The Acheson process is a method of synthesizing silicon carbide (SiC) and graphite invented by Edward Goodrich Acheson and patented by him in 1896.
The Acheson process is a method of synthesizing silicon carbide (SiC) and graphite invented by Edward Goodrich Acheson and patented by him in 1896.
The process consists of heating a mixture of silicon dioxide (SiO2), in the form of silica or quartz sand, [1] and carbon, in its elemental form as powdered coke, in an iron bowl. [2]
In the furnace, the silicon dioxide, which sometimes also contains other additives along with ferric oxide and saw dust is melted surrounding a graphite rod, which serves as a core. These rods are inserted in such a way that they are held in contact with each other through the particles of coke, which is commonly called coke bed. An electric current is passed through the graphite rods which heats the mixture to 1700–2500 °C. [1] The result of the carbothermic reaction is a layer of silicon carbide (especially in its alpha and beta phases) [1] forming around the rod and emission of carbon monoxide (CO). There are four chemical reactions in the production of silicon carbide: [3]
This overall process is highly endothermic, with a net reaction [1]
In 1890 Acheson attempted to synthesize diamond but ended up creating blue crystals of silicon carbide that he called carborundum. [4] He found that the silicon vaporized when overheated, leaving graphite. He also discovered that when starting with carbon instead of silicon carbide, graphite was produced only when there was an impurity, such as silica, that would result in first producing a carbide. He patented the process of making graphite in 1896. [5] After discovering this process, Acheson developed an efficient electric furnace based on resistive heating, the design of which is the basis of most silicon carbide manufacturing today. [6]
The first commercial plant using the Acheson process was built by Acheson in Niagara Falls, New York, where hydroelectric plants nearby could cheaply produce the necessary power for the energy intensive process. [6] By 1896, The Carborundum Company was producing 1 million pounds of carborundum. [7] Many current silicon carbide plants use the same basic design as the first Acheson plant. In the first plant, sawdust and salt were added to the sand to control purity. The addition of salt was eliminated in the 1960s, due to it corroding steel structures. The addition of sawdust was stopped in some plants to reduce emissions. [3]
To manufacture synthetic graphite items, carbon powder and silica are mixed with a binder, such as tar, and baked after being pressed into shape such as that of electrodes or crucibles. [8] [9] They are then surrounded with granulated carbon acting as a resistive element that heats them. In the more efficient Castner lengthwise graphitization furnace, the items to be graphitized, e.g. rods, are heated directly by placing them lengthwise end-to-end in contact with the carbon electrodes so that current flows through them, and the surrounding granulated carbon acts as a thermal insulator, but otherwise the furnace is similar to the Acheson design. [10] [11]
To finish the items, the process is run for approximately 20 hours at 200 V with a starting current of 300 A (60 kW ) for a furnace approximately 9 meters long by 35 cm in width and 45 cm in depth, and the resistance drops as the carbon heats due to a negative temperature coefficient, causing the current to increase. [2] Cool down takes weeks. The purity of graphite achievable using the process is 99.5%. [12]
Silicon carbide was a useful material in jewelry making due to its abrasive properties, and this was the first commercial application of the Acheson process. [3]
In the 1940s, first the Manhattan Project and then the Soviet atomic bomb project adopted Acheson process for nuclear graphite manufacturing (see details there).
The first light-emitting diodes were produced using silicon carbide from the Acheson process. The potential use of silicon carbide as a semiconductor led to the development of the Lely process, which was based on the Acheson process, but allowed control over the purity of the silicon-carbide crystals. [13]
The graphite became valuable as a lubricant and for producing high-purity electrodes.
There is sufficient evidence in humans for the carcinogenicity of occupational exposures associated with the Acheson process. Occupational exposures associated with the Acheson process cause cancer of the lung. [14]
Graphite is a crystalline allotrope (form) of the element carbon. It consists of many stacked layers of graphene, typically in the excess of hundreds of layers. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on a large scale for uses in many critical industries including refractories (50%), lithium-ion batteries (18%), foundries (10%), lubricants (5%), among others (17%). Under extremely high pressures and extremely high temperatures it converts to diamond. Graphite's low cost, thermal and chemical inertness and characteristic conductivity of heat and electricity finds numerous applications in high energy and high temperature processes.
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2, commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant families of materials, existing as a compound of several minerals and as a synthetic product. Examples include fused quartz, fumed silica, opal, and aerogels. It is used in structural materials, microelectronics, and as components in the food and pharmaceutical industries. All forms are white or colorless, although impure samples can be colored.
Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its carbon appears: white cast iron has its carbon combined into an iron carbide named cementite, which is very hard, but brittle, as it allows cracks to pass straight through; grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.
Silicon carbide (SiC), also known as carborundum, is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal since 1893 for use as an abrasive. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests. Large single crystals of silicon carbide can be grown by the Lely method and they can be cut into gems known as synthetic moissanite.
Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. It is a part of the chlorosilane family.
Industrial processes are procedures involving chemical, physical, electrical, or mechanical steps to aid in the manufacturing of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry.
In materials science, a refractory is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium. Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.
Edward Goodrich Acheson was an American chemist. Born in Washington, Pennsylvania, he was the inventor of the Acheson process, which is still used to make silicon carbide (carborundum) and later a manufacturer of carborundum and graphite.
An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc.
Glass-like carbon, often called glassy carbon or vitreous carbon, is a non-graphitizing, or nongraphitizable, carbon which combines glassy and ceramic properties with those of graphite. The most important properties are high thermal stability, high thermal conductivity, hardness (7 Mohs), low density, low electrical resistance, low friction, extreme resistance to chemical attack, and impermeability to gases and liquids. Glassy carbon is widely used as an electrode material in electrochemistry, for high-temperature crucibles, and as a component of some prosthetic devices. It can be fabricated in different shapes, sizes and sections.
Carbothermic reactions involve the reduction of substances, often metal oxides (O2-), using carbon (C) as the reducing agent. The reduction is usually conducted in the electric arc furnace or reverberatory furnace, depending on the metal ore. These chemical reactions are usually conducted at temperatures of several hundred degrees Celsius. Such processes are applied for production of the elemental forms of many elements. The ability of metals to participate in carbothermic reactions can be predicted from Ellingham diagrams.
Ferrosilicon is an alloy of iron and silicon with a typical silicon content by weight of 15–90%. It contains a high proportion of iron silicides.
Aluminium carbide, chemical formula Al4C3, is a carbide of aluminium. It has the appearance of pale yellow to brown crystals. It is stable up to 1400 °C. It decomposes in water with the production of methane.
Zinc smelting is the process of converting zinc concentrates into pure zinc. Zinc smelting has historically been more difficult than the smelting of other metals, e.g. iron, because in contrast, zinc has a low boiling point. At temperatures typically used for smelting metals, zinc is a gas that will escape from a furnace with the flue gas and be lost, unless specific measures are taken to prevent it.
Nanoball batteries are an experimental type of battery with either the cathode or anode made of nanosized balls that can be composed of various materials such as carbon and lithium iron phosphate. Batteries which use nanotechnology are more capable than regular batteries because of the vastly improved surface area which allows for greater electrical performance, such as fast charging and discharging.
Carbide-derived carbon (CDC), also known as tunable nanoporous carbon, is the common term for carbon materials derived from carbide precursors, such as binary (e.g. SiC, TiC), or ternary carbides, also known as MAX phases (e.g., Ti2AlC, Ti3SiC2). CDCs have also been derived from polymer-derived ceramics such as Si-O-C or Ti-C, and carbonitrides, such as Si-N-C. CDCs can occur in various structures, ranging from amorphous to crystalline carbon, from sp2- to sp3-bonded, and from highly porous to fully dense. Among others, the following carbon structures have been derived from carbide precursors: micro- and mesoporous carbon, amorphous carbon, carbon nanotubes, onion-like carbon, nanocrystalline diamond, graphene, and graphite. Among carbon materials, microporous CDCs exhibit some of the highest reported specific surface areas (up to more than 3000 m2/g). By varying the type of the precursor and the CDC synthesis conditions, microporous and mesoporous structures with controllable average pore size and pore size distributions can be produced. Depending on the precursor and the synthesis conditions, the average pore size control can be applied at sub-Angstrom accuracy. This ability to precisely tune the size and shapes of pores makes CDCs attractive for selective sorption and storage of liquids and gases (e.g., hydrogen, methane, CO2) and the high electric conductivity and electrochemical stability allows these structures to be effectively implemented in electrical energy storage and capacitive water desalinization.
The Submerged-arc furnace for phosphorus production is a particular sub-type of electric arc furnace used to produce phosphorus and other products. Submerged arc furnaces are mainly used for the production of ferroalloys. The nomenclature submerged means that the furnace's electrodes are buried deep in the furnace burden. A reduction reaction takes place near the tip of the electrodes to facilitate the furnace's process.
GrafTech International Ltd. is a manufacturer of graphite electrodes and petroleum coke, which are essential for the production of electric arc furnace steel and other metals. The company is headquartered in Brooklyn Heights, Ohio and has manufacturing facilities in Calais, France, Pamplona, Spain, Monterrey, Mexico, and St. Marys, Pennsylvania.
The Lely method, also known as the Lely process or Lely technique, is a crystal growth technology used for producing silicon carbide crystals for the semiconductor industry. The patent for this method was filed in the Netherlands in 1954 and in the United States in 1955 by Jan Anthony Lely of Philips Electronics. The patent was subsequently granted on 30 September 1958, then was refined by D. R. Hamilton et al. in 1960, and by V. P. Novikov and V. I. Ionov in 1968.
Filamentous carbon is a carbon-containing deposit structure that refers to several allotropes of carbon, including carbon nanotubes, carbon nanofibers, and microcoils. It forms from gaseous carbon compounds. Filamentous carbon structures all contain metal particles. These are either iron, cobalt, or nickel or their alloys. Deposits of it also significantly disrupt synthesis gas methanation. Acetylene is involved in a number of method of the production of filamentous carbon. The structures of filamentous carbon are mesoporous and on the micrometer scale in dimension. Most reactions that form the structures take place at or above 280 °C (536 °F).