Abstract
The technology of processes akin to diamond synthesis, which involve the application of very high pressures, has advanced markedly in recent years. There has been little comparable advance in the field of organic synthesis at pressures between 5 and 40 kb, probably because it is difficult to maintain a purely hydrostatic pressure, to provide for a significant working volume, to accommodate more than trivial volume changes, or to work with liquid media. For such purposes piston–cylinder devices have an advantage over those depending on an extrudable gasket (e.g. the ‘tetrahedron’ or the ‘belt’) in that the high compressibilities of organic compounds can be readily accommodated and by adoption of suitable sealing rings fluid transmitting media can be used.
The design of a 25-kb reaction vessel suitable for research purposes was undertaken as part of a continuing programme at the National Physical Laboratory. The box-like frame is welded up from standard channel iron and houses a cheap 100-ton ram. The piston-cylinder assembly is interchangeable and is easily removed from the frame. The cylinder is of autofrettaged Hecla 174 steel and has the simplest possible form, being free from screw-threads and requiring no accurate internal grinding, since there is no physical contact with the piston. The seals are of the supported O-ring type and possess a number of important advantages which will be outlined.
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