High-temperature Optical Cell Research Articles

Micro FT-IR spectroscopic measurements of CH4: Experimental calibration with high-pressure and high temperature optical cell (HPOC)

Fourier transform infrared spectroscopy (FTIR) is a prevalent nondestructive in situ analytical technique widely employed for the qualitative characterization of natural fluid inclusions. Presently, the quantitative determination of the temperature, pressure, and composition of natural inclusions stands as a pivotal challenge in the geological application of laser spectroscopy. Through the integration of the capillary high-pressure optical cell (HPOC) technique and Fourier transform infrared spectroscopy, infrared quantitative models for the C–H symmetric stretching band (v3) in the vapor phase of CH4 under varying temperature (40–200 °C) and pressure (20–500 bar) conditions are established for the first time. This accomplishment is achieved through fitting and calculation of infrared spectra. A linear quantitative relationship and the dynamic evolution of infrared spectral parameters (peak area, full width at half maximum, peak height ratio, and peak shifts) concerning temperature, pressure, and density are meticulously investigated. The findings reveal that the peak area and full width at half maximum exhibit an upward trend with increasing pressure and density, and are inversely proportional to temperature. The height ratio (P band/Q band, R band/Q band) experiences an increase as density escalates. Moreover, the CH4v3 band position shows a higher wavenumber shift with increasing temperature, while its position correlates negatively with pressure and density. Thus, this method demonstrates its applicability in deducing the PVT-x properties of CH4-bearing systems, including CH4-rich fluid inclusions, CH4 content within hydrocarbon inclusions, and experimental fluid investigations. In contrast to the Raman quantitative approach, the infrared quantitative formula can be universally adopted in any infrared laboratory owing to the quantitative theory (Beer–Lambert law) governing infrared absorption spectra. By collecting Raman spectra and infrared spectra of pure methane fluid inclusions from the central region of the Alps and subsequently calculating the results using two distinct quantitative methods for fluid inclusions, we have demonstrated the feasibility of applying infrared spectroscopy in natural fluid inclusion studies.

VLE measurements of biphenyl in supercritical binary mixture of (0.527propane/0.473n-butane)

In the present work, new VLE data of biphenyl in supercritical binary mixture (solvent) of (0.527propane/0.473n-butane) are reported for three selected isotherms of (403, 423, and 443) K for pressures up to 6.65 MPa. The VLE property (PTxy) measurements were performed using a new recently developed high-pressure and high-temperature optical cell with a volume of 117 cm3. The concentrations of the liquid and gas equilibrium phases were measured independently without breaking the phase equilibrium (PT) conditions during the sampling procedure from each phase. This allows considerable increase the accuracy of the concentration determination of the equilibrium phases using gravimetric method, especially for vapor phase. The values of the critical parameters TC=403±0.2K,PC=4.25±0.03MPa,x=0.051±0.006 mole fraction of biphenyl; TC=423±0.2 K,PC=5.55±0.03MPa,x=0.06±0.006 mole fraction of biphenyl; and TC=443±0.2K,PC=6.80±0.03MPa,x=0.09±0.006 mole fraction of biphenyl for the mixture (0.527 propane / 0.473n-butane) + biphenyl have been estimated from the experimental VLE data near the critical point. The measured VLE properties (PTxy relationship) of (0.527 propane / 0.473n-butane) + biphenyl mixture was presented in various projections P-x for different isotherms, T-x for various isobars, and P-T projection. The combined expanded uncertainty of the temperature, pressure, and concentration measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.15 K, 0.22 % (or 0.0022P), and 0.03, respectively.

New Design of the High-Pressure Optical Cell for Vapor–Liquid Equilibrium Measurements. Supercritical Binary Mixture (Propane/n-Butane) + Acetophenone

A new design of the high-pressure and high-temperature optical cell has been developed for precise measurements of the vapor–liquid equilibrium (VLE) properties of multicomponent mixtures at pressu...

High-pressure, high-temperature optical cell for mid-infrared spectroscopy

The design, characterization, and operation of a new high-temperature, high-pressure optical cell for infrared spectroscopy is presented. The optical cell uses 16 cm CaF2 window rods to penetrate the temperature gradient between the heated optical path length and the ambient conditions surrounding the system. Along the 21.3 cm optical path length, good temperature uniformity was measured with deviations being less than 2.4% of the mean absolute temperature. Further characterization of the optical cell revealed usable transmission up to ∼ 8 µm and pressure stability from vacuum to over 30 atm. Moreover, stable operation of the optical cell during simultaneous heating and pressurization to 800 K and over 30 atm was demonstrated. To illustrate the utility of the new facility, high-resolution measurements of the R-branch in the fundamental absorption band of nitric oxide near 5.2 µm were collected at several pressures (1-34 atm) and temperatures (294–802 K) using an external cavity quantum cascade laser. The measured spectra were compared with Voigt line shape simulations using the HITRAN/HITEMP databases. At high gas densities, deviations from the Voigt line shape model are observed, emphasizing the need to further study infrared molecular spectra at high temperatures and pressures.

High temperature comparison of the HITRAN2012 and HITEMP2010 water vapor absorption databases to frequency comb measurements

The HITEMP2010 and HITRAN2012 databases are important tools for predicting molecular absorption under various environmental conditions. At room temperature, the databases can be quite accurate, owing to their development using room temperature absorption data. However, at elevated temperatures common to combustion and planetary research, their broadband accuracy is largely unexplored. We utilize a dual frequency comb spectrometer and a high temperature optical cell to assess the capability of these databases to accurately predict water vapor absorption for over 600 transitions at conditions up to 1300K from 6800cm−1 to 7200cm−1. We demonstrate that at 1300K, HITEMP2010 and HITRAN2012 accurately predict the existence and position (within 0.033cm−1) of >99% of transitions with an intensity greater than 1E−28 (cm−1/molecule cm−2), which is the approximate minimum detectable intensity for our absorption spectra. Of the slightly less than 1% of transitions that are misreported, all have linestrengths below 1E−23 (cm−1/molecule cm−2). HITEMP more often predicts transitions that are not observed in the absorption spectra, while HITRAN more often fails to predict an observed line. Updated temperature-scaling coefficients for air-broadening and updated line assignments improve the high temperature performance of HITRAN compared to HITEMP for lineshapes and positions. Our analysis also shows that adding simple temperature-scaling relationships for air-pressure shift and self-broadening half width increase the predictive accuracy of simulations using both databases, and should be employed whenever transition-specific information is unavailable.

Electromagnetically induced transparency and two-photon absorption in the ladder system in thin columns of atomic vapors

Experimental results of the study of processes of electromagnetically induced transparency (EIT) and two-photon absorption (TPA) are presented for the ladder Ξ-system obtained using the 5S-5P-nD, mS system of levels of the 85Rb and 87Rb atoms with n = 5, 26, and 27 and m = 39 and 48. To perform these studies, a high-temperature optical cell was designed with several regions with the following thicknesses L: 2 mm, 0.7 mm, and the region of 2–6 μm. The advantages of using thin cells over ordinary cells several centimeters thick are demonstrated. It is shown that the EIT resonance parameters for n = 5, 26, and 27 deteriorate insignificantly for thickness down to 700 μm. The TPA is recorded with the cell thickness decreasing down to L = 6 μm. It is shown that using the EIT and TPA processes makes it possible to measure the hyperfine and fine structures of highlying atomic levels. The influence of the cell walls is appreciable in recording the EIT resonances in the system 5S-5P-39S with L = 0.7 mm and in the system 5S-5P-48S with L = 2 mm. Possible applications of the processes studied are indicated.

Compositional Dependence of Wetting and Contact Angles in Solid-Liquid-Liquid Systems under Realistic Environments

The Dual Drop Dual Crystal (DDDC) contact angle measurement technique has been used in this study with a high-pressure high-temperature optical cell apparatus to measure dynamic contact angles in rock-oil-brine systems at realistic reservoir conditions of temperature and pressure. The experimental observations with live, stocktank, de-asphalted and de-resined crude oils indicate that the stability of oil, which determines the precipitation of asphaltenes for wettability alteration, is controlled by the entire oil composition. The ionic interactions caused by the brine composition and surface charged behaviour of rock substrates have been identified as another main mechanism that can affect wetting and contact angles in solid-liquid-liquid systems.

A Combined Differential Thermal Analysis and Spectrophotometric Cell

A high temperature optical cell which allows simultaneous monitoring of thermally induced transformations by differential thermal analysis has been designed and constructed. The α → β phase transformation in both evaporated thin films and bulk phthalocyanine has been studied with the cell and transformation rates determined. The rate constants were approximately three orders of magnitude larger for the bulk sample than for the evaporated films.