Cell with diamond anvils

The cell with diamond anvils (in English diamond anvil concealment or DAC) is a Technique making it possible to subject a material to very high pressures and temperatures jointly. This capacity makes this device fundamental in several fields related to the Science of the materials as in Géologie where the conditions existing in the terrestrial coat can be reproduced.

Principle

The Pression is a Force applied to a Surface, whose formula is the following one:

$p= \ frac {F} {S}$

Where p is the exerted pressure, F the force applied and S surface.

To reach high pressures, one can act on two aspects:

the force applied that one increases
surface that one decreases

The cell with diamond anvils exploits mainly this second aspect by reducing surface. Thus, an important force is applied to a small surface. Thus of high pressures are produced.

The sample which one wishes to study is placed in a sleeve (or joint) metal to ensure the sealing of the medium. Two diamonds are useful act as anvil and has a presentiment of the sample.

The Diamant has several properties which make it ideal for this kind of use:

it is the natural material hardest which one knows and resists without becoming deformed with very high pressures
it has excellent optical property, which when it is pure, makes it transparent to most of the electromagnetic Specter, thus allowing to study the sample through diamonds.

Thus pressures going up to 360 GPa (3,6 million times the Atmospheric pressure) and from the temperatures of: 5000 Kelvin S (more: 4700 °C) can be reached.

Measure pressure

The measurement of the pressure exerted thanks to glares of Rubis which are inserted with the sample. These glares are ensuites lit by a laser and in answer emit a Fluorescence which varies according to the pressure.

Heating

The heating of the cell is carried out by resistive Four S for the temperatures going until: 1500 Kelvins (a little more: 1200°C) or: 2000 Kelvins (a little more: 1700°C) according to the assemblies. With this technique, the temperature is measured by a Thermocouple. These two techniques were developed with the National Office off Standard (NBS), today known under the name of National Institute of Standards and Technology (NIST), by Charles E. Weir, Alvin Van Valkenburg, Ellis R. Lippincott and Elmer NR. Bunting.

The National Office off Standard (NBS) being an American federal institution, Alvin Van Valkenburg obtains free diamonds to design its anvil. These diamonds had been confiscated by the US government with diamond trafficker. This aspect is important, the development of the cell with diamond anvils would doubtless have been slowed down if the researchers had been obliged to pay diamonds, because a certain number were destroyed before designing a functional instrument

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