Paul E. Field

EQUILIBRIUM VAPOR CELL FOR QUANTITATIVE IR ABSORBANCE MEASUREMENTS

Infrared absorbance measurements through a gas flow cell are made with the closed-loop circulation of vapor/air mixtures equilibrated with the use of temperature-regulated aqueous solutions. Constant reproducible vapor pressures of organic solutes are established with the equilibrated aqueous solutions. The water solvent depresses the vapor pressure of the pure organic solutes of methanol, ethanol, isopropanol, acetone, and methyl ethyl ketone (MEK). Knowledge of the solution liquid mole fractions, the pure component vapor pressures, and the Wilson coefficients permits determination of the solute vapor pressures to within 2% accuracy. Reliable aqueous solution preparation requires only the correct weighings of pure constituent materials before mixing to achieve the targeted solute liquid mole fractions. Absorbances are measured for four of the five solutes over a range of seven concentrations and for MEK over four concentrations. These concentrations show the absorbance region of adherence to Beers law with an experimental precision of approximately ±2% for the solutes studied. Absorptivities that are calculated from the Beers law slope are compared to the available infrared absorbance data.

GAS SOLUBILITY IN MOLTEN SALTS

Interest in the solubilities of nonreactive gases in molten salts stemmed originally from the technological need developed as a consequence of gaseous fission products of radiated molten salts. A secondary technological development associated with industrial uses of molten salts as heat treatment baths, electrolytes, and metallurgical slags led to other studies of the influence of various gases and vapors on the physical and chemical properties of the fused salts. Systematic research of gaseous solutions of molten salts has lagged behind technological studies and lies considerably more dormant than analogous studies in water and organic solvents. Theoretical studies of the liquid state and solution theory, on the other hand, have been pursued which provide applications to ionic liquid solvents such as the simpler molten salts.

Aqueous Ammonia Vapor-Liquid Equilibria: Entropy and Temperature Dependence of Wilson Coefficients

This study extends a model for nonideal solution behavior by considering the temperature dependence of the coefficients in the Wilson equation for the aqueous ammonia system. Twenty-seven isothermal sets of experimental PXY data up to 2 MPa (20 atm) pressure (284 points) were analyzed using an objective function based on the excess Gibbs free energy to determine the pair of Wilson coefficients for each data set. Evaluation of these results supports the interpretation of the interaction parameters in Wilsons equation as temperature-dependent entropy functions. Comparison of computed results is made with four categories of vapor–liquid equilibrium (VLE) data: (1) primary PTXY, (2) refined PTXY, (3) secondary PTXY or PTM, and (4) partial. Excellent agreement is found with computed results for all but two of these VLE data sets in the region of rapidly changing vapor composition up to 90 mole % of ammonia. A comparison is also made to the only three previously published single-temperature (isothermal) pairs of Wilson coefficients with better agreement in Y, for all three cases, and in P, for two cases. A straightforward procedure is outlined to estimate any set of PTXY values (in the range P < 2 MPa, Y < 0.9) for the aqueous ammonia system.

Mirror Velocity Sampling Errors in a Michelson Interferometer

ABSTRACT Mirror velocity variations in a continuous mirror drive Michelson interferometer result in erroneous interferogram sampling. The effects of both systematic and random mirror fluctuations are evaluated. Four methods of evaluation provide a means to quantify the importance of mirror velocity errors in the Fourier spectrometers performance as a spectroradiometer. The four methods are time interval signal analysis, sine wave test, optical chopper modulation, and examination of consecutive interferograms. Examination of consecutive interferograms includes the monitoring of a constant blackbody infrared radiation source as well as an interposed ammonia sample cell for wavenumber axis registration. Each method furnishes a known input to the interferometer modulation equation (i.e. 2uv=f) and permits an internal validation of the interferometer mirror velocity evaluation results.

Infrared spectral evaluation of methanol/ammonia vapor mixtures

Vapor analytes of methanol and ammonia are quantitatively generated separately and as mixtures in the presence of water vapor. Generation of these analytes relies on the vapor liquid equilibria properties of associated aqueous solutions for delivering targeted vapor amounts into an equilibrium vapor cell. Gravimetric solution preparation and maintaining a constant solution temperature permits control of the analyte amount that is delivered to the optical equilibrium vapor cell. A laboratory Fourier transform infrared spectrometer examines the fixed path length optical cell contents. This examination furnishes vapor-phase infrared absorbances for analyte mixtures in the Beers Law concentration range. Literature vapor liquid equilibrium data and infrared absorbance measurements show that the methanol/ammonia binary compontents of the ternary aqueous solutions of this study exhibit ideal solution behavior.

Vapor mixture generation for infrared sensor evaluation

The use of the equilibrium vapor cell method quantitatively supplies one or more analytes in the presence of water vapor by using the vapor liquid equilibrium properties of aqueous solutions to delivery target vapors. This study demonstrates vapor generation of ammonia, ethanol, and ammonia/ethanol mixtures from aqueous solutions. Gravimetrically prepared aqueous solutions of ethanol and/or ammonia along with vapor liquid equilibrium data permits assessment of the mixed vapor target amounts delivered into an optical cell. Acquisition of the infrared vapor phase spectra is completed with a laboratory spectrometer for the target vapors in the Beers law concentration region using a fixed pathlength optical cell. Even though ideal solution behavior is assumed for the ethanol/ammonia interactions in the ternary solutions, the infrared spectral results between the binary and ternary solutions are shown to compare favorably.