Orientador: Estevão Tomomitsu Kimpara / Banca: Alvaro Della Bona / Banca: José Henrique Rubo / Banca: Mário Alexandre Coelho Sinhoreti / Banca: Guilherme de Siqueira Ferreira Anzaloni Saavedra / Resumo: Testou-se o efeito de diferentes formas de tratamento da superfície cerâmica após condicionamento com ácido hidrofluorídrico (HF) na resistência à fratura de coroas cerâmicas à base de dissilicato de lítio. Quarenta terceiros molares humanos receberam um preparo convencional para coroa total. Após escaneamento digital dos preparos, blocos cerâmicos foram usinados pelo sistema CAD/CAM para obtenção das coroas. A espessura da película de cimento das coroas ao preparo foi verificada com silicone de adição. As coroas foram distribuídas nos 4 grupos conforme o tratamento da superfície cerâmica (n=10): (HF)- HF à 4.9% por 20s + spray ar-água por 30s; (HFN)- HF + agente neutralizador por 5 min (N); (HFU) - HF + banho sônico por 5 min (U); e (HFNU)- HF + N + U. Após aplicação de uma camada de silano (60s), as coroas foram cimentadas com cimento resinoso dual. Uma carga compressiva de 1000Kg foi aplicada no centro da face oclusal da coroa com velocidade de 1 mm/min até a fratura. Os dados foram analisados por ANOVA e Tukey (α=0,05). A carga média de fratura (Kgf) foi: HF = 169,92 ± 21,37; HFN = 187,34 ± 34,79; HFU = 166,63 ± 40,22 e HFNU = 175,26 ± 40,22. O tratamento da superfície cerâmica após condicionamento ácido não influenciou significativamente (p>0.05) na resistência à fratura das coroas cerâmicas testadas, sugerindo que é desnecessário qualquer tratamento adicional para remoção de resíduos após o uso de HF e lavagem com jato de água-ar / Abstract: The effect of different ceramic surface post hydrofluoric acid (HF) etching cleaning protocols in the fracture strength of lithium dissilicate glass ceramic crowns were evaluated. Forty maxillary third human molars received a conventional full preparation. Crowns were obtained from the digital scanning of the preparations and CAD/CAM blocks machining. Crown cement film thickness was evaluated with vinyl polysiloxane. The crowns were allocated in 4 groups according to the ceramic surface treatment (n=10): (HF)- 4.9% HF for 20s + water spray for 30s; (HFN)- HF + neutralizing agent for 5 min (N); (HFU) -: HF+ sonic bath for 5 min (U) and (HFNU): HF + N + U. After a silane coat (60s), crowns were cemented with dual cure cement. A compressive load of 1000Kg was applied in the occlusal surface center at crosshead speed of 1mm/min until the fracture. Data were analyzed by one-way ANOVA and Tukey tests (α = 0.05). Fracture strength mean for each group was (Kgf): HF = 169.92 ± 21.37; HFN = 187.34 ± 34.79; HFU = 166.63 ± 40.22 e HFNU = 175.26 ± 40.22. There was no statistical difference as the surface treatment (p>0.05) suggesting that it is not necessary any additional ceramic surface treatment in order to remove debris after using of HF and air-water spray rinsing / Doutor

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.

This in vitro study evaluated the bond and compression strength of cemented leucite reinforced glass ceramics in bovine tooth enamel, comparing three etching times with hydrofluoric acid 10% of the ceramic surface (20, 60 and 90 seconds) and two adhesive treatments (adhesive system + silane and universal adhesive system). For the bond strength test, 120 ceramic cylinders (2mm diameter x 2mm length; n=20) were etched and cemented (80m thick) in enamel with a dual resin cement, varying the adhesive treatment, obtaining the groups: UEXC20s, UEXC60s, UEXC90s, USBU20s, USBU60s, USBU90s. After 24 hours, the shear bond strength test was performed on a universal test machine (0.5mm/min, 50kgf). For the compression test, 30 ceramic plates (5x5mm with 1mm thick, n=5) were etched, received the same adhesive treatments and were cemented (80m) in enamel, obtaining the following groups: CEXC20s, CEXC60s, CEXC90s, CSBU20s, CSBU60s, CSBU90s. After 24 hours of cementation, the compression test (0.5mm/min, 500kgf) was performed. Statistical analysis was performed using two-way ANOVA and Tukey test (=.05). For the shear bond strength test significant differences were found among the adhesives (p<.05). For the etching times there were no differences (p=.059). However, there was a significant interaction between the adhesives and the etching times (p=.021). At 60 seconds, the Silane + ExciTE F DSC Adhesive presented the highest bond strength values (47.53±16.70Mpa). And at 20 seconds, the Universal adhesive presented the lowest bond strength values (27.72±10.76Mpa). For the compression test there were no significant differences between the adhesives (p=.571) and between the times (p=.154). The group that presented the highest values of compression force was the Universal adhesive at 60 seconds (1757.89±200.47N). The lowest values were also the Universal adhesive, but at 90 seconds (1213.30±546.34N). The study concluded that the silane associated with the ExciTE F DSC adhesive showed the highest bond strength values at the etching time of 60 seconds with 10% hydrofluoric acid, without compromising the compressive strength of the leucite reinforced ceramic. / Este estudo in vitro avaliou a resistência de união e compressão da cerâmica reforçada por cimentada em esmalte de dentes bovinos, comparando-se três tempos de condicionamento com ácido fluorídrico 10% da superfície cerâmica (20, 60 e 90 segundos) e dois tratamentos adesivos (sistema adesivo + silano e sistema adesivo universal). Para o teste de resistência de união (U), 120 cilindros cerâmicos (2mm diâmetro x 2mm comprimento; n=20) foram condicionados e cimentados (80 m de espessura) em esmalte, com cimento resinoso dual, variando-se o tratamento adesivo, obtendo-se os grupos: UEXC20s, UEXC60s, UEXC90s, USBU20s, USBU60s, USBU90s. Após 24h, foi realizado o teste de cisalhamento (0,5mm/min, 50kgf). Para o teste de compressão (C), 30 placas cerâmicas (5x5mm com 1mm de espessura; n=5) foram condicionadas, receberam os mesmos tratamentos adesivos e foram cimentadas (80m) em esmalte, obtendo-se os grupos: CEXC20s, CEXC60s, CEXC90s, CSBU20s, CSBU60s, CSBU90s. Após 24h da cimentação, foi realizado o teste de compressão (0,5mm/min, 500kgf). Foi realizada a análise estatística por meio de ANOVA dois critérios e teste de Tukey (P < 0,05). Para o teste de cisalhamento diferenças significativas foram encontradas entre os adesivos (p<0,05). Para os tempos de condicionamento não houve diferenças significativas (p=0,059). No entanto, houve interação significativa entre os adesivos e os tempos de condicionamento (p=0,021). No tempo de 60 segundos, o silano + adesivo ExciTE F DSC apresentou os maiores valores de resistência de união (47,53±16,70Mpa). E no tempo de 20 segundos, o adesivo Universal apresentou os menores valores de resistência de união (27,72±10,76Mpa). Para o teste de compressão não houve diferenças significativas entre os adesivos (p=0,571) e entre os tempos (p=0,154). O grupo que apresentou maiores valores de força de compressão foi o adesivo Universal no tempo de 60 segundos (1757,89±200,47N). Já os menores valores, foi também o adesivo Universal, mas no tempo de 90 segundos (1213,30±546,34N). Pode-se concluir que, o Silano associado ao adesivo ExciTE F DSC, mostrou os maiores valores de resistência de união no tempo de condicionamento de 60 segundos com ácido fluorídrico a 10%, sem comprometer a resistência a compressão da cerâmica reforçada por leucita.

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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.

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M.Sc. (Physics) / Please refer to full text to view abstract

OBJECTIVES: This in-vitro study aimed to evaluate the effect of hydrofluoric acid etching and airborne particle abrasion on zirconia bond strength, using three different types of cement. To assess the impact of hydrofluoric acid etching on zirconia surface roughness and investigate the effect of hydrofluoric acid etching on zirconia's surface topography, microstructure, and crystal structure. MATERIALS AND METHODS: Crown-abutment simulation systems were constructed, using a custom-made zirconia tapered ring model and tapered titanium pin-abutments. Twelve groups were included in the study and classified according to the surface treatment and type of cement used. Each group had 10 specimens for a total of 120 test specimens. The fully sintered zirconia ring was alumina particle abrasion (APA) treated with a 50-μm alumina and/or etched with 9.5% HF acid, solution for 1 minute. The Ti pin was APA treated with 125-μm alumina. Three different types of cement were used: one RMGIC (GC FujiCem Evolve) and two resin composite types of cement (Panavia SA Universal and Panavia V5). A cementing jig was used to standardize the cementation process of the titanium pins to the zirconia rings. An Instron was used to obtain the retention load values. The failure load between the zirconia ring and the titanium pin was determined using an axial pullout test and the values were statistically analyzed for the effects of etching treatment, APA treatment, and cement type using JMP Pro 16. Zirconia-disk specimens were constructed using a custom-made disk model. Thirteen groups were included in the study and classified according to the hydrofluoric acid etching concentrations, consistencies, and timing used. Each group had 3 specimens. The total specimen size was thirty-nine specimens. Disks were polished and etched using 5% HF, 9.5% HF, and 40% HF acid etching concentrations, gel, and solution consistencies, and for 1 and 15 minutes of etching time. Disks were examined with an SEM, X-Ray diffractometer, and a profilometer for microstructure, crystallography, and surface roughness, respectively. RESULTS: HF acid-etching treatment significantly increased retention load compared to non-etched groups. There was no significant difference in retention load between APA-treated and non-APA-treated groups. Groups cemented with Panavia V5 showed a higher retention load compared to GC FujiCem Evolve and Panavia SA Universal. There was no significant difference in the surface roughness among the etched groups and the control groups. Roughening of the crystal boundaries with irregularities and pits was observed under SEM. As etching time and concentration increased the surface became rougher and more irregular. There were no obvious crystal structure differences between the etched groups and non-etched groups. CONCLUSIONS: Significantly different retention loads were found among tested groups. Hydrofluoric acid etching increases the bond strength of zirconia and titanium, using resin composite cement. Using hydrofluoric acid etching to pre-treat the zirconia surface may be an alternative approach to obtain sufficient bonding strength.

SiO₂ is the most abundant oxide in the earth and its properties, behaviors and interactions are of immense scientific and technological importance. Of particular importance are the interactions of silica with aqueous fluids because these fluids are present in nearly every natural setting. The dissolution of silica and glass by HF plays a very important role in technology and is widely used for the etching of silica and silicate glasses in the glass industry, in the flint industry, in surface micromachining, in etching of glass fibers for near-field optical probes, in the creation of frosted surfaces for decorative applications like frosted glass and cosmetic vials. I performed 57 batch reactor experiments in acidic fluoride solutions to measure the dissolution rate of quartz. Quartz dissolution rate data from other published studies were combined with the rate data from my experiments and these 75 data were analyzed using multiple linear regression to produce an empirical rate law for quartz r_qz = 10^-4.53 (e^-18932/RT) a_HF^1.18 a_H⁺^-0.39 where -5.13 < a_HF < 1.60, -0.28 < pH < 7.18, and 25 < T < 100 °C. Similarly, 97 amorphous silica dissolution rate data from published studies were analyzed using multiple linear regression to develop an empirical rate law for amorphous silica r_as = 10^0.48 (e^-34243/RT) a_HF^1.50 a_H⁺^-0.46 where -5.13 < a_HF < 1.60, -0.28 < pH < 7.18 and 25 < T < 70 °C. An examination of the empirical rate laws suggests that the rate-determining step in the reaction mechanism involves a coordinated attack of HF and H⁺ on the Si-O bond where the H⁺ ion, acting as a Lewis acid, attacks the bridging O atom, while the F end of a HF molecule, acting as a Lewis base, attacks the Si atom. This allows a redistribution of electrons from the Si-O bond to form a O-H and a Si-FH bond, thus "breaking" the Si-O bond. In order to quantify the effect of fluoride on the dissolution of silica, I also performed a series of 81 quartz dissolution and 20 amorphous silica dissolution experiments in batch reactors over a pH range of 0 to 7 to investigate the effect of H⁺ on silica dissolution rates. Between pH 3.5 and 7 silica dissolution rates are independent of pH, but they increase significantly below pH 3.5, so that the dissolution rate of both quartz and amorphous silica at pH 0 is more than an order magnitude faster than the dissolution rate at pH 3.5. I found that the empirical rate law for the dissolution of the"disturbed surface" of quartz in the pH range of 0 to 3.5 is r_qz,pH = 10^-0.23 (e^-59392/RT) a_H⁺^0.28 where 0 < pH < 3.5 and 25 < T < 55°C. The empirical rate law for amorphous silica dissolution in the pH range 0 to 3.5 is r_qz,pH = 10^0.56 (e^-64754/RT) a_H⁺^0.40 where 0 < pH < 3.5 and 25 < T < 55°C. Based on the empirical rate laws I suggest that the rate-determining step in the reaction mechanism involves a coordinated attack of H₃O⁺, acting as a Lewis acid reacts, on a bridging O atom and the O end of a H₂O, acting as a Lewis base, on the Si atom. This results in a redistribution of electrons from the Si-O bridging bond to form two Si-OH surface species. / Ph. D.

Niobium (Nb) has the highest superconducting transition temperature (9.2 K) of the pure metals, which makes it the most used material for the construction of superconducting radio frequency (SRF) accelerators. The performance of the accelerator is critically dependent upon the quality of Nb surface. Electropolishing (EP) in hydrofluoric acid (HF)-containing electrolytes is the currently accepted treatment process. The presence of HF is necessary for the removal of the passive oxide surface film formed in aqueous electrolytes. But HF is hazardous and must be contained without human exposure and eliminated in an environmentally appropriate manner. In the present dissertation project, HF-Free EP of Nb was performed in sulfuric acid-methanol electrolytes. Sulfuric concentrations of 0.1 M, 0.5 M, 1 M, 2 M, and 3 M were used. Cyclic voltammetry and potential hold experiments were performed in cells of both two-electrode and three-electrode setups to evaluate the electrochemical process. The influence of electrolyte concentration, temperature, and EP duration was investigated. At room temperature, both the corrosion rate and the surface quality obtained were comparable to those currently obtained with HF-based processing. With decreasing temperature, the mean current level decreased and the surface quality improved substantially. For a desired average material removal of 100 μM, nanometer scale surface roughness was obtained under multiple conditions. Mechanism of EP was also investigated by electrochemical impedance spectroscopy (EIS). The EIS diagram indicates the presence of a compact film during EP at mass transport controlled limiting current and a film-free surface during EP at ohmic controlled current. Transfer from a film-free surface to an anodic film precipitation with decreasing temperature was also observed. Microsmoothing is only achieved under mass transport control. Nb⁵⁺ ions are determined to be the mass transport limiting species. / Ph. D.