Thesis, PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Anglo Research is due to commission a novel pilot plant for the manufacturing of titanium metal from ilmenite ore. The process requires the use of hydrofluoric acid, a very toxic chemical, in large volumes. A health and environmental study and legislative requirements of the process were thus required before commencing with the plant design. Metallurgical processes have resulted in some degree of environmental impact, from water, air and soil pollution. A prominent example is acid mine drainage, which pollutes ground water. It is therefore important to ensure that proper steps are taken in minimising or mitigating negative environmental effects when developing new process routes. Hydrofluoric acid (HF) is classified as extremely toxic. This acid is very aggressive physiologically because of the fluoride ion which penetrates the skin and robs the bone tissue of calcium. Because of the hazardous nature of HF, the following legislations were reviewed: o Hazardous Substances Act 15 of 1973 o Occupational Health & Safety Act of 1993 o National Road Traffic Act 93 of 1996: Chapter VIII o National Environmental Management Act 107 of 1998 o Environmental Conservation Act 73 of 1989 HF has been used in many other industrial applications including manufacturing of fluorocarbons and other chemicals, aluminium manufacturing, petroleum alkylation and uranium purification. Steps should be taken to minimise exposure to hydrofluoric acid in areas where there is a likelihood of worker exposure. Control measures include, but are not limited to, elimination/substitution and process modification, isolation, engineering controls, administrative controls, and use of personal protective equipment and hazard communication. HF is corrosive to most metals and materials of construction suitable for HF include fluoropolymers and other metal alloys such as nickel based alloy 400. Every design aspect of the plant must be done in a way that minimises the environmental and worker exposure to HF. Once safety of the plant design has been extensively reviewed, the pilot plant can then be built. The success of this campaign will be based not only on the achievement of process and product specification, but also on whether it was run without any incidents.

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2002. / Includes bibliographical references.

Thesis (Ph. D.)--Princeton University, 1917.

Thesis (Ph. D.)--Princeton University, 1917.

Thesis (Ph. D.)--School of Electrical and Computer Engineering, Georgia Institute of Technology, 2004. Directed by James Meindl. / Includes bibliographical references (leaves 58-60).

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O tratamento ortodôntico em adultos, nos últimos tempos, tem ganhado popularidade na tentativa de melhorar a estética e a função. No entanto, é uma característica comum nestes pacientes, ter os dentes restaurados com facetas de resina, coroas metalo-cerâmicas e/ou porcelana pura. Neste contexto, o ortodontista se defronta com o desafio de colar braquetes em diferentes sistemas cerâmicos, de capacidade desconhecida de resistir às forças de cisalhamento. Portanto, os objetivos deste trabalho foram: 1) Verificar se a força de cisalhamento em braquetes colados em superfícies de porcelana feldspática e AllCeram é afetada por diferentes tempos de ataque com ácido hidrofluorídrico e 2) Observar se existe uma relação direta entre os valores obtidos da força de cisalhamento e o índice remanescente de adesivo (IRA). Sessenta espécimes de porcelana em formato cilíndrico foram aleatoriamente divididos em 3 grupos de 20 espécimes de acordo com o tempo de ataque do ácido hidrofluorídrico de 1 minuto, 30 segundos e 15 segundos (grupos 1, 2 e 3 respectivamente). Outros sessenta espécimes de porcelana AllCeram, com o mesmo formato e divididos da mesma maneira de acordo com o tempo de ataque ácido (grupos 4, 5 e 6 respectivamente). A colagem dos braquetes na superfície cerâmica incluiu aplicação de silano, colocação de resina fotoativada sobre a base do braquete e cimentação com força padronizada de 500g. Vinte e quatro horas após a cimentação, os espécimes foram submersos em água destilada a 37OC e submetidos ao teste de resistência ao cisalhamento em uma máquina de ensaio universal, com velocidade de 0,5 mm/min, cujos valores registrados em Kgf e convertidos em MPa. O tipo de falha também foi egistrado usando o IRA através de um estereoscópio com magnificação de 4x. A força de cisalhamento mais alta foi registrada no grupo 1 (21.21 MPa), que foi significativamente diferente dos grupos 2, 3, 4, 5 e 6 (11.01, 10.64, 14.31, 10.59, 10.39 MPa, respectivamente). Os valores mais baixos encontrados nos grupos remanescentes não diferiram entre si. A mediana dos escores do IRA para os grupos 1, 2, 3, 4, 5 e 6 foi 2, 3, 3, 0, 3, e 3, respectivamente. O grupo 1 (porcelana feldspática 1 minuto) foi afetado pelos diferentes tempos de ataque com ácido hidrofluorídrico, quando comparado aos grupos 2 e 3, ao passo em que os grupos 4, 5 e 6 de porcelana AllCeram não foram. Não houve relação direta entre o escore do IRA e os valores da força de cisalhamento. / Orthodontic treatment in the adult population has lately gained popularity in an attempt to improve esthetic and function. It is, however, a common feature in these patients, that their dentition is restored by resin veneers, porcelain fused to metal and all ceramic crowns. In this context, the orthodontist faces the challenge of bonding brackets to different porcelain based materials, of unknown ability to resist shear forces. Thus, the aim of this investigation was: 1) to test the null hypothesis that shear strength of brackets bonded to feldspathic and AllCeram porcelain surfaces is not affected by different hydrofluoridric etching times and 2) to test the null hypothesis that there is no direct relation between shear strength values and the adhesive remanescent index (ARI). Sixty feldspathic porcelain disc shaped specimens were randomly divided into 3 groups of 20 each, according to hydrofluoridric acid etching time of either 15, 30 seconds and 1 minute (groups 1, 2 and 3, respectively). Another 60 AllCeram specimens of the same shape were subjected to the same division, according to etching time (groups 4, 5, and 6 respectively). Bonding the brackets to the porcelain surfaces included silane coating, an overlying photoactivated resin and a standardized 500g cementation force. Twenty-four hours after cementation, at 37oC in destilled water, specimens were subjected to a shear force in a universal testing machine at a cross-head speed of 0,5mm/min and shear values registered in Kgf and then converted to MPa. Type of failure was lso recorded using ARI by means of a stereoscope at 4x augmentation. The highest shear strength was found for group 1 (21.21 MPa), which was significantly different than groups 2, 3, 4, 5, and 6 (11.01, 10.64, 14.31, 10.59, 10.39 MPa). The lower values found in the remaining groups were not different among each other. Median ARI scores for groups 1, 2, 3, 4, 5, and 6 were 2, 3, 3, 0, 3, and 3, respectively. The first hypothesis must be partially rejected since only feldspathic porcelain group 1 was affected by different hydrofluoric etching times, when compared to groups 2 and 3, while AllCeram groups 4, 5, and 6 were not. On the other hand, the second null hypothesis must be accepted since no direct relation between ARI score and shear strength values could be determined.

No contexto de refino de petróleo, alquilação é o processo pelo qual se produz uma corrente de hidrocarbonetos chamada de alquilado, na faixa da gasolina, a partir de olefinas leves (propeno, butenos) e isobutano. A demanda por alquilado como corrente integrante do pool de gasolinas de uma refinaria tem aumentado ao longo das duas últimas décadas devido a diversos fatores, sendo o principal a adoção de normas mais restritivas para a qualidade de combustíveis automotivos. No presente trabalho foi desenvolvido e validado um modelo matemático fenomenológico capaz de representar adequadamente as reações químicas envolvidas no processo de alquilação catalítica que utiliza ácido fluorídrico como catalisador, bem como estimar o rendimento de produto e subprodutos da reação e a qualidade do alquilado, representada pelo teor de tri-metil-pentanos (TMP) e di-metil-hexanos (DMH) no alquilado. A construção do modelo foi baseada em balanços de massa e energia no conjunto reacional, utilizando mecanismos cinéticos disponíveis na literatura, sendo os seus parâmetros cinéticos estimados por regressão não linear a partir de literatura. O modelo foi validado com dados obtidos em uma unidade industrial de propriedade da Petrobrás, localizada em Cubatão. Os resultados obtidos permitem afirmar que o modelo apresentou boa resposta para a identificação do consumo de reagentes e rendimento de produtos. Sua resposta tendeu a subestimar a quantidade de frações pesadas do alquilado. / Alkylation is the process which light hydrocarbons (like butenes and iso-bute) are transformed into heavier hydrocarbons, called alkylate. The alkylate demand as a gasoline component has been growing since the middle 90s, mostly due to more severe quality requirements for gasoline. This work proposes a mathematical model that accounts for the main chemical reactions for a HF Alkylation Unit. The alkylate yield and quality, described by its composition, are also represented as well. This model as based on mass and energy balances for the alkylation reactor, using the most accepted kinetic mechanism available at literature. The model constants were estimated by non-linear regression with available data from literature. The model validation was performed comparing the simulation results with data collected at an industrial Alkylation unit at Cubatão, Brazil, without further parameter adjustment. The results show a good model response for the consumption of reagents and alky yield. The model, however, underpredicts the yield of heavier fractions.