Optical cells, measuring pressures

An optical cell for pressures of up to 200 MPa and temperatures to 200°C is presented in Chapter 4.3.4. The cell can be coupled with a commercial Raman spectrometer to measure the course of the intensity of a bond s signal with time. By calibration, the intensity versus time curve can be converted into a concentration versus time curve, from which the rate of reaction and kinetic parameters can be evaluated. The method is explained in Chapter 3.3.2, considering the decomposition of an organic peroxide. 

Optical absorption, of hydrogenated and hydrogen- free films, 17 206 Optical amplifiers, 11 145-146 Optical applications U.S. patents in, 12 614t of vitreous silica, 22 440-441 Optical cavities, 14 849 Optical cells, for high pressure measurements, 13 417-419 Optical coatings, cerium application,... 

Huffman, D. R., L. A. Schwalbe, and D. Schiferl, 1982. Use of smoke samples in diamond-anvil cells to measure pressure dependence of optical spectra application to the ZnO exciton, Solid State Commun. (in press). 

The apparatus used are mostly stirred-tank-, tubular-, and differential recycle reactors. Also, optical cells are used for spectroscopic measurements, and differential thermal-analysis apparatus and stopped flow devices are applied at high pressures. 

Fig. 4.3-29. Optical cell for spectroscopic measurements under high pressure Max. pressure, 200 Mpa max temperature, 200°C.

The spinodal and the cloud point can be determined as a function of pressure and temperature (up to 150C, 1000 bar) via light-scattering measurements [41]. The intensity of the scattered light of the polymer solution is measured in a high-pressure optical cell during a pressure pulse in the polymer solution. 

The steady-state fluorescence measurements of pyrene in supercritical CO2 were made with a spectrometer assembly consisting mainly of Kratos optical parts. The custom built high pressure optical cell is equipped for detection at 90°. The emission was detected with a Hammamatsu IP-28 photomultiplier tube. The... 

FIGURE 7.1 Schematic presentation of a pill-box optical cell for measurements on solutions at high hydrostatic pressures. The slot and hole allow the pill-box cell to be filled and extra liquid to be released on closing the cell. 

In the next section the rare-earth compounds that have been studied by optical means under pressure so far will be reviewed. Then, after a brief introduction of the most commonly used high pressure device, the diamond anvil cell, sect. 4 presents a discussion of the pressure-induced changes of the crystal-field levels and their interpretation. In sects. 5 and 6 some aspects of the dynamical effects under pressure are discussed. These include lifetime and intensity measurements, the influence due to excited configurations and charge transfer bands, and the electron-phonon coupling. 

Experimental results are presented for high pressure phase equilibria in the binary systems carbon dioxide - acetone and carbon dioxide - ethanol and the ternary system carbon dioxide - acetone - water at 313 and 333 K and pressures between 20 and 150 bar. A high pressure optical cell with external recirculation and sampling of all phases was used for the experimental measurements. The ternary system exhibits an extensive three-phase equilibrium region with an upper and lower critical solution pressure at both temperatures. A modified cubic equation of a state with a non-quadratic mixing rule was successfully used to model the experimental data. The phase equilibrium behavior of the system is favorable for extraction of acetone from dilute aqueous solutions using supercritical carbon dioxide. 

The detection limits of individual PCAH will be determined by injecting known amounts into a flame. An estimate of the limit for pyrene can be obtained from the atmospheric pressure cell measurements. Pyreene was detected in the cell at 50°C and 1 atm of air, where its vapor pressure is about 0.1 milli-torr, or about 0.1 ppm. While this limit can be improved by optimization of the optics and electronics, it is sufficient to detect pyrene in the concentrations expected from probe measurements. 

Figure 2 The stronger component of the 1S-2S two photon transition in deuterium. The signal is the normalised Lyman-a fluorescence observed as a function of the frequency difference between lasers LI and L2 (fig. 1) when LI is locked to the appropriate transition (b2) in 13°Te2. The measured offset frequency is 20 MHz greater than the true value because of the shift introduced by the acousto-optic modulator. The pressure in the deuterium cell was 270 mtorr...

Beyond this, the combination of a high pressure optical cell with a magnetic coupling balance provides a possibility to measure the weight of the liquid drop and the related density difference between the drop phase and the surrounding fluid phase with time. Thus, a relation between the mass transfer across the fluid interface and the interfacial tension can be detected. 

The phase equilibria unit shown in picture 3 is a useful completion for the SFE pilot units. It is built for measurements and detection of phase equilibria and phase transitions by optical and analytical means. The picture from the optical cell is transmitted through the sapphire windows by the directly connected camera system and is displayed on the monitor in the front panel. Whenever samples are drawn out of the cell the directly connected counterbalance piston moves, thus keeping the pressure in the cell constant even during sampling operations. 

The optical high pressure cell shown in figure 2 was developed for spectroscopic investigations at pressures ranging from 1 to 400 bar and temperatures from 20 to 150 °C. The optical cell has a low-cost construction and shows versatile application possibilities (e g. variable optical path length, fluorescence measurements). The temperature is measured in direct contact with the fluid. 

Composition of the Phases. In a separate series of experiments the compositions of the gas and liquid phases were determined by a combination of material balances and spectrophotomqtric determinations of the concentration of NO2 in a sample withdrawn from the vessel. The procedure was similar to that described for the determination of a, except that the NO was purified further by passing it through silica gel (12) at dry ice temperature as the gas burette was filled. Measured quantities of NO were introduced to the equilibration vessel until the total pressure was 1 atm. as described previously. After equilibration a sample was withdrawn into a borosilicate glass optical cell, 2 cm. X 18 cm. diameter (.— 5 cc.). The absorbance of the sample at 25°C. was determined with a Cary Model 11 spectrophotometer at 4360A. Using an absorbtivity of 0.0105 0.002 (mm. Hg)" cm." as determined by calibration at a series of NO2 pressures at 25°C. as has been done previously (10, 18, 22, 24), the partial pressure of NOo in the optical cell was calculated. 

A dilute mixture of a solute in supercritical fluid is introduced into a high pressure optical cell, equipped for 90 degree detection with a 1.3 cm pathlength. The windows are 6 mm thick fused quartz discs. The pressure in the optical cell is measured with a Texas Instruments model 140 pressure gauge, which has an accuracy of 0.2 bar. The temperature in the optical cell is controlled with a custom built precision temperature controller that is good to 0.02 C. The temperature is measured by recording the resistance of an Omega type 44032 thermistor. The... 

Direct observations of Tm (P) and AV may be made in a sapphire optical cell with simple screw-press pump by measuring the offset in the pressure versus volume curve. AH can be measured at room pressure using a simple differential calorimeter comprised of two paper nut cups outfitted with kitchen thermistors and containing water in one and a standard solid material in the other for which the heat capacity curve is known. Direct observations of pressure-release freezing of water (as compared to pressure-release melting in silicates) may be observed in such an optical pressure cell by sudden release of pressure. 

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