Pressure measurement ruby fluorescence method

With the development of the rapid, accurate, routine and convenient ruby fluorescence method of pressure measurement at NIST in 1972, the problem of pressure calibration and measurement, a major obstacle to widespread use of the DAC, was removed [7]. As a result of this development, the DAC experienced an unprecedented expansion in its use and acceptance by the high pressure community as a tool for physical and chemical investigations. 

As noted above, a combination of high pressure diamond anvil techniques, all utilizing the ruby fluorescence method of pressure measurement, were used to carry out these experiments. These include (1) Fourier transform infrared (FTIR) spectroscopy for the kinetic measurements [9-11], (2) energy dispersive x-ray powder diffraction for crystallographic identification of the observed polymorphic forms and also compression measurements [12], (3) optical polarizing microscopy... 

Since diamond is transparent to visible light, the easiest method of measuring the pressure is with the ruby-fluorescence (Al203 Cr ) scale. The fluorescence associated with the Rj and R2 transitions of the ion around 14400 cm at ambient pressure shifts by —7.57 cm GPa under pressure, and pressure variations of —100 GPa can be measured with a modest spectrometer. Excitation-argon-laser powers of —10 mW are sufficient to obtain measurable signals from ruby chips with a volume of —1000 (cm. A chromium content in the ruby of anywhere between 500 and 5000 p.p.m. 

To be referred to next is the most modern diamond anvil type, generating pressures of order of 10-100 GPa. The cell illustrated in Figure 6(e) consists of two gem diamonds with optically flat surfaces, between which a sample confined in a drilled hole of a thin metal gasket is sandwiched. To attain isostatic compression an inert gas or an organic liquid, like a 4 1 volume mixture of methanol and ethanol, is contained with the sample. The generated pressure is measured directly from the pressure shift of the fluorescence line of ruby powder mixed with the sample. Temperatures to 5000 K can be obtained by laser heating. The quantity of sample confined in a typically 0.1-mm-wide hole is extremely small, just a few microcrystals. At present, research has focused on in situ observations using X-ray and other optical methods, rather... 

For monitoring the pressure in anvil cells we use the frequncy shift of internal, chemically inert pressure calibrants. For Raman spectroscopic measurements, the most commonly used method is based on the pressure-induced frequency shift of the fluorescence line of a small piece of ruby that is placed in the sample compartment of the cell, next to the sample [1]. For infrared spectroscopic measurements, we have developed a quartz pressure scale [9], a BaSO pressure scale [10], and an HOD pressure scale [11], In the case of the first two techniques, a small amount of powdered quartz or BaSO powder are placed in the sample hole on the gasket, together with the sample under investigation. The infrared spectra of quartz or BaSO, which are relatively simple, are recorded simultaneously with the spectrum of the sample and the pressure on the sample b then determined from the frequency shift of the infrared bands of quartz or BaSO. The HOD pressure scale was developed specifically for aqueous solutions. In this case, the pressure in solution is determined from the frequency shift of the uncoupled O-H stretching band of residual HOD in DjO solutions, or from the uncoupled O-D stretching band of residual HOD in HjO solutions [11]. 

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