Bridgman anvil

All static studies at pressures beyond 25 GPa are done with diamond-anvil cells conceived independently by Jamieson [32] and by Weir etal [33]. In these variants of Bridgman s design, the anvils are single-crystal gem-quality diamonds, the hardest known material, truncated with small flat faces (culets) usually less than 0.5 nun in diameter. Diamond anvils with 50 pm diameter or smaller culets can generate pressures to about 500 GPa, the highest static laboratory pressures equivalent to the pressure at the centre of the Earth. 

Research. A significant impact on research at high pressure has come about with the use of gem quaHty diamonds as Bridgman-type anvils in a smaU compact high pressure device (40—42). With this type of apparatus, pressures greater than those at the center of the earth (360 GPa = 3.6 Mbars) have been reached, and phase transformations of many materials have been studied. Because of the x-ray transparency of diamond, it is possible to determine the stmcture of the phases under pressure. Because of the strenuous environment, crystals selected for this appHcation have to be of very high quaHty. 

In the Bridgman anvil device the sample is compressed between supported anvils of tungsten carbide, and lateral containment is ensured by a gasket that can be made of pyrophyllite or metallic material. A variety of cells based on the Bridgman opposed anvils has been developed [38 0]. Pressures up to 20GPa... 

Figure 5. Different types of opposed-anvil devices (a) Bridgman (b) Drickamer (c) girdle (d) belt (e) sample area of the toroidal anvil.

In recent years, low-temperature Bridgman anvil apparatus combined with modern instrumentation has led to extensive studies of the superconducting state for pressures up to 50 GPa at temperatures down to 0.05 K. It is found that the 1-atm superconducting substances, such as lead,... 

FIGURE 1 shows the equilibrium pN2 - T curves for AIN, GaN and InN. The curve for AIN was calculated by Slack and McNelly [6], The one for GaN was determined by Karpinski and Porowski [5] based on gas pressure and Bridgman anvil experiments performed by Karpinski et al [4], The curve for InN was obtained by Grzegory et al [7] and follows from differential thermal analysis (DTA) and annealing of InN at high N2 pressure. The curves for GaN and InN deviate from linear dependence at... 

The pressure vessel used in these experiments was a set of anvils similar to that described by Bridgman (2). The necessary thrust was developed with a hydraulic press of 100-, 200-, or 500-ton capacity, depending on the total force needed. The total force required depends on the nature and diameter of the sample. 

Figure 10 Diffraction geometry with diamond anvils (a) Merrill-Bassett-like geometry (b) Bridgman-like geometry but with both transparent anvils and gasket. (From Ref. 96.)...

Fig. 33. Polarized emission spectra of single-crystal Ba[Pt(CN)4] 4 H20 at different hydrostatic pressures (T = 295 K)133). The emission intensities at different pressures cannot be compared. The excitation wavelength was varied with pressure to fit approximately the maximum of the E c polarized reflectance. For the high pressure investigations a modified sapphire cell of Bridgman s opposed anvil type was used. The pressure was determined by the amount of red-shift of the Rt- and R2-lines167) of ruby crystals placed around the sample...

Static and shock wave compressions are the two remarkably different ways for generating pressures above 1 GPa. Here, only apparatus generating static pressures of more general use will be considered. These are classified into several types, piston-cylinder, Bridgman anvU, belt, multi-anvil, and cascaded multi-anvil types. The available pressure range depends on the type and also on the volume of the sample chamber used. It is 2 4 GPa with the piston-cylinder type, 5-8 GPa with the belt type, 10-20GPa with... 

The Bridgman anviP is illustrated in Figure 6(a). Tapered anvils made of WC are supported by steel rings. The sample (or sample cell) is surrounded by a gasket made of pyrophyUite. 

Figure 6 Essential parts of high pressure apparatus of (a) the Bridgman type, (h) the belt type, (c) the cubic anvil type, (d) the 6-8 split sphere anvil type, and (e) the diamond anvil type...

The third category (Section 3) deals with DACs. Although, in principle, these cells are simple, Bridgman opposed-anvil systems which should belong to the second category, in practice they have such original characteristics and widespread applications that it is more convenient to treat them separately. 

The principle of a Bridgman opposed-anvil apparatus is shown in Fig. 1.13. The sample is compressed between supported tungsten carbide (WC) anvils. It is contained by gaskets which may be pyrophyllite or metallic materials, depending on the measurement to be performed. This design makes use of the massive-support mechanism, in that the maximum pressure which may be... 

Fig. 1.13 The principle of a Bridgman opposed-anvil apparatus. (From reference 1.)...

Fig. 3.44 Various high-pressure cells used for Mossbauer spectroscopy. (a) hydraulic cell with beryllium windows for p<250 MPa, (b) the same for p<1GPa, (c) Simple Bridgman anvil cell for y-ray transmission through the gasket, (d) as for (c), transmission through the anvils, (e) Belt-type cell with hollowed anvil, and (f) DAC. (Reprinted with permission from the publisher.)...

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