Niobium carbide physical characteristics, preparation methods, and main uses

wallpapers Industry 2020-06-15
Niobium carbide, black cubic crystal or purple-gray powder; belongs to the sodium chloride type cubic crystal system; insoluble in cold and hot hydrochloric acid, sulfuric acid, nitric acid, only soluble in hot mixed solution of hydrofluoric acid and nitric acid; has a high melting point (3500 ℃), high hardness (microhardness>235GPa, harder than corundum), excellent chemical stability (stable at 1000~1100℃, rapidly oxidized to niobium pentoxide at above 1100℃); easy to melt in carbonization Titanium, zirconium carbide, tungsten carbide and other compounds form a reliable solution with a homogeneity, so they can be used to make cermets, heat-resistant alloys and cemented carbides; they can be used as additives for cemented carbides, which significantly increase the heat of cemented carbide Hardness and resistance to thermal shock, heat pressure, and oxidation; cutting tools made with it also have excellent thermal hardness, thermal shock, and thermal oxidation resistance; at the same time, the composite materials prepared by it have also been widely Used in fusion reactor, machining, metallurgy, aerospace and other fields.

1. Niobium pentoxide carbon thermal reduction method
Under the protection of high temperature, vacuum or inert gas, niobium pentoxide, and carbon undergo carbonization reaction to form carbides. In industry, niobium pentoxide and carbon black are usually used as raw materials to prepare niobium carbide. First, niobium pentoxide and carbon black are mixed into a carbonized material according to the ratio. After thoroughly mixed, they are filled into a graphite crucible and put into a carbonization furnace in an inert Heat to 1600~1800℃ under gas or vacuum conditions for the first Carbonization, then add carbon black and mix thoroughly, then put it into the carbonization furnace and heat to 1800~1900℃ under inert gas or vacuum for the second time Carbonization, that is, niobium carbide products. The main reaction formula is as follows: Nb2O5+C=2NbO2+CONbO2+3C=NbC+2CO The disadvantage of this method is that the mixture of niobium pentoxide powder and carbon black (or graphite) powder is not uniform, and the carbon black (or graphite) powder The low activity makes the reaction of niobium pentoxide incomplete and eventually becomes the impurity of the product. Also, the carbon black (or graphite) powder remaining in the niobium carbide powder has low activity. A higher temperature (>600°C) is required for decarburization to remove carbon monoxide or carbon dioxide in an oxidizing atmosphere. The higher the temperature, The higher the oxygen content in the powder, the lower the quality of the niobium carbide powder.
2. Metal niobium carbonization
In this method, niobium powder (Nb2O5 or Nb2O3) produced by reduction of hydrogen gas with niobium powder or hydrogenated niobium powder is mixed with carbon black in an equimolar ratio, after being thoroughly mixed, it is heated to 1600~1700 in vacuum or inert gas protection ℃, make it directly carbonized to get niobium carbide. The main reaction formula is as follows: 2NbC+C=Nb2CNb2C+C=2NbC The advantage of this method is high production efficiency; the disadvantage is that the produced niobium carbide particles are coarse and the carbon content in the residue is high.
3. Chemical vapor reaction

This method uses niobium pentachloride vapor, hydrogen, and methane mixed gas as raw materials to prepare niobium carbide. The mixture gas of niobium pentachloride vapor and nitrogen is electrically heated by a tungsten wire with a temperature above 1000°C to form a metal niobium layer on the surface of the tungsten wire, and then continue to be energized to raise the temperature to 1300°C. Then methane and The mixed gas of hydrogen make niobium carbonized into niobium carbide and deposited on the surface of the hot tungsten wire. The main reaction formula is as follows: NbCl+5/2H2=Nb+5HClNb+CH4=NbC+2H2 The advantage of this method is less powder agglomeration, good dispersion, and the disadvantage is high production cost.

4. Auxiliary metal bath method

This method uses cobalt as an auxiliary metal. Niobium and cobalt are formed into a metal bath with a mass ratio of 1:2, filled into a pure graphite crucible, heated to 1800°C in a Taman furnace with argon flow (completed within 1 hour) and kept warm, and cooled After 2~3h to room temperature; the cobalt was dissolved and removed with concentrated hydrochloric acid to obtain powdered NbC with a particle size of 100~200μm, containing 11.3% of bound carbon and 0.3% of free carbon. The NbC prepared by this method is the same as TaC, characterized by the low impurities, primarily oxygen and nitrogen (both less than 0.01%).
5. Reaction ball milling

The reaction ball milling method uses metal or alloy powder to produce niobium carbide products by chemical reaction with other elements or compounds during the ball milling process. The leading equipment of the reactive ball milling method is a high-energy ball mill, which is mainly used to prepare ultrafine crystal niobium carbide products.

6. Preparation method of ultrafine niobium carbide

(1) Carbide, the first carbonized niobium pentoxide first by ball milling, sieving, etc., then carrying out the second Carbonization in a vacuum, then sample and analyze it to get the finished product.
(2) The compressed niobium hydroxide is dried at 180~250℃ for 6~12h to remove moisture, and the niobium hydroxide powder with a particle size of 20~90nm is obtained. It is compared with carbon black according to the mass ratio of 1: (0.225~0.235) Evenly mixed, carbonized in a vacuum furnace, controlling the carbonization temperature at 1280~1350℃ and continuously evacuated; when the vacuum degree reaches 10~12Pa, the carbonization process is ended, cooling 12~16h, the ball milling of the discharge is costly Niobium carbide powder with a grain size of fewer than 0.8 μm. The following two reactions occur during vacuum carbonization: 2Nb(OH)5=Nb2O5+5H2ONb2O5+7C=2NbC+5CO2
(3) Mechanical alloying method: using niobium powder and graphite as raw materials, the ultra-fine niobium carbide powder was successfully prepared under a ball-to-material ratio of 30:1, a ball milling speed of 300r/min, and a ball milling of 20h. The addition of 1.5% as a process control agent in the experiment reduced the synthesis time of niobium carbide by 10 hours; meanwhile, the particle size of the powder obtained by ball milling with the process control agent was more uniform.

1. Application in composite materials

(1) Multi-phase ceramics are one of the raw materials of multi-phase ceramic materials. With their high hardness, high melting point, excellent chemical stability, and conductivity, the multi-phase ceramic materials are often used in wear-resistant parts and cutting Tool and electrode fields.
(2) Cemented carbide can be used as an inhibitor for the growth of cemented carbide grains and form a third dispersed phase with WC and Co, together with other carbides, which can significantly improve the hot hardness heat resistance of cemented carbide Impact, heat and pressure resistance. Since niobium carbide has the advantages of improving the hardness of the alloy and improving the fracture toughness of the composite, it can be used to prepare cemented carbide tool materials with excellent cutting performance.
(3) The hard niobium carbide hard phase of the surfacing electrode enters the structure of the surfacing layer, so that the welding layer has a better wear-resistant skeleton, and the wear resistance is much improved. The wear-resistant alloy of this electrode welding is 1.2-1.8 times higher than the quenched 45 steel (HRC50) and 2.4-3.6 times higher than the Fe-Cr-C-B wear-resistant alloy. At the same time, the wear-resistant surfacing layer does not require preheating when welding and can be surfacing on the surface of the workpiece. The small cracks generated on the surface can release the stress of the surfacing layer and will not diffuse into the base material. d. Steel strengthening phase Adding a small amount of niobium carbide in the steelmaking process can achieve the effect of precipitation strengthening and fine crystal strengthening, thereby improving the comprehensive mechanical properties of steel.
(4) Aerospace components are used as preparation materials for many aerospace equipment components such as turbine rotors, gas rudders, blades, engine nozzle linings, and nuclear reactor structural parts.
2. Application in coating materials

(1) Niobium carbide coated on the mold steel surface as a metal carbide has high hardness, heat resistance, and wear resistance. Therefore, painting it on steel indicates that the wear resistance of the mold surface can be improved.
(2) The coating of metal workpieces is compounded with a niobium carbide layer on the surface of the base of the metal workpiece, which significantly improves the surface hardness, which can reach more than HV2800, and at the same time increases the working temperature of the workpiece and the density of the organization, thereby extending its service life. The niobium carbide coating can be achieved on the surface of the cast iron piston ring through chemical liquid deposition treatment. This coating is firmly bonded to the substrate; this coating piston ring has both an excellent pocket-shaped oil storage structure and the advantages of high hardness, which can be significant Reduce the sliding friction coefficient of lubricating medium and diesel engine oil lubrication, significantly improve its wear resistance, at the same time can reduce the friction loss of diesel engine, improve diesel engine performance.
(3) The high-temperature components of other niobium carbide coated spacecraft adopt niobium carbide coating, which can significantly improve the service life. In the electronics industry, the intermediate layer material of the electron emission tube uses ultra-fine cobalt-containing niobium carbide, which significantly increases the emissivity of the grid surface, reducing the grid temperature and reducing the thermal emission of the grid, thereby prolonging the electron emission tube. Life.
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