Rhenium is a rare refractory metal with high melting point, high strength, good plasticity and excellent mechanical stability. Its melting point is second only to tungsten, up to 3180 ℃. Rhenium has no brittle critical transition temperature. Rhenium has good creep resistance under high temperature, rapid cooling and rapid heating conditions. It is suitable for ultra-high temperature and strong thermal shock working environment. Its tensile strength at room temperature exceeds 1172 MPa, At 2200 ℃, it can still be maintained above 48 MPa, far more than other metals. Rhenium has very good thermal shock resistance at high temperature. At 2200 ℃, the engine nozzle made of rhenium can withstand 100000 thermal fatigue cycles without failure. In addition, rhenium has very good wear resistance and corrosion resistance. Its wear resistance is second only to osmium. It can maintain good chemical inertia for most gas except oxygen, will not be corroded by hot hydrogen, and its permeability to hydrogen is very low. Because of its series of excellent properties, rhenium and its alloys are widely used in petrochemical, electronic industry, aerospace and other industries. Rhenium has become one of the most important new materials in modern high-tech fields.

Application status of rhenium and rhenium alloys

1.1 petrochemical industry

Rhenium is most used as a catalyst in petrochemical industry (accounting for more than 60% of all rhenium). Because the electronic structure of rhenium is easy to release five electrons in the unsaturated 4D layer, and two electrons in the 6S layer are easy to participate in the formation of covalent bonds, coupled with its large lattice parameters, rhenium and its compounds have excellent catalytic activity, PT re was the earlier catalyst system used in the platinum reformer for manufacturing high octane gasoline, and the consumption of rhenium accounted for more than 70% of the world rhenium consumption at that time. Since the continuous catalytic regeneration (CCR) platinum reconnection process was developed by universal petroleum products, Pt RC was no longer used as catalyst in this process, and the application of rhenium decreased. However, recent reports have pointed out that the effectiveness of platinum and tin catalysts used in CCR process is not ideal, and RT. re catalytic system has been reapplied. In addition, rhenium is used as a catalyst for the production of unleaded gasoline and automobile exhaust purification; Use NH. Re04 / C was used as catalyst for cyclohexane dehydrogenation and ethanol dehydrogenation; Re207 converts S02 to S03

And a good catalyst for converting hn02 to hn03. In addition, the composite material with rhenium and rhenium alloy plated on the surface of metals and alloys can also be used for anti-corrosion and anti-corrosion in petrochemical industry, especially to prevent the corrosion of hydrochloric acid. The method of electrolytic plating rhenium on copper, brass and nickel and the method of vapor deposition 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 thermal components, anti-oxidation coatings, etc. A series of alloys with high temperature resistance, corrosion resistance and wear resistance can be made from rhenium and other metals. For example, re25-w was once the material of nuclear reactor of space station; Re PT is used as the structural material of atomic energy reactor and can resist the corrosion of hot body at 1000 ℃; Re. Mo alloy still has high mechanical strength at 3000 ℃, which can be used to manufacture high temperature and high temperature of supersonic aircraft and missiles

Strength components. Since the 1980s, the ultramet company under NASA began to study the liquid rocket engine combustion chamber with rhenium as the matrix and iridium as the coating, and has been successfully prepared and applied to the satellite attitude control engine. Ultramet also deposited metal rhenium coating on graphite matrix by CVD method to be used as gas rudder of rocket engine. Experiments show that metal rhenium can combine well with graphite or C.C matrix. Compared with other hard metal carbides, the combination of rhenium and graphite or C.C is plastic and has good thermal compatibility. Therefore, its melting point is higher than that of other hard metal carbides, and it presents chemical inertia in the presence of waste gas. Because metal rhenium also has thermal hydrogen corrosion resistance and low hydrogen permeability, it is used to make the heat exchange device of solar rocket. Through this heat exchange device, the heat energy of solar radiation is transferred to hydrogen, and then the hydrogen is sucked into the rhenium tube to generate thrust. Its maximum working temperature can reach 2500 ℃. In recent years, the amount of rhenium in Superalloys has exceeded that in catalysts, and its super heat resistant alloy has become the most important application field.

1.3 metallurgical industry

Rhenium can be used as alloy additive in metallurgical industry. Adding rhenium into the alloy can greatly improve the properties of the alloy, especially as an additive of tungsten or molybdenum, it can improve the strength of tungsten and molybdenum alloys, overcome the brittle tendency of these metals after recrystallization, improve the formability and weldability of metals, and make tungsten and molybdenum alloys have better firmness and stability. The tensile strength of molybdenum rhenium alloy is more than 2 times higher than that of pure molybdenum, there is no delamination, and the processability is also better than that of pure molybdenum. Molybdenum rhenium alloy is non-magnetic, which can be used to seal metal and glass, as protective sleeve of high-temperature thermocouple and parts of high-temperature furnace. 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 up to 3260 mpa2, its wear resistance is several times greater than pure tungsten, it is easy to weld, and the processing temperature range is wide. Adding rhenium to platinum and rhodium alloys can improve the 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 corrosion resistance, high hardness and high hot electron emission performance. They are good electrical contact materials. Even partial oxidation does not affect their conductivity. They are especially suitable for environments with high temperature and humidity. Rhenium is widely used in heating elements, thermocouples, special wires and electronic tubes because of its high temperature resistance. In this field, the most prominent application of rhenium is the manufacture of ultra-high temperature emitters. Made by Tokyo tungsten company, Japan

As a high-temperature emitter coated with rhenium based niobium, tantalum alloy and molybdenum composite system on the substrate of tungsten single crystal directional functional material, the hot electron discharge effect is increased by 20%, the current density is greatly increased, and the thermoelectric emission performance is improved. W-Re and w-th.re alloys are used as electron tube components, which can improve the strength of electron tube components and make heating wires of heaters, which can avoid damage even after recrystallization and carburization. Because of its low vapor pressure, rhenium can be used as nickel matrix cathode instead of nickel. Alloys or coating materials composed of rhenium and tungsten, molybdenum or platinum group metals are widely used in the electronic industry because of their high melting point, high resistance and good stability to the environment. Tungsten wire doped with 3% - 20% RE or coated with h4re04 is not as brittle as tungsten wire, but also can improve its elongation and resistance, and has high impact and vibration resistance. Therefore, it has shown its important applications in vacuum technology and electronic devices or filaments in places prone to vibration, such as X-ray target, flash lamp, acoustic spectrometer, high vacuum voltage measuring component, tungsten rhenium wire of aircraft bulb, etc "Lead.

Manufacturing method of rhenium device

Rhenium has a series of excellent properties and has a wide prospect in the fields of national defense, aerospace and so on. However, the preparation and processing of rhenium is relatively difficult. At present, the manufacturing of rhenium devices mainly includes electrochemical deposition, powder metallurgy, physical vapor deposition and chemical vapor deposition.

2.1 electrochemical deposition

Generally speaking, refractory metals are relatively difficult to prepare because of their high melting point. However, compared with other refractory metals, some salts of metal rhenium have good solubility, which makes it possible to prepare Rhenium by electrochemical deposition. Rhenium coating or rhenium film can be prepared at lower temperature by electrochemical method. At present, this technology has been widely used in metal industry Prepare rhenium coating on the surface. The chemical reaction equation of electrochemical deposition of rhenium can be expressed as follows:

Re04‘+4H20+7e—}ReO+80H。(1)

Re04"+4H++7 e_÷ReO+4H2 (2)

Wherein, formula (1) and formula (2) are the reaction equations for electrochemical deposition of rhenium in alkaline and acidic solutions, respectively It can be seen that when re04 is reduced to metal rhenium, it must accept 7 electrons, but in this strong oxidation atmosphere, the purity of the deposited rhenium is likely to be difficult to improve due to oxidation. In addition, the reduction of rhenium requires a relatively high potential difference, so when re04 is reduced, other reactions may occur, affecting the deposition efficiency and surface quality of rhenium Quantity and purity. Finally, the enrichment of re04 - in the cathode region during the deposition process will be strongly rejected by the cathode itself. Although rhenium coating can be obtained quickly at lower temperature by optimizing reaction parameters, such as appropriate solution concentration and deposition voltage, there are a series of shortcomings in electrochemistry, such as loose structure, poor uniformity and low dimensional accuracy of the deposited products The preparation of rhenium components such as rhenium pipes and wires is limited

2.2 powder metallurgy

Powder metallurgy is an effective method for preparing refractory metals. At present, it is widely used in manufacturing metal rhenium products. By using cold isostatic pressing powder metallurgy technology, the manufacturing time and material loss range of parts are greatly reduced. At the same time, because the wall thickness of parts can be controlled by controlling the amount of filled powder, the NT accuracy of parts is also greatly improved. Powder metallurgy The manufactured part body is heated to 1500 ℃ for pre sintering, and then heated to 2200 ℃ for final sintering. After hot isostatic pressing, the dimensional accuracy is further improved. After hot isostatic pressing, the parts with very high dimensional accuracy can be prepared by wire cutting, rough grinding, fine grinding and polishing. At present, rhenium alloy company of the United States has applied this technology The thin-walled parts with wall thickness of 4 mm can be prepared by powder metallurgy. Although some metal rhenium components can be prepared by powder metallurgy, there are considerable difficulties in powder metallurgy for structural parts with complex shape, small diameter and thin wall thickness

Both vapor deposition and chemical vapor deposition have advantages [17,1].

2.3 electron beam physical vapor deposition

Electron beams - physical vapor deposition (EB. PVD) Eb.pvd is a kind of physical vapor deposition method and an effective method for net forming rhenium products and rhenium films. Eb.pvd technology is a material preparation technology in which high-energy focused electron beam is hit on the source material in vacuum to condense the volatilized source material molecules 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 Degree, deposition time, furnace chamber pressure, distance between volatilization source and substrate, electron beam power, etc. the advantage of this technology is that the composition and structure of the coating can be flexibly controlled. When multiple volatilization sources of different components are used, coatings with different components can be obtained. Different structures can be obtained by adjusting deposition rate and deposition thickness. Combined substrate disappears The thin-walled metal rhenium component can be prepared by EB-PVD technology. In this process, a relatively thick metal rhenium plating layer is deposited on the molybdenum substrate, and finally the substrate is removed by electrochemical method.

2.4 chemical vapor deposition (CVD)

Rhenium tubes are generally prepared by chemical vapor deposition (CVD) Rational chemical vapor deposition (CVD) is a new technology that uses the principle of chemical reaction to precipitate solid substances from vapor substances and deposit them on the working surface to form coating films. Through CVD, metal rhenium films with a thickness of several millimeters can be obtained on the substrate surface. Moreover, the purity of metal rhenium prepared is very high, up to 99.99% ~ 99.999%, and its density can be reached 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. The pipe of the required size can be obtained at one time from the raw materials to avoid cumbersome processing procedures. The chemical vapor deposition rhenium pipe has few voids and defects and depends on the mold core (MO) There are fine equiaxed crystals on one side, and then coarse columnar crystals. Secondary deposition can make the columnar crystals discontinuous and achieve an ideal structure. At the same time, compared with powder metallurgy and eb.pvd, the performance of metal rhenium materials prepared by chemical vapor deposition is better. Rhenium iridium combustion chamber has been successfully prepared by Kunming Precious Metals Institute in China through chemical vapor deposition However, it is still far from being practical.

3 conclusion

At present, rhenium is mainly used in petrochemical, aerospace and metallurgical industries. 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, powder metallurgy, electronic Cambodia, physical vapor deposition and chemical vapor deposition. These four basic manufacturing methods have their own advantages, but combined with production In terms of product demand, performance requirements, preparation operability and manufacturing cost, chemical vapor deposition method should be ideal and feasible

It is the most promising manufacturing technology at present.