Acheson process

The Acheson process is the oldest and still most important graphitization process. The carbon articles are placed with their long axes perpendicular to the direction of the electrical current in the furnace bed and are surrounded with a resistive bed of granular coke in which most of the Joule heat is produced. A constant furnace resistance is essential for uniform product quality (avoidance of local temperature peaks). The way in which the furnace is loaded is therefore critical. 

In Acheson furnaces articles with very different shapes can be graphitized, making the process very versatile. The capacities of currently operated furnaces range up to net loads of 100 t or more. A typical Acheson furnace is 12 to 15 m long and 3 to 3.5 m wide and is loaded with 35 to 55 t of carbon articles. After a heating time of 3 days final 

Acheson process, most important graphitization process  

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Acheson process Achlorhydria Achondrites Achromatic hologram Achromobacter sp. Achromycin Achromycin [60-54-8]... 

The "conventional" methods for the preparation of SiC and Si3N4, the high temperature reaction of fine grade sand and coke (with additions of sawdust and NaCl) in an electric furnace (the Acheson process) for the former and usually the direct nitridation of elemental silicon or the reaction of silicon tetrachloride with ammonia (in the gas phase or in solution) for the latter, do not involve soluble or fusible intermediates. For many applications of these materials this is not necessarily a disadvantage (e.g., for the application of SiC as an abrasive), but for some of the more recent desired applications soluble or fusible (i.e., proces-sable) intermediates are required. 

The conventional production method for SiC - the reaction of coke and sand (Acheson process) -does not involve soluble or fusible intermediates. For many applications of silicon carbide this fact is not necessarily a disadvantage, but for the preparation of ceramic composites such intermediates are required. 

These forms of carbon are also known to have some order, so they are not completely amorphous. When appropriately prepared (so-called activated charcoal), charcoal has an enormous surface area, so it is capable of adsorbing many substances from both gases and solutions. As was described in Chapter 11, coke is used on an enormous scale as a reducing agent in the production of metals. The "amorphous" forms of carbon can be transformed into graphite by means of the Acheson process, in which an electric current heats a rod of the "amorphous" form. 

Castner (1) A process for making graphite articles, invented by H. Y. Castner in 1893. It uses lengthwise graphitization, unlike the Acheson process, which uses transverse graphiti-zation. 

Application of carbo-thermal reduction. This is a synthesis process for the preparation of powders of carbides, nitrides and borides. Carbon may be graphite, coke, pyrolysed organic polymers. A reference process may be the Acheson process for the production of SiC ... 

The Acheson process sometimes also includes sawdust and salt in lesser amounts together with the coke and silica. The sawdust creates channels that help impurities escape and the salt creates free chorine, which reacts with metal impurities that become volatile. Thus, the means to purify synthetic SiC have been employed since the beginning. 

Figure 1.1 The Acheson process. The figure also shows the voids in which Acheson found the SiC crystals. (From [1 7]. 1963 Philips. Reprinted with permission.)...

Acheson process Achlorhydria Achondrites Achromatic hologram Achromobacter sp. 

Achieving the required degree of desulfurization dictated electrothermal heating. Fixed-bed electrothermal furnaces of the Acheson type were initially considered for use directly with granular coke but the test results were disappointing. The product of the Acheson furnace was not uniform in its sulfur content. Adaptation of the Acheson Process, which is a batch process, presented problems in materials handling that were considered very difficult to resolve at the 10,000 tons per year capacity determined to be the... 

The crystal structure of Desulco is substantially more ordered than that of the starting petroleum coke but, not as ordered as that of a synthetic graphite made by the Acheson process,... 

Acheson process — (Edward Goodrich Acheson March 9, 1856, Washington, USA - June 6, 1931, New York City, USA, American chemist, inventor (abrasive Carborundum 1891) and industrialist, coworker of Edison 1881-1883, president of The Electrochemical Society 1908-1909). Coke and quartz (silica) are pressed and heated in an electric furnace at 800-1300 °C, subsequent graphitization proceeds at 2000-2200 °C. Formation of graphite under these conditions is attributed to growth of initially already present small graphite particles and/or decomposition of initially formed SiC. See also graphite electrode. 

Furthermore, these amorphous forms of carbon can be transformed into graphite by means of the Acheson process in which an electric current heats a rod of the amorphous form. 

Acheson process, 566 Acid-initiated ring-opening polymerization comparison widi base-initiated process, 79 kinetics, 79-80 mechanism, 79-81 rate retardation by water, 81 relative reactivities of cyclosiloxanes, 79 step-growth process, 79 Acyclic oligosilanes, photochemical transformations, 432/-433/ Acylsilanes... 

Graphite, of which the natural supply is limited, is manufactured in various ways depending upon the purpose for which it is intended. Finely divided material, pure and soft for lubrication, is produced in the Acheson process. In this, powdered coke is heated for about a day to temperatures reaching 2500°, by letting it serve as the resistance in an electric furnace. The conversion to graphite is probably catalysed by the presence of a little silicon derived from the coke or the furnace walls. 

Silicon carbide is manufactured industrially by the electrochemical reaction of high purity quartz sand with carbon in an electric resistance furnace (Acheson process) ... 

Industrial manufacture of SiC is carried out using the Acheson process by reacting SiOi with carbon in an electric furnace... 

Silicon carbide is remarkable for its unusually large variety of different morphologies, which differ in their stacking sequences of hexagonal and rhombohedral layers. All hexagonal and rhombohedral forms are often simply described as a-SiC. The commercially available SiC produced by the Acheson process is a-SiC. 

In another process metallic silicon is evaporated in an electrical arc and reacts with methane to silicon carbide. A disadvantage of all gas phase processes is their high cost compared with the Acheson process. 

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