TaC Tantalum Carbide powder
Chinese name: tantalum carbide
EINECS No.: 235-118-3
Molecular formula: CTa
Molecular weight: 192.96
Melting point: 3880 ℃
Crystal form: light brown metallic cubic crystalline powder, belonging to sodium chloride cubic crystal system.
Resistance: 30 Ω at room temperature
Properties: insoluble in water, insoluble in inorganic acid, soluble in mixed acid of hydrofluoric acid and nitric acid and decomposable. Strong antioxidant capacity, easy to be melted and decomposed by potassium pyrosulfate.
Application: (1) Tantalum carbide has high hardness, high melting point and high temperature performance, and is mainly used as an additive for cemented carbide. The addition of tantalum carbide can refine the grain of cemented carbide, which can significantly improve its thermal hardness, thermal shock resistance and thermal oxidation resistance. For a long time, it relies on adding a single tantalum carbide to tungsten carbide (or tungsten carbide and titanium carbide), mixing with the binder metal cobalt, forming and sintering to produce cemented carbide. In order to reduce the cost of cemented carbide, tantalum and niobium composite carbides are often used. At present, the main tantalum and niobium composites are TaC: NbC: 80:20 and 60:40, and the maximum amount of niobium carbide in the composites reaches 40% (generally considered not to exceed 20%). In the production of cemented carbide, TAC mainly plays a role in inhibiting the grain growth of the alloy, improving the red hardness and wear resistance of the alloy, enhancing the oxidation resistance and corrosion resistance of the alloy, and improving the structure of the alloy. In common tungsten cobalt and tungsten cobalt titanium cemented carbide, only 0.3% - 0.4% can be added. TaC cannot be wetted by cobalt alone, and WC and TiC solid solutions need to be matched.
(2) It is used as additive for powder metallurgy, cutting tools, fine ceramics, chemical vapor deposition, hard wear-resistant alloy tools, tools, moulds and wear-resistant and corrosion-resistant structural parts to improve the toughness of the alloy. The sintered body of tantalum carbide shows golden yellow and can be used as watch decoration.
(1) Reduction method
The preparation process mainly includes mixing tantalum oxide or carbon powder with carbon, and producing tantalum carbide by primary and secondary carbonization under high temperature, hydrogen protection or vacuum conditions. The reason for the need for secondary carbonization is that the first carbonization is not complete due to various factors, and the combined carbon, free carbon and impurities in the product are difficult to meet the requirements. The excessive carbon and tantalum in the secondary carbonization under vacuum conditions form carbides. The main factors affecting the quality of carbides are: carbon content, raw material size and purity, charging method, carbonization temperature, carbonization time, secondary carbonization, etc. The above method can only prepare bulk or large granular TaC.
From the industrial point of view, the carbothermal reduction of metal oxides is the most widely used method, but its reduction temperature is above 1500 ℃, and the reaction rate is very slow. When the reaction temperature is higher, the TaC particles are easy to grow, reducing its mechanical properties. In industry, micron-sized tantalum carbide powder is prepared by ball milling method. The method is to mix solid carbon ball and tantalum pentoxide and then ball milling in vacuum and argon atmosphere. At 1700 ℃, reduction and carburization treatment can be carried out to obtain particle size larger than 2 μ M of tantalum carbide powder. In order to speed up the reaction speed and improve the defects of traditional methods, microwave reduction method can well improve the powder diffusion rate, reduce the reaction temperature by 50-100 ℃, shorten the processing time, save energy and save costs. The preparation process is as follows: Ta2O5+carbon black is reduced by microwave at 1250 ℃ - 1500 ℃, the heating rate is more than 100 ℃/min, and when the temperature is more than 1400 ℃, Ta2O5 is converted to TaC without generating any mesophase or Ta low-valent oxide.
Chemical method is a common solid phase method to prepare TaC. Under certain conditions, the chemical reaction between T and C directly generates TaC: Ta (s)+C (s) → TaC (s)
(3) Chemical vapor deposition
TaC coating prepared by CVD method needs to use the source material - TaCl5. TaCl5 is gasified at 500K, and the gasified TaCl5 is poured into the CVD furnace as a gas source, and deposited with other introduced reducing atmosphere to generate TaC. The reaction process is as follows:
Storage conditions: inert gas anti-static packaging should be sealed and stored in a dry and cool environment, and should not be exposed to the air for a long time.
Tantalum carbide (TaC) is an ultra-high temperature ceramic material. The so-called ultra-high temperature ceramics (UHTCs) usually refer to a class of ceramic materials, such as ZrC, HfC, TaCHfB2, ZrB2, HfN, etc., whose melting point exceeds 3000 ℃ and which are used in high temperature and corrosive environments (such as oxygen atom environment) above 2000 ℃. The melting point of tantalum carbide is up to 3880 ℃, with high hardness (Mohs hardness 9~10), large thermal conductivity (22W · m-1 · K-1), large bending strength (340~400MPa), and small coefficient of thermal expansion (6.6 × 10-6K-1), and exhibits excellent thermochemical stability and excellent physical properties. It has good chemical compatibility and mechanical compatibility with graphite and C/C composites. Therefore, TaC coatings are widely used in aerospace thermal protection, single crystal growth, energy electronics, medical devices and other fields.
1) TaC has excellent thermochemical stability and excellent physical properties, and has good chemical compatibility and mechanical compatibility with graphite. The preparation of TaC coating on the surface of graphite can effectively enhance its oxidation resistance, corrosion resistance, wear resistance and mechanical properties. Especially suitable for growing GaN or AlN single crystals in MOCVD equipment and SiC single crystals in PVT equipment, the quality of the grown single crystals is significantly improved. Due to the excellent acid and alkaline resistance of TaC coatings to H2, HCl, and NH3, in the silicon carbide semiconductor industry chain, TaC can also fully protect graphite matrix materials and purify the growth environment during epitaxial processing such as MOCVD.
2) Porous tantalum carbide ceramics can better realize vapor component filtration, adjust local temperature gradient, guide material flow direction, control leakage, etc.
3) With the development of modern aircraft such as aerospace, rockets, and missiles towards high speed, high thrust, and high altitude, the requirements for their surface materials to have high temperature resistance and oxidation resistance under extreme conditions are also increasing. When an aircraft enters the atmosphere, it faces extreme environments such as high heat flux density, high stagnation point pressure, and fast airflow erosion, as well as chemical erosion caused by reactions with oxygen, water vapor, and carbon dioxide. When an aircraft flies out and into the atmosphere, the air around its nose cone and wings is subjected to severe compression and generates significant friction with the aircraft surface, resulting in the surface being heated by airflow. In addition to aerodynamic heating during flight, the surface of the aircraft is also affected by solar radiation, environmental radiation, and other factors, resulting in a continuous increase in surface temperature. This change will seriously affect the service condition of the aircraft. TaC is a member of the ultra-high temperature resistant ceramic family. Its high melting point and excellent thermodynamic stability make it widely used in the hot end of aircraft, such as protecting the surface coating of rocket engine nozzles.
4) TaC also has broad application prospects in fields such as cutting tools, grinding materials, electronic materials, and catalysts. For example, adding TaC to hard alloys can prevent grain growth, increase hardness, and improve their service life; TaC has good conductivity and can form non stoichiometric compounds. The conductivity varies with the composition, making it an attractive application prospect in the field of electronic materials; In terms of catalytic dehydrogenation of TaC, some researchers have studied the catalytic performance of TiC and TaC, indicating that TaC has little catalytic activity at lower temperatures, but its catalytic activity significantly increases above 1000 ℃. Research on the catalytic performance of CO has found that the catalytic products of TaC at 300 ℃ include methane, water, and a small amount of olefins.