The Leighton group has long been interested in developing strained silanes for their use in polyketide synthesis. Recently, our interests have led us to develop a new type of silicon Lewis acid and catalyst with high levels of reactivity. Upon activation with a thiourea, a stabilized silylium ion is formed allowing for the facile allylation of aldehydes and ketones, in addition to Diels-Alder catalysis. This represents one of the first examples of the merger between anion-binding catalysis and silylium ion catalysis. Our group’s interest in strained silanes has also led us to investigate their conductance properties in molecular break junctions. To further understand the nature of the bond-ruptured species we have proposed new synthetic targets and have described herein our progress towards synthesizing these targets.

It is widely accepted that the continued increase of processor performance requires at least partial replacement of electronic interconnects with their photonic counterparts. The implementation of optical interconnects requires the realization of a silicon-based light source, which is challenging task due to the low emission efficiency of silicon. One of the main approaches to address this challenge is the use of doping of silicon based matrices with optical centers, including erbium ions. Erbium ions incorporated in various hosts assume the trivalent state (Er3+) and demonstrate a transition at 1.54 μm, coinciding with optical transmission windows in both silicon and silica. Due to the low absorption cross-section and discrete energy levels of the Er3+ ion, indirect excitation is necessary. In late 90s it was demonstrated that the incorporation of excess silicon in erbium-doped silica results in strong erbium sensitization, leading to an increase of the effective absorption cross-section by orders of magnitude. The sensitization was considered to occur via silicon nanocrystals that formed at high annealing temperatures. While a large increase of the absorption cross-section was demonstrated, the incorporation of Si nanocrystals was found to result in a low concentration of excited erbium, as well as silicon related free-carrier absorption. The focus of this dissertation is the investigation of the nature of the sensitization mechanism of erbium in silicon-rich silica. The results presented in the dissertation demonstrate that erbium in silicon-rich silica is predominantly excited by silicon-excess-related luminescence centers, as opposed to the commonly considered silicon nanocrystals. This is a remarkable conclusion that changes the view on the exact origin of erbium sensitization, and that resolves several technical challenges that exist for nanocrystal-based sensitization. The work shows that the density of indirectly excited erbium ions is significantly larger in samples without silicon iii nanocrystals (annealed at T < 1000°C) as opposed to samples with silicon nanocrystals (annealed at T > 1000°C). The density of indirectly excited erbium ions, defining the maximum achievable gain, was demonstrated to be approximately excitation wavelength independent, while the effective erbium absorption cross-section was shown to significantly depend on the excitation wavelength. The excitation mechanism of erbium by luminescence centers was shown to be fast ( < 30 ns) and capable of erbium sensitization to different energy levels. This multilevel nature of erbium excitation was demonstrated to result in two different mechanisms of the excitation of the first excited state of erbium: fast ( < 30 ns) direct excitation by the luminescence centers, and slow ( > 2.3 μs) excitation due to the relaxation of erbium ions excited into higher energy levels to the first excited state. Based on photoluminescence studies conducted in the temperature range 15 - 300K it was shown that the relaxation efficiency of erbium from the second excited state to the first excited state (responsible for the slow excitation mechanism) is temperature independent and approaches unity. The relative stability of the optical properties demonstrated in the temperature range 20 - 200°C, implies that relatively stable optical gain can be achieved under realistic on-chip operating conditions. The optimum Si excess concentration corresponding to the highest density of sensitized Er3+ ions is shown to be relatively insensitive to the presence of Si nanocrystals and is ~ 14.5 at.% and ~ 11.5 at.% for samples without and with Si nanocrystals respectively. The presented results and conclusions have significant implications for silicon photonics and the industrial application of Er doped SiO2. The work shows that in order to sensitize erbium ions in silicon-rich silica there is no need for the presence of silicon nanocrystals, and consequently lower fabrication temperatures can be used. More importantly, the results strongly iv suggest that higher gain values can be acquired in samples annealed at lower temperature (without silicon nanocrystals) as compared to samples annealed at high temperatures (with silicon nanocrystals). In addition, the maximum gain is predicted to be relatively independent of excitation wavelength, significantly relaxing the requirements on the pump source. Based on the experimental results it is predicted that relatively stable performance of erbium-doped siliconrich silica is possible up to typical processor operating temperatures of ~ 80 - 90°C making it a viable material for on-chip devices. The results suggest that low temperature annealed erbiumdoped silicon-rich silica is a preferable material for on-chip photonic devices as compared with its high temperature annealed counterpart.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24179号 / 理博第4870号 / 新制||理||1697(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 水畑 吉行, 教授 若宮 淳志, 教授 倉田 博基 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The future of magnesium sems to be as a structural material due to its light weight and ether excellent physical properties. In the chemical industry the use of the metal as a structural material is limited by its rapid corrosion, particularly in the presence of acids and salts. The recently developed silicone resins appear to be logical materials for use as a protective coatings for magnesium under these conditions due to their properties of heat resistance, chemical resistance, and water repellency. The purpose of this investigation was to evaluate the silicone resins (DC 801, 802, 803, and 804) as corrosion protective coatings for magnesium alloys, and to determine the cause of difficulties encountered in the application of the resins to magnesium. In flexibility and adhesion tests of the resins applied to magnesium alloy FS-1 and cured at 225°C. for periods of 1, 8, and 16 hours, it was found that resins 801 and 802 had excellent properties, but that resins 803 and 804 were unsatisfactory. It was found that resins 802 and 804 have excellent oil resisting properties in oil resistance tests of the resins in contact with Texas crude oil at 100°C. for four hours. Resin 801 was found to be satisfactory only when baked for a period of 16 hours or more at 225°C. Resin 803 was found to be unsatisfactory due to crazing. Cobalt naphthenate was shown to be a more efficient curing accelerator than benzoyl peroxide when used in a concentration of 0.30% based on the solid resin content. Benzoyl peroxide was proved to be better than no curing accelerator at all. Polymerization tests of silicone resins 802 and 803, conducted in atmospheres of oxygen, nitrogen, carbon dioxide, and air for five hours at a temperature of 220°C ± 20°C., showed that oxygen is not necessary for the polymerization of the resins. Service tests were conducted, on magnesium alloy YS-1 heat exchanger tubes coated with the silicone resins, by means of a double pipe, single pens heat exchanger. A three per cent sodium chloride solution was used as a corrosive medium at a flow rate of seven g.p.m. Steam at 260°F. Was used as a heating medium, and the outlet and inlet temperature difference of the apparatus was 17°F ± 4°F. The duration of the tests were from two to six hours. From the results of these tests it was found that resins 801 and 802 are not satisfactory protective coatings for magnesium, due to penetration of the corrosive medium at pinholes in the film. Silicone resins 803 and 804 were found to be unsatisfactory protective coatings for magnesium due to erasing of the resin film. The failure of the resin films was shown not be due to chemical attack by the sodium chloride solution; but due to mechanical failure caused by the corrosion products of the metal formed under the resin, by the corrosive medium penetrating to the metal substrate through mechanical defects in the film. / M.S.

A study has been undertaken with the aim of preparing appropriately functionalised polyhedral oligomeric silsesquioxane (POSS) compounds to be used in ambient-cure chemistry. Numerous epoxy-functionalised compounds have been designed and synthesised and these materials have been characterised in order to determine their chemical structure. These compounds have also been incorporated into existing polymerisation reactions to test whether these materials could be used in the protective coatings industry. A glycidyl-functionalised POSS compound was prepared and reacted with a series of amines to produce ambient-cured polymers which could be used in the coatings industry. There were also a series of experiments undertaken on these polymers to identify the processes at work and to test how they compare to industry standards. As a direct comparator to this work, another set of results was obtained with a cyclic-siloxane material incorporated into the systems in place of the POSS. A linear analogue was also tested. The reactions proved to be a success and an appropriate data-set was yielded. During the synthesis of POSS precursors there are a series of residual materials produced. These materials have also been studied in this project. It was anticipated that these would behave in a similar way to the POSS compounds however the same functionality was never achieved as had been with the POSS. Ambient-cured polymers have also been targeted from a basic hydride-functionalised POSS compound and a polybutadiene system. The appropriate reactions unfortunately never took place as anticipated but there were a series of tests undertaken to identify the processes at work. A study has also been undertaken using near-I.R. to track the curing reactions. From this data, the extent of cure could be studied and the make-up of the reaction could be investigated in more detail.

At the end of this thesis, the 1H and 13C {1H} NMR spectra of all the new compounds are listed in the Appendix. / Chapter 1 presents an overview of BODIPYs, including their general synthesis, properties, reactivities, and applications. The use of these compounds as photosensitizers for photodynamic therapy and fluorescent sensors for metal ions is highlighted. / Chapter 2 reports the synthesis, spectroscopic characterization, photophysical propreties, and in vitro photodynamic activities of a series of symmetrical distyryl BODIPYs substituted with one to five hydrophilic oligoethylene glycol monomethyl ether chain(s). In general, these compounds are essentially non-aggregated in DMF, resulting in a strong fluorescence emission and relatively high efficiency in generating singlet oxygen. Being formulated with 0.05% Tween 80, these compounds act as efficient photosensitizers. The compound which contains five triethylene glycol monomethyl ether chains exhibits the highest photocytotoxicity with an IC50 value as low as 7 nM toward HT29 human colorectal carcinoma cells. The high photodynamic activity of this compound can be attributed to its high efficiency in generating singlet oxygen, low aggregation tendency, and high cellular uptake. In addition, this compound also has a strong and selective affinity to the endoplasmic reticulum of the cells, causing cell death mainly through apoptosis. / Chapter 3 reports a related study on a series of unsymmetrical distyryl BODIPYs. These compounds possess three triethylene glycol monomethyl ether chains and another substituent at the other styryl group. The effects of this substituent on the photophysical properties, aggregation behavior, cellular uptake, and subcellular localization have been explored. Furthermore, their in vitro photodynamic activities have also been evaluated and compared with those of symmetrical analogues reported in Chapter 2. / Chapter 4 describes a novel ratiometric near-infrared fluorescent dye based on distyryl BODIPY with a 4-dimethylaminophenylethynyl group at the 2- and 6-positions. This compound exhibits a remarkable blue-shift in its absorption and fluorescence emission positions upon protonation with trifluoroacetic acid in organic solvents or HC1 in water in the presence of 0.05% Tween 80. These changes can be made reversible upon addition of a base. / Chapter 5 describes two monostyryl BODIPYs which contain two or four water-soluble amide chains as the metal chelators. The photophysical properties of these compounds and their spectral response to various metal ions have been investigated. The results show that the compound with two amide chains can detect Zn2+ ion in MeCN. They bind in a 1:1 stoichiometry with a binding constant of 2.2 x 104 M-1 . The fluorescence emission increases remarkably in intensity and shifts substantially to the blue from 620 to 572 nm due to the inhibition of the intramolecular charge transfer. The compound which contains four amide chains can detect Cd2+ ion with a high selectivity in phosphate buffered saline. / Chapter 6 reports the synthesis and spectral properties of a silicon(IV) phthalocyanine with two axial bis(2-picolyl)amine moieties which act as the binding sites for metal ions. The effects of various metal ions on its absorption and fluorescence spectra have been examined. The results indicate that this compound shows a relatively high sensitivity to Zn 2+ ion. Moreover, the proposed binding mode and the sensing mechanism are also discussed. / This thesis describes the synthesis and characterization of several series of functional boron dipyrromethenes (BODIPYs) and a silicon(IV) phthalocyanine. Their applications as efficient photosensitizers in photodynamic therapy and selective fluorescent sensors for metal ions are also reported herein. / He, Hui. / Adviser: Dennis Kee Pui Ng. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Photodynamic therapy (PDT) is a minimally invasive treatment modality for some human diseases, including cancer. To destroy the targeted cells or tissues, PDT relies on the reactive oxygen species (ROS) generated from a series of photochemical reactions by the light-activated photosensitizers administered to the patients. Many dyes could be modified to become photosensitizers. The BODIPY-based fluorophores could be converted into potent photosensitizers with highly efficient singlet oxygen generation as well as considerable brightness of fluorescence. Some of them exhibit potent in vitro PDT effects. However, carriers are often required for an effective delivery of the BODIPY-based dyes in biological system. / Silica nanoparticles are ceramic-based materials prepared by condensation of silanes along the surfactant-based templating agents. Mesoporous silica nanoparticles (MSNs) and organically modified silica nanoparticles (OMSNs) represent two major types of silica nanocarriers used for loading of photosensitizers in PDT. Typical MSNs have a diameter of 100-500 nm and a highly ordered hexagonal porous structure for loading of guest molecules. The OMSNs are smaller in size (diameter ~20 nm). Both MSNs and OMSNs are known to be chemically inert and biocompatible. Therefore, they were selected as the carriers for BODIPY-based photosensitizers in the present study. / A BODIPY-based photosensitizer with an absorption maximum at the red region (~660 nm) was modified to carry a carboxyl group at the meso-position. This photosensitizer was conjugated to an amine-functionalized MSN of diameter 80-120 nm by a post-synthesis grafting approach. This strategy allowed the entrapment of delicate dyes by the MSN under mild reaction conditions. The resulting composites with different photosensitizer loading were all spherical and with diameter from 80-120 nm. Dispersing the composites in H₂O, the fluorescence emission was moderately quenched due to dye aggregation. However, compared with the surfactant solubilized free dye, the MSN conjugated BODIPY produced singlet oxygen more efficiently. The dye loading per the unit mass of MSN did not impose any significant effect on the photophysical properties of the composites. The in vitro PDT effects of the BODIPY-based dye entrapped in the MSN were evaluated by using the human adenocarcinoma cells HT-29. The dyes loaded in the MSNs were more cytotoxic than the free dye, but slightly less cytotoxic when compared with the surfactant-formulated dye. The rate of intracellular ROS production of the MSN entrapped dye was much higher than that of the free dye with or without surfactant, which was consistent with the results obtained in the studies of the photophysical properties. The dye in MSN was more efficient as an inducer of apoptosis than the dye in surfactant, as shown by the annexin V/PI staining. Subcellular localization studies using confocal microscopy revealed that the dye in MSN was mainly found in endoplasmic reticulum and lysosome of the cells. / This amine-functionalized MSN platform was further modified on the surface. On a batch of amine-bearing MSN (~200 nm in diameter) loaded with the BODIPY-based photosensitizer, a layer of polyethylene glycol (PEG) was grafted. The PEG layer was comprised of short PEG chains (~15 repeating units) with a methyl end and another long PEG chains (~44 repeating units) with an azide end. The alkyne-modified tLyP-1 peptide targets the cancer cell and blood vessel surface marker, neuropilin, was conjugated to the MSN via azide-alkyne Huisgen cycloaddition (click reaction). Unlike many other reported designs of photosensitizer-MSN composites utilizing only amine functionalization, this approach prevented the competition for conjugation site between the photosensitizer and the targeting ligand. The use of click reaction allowed a greater feasibility in targeting ligand design. In H₂O, the surface decorated composites could still generate singlet oxygen as effectively as the bare composite. The in vitro PDT effects toward human prostate adenocarcinoma cells PC-3 with a high level of neuropilin expression of the composites were evaluated. The peptide-bearing MSN had a faster initial uptake in cells, which could be moderately suppressed by the addition of free peptide. The peptide-linked MSN had a higher photocytotoxicity toward the PC-3 cells when compared with the MSN without the peptide due to the enhanced cellular uptake. Both composites were confined to the lysosome of the cells, which might be the consequence of lacking surface positive charge to help endosomal escape. Therefore, further optimization of the composite by adjusting the PEG loading, chain length and the amount of targeting ligand loading should be made. / OMSNs are homogenous spherical particles with a smaller size (~20 nm). The capability of OMSNs to be multi-functional dye nanocarriers was also explored. Besides a BODIPY-based photosensitizer, a phthalocyanine-based photosensitizer and an aza-BODIPY-based imaging dye were also chosen for OMSN entrapment. It was found that only those surfactant-soluble dyes could be successfully entrapped in the OMSNs. Dyes in OMSNs remained non-aggregated, thus emitting a bright fluorescence. The photosensitizers generated singlet oxygen with the same efficiency as the surfactant-formulated free dyes. The potency of the OMSN-entrapped photosensitizers toward the HeLa derived KB cells was similar to that of the surfactant-solubilized free dyes. OMSNs are hence alternative carrier to the surfactant-based emulsifiers for in vitro photosensitizer delivery. To decorate the surface of OMSN, folate was conjugated to the composite by one-pot approach. However, the resulting composite failed to exhibit any tumor targeting effect toward KB cells having a high level of folate receptor expression. Besides, in order to prevent premature dye leakage in culture media as a result of the interaction with serum proteins, an attempt was also made to prepare OMSNs with a covalently linked BODIPY-based dye. However, the conjugated dye was aggregated, which diminished the singlet oxygen generation and quenched the fluorescence of the composites, although the surface of this composite was successfully decorated with PEG or the azide-bearing silane. / In conclusion, the BODIPY-based photosensitizers could be entrapped in MSNs and OMSNs could be successfully delivered into cancer cells in vitro. The PDT effects induced by these composites were often comparable to those caused by the the surfactant-solubilized dyes. Although surface decorations could be made for the particles, further fine adjustment on the surface properties of the composites is needed to improve the specificity and potency of the composites in the future. / 光動力治療(PDT)可用作治療一些人類疾病如癌症。這種低創傷度治療模式的主要原理是先把光敏劑注入病人體內，然後以光照射患處，激活當中的光敏劑。經過一系列的光化學反應後，病患組織附近的氧分子會被光敏劑轉化成為活性氧物種，從而破壞病變的組織或細胞。在眾多可改造成光敏劑的染色劑中，氟硼二吡咯(BODIPY)熒光團可以轉成兼具高活性氧轉化率及強熒光的光敏劑。研究顯示，部份BODIPY衍生的光敏劑在細胞實驗中有強大的PDT效果。可是，這些光敏劑往往需要由載體輔助才可以送達目標組織或細胞。 / 二氧化矽納米粒子是由硅烷在介面活性劑模板上聚合而成的陶瓷基類納米粒子，其中介孔二氧化矽納米粒子(MSN)和有機改造二氧化矽納米粒子(OMSN)為兩種最常用的光敏劑載體。MSN的直徑通常介乎100至500納米，並有高度整齊排列的六角介孔以供承載客分子。OMSN則比較細小，直徑約20納米。MSN和OMSN皆為化學惰性以及生物相容的物料，所以在本研究中它們被選為BODIPY類光敏劑的載體。 / 在一個BODIPY光敏劑（它的吸收峰位於紅光，波長約660納米範圍內）上，羧基被加到中央位置上。這個帶羧基的光敏劑可以嫁接到己成形的帶胺功能團MSN上。由於後合成嫁接法可以於溫和的條件下進行，相信其亦可應用其他脆弱的染色劑及帶胺MSN的連結上。即使有不同光敏劑載入量，同一系列的合成物的直徑皆是80至120納米。當這些合成物分散在水中，MSN內光敏劑會因聚合作用，其熒光強度會明顯減弱。可是，比起沒有載體或以介面活性劑配方的光敏劑，包裹於MSN內的光敏劑能更有效的產生活性氧。在光物理的測試中，光敏劑的承載量對MSN化合物的光物理性質俱沒有明顯的影響。 / 對人工培植的人類大腸腺癌細胞HT-29而言，承載於MSN內的光敏劑的比沒有載體的具光毒性。可是對比起以介面活性劑配方的BODIPY，承載於MSN內的光敏劑還是光毒性稍弱。另外，承載於MSN內的光敏劑在細胞內產生活性氧的效率，遠高於介面活性劑配方內、或沒有載體的光敏劑，這項發現跟光物理的檢測結果類近。另外，annexin v/PI染色實驗結果顯示，MSN承載的光敏劑能更有效的引發細胞淍亡。共焦顯微鏡進行的細胞內定位法顯示，MSN承載的光敏劑主要分佈在內質網和溶酶體之中。 / 這類帶胺官能團的MSN的粒子表面可作進一步修飾。本研究嘗試用聚乙二醇層修飾一種直徑約200納米、以及載有BODIPY光敏劑的MSN。該聚乙二醇層由帶甲基端的短鏈(約15個重複單位)和帶疊氮端的長鏈(約44個重複單位)PEG組成。然後，以疊氮──炔烴Huisgen環加成法（點擊反應）將帶炔烴的tLyP-1短肽連接到PEG上。該tLYP-1短肽對在一些癌細胞和癌組織血管上常見的neuropilin有高度結合親和力，故可作靶向分子使用。另外，本研究裏採用的嫁接方法跟現時常用於只有胺官能團的MSN處理法不同：光敏劑和靶向份子是分別連接於MSN的胺和疊氮官能團上，故能避免光敏劑與靶向分子競爭。同時因為使用簡易的點擊化學反應，靶向分子的設計可以有更多選擇。 / 在水中，有和沒有表面修飾的MSN同樣有效地產生活性氧。對人工培植、並在細胞表面高度表達neuropilin的人類前列腺癌細胞PC-3而言，帶tLyP-1的MSN合成物有更高光毒性，其中的原因包括帶tLyP-1的MSN有更快的攝入初速。另外，自由的tLyP-1短肽可稍為抑制這種MSN合成物的細胞吸收，亦可見tLyP-1足以影響MSN的細胞攝入。可是，不論有沒有帶短肽，兩種以PEG修飾的MSN皆是因為沒有表面電荷而無法逃離細胞的溶酶體，以致其PDT效果改善幅度有限。所以在往後的研究，PEG的覆蓋量、長度和靶向分子的接連率需作進一步探討。 / OMSN是直徑約20納米均勻的圓形粒子。本研究亦會探討如何可以用OMSN作為多功能的染色劑載體。除了BODIPY光敏劑之外，另一個鋅酞菁和一個氮雜氟硼二吡咯的熒光顯影劑亦包裹在OMSN中。結果顯示，只有可以用介面活性劑溶解的染色劑才可以成功包進OMSN之內。OMSN內的染色劑基本上沒有聚合現象，故能發出強熒光，而包覆在光敏劑之內的光敏劑轉化氧作活性氧的效率跟介面活性劑配方的光敏劑一樣。 / 不論是鋅酞菁或BODIPY，包裹在OMSN內的光敏劑對在人工培植、及源自HeLa的KB癌細胞的PDT效果跟介面活性劑配方的光敏劑相若。因此，OMSN可替代活性介面劑作為光敏劑的載體。本研究亦嘗試在OMSN的表面上以葉酸作修飾。可是，即使用了表面上有大量的葉酸受體的KB細胞，葉酸修飾過的OMSN並沒有靶向性。另外，為了解決OMSN內吸附的染色劑會因粒子與血清蛋白的互動而漏出粒子外的問題，本研究亦嘗試將OMSN與BODIPY衍生的光敏劑以共價鍵連結。同時其表面亦以帶疊氮聚乙二醇層作修飾。可是，BODIPY光敏劑在以這些OMSN合成物內有嚴重的聚合現象，以致於活性氧產生和熒光亮度大幅度減弱。 / 總括來說，本研究內設計的BODIPY衍生的光敏劑皆可以用MSN或OMSN來承載，並成功送達至人工培植的癌細胞內。這些化合物的PDT效果往往媲美那些以介面活性劑配方的同類光敏劑。雖然證明了這些粒子表面可以予以修飾，其表面修飾層仍需要進一步的改善，以增強它們的靶向專一度和PDT功效。 / Yeung, Sin Lui. / Thesis Ph.D. Chinese University of Hong Kong 2015. / Includes bibliographical references (leaves 148-159). / Abstracts also in Chinese. / Title from PDF title page (viewed on 24, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Bibliography: leaves 177-193 / v, 193 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Organic Chemistry, 1985

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

<p>The thermodynamic conditions for the behaviour of silicon in the lower part of the blast furnace have been the focus of the thesis. More specifically, the influences of temperature, carbon activity, total gas pressure and Fe reoxidation on silicon have been studied.</p><p>Calculations show that an increased temperature gives higher equilibrium ratio between silicon in hot metal and slag. Furthermore, laboratory reduction studies shows that the carbon activity in the cohesive zone increase with an increased reduction time. Increased carbon activity will increase the equilibrium silicon content in liquid metal.</p><p>Equilibrium calculations based on tapped hot metal and slag shows that the equilibrium silicon content of the liquid metal phase is higher than measured at tapping. Around the raceway area the equilibrium silicon content is very high. The high equilibrium silicon content makes it important to differ between the conditions under operation and the conditions of samples taken out of the blast furnace before studied. The equilibrium silicon content is strongly correlated to the CO gas partial pressure. Often this partial pressure is changed during sampling and cooling of samples. At tapping the equilibrium partial pressure of CO has been calculated to higher values than the total gas pressure inside the blast furnace.</p><p>Metal droplets found in tapped slags are probably formed by reduction of FeO. In the periphery part of the lower part of the blast furnace, it is believed that mainly FeO oxidises silicon in hot metal. It is not expected that the metal droplets in the slag is formed if FeO oxidises dissolved silicon. Instead, the iron droplets may form at reactions with gas, coke carbon or coal powder carbon. Around some droplets increased magnesium content has been found. This may be due to reactions with gaseous magnesium that, according to thermodynamic conditions, is easy to form. It has been reported that much FeO may be formed in the raceway area. The metal droplets may indicate how much FeO that reacts with other components than liquid iron. The iron found in metal droplets in the slag corresponds to between 0.02 and 0.2 wt-% FeO in the slag.</p>