Bevelled diamonds

Figure 10. Pressure distribution between beveled diamond culets under two different loads. The central flat region, where the sample is confined, is 10 pm in diameter while the rest of the culet is immersed in the gasket material. The lower picture schematically shows the diamond culets corresponding to the two pressure profiles. The shaded area indicates the extent of the diamond deformation at the highest load. (Adapted from Ref. 149.)...

The diamond anvils are typically gemstone quahty and weigh about 0.2 carat. Since pressure is simply force per unit area and the upper force hmit is determined by the strength limits of the components of the cell, the diameter of the diamond culet ultimately determines the maximum achievable pressure. No definitive relationship between the culet diameter and maximum pressure is available, but with a well-designed cell one can typically expect to reach pressures of 100 kbar with 700 pm culets, 500 kbar with 400 pm culets, and 1 Mbar with 200 pm culets [77]. Bevelled diamonds are recommended for pressures above 1 Mbar [77,80-82]. Sapphire [83,84] and cubic zirconia [85] are less expensive alternatives to diamond, but are not as strong and can be used only to 100 and 30 kbar, respectively. 

Figure 8. Diamond tips employed, in order of increasing final pressure, in experiments with the DAC (a) standard, (b) bevel, (c) double-bevel.

Figure 6.2. The crystalline habit of lactose a-hydrate. (A) Prism, formed when velocity of growth is very high. (B) Prism, formed more slowly than prism A. (C) Diamond-shaped plates transition between prism and pyramid. (D) Pyramids resulting from an increase in the thickness of the diamond. (E) Tomahawk, a tall pyramid with bevel faces at the base. (F) Tomahawk, showing another face which sometimes appears. (G) The form most commonly decribed as fully developed. (H) A crystal having 13 faces. The face shown in F is not present. (I) A profile view of H with the tomahawk blade sharpened. (From van Krevald and Michaels 1965. Reprinted with permission of the Journal of Dairy Science 48(3), 259-265.)...

Pressure was generated with a diamond anvil cell (DAC) employing beveled anvils with central flats ranging from 20 to 100 jim and flat diamonds with 200-500 pm culets. Two types of DAC were used modified (to match a continuous flow He cryostat) Mao-Bell cell for operations at room and low temperatures [41] and a Mao-Bell high-T external heating cell [42]. The latter one is equipped with two heaters and thermocouples. Four experiments were performed at RT aiming to highest pressure and the final pressures varied from 180 to 268 GPa. For low-temperature measurements we used a continuous-flow He cryostat, which allowed infrared and in situ Raman/ fluorescence measurements. More details about our IR/Raman/fluorescence setup at the NSLS are published elsewhere [41]. 

Fig. 1.23 (a) Diamond tips with flat (top) and bevelled (bottom) culets. (b) The usual shapes of diamond anvils left) brilliant cut, and right) Drukker-Dubbledee standard. (Reprinted with permission from J. Phys. E., 22, 913, (1989).)... 

Here, a small piece of dried material is first impregnated using epoxy resin and cut to a thin slice (of dimensions 1.7 x 1.7 x 0.7 mm ) using a diamond saw with isopropanol as a lubricant. It is thinned down mechanically to a bevel by means of the Tripod method to yield a thickness of about 20-30 pm on the thick side. Diamond lapping film discs of 30, 15, 6, 3, 1 and 0.5 pm are used to progressively reach the final thickness. Isopropanol is used as a lubricant. 

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