high shock and vibration resistance, so it is in vacuum Technology and electronic devices or filaments in places prone to vibration have demonstrated their important uses, such as X-ray targets, flash lamps, acoustic spectrometers, high-vacuum voltage measurement components, and tungsten rhenium wires for aircraft bulbs.

2.Manufacturing method of rhenium device

Rhenium has a series of extremely excellent properties and has a wide range of prospects in the fields of national defense and aerospace. However, the preparation and processing of rhenium is more difficult. At present, the manufacture of rhenium devices mainly includes four methods: electrochemical deposition, powder metallurgy, physical vapor deposition and chemical vapor deposition.

2.1 Electrochemical deposition method
Generally speaking, because of its high melting point, refractory metals are relatively difficult to prepare. However, compared with other refractory metals, certain salts of metal rhenium have good solubility, which makes it possible to use electrochemistry. Preparation of rhenium by deposition method. Using electrochemical methods, rhenium coatings or rhenium films can be prepared at lower temperatures. At present, this technology has been widely used to prepare rhenium coatings on metal surfaces. The chemical reaction equation of the electrochemical deposition method of rhenium can be expressed as follows:
Re04‘+4H20+7e—}ReO+80H. (1)
Re04"+4H++7 e_÷ReO+4H2 (2)
Among them, formula (1) and formula (2) are the reaction equations of electrochemical deposition of rhenium under alkaline and acidic solution conditions, respectively. It can be seen from formulas (1) and (2) that Re04 is reduced to metal rhenium, which must accept 7 electrons, but in the case of a strong oxidizing atmosphere, the deposited rhenium is likely to be oxidized. It is difficult to improve its purity. In addition, the reduction of rhenium requires a relatively high potential difference, so when Re04 is reduced, other reactions may occur along with it, which affects the deposition efficiency, surface quality and purity of rhenium. Finally, the enrichment of Re04- in the cathode region during the deposition process will be strongly repelled by the cathode itself. Although optimized reaction parameters, such as proper solution concentration and deposition voltage, can obtain rhenium coatings relatively quickly at lower temperatures, there are a series of shortcomings in electrochemistry itself, such as loose structure of the deposited product, poor uniformity, and dimensional accuracy Low level is limited to the preparation of rhenium components such as rhenium pipes and wires.

2.2 Powder metallurgy
Powder metallurgy is a relatively effective method for the preparation of refractory metals, and is currently widely used in the manufacture of metal rhenium products. Using cold isostatic pressing powder metallurgy technology, the manufacturing time of parts and the extent of material loss are greatly reduced. At the same time, because the wall thickness of the parts can be controlled by controlling the amount of powder filled, the accuracy of the parts' NT is also greatly improved. The parts produced by powder metallurgy are heated to 1500°C for pre-sintering, and then heated to 2200°C for final sintering and then subjected to hot isostatic pressing, which further improves the dimensional accuracy. After hot isostatic pressing, the products are processed by wire cutting, rough grinding, fine grinding and polishing, which can produce parts with very high dimensional accuracy. At present, the American Rhenium Alloy Company has applied this technology to produce a wall thickness of 4 mm thin-walled parts. Although some metal rhenium components can be prepared by powder metallurgy method, there are considerable difficulties in powder metallurgy method for structural parts with complicated shapes, small diameters and relatively thin wall thickness. And in these respects, the physical
Both vapor deposition and chemical vapor deposition have advantages [17,1 cited.

2.3 Electron beam-physical vapor deposition method
Electron beam. Physical vapor deposition (EB.PVD) is a type of physical vapor deposition, and it is an effective method for net shaping of rhenium products and rhenium films. EB. PVD technology is a material preparation technology in which high-energy focused electron beams are hit on the source material in a vacuum, and the volatilized source material molecules are condensed on the substrate. The formation of the coating is divided into two steps: nucleation and growth. The deposition rate and coating thickness depend on the volatilization rate, deposition time, furnace pressure, the distance between the volatilization source and the substrate, and the electron beam power. The advantage of this technology is that the composition and organization of the coating can be flexibly controlled. In the case of using multiple volatilization sources of different components, coatings with different compositions can be obtained, and the deposition rate and thickness of the deposition can be adjusted. Different organizations. Combined with the matrix disappearance method, thin-walled components of metal rhenium can be prepared by EB-PVD technology. In this process, a thicker metal rhenium is deposited on the molybdenum matrix. Finally, the electrochemical method is used to remove the substrate, and the metal rhenium component flx 21 can be obtained.

2.4 Chemical Vapor Deposition (CVD)
The preparation of rhenium tubes generally adopts chemical vapor deposition (CVD). Chemical vapor deposition is a new technology that uses the principle of chemical reaction to separate solid phase substances from gas phase substances and deposit them on the working surface to form a coating film. Through chemical vapor deposition, a metal rhenium film with a thickness of several millimeters can be obtained on the surface of the substrate. In addition, the purity of the prepared metal rhenium is very high, reaching 99.99% to 99.999%; its density can reach more than 99.5% of the theoretical value. Due to the characteristics of chemical vapor deposition,
The application of this method has advantages for the preparation of difficult-to-process metals, and pipes of the required size can be obtained from the raw materials at one time, avoiding cumbersome processing procedures. The chemical vapor deposition rhenium tube has very few voids and defects. There are small equiaxed crystals on the side of the mold core (Mo), and then coarse columnar crystals. The secondary deposition can make the columnar crystals discontinuous to achieve a more ideal structure. form. At the same time, with the powder metallurgy method and EB. Compared with PVD and other methods, the performance of metal rhenium materials prepared by chemical vapor deposition method is better. The domestic Kunming Precious Metals Institute successfully prepared rhenium by chemical vapor deposition. Iridium combustion chamber, but there is still a certain distance from the practical.

3.Conclusion

At present, the main uses of rhenium are concentrated in the petrochemical industry, aerospace, metallurgical industry, etc. How to develop new application fields is the goal of further development in the future. The preparation methods of rhenium and its alloys mainly include electrochemical deposition and powder metallurgy. , Electronic card. Physical vapor deposition, chemical vapor deposition, etc., these four basic manufacturing methods have their own advantages, but in view of product requirements, performance requirements, preparation operability and manufacturing costs, chemical vapor deposition should be the ideal one. and also
It is currently the most promising manufacturing technology.