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I. 铌 : From ore to complex products
(1) 铌 market
In 1999, 87.60% of the world production of niobium (Nb 50.6M1b) are used to produce high-strength low-alloy (HSLA), made of stainless steel niobium iron raw materials. About 2% is used to produce special alloys such as NbTi, NbZr and NbCu, and 10% is used to produce chemical products such as Nb 2 O 5 , NbCL 5 and vacuum FeNb, NiNb.
Table 1 铌 Product Delivery Form 1990-1999
(2) Production of niobium alloys and niobium compounds
Niobium alloys such as FeNb supplied to the steel and stainless steel industries are mainly produced from pyrochlore concentrates, while niobium compounds in the non-ferrous metal market are mainly produced from coltan, coltan, rutile and tin slag.
Obtaining and process of pyrochlore concentrate powder:
The content of 50% to 60% of Nb 2 O 5 is produced by carbonized or weathered pyrochlore by reasonable steps such as crushing, grinding, magnetic separation and flotation. The pyrochlore mine from Araxa can be directly used for the production of ferroniobium. Most pyrochlore concentrates are pretreated by chemical treatment before they are obtained. Usually, even Araxa concentrates should be removed first. Pb, P and S .
(3) Production process of bismuth iron
FeNb past pyrochlore product is produced by aluminum thermal reduction. Since 1944, the production of niobium iron began to be produced in electric arc furnaces. This has improved the process control, strengthened the control of gas impact, increased production capacity, and greatly reduced aluminum consumption.
Production process for the production of niobium compounds and alloys from coltan and coltan in the non-ferrous metals market.
Both hydrazine and hydrometallurgical bismuth compounds and bismuth alloys are available for both the chlorination process and the hydrometallurgy.
(4) Chlorination method
The chlorination process is a production process that has been replaced by an extraction process. It is now mainly used for the treatment and production of tantalum waste and FeNb alloys. The reduction of ore concentrate by chlorination has been abandoned because hydrometallurgy is simpler and more economical.
As shown in Fig. 1, the niobium-containing waste and the niobium iron are smelted together in NaCl-FeCl 3 to chlorinate the product NaCl-FeCL 3 . The reaction process is as follows:
FeNb+NaCl+7NaFeCl 4 -NbCl 5 +8NaFeCl 3 (1)
8NaFeCl 3 +4Cl 2 -8NaFeCl 4 (2)
Figure 1 Process for the preparation of ruthenium compounds by chlorination
The reaction temperature is 500 ~ 600 ℃, and volatile products TiCL 4 SiCL 4 volatiles in a molten salt pool, NbCL 5, TaCL 5 and WoCL 4 deg.] C having a boiling point between 228 and 248 deg.] C, and these compounds must be separated by distillation, chloro ferroalloy It can produce a large amount of very pure barium chloride. This pure chloride can be hydrolyzed by steam to produce high-purity cerium oxide or further produced with alcohol to form alkoxide. NbCL 5 contains not more than 5ppm bismuth and 1 to 2ppm of other metal impurities. .
(5) Wet production process of bismuth compounds
Most of the ruthenium and osmium compounds are now produced by a fluorination process, including the solution extraction process shown in Figure 2.
FIG wet tantalum and niobium production process 2
Both coltan and coltan, whether enriched in natural form or from dross, undergo HF acid decomposition at a specific temperature, and the symbiotic elements and strontium co-dissolve in the form of H 2 NbF 7 and H 2 TaF 7 After filtration and impurity removal (alkaline fluoride and rare elements), the liquid phase is extracted with an organic phase such as MZBK in a continuous mixing tank or mixing column containing HF acid, and is retained in the organic phase, and the impurity elements are as Fe, Mn, Ti, etc. remain in the aqueous phase and the residual liquid.
The organic phase has a content of Nb 2 O 5 +Ta 2 O 5 of 150-200 g/l, and the organic phase is usually 6-15 N, and then selectively extracted or backwashed with H 2 O or H 2 SO 4 solution, and the aqueous phase contains Fluoroantimonic acid and residual HF acid, while fluoroantimonic acid remains in the organic phase. The ruthenium containing liquid contains a small amount of MIBK and a small amount of hydrazine extracted together.
The organic phase enters the next Ta/Nb extraction step. Precipitation is carried out by introducing ammonia or liquid ammonia into the mash to obtain Nb(OH) 5 . The organic phase is extracted or washed with steam, water or dilute ammonia. Ta(OH) 5 is precipitated from ammonia gas, or potassium salt is added to the mash to form K 2 TaF 7 .
The precipitation of oxides can be produced batchwise or continuously. The hydroxides are filtered and dried at 1100 ° C or higher. Different applications require different particle size distributions, and there are different precipitation, drying and roasting conditions. Due to the different quality requirements, direct or indirect roasting in the heating chamber or converter, the furnace composition has a great influence on the purity of the oxide. For example: Inconel furnace impurities will bring Ni and Cr, so that after a reasonable process control tantalum and niobium products are high yield (> 95%) and high purity (> 99.9%), these advances have the following ways:
1. Improve process control conditions
2. Precisely control and monitor process parameters such as content, acidity and flow
3. Improve the use of equipment such as flow control equipment, special materials equipment such as reinforced plastic or special ceramic lining drying and roasting equipment
4, the use of precision analytical instruments, such as GDMS
   Second, bismuth compounds
Antimony compounds account for only about 10% of the entire plutonium market. Commercialization has been achieved in a variety of different applications in electronics. In its applications, applications as catalysts, optical glass, coatings, etc. are as important as metal powders in capacitor applications.
铌 can be subdivided into single crystal, dielectric ceramic, piezoelectric ceramic and ferrite applications in electronics.
Different qualities of niobium oxide are commonly used as base materials, while for commercial compounds such as barium chloride or ethoxylated cesium, only a small portion of the market is considered.
(1) Application of bismuth compounds
Lithium niobate : In the production of lithium niobate single crystal, Nb 2 O 5 is required to have a high purity (>99.99%), although this quality requirement can be easily obtained in the chlorination process, but with the wet process Continuously improved, the high purity Nb 2 O 5 produced by wet process can also be selected.
Integrated optical circuits and surface acoustic wave devices account for the bulk of the lithium niobate market.
Production of lithium niobate single crystal: LN single crystal is produced by the Zhuoclahl method. Nb 2 O 5 and LiCO 3 are mixed and pre-reacted to form LN polycrystals, in order to pull out uniform crystals, and control the ratio of components in LiNbO 3 .
The polycrystal was placed in a platinum crucible, placed in a refractory chamber and heated by radio waves (at 1253 ° C), and a rotating seed crystal was placed under the LiNbO 3 bath and the monomer was slowly pulled out. The single crystal is then sliced ​​and polished to the desired form.
Figure 3 Method for producing LN and LT single crystals by Czochralski method
Surface acoustic wave device (SAW): A set of metal electrodes are attached to a crystal piece by vacuum deposition to form a surface acoustic wave filter. They act as input and output poles for surface waves, and the signals are adjusted to different forms as they pass through the filter. SAW devices are commonly used in televisions, game consoles, video recorders, and military applications such as encoders/decoders. The growth of mobile phones in recent years has also contributed to the growth of the LN market, while lithium niobate (LN) has also shared a portion of the market, but he is mainly used for bandwidth at high frequencies.
Integrated optical circuit: The integrated optical circuit consists of one or more optical components such as optical modulators. Optical modulators allow light to travel in the desired direction. LN is also used in other applications such as amplifiers, wavelength filters, converters and amplitude modulators. Their propagating signals are light relative to electronic integrated circuits. The use of light to propagate signals has weight reduction, multiplex transmission (waves of different wavelengths can be synchronized and independently propagated), no crosstalk (no mutual electromagnetic induction, high reliability, and faster propagation speed than electrons in wires and large broadband. Max. The advantage is low loss and the ability to propagate millions of signals in the same fiber.
In the signal compilation and propagation, there must be an amplitude modulator inside and outside, and the internal amplitude modulator controls the opening and closing of the optical path. This leads to instability of the wavelength and ultimately reduces the propagation distance. To avoid this problem, the LN modulator is externally adjusted to ensure its quality. WDM (wavelength packet multiplexing) requires long-distance transmission, TDM (multi-time division) Road transmission) also requires long distance transmission.
Dielectric Ceramics: Usually capacitors are used to store energy. He is made up of two plates. Its energy storage capacity is given by the following equation.
C=KA/d
The size of the capacitor (C) is determined by the area of ​​the two plates (A), the thickness of the dielectric layer (d), and the dielectric constant (K). Due to space limitations, increasing the capacitance is achieved by reducing the thickness of the dielectric layer or using a material with a high dielectric constant. Table 2 shows the dielectric constants of the different materials.
Table 2 Dielectric constants of the same materials
Material
Dielectric constant (K)
air
1
lead
10
water
81
Titanium dioxide
100
Potassium citrate
700
Barium titanate
4000
Improved barium titanate
10000
Lead magnesium citrate
20000
The difference between PMN and BT is a high dielectric constant and a low sintering temperature, and the sintering temperature is lower than 1000 ° C, so that the silver palladium electrode replaces the pure palladium electrode, thereby saving the cost.
Unfortunately, the production of PMN is difficult because a "green stone phase" with a lower dielectric constant replaces the desired "ptrowskite" phase formation during sintering. The HC Starck development therefore changed the process to produce PMN, preventing the formation of undesirable phases.
However, in the MLCC'S, the electrode of the ruthenium compound is changed from pure palladium or Ag/Pd to Ni. The Ni electrode needs to be reduced in sintering, which makes it impossible to add ruthenium oxide. The substitute is a rare metal oxide. In addition, leaded products such as PMN may also be banned for environmental reasons.
Piezoelectric ceramics: In order to comply with the use of the electronic field, the required properties of piezoelectric ceramics are changing. Conversely, in order to comply with the pressure, they must prevent electron polarization (polarization). Therefore, pressure ceramics convert electrical energy into chemical energy or chemical. Can be converted into electrical energy. So they can be used as:
1. High pressure control
2, mechanical vibration detection
3, the application of voltage control pressure
4, frequency control
5, sound wave or ultrasonic generation
Common applications include ultrasonic cleaning from buzzers, filters, firearms, and sonar devices. Recently, the automotive industry has applied it to sensors for piezoelectric actuation and braking systems of fuel injection systems.
PMN shows excellent dielectric flexibility, but because of its high cost, it is limited in use with high precision. Optical advances have been enhanced by the use of PMN actuators on the Hubble telescope. Lead zirconate titanate (PZT) is now widely used and replaces previously used BT in items b), c) and e). PZT is a relatively high and relatively inexpensive material in piezoelectric applications. However, the characteristics of the piezoelectricity need to be adapted to the application, because
This needs to be mixed. PZT has a perovskite structure ABO 3 , and A and B ions can be partially replaced by higher (donor) or lower (recipient). Nb 5 + usually replaces Ti 4 + (more processed, high DK and Dielectric loss), as opposed to base Pb2+ (hard treatment, low DK and low loss). A typical example is the incorporation of bismuth into PZT ceramics as a sensor assembly for ultrasonic testing of machines. For cerium oxide or cerium oxalate, several such as potassium citrate, nickel ruthenate, titanium ruthenate, etc., which are produced by HC Starck, can be used as dopants.
Ferrite: Ferrite is the magnetic material of ceramic materials. It can be divided into hard (permanent magnetism) and soft (temporary magnetism) according to its magnetic properties. The matrix of soft ferrite is MnZn and NiZn. The main application of ferrite is in transformers and inductors, energy conversion and suppression in telecommunications, where new ferrites must meet high efficiency requirements. In addition, cerium oxide or lanthanum oxalate also increases the magnetic properties of its ferrite, such as by affecting its particle size growth and particle size concentration to change its energy loss, electrical resistance and magnetic residence rate. Therefore, the additional cerium compound enters the soft ferrite to ensure its High quality requirements. However, the basic principle of the additional enthalpy remains unclear.
Catalysis: Cerium oxide can be used as a different catalyst due to its acidity and oxidizability. Recently, a number of patented and disclosed ruthenium compound catalysts have emerged. For example, catalytic oxidation of propylene to propylene oxime has been achieved. The molecular acceptor of ruthenium is 0.1 under mixed metal oxidation catalysis, and the main composition is Mo. In order to obtain all the elements of the same type of mixture, a soluble complex is required, so HC Starck increases the quality of yttrium oxalate to replace cerium oxide.
Recently, antimony compounds have been used less in catalysts. However, academic and applied research for the development of industry is still very active, so the use of antimony compounds as catalysts will continue to grow.
Coatings: Titanium-based yellow coatings are nickel strontium titanate and strontium titanate. These coatings compete with cadmium yellow coatings and lead-based yellow coatings. However, their use will be harmful to the environment and human health, because lead, cadmium and antimony are poisonous. One solution is to replace niobium with niobium strontium titanate and chrome titanate. The potential of bismuth oxide has so far been difficult to estimate.
Optical glass: In special lenses for cameras and photocopiers, high refractive index and light weight are desirable. The addition of 30% high-purity cerium oxide and cerium oxide can achieve higher refraction and is less affected by the environment. The weight increase of cerium oxide is the same as that of cerium oxide, which is important for the competition with plastic lenses. However, a slight yellow light does limit its application.
Metal bismuth and bismuth based alloys: pure metal bismuth and bismuth based alloys account for only 2.5% of the world market output. The growth in the late 1990s was mainly due to the new ion accelerators. A total of 400 tons of titanium alloy was required at Cern's Large Hadron Collider. And 23t pure metal enamel.
Table 3 Freight volume of niobium and niobium based alloys (t)
Application of metal bismuth
Most metal ruthenium is used in the production of ruthenium based alloys and high purity ruthenium oxide. Other pure metal ruthenium applications are as follows:
1. Corrosion resistance (loss of cathodic protection anode ICCP)
2, high temperature parts (furnace)
3. Medical application (surgical transplantation)
4, sputtering target (glass and electronics industry, shaving knife)
5, electronics applications (electrolyte capacitors, permanent magnets)
6. Nuclear weapons components (fast electronic response)
(2) Production of metal bismuth
A number of niobium production processes are described in the literature, however, they cannot be used in industrial production due to their uneconomical, low product purity and the like. The most important raw materials for these production processes are:
1. Niobium oxide (Nb 2 O 5 )
2. Potassium fluoroantimonate (F 2 NbF 7 )
3. Barium chloride (NbCl 5 )
4. Alkoxide (Nb(OR) 5 )
(3) Reduction of cerium oxide
Aluminothermic/magnesium thermal reduction: Most bismuth metals (>90%) are produced by aluminothermic reduction of yttrium oxide
3Nb 2 O 5 +10Al→2Nb+5Al 2 O 3
The high-purity cerium oxide (>99.5%) is mixed with the aluminum metal powder and then reduced after being ignited in a vertical device. Usually, the excess aluminum-formed yttrium aluminum alloy (31.32) ATR (aluminothermic reduction) product is used as an electric arc furnace to produce high-purity lanthanum (33) from vacuum or electron beam production. The excess coefficient of aluminum determines the yield of bismuth. And its oxygen content can also be reduced in the same manner with an alkali metal such as magnesium.
Nb 2 O 5 +5Mg→2Nb+5MgO
However, although it is known that an alkali metal or hydrogen can be used to reduce cerium oxide, none of these processes are applied to industrial production.
Carbothermal reduction: multi-stage process can reduce cerium oxide by carbon
Nb 2 O 5 +5C→2Nb+5CO
Nb 2 O 5 is mixed with carbon and then compressed into tablets, which are reduced by a two-step process in a vacuum furnace to produce a base metal (direct reduction). In the first stage, the oxide is 15% more than the theoretical amount. In the second stage, excess oxide is reduced with an excess of reducing agent and the mixture is heated in a vacuum oven at a high temperature (~2000 ° C) to complete the reduction reaction.
Another process (indirect reduction) in the first stage is to reduce the formation of niobium carbide by heating a mixture of Nb 2 O 5 and carbon black or graphite in a vacuum furnace. In the second phase. The resulting NbC and pure Nb 2 O 5 were pressed and heated in a vacuum oven at a high temperature (~1950 ° C) to form a base metal (41.43).
Nb 2 O 5 +7C→2NbC+5CO
Nb 2 O 5 +5NbC→7Nb+5CO
Generally, the base metal formed by the pure Nb 2 O 5 initially contains only carbon and oxygen (such as NbC, Nb 2 O 5 , NbO 2 , NbO), and can be refined and purified by a further high temperature process (electron beam melting).
Some changes were made in the carbothermal reduction of Nb 2 O 5 : in the first stage, the mixture of Nb 2 O 5 and carbon black after pressing was reacted with ammonia at approximately 1570 ° C to form NbN in a production furnace. This mixture decomposes at a higher temperature (~2100 ° C) to form a base metal. The main advantage of this process is that nitriding and denitrification can be done in a single step without any intermediates, no matter how successful the process is in small experiments, it is not used in industrial production.
Nitrogen reduction: Niobium is formed by reduction of Nb 2 O 5 in three stages by ammonia. In the first stage, cerium oxide is treated with ammonia at 650 ° C to 850 ° C to form an oxynitrate phase, and the oxynitrate phase is The ammonia is further reacted at a high temperature (1100 to 1500 ° C) to form cerium nitrate. In the final stage, cerium nitrate is decomposed in a vacuum furnace at about 2000 ° C to form a reduction of the cerium metal halide and the alkoxide.
Hydrogen reduction: In the past, base metal was usually obtained by reducing NbCl 5 with hydrogen. Today, there are many ways to reduce NbCl 5 with hydrogen. No matter how high the purity of the base metals obtained by these methods, none of these methods are now used for large-scale production. Due to their high cost, hydrogen reduction of antimony halides and decyl alkoxides is limited to specific needs, such as the preparation of tantalum flakes by chemical vapor deposition (CVD).
Metal thermal reduction: Reduction of potassium fluoroantimonate (F 2 NbF 7 ) does not resemble the production of hydrazine products and does not give industrial significance. Since the product contains more F 2 salt and has strong water absorption, it leads to the formation of highly corrosive fluorooxophosphate (such as F 2 NbOF 5 ).
Metal thermal reduction of NbCl 5 with sodium, magnesium and zinc has also been reported, however, these methods have no industrial prospects.
Electrochemical Reduction: Very pure ruthenium can also be obtained by electrochemical reduction of NbCl5 or K2NbF7 from an oxygen-free molten salt system (eg KCl-NbCl, KCl-KF, etc.), however, these systems are current inefficient and highly corrosive. . Moreover, these methods are not likely to be used in industrial production for the most extensive range of knowledge we currently have. However, academic interest and research activities on electrolysis remain at a high level (62-66).
Capacitor grade tantalum powder production process
The solid electrolytic capacitor includes a porous tantalum metal sintered tube (anode) embedded in a twisted wire and an irregular Ta 2 O 5 insulating layer which is anodized at the plane of the tube. The porous body of the anode is filled with a cathode material (such as MnO 2 , a conductive polymer), the cathode is connected by wires and sealed with an epoxy resin, and FIG. 4 is a general design of a chip tantalum capacitor.
Figure 4 Chip capacitor design
In the last forty years, the goal of numerous studies has been to find alternatives to electrolytic capacitors. Logical alternatives are usually 铌 because of their similar chemical properties. In addition, although the growth rate of the oxide per volt (Nb 2 O 5 - 2.9 nm / v, Ta 2 O 5 - 1.9 nm / v) can be partially ignored. The random ruthenium pentoxide has a higher dielectric constant relative to Ta 2 O 5 (Nb 2 O 5 is -42, and Ta 2 O 5 is -27). In the late 1950s, due to the shortage of resources, the former Soviet Union began to manufacture tantalum capacitors in order to meet the needs of the military. However, at the time, the production conditions were not satisfactory, and only low purity and low specific surface area tantalum powder could be produced. This leaves the powder as a capacitor material leaving a broader international market. The replacement of solid electrolytic capacitors by tantalum powder must meet very complex requirements:
1. High chemical purity (>99.9%), especially for "harmful" elements such as C, Fe, Cr, Ni, Al, Na, F
2, high specific surface area to store high power
3, open pore structure to make the pre-electrode better sealed
4, small particle distribution range and good flow capacity to meet the application of automatic high-speed extrusion
5, powder and silk have good sintering properties
Figure 5+6 Magnesium vapor reduction to obtain the form of tantalum powder
The main problem with the application of magnesium thermal reduction is that it has a strong heat absorption property, which is difficult to control. After the mixture of reduced metal of cerium oxide is burned, the reaction proceeds rapidly and reaches a very high temperature (>1000 ° C) in a few seconds. Since it is difficult to control at high temperatures and pressures, for example, due to the requirement for better temperature rise, this requires higher reactor materials. In particular, for batch reproducibility, a narrower particle size distribution is required. For these reasons, all of the mentioned processes are unable to produce high performance high purity tantalum powder to meet the needs of capacitors. In contrast, heating magnesium to reduce Nb 2 O 5 with magnesium vapor is easier to control. A key step in the new process has recently been developed at HCStarck to produce very pure tantalum powder (purity close to 99.9%) with a unique, spongy specific surface topography (Figure 5+6).
In addition, this new process can be produced in a number of different forms of equipment, such as tube furnaces, suspended bed reactor converters, and the like. As shown in Figure 7, according to the required powder characteristics (purity, physical properties, etc.), reduction of Nb 2 O 5 to prepare tantalum powder or in one step, two steps (by means of Nb 2 O 5 ) or three steps (by means of Nb 2 O 5 and NbO) is completed.
Figure 7 Production process of capacitor grade tantalum powder
The specific surface area of ​​the tantalum powder produced by this process has a large variation range, which will affect the specific volume of the powder. The physical properties of this new powder are very close to that of capacitor grade tantalum powder (flow properties, bulk density, etc.), for which reason they can be produced using the same equipment and processes used to produce tantalum capacitors.
The new glutinous rice characteristic parameters are shown in Table 4.
Table 4 Characteristic parameters of magnesium steam reduction to extract bismuth powder
Recently, many capacitor manufacturers have placed extremely high evaluations on these powders and have experimented with the feasibility of producing good solid electrolytic tantalum capacitors with high specific volume and low leakage. Tantalum capacitors have a lower volume than aluminum electrolytic capacitors. Due to the requirements on the surface of the capacitor, tantalum capacitors will hope to replace OS-CON-type aluminum capacitors with better stability and smaller size.
Recently, two major improvements have been made to the new meal in the HC Starck laboratory. First, the ruthenium anodized oxide film is treated with vanadium , which improves the characteristics of the insulating layer compared to the pure ruthenium oxide film. In addition, by means of impedance spectroscopy and calculation of the Schottky-Mott diagram, it was found that the oxygen vacancy density in the oxide layer produced after the ruthenium anodization after treatment with vanadium was reduced and almost the same as the Ta 2 O 5 layer. For this reason, the vanadium-treated anodized tube indicates that there is no specific BIAS function relationship for the crucible (as shown in Figure 8).
Fig. 8 Deviation relationship between Ta, Nb and Nb doped V anode capacitors
The second finding is that the specific volume of the new bismuth powder and bismuth is significantly increased after alloying. For example, the Nb-25Ta alloy powder prepared by reducing Nb 2 O 5 /Ta 2 O 5 with gaseous magnesium shows that its specific specific volume is more than twice that of the equivalent surface area pure tantalum powder, and it is found to adhere to Nb 2 O 5 and Ta 2 O. The growth ratio of these alloy insulating oxide layers between 5 was 2.4 nm/v, and the dielectric constant (Σ~65) of the mixed oxide Nb 2 O 5 /Ta 2 O 5 was significantly higher than that of pure Nb 2 O 5 .
  Five, the refinement of 铌
For most applications, the crude ruthenium metal produced by the reduction method as described above must be refined in order to remove the raw material or impurities introduced during the treatment stage. Usually, high temperature treatment is used to remove most of the impurities by vaporization due to the high melting point of the ruthenium. The smelting usually has to be carried out in a vacuum or a very pure inert gas due to the strong reaction of hydrazine with oxygen, nitrogen and the like. The two most common methods are electron beam melting (EBM) and plasma melting. In an electron beam furnace, electrons excited by high voltage are aligned with the ruthenium electrode. Part of the energy is converted to heat, which melts the electrode and maintains the liquid state of the base metal while the impurities vaporize. The liquid metal solidifies in cold heading and the formed ingot can be removed from the furnace. The current standard EB furnace uses a method called "drip smelting", but in the future, when the high-energy furnace is developed, the smelting of the hearth will eventually become more effective. Efficient refining is not possible with a single smelting cycle; in practice, the produced niobium ingot must be remelted several times. The melting rate (Kg Niob/h) of the first step of smelting (mainly scouring step) is mainly based on the amount of raw materials input. Because of the high content of aluminum and oxygen (NbO for gasification), the efficiency of ATR 低 is low, aluminum and oxygen impurities Must evaporate. With current technology, the crude ATR ingot must be remelted 2 to 3 times before reaching a high purity crucible. The EB melting and smelting technology produces a base metal impurity of less than 50 ppm and metal impurities (mainly Ta and W) of less than 500 ppm.
Due to their high energy density, plasma furnaces can also be used to refine niobium. In this way, the crude metal is smelted with several portable ion guns. The product was scoured with another plasma gun. The disadvantage of this method is that the vapor pressure generated by the impurities is higher than the furnace pressure that can be released.
Ultra high purity germanium can be prepared from electron beam melting metals using several sophisticated methods. The refractory impurity metal (such as Ta, W) is similar to the vapor pressure of Nb and cannot be removed by electron beam or plasma melting. Their removal method requires the application of selected physicochemical methods. The thermodynamic and kinetic properties are different from those of the main metals and their compounds. For other metals niobium, tantalum main purification method is based on molten salt electrolysis and the effect of the iodide.
The electrolyte of the electronic scouring process is generally a low melting point LiP-NaF-KF molten salt containing pure K 2 NbF 7 . Molten salt electrolysis requires several conditions, such as pre-purification of the base metal (EB smelting) and electrolytes. At the same time, it is strictly avoided that oxygen or water vapor enters the electrolyte.
Compared to bismuth, ultra-high purity enamel can also be produced by modifying the Van Arkel De Borer process. In this process, the crude ruthenium metal is first iodinated to a low ruthenium iodide. The hydrazine iodide decomposes at a temperature of >700 ° C to give a high purity base metal.
By using these methods, it is possible to obtain a base metal having almost no intermediate impurities of less than 1 ppm.
   Sixth, bismuth alloy
Commercial niobium alloys are poor in strength and super-ductility, and 70% niobium alloys require cold working before annealing. As a result, it is easy to produce a niobium alloy having a complicated structure and a low density. Usually people prefer to use niobium alloys instead of other refractory metals such as molybdenum , niobium and tungsten. In the 1960s, many high temperature niobium alloys were developed, primarily for nuclear and aerospace applications; however, further development has been limited since the early 1970s. Today, niobium alloys are also used in smart body equipment. Transport satellites and a wide range of high temperature components, however, due to their sensitivity to oxidation and long-term operation at high temperatures, the application of these alloys will be more widely used in other applications.
Although these elements increase the strength and hardness, toughness, sensitivity and texture of the alloy to be equal to or better than pure niobium, in most cases, the niobium, titanium and vanadium alloys are rapidly formed and the formation process is complicated. All other alloying elements greatly reduce toughness, sensitivity and texture. In general, niobium alloys are more tolerant of picking up impurities than other opposite metals (such as Zr, Ti), since these impurities can greatly reduce the degree of stretch, mainly the edge of the particles. For example, the mechanical properties of these alloys are significantly deteriorated after the incorporation of copper .
In order to improve the oxidation resistance at high temperatures, niobium alloys are widely wrapped by special processes, such as silicon, and most niobium alloys are produced by electron beam, plasma and vacuum arc melting using appropriate additive elements. For large ingots, it is required to use two melts to produce suitable ingots with suitable ingredients. Today, the most common alloys additive is titanium, zinc, tungsten, tantalum and hafnium, in the smelting process, in which they can enter the stable.
Another promising method for the production of niobium alloys is electrowinning from molten salts, such as from Kel-KF-K 2 ZrF 6 -K 2 NbF 7 systems.
Niobium based alloys can also be prepared by powder metallurgy. Several methods are available for the preparation of niobium alloy powders, including gas-atomization, calcination, mechanical fusion, high temperature diffusion or hydride dehydrogenation processes. However, when these methods are used, oxidation and introduction of impurities are difficult to avoid and expensive.
The most important applications of bismuth based alloys are:
(1) Accurately support the atomic number of sodium vapor lamps (Nb-1Zr)
(b) as MRI (magnetic resonance imaging), NMR (nuclear magnetic resonance), SMES (superconducting magnetic energy storage) SQVID (superconductor quantum energy device), superconductor of ion accelerator (such as Nb-50Ti, Nb 2 Sn)
(3) Rocket boosters and spouts in aerospace applications (eg Nb-10Hf-1Ti)
(4) Structural materials in the nuclear industry (eg Nb-40Ta)
Other compounds, such as Nb 3 Al, are attracting interest as candidate materials for A-15 superconductors, exhibiting higher transition temperatures than Nb-Ti alloys and being able to withstand higher electronic fields. In addition, due to their high melting point and super strength, these alloys are more desirable for use in high temperature structural materials.