Chinese name: Tantalum carbide
CAS No.12070-06-3
EINECS number: 235-118-3
Molecular formula: CTa
Molecular weight: 192.96
Melting point: 3880℃
Boiling point: 5500℃
Hardness: 2100HV0.05
Crystal type: light brown metallic cubic crystalline powder, belongs to sodium chloride cubic crystal system.
Density: 14.3g/cm3
Resistance: 30Ω at room temperature
Properties: Insoluble in water, insoluble in inorganic acid, soluble in hydrofluoric acid and nitric acid mixed acid and can be decomposed. Strong antioxidant ability, easy to be fused and decomposed by potassium pyrosulfate.
Applications: (1) tantalum carbide hardness, high melting point, high temperature performance, mainly used as carbide additives. The addition of tantalum carbide can refine the grain of cemented carbide, and its thermal hardness, thermal shock resistance and thermal oxidation resistance are significantly improved. Long-term dependence on a single tantalum carbide added to tungsten carbide (or tungsten carbide and titanium carbide), mixed with the binder metal cobalt, forming, sintering to produce cemented carbide. In order to reduce the cost of tungsten carbide, often use tantalum niobium complex carbide, the main use of tantalum niobium complex are: TaC: NbC is 80:20 and 60:40 two, the highest amount of niobium carbide in the complex reached 40% (generally considered not more than 20% is good). In the production of cemented carbide, TAC mainly plays a role in inhibiting the growth of alloy grains, 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 ordinary tungsten cobalt and tungsten cobalt titanium carbide only 0.3%-0.4% can be added, TaC can not be wet by cobalt alone, need to match WC and TiC solid solution.
(2) Used in powder metallurgy, cutting tools, fine ceramics, chemical vapor deposition, hard wear-resistant alloy cutting tools, tools, molds and wear-resistant structural components additives to improve the toughness of the alloy. Tantalum carbide sintered body shows gold color, can be used as a watch decoration.
Preparation method:
(1) Reduction method
The preparation process is mainly: tantalum oxide or carbon powder is mixed with carbon, and primary and secondary carbonization is performed to produce tantalum carbide 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 the influence of various factors, and the combined carbon, free carbon and impurities in the product are difficult to meet the requirements. Secondary carbonization: excess carbon and tantalum form carbides under vacuum conditions. The main factors that affect the quality of carbide are: the amount of carbon, the particle size and purity of raw materials, the charging mode, carbonization temperature, carbonization time, secondary carbonization and so on. The above methods can only prepare TaC in bulk or large granular form.
From an industrial point of view, the carbothermal reduction method of metal oxides is the most widely used method, but its reduction temperature is above 1500℃, the reaction rate is very slow, and TaC particles are easy to grow when the reaction temperature is higher, reducing its mechanical properties. In industry, the use of ball milling method to prepare micron-grade tantalum carbide powder, the method is to mix solid carbon balls and tantalum pentoxide in a vacuum and argon atmosphere ball milling, at 1700℃ high temperature, reduction and carburizing treatment, can get a particle size of more than 2μm tantalum carbide powder. In order to speed up the reaction speed and improve the defects of the traditional method, the 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: Ta2O5+ carbon black at 1250℃-1500℃ microwave reduction, heating rate is greater than 100℃/min, more than 1400℃, Ta2O5 completed conversion to TaC, without generating any intermediate phase or Ta low-cost oxide.
(2) Legalization
Chemical method is a common solid phase process for TaC preparation. Under certain conditions, the chemical reaction between T and C directly generates TaC: Ta (s) +C (s) →TaC (s)
(3) chemical vapor deposition method
The source material -TaCl5 is used to prepare TaC coating by CVD method. TaCl5 is vaporized at 500K, and the vaporized TaCl5 is poured into the CVD furnace as a gas source and deposited together with other imported reducing atmospheres to generate TaC. The reaction process is as follows:
TaCl5+CmHn+H2→TaC+HCl+H2
Storage conditions: inert gas anti-static packaging, should be sealed in a dry, cool environment, should not be exposed to the air for a long time.
Tantalum carbide (TaC) is a kind of ultra-high temperature ceramic material, the so-called ultra-high temperature ceramics (UHTCs) usually refers to the melting point of more than 3000℃, and in the high temperature and corrosion environment above 2000℃ (such as oxygen environment) used in a class of ceramic materials, such as ZrC, HfC, TaCHfB2, ZrB2, HfN and so on. Tantalum carbide melting point is as high as 3880℃, with high hardness (Mohs hardness 9 ~ 10), large thermal conductivity (22W·m-1·K-1), large bending strength (340 ~ 400MPa), and small thermal expansion coefficient (6.6× 10-6k-1), and shows excellent thermochemical stability and excellent physical properties. It has good chemical and mechanical compatibility with graphite and C/C composite materials, so TaC coating is widely used in aerospace thermal protection, single crystal growth, energy electronics, and medical devices.
Application field:
1) TaC has excellent thermochemical stability and excellent physical properties, and has good chemical 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. It is especially suitable for growing GaN or AlN single crystal in MOCVD equipment and SiC single crystal in PVT equipment, and the quality of the single crystal grown is obviously improved. Because TaC coating has excellent acid and alkali resistance to H2, HCl, NH3, in the silicon carbide semiconductor industry chain, TaC can also completely protect the graphite matrix material in the epitaxial treatment process such as MOCVD, and purify the growth environment.
2) Porous tantalum carbide ceramics can better achieve gas phase component filtration, adjust the local temperature gradient, guide the direction of material flow, control leakage and so on.
3) With the development of modern aircraft such as aerospace spacecraft, rockets and missiles in the direction of high speed, high thrust and high altitude, the requirements for high temperature resistance and oxidation resistance of their surface materials under extreme conditions are also increasing. When the vehicle enters the atmosphere, it is faced with extreme environment such as high heat flux, high stagnation pressure and fast airflow erosion speed. At the same time, it is faced with chemical ablation caused by reaction with oxygen, water vapor and carbon dioxide. When the aircraft flies out and into the atmosphere, the air around the nose cone and wing will be severely compressed and produce greater friction with the surface of the aircraft, resulting in the surface of the air flow heating. In addition to aerodynamic heating during flight, the surface of the aircraft will also be affected by solar radiation and environmental radiation during flight, so that the surface temperature of the aircraft will continue to rise, which will seriously affect the service status of the aircraft. TaC is a member of the ultra-high temperature ceramic family. Its high melting point and excellent thermodynamic stability make TaC widely used in the hot end of aircraft, for example, it can protect the surface coating of rocket engine nozzle.
4) TaC also has a wide range of applications in cutting tools, abrasive materials, electronic materials and catalysts. For example, adding TaC to cemented carbide can prevent the grain growth of cemented carbide, increase the hardness of cemented carbide, and improve its service life; TaC has good electrical conductivity, and can be composed of non-stoichiometric compounds, the electrical conductivity varies with different components, which makes TaC has attractive application prospects in the field of electronic materials. In terms of the catalytic dehydrogenation of TaC, studies on the catalytic performance of TiC and TaC have shown that at low temperatures, TaC basically has no catalytic activity, but at higher than 1000℃, its catalytic activity increases significantly. The study on the catalytic performance of CO found that the catalytic products of TaC at 300℃ include methane, water and a small amount of olefin.
