Browsing by Subject "boron"
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Item Boron-based Additives in Oil and Grease for Wind Turbine Applications(2013-06-25) Kim, Jun-HyeokThis research investigates the tribological performance of crystalline and amorphous powders of boron as additives in lubricants: grease and mineral oil for potential applications of wind turbine. This research is focused on the wear resistance and lubricity performance of boron powders. Experimental approach was used in this research. Several experiments were conducted including API RP 7A1 thread compound test, pin-on-disk tribometer experiment, stribeck curve analysis and surface analysis. It is possible to obtain fundamental principles of boron powder as additives in lubricants from these experiments. The results indicate that amorphous boron powder is beneficial for lubricants additive, while crystalline boron powder showed that it is not proper as an additive, since there were a lot of traces of abrasive wear. According to the results amorphous boron powder provided anti-wear and better lubricity properties in the lubricants. The observation and understanding obtained here will be beneficial for the lubrication industry. This research will provide basic principle of boron powder and possibilities of boron powder as additive in lubricants. This thesis is composed of six chapters. The first chapter is about general ideas of lubrication from problems to emulsion techniques, followed by chapter II, motivation and objectives. Chapter III provides experimental details including boron powder?s properties and basic information will also be discussed in this chapter. Finally obtained results will be discussed in the chapter IV and V followed by chapter VI conclusions and future recommendations.Item Synthesis and Study of Boron and Antimony Lewis Acids as Small Anion Receptors and Ligands Towards Transition Metals(2012-02-14) Wade, CaseyAlthough fluoride is used at low concentrations in drinking water as a means of promoting dental health, it poses a danger at high exposure levels where it can lead to skeletal fluorosis or other adverse effects. Cyanide is notoriously toxic, and its large scale use in industrial processes warrants the need for close monitoring to remain aware of potential contamination of water sources and other environmental resources. Based on these considerations, it is critical to continue to develop improved methods of monitoring fluoride and cyanide concentrations in water. However, molecular recognition of these anions in water poses considerable challenges. For fluoride, this is due largely to its high hydration enthalpy (?Ho = -504 kJ mol-1), which drastically reduces its reactivity in water. Additionally, the strong basicity of cyanide (pKa of (HCN) = 9.3) may obscure its detection in neutral water due to protonation. In addition to achieving detection of these anions in water, it is most desirable to have information of the detection event relayed in the form of a positive, rather than negative, response (i.e., turn-on vs turn-off). The general strategy of appending cationic groups to triarylboranes imparts beneficial Coulombic, inductive, and sometimes chelate effects that have allowed a number of these Lewis acidic receptors to sense fluoride and cyanide in aqueous environments. With the goal of developing new triarylborane-based receptors that show enhanced affinities for these anions, as well as turn-on responses to detection, a series of pyridinium boranes were synthesized and studied. Having recognized that the inherent Lewis acidity of antimony(V) species might be exploited for anion sensing, we also describe initial studies on the ability of tetraorganostibonium ions (R4Sb+) and cationic transition metal-triarylstibine complexes (R3SbM+) to complex fluoride. Finally, the electropositivity of antimony and its ability to form stable compounds in both the +3 and +5 oxidation states have led us to begin investigations into the bonding and redox reactivity of novel metal stibine/stiborane complexes.Item Synthesis, characterization, anion complexation and electrochemistry of cationic Lewis acids(2009-05-15) Chiu, Ching-WenOwing to the favored Coulombic attraction between the ammonium group and anion which stabilizes the B-F/B-CN bond against heterolysis, cationic borane [25]+ has great affinity toward anions than its neutral analog, and is capable of capturing fluoride or cyanide from water under bi-phasic conditions. By placing the fluorophilic silyl group adjacent to an electrophilic carbocation, a novel fluoride sensor [45]+ was obtained. Sensing occurs via a fluoride induced methyl migration from the silicon to adjacent electrophilic methylium center which is unprecedented. As a result of its strong fluoride affinity, [45]+ is able to react with KF in aqueous media at pH 7.0. The electrochemistry study of these cationic Lewis boranes reveals that the cationic character of these boranes serves to decrease their reduction potential and increase the stability of the resulting radicals. In this part of the research, we have prepared a cationic borane [27]+, which features two reversible reduction waves at -0.86 and -1.56 (vs. Fc/Fc+) corresponding to the formation of stable neutral and anionic derivatives. The one-electron reduction of [27]+ leads to the formation of a boron containing neutral radical featuring an unusual boron-carbon one-electron ? bond. Further reduction of 27? results in the formation of the borataalkene derivative [27]-, which features a formal B=C double bond. The structural changes accompanying the stepwise population of the B-C ?-bond are also determined, and this sequential population of B-C ?-bonding orbital is also supported by theoretical computations. In order to understand the impact of the cationic nature of these boranes on their oxidative power, three novel cationic boranes ([34]+, [35]2+, and [36]3+) have been synthesized and their oxidative power were examined via cyclic voltammetry. The CV data of these compounds shows that the reduction potential of these triarylboranes is linearly proportional to the number of the pendant cationic substituents. Substitution of a mesityl group by an ArN+ group leads to an increase of the reduction potential by 260 mV.