Anvil, transparent

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. 

Figure 4.29. Sample assembly for optical shock temperature measurements. The sample consists of a metal film deposited on a transparent substrate which serves as both an anvil and a transparent window through which thermal radiation is emitted. Rapid compression of gases and surface irregularities at the interface between the sample film and the driver produce very high temperatures in this region. The bottom portion of the figure illustrates the thermal distribution across through the assembly. (After Bass et al. (1987).)...

As discussed previously, the anvil seats on which the diamond anvils are mounted have traditionally been made of X-ray transparent beryllium (Fig. 6a), although other hard, low-Z materials have also been used, such as B4C and BN. The disadvantage of all of these is the large background scatter that arises once the... 

The assemblies of the transparent anvil drop weight apparatus and the instrumented drop weight apparatus are shown in Figures 3.12 and 3.13... 

Figure 3.12 Transparent anvil drop weight apparatus. Reprinted with permission from Field, J.E., Swallowe, C.M., Palmer, S.J.P., Pope, P.H., and Sundarajan, R. (1985) Proc. 8th Symp. (Inti) on Detonation 1985, Naval Surface Warfare Center, USA.

Ammonium Chlorite, NH4C102, pale yel, transparent crysts, mp dec rapidly on heating. According to Mellor(Ref 1), this compd was first obtd in soln by N.Millon(184 3) on saturating an aq soln of chlorous acid with ammonia. Levi(Ref 2) prepd the compd in the form of delq ndls which exploded on percussion on an anvil... 

Thin films of silicates have been produced by pressing powders in a diamond anvil cell (Hofmeister 1997), by cutting grain samples to submicron thick slices with an ultra-microtome (Bradley et al 1999), by electron-beam evaporation (Djouadi et al. 2005), and by laser deposition in a vacuum (Brucato et al. 2004). On one hand, powders produced in a laboratory are directly measured in transmittance when they are embedded in a matrix of transparent materials (e.g. KBr or polyethylene). On the other hand, reflectance measurements do not require the use of matrices powders of selected-size grains are directly measured with an appropriate optical accessory. Through measurements in both transmittance and reflectance, it is possible to evaluate the optical constants of a material. These are certainly the physical parameters... 

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.)...

The operating principle of a DAC is elegantly simple (Figure 15). A gasket of metal foil (usually steel, W or Re) is placed between the diamond anvils. A hole drilled in the center of the gasket contains the sample immersed in a hydrostatic liquid. The anvils are mounted on beryllium (for X-ray transparency) back-plates, to which force is apphed by an inflatable membrane, a level-arm mechanism or just by tightening screw-bolts. Thus a hydrostatic compression is achieved. Such cells can be operated also at high and low temperature, and are also suitable for spectroscopic studies, since diamond is an ideal transmitter of heat and of all types of radiation. 

Figure 11 The diamond-anvil cell has emerged as the dominant and most versatile tool for achieving high pressures (up to millions times of the atmospheric pressure). It uses two diamond anvils, which exert pressure and serve as windows on the sample. A metal gasket confines the sample and supports the anvils. Because diamond is the strongest material known and is transparent over a wide range of the electromagnetic spectrum, various high-pressure experiments are performed using synchrotron radiation...

For pressure generation in X-ray diffraction and spectroscopy, the Diamond Anvil Cell is the most versatile tool. Using diamond as the anvil material combines the advantages of mechanical hardness and transparency for electromagnetic radiation. ... 

A diamond-anvil-cell (DAG) is a small high pressure cell most suitable for the spectroscopic measurement of molecular or atomic diffusion. The DAG is used for various kinds of spectroscopic investigations on liquids and solids at pressures up to several tens of GPa [19-22]. The optically transparent nature of diamond over a wide wavelength span allows in situ optical measurements in combination with conventional equipment such as visible light or infrared spectrometers. The protonic diffusion in ice is measured by a traditional diffusion-couple method, in the present case, with an H2O/D2O ice bilayer. The mutual diffusion of hydrogen (H) and deuteron (D) in the ice bUayer is monitored by measuring the infrared vibrational spectra. The experimental details are described in the following sections. 

The extraordinary properties of diamond including hardness, high thermal conductivity, and transparency over large portions of the electromagnetic spectrum make it an ideal material for anvils that also serve as windows. All of the analytical techniques described here take advantage of these properties. 

The anvil seats transmit a force to the anvil tables of the order of 10 kN. Thus the seats are subjected to a normal stress of some 2 GPa, for a 3 mm diameter table. This value may well be exceeded for ultrahigh-pressure work. Thus seats are most often made of tungsten carbide with an optical finish. In some X-ray measurements, beryllium seats have to be used, for their transparency. The mechanical performance is then drastically decreased, and the beryllium must be machined in specialized workshops. Single-crystal sapphire has been used, to provide an increased optical aperture. ... 

---