Stephen F. Agnew

INFRARED STUDY OF WATER SORPTION ON Na-, Li-, Ca-, AND Mg-EXCHANGED (SWy-1 AND SAz-1) MONTMORILLONITE

An environmental infrared microbalance (EIRM) cell was used to study H2O sorption on two montmorillonite samples as a function of water content and type of exchangeable cation. The vibrational spectra showed that H2O sorbed to the clay at low-water content was strongly influenced by the exchangeable cation and by the close proximity to the clay surface. At water contents <6 H20 molecules per exchangeable cation, the H-O-H bending mode of H2O (v2 mode) shifts to a lower frequency and is characterized by an increase in molar absorptivity. In contrast, the positions of the asymmetric and symmetric OH-stretching modes of sorbed water (v1 and v3 modes) shift to higher energies. These observations indicate that H2O molecules sorbed to the clay surface at low-water content are less hydrogen bonded than in bulk H2O. In addition, the vibrational-stretching and bending bands of the structural OH groups of the 2:1 layer are also strongly influenced by H2O content and type of exchangeable cation. By using the EIRM cell, the molar absorptivities of the structural OH-bending vibrations were measured as a function of H2O content. The position and molar absorptivity of the structural OH-bending bands at 920, 883, and 840 cm-1 are strongly influenced by H2O content and type of exchangeable cation. The molar absorptivity of the 920-cm-1 band, which is assigned to the AlAlOH group, decreased strongly at low-H2O content. This reduction in intensity is assigned to a dehydration-induced change in orientation of the structural OH groups resulting from the penetration of H2O molecules into siloxane ditrigonal cavities that are not associated with a net negative charge from isomorphous substitutions.

POLARIZED SINGLE-CRYSTAL FOURIER-TRANSFORM INFRARED MICROSCOPY OF OURAY DICKITE AND KEOKUK KAOLINITE

Single-crystal Fourier-transform infrared (FTIR) spectra of Keokuk kaolinite and Ouray dickite were obtained with an FTIR microscope. Although numerous IR, FTIR, and Raman spectra of polycrystalline kaolinite and dickite can be found in the literature, the present data represent the first reported single-crystal vibrational spectra for these clay minerals. The orientation of the crystallographic axes of dickite was determined using a cross-polarizing optical microscope fitted with an 550-nm optical retardation plate. Assignment of the inner hydroxyl group OH1 to the 3623-cm-1 band was confirmed, and the angle of this OH group to the b-axis was determined to be 47° based upon the measured dichroic ratio. The 3702-3710-cm−1 absorption feature appeared to consist of two closely spaced bands having slightly different polarization behavior. The inner-surface hydroxyl group OH3 was assigned to the absorption bands at 3710 cm−1. The calculated angle of the OH3 groups to the b-axis was found to be 22°, which agrees well with the angles determined by X-ray powder diffraction and neutron diffraction. The remaining hydroxyl groups, OH2 and OH4, were assigned to the 3656 cm-1 band; the angle of the OH2 and OH4 groups to the b-axis was measured at 45°. The polarization behavior of the OH-deformation bands of dickite at 911, 937, and 952 cm−1 was found to be similar to that observed in the OH-stretching region. Single-crystal FTIR spectra of Keokuk kaolinite showed that rotation of the electric vector around the c/z axis in the ab plane of kaolinite resulted in a behavior distinct from that of dickite. The OH-stretching bands of kaolinite were found to be considerably more polarized than the corresponding bands of dickite. This is related directly to the fact that dickite possesses a glide plane (space group Cc) compared with kaolinite, which does not (space group C1).

Infrared studies of autoionization of thin films of dinitrogen tetroxide

The autoionization of dinitrogen tetroxide to form nitrosonium nitrate in thin films at 150–200 K has been studied using infrared absorption spectroscopy. It is found that at these temperatures and low pressure the process is intramolecular, involving only one of two isomers of the nitrite form (ONONO2). (AIP)

Extended interactions in the ε phase of oxygen

The high pressure infrared and Raman spectra for the e phase of a series of oxygen samples, 16O2, 16O2 with 10% 18O2, and 18O2 with 6% 16O 18O, are reported. Assignments are made for the fundamental, combination, and isotope‐induced features of this phase of solid oxygen based on a simple model that incorporates a pairwise interaction betweeen nearest‐neighbor oxygen molecules within the molecular oxygen plane, with pairs forming extended chains. Vibrational analysis on this chain with two interaction force constants reproduces all of the features that we have observed.

IR study of the chemistry of boundary lubrication with high temperature and high pressure shear

Abstract A unique diamond anvil cell has been constructed which permits the spectroscopic study of boundary layers under conditions of high temperature, high pressure and shear. We have used this cell in combination with Fourier transform IR spectroscopy to probe the function of stearic acid and zinc dialkyldithiophosphate (ZnDDP) as boundary layer enhancer. We have shown that thick boundary layers (about 1 μm) of stearic acid continue to exist at pressures as high as 5.0 GPa (725 000 lbf in−2). We have also demonstrated that the decomposition of ZnDDP in mineral oil under static high pressure and high temperature is first enhanced by increasing the pressure, reaching a maximum at about 0.7 GPa (about 10 000 lbf in −2), and is thereafter retarded by further increases in pressure. This result suggests that the decomposition of ZnDDP is triggered by pressure increases associated with boundary lubrication rather than by frictional heating. The decomposition results in the formation of a thick inorganic protective film at those surfaces associated with high wear.

Infrared spectra and structure of thin films of solid oxygen: A metastable phase

The infrared absorption spectra of thin films of solid oxygen prepared by vapor deposition is examined in detail. It is shown that at deposition temperatures between 8 and 11 K the film consists of a mixture of α‐O2 and a metastable phase we call m‐O2. The spectrum of CO in an O2 matrix is shown to be a good marker for the presence of m‐O2 and is informative concerning the structure of this metastable phase. Studies of mixtures of 18O2 and 16O2 indicate that the structure of m‐O2 is complex with four nonequivalent sites for O2 molecules and at least eight molecules per unit cell. The isotopic studies suggest the presence of weakly bound dimers as well as tetramers or higher multimers in m‐O2. It is shown that the presence of a few percent impurities such as nitrogen or argon allow the formation of and increase the stability of m‐O2 at higher temperatures. However, with or without impurities, at deposition temperatures below 8 K less m‐O2 is formed, and deposition at 5 K leads to no m‐O2 but only poorly cr...

A MOLALITY-BASED BET EQUATION FOR MODELING THE ACTIVITY OF WATER SORBED ON CLAY MINERALS

The Brunauer-Emmett-Teller (BET) theory models the effective specific surface area and water content of solids as a function of the relative vapor pressure of water. A modified form of the BET equation has been used successfully to model water activity in concentrated electrolyte solutions as a function of electrolyte concentration. This modified form, referred to here as the Stokes-Robinson BET model, is based on the electrolyte molality rather than on the mass of solute sorbed. The present study evaluates the Stokes-Robinson form of the BET equation to model water-sorption data on two smectites with different layer charges. One smectite was saturated with Na+ and another with Na+, Ca2+, or Mg2+. These results are compared to the Stokes-Robinson BET results of aqueous electrolyte solutions. Given published data on cation exchange capacities and water-vapor sorption isotherms for various clays, the molality of the aqueous phase in contact with the clay surface is calculated and related to water activity. The Stokes-Robinson BET model was found to describe accurately the water activity as a function of cation molality below water activities of 0.5 for the smectites. Good relative agreement was obtained between the number of water binding sites predicted by the model and the experimental data reported in the literature for other smectites. Water molecules were found to have a significantly greater affinity for montmorillonite than electrolyte solutions with the same cation molality as the montmorillonite interlayer. This modified BET approach simplifies water-activity modeling in highly saline environments because the same equation can be used for both the liquid- and mineral-surface phases.

Microstructural Properties of High Level Waste Concentrates and Gels with Raman And Infrared Spectroscopies

Nearly half of the high level radioactive waste stored at Hanford is composed of highly alkaline concentrates referred to as either salt cakes or Double-Shell Slurry (DSS), depending on their compositions and processing histories. The major components of these concentrates are water, sodium hydroxide, and sodium salts of nitrate, nitrite, aluminate, carbonate, phosphate, and sulfate. In addition, there are varying amounts of assorted organic salts such as EDTA, glycolate, and citrate. Although measurements of the bulk properties of these wastes (e.g. viscosity, gel point, density) have been reported, little is known about how the macroscopic characteristics are related to the microscopic physico-chemical properties. Viscosity, solids volume percent, and gas retention can dramatically change with relatively small changes in composition and temperature. Furthermore, these same properties are important in determining safe storage conditions as well as in planning retrieval, pretreatment, and disposal of the wastes. The focus of this effort will be on aluminate chemistry since large inventories of waste with aluminum are located at Hanford and Savannah River and little is known about the microstructure of these complex mixtures.

Comparisons of Historical Process Estimates with Tank Waste Assays

There are few problems within the U.S. DOE complex as difficult as is the disposition of DOE’s fifty-year legacy of defense wastes. This problem faces all of DOE’s facilities to some extent, but none have such a large and complicated waste history as the Hanford Site. The Hanford Site represents DOE’s most complex waste site because it not only involves the majority of waste and that waste is the most complicated, but also because the Hanford Site involves a multitude of interlocking and overlapping issues.