Metal carbides are one class of important high-performance material with excellent properties, including high hardness, high melting point, and good electrical conductivity. Among them, transition metal carbides have played an important role in modern industries because of their superior performance. This article will introduce metal carbides and 8 important transition metal carbide powders.
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Metal carbides (Metallic Carbides) are inorganic compounds composed of metal and carbon elements. They exhibit high hardness, high melting point, good electrical conductivity, and chemical stability.
Metal carbides are compounds formed by the combination of metal atoms and carbon atoms. The carbon element usually exists in the form of an anion (C⁴⁻) and bonds strongly with metal ions. Depending on the metal element, the carbides can exhibit metallic, ceramic, or mixed characteristics.
The general chemical formula for metal carbides is:
M represents a metal element (e.g., Ti, W, Ca).
C represents carbon.
x and y are integers indicating the ratio of metal to carbon.
Examples include:
The composition and properties of metal carbides allow for their division into four main types:
The first type is Transition Metal Carbides, including titanium carbide (TiC), tungsten carbide (WC) and tantalum carbide (TaC). These carbides have high hardness, high melting point, good conductivity and chemical stability, and are widely used in cutting tools, high temperature materials and coatings.
The other class is Main Group Metal Carbides. Some examples include calcium carbide (CaC₂) and beryllium carbide (Be₂C). These kinds of carbides are primarily ionic with relatively low hardness and can react with water, liberating the gas and thus often find applications as chemical raw materials or gas generators.
The third type is Metalloid Carbides such as silicon carbide (SiC) and boron carbide (B₄C). These carbides have extremely high hardness, high temperature resistance and chemical stability, and are widely used in abrasives, bulletproof materials and electronic component manufacturing.
The fourth type is rare Rare Earth Metal Carbides, typical examples of which include uranium carbide (UC) and thorium carbide (ThC₂). This kind of carbide has a high melting point, high density, and good thermal conductivity, and is mainly used in the nuclear energy field and high-temperature structural parts.
Different types of metal carbides have obvious differences in structure, properties and applications.
Transition metal carbides are highly regarded for their excellent properties. With advancements in 3D printing and nanomaterials, the application potential of transition metal carbides has further expanded. Below are some classic transition metal carbide powders:
Titanium carbide powder is a transition metal carbide composed of titanium and carbon, with the chemical formula TiC. It features high hardness, a high melting point (approximately °C), and excellent chemical stability, typically appearing gray-black in color.
Owing to superior resistance to wear and electrical conductivity, it is extensively used in hard alloy, metal ceramics, and tool coating. In addition, TiC often acts as an added reinforcing phase in high-temperature structural materials to increase the strength and heat resistance of composites.
Fig 1. The structure of titanium carbide
Tungsten carbide powder is a hard material composed of tungsten and carbon, with the chemical formula WC. It has a hardness close to that of diamond, a high melting point of °C, and excellent thermal conductivity and corrosion resistance.
It finds huge applications in producing hard alloy tools, drill bits, wear parts, and mining machinery tools. It is also an essential raw material for thermal spray coatings, which protect the surfaces of machinery and prolong service life.
When combined with cobalt, tungsten carbide powder forms Tungsten Carbide Cobalt powder, which combines high hardness with good toughness.
Fig 2. Components made of tungsten carbide
Tantalum carbide powder (TaC) is a high-melting-point carbide (°C) and one of the compounds with the highest known melting points. It exhibits excellent heat resistance, chemical inertness, and high electrical conductivity.
TaC powder is primarily used in aerospace applications, such as rocket nozzles, thermal protection coatings, and nuclear industry materials. Additionally, it serves as an additive in Cemented carbides to enhance wear resistance and oxidation resistance.
Fig 3. Molecular structure of tantalum carbide and Tantalum Carbide Ceramics
Niobium carbide powder is composed of niobium and carbon, with the chemical formula NbC. It is characterized by high hardness, a melting point of approximately °C, and excellent corrosion resistance.
NbC powder is widely used as a hardening agent in the steel industry, as well as in cutting tools and abrasion-resistant materials. Besides its use in superconducting materials and high-temperature operating alloys, NbC acts to increase strength and thermal shock resistance.
Fig 4. Molecular structure of niobium carbide
Vanadium carbide powder is a transition metal carbide composed of vanadium and carbon, with the chemical formula VC. It features high hardness, a melting point of approximately °C, and good electrical conductivity, with relatively low density.
VC powder is normally used as a grain refiner in hard alloys and can greatly improve material hardness and toughness. The application fields are in high-temperature materials, metal ceramics, aerospace, and tool manufacturing.
Fig 5. Structure of vanadium carbide
Hafnium carbide powder is a kind of ultra-high temperature carbide, which consists of hafnium and carbon. The chemical formula is HfC. It has the highest melting point among all the known materials, reaching °C.
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HfC powder is characterized by high hardness, excellent electrical conductivity, and chemical stability. It is widely used in aerospace, especially for rocket engine nozzles and thermal protection coatings. Besides, HfC is also applied as a reinforcement material to hard alloys and metal ceramics, which improves the performance of these materials under extreme conditions.
Fig 6. Hafnium Carbide Powder
Zirconium carbide powder, with the chemical formula ZrC, is a transition metal carbide composed of zirconium and carbon. It has a high melting point of °C and is known for its high hardness, excellent heat resistance, and oxidation resistance.
ZrC powder is primarily used in high-temperature materials, such as refractories, rocket nozzles, and nuclear industry coatings. It is also applied in metal ceramics and cutting tools to improve wear resistance and thermal shock performance.
Fig 7. Zirconium Carbide Powder
Molybdenum carbide powder is a transition metal carbide composed of molybdenum and carbon, with the chemical formula Mo₂C. It features a high melting point of °C, high hardness, excellent catalytic properties, and good electrical conductivity and chemical stability.
Mo₂C powder is mainly used in catalyst applications, such as hydrodesulfurization and hydrogen evolution reactions, as a substitute for precious metals. It is also employed in wear-resistant materials, high-temperature structural components, and as a reinforcing phase in ceramic composites to enhance hardness and heat resistance.
Stanford Advanced Materials offers a wide range of carefully produced carbides in different grades for use in cemented carbides, wear-resistant components, high-temperature components, and thermal spray coatings.
Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.[3]
The pure material is colorless, while pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), C (carbon), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.[4]
Applications of calcium carbide include manufacture of acetylene gas, generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer, and steelmaking.
Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2,200 °C (3,990 °F).[5] This is an endothermic reaction requiring 110 kilocalories (460 kJ) per mole[6] and high temperatures to drive off the carbon monoxide. This method has not changed since its invention in :
The high temperature required for this reaction is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. The carbide product produced generally contains around 80% calcium carbide by weight. The carbide is crushed to produce small lumps that can range from a few mm up to 50 mm. The impurities are concentrated in the finer fractions. The CaC2 content of the product is assayed by measuring the amount of acetylene produced on hydrolysis. As an example, the British and German standards for the content of the coarser fractions are 295 L/kg and 300 L/kg respectively (at 101 kPa pressure and 20 °C (68 °F) temperature). Impurities present in the carbide include calcium phosphide, which produces phosphine when hydrolysed.[7]
This reaction was an important part of the Industrial Revolution in chemistry, and was made possible in the United States as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century.[8] The electric arc furnace method was discovered in by T. L. Willson, and independently in the same year by H. Moissan.[9][10][11] In Jajce, Bosnia and Herzegovina, the Austrian industrialist Josef Kranz and his "Bosnische-Elektrizitäts AG" company, whose successor later became "Elektro-Bosna", opened the largest chemical factory for the production of calcium carbide at the time in Europe in . A hydroelectric power station on the Pliva river with an installed capacity of 8 MW was constructed to supply electricity for the factory, the first power station of its kind in Southeast Europe, and became operational on 24 March .[12]
Calcium carbide is a calcium salt of acetylene, consisting of calcium cations Ca2+ and acetylide anions −C≡C−. Pure calcium carbide is a colourless solid. The common crystalline form at room temperature is a distorted rock-salt structure with the C2−2 units lying parallel.[13] There are three different polymorphs which appear at room temperature: the tetragonal structure and two different monoclinic structures.[1]
The reaction of calcium carbide with water, producing acetylene and calcium hydroxide,[5] was discovered by Friedrich Wöhler in .
This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.
Today acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes are produced this way annually (see acetylene preparation).
In China, acetylene derived from calcium carbide remains a raw material for the chemical industry, in particular for the production of polyvinyl chloride. Locally produced acetylene is more economical than using imported oil.[14] Production of calcium carbide in China has been increasing. In output was 8.94 million tons, with the capacity to produce 17 million tons.[15]
In the United States, Europe, and Japan, consumption of calcium carbide is generally declining.[16] Production levels in the US during the s were 236,000 tons per year.[13]
Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:[5]
Commonly known as nitrolime, calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, H2N−C≡N.[5]
Calcium carbide is used:
Calcium carbide is used in carbide lamps. Water dripping on carbide produces acetylene gas, which burns and produces light. While these lamps gave steadier and brighter light than candles, they were dangerous in coal mines, where flammable methane gas made them a serious hazard. The presence of flammable gases in coal mines led to miner safety lamps such as the Davy lamp, in which a wire gauze reduces the risk of methane ignition. Carbide lamps were still used extensively in slate, copper, and tin mines where methane is not a serious hazard. Most miners' lamps have now been replaced by electric lamps.
Carbide lamps are still used for mining in some less wealthy countries, for example in the silver mines near Potosí, Bolivia. Carbide lamps are also still used by some cavers exploring caves and other underground areas,[17] although they are increasingly being replaced in this use by LED lights.
Carbide lamps were also used extensively as headlamps in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps.[18]
Calcium carbide is sometimes used as source of acetylene, which like ethylene gas, is a ripening agent.[19] However, this is illegal in some countries as, in the production of acetylene from calcium carbide, contamination often leads to trace production of phosphine and arsine.[20][21] These impurities can be removed by passing the acetylene gas through acidified copper sulfate solution, but, in developing countries, this precaution is often neglected.
Calcium carbide is used in toy cannons such as the Big-Bang Cannon, as well as in bamboo cannons. In the Netherlands calcium carbide is used around new-year to shoot with milk churns.[22]
Calcium carbide, together with calcium phosphide, is used in floating, self-igniting naval signal flares, such as those produced by the Holmes' Marine Life Protection Association.
Calcium carbide is used to determine the moisture content of soil. When soil and calcium carbide are mixed in a closed pressure cylinder, the water content in soil reacts with calcium carbide to release acetylene whose pressure can be measured to determine the moisture content.[23][24]
Calcium carbide is sold commercially as a mole repellent.[25] When it comes into contact with water, the gas produced drives moles away.[26]
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