Piston-cylinder apparatus

The piston-cylinder apparatus is a solid media device, used in Geosciences and Material Sciences, for generating simultaneously high pressure (up to 6 GPa) and temperature (up to 1700 °C). Modifications of the normal set-up can push these limits to even higher pressures and temperatures. A particular type of piston-cylinder, called Griggs apparatus, is also able to add a deviatoric stress on the sample.
The principle of the instrument is to generate pressure by compressing a sample assembly, which includes a resistance furnace, inside a pressure vessel. Controlled high temperature is generated by applying a regulated voltage to the furnace and monitoring the temperature with a thermocouple. The pressure vessel is a cylinder that is closed at one end by a rigid plate with a small hole for the thermocouple to pass through. A piston is advanced into the cylinder at the other hand.

Sir Charles Parsons was the first to attack the problem of generating high pressure simultaneously with high temperature. His pressure apparatus consisted of piston-cylinder devices that used internal electrical resistance heating. He used a solid pressure transmitting material, which also served as thermal and electrical insulation. His cylindrical chambers ranged in diameter from 1 to 15 cm. The maximum pressure at the temperature he reported was of the order of 15000 atm (corresponding to ~1.5 GPa) at 3000 °C.
Loring L. Coes, Jr., of the Norton Co., was the first person to develop a piston-cylinder device with capabilities substantially beyond those of the Parsons device. He did not personally publish a description of this equipment until 1962. The key feature of this device is the use of a hot, molded alumina liner or cylinder. The apparatus is double ended, pressure being generated by pushing a tungsten carbide piston into each end of the alumina cylinder. Because the alumina cylinder is electrically insulating, heating is accomplished, very simply, by passing an electric current from one piston through a sample heating tube and out through the opposite piston. The apparatus was used at pressures as high as 45000 atm (corresponding to ~4.5 GPa) simultaneously with a temperature of 800 °C. Temperature was measured by means of a thermocouple located in a well. At these temperature and pressure conditions, only one run is obtained in this device, the pistons and the alumina cylinder both being expendable. Even at 30000 atm (corresponding to ~3.0 GPa) the alumina cylinder is only useful for a few runs, as is also the case for the tungsten carbide pistons. The expense of using such a device is great.
Nowadays both the piston and the cylinder are constructed of cemented tungsten carbide and electrical insulation is provided in a different manner than in the device of Coes. In particular, the basis for the modern piston-cylinder apparatus is given by the design described by Boyd and England in 1960, which has been the first machine that allowed experiments under upper mantle conditions to be routinely carried out in a laboratory.

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