Can the multianvil apparatus really be used for high-pressure deformation experiments?

Past claims of the suitability of the MA-8 multianvil press as a deformation apparatus may have been overstated. On the basis of measurements of final octahedron size and of guide block displacement as a function of time, using the 10/5, 14/8, and 18/11 assemblies (octahedron edge length in mm/truncation edge length in mm) with MgO octahedra and pyrophyllite gasketing, it appears that at run conditions of interest to most researchers there is no appreciable time-dependent creep of gaskets and octahedra. All inelastic deformation occurs at rather low pressures: below about 10 GPa for the 10/5, 7 GPa for the 14/8, and 6 GPa for the 18/11 assemblies, with substantial uncertainties in these pressures. Above these limits all deformation of the pressure medium is elastic. Pressure stepping as a means of increasing the inelastic deformation rate of a sample is probably ineffective. Displacement measured at the guide blocks, previously believed to indicate deformation of the gaskets and octahedron, appears now to be unrelated to creep of these components. The calibrations have not been exhaustive and there is considerable scatter in some of the size measurements, so the above conclusions are not unequivocal. The calibrations do not exclude the possibility of deformation of a few tens of microns after the attainment of high pressure. Efforts to impose permanent shape change to samples at high pressure and temperature simply by relying on long run durations must be viewed with skepticism. There may be possibilities for deformation in the multianvil apparatus if materials of contrasting elastic modulus are used to differentially load a sample during pressure stepping