Tracy Hall's "Belt" Apparatus

These are the three components that comprised the "belt" apparatus in which diamonds were first synthesized.  The reaction cell with the graphite and other components was placed in the hole in the center of the belt (being held in the picture) and the two anvils compressed the specimen.  The soapstone "flowerpot" (so called because of its shape) that the cell was in extrudes into the space between the belt and the anvils and binds there, maintaining the pressure between the two anvils.

 

While Dr. Hall was not the first to use soapstone, this was one aspect of the genius of this device.  The principle is that to achieve high pressure you simply reduce the volume the sample.  In theory, a piston (or a pair of pistons) in a cylinder is the ideal way to achieve that.  In practice, however, a straight piston is very limited in the amount of pressure it can undergo without breaking.

 

The design of Dr. Hall's belt apparatus enabled it to combine the decreasing volume characteristics of a piston-in-cylinder device with the rugged strength of the saucer apparatus by trapping the pressure with a semi-fluid gasketing medium.

The belt apparatus is still used by many major diamond manufacturers today.

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