New determination of the bismuth I-II equilibrium pressure: a proposed modification to the practical pressure scale

Abstract

A new high-pressure instrument has been developed with the pressure uncertainty characteristic of free-piston gauges in the 3000 MPa range. It consists of an end-loaded piston-cylinder apparatus modified to use argon as a pressure medium. Pressure is determined from the piston force and the piston seal area with minor corrections for vessel bore dilation and seal friction. Bore dilation is approximately 0.36 % and double-valued friction for the piston seal ranges from about 1 % to 2 %. A force-balance analysis of the piston seal indicates that the friction is highly symmetric. The equilibrium pressure of the Bi I-II transition has been determined in this apparatus to serve as a reference point on the practical pressure scale.Transition pressure measurements were made on 99.9999 % pure polycrystalline bismuth. Small piston force excursions were made with both phases present to determine the equilibrium pressure which is insensitive to reaction rate. The Bi I-II equilibrium pressure is (2520 ± 5) MPa at 25 C. This value is 30 MPa (1.2 %) lower than Heydemann's [1] value of (2550 ± 6) MPa. It is 8 MPa (0.3 %) higher than the value of (2512 ± 3) MPa from Sekoyan et al. [2].

Ultrafast Dynamic Compression Technique to Study the Kinetics of Phase Transformations in Bismuth

“…Pursuit of a detailed understanding of pressure-induced structural phase-transformation kinetics has been an active area of theoretical and experimental research in condensed-matter physics for several decades [1][2][3][4][5][6][7][8][9]. Despite this, there remains a lack of quantitative data primarily due to the limitations in experimental techniques to measure these extremely rapid phenomena.…”

New Developments in Deformation Experiments at High Pressure

“…A recent development is an apparatus built by Getting (Getting 1998;Getting and Spetzler 1993) that combines aspects of the solid-medium and fluid-triaxial deformation machines. Getting's is a piston-cylinder device that features precision packings that are sufficiently tight to contain solid argon (an exceedingly weak solid) but sufficiently reproducible in their frictional behavior that much of the uncertainty in stress introduced by piston friction can be accounted for by calibration.…”

“…Getting's is a piston-cylinder device that features precision packings that are sufficiently tight to contain solid argon (an exceedingly weak solid) but sufficiently reproducible in their frictional behavior that much of the uncertainty in stress introduced by piston friction can be accounted for by calibration. Getting (1998) claims pressure uncertainty at P = 3 GPa at the extraordinary level of a few MPa. If this resolution applies also to the sum of σ 1 + P, as expected, it may mean that rock strengths can be measured with a resolution that is comparable to that of many triaxial gas rigs that operate at far lower pressures.…”

Laboratory Sharing to Improve Rock Deformation Research

“…The great advantage of this modification would be that it would dramatically improve the precision of the differential stress measurements by reducing the influence of piston friction on that measurement. In fact, such a machine has already been built (and since destroyed) and usedsuccessfullytenyearsagotosubjectasampletoapressureof~3GPaforhydrostatic pressure studies [BurnleyandGetting, 2012;Getting, 1998] ( Figure 10). It is high time to breathelifeintothisexistingdesignandimplementitforadeformationapparatuswithtwo concentric pistons (one for pressure, one for differential stress)liketheGriggsRig.…”

“…In addition to Figure 11. VascoMax C350 maraging steel miter ring pressure seal that has been successfully used to seal argon at 3.0 GPa pressure with low friction [Burnley and Getting, 2012;Getting, 1998]. …”