Cryogenic recovery of unquenchable high-pressure samples using a multianvil device

A simple modification has been made to the standard Walker-style 6-8 multianvil apparatus, to allow samples to be depressurized at low temperatures. This is done by introducing a coolant, in this case liquid nitrogen, into the sample area during decompression. Thus low-temperature recovery techniques, which have been used previously in a few instances in the diamond-anvil cell and piston-cylinder apparatus, have been extended to the multiple anvil, allowing large samples of some unquenchable phases to be recovered from high pressures. Two large (60 mg. each) samples of calcium hydroxide (Ca(OH)₂) and three samples of calcium deuteroxide (Ca(OD)₂), both in the unquenchable high pressure Eul₂ (baddeleyite-related) form, have been recovered from 9 GPa and 400 ° C using this technique. The recovered samples are shown by Raman spectroscopy to retain the high pressure structure at 85 K. During heating at 10 K per minute, the material begins to revert to the low pressure portlandite phase at 223 K, and the reversion is complete by 275 K. This recovery technique can be used subject to certain kinetic conditions, but in general the outcome cannot be predicted and an experiment needs to be performed for each material of interest.