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A diamond anvil cell (DAC) is a device used by Physicists to exert extreme Pressure s on a material. It consists of two opposing cone-shaped Diamond s squeezed together. The resultant high pressures — in excess of a million atmospheres — are produced when force is applied to small areas of the opposing diamond culets. The device has been used to simulate the extreme pressures existing in the hearts of , thought to be the major component of the Earth's Mantle . PRINCIPLE The operation of the diamond anvil cell relies on a simple principle: where p is the pressure, F the applied force, and A the area. Therefore high pressure can be achieved by applying a moderate Force on a sample with a small area, rather than applying a large Force on a large area. In order to prevent deformation and even breakage of the Anvil s that apply the force, they must be made from a very hard and virtually incompressible material: diamond. HISTORY Diamond . The first prototypes were limited in their pressure range and there was not a reliable way to Calibrate the pressure. During the following decades many investigators have used DACs and following their experience many innovative improvements were introduced, the most important being the use of Gasket s and the Ruby pressure calibration. The DAC evolved to be the most powerful lab device for generating static high pressure. The range of static pressure attainable today extends to the pressures prevailing in the earth’s center (~360 GPa). A large number of scientists make use of the diamond anvil cell including Dave Mao and James Badro . COMPONENTS There are many different DAC designs but all of them have three main components: (1) The Force -generating device — relies on the operation of either a Lever arm, tightening Screw s, or Gas Pressure applied to a membrane. In all cases the Force is Uniaxial and is applied to the tables (bases) of the two Anvil s (2) Two opposing Diamond Anvil s — made of high Gem quality, flawless diamonds, usually with 16 facets. They typically weigh 1/8 to 1/3 Carat (25 to 70 mg). The culet (tip) is ground and polished to a hexadecagonal surface parallel to the table. The culets of the two Diamond s face one another, and must be perfectly Parallel in order to produce uniform Pressure and to prevent dangerous Strain s. (3) in a cavity between the Diamond s, and to prevent anvil failure by supporting the Diamond tips, thus reducing Stresses at the edges of the culet. USES Prior to the invention of the diamond anvil cell static high-pressure apparatus required large hydraulic presses which weighed several tonnes and required large specialised laboratories. The simplicity and compactness of the DAC make it a tool than can be accommodated in a wide variety of experiments. Some of the contemporary DACs can easily fit into a Cryostat for low-temperature measurements, and for use with a Superconducting Electromagnet . In addition to being hard, Diamonds have the advantage of being transparent to a wide range of the Electromagnetic Spectrum from Infrared to Gamma Rays , with the exception of the far Ultraviolet and soft X-rays . This makes the DAC a perfect device for Spectroscopic experiments and for Crystallographic Studies using hard X-rays . A variant of the diamond anvil, the hydrothermal diamond anvil cell (HDAC) is used in experimental petrology/geochemistry for the study of aqueous fluids, silicate melts, immiscible liquids, mineral solubility and aqueous fluid speciation at geologic pressures and temperatures. The HDAC is sometimes used to examine aqueous complexes in solution using the synchrotron light source techniques XANES and EXAFS . EXTERNAL LINKS
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