The oxidation of arsenic(III) by chromium(VI) requires the postulation of uncommon oxidation states as reactive intermediates. The possible intermediates of chromium are the divalent, tetravalent, and pentavalent states. Recently arsenic(IV) has been postulated as a reactive intermediate in certain oxidations of As(III). A detailed study of the reaction rate law in various solutions has been carried out in order to determine the nature of the intermediates found in the Cr(VI)-As(III) reaction. The effects of hydrogen ion and buffer concentrations have been determined. The mechanism postulated depends upon the solution in which the reaction occurs. The kinetics of the chromium(VI)-arsenic(III) reaction have been measured in perchloric acid solutions, acetic acid solutions, acetic acid-acetate buffers, ammonium nitrate solutions, and dihydrogen phosphatemonohydrogen phosphate buffers. The rate laws are: Perchloric Acid - -d[Cr(VI)]/ dt = [k₀ + k_H[H⁺] + k_H² [H⁺]²] (K’ [As (III)][Cr(VI)])/(l+K’[As(III)]) Acetic Acid-Acetate Buffers - -d[Cr(VI)]/ dt = [k₀ + k_HOAc[HOAc]} (K’ [As (III)][Cr(VI)])/(l+K’[As(III)]) Acetic Acid - -d[Cr(VI)]/ dt = [k₀ + k’_HOAc[HOAc]] (K’ [As (III)][Cr(VI)])/(l+K’[As(III)]) H₂PO₄⁻- HPO₄⁻² Buffers - -d[Cr(VI)]/ dt = (kK”[As(III)][Cr(VI)][H₂PO₄⁻])/(1+k”[H₂PO₄⁻]) Ammonium Nitrate Solutions - -d[Cr(VI)]/ dt = k₂ [As(III)][Cr(VI)] The reaction studied was the oxidation of As(III) by Cr(VI} according to the stoichiometry 3 As(III) + 2 Cr(VI) = 3 As(V) + 2 Cr (III) Rate data were obtained spectrophotometrically and by iodometric titration depending upon the region being investigated. At high As(III)-low Cr(VI), the Cr(VI) concentration was followed as a function of time at 350 mu using a Beckman DU spectrophotometer. The validity of Beer's law with respect to Cr(VI) was checked. At low As(III)-high Cr(VI), the unreacted As(III) concentration was determined by iodometric titration. In phosphate buffers, the HCrPO₇⁻² complex is indicated as an oxidizing agent. In the other systems, the following mechanism is consistent with the experimental facts. As(III) + HCrO₄⁻ [stacked right and left arrows with K above] As(III) · HCrO₄ As (III), As(III) · HCrO₄⁻ [right arrow with kₒ above] products, rate determining As(III) · HCrO₄⁻ + HOAc [right arrow with K_HOAc above] products, rate determining As(III) · HCrO₄⁻ + H⁺ [right arrow with k_H] products, rate determining In perchloric acid, H₂CrO₄is indicated as participating in the oxidation by the following steps: HCrO₄⁻ + H⁺ [stacked right and left arrows with Kₐ above] H₂CrO₄, ₂CrO₄ + As(III) [stacked right and left arrows with K above] As(III) · H₂CrO₄ The decomposition of As(III}•H₂CrO₄ is also acid catalyzed. In the mechanism described above, the products of the rate determining steps are arsenic(V) and chromium(IV). The existence of chromium(IV) is supported by the induced oxidation of ferrocyanide by the As(III)-Cr(VI) reaction. The chromium(IV) reacts immediately with chromium(VI) to form chromium(V) which can oxidize As(III) to As(V) directly. This is in agreement with the experimentally observed stoichiometry and accounts for the use of K' in the rate laws where K’ is actually 2K. The value of K is obtained from plots of 1/k_m versus 1/As(III). The value of K which describes all data reported is 17.2 1.mole⁻¹. In all three systems, perchloric acid, acetic acid, and acetic acid-acetate, the same kₒ is obtained. The specific rate constant for the acetic acid catalysis is 1.99 x 10⁻³ 1.⁻² mole² sec.⁻¹. Comparison of k"_HOAc terms for acetic acid and acetic acid-acetate solutions shows that k”_HOAc for the acid solution is larger than that for the buffers. This difference is explained on the basis of a medium effect. / Doctor of Philosophy

A study of six liquid chromatographic column packing materials was conducted. The materials investigated were: SI-60, SI-100, ALOX T, RP-2, RP-8, and RP-18 (E. M. Laboratories, Elmsford, N.Y.). The column packing materials had an average particle diameter of 10 µm and were slurry packed into stainless steel columns that were 3 mm i.d. and 250 mm in length. Two series of probe compounds were utilized to investigate the differences in selectivity exhibited by the column packing materials in the normal phase mode and in the reversed phase mode. A column oven which controlled temperature to within ± 0.2 °C over the range of 0°C to 100°C was utilized throughout the work. Four different mobile phases were used, two for the normal phase work and two for the reversed phase work. The effect of temperature was investigated in both the normal phase mode (20°C - 50°C) and in the reversed phase mode (20°C - 80°C). The results of the selectivity study indicate that the column temperature can have a pronounced effect in normal phase liquid chromatography. As temperature increased, k' values went through a minimum in some cases, indicating a change in retention mechanism. As the temperature is increased, the retention of the compounds may be increased, decreased, or remain constant. RP-2 is a versatile column packing material which is useful in both the normal phase mode and the reversed phase mode. In the normal phase mode it behaves as a low surface area adsorption column and of the three adsorbents, (SI-60, SI-100, and RP-2), it has the widest scope. In the reversed phase mode it also has the widest scope of the three reverse phase columns studied (RP-2, RP-8, and RP-18). In reversed phase liquid chromatography, increases in retention as temperature was increased were not observed and plots of log k' vs. temperature in °C resulted in straight lines with very similar slopes. Column temperature is however an important operating parameter which is useful in optimizing separations. Temperature was found to have little effect on the efficiency of the columns but was found to have a significant effect on the scope of the column packing materials in both the normal phase mode and in the reversed phase mode. When utilizing high surface area column packing materials or column packing materials with a high percentage of hydrocarbon bonded phase, temperature control is essential in order to obtain the best reproducibility. / Doctor of Philosophy

Surface Acoustic Wave delay lines have been used as probes for chemical analysis. The interaction between matter adjacent to the SAW device surface and the propagating Raleigh wave caused measurable changes in the amplitude, phase and resonant frequency of the wave. The effectiveness of various electronic detection schemes was evaluated along with the response of the device to changes in pressure and temperature. A lithium niobate SAW device was used as a detector for gas chromatography. Frequency shifts of a SAW oscillator provided the highest sensitivity to compounds eluting from the G.C. column. Sensitivity and specificity of the detector to polar and non-polar organic compounds was greatly enhanced by thin chemical coatings applied to the detector surface. Submicrogram quantities of material were easily detected. Linearity and dynamic range of the detection system was poor. Numerous refinements remain to be made which could significantly improve performance. Thermomechanical analysis of thin polymer films were accomplished using a 32 MHz quartz delay line. Very large wave amplitude shifts were observed as the polymer reached its glass transition temperature. Tg measurements were performed on samples clamped to the surface and cast on the surface. Agreement with low frequency dynamic mechanical measurements was good for the clamped specimens, indicating the absence of wave coupling. Specimens cast on the surface experienced large Tg shifts and therefore were coupled to the surface wave. More subtle transitions were also detected. A crystalline transition around room temperature in a TEFLON film clamped to the SAW device provided an easily observed shift in SAW amplitude. Explanations of this behavior have been proposed. The SAW device also provided an ideal vehicle for examining the behavior of thin photoresist films on the surface. Information on solvent evaporation processes and photo-induced crosslinking rate was obtained. The attractive features of the device for polymer thermomechanical analysis include low cost, ruggedness, high sensitivity and ease of use. / Ph. D.

A study was made with the objectives: 1. Evaluation of a micro-adsorption detector for use in liquid chromatography. 2. Evaluation of a micro-adsorption detector for use in gas ch.ranatography. 3. Investigation of the micro-adsorption cell as a tool for screening chromatographic systems, in adsorption studies, and as a micro-calorimeter. The micro-adsorption detector was found to have sufficient sensitivity to detect nanogram quantities of a component in either a liquid or gaseous carrier, and to have a linear dynamic range of 10²-10³. These qualities, combined with the selectivity of the detector indicate its usefulness in both liquid and gas chromatographic operations. The major limitation to its use is the characteristic adsorption/desorption responsive curve, which requires increased column lengths or resolution over other detectors such as the UV detector. In addition a semi-quantitative correlation between MAD response and chromatographic retention times indicates that the detector has significant potential as a screening tool for separation systems. By means of a calibration apparatus the detector response was characterized in terms of heat flux and temperature differential, and heats of absorption were calculated at concentrations of 10⁻⁴- 10⁻⁶ molar. These compared favorably with those literature values which were available close to these concentrations. / Ph. D.

On-line HPLC/Spectrofluorometric techniques have been applied to the determination of polycyclic aromatic hydrocarbons (PAHs) in coal-derived products. The PAHs were isolated by preparative silica gel columns with a hexane mobile phase, and fractionated into five samples based on the number of condensed rings. Each fraction was separated by reverse phase HPLC with an acetonitrile/water mobile phase. Compounds were detected by means of on-line fluorescence detection. Naphthalene, pyrene, fluoranthene, benzo(a)anthracene and benzo(a)pyrene were verified by comparing the excitation and emission spectra obtained by a stop-flow technique with those of PAH standards. A Picramido bonded phase packing was prepared by the reaction of picryl chloride and amino bonded phase silica gel, forming a charge-transfer active phase. The retention mechanism of aromatic hydrocarbons on the picramido bonded phase column was studied in three ways: electronic effects (Hammett cr function); temperature effects on heats of adsorption and solvent effects on capacity factors. Chromatographic properties of the picramido bonded phase column were compared to those of silica gel and amino bonded phase columns. An on-line LC/LC column switching system was developed for PAH analysis of solvent refined coal (SRC). It utilized a guard column, an amino bonded phase, and a picramido bonded phase column. The guard column prevented the highly polar materials from entering the analytical columns; the amino bonded phase column separated PAH materials into groups based on an adsorption mechanism; the picramido bonded phase column separated PAHs based on charge-transfer mechanism, and provided better resolution. / Ph. D.

In the first part of this two part thesis, interaction parameters of nitrocellulose with various solvent systems were investigated by Inverse Gas Chromatography. From these data, the solubility parameters of nitrocellulose were determined at a series of nitration levels which were used to guide the selection of suitable plasticizers for nitrocellulose films. Subsequent dynamic mechanical experiments were then used to evaluate the effectiveness of the blend formulations in broadening the glass transition dispersion of the nitrocellulose blended films; in addition, stress-strain experiments were done in order to evaluate the tensile modulus of the nitrocellulose blends. In the second part of this thesis, both dynamic mechanical thermal analysis and dielectric thermal analysis were used to evaluate the relaxation properties of thin film polysulfone coatings and the effect of substrate surface topography on these properties. Both dynamic mechanical and dielectric thermal analysis revealed that the topographical nature of the substrate influenced the linear viscoelastic properties of the thin film coatings and that the extent of this influence was dependent on the coating thickness. / Master of Science

N-type GaAs is a potentially useful semiconductor in liquid junction type solar cells. Corrosion and corrosion suppression on an n-type GaAs semiconductor in both light and dark has been studied. The application of non-electroactive layers for corrosion suppression on semiconductor electrodes is a relatively new field. GaAs corrodes to form Ga(III) and As(III) solution species during photocurrent generation. The corrosion rate is determined electroanalytically in acidic media by measuring As(III) using differential pulse polarography (DPP). In neutral electrolytes a rotating ring-disc experiment measured the efficiency of hole-transfer to a redox couple. Two protecting processes have been utilized. Silanization and electrochemical polymerization of divinylbenzene and phenol were used to deposit non-electroactive layers on the electrode surface. The polyphenylene oxide coating partially suppressed corrosion in acid electrolytes. However, the coatings did not improve hole transfer efficiency in neutral electrolytes. / Master of Science

Lewis acid/base interactions were shown to play an important role in the optimization of the interfacial adhesion of reinforcing carbon fibers to thermoplastic polymer matrices. Inverse gas chromatography (IGC) and x-ray photoelectron spectroscopy (XPS) were used to characterize the acid/base nature of the carbon fiber surfaces. Capillary column IGC (CIGC) was used to determine the acid/base nature of thermoplastic polymer surfaces. To quantify the non-dispersive (acid/base) interactions, the dispersive component had to be factored out by separate experiments. The carbon fibers (both surface pretreated and untreated) were found to be predominantly acidic while the polymer matrices (polysulfone, polycarbonate, and polyetherimide) exhibited basic properties. Single fiber fracture tests showed that increased acidity in the fiber surfaces (as a result of surface pretreatment) resulted in a significant improvement in the interfacial adhesion to the basic polymers. The acid/base interactions, however, were not solely responsible for the most favorable adhesion. The dispersive component and thus, the carbon fiber structure also played a role. / Master of Science

The preferential adsorption of n-decanol, n-decylamine, n-decanoic acid, and ethyl octanoate from binary solutions with heptane onto alumina was studied. The net surface excess isotherms were measured and resolved into component isotherms. The heat of immersion of the alumina in n-decanol, ethyl octanoate, and n-decanoic acid solutions was measured. The heats of immersion support the resolved isotherms which indicate that the order of preferential adsorption is n-decanoic acid > n-decanol ≃ n-decylamine ≃ ethyl octanoate. However, adsorption equilibrium constants calculated for each system indicate that the order of preferential adsorption is ethyl octanoate > n-decanol > n-decylamine > n-decanoic acid. An explanation for the discrepancy is put forth. A theoretical model of surface heterogeneity is also applied to the data for the ethyl octanoate and n-decanol systems. The reasonable fit of the model in each case suggests that the alumina surface is heterogeneous. / Master of Science

X-ray photoelectron spectroscopy (XPS) has been used to study the bonding of adsorbed metal cations to clay minerals. Binding energy differences of the adsorbed metal cations can be related to changes in the electron density or charge on the atom of interest. Adsorption experiments were carried out in aqueous solution at controlled pH's of 2, 4, 6, 8, and 10 for Ba²⁺, Co²⁺, Cr³⁺, adsroption on the clays kaolinite and ripidolite. Solution processes were monitored by measuring the solution concentrations of dissolved silica and the metal ions Fe³⁺, Mg²⁺, K⁺, Al³⁺, Cr³⁺, and Co²⁺ at the beginning and the end of the experiment. Atomic absorption spectroscopy was used to determine the metal ion concentrations and dissolved silica was determined spectrophotometrically as a molybdate complex. Examination of the adsorbed cation species on the clay surface by XPS indicated that the clays behaved as nucleation centers at or near the pH of precipitation of the cations. Further it was found that high spin Co²⁺ in solution became low spin Co²⁺ or formed a highly covalent bond when adsorbed on kaolinite at pH's 4, 6, and 7 and on ripidolite at pH 2 and 4. Finally, if the clay has a negatively charged surface which donates some of its charge to the positive cation, then the barium XPS data indicated that ripidolite has a greater negative surface charge than kaolinite. This idea was supported by calculations of the surface charge density from CEC and surface area data. / Master of Science