Some simplifications to multianvil devices for high pressure experiments

We describe a simplified multianvil system for high pressure and high temperature experiments based on the well-established octahedron-within-cubes geometry in use in many other laboratories. Departures in design from previous devices using this geometry include (1) use of a loose supporting ring that accommodates appreciable elastic strain under loading from within by an unanchored cylindrical cluster of removable tool steel wedges, (2) choice of height to diameter of the cylindrical cluster of wedges so that the negative cube geometry of the interior cavity that they surround does not have its angular relationships distorted under appreciable strain, (3) casting of composite gasket materials directly upon low porosity octahedral pressure media. The first two of these departures from established practices allow a drastic reduction in hardware cost, bulk, and production difficulty relative to current installations. The assembled multianvil module is cost effective, as well as being small and light enough to be inserted by hand in many of the standard hydraulic presses used for piston-cylinder work. The third departure reduces the risk of blowouts, of tedium, and of irreproducibility (during learning stages) of the normal procedure of cutting and attaching pyrophyllite gaskets. Using gaskets of Al₂O₃ in epoxy on a range of standard sizes of chrome magnesia octahedra, we are able to reproduce standard calibration point transitions with the same forces (and in some cases somewhat less force) required by other laboratories to achieve the same transitions with pyrophyllite gaskets. The overall performance of pressure, volume, and temperature (PVT) for this design is comparable to or better than extant octahedron-within-cubes devices. These developments should make multianvil experiments accessible to many existing piston-cylinder laboratories at modest incremental cost.