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Investigation of AISI 1040 steel corrosion H(2)S solution containing chloride ions by digital image processing coupled with in electrochemical techniques

ZIMER, Alexsandro Mendes; RIOS, Emerson Costa; MENDES, Paulo de Carvalho Dias; GONCALVES, Wesley Nunes; BRUNO, Odemir Martinez; PEREIRA, Ernesto Chaves; MASCARO, Lucia Helena
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
157.70923%
This paper presents a study of AISI 1040 steel corrosion in aqueous electrolyte of acetic acid buffer containing 3.1 and 31 x 10(-3) mol dm(-3) of Na(2)S in both the presence and absence of 3.5 wt.% NaCl. This investigation of steel corrosion was carried out using potential polarization, and open-circuit and in situ optical microscopy. The morphological analysis and classification of types of surface corrosion damage by digital image processing reveals grain boundary corrosion and shows a non-uniform sulfide film growth, which occurs preferentially over pearlitic grains through successive formation and dissolution of the film. (C) 2011 Elsevier Ltd. All rights reserved.; CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo da repassivação da armadura em concretos carbonatados através da técnica de realcalinização química.; Carbonated concrete steel repassivation study through chemical realkalisation technique.

Araújo, Fernanda Wanderley Corrêa de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 14/09/2009 PT
Relevância na Pesquisa
390.68594%
Esta pesquisa estudou o método de realcalinização química (RAQ), através da absorção e difusão de soluções alcalinas na superfície do concreto carbonatado. Neste estudo foram utilizadas três espécies químicas para obtenção das soluções alcalinas: carbonato de sódio, hidróxido de potássio, e hidróxido de cálcio. Para avaliar a eficácia desta nova técnica de reabilitação, foram realizadas medidas de profundidade de carbonatação e de realcalinização, medidas eletroquímicas de potencial de corrosão e de espectroscopia de impedância eletroquímica (EIE) para a verificação do estado da armadura, ensaios de imersão, absorção e ascensão capilar em concretos de referência, carbonatados e realcalinizados. Em razão da falta de conhecimento sobre a eficácia da técnica de realcalinização eletroquímica (RAE) em relação à repassivação da armadura, em paralelo foi realizado o estudo da repassivação das armaduras na RAE. Em relação à durabilidade da técnica, foi avaliada a resistência do concreto recuperado quando submetido a um novo ciclo de carbonatação acelerada, analisando as novas profundidades de carbonatação para cada solução alcalina estudada. Na repassivação da armadura com a técnica de RAE...

Desenvolvimento de um sistema de medidas de tribocorrosão

Santos, Claudia Beatriz dos
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
179.3502%
Em muitos sistemas tribológicos os materiais em contato estão expostos a um meio corrosivo e, assim, são submetidos simultaneamente a solicitações mecânicas e químicas ou eletroquímicas. Como exemplo típico tem-se os implantes ortopédicos e bombas químicas. A interação destas solicitações pode ser chamada de tribocorrosão e tem sido estudada há muitos anos sob diferentes enfoques. Eletroquímicos e cientistas em corrosão têm se interessado no estudo da cinética de repassivação de superfícies metálicas ativadas através do risco. Já os tribologistas têm seu interesse voltado para a o efeito da oxidação superficial no processo de desgaste mecânico. Mais recentemente, a atenção sobre a dependência mútua dos mecanismos mecânicos e eletroquímicos tem crescido. No estudo desta interação, o uso de métodos eletroquímicos são bastante adequados, uma vez que permitem a simulação do efeito corrosivo do meio através da imposição de potenciais, tendo como resposta densidades de corrente. Este trabalho trata do desenvolvimento de um sistema de medidas de tribocorrosão. Este sistema envolve os seguintes aspectos: controle dos parâmetros tribológicos e eletroquímicos e o uso célula eletroquímica de interface (STCzelle). Os parâmetros tribológicos foram aplicados através de um tribômetro que permite movimentos de deslocamento linear. Para aplicação e controle dos parâmetros eletroquímicos foi utilizado um potenciostato/galvanostato EG&G PAR 273. A célula eletroquímica de interface (STCzelle) possui a configuração de três eletrodos...

Electrochemical behaviour of heat-treated Al-Zn-Mg alloys in chloride solutions containing sulphate

Moreira, A. H.; Benedetti, A. V.; Sumodjo, PTA; Garrido, J. A.; Cabot, P. L.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 2823-2831
ENG
Relevância na Pesquisa
157.70923%
The electrochemical corrosion and passivation of Al-5Zn-1.7Mg-0.23Cu-0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion...

Electrochemical noise analysis of chalcopyrite carbon paste electrodes by Acidithiobacillus ferrooxidans

Horta, Daniela G.; Bevilaqua, Denise; Acciaric, Heloisa A.; Garcia Jr., Oswaldo; Benedettie, Assis V.
Fonte: Trans Tech Publications Ltd Publicador: Trans Tech Publications Ltd
Tipo: Conferência ou Objeto de Conferência Formato: 83-86
ENG
Relevância na Pesquisa
157.70923%
The electrochemical response of chalcopyrite was studied using electrochemical noise analysis (ENA). The assay was carried out under constant aeration using 30 mL in two electrochemical cells containing iron-free mineral salts solution. These cells were initially monitored for 56 hours, After 72 hours, 7.25x 10(10) cells mL(-1) of A, ferrooxidans strain LR were added in both cells and monitored until 128 h. Subsequent to this period, 0.927 mmol L-1 of silver ions and 400 mmol L-1 of chloride ions were added each one separately. Both conditions were monitored until 168 hours. According to results obtained, it was observed that Cl- ions addition induced an accelerated corrosion process. However, there is a tendency of the system to reach the stationary state due to repassivation of the electrodic surface. In the other side, the Ag+ addition contributed for the maintenance of the oxidant atmosphere, in spite of controversial effect caused by considerable variations in the R-n values, resulting in a instability in the chalcopyrite reactivity.

Influence of the heat treatment in the electrochemical corrosion of Al-Zn-Mg alloys

Cabot, P. L.; Centellas, F.; Garrido, J. A.; Rogríguez, R. M.; Brillas, E.; Pérez, E.; Benedetti, A. V.; Sumodjo, P. T A
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 541-552
ENG
Relevância na Pesquisa
157.70923%
The localized corrosion of Al-(5.03%)Zn-(1.67%)Mg-(0.23%)Cu alloys and high purity Al has been studied using electrochemical techniques, optical microscopy, SEM and EDX. The samples were previously submitted to different heat treatments in which coherent and incoherent MgZn 2 precipitates with different distribution and aggregation degree were produced. The influence of NaCl and Na 2SO 4, dissolved oxygen, immersion time and convection were studied. In NaCl solutions, pitting potentials for the alloys were more negative than for aluminium, indicating an increase in their susceptibility to localized corrosion. Moreover, annealed and cold-rolled alloys presented more negative pitting and repassivation potentials than those submitted to age hardening with direct or interrupted quenching. In annealed and cold-rolled samples, pit nucleation and propagation takes place in the zones where MgZn 2 is accumulated. In the case of the age-hardened alloys, a double pitting behaviour is observed, the first one in the magnesium and zinc enriched regions and the second in the matrix. While the cold water quenched alloy is susceptible to stress corrosion craking, the alloy submitted to the interrupted quenching process is less susceptible to intergranular attack. The sulphate ion shifts the pitting potential of aluminium and the alloys by chloride towards more positive values because it impedes local accumulations of the latter. © 1992 Chapman & Hall.

Tribocorrosion behaviour of titanium in artificial saliva solutions

Vieira, A. C.; Ribeiro, A. R.; Rocha, L. A.; Celis, J. P.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2004 ENG
Relevância na Pesquisa
157.70923%
Dental implants are used to replace teeth lost due to decay, trauma or periodontal disease. In last years, the demand for such implants has increased exponentially due mostly to the ageing of the population and/or increased reliability of implant therapy. To choose a material for a particular rehabilitation treatment different characteristics must be considered such as mechanical strength, elastic properties, machinability, chemical resistance, etc. There is, however, one aspect that is always of prime importance; namely how the tissue at the implant site responds to the chemical disturbance imposed by the presence of a foreign material. In this work, commercially pure titanium (grade 2) was selected mainly due to its excellent corrosion behaviour and biocompatibility, that make this material one of the most used in dentistry. The tribocorrosion behaviour of the material in conditions simulating mastication, when in contact with artificial saliva solutions was investigated. Corundum was used as counterface material. The tests were performed, at MTM- KULeuven (Belgium), in a fretting machine specially adapted for tribocorrosion experiments. A normal load of 2 N was applied to the specimens and a displacement amplitude of 200µm at a frequency of 1 Hz. The number of cycles was varied between 5.000 and 10.000. In order to simulate different environmental conditions...

Tribocorrosion studies on commercially pure titanium for dental applications

Rocha, L. A.; Ribeiro, A. R.; Vieira, A. C.; Ariza, E.; Gomes, J. R.; Celis, J. P.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /06/2005 ENG
Relevância na Pesquisa
157.70923%
Tribocorrosion refers to a complex degradation of materials occurring due to the interaction between a tribological process and a corrosive environment. From the tribological point of view, the interaction with the material may include sliding or abrasive wear, erosion, impact, fretting or fatigue processes. The environmental solicitation may result from temperature, humidity, liquids or gases in permanent or intermittent contact with the materials. Failure in the metallic part or of the metal/ceramic interfaces existing in dental restorations, such as crowns and bridges, are still relatively frequent. Also, excessive degradation of dental materials is sometimes observed in other dental materials. Most of the failures are due to the simultaneous action of mechanical (wear, fretting and fatigue) and chemical (saliva) solicitations. As a consequence, the investigation of the tribocorrosion mechanisms in such systems becomes essential. Regarding this aspect, in last years particular focus is being given to the exploitation of electrochemical methods as a tool for the investigation of the combined corrosion-wear degradation of the materials. Also, it is known that the mechanical contact geometry is of crucial importance regarding the degradation behaviour. In this work the tribocorrosion behaviour of commercially pure titanium in contact with artificial saliva solutions was investigated. Tests were conducted in a reciprocating sliding geometry with movement amplitudes varying from 200 m (fretting) up to 6 mm (wear)...

Electrochemical study of the repassivation of titanium in different artificial saliva solutions

Vieira, A. C.; Rocha, L. A.; Ariza, E.; Celis, J. P.
Fonte: ECS - The Electrochemical Society Publicador: ECS - The Electrochemical Society
Tipo: Conferência ou Objeto de Conferência
Publicado em /05/2005 ENG
Relevância na Pesquisa
312.02379%
The passive film presented at the dental implant surfaces can be damaged or eventually destroyed during insertion and implantation into hard tissue due to abrasion/wear with bone or other materials. However, when the wear action stops, the surface will tend to regenerate immediately, and a new passive film will be formed. In such conditions we are in the presence of a tribo-electrochemical phenomenon which comprises the analysis of two different processes and of the synergism effects between them. In fact, the mechanisms of mechanical degradation due to wear might be influenced by the presence of a corrosive environments, but the electrochemical behaviour of the material is likely to be modified by the presence of the mechanical solicitation and by the presence of wear debris and/or the formation of tribolayers. Also, the repassivation kinetics of the tribocorrosion system during or after mechanical damage becomes an important issue to be studied. This work deals with the study of the repassivation of titanium when in contact with artificial saliva solutions, after mechanical damage. Samples were immersed in different kinds of artificial saliva solutions (artificial saliva (AS), AS + citric acid, AS + anodic, cathodic or organic inhibitor). After stabilisation the passive film was mechanically disrupted and the open-circuit potential (OCP) was monitored both during the mechanical damage and until the repassivation was completed. Additionally...

Repassivation of commercially pure Ti in different saliva solutions under tribocorrosion conditions

Vieira, A. C.; Rocha, L. A.; Ariza, E.; Gomes, J. R.; Celis, J. P.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2005 ENG
Relevância na Pesquisa
410.40027%
The surface of dental implants can undergo wear during insertion and implantation into hard tissue, or, in some conditions, during its lifetime. As a consequence, the passive film presented at the implant surface can be damaged or even totally destroyed. However, if the wear action stops the surface might regenerate, giving origin to a new passive film. As all the process occurs in the presence of a chemical aggressive environment, human saliva, the material is under tribocorrosion conditions. It is also possible to introduce the concept of tribo-electrochemistry which may include two main research areas: the tribocorrosion, where the mechanical solicitations in corrosive environments are studied, and the electrochemistry of film free surfaces, where repassivation kinetics is studied after the removal of the protective oxide film on a passive metal. The main aim of this work was to study the repassivation evolution of commercially pure Ti in artificial saliva solutions. Grade 2 commercial pure titanium samples were subjected to a small alternative sliding in a pin-on-plate tribometer against a corundum ball. At the same time, open-circuit potential (OCP) measurements were performed, before, during and after mechanical disruption of the passive film. Also...

Influence of pH and corrosion inhibitors on the tribocorrrosion of titanium in artificial saliva

Vieira, A. C.; Ribeiro, A. R.; Rocha, L. A.; Celis, J. P.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2006 ENG
Relevância na Pesquisa
157.70923%
Dental implants are used to replace teeth lost due to decay, trauma, or periodontal iseases. Dental implants are most of the times ubjected tomicro-movements at the implant/bone interface or implant/porcelain interface (due to the transmitted mastication loads) and chemical solicitations (oral environment). Such implant becomes part of tribocorrosion system, which may undergo a complex degradation process that can lead to implant failure. In this work, the fretting–corrosion behaviour of titanium grade 2 in contact with artificial saliva was investigated under fretting test conditions. Citric acid was added to artificial saliva to investigate a pH variation on the tribocorrosion behaviour of the material. Additionally, three different inhibitors were added to investigate cathodic and anodic reactions on the electrochemical response. Also, the influence of inhibitors included in the formulation of tooth cleaning agents or medicines was investigated. Degradation mechanisms were investigated by electrochemical noise technique that provided information on the evolution of corrosion potential and corrosion current during fretting tests. Depassivation and repassivation phenomena occurring during the tests were detected and discussed. Considering the influence of corrosion inhibitors...

Fretting-corrosion behaviour and repassivation evolution of Ti in artificial saliva solutions in the presence of corrosion inhibitors and pH variations; Comportamento de Ti comercial em sistemas de fretting corrosão e evolução da repassivação, em soluções de saliva artificial, na presença de inibidores de corrosão e com alterações de pH

Vieira, A. C.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Dissertação de Mestrado
Publicado em 15/12/2006 ENG
Relevância na Pesquisa
297.66176%
Dissertação de Mestrado em Processamento e Caracterização de Materiais; Degradation of Ti dental implants is a common process usually caused by mechanical stress and/or by the physiological environment (human saliva) that surround the implant. These types of implant are most of the time subjected to micro-movements at the contact region with bone or at the implant/porcelain interface (due to the transmitted mastication loads) and chemical solicitations (oral environment). Such implant becomes part of a tribocorrosion system, which may undergo a complex degradation process that can lead to implant failure. Additionally, the passive film, which naturally grows on the metallic implant surface, can be scratched or destroyed during the insertion and implantation into the hard tissue by abrasion with bone and other materials. In this work, two different tribological arrangmets were studied. Fretting-corrosion and reciprocating pin-on-plate tests were performed in different equipments specially adapted for tribocorrosion experiments. Artificial saliva was used as electrochemical solution and an alumina ball (Ф = 10 mm) was used as counterbody. Citric acid was added to artificial saliva in order to investigate the influence of a pH variation on the tribocorrosion behaviour of the material. Additionally...

Effect of oral biofilms on the biotribocorrosion of titanium

Souza, J. C. M.; Ariza, E.; Henriques, Mariana; Oliveira, Rosário; Teughels, W.; Rocha, L. A.; Celis, J. P.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 08/09/2009 ENG
Relevância na Pesquisa
157.70923%
The oral cavity is a complex environment where corrosive substances from dietary, human saliva and oral biofilms may accumulate in retentive areas of implant-supported prostheses promoting a corrosion of their surfaces. On the other side, during mastication, micro-movements may occur in artificial joints causing a relative contact motion between surfaces. Both processes result in a tribocorrosion system. The objective of this work is to investigate the in-vitro tribocorrosion behavior of titanium covered by biofilms and immersed in artificial saliva. Reciprocating sliding wear tests coupled with electrochemical techniques were performed at 25 o C on titanium samples covered or not with biofilms. Mixed biofilms of Candida albicans and Streptococcus mutans were grown at 37 oC on titanium surfaces for 9 days in Tryptic Soy Broth medium, containing mucin, yeast extract, peptone and sucrose. The open-circuit potential (OCP) was measured until stabilization in artificial saliva. After that, electrochemical impedance spectroscopy (EIS) measurements were carried out at open circuit potential. Subsequently, sliding tests were performed at normal loads of 0.1, 0.2 and 3 N, at a sliding frequency of 1 Hz, and linear displacement amplitudes of 0.5 and 2 mm using a tribometer equipped with a test viewer software. During the sliding tests...

THE RECOVERY OF TRANSMISSIVITY IN PASSIVE IRON WIRES AS A MODEL OF RECOVERY PROCESSES IN IRRITABLE LIVING SYSTEMS : PART II.

Lillie, Ralph S.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/11/1920 EN
Relevância na Pesquisa
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1. Passive iron (steel) wires, when activated after prolonged immersion in nitric acid of 55 to 90 per cent concentration (volumes per cent of HNO3, specific gravity 1.42) revert spontaneously to the passive state, after a temporary reaction which is transmitted rapidly over the whole length of wire. The duration of this reaction at any region decreases rapidly with increase in the concentration above a certain critical limit of 52 to 54 per cent. In weaker acid (50 per cent and lower) the reaction continues uninterruptedly until all the metal is dissolved. 2. Immediately after this automatic repassivation the wire fails to transmit activation through more than a short distance (1 to 2 cm.); if left undisturbed in the acid it recovers by degrees its power of transmission (as measured by the distance traveled by an activation wave), at first slowly, then more rapidly; eventually, after an interval varying with the concentration of acid and the temperature, the activation wave is transmitted through an indefinite distance as before. 3. The return of complete transmissivity in 55 per cent acid occupies less than a minute (at 20°); in stronger acid it is more gradual, requiring in 90 per cent acid 20 minutes or more. This "complete recovery time" is nearly proportional to the excess of concentration of acid above the limiting value of 53 to 54 per cent. 4. In a given solution of acid the rate of recovery exhibits a temperature coefficient closely similar to that of most chemical reactions at this temperature (3–20°)...

THE CONDITIONS OF RECOVERY OF TRANSMISSIVITY OF NEWLY REPASSIVATED IRON WIRES IN NITRIC ACID

Lillie, Ralph S.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/01/1931 EN
Relevância na Pesquisa
157.70923%
1. Passive steel wires were activated in a bath (Bath A) containing 70 v. per cent HNO3 (in which they undergo prompt repassivation), and immediately transferred to a second bath (Bath B) containing HNO3 of a concentration varying in different experiments. After varying intervals in this bath they were transferred while still passive to a third bath (Bath C) containing strong HNO3 (70 or 100 v. per cent) and there immediately activated. 2. During the immersion in Bath B the wires progressively recover their ability to transmit activation waves in strong HNO3. The measure of this recovery is the distance travelled by the activation waves in Bath C after the varying times of exposure in Bath B. Transmissivity as thus measured is at first incomplete (decremental) and later becomes complete. The minimal exposures in Bath B required to render wires completely transmissive in the strong acid of Bath C were determined for concentrations of HNO3 between 10 and 100 v. per cent. With 100 v. per cent HNO3 in Bath C, these exposures range from 40 minutes or more in 15 v. per cent to 10 minutes in 100 v. per cent HNO3 (temperature 19–20° in all baths). 3. The time required for complete recovery varies inversely with the concentration of the acid in the recovery bath (Bath B)...

ACTIVATION OF PASSIVE IRON AS A MODEL FOR THE EXCITATION OF NERVE

Bonhoeffer, K. F.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/09/1948 EN
Relevância na Pesquisa
157.70923%
The activation by cathodic polarization of passive iron in concentrated nitric acid (d = 1.4) has been investigated. 1. For short current pulses (1 msec. or less) a transient activation occurs when the product of current density and time exceeds a certain value. This limiting value is here designated as the "threshold." It is of the order of magnitude of 200 x 10–6 coulomb/cm.2. 2. After activation and repassivation the threshold is temporarily several times higher than before. This "refractory state" is due to the presence of nitrous acid and of oxide layers. The return of the threshold to normal values occurs in seconds or minutes, depending on the variety of iron wire. 3. Immediately after a subthreshold current pulse the threshold is reduced (summation). However, if the second pulse occurs a certain interval of time after the first the wire exhibits a certain degree of refractoriness (Gildemeister effect). 4. Oscillographic measurements reveal the existence of a latent period between the application of the stimulating pulse and the establishment of the active state. The duration of this latent period depends on the strength of the current pulse. 5. There exists a minimum current density (rheobase) below which no activation occurs however long the current is applied. Depending on the variety of iron used this current density varies between about 1 and 10 ma./cm.2. To produce activation a current of rheobasic strength does not have to be applied for an infinite time but only for about 100 msec. (maximum utilization time). Activation becomes manifest some time after termination of the activating pulse. 6. With currents of slowly increasing strength it is possible to reach current strengths several times higher than rheobase without obtaining activation (accomodation). Accomodation to a large extent depends on the variety of iron used. Details are given for currents increasing with a time constant of 0.5 second. 7. Potential measurements on wires in the refractory state show the existence of after potentials. Wires in the refractory state which are cathodically polarized show peculiar oscillograms. Both types of experiments point to the formation of nitrous acid as an essential element in the course of events. 8. With current densities only slightly above rheobase all wires exhibit simple activations only. With higher current densities certain types of wires exhibit periodic activations. The range of current densities in which such periodic activations occur varies with the type of wire. The lower limit is sometimes quite close to the rheobase. 9. A theory of periodic activations is presented which is modelled on the theory of self-excitatory electrical oscillations. As variables describing the state of the wire...

Synthesis and Bioconjugation of 2 and 3 nm-diameter Gold Nanoparticles

Ackerson, Christopher J.; Jadzinsky, Pablo D.; Sexton, Jonathan Z.; Bushnell, David A.; Kornberg, Roger D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 17/02/2010 EN
Relevância na Pesquisa
157.70923%
By adjustment of solvent conditions for synthesis, virtually monodisperse 4-mercaptobenzoic acid (p-MBA) monolayer-protected gold nanoparticles, 2 and 3 nm in diameter were obtained. Large single crystals of the 2 nm particles could be grown from the reaction mixture. Uniformity was also demonstrated by the formation of two-dimensional arrays and by quantitative high-angle annular dark-field scanning transmission electron microscopy. The 2 and 3 nm particles were spontaneously reactive for conjugation with proteins and DNA, and further reaction could be prevented by repassivation with glutathione. Conjugates with antibody Fc fragment could be used to identify TAP-tagged proteins of interest in electron micrographs, through the binding of a pair of particles to the pair of protein A domains in the TAP tag.

The atomic force microscope as a mechano–electrochemical pen

Obermair, Christian; Wagner, Andreas; Schimmel, Thomas
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 04/10/2011 EN
Relevância na Pesquisa
157.70923%
We demonstrate a method that allows the controlled writing of metallic patterns on the nanometer scale using the tip of an atomic force microscope (AFM) as a “mechano–electrochemical pen”. In contrast to previous experiments, no voltage is applied between the AFM tip and the sample surface. Instead, a passivated sample surface is activated locally due to lateral forces between the AFM tip and the sample surface. In this way, the area of tip–sample interaction is narrowly limited by the mechanical contact between tip and sample, and well-defined metallic patterns can be written reproducibly. Nanoscale structures and lines of copper were deposited, and the line widths ranged between 5 nm and 80 nm, depending on the deposition parameters. A procedure for the sequential writing of metallic nanostructures is introduced, based on the understanding of the passivation process. The mechanism of this mechano–electrochemical writing technique is investigated, and the processes of site-selective surface depassivation, deposition, dissolution and repassivation of electrochemically deposited nanoscale metallic islands are studied in detail.

Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 sol–gel layers

Burnat, B.; Dercz, G.; Blaszczyk, T.
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
157.70923%
The aim of this study was to demonstrate the relationship between the structural and corrosion properties of an ISO 5832-9 biomedical alloy modified with titanium dioxide (TiO2) layers. These layers were obtained via the sol–gel method by acid-catalyzed hydrolysis of titanium isopropoxide in isopropanol solution. To obtain TiO2 layers with different structural properties, the coated samples were annealed at temperatures of 200, 300, 400, 450, 500, 600 and 800 °C for 2 h. For all the prepared samples, accelerated corrosion measurements were performed in Tyrode’s physiological solution using electrochemical methods. The most important corrosion parameters were determined: corrosion potential, polarization resistance, corrosion rate, breakdown and repassivation potentials. Corrosion damage was analyzed using scanning electron microscopy. Structural analysis was carried out for selected TiO2 coatings annealed at 200, 400, 600 and 800 °C. In addition, the morphology, chemical composition, crystallinity, thickness and density of the deposited TiO2 layers were determined using suitable electron and X-ray measurement methods. It was shown that the structure and character of interactions between substrate and deposited TiO2 layers depended on annealing temperature. All the obtained TiO2 coatings exhibit anticorrosion properties...

Behaviour of corroded steel in a Ca(OH)2-saturated solution and in cement mortar. Possibility of rehabilitation; Comportamiento del acero precorroído en solución saturada de Ca(OH)2 y en mortero de cemento. Posibilidades de rehabilitación

Miranda, J. M.; Otero, Eduardo; González Fernández, José Antonio; Hernández, L. S.
Fonte: Consejo Superior de Investigaciones Científicas (España) Publicador: Consejo Superior de Investigaciones Científicas (España)
Tipo: Artículo
SPA
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The present study compared the response of rust-free and corroded steel electrodes in Ca(OH)2-saturated solutions and in cement mortar, essentially defined in terms of polarization resistance as measured with gravimetric, metallographic and electrochemical methods. Answers were sought for the following questions, which persist despite the use of reinforced concrete (RC) in building for over a century: At what corrosion rate is RC durability seriously compromised? Does restoration of the initial conditions in properly manufactured concrete guarantee repassivation of corroded steel? Does the use of inhibitors enhance repassivation? Does the nature of the corrosion products have any significant effect on the response of corroded steel reinforcement? The results obtained in indicated that the effectiveness of preventive methods is much more closely related to the degree of existing corrosion than to the nature of the corrosion products.; En el presente trabajo se analizan las respuestas de electrodos de acero, limpios y precorroídos, en soluciones saturadas de Ca(OH)2 y en mortero de cemento, recurriendo para ello a técnicas gravimétricas, metalográficas y electroquímicas, esencialmente a medidas de resistencia de polarización. Se intenta encontrar respuesta a las siguientes dudas persistentes después de más de un siglo de utilización de las estructuras de hormigón armado (EHA): ¿qué velocidades de corrosión comprometen seriamente la durabilidad de las EHA? ¿La restauración de las condiciones iniciales de un hormigón correctamente fabricado garantiza la recuperación del estado pasivo en los refuerzos ya corroídos? ¿La utilización de inhibidores facilita la repasivación de los refuerzos? ¿Cambia la naturaleza de los productos de corrosión sustancialmente la respuesta de las armaduras ya corroídas? Los resultados obtenidos indican que la eficacia de las medidas preventivas resulta mucho más condicionada por el grado de corrosión ya exhibido por los refuerzos que por la naturaleza de los productos de corrosión.; Peer reviewed