Optical high-pressure cell

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... 

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 apparatus used to perform vibrational relaxation experiments in supercritical fluids consists of a picosecond mid-infrared laser system and a variable-temperature, high-pressure optical cell (68,73). Because the vibrational absorption lines under study are quite narrow (<10 cm-1), a source of IR pulses is required that produces narrow bandwidths. To this end, an output-coupled, acousto-optically Q-switched and mode-locked Nd YAG laser is used to synchronously pump a Rhodamine 610 dye laser. The Nd YAG laser is also cavity-dumped, and the resulting 1.06 pm pulse is doubled to give an 600 u.l pulse at 532 nm with a pulse duration of "-75 ps. The output pulse from the amplified dye laser ("-35 uJ at 595 nm, 40 ps FWHM) and the cavity-dumped, frequency-doubled pulse at 532 nm... 

The high-pressure optical cell is comprised of a Monel 400 body, gold or teflon O-rings, and CaF2 or sapphire windows. The two windows are secured using an opposed force-type seal incorporating Belleville spring washers. The cell is essentially leak-free at pressures up to 3000 psia ( -200 atm). 

The pendant drop method was applied in order to determine interfacial tension and was carried out by photographing the drop in a high pressure optical cell evaluating the contour... 

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. 

Fig. 2. High temperature high pressure optical cell used at the University of Tokyo, (a) Schematic diagram of the optical cell (b) Sealing mechanism of a Sapphire window.

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... 

The inner volume and maximum working pressure of the high-pressure optical cell for the Raman spectroscopic analysis were 0.2 cm and 400 MPa, respectively. The cell had a pair of sapphire (or quartz) windows on both the upper and lower sides. The thermostated water was circulated constantly in the exterior jacket of the high-pressure optical cell. A ruby ball was enclosed to agitate the contents by the vibration from outside. 

Figure 4 Raman spectra of rotation for H2 (a), and intramolecular vibration for H2 (b) and CO2 (c) molecules in the gas and hydrate phases at 280.1 K and 4.3 MPa. The mole fraction of THF is 0.056. The high base line less than 520 cm and the broad peaks at 600, 810 and 1060 cm are due to the quartz window of high-pressure optical cell.

A survey of high-pressure optical cells has been given in the books by Isaacs and by Sherman and Stadtmuller. However, only a few of the cells described in these books are suitable for vibrational spectroscopy studies under conditions of simultaneous high pressure and high temperature. Cells which meet these requirements and which can be used up to 7 kbar and 700 °C... 

Fig. 6.3 A schematic diagram of a separator unit complete with a Teflon finger (1) connection to high-pressure optical cell, (2, 3) O-rings, (4) Teflon finger, (5) pressure liquid for the optical cell, (6) pressure liquid for the high-pressure pump, and (7) connection to the high-pressure pump. ...

Autoclaves, high-pressure optical cells, valves, pumps, gauges, fittings, and intensifiers to 7 kbar... 

Fig. 1.4. Schematic presentation of a "pill-box optical cell for measurements in a high pressure optical cell. The slot and hole allow the pill-box cell to be filled and extra liquid to be released on closing the cell.

Water-in-C02 microemulsion was used to dissolve metal salts in the production of nanoparticles via RESOLV. In order to evaluate the solubility of Cu(N03)2, for example, the same microemulsion as that used in the rapid expansion was prepared in a high-pressure optical cell. With Cu(N03>2 in the water phase, which exhibited the distinctive blue color of aqueous Cu (70), the microemulsion appeared homogenous. According to the observed absorbance (the band centered at 740 nm), the Cu(N03)2 salt was completely dissolved in the PFPE-NH4-stabilized water-in-C02 microemulsion. The other metal salts were similarly soluble, resulting in microemulsions that appeared equally homogeneous. 

Figure 16. High-pressure optical cell for static solubility measurements (1 = soft-iron wire, 2 = Bridgman piston, 3 = screw cap, 4 = thrust collar, 5 = teflon packing, 6 = inner Bridgman piston, 7 = cap of autoclave, 8 = sliding piston, 9 = body of autoclave, 10 = window fitting, 11 = sapphire window, 12 = sample container, 13 = sealing screw, 14 = stirring rod for details see [45,76]).

Often a phase transition between two liquid crystalline phases is associated with a change in texture, which is characteristic for a special phase. The observation of the sample in the high pressure optical cell by a polarizing microscope then offers the advantage not only of detecting the phase transition but also of identifying the type of the involved liquid crystalline phases [13, 17]. 

An opposed diamond anvil cell was used as a high pressure optical cell. For getting good textures a 0.1 mm thick gasket made of hardened steel was used. A Sm-N transition is identified by a change from the Schlieren to the focal conic texture with ellipses. The monotropic SmB phase shows a mosaic texture. 

At a constant Wq value of 4, the observed absorbance increases linearly with Cu(N03)2 concentration in the water core (Figure 43) up to the maximum solubility of about 3.5 M (274). Since the reverse micelles are homogeneously distributed in the continuous-phase CO2 in the high-pressure optical cell, the Cu(N03)2 concentration with respect to the cell volume can be used... 

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