Diamond compression cell

Beam Condensers.4c Beam condensers are used to focus the IR radiation from a beam that is typically 8 mm in diameter to one that is around 2 mm at the sample plane. This allows the analysis of 50-100 resin beads without KBr dilution. A diamond compression cell is used to flatten beads and to support the sample throughout the measurement. The same diamond cell without beads is then used to record a background spectrum. 

Fibrous materials may be analyzed by a number of different methods, including the standard method for sample preparation—compressed halide pellets. In this latter case, normally the fiber structure is destroyed during sample preparation. Alternatively, one can consider using diffuse reflectance, photoacoustic, or infrared microscopy. With due consideration to the preparation procedures, the fibers may be retained in their original form with these methods. In some cases, such as with IR microscopy, it is possible to study the orientation characterisitics of the fiber material and to correlate this information to certain mechanical properties of the fiber. The use of IR polarizers is imphed with this type of measurement. Diamond compression cells work well for single-filament fibers by both transmission (diamond anvil cell) and ATR. 

Several methods are also available for determination of the isothermal compressibility of materials. High pressures and temperatures can for example be obtained through the use of diamond anvil cells in combination with X-ray diffraction techniques [10]. kt is obtained by fitting the unit cell volumes measured as a function of pressure to an equation of state. Very high pressures in excess of 100 GPa can be obtained, but the disadvantage is that the compressed sample volume is small and that both temperature and pressure gradients may be present across the sample. 

Fig. 1 Schematic diagram of a diamond anvil cell (DAC). The sample, pressure calibrant and hydrostatic fluid are loaded into the gasket hole, which is then compressed between the culets of the two diamond anvils...

FTIR Microspectroscopy.3 A microscope accessory coupled to a liquid-nitrogen-cooled mercury-cadmium-telluride (MCT) detector can be used to obtain an IR spectrum. This is possible in both the transmission and reflectance modes. Several beads are spread on an IR-transparent window (NaCl, KBr, diamond) and possibly flattened via a hand-press or a compression cell. The IR beam is focused on a single bead using the view mode of the microscope. The blank area surrounding the bead is isolated using an adjustable aperture, and a spectrum is recorded using 32 scans (<1 min). A nearby blank area of the same size on the IR transparent window is recorded as the background. 

The e - y transition boundary was determined by measuring the resistance changes during the transition in a high-compression belt apparatus (Bundy, 1965) and in an internally heated diamond-anvil cell (Boehler, 1986 Mao et al, 1987). The boundary was also determined by in situ X-ray diffraction measurements in an internally heated diamond-anvil cell (Boehler, 1986 Dubrovinsky et al, 1998), in a laser-heated diamond-anvil cell (Shen et al, 1998), and in a multi-anvil apparatus (Funamori et al, 1996 Lfchida et al, 2001). The boundaries determined by Mao et al. (1987), Shen et al (1998), and Lfchida et al (2001) are in good agreement, but are all at —75 K higher temperature (or —2 GPa lower pressure) than the boundary determined by Funamori et al. (1996), Boehler (1986), and Bundy (1965). 

Since the 1990s the combination of diamond anvil cell (DAC) techniques with imaging plate detectors has turned the investigation of compressibility and... 

The microstructures of the consolidated and deformed samples were characterized by X-ray diffraction, optical and electron microscopy (SEM and TEM). The samples for mechanical testing have been prepared by spark erosion. The linear thermal expansion was determined by using a thermomechanical system (TMA). The temperature-dependent elastic moduli have been measured by the resonance frequency and the pulse-echo method. The bulk moduli were determined by synchrotron radiation diffraction using a high-pressure diamond-die cell at HASYLAB. The compression and creep tests were performed with computer-controlled tensile testing and creep machines. 

Shock-compressed carbon dioxide exhibits a strong slope change in the Hugoniot (recall Fig. 1), a clear indication of chemical reaction, at around 40 GPa and estimated temperature of 4500 K [1]. The previous theoretical calculation has confirmed that it is indeed due to chemical dissociation of carbon dioxide to elementary products such as diamond and oxygen. In recent diamond-anvil cell experiments [74], the similar dissociative products, lonstaleite diamond and oxygen have also been observed from the quenched products after laser-heating of CO2 samples at 67 GPa. The transition temperatures were estimated to be about 2500 K at 35 GPa, substantially lower than the estimated shock transition temperature 4500 K. 

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