Excessive levels of sulfur in the ecosphere are generally found to be detrimental to man and his environment. Four inorganic forms of sulfur are singled out as common constituents of natural and pollutant systems: sulfide (S²⁻), elemental sulfur (S⁰), sulfite (SO₃²⁻), and sulfate (SO₄²⁻). Progress toward characterizing the chemical interactions and toxicity of these species is retarded by the lack of suitable analytical procedures for determining the forms of sulfur in complex solid matrices. An extensive survey of the literature reveals that conventional analyses for sulfur are numerous, but that most techniques are restricted to solutions containing only one type of sulfur. A few complex and cumbersome analytical schemes have been devised, however, for the determination of mixtures of sulfur species in solution. Solubilization of the sample prior to analysis not only adds a step to the procedure, but it also increases the number of variables and the uncertainty associated with the results. The direct determination of sulfur in solids is an alternative to extraction which avoids many of its pitfalls. A critical review of the methods available discloses a paucity of analytical techniques capable of determining individual sulfur species in solid mixtures. X-Ray methods such as X-ray fluorescence and X-ray photoelectron spectroscopy rank the highest as potentially useful probes for eliciting information concerning the oxidation state of sulfur in solids. Routine quantitative work is impeded by the inability to examine bulk properties and the relative lack of sensitivity inherent in X-ray techniques. This apparent analytical void has led to the development of a new technique which can be applied to the determination of inorganic sulfur in solids: time resolved molecular emission spectrometry (TRMES). Solid samples are placed in a small, quartz-lined cavity at the end of a stainless steel rod and the rod is positioned in a low temperature flame, in line with the entrance slit of monochromator. The resulting molecular sulfur emission is monitored at 383.6 nm and is linearly related to sulfur content between at least 10⁻⁵ to 10⁻⁷ g. Qualitative identification of sulfide, elemental sulfur, sulfite, and sulfate is afforded by the separate, time dependent emission responses which are observed. Detection limits are species dependent and theoretically, in a 1.5-mg sample, range from 0.2 pg for sulfite to 8ng for sulfate. In practice, quantitation at these low levels is hindered by inhomogeneous standards. Effects due to different bulk matrices, the presence of two or more sulfur species in a sample, or interferences from counterions are minimal or have not been detected. TRMES provides an alternative to aspirating the sample into the flame and greatly reduces the amount of sample that is required. In addition, the cavity serves to confine the sample and the resultant emission to a small, predetermined region of the flame. This enhances sensitivity and allows one to choose the optimum sample position in the flame. Standard flame emission instruments may be readily adapted to this technique by the addition of a simple, easily fabricated sample introduction device. The utility of TRMES is demonstrated by the determination of sulfur species in several complex matrices, including: coal (S₂²⁻); copper and lead smelter particulates (S²⁻, SO₃²⁻, SO₄²⁻); deep-sea ferromanganese nodules (S⁰); and geologic materials (S²⁻, SO₄²⁻).

Interactions between certain fuel sulfur compounds and nitric oxide (NO) in turbulent gaseous and distillate oill diffusion flames were experimentally investigated utilizing a 75,000 Btu/hr laboratory combustor. Aerodynamics, air preheat conditions, and overall excess air conditions were varied to determine their role on any such interaction. Results indicated that addition of sulfur dioxide (SO₂) to natural gas flames could enhance or inhibit NO emissions. Local flame stoichiometry and temperature, which were influenced by fuel injector type, determined which effect was observed and the extent to which it occurred. Thiophen (C₄H₄S) and pyridine (C₅H₅N) were added to #2 diesel oil to determine effects of fuel sulfur on conversion of chemically bound fuel nitrogen to No. No discernible effect was observed at "zero" air preheat conditions. No emissions were enhanced at high air preheat conditions. Addition of SO₂ to natural gas flames doped with ammonia (NH₃) produced a significant increase in conversion of NH₃ to NO at high air preheat conditions. Inhibition effects were explained in terms of homogeneous catalysis of recombination reactions by SO₂. Hydrogen abstraction reactions involving reduced sulfur species and other oxidation reactions involving SO₂, or a reduced form, were considered to explain the enhancement effect.

Lithium-ion batteries are leading the path for the power sources for various portable applications, such as laptops and cellular phones, which is due to their relatively high energy density, stable and long cycle life. However, the cost, safety and toxicity issues are restricting the wider application of early generations of lithium-ion batteries. Recently, cheaper and less toxic cathode materials, such as LiFePO₄ and a wide range of derivatives of LiMn₂O₄, have been successfully developed and commercialized. Furthermore, cathode material candidates, such as LiCoPO₄, which present a high redox potential at approximately 4.8 V versus Li⁺/Li, have received attention and are being investigated. However, the theoretical capacity of all of these materials is below 170 mAh g⁻¹, which cannot fully satisfy the requirements of large scale applications, such as hybrid electric vehicles and electric vehicles. Therefore, alternative high energy density and inexpensive cathode materials are needed to make lithium batteries more practical and economically feasible. Elemental sulfur has a theoretical specific capacity of 1672 mAh g⁻¹, which is higher than that of any other known cathode materials for lithium batteries. Sulfur is of abundance in nature (e.g., sulfur is produced as a by-product of oil extraction, and hundreds of millions of tons have been accumulated at the oil extraction sites) and low cost, and this makes it very promising for the next generation of cathode materials for rechargeable batteries. Despite the mentioned advantages, there are several challenges to make the sulfur cathode suitable for battery use, and the following are the main: (i) sulfur has low conductivity, which leads to low sulfur utilization and poor rate capability in the cathode; (ii) multistep electrochemical reduction processes generate various forms of soluble intermediate lithium polysulfides, which dissolve in the electrolyte, induce the so-called shuttle effect, and cause irreversible loss of sulfur active material over repeat cycles; (iii) volume change of sulfur upon cycling leads to its mechanical rupture and, consequently, rapid degradation of the electrochemical performance. A variety of strategies have been developed to improve the discharge capacity, cyclability, and Coulombic efficiency of the sulfur cathode in Li/S batteries. Among those techniques, preparation of sulfur/carbon and sulfur/conductive polymer composites has received considerable attention. Conductive carbon and polymer additives enhance the electrochemical connectivity between active material particles, thereby enhancing the utilization of sulfur and the reversibility of the system, i.e., improving the cell capacity and cyclability. Incorporation of conductive polymers into the sulfur composites provides a barrier to the diffusion of polysulfides, thus providing noticeable improvement in cyclability and hence electrochemical performance. Among the possible conductive polymers, polypyrrole (PPy) is one of the most promising candidates to prepare electrochemically active sulfur composites because PPy has a high electrical conductivity and a wide electrochemical stability window (0-5 V vs Li/Li⁺). In the first part of this thesis, the preparation of a novel nanostructured S/PPy based composites and investigation of their physical and electrochemical properties as a cathode for lithium secondary batteries are reported. An S/PPy composite with highly developed branched structure was obtained by a one-step ball-milling process without heat-treatment. The material exhibited a high initial discharge capacity of 1320 mAh g⁻¹ at a current density of 100 mA g⁻¹ (0.06 C) and retained about 500 mAh g⁻¹ after 40 cycles. Alternatively, in situ polymerization of the pyrrole monomer on the surface of nano-sulfur particles afforded a core-shell structure composite in which sulfur is a core and PPy is a shell. The composite showed an initial discharge capacity of 1199 mAh g⁻¹ at 0.2 C with capacity retention of 913 mAh g⁻¹ after 50 cycles, and of 437 mAh g⁻¹ at 2.5 C. Further improvement of the electrochemical performance was achieved by introducing multi-walled carbon nanotubes (MWNT), which provide a much more effective path for the electron transport, into the S/PPy composite. A novel S/PPy/MWNT ternary composite with a core-shell nano-tubular structure was developed using a two-step preparation method (in situ polymerization of pyrrole on the MWNT surface followed by mixing of the binary composite with nano-sulfur particles). This ternary composite cathode sustained 961 mAh g⁻¹ of reversible specific discharge capacity after 40 cycles at 0.1 C, and 523 mAh g⁻¹ after 40 cycles at 0.5 C. Yet another structure was prepared exploring the large surface area, superior electronic conductivity, and high mechanical flexibility graphene nanosheet (GNS). By taking advantage of both capillary force driven self-assembly of polypyrrole on graphene nanosheets and adhesion ability of polypyrrole to sulfur, an S/PPy/GNS composite with a dual-layered structure was developed. A very high initial discharge capacity of 1416 mAh g⁻¹ and retained a 642 mAh g⁻¹ reversible capacity after 40 cycles at 0.1 C rate. The electrochemical properties of the graphene loaded composite cathode represent a significant improvement in comparison to that exhibited by both the binary S/PPy and the MWCNT containing ternary composites. In the second part of this thesis, polyacrylonitrile (PAN) was investigated as a candidate to composite with sulfur to prepare high performance cathodes for Li/S battery. Unlike polypyrrole, which, in addition of being a conductive matrix, works as physical barrier for blocking polysulfides, PAN could react with sulfur to form inter- and/or intra-chain disulfide bonds, chemically confining sulfur and polysulfides. In the preliminary tests, PAN was ballmilled with an excess of elemental sulfur and the resulting mixture was heated at temperatures varying from 300°C to 350°C. During this step some H₂S gas was released as a result of the formation of rings with a conjugated π-system between sulfur and polymer backbone. These cyclic structures could ‘trap’ some of the soluble reaction products, improving the utilization of sulfur, as it was observed experimentally: the resulting S/PAN composite demonstrated a high sulfur utilization, large initial capacity, and high Coulombic efficiency. However, the poor electronic conductivity of the S/PAN binary composite compromises the rate capability and sulfur utilization at high C-rates. These issues were addressed by doping the composite with small amounts of components that positively affected the conductivity and reactivity of the cathode. Mg₀.₆Ni₀.₄O prepared by self-propagating high temperature synthesis was used as an additive in the S/PAN composite cathode and considerably improved its morphology stability, chemical uniformity, and electrochemical performance. The nanostructured composite containing Mg₀.₆Ni₀.₄O exhibited less sulfur agglomeration upon cycling, enhanced cathode utilization, improved rate capability, and superior reversibility, with a second cycle discharge capacity of over 1200 mAh g⁻¹, which was retained for over 100 cycles. Alternatively, graphene was used as conductive additive to form an S/PAN/Graphene composite with a well-connected conductive network structure. This ternary composite was prepared by ballmilling followed by low temperature heat treatment. The resulting material exhibited significantly improved rate capability and cycling performance delivering a discharge capacity of 1293 mAh g⁻¹ in the second cycle at 0.1 C. Even at up to 4 C, the cell still achieved a high discharge capacity of 762 mAh g⁻¹. Different approaches for the optimization of sulfur-based composite cathodes are described in this thesis. Experimental results indicate that the proposed methods constitute an important contribution in the development of the high capacity cathode for rechargeable Li/S battery technology. Furthermore, the innovative concept of sulfur/conductive polymer/conductive carbon ternary composites developed in this work could be used to prepare many other analogous composites, such as sulfur/polyaniline/carbon nanotube or sulfur/polythiophene/graphene, which could also lead to the development of new sulfur-based composites for high energy density applications. In particular, exploration of alternative polymeric matrices with high sulfur absorption ability is of importance for the attainment of composites that possess higher loading of sulfur, to increase the specific energy density of the cathode. Note that the material preparation techniques described here have the advantage of being reproducible, simple and inexpensive, compared with most procedures reported in the literature.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 217-233).

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Domestic mineral consumption is defined as a net sum of apparent consumption plus embodied mineral contained in net imported goods. The U.S. is a net importer of copper-containing products, such as automobiles, electrical products, and construction and industrial machinery. Embodied copper which is contained in net imports of these products constitute part of domestic copper consumption. On the other hand, the U.S. is a net exporter of sulfur-using/embodying products, such as fertilizers and grains. The sulfur which is contained/employed in manufacturing exported products is not actually part of domestic sulfur consumption. Net embodied U.S. imports (exports) of copper (sulfur) are estimated. For copper, it is shown that domestic U.S. consumption is understated and increasing, intensity of use is constant rather than decreasing, and, in general, forecast increases in domestic consumption of copper are due mainly to embodied copper imports. For sulfur, it is shown that domestic consumption is overstated and declining; domestic intensity of use is also declining. The domestic copper and sulfur industries will be differentially impacted as a result of this increased reliance on overseas markets.

The growth of the layer formed on atomically clean lithium metal upon exposure to SO₂ gas is sequentially studied by controlling the quantity of gas reacted with the surface in a specially constructed vacuum system. A Fast Fourier Transform algorithm for the removal of instrumental broadening, and quantized and inelastic electron loss processes from the background of an Auger spectrum is presented. The deconvolved peaks for the S(LMM) and O(KKL) valence transitions are used to determine the molecular composition of the layer at each stage of its formation. The associated peak areas give the quantity of SO₂ reacted with the surface and the relative amounts of sulfur and oxygen present in each layer. The results indicate that two distinct layers of different composition are formed. The lower layer is a complete monolayer of Li₂O/Li₂S in a two-to-one ratio. The upper layer is thicker and consists of LiS₂O₄ and LiS₂O₃ in a 50% mixture. The formation of the upper layer is observed only after exposures of the surface to partial pressures of SO₂ greater than one millitorr. A model to explain the formation of the two layers and the observed pressure dependence is given. A flow method is used to study the kinetics of the Li-SO₂ reaction at submonolayer coverages. The pressure in a reaction vessel is monitored as a function of time when a fresh Li surface is exposed. A reaction order between 0.5 and 0.9 results, indicating that the surface of the scraped Li is energetically heterogeneous with respect to sites available for adsorption. An Arrhenius plot of the data indicates that the activation energy for the dissociative chemisorption to form the first monolayer lies between 2 and 5 kcal/mole. The sources for site heterogeneity and the activation energy are discussed. The resulting molecular model is used in combination with preliminary electrochemical results to compare the gas phase layer with the film formed on Li anodes in the Li/SO₂ ambient temperature battery. The model proves to be useful in explaining storage and discharge characteristics of the battery that are due to the presence of the anodic film.

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