Acheson method

It is often observed in tiny crystals of micrometer order, such as clay minerals, that the entire surface of a crystal face is covered by elementary spiral layers originating from one screw dislocation (Fig. 5.3). Figure 5.10(a) shows such an exceptional case observed on a (0001) face of a SiC crystal synthesized by the Acheson method. However, such a situation is almost exceptional on crystal faces larger than millimeter size, and is encountered only on crystals synthesized under very precisely controlled conditions. In general, there are many growth centers on one crystal face, and steps from these centers bunch together to form macro-steps, which constitute the step patterns of the face. 

Aqueous gelcasting of SiC was carried out using dimethylacrylamide (DMAA) as the monomer, and A,A -melhylenebisacryIamide(MBAM,AIdrich) as the crosslinker. The initiator here we used was 2,2 -azobis[2-(2-imidazolin- 2-yl)propane] (AZIP), a kind of water soluble azo-initiator. Commercially available SiC powder (FCP-15, Saint-Gobain Ceramics Department, Norton, Norway) produced by the Acheson method was used in this study. The average particle size and a... 

Bulk SiC substrates made by the Acheson method or the Lely method have been used as the substrates for growth of a-SiC. Recently, SiC wafers sliced from an SiC ingot grown by the modified Lely method have been used. Usually, ((X)01) Si or ((X)01) C surfaces are used. Here, homoepitaxial growth of SiC by CVD using an SiH4-C3Hg-H2 reaction gas system is illustrated... 

However, even this second method, including the one modified later by Acheson and co-workers [84JCR(M) 1301], was ineffective in realizing our imaginary compounds (la-c, 2, 3, etc.). Their birth and the start of studies on the verification of the 1-Hydroxyindole Hypotheses had to wait until 1989 when Somei s method, the third method, was discovered. 

Pedras and co-workers (98P1959) isolated a phytoalexin from Wasabi (Wasabia japonica, syn. Eutrema wasabi) and determined its structure to be methyl l-methoxyindole-3-carboxylate (109) (Scheme 38). Compound 109 had already been synthesized by Acheson and co-workers [78JCS(P1)1117] in ten steps from o-nitroaniline. Pedras and co-workers (98P1959) combined our tungstate method and Acheson s work, and synthesized 109 in 9% overall yield but in an impure state. 

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. 

The ultraviolet absorption spectra have been used to distinguish between the tautomers obtained by addition of dimethyl acetylene-dicarboxylate to pyridines. The 4/f-quinolizines show a band around 265 mfi. which is missing from the spectra of the 9a/f-quinolizines. Acheson and Taylor26 have successfully used this information to settle the constitution of the stable and labile adducts obtained by the action of acetylenedicarboxylic esters on pyridines. The ultraviolet spectra of the stable adducts formed by the above methods show... 

Edward Goodrich Acheson patents a method for making carborundum... 

Karl Bayer first separated alumina from bauxite ore. This method, known as the Bayer process, is stiU used to purify alumina. In 1893, Edward Goodrich Acheson, an American chemist, electronically fused carbon and clay to create carborundum, also known as synthetic silicon carbide, a highly effective abrasive. 

Other innovators include brothers Pierre and Jacques Curie, French physicists who discovered piezoelectricity around 1880 French chemist Henri Moissan, who combined silicon carbide with tungsten carbide around the same time as Acheson and German mathematician Karl Schroter, who in 1923 developed a liquid-phase sintering method to bond cobalt with the tungsten-carbide particles created by Moissan. 

The classic method of manufacturing industrial-grade sihcon carbide is the Acheson process, as patented in 1893 (Acheson, 1893). Today, in excess of 800000 tons of SiC are manufactured worldwide via this process, which is based on the carbothermal reduction of Si02 whereby quartz sand and petroleum coke are mixed and heated electrically to a temperature of about 2000 °C. Consequently, the intermediate product Si combines with carbon to form essentially hexagonal a-SiC in one or more of its polytypic structures according to ... 

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