Mj. Walter et al., CHARACTERIZING EXPERIMENTAL PRESSURE AND TEMPERATURE CONDITIONS IN MULTI-ANVIL APPARATUS, Canadian journal of physics, 73(5-6), 1995, pp. 273-286
Octahedral media made of MgO-5%Cr2O3, with edge lengths of 18, 14, and
10 mm are used as pressure cells in experiments in a multi-anvil soli
d media apparatus at pressures of 4 to 27 GPa and temperatures to >270
0 degrees C. Calibrations of press-load versus sample pressure: are ba
sed on room-temperature and high temperature phase transitions, and ar
e accurate to within +/-0.5 GPa. Calibrations of the temperature distr
ibution were made in the central portion of the furnaces (graphite or
LaCrO3) in the various sample assemblies used routinely in this labora
tory. The following gradients away from the furnace midlines were obse
rved: 18 mm: high-T straight graphite (-100 degrees C mm(-1)), high-T
stepped graphite (+25 degrees C mm(-1)), low-T stepped graphite (-20 d
egrees C mm(-1)), high-T stepped LaCrO3 (-50 degrees C mm(-1)); 14 mm:
high-T stepped LaCrO3 (-70 degrees C mm(-1)); 10 mm: straight LaCrO3
(-200 degrees C mm(-1)). The effect of increasing the wall thickness o
f the central segment of the furnace (''stepping'') is to reduce the t
emperature gradient relative to a straight design. The relative effect
of pressure on W3Re-W25Re and Pt-Pt13Rh thermocouples was measured by
comparison of apparent temperatures recorded by each type in a given
experiment. Corrections for the effect of pressure on thermocouple emf
depend on the temperature distribution in the gasket regions surround
ing the pressure cell, where pressure is reduced to ambient conditions
. The temperature of this pressure seal controls the magnitude of the
effect of pressure on thermocouple emf. Because this temperature: will
vary depending on the assembly, no universal pressure correction can
be derived.