O papel do fl��or como agente corrosivo dos fios ortod��nticos

O tratamento ortod��ntico insere-se numa ��rea da medicina dent��ria que se dedica ao estudo das formas de prevenir, interceptar e corrigir as m��s posi����es dos dentes e dos maxilares. Durante este tratamento �� importante que os pacientes consigam manter uma boa higiene oral dos dentes e do aparelho, o que requer precis��o e tempo. Para ajudar a manter a higiene oral os pacientes recorrem frequentemente ao uso de produtos fluoretados, que apesar dos seus benef��cios como agentes na preven����o da c��rie t��m consequ��ncias no tratamento ortod��ntico nomeadamente na corrosão dos fios ortod��nticos. Atrav��s de uma revis��o da literatura pretende-se explorar a rela����o entre o uso de fl��or durante o tratamento ortod��ntico com a corrosão dos fios mais usados nesse mesmo tratamento. Materiais e M��todos: Nesta revis��o de literatura realizou-se pesquisa nas bases de dados electr��nicas ���Medline/PubMed���, e ���B-On���; refer��ncias bibliogr��ficas de artigos; livros de Medicina Dent��ria e pesquisa narrativa. Conclus��o: O uso de agentes fluoretados t��picos pode induzir uma diminui����o das propriedades mec��nicas dos fios ortod��nticos nomeadamente do n��quel-tit��nio, e consequentemente provocar o prolongamento do tratamento ortod��ntico. Os Ortodontistas devem ter em considera����o o tipo de fio usado no tratamento no momento da prescri����o de colut��rios e outros agentes fluoretados.

Durabilidade de colectores solares t��rmicos: novas compet��ncias do LNEG para as empresas [Comunica����o oral]

Palestra no ��mbito do projeto DURASOL

Estudo do Sujamento da Superf��cie de Transfer��ncia de Calor do Evaporador de uma Bomba de Calor aquecido pelo efluente de uma f��brica de pasta para papel

O presente trabalho tem como principal objectivo a avalia����o do sujamento da superf��cie de transfer��ncia de calor do evaporador de uma bomba de calor, quando se utiliza o efluente da f��brica de pasta e papel da Portucel Soporcel em Cacia como fluido de aquecimento. Para a realiza����o deste estudo montou-se uma instala����o, composta por uma bomba de calor, um circuito de ��gua de arrefecimento do condensador da bomba de calor e um circuito de ��gua residual quente para o aquecimento do evaporador da bomba de calor. O ensaio decorreu durante um per��odo de 84 dias, durante o qual foram registadas as temperaturas em v��rios pontos dos circuitos e os caudais de circula����o. A evolu����o temporal da quantidade de calor transferida no evaporador, assim como, a compara����o do coeficiente global de transfer��ncia de calor em condi����es ideias e experimentais, permitiu verificar que a raz��o U/U0 para o evaporador da bomba de calor n��o teve um comportamento decrescente ao longo do per��odo de ensaio, permitindo concluir que, nas condi����es operat��rias da experi��ncia, n��o ocorreu sujamento na superf��cie do evaporador. No estudo de corrosão do cobre quando exposto �� ��gua residual em quest��o, obteve-se, para a velocidade de corrosão, o valor de 1,56 mg/(dm2 .dia), indicando assim que a corrosão do cobre naquele meio �� praticamente inexistente.

Sensoriamento ��ptico quase-distribu��do aplicado ao monitoramento de trocadores de calor de usinas hidrel��tricas

This work aims to develop optical sensors for temperature monitoring in hydroelectric power plant heat exchangers. The proposed sensors are based on the Fiber Bragg Gratings technology. First of all, a prototype with three sensors inscribed in a same fiber was developed. This fiber was then fixed to a conventional Pt100 sensor rod and inserted in a thermowell. The ensemble was then calibrated in a workbench, presenting a maximum combined uncertainty of 2,06 ��C. The sensor was installed in one of the heat exchangers of the Salto Os��rio���s hydroelectric power plant. This power plant is situated in the Igua��u river, at the Paran�� state. Despite the satisfactory results, the sensor was improved to a second version. In this, fifteen optical Bragg sensors were inscribed in a same fiber. The fixation with a conventional sensor was no longer necessary, because the first version results comproved the efficiency and response time in comparison to a conventional sensor. For this reason, it was decided to position the fiber inside a stainless steel rod, due to his low thermal expansion coefficient and high corrosion immunity. The utilization of fifteen fiber Bragg gratings aims to improve the sensor spatial resolution. Therefore, measurements every ten centimeters with respect to the heat exchanger���s height are possible. This provides the generation of a thermal map of the heat exchanger���s surface, which can be used for determination of possible points of obstruction in the hydraulic circuit of the heat exchanger. The heat exchanger���s obstruction in hydroelectric power plants usually occur by bio-fouling, and has direct influence in the generator���s cooling system efficiency. The obtained results have demonstrated the feasibility in application of the optical sensors technology in hydroelectric power plants.

Caracteriza����o elementar de ligas met��licas em implantes dent��rios

An ideal biomaterial for dental implants must have very high biocompatibility, which means that such materials should not provoke any serious adverse tissue response. Also, used metal alloys must have high fatigue resistance due the masticatory force and good corrosion resistance. These properties are rendered by using alpha and beta stabilizers, such as Al, V, Ni, Fe, Cr, Cu, Zn. Commercially pure titanium (TiCP) is used often for dental and orthopedic implants manufacturing. However, sometimes other alloys are employed and consequently it is essential to research the chemical elements present in those alloys that could bring prejudice for the health. Present work investigated TiCP metal alloys used for dental implant manufacturing and evaluated the presence of stabilizing elements within existing limits and standards for such materials. For alloy characterization and identification of stabilizing elements it was used EDXRF technique. This method allows to perform qualitative and quantitative analysis of the materials using the spectra of the characteristic X-rays emitted by the elements present in the metal samples. The experimental setup was based on two X- rays tubes (AMPTEK Mini X model with Ag and Au targets), a X-123SDD detector (AMPTEK) and a 0.5mm Cu collimator, developed due to the sample characteristics. The other experimental setup used as a complementary technique is composed of an X-ray tube with a Mo target, collimator 0.65mm and XFlash (SDD) detector - ARTAX 200 (BRUKER). Other method for elemental characterization by energy dispersive spectroscopy (EDS) applied in present work was based on Scanning Electron Microscopy (SEM) EVO�� (Zeeis). This method also was used to evaluate the surface microstructure of the sample. The percentual of Ti obtained in the elementary characterization was among 93.35 �� 0.17% and 95.34 �� 0.19 %. These values are considered below the reference limit of 98.635% to 99.5% for TiCP, established by Association of metals centric materials engineers and scientists Society (ASM). The presence of elements Al and V in all samples also contributed to underpin the fact that are not TiCP implants. The values for Al vary between 6.3 �� 1.3% and 3.7 �� 2.0% and for V, between 0.26 �� 0.09% and 0.112 �� 0.048%. According to the American Society for Testing and Materials (ASTM), these elements should not be present in TiCP and in accordance with the National Institute of Standards and Technology (NIST), the presence of Al should be <0.01% and V should be of 0.009 �� 0.001%. Obtained results showed that implant materials are not exactly TiCP but, were manufactured using Ti-Al-V alloy, which contained Fe, Ni, Cu and Zn. The quantitative analysis and elementary characterization of experimental results shows that the best accuracy and precision were reached with X-Ray tube with Au target and collimator of 0.5 mm. Use of technique of EDS confirmed the results of EDXRF for Ti-Al-V alloy. Evaluating the surface microstructure by SEM of the implants, it was possible to infer that ten of the thirteen studied samples are contemporaneous, rough surface and three with machined surface.

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.

Segmentos an��tomo-cir��rgicos arteriais do rim de cutia (Dasyprocta prymnolopha)

Foram estudados 20 pares de rins decutias (Dasyprocta prymnolopha Wagler, 1831), com o objetivo de descrever os segmentos an��tomo-cir��rgicos arteriais. As art��rias renais foram injetadas com solu����o de Vinilite corada, e os rins foram submetidos �� corrosão ��cida para a obten����o dos moldes vasculares. Observou-se que as art��rias renais da cutia, sempre ��nicas, dividiram-se em art��ria setorial ventral e art��ria setorial dorsal, caracterizando dois setores renais separados por plano avascular. As art��rias setoriais penetraram no hilo renal (100% dos casos). Estes vasos deram origem aos ramos segmentares respons��veis pela irriga����o de territ��rios independentes em cada setor, os segmentos arteriais renais. No rim direito foram observados 3 (60%), 4 (35%) e 5 segmentos (5%) no setor arterial ventral e 3 (30%), 4 (45%), 5 (20%) e 6 (5%) segmentos no setor dorsal e, �� esquerda, 2(10%), 3 (55%) e 4 (35%) segmentos no setor ventral e 3 (25%), 4 (50%) e 5 (25%) no dorsal. Com base na distribui����o arterial nos rins de cutia, observaram-se setores e segmentos arteriais independentes, sendo poss��vel, desta forma, a realiza����o de setoriectomia e segmentectomia nesta esp��cie.

Estudo da sinteriza����o do aço inox 316L refor��ado com 3% Carbeto de T��ntalo - TaC

The present work shows a contribution to the studies of development and solid sinterization of a metallic matrix composite MMC that has as starter materials 316L stainless steel atomized with water, and two different Tantalum Carbide TaC powders, with averages crystallite sizes of 13.78 nm and 40.66 nm. Aiming the metallic matrix s density and hardness increase was added different nanometric sizes of TaC by dispersion. The 316L stainless steel is an alloy largely used because it s high resistance to corrosion property. Although, its application is limited by the low wear resistance, consequence of its low hardness. Besides this, it shows low sinterability and it cannot be hardened by thermal treatments traditional methods because of the austenitic structure, face centered cubic, stabilized mainly in nickel presence. Steel samples added with TaC 3% wt (each sample with different type of carbide), following a mechanical milling route using conventional mill for 24 hours. Each one of the resulted samples, as well as the pure steel sample, were compacted at 700 MPa, room temperature, without any addictive, uniaxial tension, using a 5 mm diameter cylindrical mold, and quantity calculated to obtain compacted final average height of 5 mm. Subsequently, were sintered in vacuum atmosphere, temperature of 1290��C, heating rate of 20��C/min, using different soaking times of 30 and 60 min and cooled at room temperature. The sintered samples were submitted to density and micro-hardness analysis. The TaC reforced samples showed higher density values and an expressive hardness increase. The complementary analysis in optical microscope, scanning electronic microscope and X ray diffractometer, showed that the TaC, processed form, contributed with the hardness increase, by densification, itself hardness and grains growth control at the metallic matrix, segregating itself to the grain boarders

Avalia����o de heterociclo do tipo mesoi��nico solubilizado em sistema microemulsionado para aplica����o em dutos

The efficiency of inhibition to corrosion of steel AISI 1018 of surfactant coconut oil saponified (SCO) and heterocyclic type mesoionics (1,3,4-triaz��lio-2-tiolato) in systems microemulsionados (SCO-ME and SCO-ME-MI) Of type O/A (rich in water emulsion) region with the work of Winsor IV. The systems microemulsionados (SCO-ME and SCO-ME-MI) were evaluated with a corrosion inhibitor for use in saline 10,000 ppm of chloride enriched with carbon dioxide (CO2). The assessment of corrosion inhibitors were evaluated by the techniques of linear polarization resistance (LPR) and loss of weight (MW) in a cell instrumented given the gravity and electrochemical devices. The systems were shooting speed of less than 60 minutes and efficiency of inhibition [SCO-ME (91.25%) and SCO-ME-MI (98.54%)]

Obten����o de nanopart��culas de hexaferrita de b��rio pelo m��todo pechini

In this study barium hexaferrite was (general formulae BaFe12O19) was synthesized by the Pechini method under different conditions of heat treatment. Precursors like barium carbonate and iron nitrate were used. These magnetic ceramic, with magnetoplumbite type structure, are widely used as permanent magnet because of its excellent magnetic properties, such as: high Curie temperature, good magnetic anisotropy, high coercivity and corrosion resistance. The samples were characterized by thermal analysis (DTA and TG), X- ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) end Vibrating sample Magnetometer (VSM). The results confirm the expected phase, which was reinforced according to our analysis. A single phase powder at relatively high temperatures with particle sizes around 100 nm was obtained. The characteristic magnetic behavior one of the phases has been noted (probably superparamagnetic material), while another phase was identified as a ferrimagnetic material. The ferrimagnetic phase showed vortex configuration with two central and slightly inclined plateaus. In general, increase of heat treatment temperature and time, directly influenced the technological properties of the samples

Sinteriza����o de aço inoxid��vel refor��ado com part��culas nanom��tricas dispersas de carbeto de ni��bio - NbC

Metal powder sintering appears to be promising option to achieve new physical and mechanical properties combining raw material with new processing improvements. It interest over many years and continue to gain wide industrial application. Stainless steel is a widely accepted material because high corrosion resistance. However stainless steels have poor sinterability and poor wear resistance due to their low hardness. Metal matrix composite (MMC) combining soft metallic matrix reinforced with carbides or oxides has attracted considerable attention for researchers to improve density and hardness in the bulk material. This thesis focuses on processing 316L stainless steel by addition of 3% wt niobium carbide to control grain growth and improve densification and hardness. The starting powder were water atomized stainless steel manufactured for H��gan��s (D 50 = 95.0 &#956;m) and NbC produced in the UFRN and supplied by Aesar Alpha Johnson Matthey Company with medium crystallite size 16.39 nm and 80.35 nm respectively. Samples with addition up to 3% of each NbC were mixed and mechanically milled by 3 routes. The route1 (R1) milled in planetary by 2 hours. The routes 2 (R2) and 3 (R3) milled in a conventional mill by 24 and 48 hours. Each milled samples and pure sample were cold compacted uniaxially in a cylindrical steel die (�� 5 .0 mm) at 700 MPa, carried out in a vacuum furnace, heated at 1290��C, heating rate 20��C stand by 30 and 60 minutes. The samples containing NbC present higher densities and hardness than those without reinforcement. The results show that nanosized NbC particles precipitate on grain boundary. Thus, promote densification eliminating pores, control grain growth and increase the hardness values

Desenvolvimento de tubula����o em comp��sito polim��rico revestida externamente com poliuretano de alta densidade

Pipelines for the transport of crude oil from the production wells to the collecting stations are named production lines . These pipes are subjected to chemical and electrochemical corrosion according to the environment and the type of petroleum transported. Some of these lines, depending upon the composition of the fluid produced, may leak within less than one year of operation due to internal corrosion. This work aims at the development of composite pipes with an external protecting layer of high density polyurethane for use in production lines of onshore oil wells, meeting operational requirements. The pipes were manufactured using glass fibers, epoxy resin, polyester resin, quartz sand and high density polyurethane. The pipes were produced by filament winding with the deposition of high density polyurethane on the external surface and threaded ends (API 15 HR/PM-VII). Three types of pipes were manufactured: glass/epoxy, glass/epoxy with an external polyurethane layer and glass/epoxy with an intermediate layer of glass fiber, polyester, sand and with an external polyurethane layer. The three samples were characterized by Scanning Electronic Microscopy (SEM) and for the determination of constituent content. In addition, the following tests were conducted: hydrostatic test, instant rupture, shorttime failure pressure, Gardner impact, transverse stiffness and axial tension. Field tests were conducted in Mossor�� RN (BRAZIL), where 1,677 meters of piping were used. The tests results of the three types of pipes were compared in two events: after two months from manufacturing of the samples and after nine months of field application. The results indicate that the glass/epoxy pipes with an intermediate layer of fiber glass composite, polyester e sand and with an external layer of high density polyurethane showed superior properties as compared to the other two and met the requirements of pressure class, axial tensile strength, transverse stiffness, impact and environmental conditions, for onshore applications as production lines

Estudos de Durabilidade Frente ao Ataque ��cido de Comp��sitos Portland-Pol��mero para Cimenta����o de Po��os de Petr��leo

Portland-polymers composites are promising candidates to be used as cementing material in Northeastern oil wells of Brazil containing heavy oils submitted to steam injection. In this way, it is necessary to evaluate its degradation in the commonly acidizind agents. In addition, to identify how aggressive are the different hostile environments it is an important contribution on the decision of the acidic systems to be used in. It was investigated the performance of the Portland-polymer composites using powdered polyurethane, aqueous polyurethane, rubber tire residues and a biopolymer, those were reinforced with polished carbon steel SAE 1045 to make the electrochemical measurements. HCl 15,0 %, HCl 6,0 % + HF 1,5 % (soft mud acid), HCl 12,0 % + HF 3,0 % (regular mud acid) and HAc 10 % + HF 1,5 % were used as degrading environment and electrolytes. The more aggressive acid solution to the plain Portland hardened cement paste was the regular mud acid, that showed loss of weight around 23.0 %, followed by the soft mud acid, the showed 11.0 %, 15.0 % HCl with 7,0 % and, at last the 10.0 % HAc plus HF 1.5 % with just 1.0 %. The powdered polyurethane-composite and the aqueous polyurethane one showed larger durability, with reduction around 87.0 % on the loss of weight in regular mud acid. The acid attack is superficial and it occurs as an action layer, where the degraded layer is responsible for the decrease on the kinetic of the degrading process. This behavior can be seen mainly on the Portland- aqueous polyurethane composite, because the degraded layer is impregnated with chemically modified polymer. The fact of the acid attack does not have influence on the compressive strength or fratography of the samples, in a general way, confirms that theory. The mechanism of the efficiency of the Portland-polymers composites subjected to acid attack is due to decreased porosity and permeability related with the plain Portland paste, minor quantity of Ca+2, element preferentially leached to the acidic solution, wave effect and to substitute part of the degrading bulk for the polymeric one. The electrolyte HAc 10 % + HF 1,5 % was the least aggressive one to the external corrosion of the casing, showing open circuit potentials around +250 mV compared to -130 mV to the simulated pore solution to the first 24 hours immersion. This behavior has been performed for two months at least. Similar corrosion rates were showed between both of the electrolytes, around 0.01 &#956;A.cm-2. Total impedance values, insipient arcs and big polarization resistance capacitive arcs on the Nyquist plots, indicating passivity process, confirm its efficiency. In this way, Portlandpolymers composites are possible solutions to be succeed applied to oilwell cementing concomitant submitted to steam injection and acidizing operation and the HAc 10,0 % + HF 1,5 % is the less aggressive solution to the external corrosion of the casing

Estudo sobre o efeito dos par��metros de processamento dos p��s e sinteriza����o do aço inox 316l refor��ado com NbC

This masther dissertation presents a contribution to the study of 316L stainless steel sintering aiming to study their behavior in the milling process and the effect of isotherm temperature on the microstructure and mechanical properties. The 316L stainless steel is a widely used alloy for their high corrosion resistance property. However its application is limited by the low wear resistance consequence of its low hardness. In previous work we analyzed the effect of sintering additives as NbC and TaC. This study aims at deepening the understanding of sintering, analyzing the effect of grinding on particle size and microstructure and the effect of heating rate and soaking time on the sintered microstructure and on their microhardness. Were milled 316L powders with NbC at 1, 5 and 24 hours respectively. Particulates were characterized by SEM and . Cylindrical samples height and diameter of 5.0 mm were compacted at 700 MPa. The sintering conditions were: heating rate 5, 10 and 15&#9702;C/min, temperature 1000, 1100, 1200, 1290 and 1300&#9702;C, and soaking times of 30 and 60min. The cooling rate was maintained at 25&#9702;C/min. All samples were sintered in a vacuum furnace. The sintered microstructure were characterized by optical and electron microscopy as well as density and microhardness. It was observed that the milling process has an influence on sintering, as well as temperature. The major effect was caused by firing temperature, followed by the grinding and heating rate. In this case, the highest rates correspond to higher sintering.