High Pressure Methods

Man is ever emulating nature. In his attempts to duplicate pressures that exist in the universe, however, he falls short of the tremendous pressures that are to be found. For example, the pressures thought to exist at the centers of the white dwarf stars are of the order of 10 15 atmospheres. At the present time the highest static pressures attainable by man are about 2 x 10 5 atmospheres. It is somewhat paradoxical that the tremendous pressures that are found at the centers of the white dwarf stars are produced by one of nature's weakest forces, namely, the force of gravitation. In our own small section of the universe it is of interest to note that the pressure at the center of the sun is about 10 11 atmospheres, while the pressure at the center of the earth is of the order of 10 6 atmospheres. Before proceeding with a discussion of high pressure methods, it will be enlightening to consider pressure in terms of energy. All forms of energy can be represented as the product of two conjugate quantities, one of which is intensive and the other capacitive. For example, heat energy may be represented as the product of an intensive factor, temperature, by a capacitive factor, heat capacity. Similarly electrical energy, commonly expressed in watts, may be represented by the product of voltage and amperage. Pressure is the intensive factor associated with a type of mechanical energy. Its corresponding conjugate quantity is the volume change accompanying the application of pressure. The range of phenomenological changes that can be produced in matter by the application of energy is qualitatively dependent on the magnitude of the intensive quantity associated with the energy. In order to explore the range of phenomena that might exist, it becomes important to vary the parameters of temperature, voltage, pressure, frequency, etc. over as wide a range as possible. Indeed, pushing the extrema to the greatest possible limits is recognized today as one of the best ways to advance the frontiers of science. Until recently the pressures available to man have not been intense enough to do more than effect small perturbations upon matter. To obtain an idea of the pressures that might be required to produce significant changes in matter, it is helpful to contrast pressure with temperature. Temperatures of the order of 1000 to 2000°C have been available for thousands of years and …