Multianvil Presses

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Uniaxial Presses

The Experimental Petrology Laboratory operates two 6/8 cylindrically constrained (Walker-Type) multianvil apparatus: A 1000-tons conventional O-frame press with a cylindrical pressure module holding 32 mm second-stage WC-anvils and a 600-ton O-frame press that is mounted on a cradle that can turn the entire press by 180° including either a multi-anvil module (32mm second-stage WC-anvils) or a 14mm bore end-loaded piston cylinder module when the system is under pressure and temperature - the so called 'Shaker'.  In 2012 we installed a guide-block driven split-cylinder press, capable of generating press forces of up to 2000 tons.

Conventional multianvil apparatus are operated with both castable and prefabricated MgO-octahedra. Pressure ranges from 4.0 -25 GPa and is controlled  with worm-gear-type automatic pressure control systems. Experiments cover a wide range of subjects ranging from phase equilibria studies, material synthesis, fluid-liquid-solid equilibria to ultrasonic wave propagation studies.

 

Sintered Diamond True Split-Sphere Press

Multianvil devices are commonly based on a two stage compression mechanism: a set of six anvils (1st stage anvils, mostly hardened tool-steel) distribute force on the faces on a cubic arrangement of eight corner truncated cubes (2nd stage anvils; usually tungsten-carbide). These cubes then transmit the force on a small octahedral pressure cell, which fills the void provided by the anvil-truncations.

The maximum pressure that can be reached with commonly used uniaxial, tungsten-carbide driven multianvil presses is restricted to approximately 25 GPa due the limit strength of tungsten carbide cubes, which deform and fail at sufficiently high stresses. In order to perform experiments at even higher pressures we have developed a multianvil apparatus, which uses cubes made of sintered diamond as second stage anvils. These sintered diamond cubes are much more rigid compared to conventional tungsten-carbide cubes and thus allow significantly higher pressures to be reached. However, using sintered diamond cubes as second stage anvils requires perfectly homogeneous stresses provided by each of the 1st stage anvils, because any differential stress, as it is unavoidable in uniaxial driven presses, will cause the (expensive) sintered diamond cubes to break. For this reason, we use the method described by Kawai & Endo (1970), which employs a true ‘split sphere’ (see below) as 1st stage anvils. This configuration is compressed in an oil bath to ensure hydrostatic pressure.

Using this configuration we are able to generate pressures up to 40 GPa, which on Earth corresponds to a depth of approximately 1000 km.

 

People interested to work in our laboratories are welcome; for interesting projects, we provide access to our experimental and analytical facilities to external users, mainly through collaborations. We may be able to provide limited funding for short term visitors.

 
 
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23.05.2017
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