Thesis (Ph. D.)--Ohio State University, 1982. / Includes bibliographical references (leaves 150-157). Available online via OhioLINK's ETD Center.

The chemistry andphysics involved at the metal/atmosphereinterface is interesting both from a fundamental and an appliedperspective. Since iron is the most important of all metalsthis interface is of particular interest. The objective withthis thesis is to obtain new information on a molecular levelof the iron/atmosphere interface with a special emphasis on theinitial atmospheric corrosion. The work presented herein combines a large variety ofdifferent analytical surface science techniques. Both ultrahigh vacuum and ambient pressure investigations were conductedwith single crystals as well as polycrystalline samples. The interaction of segregated sulfur with a Fe(110) surfacewas investigated by means of atomically resolved scanningtunneling microscopy (STM). A large variety of high and lowcoverage reconstructions were reported. Comparable studies ofoxygen adsorption on the same surface were also completed.Similar to the sulfur experiments, oxygen induced a number oflow coverage reconstructions. At higher coverage, oxideformation was observed and ordered oxides could be fabricatedat elevated temperatures. The oxygen interaction with Fe(110) and Fe(100) surfaces wasalso investigated with synchrotron radiation basedphotoelectron spectroscopy. Detailed information of the initialadsorption and subsequent oxidation was obtained. The Fe 2pcore level of the clean Fe(110) surface was subject to furtherinvestigations because of its complicated line profile that wasinterpreted as an exchange split of the final state. Iron exposed to humidified air with low concentrations ofsulfur dioxide (SO2) shows a surprisingly passive behavior. Themeasured mass gain was significantly lower than that of acopper sample exposed in the same environment. In-situtechniques such as atomic force microscopy (AFM), quartzcrystal microbalance (QCM) and infrared reflection absorptionspectroscopy (IRAS) showed little or no corrosion. Initiationof corrosion was observed upon introduction of additionaloxidants. The conclusion drawn challenge the established modelfor formation and growth of sulfate nests. The condition andformation of sulfate nests are discussed in view of thegenerated in-situ observations. During further experiments, iron was exposed to humid airand sodium chloride aerosols. The surface was investigated within-situ techniques, which provided new useful information. Ahigh corrosion rate was observed and the corrosion attacks formfilaments characteristic of filiform corrosion. A schematicmodel for propagation of the corrosion filaments wasproposed. Filiform corrosion was observed on aluminum surfaces aswell. The corroded surfaces were investigated with synchrotronradiation based photoelectron microscopy and scanning over afiliform head revealed different oxidation states within the Al2p spectrum. The microscopy data was interpreted as anenrichment of aluminum chloride containing compounds within thefiliform corrosion head.

Although iron-based permeable reactive barriers are gaining importance in the treatment of groundwater contaminants, there have been field observations indicating that sulphide may affect the degradation rates of certain chlorinated ethenes. Previous observations suggest that sulphide has little effect on TCE degradation rates but can cause a significant decline in the rate of degradation of cis-DCE. This study was conducted to systematically test the effects of S2- on TCE, cis-DCE, trans-DCE, 1,1-DCE and VC. Two different concentrations of sulphide (5 and 50 mg/L) were used in the column experiments. The results showed that the rate of TCE degradation was only slightly reduce in the presence of sulphide, while there was substantial reduction in the rates of degradation of cis-DCE, 1,1-DCE and VC. Trans-DCE was affected by sulphide, however, not as severely as cis-DCE, 1,1-DCE and VC. Raman Spectra showed the presence of a small amount of sulphide precipitates, and corrosion potential measurements showed that sulphide shifted the corrosion potential of the iron to less negative values by approximately 70 mV, suggesting that the change in corrosion potential was not responsible for the preferential degradation of TCE relative cis-DCE and VC. The dominant pathway for TCE degradation is β-elimination, while that for cis-DCE and VC is generally considered to be hydrogenolysis, though there is also evidence in the literature indicating that cis-DCE and VC can also degrade by catalytic hydrogenation. The results indicate that sulphide does not inhibit β-elimination but severely limits the hydrogenolysis/catalytic hydrogenation pathway. The fact that sulphide inhibited the conversion of ethene to ethane, a known catalytic reaction, indicated that sulphide is acting as a catalyst poison. It is therefore concluded that the primary mechanism for the transformation of cis-DCE to VC and for VC to ethene is catalytic hydrogenation, and that sulphide inhibits these transformations through its role as a catalyst poison.

In this thesis five iron phthalocyanines (FePc’s), four of which having different electron withdrawing or electron donating substituents, were evaluated as 0₂ reduction reaction (ORR) catalysts. The experimental approach simulated a PEM fuel cell environment using both ex-situ electrochemical techniques and in situ fuel cell testing. The kinetic ORR parameters for the FePc species each adsorbed on a pyrolytic graphite WE were evaluated at four temperatures (20, 40, 60, 80°C) in a novel half cell using cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. Kinetic ORR parameters included the overall ORR electron transfer number, reaction rate constants, cathodic Tafel slopes, electron transfer numbers in the rate determining step, and electron transfer co-efficients. An increase in temperature from 60°C to 80°C showed a decrease in the overall electron transfer number observed for all four substituted FePc species. A mechanism was also proposed based on the experimental results. The RDE results were confirmed using a rotating ring disk electrode (RRDE). From these RRDE results, the fraction of H₂0₂ produced (XH₂₀₂) at the disk during the ORR was calculated. These XH₂₀₂ values agreed with the overall ORR electron transfer numbers from the RDE results obtained under the same conditions. lron(Il) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25 — hexadecachioro 29H,31H-phthalocyanine (FePcCI₁₆)was down selected for further investigation as the most stable and active substituted FePc species for the ORR. Both FePcCl₁₆ and the unsubstituted FePc, were supported on carbon and made into catalyst inks for carbon fibre paper (CFP) electrode testing, and then evaluated using CV in the N₂ purged, followed by the air saturated, electrolytes, respectively. Finally, MEA’s for fuel cell testing were made using FePc species catalyst ink cathodes, and commercial Pt/C anodes. The MEA’s were tested using custom designed and built fuel cell hardware. Open circuit voltages, polarization curves, and power curves were recorded. Initial results indicated the FePcCI₁₆ MEA’s showed superior stability, higher open circuit voltages, as well as better polarization and power curves when compared to the unsubstituted FePc species. It was found that FePc species with strongly electron withdrawing substituents, such as FePcCl₁₆ showed the highest stability and greatest ORR activity. FePc species, including pyrolized FeNx/C analogues, show much promise as alternatives to Pt in PEMFC’s, as well as dye sensitized solar cells (DSSC’s).

Although iron-based permeable reactive barriers are gaining importance in the treatment of groundwater contaminants, there have been field observations indicating that sulphide may affect the degradation rates of certain chlorinated ethenes. Previous observations suggest that sulphide has little effect on TCE degradation rates but can cause a significant decline in the rate of degradation of cis-DCE. This study was conducted to systematically test the effects of S2- on TCE, cis-DCE, trans-DCE, 1,1-DCE and VC. Two different concentrations of sulphide (5 and 50 mg/L) were used in the column experiments. The results showed that the rate of TCE degradation was only slightly reduce in the presence of sulphide, while there was substantial reduction in the rates of degradation of cis-DCE, 1,1-DCE and VC. Trans-DCE was affected by sulphide, however, not as severely as cis-DCE, 1,1-DCE and VC. Raman Spectra showed the presence of a small amount of sulphide precipitates, and corrosion potential measurements showed that sulphide shifted the corrosion potential of the iron to less negative values by approximately 70 mV, suggesting that the change in corrosion potential was not responsible for the preferential degradation of TCE relative cis-DCE and VC. The dominant pathway for TCE degradation is β-elimination, while that for cis-DCE and VC is generally considered to be hydrogenolysis, though there is also evidence in the literature indicating that cis-DCE and VC can also degrade by catalytic hydrogenation. The results indicate that sulphide does not inhibit β-elimination but severely limits the hydrogenolysis/catalytic hydrogenation pathway. The fact that sulphide inhibited the conversion of ethene to ethane, a known catalytic reaction, indicated that sulphide is acting as a catalyst poison. It is therefore concluded that the primary mechanism for the transformation of cis-DCE to VC and for VC to ethene is catalytic hydrogenation, and that sulphide inhibits these transformations through its role as a catalyst poison.

No description available.

No description available.

Forest soil phosphorus (P) chemical behavior was evaluated in some mid-rotation fertilized loblolly pine (Pinus taeda L.) plantations in East Texas, that differed in their site drainage characteristics. Forest floor mass and carbon content in the forest floor were determined. Total P (PT) in the forest floor, and total and Mehlich-1 P and citratedithionite (CD) and acid ammonium-oxalate (AAO) extractable P, Al, Fe, and Mn within the mineral soil upper 100 cm were determined. Colorimetric determination of AAOand CD-extractable P by the molybdenum blue ascorbic acid method, without the use of pre-digestion, was assessed by an automated continuous flow injection system. Phosphorus distribution between different operationally defined solid phases and its relationships with CD and AAO extractable Mn, Al, Fe among depth, site, drainage class and treatment were evaluated. Soil P forms were highly correlated with iron oxides across sites, drainage classes, treatments, and depth intervals with significant differences in P content and distribution in the soil profile and solid phases among drainage classes. Soil P distribution patterns differed among drainage classes, yet it followed the distribution of the iron oxides. Iron oxide’s role as a sink for soil P was higher in the well-drained compared to the poorly drained sites. Amorphous phases of iron oxides were higher in the poorly drained sites and dominated the role of iron oxides as a sink for P under the poor drainage conditions. Fertilization resulted in significantly higher forest floor mass, P content in the forest floor, and total P (PT) and CD-extractable P (Pd) in the soils’ upper 10 cm. The treatment effect on P in the forest floor, and on PT and Pd in the upper 10 cm of the mineral soil was equivalent to 6, 19, and 11% of the applied P, respectively. AAO-extractable P was highly correlated with Mehlich-1 P in the fertilized plots. Treatment and site drainage class effects on P accumulation in the different solid phases in the mineral soil and in the forest floor and the potential contribution of these pools to P availability in subsequent rotations, following clearcutting, are discussed.

<p>The chemistry andphysics involved at the metal/atmosphereinterface is interesting both from a fundamental and an appliedperspective. Since iron is the most important of all metalsthis interface is of particular interest. The objective withthis thesis is to obtain new information on a molecular levelof the iron/atmosphere interface with a special emphasis on theinitial atmospheric corrosion.</p><p>The work presented herein combines a large variety ofdifferent analytical surface science techniques. Both ultrahigh vacuum and ambient pressure investigations were conductedwith single crystals as well as polycrystalline samples.</p><p>The interaction of segregated sulfur with a Fe(110) surfacewas investigated by means of atomically resolved scanningtunneling microscopy (STM). A large variety of high and lowcoverage reconstructions were reported. Comparable studies ofoxygen adsorption on the same surface were also completed.Similar to the sulfur experiments, oxygen induced a number oflow coverage reconstructions. At higher coverage, oxideformation was observed and ordered oxides could be fabricatedat elevated temperatures.</p><p>The oxygen interaction with Fe(110) and Fe(100) surfaces wasalso investigated with synchrotron radiation basedphotoelectron spectroscopy. Detailed information of the initialadsorption and subsequent oxidation was obtained. The Fe 2pcore level of the clean Fe(110) surface was subject to furtherinvestigations because of its complicated line profile that wasinterpreted as an exchange split of the final state.</p><p>Iron exposed to humidified air with low concentrations ofsulfur dioxide (SO2) shows a surprisingly passive behavior. Themeasured mass gain was significantly lower than that of acopper sample exposed in the same environment. In-situtechniques such as atomic force microscopy (AFM), quartzcrystal microbalance (QCM) and infrared reflection absorptionspectroscopy (IRAS) showed little or no corrosion. Initiationof corrosion was observed upon introduction of additionaloxidants. The conclusion drawn challenge the established modelfor formation and growth of sulfate nests. The condition andformation of sulfate nests are discussed in view of thegenerated in-situ observations.</p><p>During further experiments, iron was exposed to humid airand sodium chloride aerosols. The surface was investigated within-situ techniques, which provided new useful information. Ahigh corrosion rate was observed and the corrosion attacks formfilaments characteristic of filiform corrosion. A schematicmodel for propagation of the corrosion filaments wasproposed.</p><p>Filiform corrosion was observed on aluminum surfaces aswell. The corroded surfaces were investigated with synchrotronradiation based photoelectron microscopy and scanning over afiliform head revealed different oxidation states within the Al2p spectrum. The microscopy data was interpreted as anenrichment of aluminum chloride containing compounds within thefiliform corrosion head.</p>

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 361-370). Available also in a digital version from Dissertation Abstracts.