In this paper, I sought to identify and develop a protocol on electrode arrays as a result of rapid aging by applying rapid current over time. We, however, apply a different approach by using phosphate buffer solution (PBS) to mimic the conditions of the body. Here we have established an in vitro protocol for accelerated aging, a process that involves testing in extreme conditions such as oxygen, heat, sunlight, humidity, and vibration aimed at speeding the normal aging process of items; on commercially available shape memory polymer electrode arrays from Qualia over a period of 30 days in PBS. Two electrode arrays were placed in 37°C and 2 were placed in 57°C. Open lead electrochemical impedance spectroscopy (EIS) was conducted on the electrode arrays. Overall, the results showed there were differences in average impedance during this accelerated aging protocol. At 37°C we see that the average impedance values increased as the electrodes were aged at 1kHz from an average of 4.15E6 to 9.14E6 Ohms. At 57°C electrode arrays 4 and 5 showed strong P values well above 0.05, but average impedance increased drastically from 3.27E6 to 9.97E6 and P value of 0.04 from measurement day 24 to day 30. This indicated to us that the electrode could be experiencing some delamination. In addition, this could be because the Qualia nerve cuffs tested were "B" grade, so changes in impedance could be due to the integrity of the device. This would tell us that these electrode arrays would not be capable to withstand long – term recording for up to 240 days. As a result, rejecting the hypothesis that this protocol would show no change in impedance levels for a simulated aging period of 240 days. Although this protocol was not in a perfect setting and the quality of the electrodes were not up to standard, this gave us insight into the electrochemical properties of SMP electrodes which will be useful when we bio-fabricate our own electrodes to study gastrointestinal (GI) disorders.

No description available.

Reverse electrodialysis (RED) is a technique that can capture electrical potential from mixing two water streams of different salt concentration through permselective ion exchange membranes. Effective design of ion exchange membranes through structure optimization is critical to increase the feasibility of salinity gradient power production by RED. In this work, we present the preparation of organic-inorganic nanocomposite cation exchange membranes containing sulfonated polymer, poly (2,6-dimethyl-1,4-phenylene oxide), and sulfonated silica (SiO2-SO3H). The effect of silica filler size at various loading concentrations on membrane structures, electrochemical properties, and the RED power performance is investigated. The membranes containing bigger-sized fillers (70 nm) at 0.5 wt% SiO2-SO3H exhibited a relatively favorable electrochemical characteristic for power performance: an area resistance of 0.85 Ω cm2, which is around 9.3% lower than the resistance of the membranes with smaller filler particles. The power performance of this nanocomposite cation exchange membrane in a RED stack showed 10% higher power output compared with the membranes containing small particle size and achieved the highest gross power density of 1.3 W m-2. Thus, further optimized combination of material properties and membrane structure is a viable option for the development of effective ion exchange membrane design, which could provide desirable electrochemical performance and greater power production by RED.

High energy density batteries have garnered much attention in recent years due to their demand in electric vehicles. Lithium-oxygen (Li-O2) batteries are becoming some of the most promising energy storage and conversion technologies due to their ultra-high energy density. They are still in the infancy stage of development and there are many challenges needing to be overcome before their practical commercial application. Some of these challenges include low round-trip efficiency, lower than theoretical capacity, and poor rechargeability. Most of these issued stem from the poor catalytic performance of the cathode that leads to a high overpotential of the battery. In this doctoral work, Li-O2 cathodes containing nanoparticles of palladium were used to alleviate this problem. Cathodes composed of palladium-coated and palladium-filled carbon nanotubes (CNTs) were prepared and investigated for their battery performance. The full discharge of batteries showed 6-fold increase in the first discharge of the Pdfilled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled CNTs also exhibited improved cyclability with 58 full cycles of 500 mAh·g-1 at current density of 250 mA·g-1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. The effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, XRD, UV/Vis spectroscopy, and visual inspection of the discharge products using scanning electron microscopy confirmed the increased stability of the electrolyte due catalyst shielding. The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on carbon nanotubes (CNT) cathodes with palladium (Pd) catalyst, Pd-coated CNT and Pd-filled CNT, have been evaluated in an ether-based electrolyte solution to develop a lithium oxygen (Li−O2) battery with a high specific energy. The electrochemical properties of CNT cathodes were studied using electrochemical impedance spectroscopy (EIS). The infrared spectroscopy and SEM are employed to analyze the reaction products adsorbed on the electrode surface of the Li-O2 battery developed using Pd-coated and Pd-filled CNTs as cathode and an ether based electrolyte. vii Studies in this dissertation conclude that the use of nanocatalysts composed of palladium improved the overall performance of the Li-O2 batteries, while shielding these catalysts from direct contact with the electrolyte prolonged the life of the battery by stabilizing the electrolyte.

The rising energy consumption worldwide is leading to significant increases in energy production with fossil fuels being the major energy source. The negative environmental impact of fossil fuel use and its finite nature requires the use of alternative sources of energy. Solar energy is a clean alternative energy source; however, its intermittent nature is a major impediment that needs to be reduced or eliminated by the development of cost effective energy storage. Thermal storage in tanks filled typically with molten salt at elevated temperatures is widely used in concentrating solar power plants to generate electricity during periods of low daytime solar radiation or night time. Similarly, electrical storage in batteries, etc. is used in conjunction with photovoltaic solar power plants. Electrochemical supercapacitors can be effectively used for electrical storage, either alone or in a hybrid configuration with batteries, for large scale energy storage as well as in electric vehicles and portable electronics. Unlike batteries’, supercapacitor electrodes can be made of materials that are either less toxic or biodegradable and can provide almost instantaneous power due to their unique charge storage mechanism similar to conventional capacitors found in most electronics. Unfortunately, the same storage mechanism prevents supercapacitors from having high energy density. The purpose of this dissertation is to investigate organic and inorganic electrode materials that can increase the specific capacitance and energy density of supercapacitors. Additionally, certain types of supercapacitor electrode materials store the charges at the electrode/electrolyte interface preventing any deformation of the material and thus increasing its cycle life by two to three orders of magnitude. Transition metal oxides, layered transition metal chalcogenides, and their composites with graphene and conducting polymers have been synthesized, characterized, and their electrochemical performances evaluated for suitability as electrode materials for supercapacitor applications. Morphology and crystalline structure characterization methods used, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), were used throughout this work. Electrochemical characterization involved cyclic voltammetry (CV), constant current charge and discharge (CCCD), and electrochemical impedance spectroscopy (EIS) in two and three electrode configuration using aqueous and organic electrolytes. Ruthenium oxide-graphene (RuO2-G) electrodes were tested in the two-electrode cell configuration and exhibit an areal capacitance of 187.5 mF cm-2 in 2M H2SO4 at a RuO2:G ratio of 10:1. Due to RuO2 high toxicity, scarcity, and high cost, manganese oxide-graphene (MnO-G) was used as an alternative but its low specific capacitance remains a major stumbling block. The electrodes’ mass loading was studied in detail to understand the effects of thickness on the measured specific capacitance. Layered transition metal chalcogenides are structurally similar to graphene but possess different characteristics. Molybdenum sulfide (MoS2) is a two-dimensional material that has lower conductivity than graphene but larger sheet spacing making it easy for other materials to intercalate and form composites such as molybdenum sulfide-polyaniline (MoS2-PANI). MoS2-PANI electrodes, with different thicknesses, were measure in a three-electrode cell configuration resulting in gravimetric capacitance of 203 F g-1 for the thinnest electrode and areal capacitance of 358 mF cm-2 for the thickest electrode; all measurements performed using 1M H2SO4 aqueous electrolyte. Attempts were also made to reduce the supercapacitor self-discharge by depositing on the electrode a blocking thin layer of barium strontium titanate (BST). The results were rather inconclusive because of the large thickness of the deposited BST layer. However, they strongly suggest that a very thin BST layer could improve the overall capacitance because of the very large dielectric constant of the BST material. Additional work is required to determine its effects on self-discharge.

In this research we have investigated electrochemical and impedance characteristics of liquid phase exfoliated graphene electrodes. The exfoliated graphene electrodes were characterized in Electrochemical Double Layer Capacitors (EDLCs) geometry. Liquid phase exfoliation was performed on bulk graphite powder in order to produces few layer graphene flakes in large quantities. The exfoliation processes produced few layer graphene based materials with increased specific surface area and were found to have suitable electrochemical charge storage capacities. Electrochemical evaluation and performance of exfoliated graphene electrodes were tested with Cyclic Voltammetry, constant current charging discharging and Electrochemical Impedance Spectroscopy (EIS) at ambient conditions. We have used several electrolytes in order to evaluate the effect of electrolyte in charge storage capacities. Specific capacitance value of ~ 47F/g and ~ 262F/g was measured for aqueous and ionic electrolytes respectively. These values are at least an order of magnitude higher than those obtained by using EDLC's electrodes fabricated with the bulk graphite powder. In addition these EDLC electrodes give consistently good performance over a wide range of scan rates and voltage windows. These encouraging results illustrate the exciting potential for high performance electrical energy storage devices based on liquid phase exfoliated graphene electrodes.

Orientadores: Roberto Ricardo Panepucci, Roberto José María Covolan / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-30T01:13:32Z (GMT). No. of bitstreams: 1 BenavidesGuevara_JesusArbey_M.pdf: 3401823 bytes, checksum: 461e1559d0928ed82b7c63870d75a3e5 (MD5) Previous issue date: 2015 / Resumo: O desenvolvimento de novas tecnologias aplicadas à pesquisa da atividade elétrica do cérebro é um dos tópicos de vanguarda na atualidade em neurociências. Nas últimas décadas, dispositivos denominados sondas neurais têm sido desenvolvidos, baseados nas técnicas atuais de produção e fabricação de biomedical (ou biological) microelectromechanical systems (Bio-MEMS). Estes dispositivos permitem registrar ou estimular eletricamente diferentes regiões do cérebro in vivo, ou conjuntos de células de cultura, in vitro. A consolidação desta nova tecnologia fornece uma ferramenta de alta precisão para pesquisa em neurociência, além de permitir seu uso clínico em condições patológicas tais como lesão medular, acidente vascular cerebral e distúrbios neurológicos, entre outras. O desenvolvimento de sondas neurais tem-se dado através de estudos que exploram diferentes possibilidades de desenho, fabricação e utilização de novos materiais, orientado pelas possíveis vantagens biológicas, de custo e de fabricação que possam ter. De particular interesse nesta área, é o entendimento dos mecanismos subjacentes ao comportamento eletroquímico durante estimulação e registro de atividade neuronal por microeletrodos do dispositivo, assim como a investigação de materiais que forneçam uma alta densidade de carga durante este processo. Neste projeto, foram fabricadas e caracterizadas sondas neurais baseadas no polímero SU-8, tanto quanto se saiba, as primeiras desenvolvidas no Brasil. Apresenta-se as metodologias empregadas nos processos de fabricação, em que foram testados diferentes protótipos de sondas e sondas funcionais com diferentes geometrias. Metais como Ti/Au, Ti, Cr/Au e TiN foram depositados por meio de sputtering e eletrodeposição. As propriedades eletroquímicas destes materiais condutores foram determinadas por técnicas de voltametria cíclica e espectroscopia de impedância eletroquímica. As sondas de Ti/Au foram as que apresentaram os melhores resultados em nossa pesquisa, tendo em vista a metodologia de fabricação utilizada, que manteve a integridade física dos microeletrodos e do dispositivo em geral, não obstante certas inomogeneidades apresentadas em diferentes etapas da fabricação, que ainda demandam um maior entendimento. Em conclusão, as sondas funcionais de Ti/Au produzidas e caracterizadas neste trabalho se apresentam como um dispositivo potencialmente adequado para registro da atividade neural em modelos animais / Abstract: The development of new technologies applied to the research of the cerebral electrical activity is one of the leading topics in neuroscience today. In recent decades, the so-called neural probe devices have been developed, based on current production and manufacturing techniques of biomedical (or biological) microelectromechanical systems (BioMEMS). These devices allow one to record or electrically stimulate different brain regions in vivo, or systems of cultured cells in vitro. The consolidation of this new technology provides a highly accurate tool for research in neuroscience, and allows their clinical use in pathological conditions such as spinal cord injury, stroke and neurological disorders, among others. The development of neural probes have been given through studies exploring different possibilities of design, manufacture and use of new materials, guided by the possible advantages they might have in terms of biology, manufacturing process and costs. Of particular interest in this area is the understanding of the mechanisms underlying the electrochemical behavior during stimulation and recording of neuronal activity by the microelectrodes of the device, as well as the research of materials providing a high density of charge during this process. In this project, were manufactured and characterized neural probes based on SU-8 polymer, to our knowledge the first developed in Brazil. The methods used in the manufacturing processes are presented for the various tested prototypes of probes and functional probes with different geometries. Metals such as Ti/Au, Ti, Cr/Au and TiN were deposited by sputtering and electrodeposition. The electrochemical properties of these conducting materials were determined by cyclic voltammetry and electrochemical impedance spectroscopy. Probes of Ti/Au showed the best results in our research, taking into consideration the manufacturing methodology, which kept the physical integrity of microelectrodes and the device in general, despite certain inhomogeneities presented in different stages of the manufacturing process, which still demand a greater understanding. In conclusion, the functional Ti/Au probes produced and characterized in this work have shown to be a potentially suitable device for recording neural activity in animal models / Mestrado / Física / Mestre em Física / 2012/151275-2 / CNPQ

Organic electronic devices are sustainable alternatives to the conventional electronics, due to their advantages of low cost, mechanical flexibility and wide range of applications. With the myriad list of organic materials available today, the opportunities to imagine new innovative devices are immense. Organic electronic devices such as OLEDs (organic light emitting diode), OPVs (Organic photovoltaics) and OFETs (organic field effect transistors) are among the leading device categories. Although OLED’s have been a huge commercial success, other categories are not lagging. Radical thinking is necessary to improve on the current performances of these devices. One such thinking is to combine the versatile ZnO (Zinc Oxide) material to organic semiconductors. This can be achieved by exploiting the dual nature of ZnO’s semiconducting and piezoelectric property. Many devices have used ZnO in combination with organic semiconductors for applications ranging from sensors, photovoltaics, OFET’s, memory and many others. The goal of the work is to incorporate the piezoelectric nature of hydrothermally grown ZnO nanowires for Opto-electronic applications. Although the initial research work was done on incorporating the piezo effect of bulk grown ZnO nanowires in improving the efficiency of an OPV, we discovered a unique memory effect in this device by incorporating ZnO nanowires in an inverted organic photovoltaic architecture. The device switched between a rectifying response in dark to resistive behavior under illumination with a finite transition time and was reversible. Since then we decided to explore few of the opto-electronic applications of this technology. The synthesis and characterization of crystalline ZnO nanowires, nanoforest and planar ZnO nanofilm are reported along with the application of these ZnO nanostructures in optoelectronic devices. Noncentro symmetry of crystalline ZnO nanostructures makes it an excellent candidate to be used as piezo functional material and these nanostructures are characterized using electrochemical cell containing ZnO electrode as the working electrode. ZnO nanostructures like nanowires, nanoforest and planar nanofilm are similarly characterized for piezo property using electrochemical technique. Different devices require distinguishing physical and electrical properties of ZnO nanostructures, hence morphology, effect of pre-strain, surface area, surface coverage and thickness of these nanostructures were evaluated for its piezoresponse. It is shown that it was possible to obtain similar piezoresponse among different ZnO nanostructures in addition to taking advantage of the structural benefits among various categories of nanostructures as per requirement. The presented research can be used as the proof-of-the-concept that ZnO nanostructures can be designed and fabricated with a prestrain to adjust the piezo response of the material under external forces. Therefore, the structure with the prestrain can be employed in various electronic and optical devices where the piezo voltage can be used for adjusting the energy band bending at an interface.

O objetivo desse estudo foi avaliar a ação de hipoclorito de sódio e ácido peracético na resistência à corrosão de titânio comercialmente puro, grau 4, (Ticp-4) em salivas artificiais, ácida e neutra, com diferentes períodos de imersão, por meio de ensaio de polarização potenciodinâmica anódica, microscopia eletrônica de varredura e espectrometria dispersiva de raios-X. Corpos-de-prova cilíndricos (5 mm x 5 mm) de Ticp-4 foram envolvidos com fio de cobre e fita isolante, este conjunto foi incluído em tubos de PVC (25 mm x 15 mm) e preenchidos com resina poliéster quimicamente ativada, após a polimerização da resina esses eletrodos de trabalho que foram polidos mecanicamente com lixas, feltros e pastas. Os 54 eletrodos de trabalho foram divididos em nove grupos (n=6) referentes às soluções e períodos de imersão: água destilada (controle), hipoclorito de sódio 1% (10 e 40 minutos), ácido peracético 0,2% (10, 30, 40 e 120 minutos) e ácido peracético 2% (30 e 120 minutos). Após serem imersos nas soluções, foram divididos em 2 subgrupos (n=3), pois os ensaios de polarização anódica foram realizados em triplicatas e utilizados dois eletrólitos, salivas artificiais pH 4,8 e pH 6,8. No ensaio de polarização anódica foi utilizada uma célula eletroquímica constituída por um eletrodo de referência do tipo calomelano saturado (ECS), um contra-eletrodo de platina e o eletrodo de trabalho constituído pelas amostras de Ticp-4, com taxa de varredura de 1 mV/s, partindo-se do potencial de corrosão (Ecorr) até 800 mVECS. Os dados do potencial de corrosão (Ecorr) e corrente de passivação (Ipass) obtidos das curvas de polarização foram analisados estatisticamente pelo teste t Student. Na comparação entre salivas ácida e neutra os valores de Ecorr e Ipass em todas soluções desinfetantes e períodos propostos não apresentaram diferença estatísitica. A comparação dos valores de Ecorr e Ipass entre água destilada (controle) e soluções desinfetantes em saliva ácida também não mostrou diferença, porém em saliva neutra houve diferença entre os valores de Ipass entre água destilada e hipoclorito de sódio 1% por 40 minutos e entre os valores de Ecorr entre água destilada e ácido peracético 2% por 120 minutos. Entre períodos de imersão, em saliva ácida, houve diferença entre os valores de Ipass do hipoclorito de sódio 1% 10 e 40 minutos e entre os valores de Ecorr do ácido peracético 0,2%. A microscopia eletrônica de varredura associada à energia dispersiva por Raio-X não mostrou diferença entre água destilada e as diferentes soluções desinfetantes frente as salivas ácida e neutra. Conclui-se que as curvas de polarização anódica foram similares em todos os ensaios, apesar das diferenças estatísticas salientadas para Ipass e Ecorr, não ocorreu corrosão superficial em quaisquer amostras após desinfecção e polarização em salivas ácida e neutra. A análise por microscopia eletrônica de varredura associada à espectrometria por dissolução de raios-X não revelaram alterações superficiais nas amostras de titânio comercialmente puro. / This study aimed to assess the corrosion resistance in a grade-4 commercially pure titanium (CP Ti-4) under action of sodium hypochlorite or peracetic acid, during different immersion periods, in acid or neutral artificial saliva for anodic potentiodynamic polarization test. Scanning Electron Microscopy (SEM) was used in conjunction with Energy Dispersive X-Ray Spectroscopy (EDS). This study aimed to assess the corrosion resistance in a grade-4 commercially pure titanium (CP Ti-4) under action of sodium hypochlorite or peracetic acid, during different immersion periods, in acid or neutral artificial saliva for anodic potentiodynamic polarization test. Scanning Electron Microscopy (SEM) was used in conjunction with Energy Dispersive X-Ray Spectroscopy (EDS). Cylindrical CP Ti-4 specimens (5 mm x 5 mm) were involved with copper wire and electrical tape, this set was enclosed in PVC pipe (25 mm x 15 mm) and filled with chemically activated polyester resin to obtain the fifty-four working electrodes which were, then, mechanically polished with sandpaper, felt and polishing paste. The 54 working electrodes were divided into nine groups (n = 6) for solutions and immersion periods: distilled water (control), sodium hypochlorite 1% (10 and 40 minutes), peracetic acid 0.2% ( 10, 30, 40 and 120 minutes) and 2% peracetic acid (30 and 120 minutes). After being immersed in the solutions, they were divided into two subgroups (n = 3), because the anodic polarization tests were performed in triplicate and two electrolytes were used: artificial saliva pH 4.8 and pH 6.8. A saturated calomel electrode (SCE) was used as a reference electrochemical electrode for the anodic polarization test with a platinum counter electrode and a working electrode consisting of CP Ti-4 samples with a 1 mV/s scan rate , starting from the corrosion potential (Ecorr) to 800 mVECS. Data for corrosion potential (Ecorr) and for passive current (Ipass) obtatined from the polarization curves were statistically analyzed by Students t-test. When comparing the Ecorr and Ipass values for acid and neutral saliva and disinfectant solutions during all the periods the statistics presented no difference. The comparison of Ecorr and Ipass values between distilled water (control) and disinfecting solutions in acid saliva also showed no difference, but in neutral saliva there was difference for the values of Ipass between distilled water and 1% sodium hypochlorite for 40 minutes and for the values of Ecorr between distilled water and 2% peracetic acid for 120 minutes. When comparing immersion periods, the acid saliva showed different Ipass values for 1% sodium hypochlorite in 10 and 40 minutes and between the Ecorr values for 0.2% peracetic acid. The scanning electron microscopy associated with Energy Dispersive X-Ray Spectroscopy showed no difference between distilled water and the different disinfectant solutions when in acid or neutral saliva. It is concluded that the polarization anodic curves for both acid and neutral saliva were similar in all trials, despite the statistical differences highlighted for Ipass and Ecorr, surface corrosion did not occur in any samples after disinfection and polarization in acidic and neutral saliva. Analysis by Scanning Electron Microscopy associated with Energy Dispersive X-Ray Spectroscopy revealed no surface changes in the commercially pure titanium samples studied.

Ligas metálicas não nobres são amplamente utilizadas em odontologia desde a segunda metade do século XX. Várias ligas metálicas para utilização em próteses sobre o implante dentário têm sido propostas nos últimos anos, visando uma melhor interação metal-cerâmica e maior resistência eletroquímica ao ambiente bucal. O objetivo deste trabalho é avaliar e comparar o comportamento eletroquímico in vitro de ligas à base de cobalto-cromo e níquel-cromo, utilizadas em supra estruturas de implantes dentários. Estas ligas foram estudadas em meios de solução aquosa de NaCl 0,15 mol L-1, saliva artificial e NaCl 0,15 mol L-1 com adição de caseína, fluoreto de sódio ou ácido acético, a partir de técnicas eletroquímicas e não eletroquímicas. Como técnicas eletroquímicas foram empregadas: medidas de potencial de circuito aberto, curvas de polarização anódica, cronoamperometria, voltametria cíclica e espectroscopia de impedância eletroquímica. As técnicas não eletroquímicas utilizadas foram: espectroscopia de absorção atômica com atomização eletrotérmica (EAA-FG), espectroscopia de fotoelétrons excitados por raios-X (XPS), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS). Foram realizados testes de citotoxicidade utilizando a metodologia de incorporação do vermelho neutro. Uma boa correlação foi estabelecida entre os resultados obtidos pelas diferentes técnicas. Em solução de NaCl e saliva artificial as ligas apresentaram a seguinte ordem de resistência à oxidação: CoCrW < NiCrMo < CoCrMo. O filme formado em meio de saliva artificial se mostrou mais protetor do que o formado em meio de NaCl para todas as ligas, indicando que componentes presentes na saliva ao se adsorverem na superfície conferem uma maior proteção à mesma. As análises por XPS confirmaram a existência de um filme rico em Cr(III) com pequena concentração de cobalto e de níquel no filme passivo. As análises por EAA-FG a potenciais mais positivos mostraram que nesta região há oxidação generalizada, com a total dissolução do filme passivo e formação de Cr(VI), Ni(IV) e Co(II). As análises por MEV-EDS, para a superfície das ligas CoCrW e NiCrMo, apresentaram uma superfície quase homogênea e composições semelhantes antes e após 8h de imersão em meio de NaCl e em saliva artificial. A caseína atuou inibindo os processos de oxidação sobre a liga CoCrW e NiCrMo e sua atuação se tornou mais intensa com o aumento do potencial. A liga NiCrMo apresentou maior resistência à corrosão em meio de caseína quando comparada com a liga CoCrW. Os íons fluoreto atuam melhorando as características passivantes do filme, mas este efeito decresce com o aumento do potencial; a presença de ácido acético causa um aumento do efeito passivante do filme, à medida que cresce o potencial. As ligas CoCrW e NiCrMo não apresentaram efeito citotóxico, de acordo com a metodologia utilizada. / No noble metallic alloys are largely employed in odontology since the second part of the XX centrury. Different alloys have been proposed in order to be used in prosthesis on dental implants at last years, with the objective to obtain electrochemical resistance to oral environment. The aim of this work is to evaluate and to compare the electrochemical behavior \"in vitro\" of Co-Cr and Ni-Cr based alloys, used on dental implants structures. These alloys were studied in 0.15 mol L-1 NaCl aqueous in the absence and presence of casein, artificial saliva, sodium fluoride and acetic acid, using electrochemical and non-electrochemical techniques. Open circuit potencial measurements, anodic polarization curves, cronoamperometry, cyclic voltametry and electrochemical impedance spectroscopy were used as electrochemical techniques. Atomic absorption spectroscopy with graphite furnace (EAA-GF), X-ray photoelectron spectroscopy (XPS), scaning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used as non electrochemical techniques. Cytotoxicity tests using the neutral red incorporation methodology were performed. A good correlation between the different techniques it was obtained. The alloys presented the following corrosion resistance order: CoCrW < NiCrMo < CoCrMo. The film formed in artificial saliva has been showed a better protective action than the observed in NaCl medium for the three studied materials as an indicative of the adsorption of substances present on saliva and the consequent inhibitive effect. XPS analysis have confirmed the presence of a Cr2O3 film with low Co(II) and Ni(II) concentrations. EAA-GF analysis at more positive potentials have shown the presence of generalized oxidation with total dissolution of the passive film resulting in Cr(VI), Ni(IV) and Co(II) ions as soluble products. MEV and EDS analysis have shown a quasi homogeneous and similar surface before and after 8h immersion in NaCl and artificial saliva. Casein has acted as inhibitor for oxidation process of CoCrW and NiCrMo in NaCl medium and its effects increases as the potential becomes more positive. The alloy NiCrMo presented a higher corrosion resistance in NaCl solution containing casein when compared to the CoCrW alloy. Ions fluoride has promoted a better performance of the film at Ecorr but its effects decreases at more positive potentials.The presence of acetic acid increases the passivating effect as potencial becomes more positive. Cytotoxicity was not observed for the alloys studied, using the described methodology