<p>A supply shortage of solar-grade silicon in recent years resulted from a rapid expansion of the solar cell industry. Therefore, many efforts have been done to obtain reliable metallurgical methods for production of SoG silicon from metallurgical grade silicon.</p> <p>In this research, refining of metallurgical grade silicon by chlorination treatment with the emphasis on Al removal was investigated. Thermodynamic calculations through Factsage confirmed the feasibility of Al removal in repeated steps of chlorination. Therefore, an Ar+SiCl₄ gas mixture with different flow rates was applied to the silicon melt by blowing and injection methods at different temperatures and the ICP-OES was used for analysis of the impurities in silicon.</p> <p>Results revealed that Al removal from silicon by chlorination treatment under the conditions employed in this study is first order reaction with respect to Al. By increasing the temperature in the chlorination process, the rate constant increases which is related to an increase in the liquid mass transfer rate. Also the observed higher rates of Al removal under injection conditions appear to be the result of improved stirring in the melt rather than an increase in the interfacial area.</p> / Master of Applied Science (MASc)

Past research regarding complexed iron has focused on the resistance to and kinetics of oxidation by O₂(aq) and the extent of stabilization. The 0.45 um filter was typically used to differentiate between dissolved and particulate iron. This research investigated Fe(II) oxidation by free chlorine and ClO₂ in the presence of DOC by varying the pH, DOC to Fe ratios, DOC sources, oxidant dosages, and contact time. Complexed iron removal by alum coagulation with and without oxidant addition was also examined. Particulate, colloidal, and soluble iron were differentiated by the use of 0.2 um filters and 100K ultrafilters. Ultrafiltration and oxidation studies revealed that, at the DOC-to-iron ratios used for this research, not all of the Fe(II) in solution was actually complexed. Thus, oxidation studies represented the oxidation of uncomplexed Fe(II) to Fe(III), which was then complexed by the higher molecular weight DOC. Results indicated that particulate iron formation (as defined as retention by a 0.2 um filter) was a function of the DOC source and oxidant used for testing. The formation of colloidal iron (as defined by retention on 100K ultrafilter) due to oxidation was dependent upon the initial DOC-to-iron ratio and the DOC source. A correlation between DOC adsorption to iron oxide solids and the solution pH, initial DOC-to-iron ratio, and the oxidant used was also evident. Complexed Fe(II) was removed from solution by alum coagulation. Oxidant addition to alum coagulation was necessary to effectively remove uncomplexed Fe(II) (in the presence of DOC) from solution. / Master of Science

The major objectives of this study were to investigate the effects of seasonal changes in Lake Manassas and its watershed (late winter to late summer), the impoundment of Broad Run, and the stratification of Lake Manassas on trihalomethane (THM)-precursors in Broad Run, upstream and downstream of the reservoir, and in Lake Manassas. An additional objective was to determine the molecular-size distributions of the dissolved organic carbon, and the THM precursors of the organic carbon pool in Lake Manassas during stratification. Raw water samples were collected from March through August on Broad Run immediately upstream of the reservoir, at two sites in the reservoir-- one approximately 0.27 miles from the dam and the second, at a more central location, 0.73 miles from the dam, and on Broad Run 2.81 miles below the dam. During stratification two samples were collected from each lake site-- one from the epilimnion, and the second from the hypolimnion. All of the samples were size fractionated by ultrafiltration and chlorinated for determination ofTHMFP. The differences in THMprecursor characteristics were determined by assessing the differences in the total organic carbon (TOC) concentrations and THM-formation potentials (THMFPs) of the various size fractions. The TOe and THM concentrations generally increased from late winter to late summer at all stations. The concentrations in Lake Manassas and in Broad Run below the dam were consistently higher than those observed in Broad Run upstream of the lake, indicating that impoundment causes an increase in levels of THM precursors. In addition, during stratification higher THM yields were produced by the predominantly low-molecular-weight precursors « 5,000) in the epilimnion of Lake Manassas, while the predominantly high-molecular-weight precursors (> 5,000 daltons) were low-yielding-THM precursors. / Master of Science

Tall oil is a mixture of rosin acids, fatty acids, and non-acids resulting from acidification of the soaps separating out from the kraft pulp process evaporator liquor. The present uses of tall oil center chiefly around its fatty acid content, but are limited for some purposes because of the rosin content. Separation of these constituents makes each available as such. The rosin, as crystalline abietic acid, has specific possibilities as a raw material. Rosin and fatty acids are separated chiefly by distillation, although chemical means and extraction have been proposed to overcome such objections as corrosion and losses as pitch, incurred in distillation. Chlorination is used as a step in the purification of tall oil, or to produce a sticky chlorinated oil, but no separation based on the use of chlorine appears to have been proposed. It was proposed in this investigation to chlorinate the fatty acid double bonds in hopes that the properties of this product would be such as to permit of a separation. The effects of solvent, light, heat, and catalysts were studied to determine the optimum conditions for such a reaction, and the effect of chlorination upon the rosin and fatty acids, respectively, under specific conditions was determined, It was found that the use of CCl₄ solvent and ultraviolet light accelerate chlorine consumption and promote the addition of chlorine, but do not entirely stifle the substitution reaction. Rosin and fatty acid double bonds are attacked to about an equal extent under these conditions. The chlorinated oil is entirely soluble in most common solvents at room temperature. Petroleum ether insolubles increase slightly over the amount obtained from untreated oil. It is recommended that the range of chlorination conditions be extended to a more complete study of possible results, and that other chemical attacks be investigated. / Master of Science

Wastewater samples were collected from both the secondary settling and the chlorine contact tanks at a secondary sewage treatment plant (trickling filter) in Blacksburg, Virginia and analyzed for fecal coliforms using three procedures. Physical parameters including total suspended solids, DO, pH, turbidity, temperature and total chlorine residual were measured in effort to ascertain their effect on fecal coliform recoveries. The three procedures employed included the multiple-tube fermentation technique that yields the most probable number (MPN), the standard MF technique (SF-MF), and a modified MF technique (IF-MF) which consisted of a lactose overlay and a 5-hour incubation period at 44.5°C. A statistical analysis of the data showed that the means of the recoveries by the IF-MF technique were significantly greater (0.01 level) than those by the SF-MF technique in both the secondary settling tank and the chlorine contact tank samples. Recoveries by the IF-MF technique were comparable to those by the MPN technique when samples from the secondary settling basin were analyzed, but not in samples from the chlorine contact tank. However, the means of the IF-MF recovery procedure were within the 95 percent confidence interval associated with the MPN. No relationships could be established between the observed variations in the physical and chemical characteristics of the treated sewage samples and the fecal coliform densities. / Master of Science

Granular activated carbon (GAC) pretreatment was evaluated for the removal of trihalomethane (THM) precursors from a surface water supply, the Occoquan Reservoir, in northern Virginia. The carbon contactors were operated in the upflow mode at flow rates of 2, 4, and 6 gpm which provided empty bed contact times (EBCT) of 26, 13, and 6.6 minutes, respectively. Reservoir raw water quality data was collected to determine what relationship existed between these measurements and the trihalomethane formation potential (THMFP) of the reservoir water. The results indicated that THM precursors, as measured by total organic carbon (TOC) and THMFP, could be removed from an untreated surface water supply by GAC contact. The degree to which THM precursors were removed was directly related to EBCT, the most effective being 26 minutes (2 gpm). GAC contact appeared to be selective for the removal of those precursors responsible for instantaneous THM concentrations i.e., those produced within a thirty minute chlorine-contact period. Those precursors responsible for THM concentrations produced after thirty minutes and for up to seven days thereafter (herein designated THMFP) appeared to be associated either with particulate matter in the raw water or with larger molecular weight organic substances which were not well adsorbed by the carbon. There were no discernible direct correlations between THMFP and the turbidity, color, TOC, chlorophyll-a concentration and algal populations in the raw water. Runoff from a rainstorm late in the period of study resulted in increases in raw water color, turbidity, and TOC concentrations, but it was impossible to determine which of these factors was responsible for the increased raw water THMFP that occurred at the same time. / Master of Science

Up-coming regulations on chlorine dioxide in drinking water treatment require low level measurement of chlorite ion (CI0₂-) and chlorate ion (CI0₃-). This research investigated analysis of CI0₂- and CI0₃-; in drinking water by flow injection analysis with iodometric detection (FIA) and ion chromatography with conductivity detection (IC). Both the FIA and IC methods were accurate for the determination of CIO₂-; and CIO₃-; in reagent water. The IC method was accurate in drinking water, however, FIA responded to chloramines and other oxidants present in drinking water causing inaccurate analysis of CIO₂-; and CIO₃-; by FIA. The two IC eluants investigated, a carbonate/bicarbonate mixture and a borate/boric acid mixture, performed well. By taking advantage of the slightly different separation abilities of each eluant, the IC method can be modified to maximize resolution of CIO₂-; and CIO₃-; in different drinking water matrices. Chlorite was unstable in chlorinated drinking water but was stable for up to three days when sodium oxalate was added and stable up to eighteen days when ethylene diamine was added as a preservative. Chlorate was stable in drinking water for up to eighteen days with or without a preservative. The propagation of errors method for determining detection limits yielded limits of detection for CIO₂- (mg/L) of 0.05 for FIA, 0.03 for the IC carbonate eluant and 0.01 for the IC borate eluant. For CIO₃- the limits of detection (mg/L) were 0.24 for FIA; 0.11 for the IC carbonate eluant and 0.02 for the borate eluant. / Master of Science

Chlorinated organic compounds (Clorg) are produced naturally in soil. Formation and degradation of Clorg affect the chlorine (Cl) cycling in terrestrial environments and chlorine can be retained or released from soil. Cl is known to have the same behaviour as radioactive chlorine-36 (36Cl), a long-lived radioisotope with a half-life of 300,000 years. 36Cl attracts interest because of its presence in radioactive waste, making 36Cl a potential risk for humans and animals due to possible biological uptake. This thesis studies the distribution and cycling of chloride (Cl–) and Clorg in terrestrial environments by using laboratory controlled soil incubation studies and a forest field study. The results show higher amounts of Cl– and Clorg and higher chlorination rates in coniferous forest soils than in pasture and agricultural soils. Tree species is the most important factor regulating Cl– and Clorg levels, whereas geographical location, atmospheric deposition, and soil type are less important. The root zone was the most active site of the chlorination process. Moreover, this thesis confirms that bulk Clorg dechlorination rates are similar to, or higher than, chlorination rates and that there are at least two major Clorg pools, one being dechlorinated quickly and one remarkably slower. While chlorination rates were negatively influenced by nitrogen additions, dechlorination rates, seem unaffected by nitrogen. The results implicate that Cl cycling is highly active in soils and Cl– and Clorg levels result from a dynamic equilibrium between chlorination and dechlorination. Influence of tree species and the rapid and slow cycling of some Cl pools, are critical to consider in studies of Cl in terrestrial environments. This information can be used to better understand Cl in risk-assessment modelling including inorganic and organic 36Cl. / Klorerade organiska föreningar (Clorg) bildas naturligt i mark och påverkar klorets kretslopp genom att de stannar kvar längre i marken. Detta stabila klor anses ha samma egenskaper som klor-36, som är en långlivad radioisotop med en halveringstid på 300 000 år. Klor-36 förekommer i olika typer av radioaktivt avfall och om klor-36 sprids i naturen finns det en potentiell risk för människor och djur genom biologiskt upptag. Syftet i denna avhandling är att öka kunskapen om fördelningen och cirkulationen av klorid (Cl-) och Clorg i terrestra miljöer med hjälp av studier i laboratoriemiljö samt en fältstudie i skogsmiljö. Resultaten visar att bildningshastigheten av Clorg är högst i barrskogsjord och rotzonen tycks vara en aktiv plats. Det finns också en större mängd Cl- och Clorg i barrskogsjordar än i betesmark och jordbruksmark. Den mest betydande faktorn som styr halterna av Cl- och Clorg är trädsort, medan geografiskt läge, atmosfäriskt nedfall, och jordmån är av mindre betydelse. Bildning och nedbrytning av Clorg sker med liknande hastigheter, men det tycks finnas två förråd av Clorg i jorden varav ett bryts ner snabbt och ett mer långsamt. Bildningshastigheten av Clorg är lägre i jordar med höga halter av kväve medan nedbrytningshastigheterna inte påverkas av kväve. Slutsatsen från studiernas resultat är att klor i hög grad är aktivt i mark och att Cl- och Clorg halterna bestäms av en dynamisk jämvikt mellan bildning och nedbrytning av Clorg. I studier av klor i terrestra miljöer bör trädsorters inverkan och nedbrytning av olika klorförråd beaktas då det kan ge varierande uppehållstider av Cl- och Clorg i mark. Denna information är viktig vid riskbedömningar av hur radioaktivt klor kan spridas och cirkulera vid en eventuell kärnkraftsolycka.

Secondary effluent from the Roger Road Wastewater Treatment Plant undergoes tertiary treatment of dual media filtration and chlorination. The tertiary effluent is recharged and subsequently extracted for irrigation in Tucson, Arizona. The fate of chlorinated organics in this recharge system was investigated in this research. Nonpurgeable organic carbon was found to reach a constant level in the groundwater after being recharged. Not all of the organic carbon was removed from the water. Nonpurgeable organic halogens increased as they flowed away from the recharge basins. Reasons for this increase were not determined. Attempts were made to define the apparent molecular weight distribution of the NPOC and the NPOX. Measured values of the two parameters were consistently greater after the analytical processing than before, making the determination impossible.

Les composites C/C sont des matériaux très utilisés dans de nombreuses applications pour leurs propriétés exceptionnelles. Néanmoins, ils présentent l'inconvénient de s'oxyder dès les basses températures. Le travail dans cette thèse a consisté en l'élaboration de dépôts de carbures de silicium (SiC) et d’hafnium (HfC) par dépôt chimique en phase vapeur (CVD) afin de protéger en surface ces composites jusqu’à 2000°C. Cette voie d'élaboration permet l'obtention de dépôts denses et continus. Dans un premier temps, une étude thermodynamique du système chimique Hf-Cl-C-H a permis d’appréhender les conditions de dépôt d’HfC et de tracer des diagrammes de dépôt directement utilisables par l’expérimentateur. Ensuite, après avoir déterminé les conditions expérimentales de chloruration de l’hafnium, étape antérieure à la CVD, et après avoir examiné les compatibilités chimiques des deux carbures par Spark Plasma Sintering (SPS), une étude expérimentale paramétrique de la CVD d’HfC a été proposée. Cela a permis la détermination des conditions optimales de dépôt permettant l’obtention d’une protection multiséquencée HfC/SiC, les conditions de dépôt du SiC étant reprises de la littérature. En plus du procédé de CVD, un autre type de concept portant sur l'enrobage de poudres d'HfC par le SiC, puis frittées par la suite, a également été traité. Enfin, les matériaux fondés sur ces deux concepts ont été testés en oxydation à très haute température. Les résultats obtenus ont permis la validation du matériau multiséquencé à 2000°C et le matériau fritté à 1500°C. / Carbon/Carbon composites are widely used materials in many fields of application for their outstanding properties. Nevertheless, these materials have the drawback of oxidizing at very low temperatures. The aim of this work consisted in depositing by means of Chemical Vapour Deposition (CVD) coatings made of silicon carbide (SiC) and hafnium carbide (HfC) in order to protect the composite up to 2000°C in an oxidizing atmosphere. This way of manufacturing has allowed reaching dense and continuous coatings. First, a thermodynamic study of the Hf-Cl-C-H chemical system has permitted to study the influence of HfC deposition parameters and to report them into deposition diagrams. Then, after the study of experimental conditions in the metallic hafnium chlorination step and the examination of chemical compatibilities of the two carbides by Spark Plasma Sintering (SPS), a parametric study of the CVD of HfC has been carried out. This has enabled determination of optimal deposition conditions of HfC in order to manufacture an HfC/SiC multilayered protection. SiC experimental conditions were taken from the literature. Besides the materials made by CVD, another kind of material protection made of HfC powder coated with SiC and then sintered has been also studied. Finally, materials based on those two protection concepts have been oxidized at very high temperature. Results have enabled to validate the multilayered protection up to 2000°C and the HfC/SiC sintered powder up to 1500°C.