Refrat��rios magnesianos de panela de aciaria: redu����o da oxida����o inicial, forma����o da fase espin��lio MgAl2O4 e resist��ncia ao dano por choque t��rmico

A campanha dos refrat��rios magnesianos aplicados como revestimento de trabalho de panelas de aciaria depende da soma de diversos fatores como resist��ncia �� corrosão, resist��ncia �� oxida����o do carbono, estabilidade termomec��nica, entre outros. A concep����o microestrutural do refrat��rio pode influenciar de forma ben��fica ou delet��ria no desempenho do refrat��rio in situ. Nesta tese de doutorado os refrat��rios magnesianos comerciais de panela de aciaria foram estudados sob tr��s diferentes aspectos: redu����o da oxida����o prematura do carbono, forma����o da fase espin��lio de alumina e magn��sio e resist��ncia ao choque t��rmico e ao dano por choque t��rmico. Para reduzir a oxida����o precoce do carbono foi desenvolvido um coating cer��mico que atua como uma eficiente barreira f��sica, reduzindo o contato do oxig��nio da atmosfera de aquecimento com o carbono presente no refrat��rio. Como resultado reduz-se a oxida����o prematura do carbono e eleva-se a vida ��til do revestimento. A forma����o da fase espin��lio de magn��sia e alumina tamb��m influencia o desempenho termomec��nico destes refrat��rios, principalmente devido ao incremento volum��trico decorrente de sua forma����o. Nesta tese foram estudados os mecanismos de forma����o desta fase in situ, demonstrando experimentalmente o caminho preferencial que leva �� forma����o desta fase mineral��gica. O comportamento termomec��nico dos refrat��rios magnesianos foi determinado em fun����o da resist��ncia ao choque t��rmico (par��metros R, R\'\'\') e quanto �� resist��ncia ao dano por choque t��rmico (par��metro R\'\'\'\' e Rst). Estes par��metros foram correlacionados com as respectivas caracter��sticas microestruturais destes refrat��rios. Os resultados apresentados por esta tese de doutorado comp��e uma importante ferramenta t��cnica para as ind��strias produtoras de aço e de refrat��rios por fornecer subs��dio t��cnico e cient��fico para fundamentar altera����es em refrat��rios j�� existentes e colaborar com o desenvolvimento de novos refrat��rios de engenharia com elevado desempenho e maior vida ��til.

Contribui����o ao estudo da jazida diamant��fera de Romaria, MG

1. Este trabalho consta de duas partes: a primeira trata do hist��rico, import��ncia, tipos de jazimentos e g��nese dos diamantes. Na segunda �� feito um estudo geol��gico, litol��gico, mineral��gico e econ��mico da jazida de diamantes de Romaria (antiga ��gua Suja), localizada na Fazenda Marrecos, munic��pio de Romaria, Estado de Minas Gerais. 2. Conhecida desde 1888, a jazida �� mencionada em trabalhos de G. Campos, Hussak, Draper e outros autores. Minerada durante algumas d��cadas por grandes companhias, passou em seguida por uma fase de abandono, voltando atualmente a ser alvo de aten����es de nova companhia. A jazida �� classificada como "secund��ria elevada". Os diamantes s��o encontrados em sedimentos fluviais de idade provavelmente neo-cret��cica ou talvez enozoica. Tais sedimentos assentam-se discordantemente sobre o arenito Botucatu e em alguns lugares, diretamente sobre o embasamento cristalino. A seq����ncia diamant��fera �� constitu��da de tr��s camadas, cujos nomes locais s��o: conglomerado Tau��, que �� um conglomerado polim��ctico basal, mal selecionado; Secundina, arenito grosseiro com intercala����es conglomer��ticas e argilosas; Gorgulho, nome dado ao solo rico em canga que recobre toda a ��rea. O Tau��, a camada mais rica em diamantes, foi estudado com maiores pormenores. Distinguem-se dois tipos desse conglomerado: o Tau�� tipo e o Tau�� at��pico. 3. O diamante da jazida de Romaria apresenta h��bito cristalino predominantemente rombododeca��drico. Alguns exemplares, quando submetidos �� luz ultra-violeta, mostraram fluoresc��ncia azul-viol��cea. Alguns mostraram anisotropia an��mala. Os cristais octa��dricos normalmente apresentam tr��gonos de corrosão nas faces de octaedro, enquanto os c��bicos, extremamente corro��dos e sempre transl��cidos, mostram nas faces de cubo pir��mides reentrantes de base quadrada. Alguns apresentam inclus��es de grafita; em um cristal examinado, constatou-se a presen��a de inclus��es de olivina e cromita. Os diamantes da jazida n��o apresentam arestas arredondadas e sinais de impacto. 4. A reserva m��nima provada da jazida �� de 2.000.000 m3 de Tau��. A capa a ser removida (Secundina e Gorgulho) tem espessura m��dia de 11 m. O teor m��dio obtido foi de 16 pontos/m3. 5. O diamante do Tau�� parece ter sofrido pouco ou nenhum transporte, sugerindo fonte prim��ria nas proximidades. A presen��a de inclus��es de olivina e cromita indica uma associa����o prim��ria de diamante com rochas ultrab��sicas. 6. Recomenda����es sobre a lavra do diamante s��o feitas no final deste trabalho.

Solu����es de reabilita����o e refor��o com GFRP: aplica����es na Regi��o Aut��noma da Madeira

Este trabalho consiste na apresenta����o de t��cnicas de reabilita����o e refor��o e a sua adapta����o ao GFRP (Glass Fiber Reinforced Polymer). O foco incidiu sobre as estruturas degradadas pela corrosão das armaduras, e apresenta-se uma vasta gama de t��cnicas de interven����o. Encamisamento, prote����o eletroqu��mica, adi����o de armaduras s��o as t��cnicas mais desenvolvidas ao longo do trabalho. S��o ainda abordados os tipos de produtos de recobrimento, as t��cnicas de aplica����o do recobrimento, bem como as ferramentas com maior utilidade para a reabilita����o e refor��o. De seguida faz-se um breve resumo das caracter��sticas e potencialidades do material GFRP, aborda-se alguns dos principais fornecedores, fazendo uma descri����o dos produtos comercializados por estes, e ainda uma an��lise de pre��os por metro linear de var��o GFRP. Por fim apresenta-se um levantamento fotogr��fico realizado na Regi��o Aut��noma da Madeira, de estruturas que apresentem sinais claros de corrosão das armaduras, com o objetivo de perceber a aplicabilidade dos var��es de GFRP na reabilita����o das mesmas. Apresenta-se ainda, uma poss��vel t��cnica de reabilita����o/refor��o para todos os casos apresentados, utilizando os var��es de GFRP. O levantamento fotogr��fico tem ainda o objetivo de perceber as principais causas de deteriora����o de estruturas na regi��o, e de criar uma base de estruturas a necessitar de interven����o urgente.

A M��scara no Paralelo On��rico d������Os Alicerces da Realidade��� de Jos�� R��gio

Visando a literatura de Jos�� R��gio, Eug��nio Lisboa refere que todo o seu texto �� ���habitado por toda uma teoria de her��is devorados pela necessidade de verem e fazerem ver. Mas s��o frequentemente personagens complicados e minados por uma lucidez corrosiva��� (Lisboa, 2001: 74-75). No conto ���Os Alicerces da Realidade��� da autoria do c��lebre escritor do s��c. XX, ��-nos apresentado um protagonista desenhado com linhas intricadamente complexas e com traços de loucura, resultantes da corrosão do ser profundamente l��cido. De facto, na diegese de ���Os Alicerces da Realidade���, Silvestre, a personagem principal, representa um funcion��rio p��blico aposentado aparentemente vulgar que, no decurso de uma vida pacata, gradualmente sofre epis��dios de alucina����o. Esta personagem masculina acaba por atribuir a tais del��rios uma l��gica poss��vel ��� para ele a ��nica ��� real e exequ��vel: a de que estaria a vivenciar um sonho. Adota, ent��o, indiferente �� sociedade circundante ��� caracterizada como falsa, mordaz, pseudo-intelectual, repressora inquestion��vel ��� atitudes rebeldes, de aliena����o e de destempero que acabam por prognosticar nada mais do que a factualidade de um dist��rbio de car��cter psiqui��trico. Com efeito, esta personagem repudia a sanidade mental, assumindo clara e obsessivamente a dem��ncia. Na verdade, resignado passivamente ao despertar do sonho, acomoda-se na aliena����o, como fuga �� realidade enfadonha e dissimulada. Assim, em diversos epis��dios, entrando num jogo perturbador, por��m viciante, o protagonista experimenta diferentes ���m��scaras���: v��rios provocadores e rebeldes ��� por isso, t��o convidativos ��� ���on��ricos��� Eus, que se op��em a um Eu real mon��tono e passivo. Na verdade, este ��ltimo representa nada mais do que o Eu social, subjugado aos preceitos de uma sociedade impass��vel, zeladora daqueles que considera ser os bons h��bitos e costumes e, por isso, norteadora de determinados padr��es comportamentais coletivos e punidora daqueles que os n��o cumprem. Com esta comunica����o, visamos analisar, n��o s�� o vasto e complexo plano on��rico que constr��i os alicerces da realidade deste her��i regiano, como ��� e principalmente ��� o tema da m��scara e do disfarce, na medida em que Silvestre, furtando-se da realidade que o rodeia, �� dominado pela frustra����o mental que consequentemente o leva at�� �� loucura e �� auto-constru����o de v��rios Eus. De facto, visamos, assim, enquadrar a tem��tica da ���m��scara regiana��� que n��tida e inequivocamente se evidencia neste conto, pois que o seu protagonista visa a ado����o de uma m��scara de ���sobreviv��ncia��� ��� um outro Eu ���, para assim contrariar uma sociedade camuflada e estranguladora da sinceridade, da independ��ncia e da individualidade genu��na, obreira do singular, ��nico e genu��no Eu.

Incrusta����o em po��o produtor de petr��leo e g��s natural: um estudo de caso

Water and gas is a common by - product of the oil production process. Production may be compromised by the precipitation of inorganic salts in both the reservoir and producing well, through scale formation. This precipitation is likely the cause of the formation damage. High temperatures and h igh pressures (HTHP) may favor the precipitation of insoluble salts. The most common types of scale in oil fields are calcium carbonate and calcium sulphate, strontium and barium sulphate. New types of scale formation have attracted special attention such as zinc sulphide and lead. This precipitation may occur in the pores of reservoir rocks, in the production string and in equipment, causing obstructions and consequent production losses. In this study, the influence of well depth on incrustation compositio n was investigated to design removal treatments and assess the behavior of these deposits along the string, through the analysis of pressure and temperature. Scale residues were recovered from the inside of the production string of an oil and gas well duri ng the string removal operation. A total of 10 samples from different depths (15.4 m to 4061.5 m) were obtained. Initially a dissolution test was conducted in weak acid, similar to that used in removal operations with this type of scale formation. Majority composition was defined and confirmed by dissolution tests using X - Ray Fluorescence Spectroscopy (XRF), X - Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) techniques. Residues with distinct characteristics were observed in different proportion s, showing a tendency toward increased and/or decreased mass with depth. In the samples closest to the surface, typical sandstone residues were found, with calcium (45% Ca) as the metal of highest concentration. The obtained results indicate correlations o f the scale types studied with the depth and, consequently, with the thermodynamic conditions of pressure and temperature.

Otimiza����o da s��ntese do AlSBA-15 para produ����o de biodiesel por transesteri-fica����o do ��leo de coco

Stimulus encouraging the production and consumption of biodiesel favors the policy of pre-serving the environment, contributing to the reduction of greenhouse gas reducing climate change. The current trend of research in this field focuses on improving these processes with the use of heterogeneous catalysts, seeing has significant advantages such as: low contamination of products, ease of separation of the catalyst from the reaction medium, possibili-ty of reuse of the catalyst, decreased corrosion problems. The objective of this research was to optimize the synthesis of AlSBA-15 for the production of biodiesel through transesterification process via ethyl route. For the optimization of hydrothermal synthesis of type AlSBA-15 catalyst has assembled a 23 factorial experimental matrix with eleven trials. The stoichiometric amounts of starting materials were varied according to different ratios Si / Al which is a factor in the experimental design, in addition to the time and temperature of aging of the synthesis gel. The material showed the best results of characterization (SBET = 591.7 (m2 / g), Vp = 0.83 (cm3 / g), Dp = 5.59 (nm), w = 6.48 (nm) was synthesized at 100 �� C for 24 hours, with a ratio Si / Al = 10.This material was applied as a heterogeneous catalyst in the reaction of ethyl transesterification as raw coconut oil in natura. Coconut oil presented suitable for obtaining biodiesel via ethyl route.The visual aspects and physical-chemical characteristics of the reaction products show that AlSBA-15 catalyst favored the reaction. According to physical-chemical analysis the order of oxidative stability of the product of the transesterification reaction was: catalytic reaction at 1500 �� C> non-catalytic reaction at 100 �� C> 100 �� C catalytic> catalytic reaction at 200 �� C Reaction. The results of oxidative stability and kinematic viscosity shows that the biodiesel produced in the catalytic sandblasting held at 150 �� C which was maintained within the ABNT NBR 7148, ABNT NBR 10441 and EN 14112.

Redu����o in situ de NIO durante a sinteriza����o de misturas NI/NIO produzidas por metalurgia do p��

The nickel alloys are widely used in the production of various materials, especially those that require mechanical strength characteristics associated with resistance to corrosion, for example, the stainless steel. Another use is the production of nickel alloy sintered from powder of metallic nickel. A promising alternative for the production of sintered components of nickel with an important reduction in costs of starting material is the use of mixtures of powders of Ni-NiO. This work aimed to study in situ reduction of NiO during sintering mixtures of Ni / NiO produced by powder metallurgy. The nickel mixtures have been processed by the technique of powder metallurgy and were pre-sintered in an oven under plasma reducing atmosphere of hydrogen. Mixtures Ni +15%NiO, Ni +25%NiO and Ni +35%NiO were studied and compared with samples consisting only of metallic Ni. Dilatometric tests were performed to study the sintering conditions of the mixtures. The consolidated material was analyzed for their microstructure and microhardness. Dilatometry graphs showed that the addition of nickel oxide in all compositions the active sintering the mixtures studied. In tests of microhardness indentations were made at different points of the sample surface. All compositions showed microhardness values close to the consolidated material from metallic nickel. However, sample containing Ni+35% NiO, showed a large dispersion of the values of microhardness tests performed at different points of the sample surface. Microstructural analysis of the material showed a higher concentration of voids and the presence of oxides in the waste composition of the mixtures Ni 35% NiO. The samples containing Ni+15%NiO showed microstructural characteristics and mechanical properties similar to metallic nickel consolidated under the same conditions of the compositions studied in this work and therefore had great potential for production of sintered nickel alloys

Aplica����o da destila����o simulada por cromatografia gasosa e da termogravimetria para a avalia����o da influ��ncia da redu����o do teor de enxofre sobre as propriedades f��sico-qu��micas do ��leo diesel

One of the main problems related to the use of diesel as fuel is the presence of sulfur (S) which causes environmental pollution and corrosion of engines. In order to minimize the consequences of the release of this pollutant, Brazilian law established maximum sulfur content that diesel fuel may have. To meet these requirements, diesel with a maximum sulfur concentration equal to 10 mg/kg (S10) has been widely marketed in the country. However, the reduction of sulfur can lead to changes in the physicochemical properties of the fuel, which are essential for the performance of road vehicles. This work aims to identify the main changes in the physicochemical properties of diesel fuel and how they are related to reduction of sulfur content. Samples of diesel types S10, S500 and S1800 were tested according with the methods of the American Society for Testing and Materials (ASTM). The fuels were also characterized by thermogravimetric analysis (TG) and subjected to physical distillation (ASTM D86) and simulated distillation gas chromatography (ASTM D2887). The results showed that the reduction of sulfur turned the fuel lighter and fluid, allowing a greater applicability to low temperature environments and safer for transportation and storage. Through the simulated distillation data was observed that decreasing sulfur content resulted in higher initial boiling point temperatures and the decreasing of the boiling temperature of the medium and heavy fractions. Thermogravimetric analysis showed a loss event mass attributed to volatilization or distillation of light and medium hydrocarbons. Based on these data, the kinetic behavior of the samples was investigated and it was observed that the activation energies (Ea) did not show significant changes throughout conversion. Considering the average of these energies, the S1800 had the highest Ea during the conversion and the S10 the lowest values

Desenvolvimento de novos biolubrificantes hidr��ulicos derivados dos ��leos de maracuj�� e de moringa in natura e epoxidados

With the increasing environmental awareness, maximizing biodegradability and minimizing ecotoxicity is the main driving force for new technological developments. Thus, can be developed new biodegradable lubricants for use in environmentally sensitive areas. The aim of this study was to obtain new bio-lubricants from passion fruit (Passiflora edulis Sims f. flavicarpa Degener) and moringa (Moringa oleifera Lamarck) epoxidized oils and develop a new additive package using experimental design for their use as a hydraulic fluid. In the first stage of this work was performed the optimization of the epoxidation process of the oils using fractional experimental design 24-1 , varying the temperature, reaction time, ratio of formic acid and hydrogen peroxide. In the second step was investigated the selectivity, thermodynamics and kinetics of the reaction for obtaining the two epoxides at 30, 50 and 70 ��C. The result of the experimental design confirmed that the epoxidation of passion fruit oil requires 2 hours of reaction, 50 ��C and a ratio H2O2/C=C/HCOOH (1:1:1). For moringa oil were required 2 hours reaction, 50 ��C and a ratio of H2O2/C=C/HCOOH (1:1:1.5). The results of the final conversions were equal to 83.09% (�� 0.3) for passion fruit oil epoxide and 91.02 (��0,4) for moringa oil epoxide. Following was made the 23 factorial design to evaluate which are the best concentrations of corrosion inhibitor and anti-wear (IC), antioxidant (BHA) and extreme pressure (EP) additives. The bio-lubricants obtained in this step were characterized according to DIN 51524 (Part 2 HLP) and DIN 51517 (Part 3 CLP) standards. The epoxidation process of the oils was able to improve the oxidative stability and reduce the total acid number, when compared to the in natura oils. Moreover, the epoxidized oils best solubilized additives, resulting in increased performance as a lubricant. In terms of physicochemical performance, the best lubricant fluid was the epoxidized moringa oil with additives (EMO-ADI), followed by the epoxidized passion fruit oil with additives (EPF-ADI) and, finally, the passion fruit in natura oil without additives (PFO). Lastly, was made the investigation of the tribological behavior under conditions of boundary lubrication for these lubricants. The tribological performance of the developed lubricants was analyzed on a HFRR equipment (High Frequency Reciprocating Rig) and the coefficient of friction, which occurs during the contact and the formation of the lubricating film, was measured. The wear was evaluated through optical microscopy and scanning electron microscopy (SEM). The results showed that the addition of extreme pressure (EP) and anti-wear and corrosion inhibitor (CI) additives significantly improve the tribological properties of the fluids. In all assays, was formed a lubricating film that is responsible for reducing the coefficient of metal-to-metal wear. It was observed that the addition of EP and IC additives in the in natura vegetable oils of passion fruit and moringa did not favor a significant reduction in wear. The bio-lubricants developed from passion fruit and moringa oils modified via epoxidation presented satisfactory tribological properties and shown to be potential lubricants for replacement of commercial mineral-based fluids.

Desenvolvimento e avalia����o tribol��gica de emuls��o O/A a partir de ��leo vegetal epoxidado para aplica����o em flu��dos de corte

The cutting fluids are lubricants used in machining processes, because they present many benefits for different processes. They have many functions, such as lubrication, cooling, improvement in surface finishing, besides they decreases the tool wear and protect it against corrosion. Therefore due to new environment laws and demand to green products, new cutting fluids must be development. These shall be biodegradable, non-toxic, safety for environment and operator healthy. Thus, vegetable oils are a good option to solve this problem, replacing the mineral oils. In this context, this work aimed to develop an emulsion cutting fluid from epoxidized vegetable oil, promoting better lubrication and cooling in machining processes, besides being environment friendly. The methodology was divided in five steps: first one was the biolubricant synthesis by epoxidation reaction. Following this, the biolubricant was characterized in terms of density, acidity, iodo index, oxirane index, viscosity, thermal stability and chemical composition. The third step was to develop an emulsion O/A with different oil concentration (10, 20 and 25%) and surfactant concentration (1, 2.5 and 5%). Also, emulsion stability was studied. The emulsion tribological performance were carried out in HFRR (High Frequency Reciprocating Rig), it consists in ball-disc contact. Results showed that the vegetable based lubricant may be synthesized by epoxidationreaction, the spectra showed that there was 100% conversion of the epoxy rings unsaturations. In regard the tribological assessment is observed that the percentage of oil present in the emulsion directly influenced the film formation and coefficient of friction for higher concentrations the film formation process is slow and unstable, and the coefficient of friction. The high concentrations of surfactants have not improved the emulsions tribological performance. The best performance in friction reduction was observed to emulsion with 10% of oil and 5% of surfactant, its average wear scar was 202 ��m.

An��lise experimental de danos em pist��es de motor �� gasolina operando com adi����o de g��s hidr��xi

The addition of hydrogen gas as an alternative fuel source has been widely used, as well reported in scientific literature. Today, several experiments are underway for the use of hydrogen generators (electrolysers) demand for motor vehicles. In all these products their ads manufacturers claim that this provides a reduction of fuel consumption, reduces the emission levels of toxic gas by the discharge and improves engine life. This research analyzes the physical structure of engine components using electrolysis on demand. To this end, a stationary system was fitted with a power generator of electricity, drum roller and adapted two electrolyzers: a dry cell and wet cell other. In steps observation were consumption analyzes in four work load ranges and observing the piston engine, which has been cut and analyzed by Optical Microscopy (OM), Scanning Electron Microscopy and Dispersive Energy (SEM-EDS), X ��� Ray Diffraction (XRD) and Confocal Microscopy, the stationary system in each step. The results showed a considerable reduction in fuel consumption and a high corrosion in the original factory piston constituted of aluminum-silicon alloy. As corrosion barrier was made a plasma nitriding in the piston head, which proved resistant to attack by hydrogen, although it has presented evidence also, of having been attacked. It is concluded that the automotive electrolysers can be a good choice in terms of consumption and reducing toxic gas emissions, but the material of the combustion chambers of vehicles must be prepared for this purpose.

Utiliza����o do tit��neo na confec����o de estruturas met��licas em pr��tese parcial remov��vel

Due to properties such as excellent biocompatibility, high resistance to corrosion and low specific weight, titanium has been considered a material of great interest for Dentistry. It has been widely used in implants and orthognathic surgeries. Recently, titanium has been seen as a feasible alternative for the fabrication of removable partial denture frameworks, either in pure titanium (99.75%) or in titanium alloy forms (Ti-6Al-4V; Ti-6A1-7Nb). Based on a review of the literature, this work studied the use of titanium for the fabrication of removable partial denture frameworks, focusing on its advantages and disadvantages as well as its characteristics. It was concluded that the use of titanium is a convenient option for partially edentulous arches rehabilitation with quite satisfactory and promising clinical results. However, the need for highly-equipped laboratories increases the cost, preventing its large scale use.

Utiliza����o do tit��neo na confec����o de estruturas met��licas em pr��tese parcial remov��vel

Due to properties such as excellent biocompatibility, high resistance to corrosion and low specific weight, titanium has been considered a material of great interest for Dentistry. It has been widely used in implants and orthognathic surgeries. Recently, titanium has been seen as a feasible alternative for the fabrication of removable partial denture frameworks, either in pure titanium (99.75%) or in titanium alloy forms (Ti-6Al-4V; Ti-6A1-7Nb). Based on a review of the literature, this work studied the use of titanium for the fabrication of removable partial denture frameworks, focusing on its advantages and disadvantages as well as its characteristics. It was concluded that the use of titanium is a convenient option for partially edentulous arches rehabilitation with quite satisfactory and promising clinical results. However, the need for highly-equipped laboratories increases the cost, preventing its large scale use.

Refor��o de pilares por confinamento com mantas de fibras de carbono: avalia����o de modelos de comportamento

A presente disserta����o incide sobre o estudo dos efeitos do confinamento com materiais comp��sitos de pol��meros refor��ados com fibras de carbono (CFRP) em pilares de estruturas de bet��o armado. A motiva����o para este estudo surge da necessidade de aprofundar conhecimentos acerca do comportamento dos pilares de bet��o refor��ados por confinamento com CFRP, uma vez que a sua aplica����o apresenta uma crescente import��ncia, por exemplo, para aumento da resist��ncia e da ductilidade de estruturas de bet��o armado. Fez-se, inicialmente, uma breve revis��o das t��cnicas de refor��o convencionais utilizadas em pilares de bet��o armado, com ��nfase no refor��o exterior com pol��meros refor��ados com fibras. A elevada resist��ncia �� tra����o, �� corrosão e �� fadiga, o baixo peso vol��mico, a versatilidade e a diversidade dos sistemas comercializados com CFRP tornam este material muito competitivo para este tipo de aplica����o. Na sequ��ncia desse estudo, realizou-se uma revis��o bibliogr��fica acerca dos modelos de comportamento que permitem prever o desempenho de pilares de bet��o confinados com CFRP, sujeitos a esfor��os de compress��o. Como forma de an��lise desses modelos, desenvolveu-se uma ferramenta num��rica em ambiente Mathworks - Matlab R2015a, que permitiu a obten����o e posterior compara����o dos diagramas de tens��o-extens��o descritos pelos modelos desenvolvidos por Manfredi e Realfonzo (2001), Ferreira (2007) e Wei e Wu (2011). Por fim, comparam-se os resultados experimentais de Paula (2003) e de Rocca (2007) com os dos modelos constitutivos referidos anteriormente, analisando-se tamb��m a influ��ncia de v��rios fatores na efic��cia do confinamento, tais como o boleamento, o n��mero de camadas de CFRP e a geometria da sec����o transversal. Foram ainda comparados e discutidos resultados relativos ao confinamento parcial de pilares. Os resultados obtidos indicam que os modelos anal��ticos representam relativamente bem o andamento das curvas do bet��o confinado para sec����es circulares, quadradas e retangulares, verificando-se as principais discrep��ncias nestas duas ��ltimas tipologias de sec����o transversal, dada a dificuldade associada �� quantifica����o de par��metros associados ao seu comportamento (por exemplo, boleamento de arestas). No entanto, verificou-se igualmente que com um adequado boleamento de arestas (e consequente aumento da rela����o entre o raio de canto e a largura da sec����o de bet��o), bem como com um aumento do n��mero de camadas de material comp��sito, �� poss��vel aumentar a tens��o resistente e a extens��o axial na rotura do bet��o �� compress��o.

Remo����o de instrumentos fraturados em Endodontia

A ��rea da Endodontia est�� em constante progresso. Os materiais utilizados nos instrumentos Endod��nticos, primordialmente, eram constru��dos com base em cordas de piano. Seguiu-se uma fase em que estes eram de aço de carbono, mas sofriam corrosão significativa devido ao cloro presente no hipoclorito de s��dio, bem como aos processos de esteriliza����o a vapor. Foi necess��rio evoluir novamente e foram introduzidos os instrumentos de aço inoxid��vel. Estes apresentavam alta resist��ncia e dureza, mas algumas desvantagens devido �� falta de flexibilidade. Atualmente, os instrumentos de NiTi proporcionam uma melhor flexibilidade e efeito de mem��ria de forma. A fratura de instrumentos em Endodontia pode ocorrer por dois grandes fatores: a tor����o e a flex��o por fadiga c��clica, podendo tamb��m ser a conjuga����o de ambos. Fatores anat��micos, como a curvatura e a largura do canal ou outros fatores como ciclos de esteriliza����o, n��mero de usos, etc., podem influenciar uma fratura mais precoce dos instrumentos. A incid��ncia da fratura de instrumentos, embora seja pouco frequente, pode ser reduzida a um m��nimo absoluto se os cl��nicos usarem as caracter��sticas de torque e de stress adequadas. Um bom conhecimento dos procedimentos cl��nicos, da anatomia, dos materiais e a utiliza����o de instrumentos como o microsc��pio podem ajudar a prevenir ou a resolver a fratura dos instrumentos. No entanto, a melhor forma de prevenir a fratura �� a sua preven����o. A desinfe����o �� o procedimento mais importante para o sucesso de um tratamento Endod��ntico, portanto para que isto seja poss��vel, �� necess��ria uma boa conforma����o canalar. A presen��a de um instrumento no interior do canal pode comprometer a desinfec����o, especialmente caso tenha ocorrido numa fase precoce da prepara����o canalar. Aquando da fratura de um instrumento, deve-se refletir sobre os procedimentos a seguir, podendo-se optar por v��rias abordagens, nomeadamente pela manuten����o do instrumento no canal e obtura����o incorporando o fragmento, pela remo����o do segmento atrav��s de diversas t��cnicas (ultrassons ou t��cnicas de microtubos, etc.), e ainda pela realiza����o do bypass ou pela cirurgia Endod��ntica. Em ��ltima inst��ncia pode ser realizada a extra����o do elemento dent��rio.