Spelling suggestions: "subject:"cathode""
121 |
Verres pour la Photostructuration / Glasses for photostructurationMaurel, Clément 10 February 2009 (has links)
Les besoins de nouvelles technologies en télécommunications motivent la recherche de matériaux participant à la formation de composants optiques. Dans ce but, l’étude de la photostructuration de nouvelles formulations de verres possédant des propriétés optiques ajustables a été réalisée. Deux cas ont été étudiés : la modification du réseau vitreux ou l’introduction d’ions photosensibles au sein du verre. - Des verres oxysulfures de germanium et de gallium ont été élaborés sous forme de massif, et sous forme de couche mince. Leurs propriétés optiques sont intermédiaires à celles des composés purs Ge(Ga)O2 et Ge(Ga)S2. La photosensibilité des verres diminue avec l’augmentation de la valeur du rapport O/S des matériaux. - L’ajout d’ions argent au sein de verres phosphates de zinc a été étudié. Plusieurs techniques de réduction de l’ion argent dans ces verres ont été explorées comme l’irradiation par faisceau électronique, par rayonnement gamma ou par Laser. Dans le cas particulier d’une irradiation par laser femtoseconde de cadence de 8 Mhz et émettant à 1030 nm, il a été possible de créer des structures optiques de 85 nm environ, donc bien inférieur à la longueur d’onde utilisée pour l’écriture. Ces premiers résultats offrent une nouvelle alternative à la création dans le futur de structures photoniques composites. / The increment of the need of new technologies in photonics is a perfect vector for the research and development of new components for integrated optics. The photostructuration of new glassy materials with novel optical properties is proposed. Two approaches have been conducted : Modification of the glass matrix or addition of photosensitive ions. - Germanium and gallium oxysulfide glasses have been elaborated into bulk glasses as well as amorphous thin films. They exhibit optical properties in between their respective pure sulphide or oxide counterpart in the Ge(Ga)O2 - Ge(Ga)S2 system. The photosensitivity of the oxysulfide glasses lowers as the oxygen/sulphur ratio of the glasses is increased. - The photosensitivity of silver ions within silver phosphate glasses was studied as well. Several techniques were used in order to trigger the reduction of silver such as gamma ray or electron beam irradiation, or laser beam exposure. Under a femtosecond laser with a repetition rate of 8 Mhz, emitting at 1030 nm, it was possible to create optical objects, below the diffraction limit, of about 85 nm. Those results are a new alternative for the creation of photonic composite structures.
|
122 |
Nouveaux alliages zinc-terres rares pour des applications anticorrosion : élaboration, propriétés et traitements de surfaces / New zinc-rare earth alloys for corrosion applications : preparation, properties and surface treatmentsGuessoum, Khadoudj 14 June 2012 (has links)
De nouveaux alliages Zn-TR1-5 %mass.(TR = Ce, La et Mischmetal : Ce 75%/La25%) ont été synthétisés par fusion sous atmosphère contrôlée et coulés sous forme de plaques. Dans ces nouveaux matériaux, les terre rare sont localisées exclusivement dans des phases intermétalliques dispersées de manière homogène dans la matrice de zinc : Zn11Ce, Zn13La ou Zn11Ce1-xLax and Zn13CeyLa1-y. Le comportement électrochimique de ces nouveaux alliages a été étudié dans un milieu corrosif de référence simulant les conditions atmosphériques. En parallèle, les phases intermétalliques pures Zn11Ce and Zn13La ont été synthétisées et leur influence électrochimique a été évaluée par voltamétrie et couplage galvanique. Les résultats montrent que les deux phases intermétalliques sont des sites cathodiques préférentiels de la réduction du dioxygène et induisent une inhibition cathodique de la corrosion des alliages Zn-TR par rapport au zinc pur. Ce phénomène est plus marqué dans le cas des alliages au lanthane. Dans le cas spécifique des alliages au cérium, une inhibition anodique a également été observée et corrélée avec une modification chimique des produits de corrosion (composés majoritairement d'hydrozincite). En fait, une faible quantitéhomogène de cérium a pu être mise en évidence dans la couche de corrosion par spectrométrie dispersive en longueur d'onde. D'après les résultats d'expériences de précipitation contrôlée de sels de cérium et zinc en milieu carbonaté, la présence de cérium dans la couche de corrosion et son caractère protecteur pourraient être attribués à la formation d'un composé mixte double lamellaire zinc-cérium. L'addition de moins de 2%mass. de cérium ou lanthane permet d'améliorer la résistance à la corrosion du zinc. Cependant, lorsque la teneur en terre-rare augmente, l'effet de couplage galvanique devient plus important et rend les alliages moins résistants que le zinc pur / New Zn-RE1-5 wt.% alloys (RE=Ce, La and Mischmetal: Ce 75%/ La 25%) were synthesized by melting under controlled atmosphere and cast in plates. In these materials, rare earth metal are exclusively present in intermetallic phases homogeneously dispersed in the zinc matrix: Zn11Ce, Zn13La or Zn11Ce1-xLax and Zn13CeyLa1-y. The electrochemical behavior of these new alloys was investigated in a reference corrosivemedium. In parallel, the pure intermetallic phases Zn11Ce and Zn13La were synthesized and their electrochemical influence was studied by voltametry and galvanic coupling. Results show that both intermetallic phases act as preferential cathodic sites of dioxygen reduction and induce a cathodic inhibition of the corrosion of the Zn-RE alloys by comparison with pure zinc. This phenomenon is much more significant in the case of lanthanum containing alloys. In the specific case of cerium addition to zinc, an anodic inhibition was also observed and correlated with a chemical modification of the corrosion products (mainly made of hydrozincite). Actually, low quantities of cerium (less than 1 at.%) have been detected homogeneously in the corrosion layer by wave-length dispersive spectrometry. From results of controlled precipitation experiments of cerium and zinc salts performed in carbonated medium, the presence of cerium in the corrosionlayer and its protective character could be attributed to the formation of a mixed double lamellar zinc-cerium product. Therefore, addition to zinc of less than 2 wt.% of cerium or lanthanum allow to improve the corrosion resistance of zinc. However, by increasing the rare earth content in the alloys, the galvanic coupling phenomenon becomes more important and makes the alloys less resistant than pure zinc
|
123 |
Intégration et caractérisation électrique d'éléments de mémorisation à commutation de résistance de type back-end à base d'oxydes métalliques.Tirano, Sauveur 13 May 2013 (has links)
Cette thèse porte principalement sur la caractérisation électrique et la modélisation physique d'éléments mémoires émergents de type OxRRAM (Oxide Resistive Random Access Memory) intégrant soit un oxyde de nickel, soit un oxyde de hafnium. Une fois la maturité technologique atteinte, ce concept de mémoire est susceptible de remplacer la technologie Flash qui fait encore figure de référence. Les principaux avantages de la technologie OxRRAM reposent sur une très bonne compatibilité avec les filières CMOS, un faible nombre d'étapes de fabrication, une grande densité d'intégration et des performances attractives en termes de fonctionnement. Le premier objectif de ce travail concerne le diélectrique employé dans les cellules. Il s'agit d'apporter des éléments factuels permettant d'orienter un choix technologique sur la méthode d'élaboration de l'oxyde de nickel (oxydation thermique ou pulvérisation cathodique réactive) puis d'évaluer les performances de cellules à base d'oyxde de hafnium. Le second objectif est d'approfondir la compréhension des mécanismes physiques responsables du changement de résistance des dispositifs mémoire par une approche de modélisation physique des phénomènes opérant lors des phases d'écriture et d'effacement, sujet encore largement débattu dans la communauté scientifique. Le troisième objectif de cette thèse est d'évaluer, par le biais de caractérisations électriques, les phénomènes parasites intervenant dans les éléments mémoires de type 1R (élément résistif sans dispositif d'adressage) et, en particulier, la décharge capacitive apparaissant lors de leur programmation (opérations d'écriture). / This work is focused on the electrical characterization and physical modeling of emerging OxRRAM memories (Oxide Resistive Random Access Memory) integrating nickel or hafnium oxide. After reaching maturity, this memory concept is likely to replace the Flash technology which is still a standard in the CMOS industry. The main advantages of resistive memories technology is their good compatibility with CMOS processes, a small number of manufacturing steps, a high integration density and their attractive performances in terms of memory operation. The first objective of this thesis is to provide enough informations allowing to orientate the elaboration process of the active nickel oxide layer (thermal oxidation, reactive sputtering) then to compare the performances of the fabricated cells with devices featuring a hafnium oxide layer. The second objective is to understand the physical mechanisms responsible of the device resistance change. A physical model is proposed allowing to apprehend SET and RESET phenomenon in memory devices, subject which is still widely debated in the scientific community. The third objective of this thesis is to evaluate electrical parasitic phenomenon observed in 1R-type memory elements (resistive element without addressing device), in particular the parasitic capacitance appearing during cell programming (writing operation).
|
124 |
Mechanistic studies of localized corrosion of Al alloys by high resolution in-situ and ex-situ probing techniquesDavoodi, Ali January 2007 (has links)
A multi-analytical approach based on in-situ and ex-situ local probing techniques was employed to investigate localized corrosion mechanisms of some aluminum alloys in chloride containing solutions, focusing on the influence of intermetallic particles (IMPs) in the alloys. In the EN AW-3003 alloy, SEM-EDS analysis revealed constituent and dispersoid IMPs. There are two types of constituent IMPs, with size ranging from 0.5 to several μm, and composition typically Al6(Fe,Mn) or Al12(Mn,Fe)3Si, respectively,having a Mn/Fe ratio of about 1:1. Fine dispersoids of 0.5 μm or less in size normally have the composition Al12Mn3Si1-2. Scanning Kelvin probe force microscopy (SKPFM measurements showed that the constituent IMPs have a higher Volta potential compared to the matrix, and the Volta potential difference increased with particle size, probably related to the composition of the IMPs. The SKPFM results also showed a Volta potential minimum in the boundary region adjacent to some larger IMPs. The open-circuit potential and electrochemical impedance spectroscopy measurements indicated local electrochemical activities occurring on the surface, and active-like dissolution in the acidic solutions, but a passive-like behavior in the near-neutral solutions. Infrared reflection-absorption spectroscopy measurements after exposure and thermodynamic calculations suggested the formation of mixtures of aluminum oxyhydroxide and acetate on the surface in acetic acid solutions. The formation and fraction of dominant species of the corrosion products depend on the pH of the solution, and aluminum chloride compounds may form at very low pH. Moreover, an integrated in-situ atomic force microscopy (AFM) and scanningelectrochemical microscopy (SECM) set-up was used to investigate the localized activities on the surface. With a dual mode probe, acting as both AFM tip and SECM microelectrode, concurrent topography and electrochemical current images were obtained on the same area of the surface. Numerical simulations of the SECM suggested a micrometer lateral resolution under favorable conditions and the ability to resolve μmsized active sites with a separation distance of about 3 μm or larger. The simulations were verified by SECM mapping of the aluminum alloys in the chloride solutions. The AFM/SECM measurements revealed enhanced cathodic activity on some larger IMPs and local anodic dissolution around larger IMPs. In-situ AFM monitoring confirmed preferential dissolution in the boundary region adjacent to some of these IMPs. The results elucidate the micro-galvanic effect and size effect of the IMPs during the initiation of localized corrosion of the Al alloys. Furthermore, differences in corrosion properties between EN AW-3003 and a newly developed Al–Mn–Si–Zr alloy were studied with a similar approach. Compared to EN AW-3003, the new alloy had a smaller number of particles with a large Volta potential difference relative to the matrix. In slightly corrosive solutions extensive localized dissolution and deposition of corrosion products occurred on EN AW-3003, whereas only a small number of corroding sites and “tunnel-like” pits occurred on the Al–Mn–Si–Zr alloy. The lower corrosion activity and the smaller tunnel-like pits resulted in lower material loss of the Al–Mn–Si–Zr alloy, which is beneficial for applications using a thin material. / QC 20100702
|
125 |
Revestimentos de polianilina e polianilina/melamina sobre aço inox 304: eletrossíntese em meio aquoso neutro e avaliação da proteção contra corrosão em meio NaCl 0,5 mol/lXavier, Marco Antonio Kresko 30 August 2013 (has links)
A polianilina é dos polímeros condutores mais estudados e com diversas aplicações, dentre elas o uso no recobrimento de aços para proteção à corrosão. Este trabalho objetivou encontrar as condições de eletrossíntese de polianilinas em meio aquoso neutro e a avaliação de proteção à corrosão, tendo como substrato o aço inox 304. As polianilinas eletrossintetizadas foram uma forma pura (PAni) e outra modificada com a adição de melamina (PAni/MM). Dentre as justificativas deste trabalho está a necessidade de aprofundar os escassos estudos em eletrossínteses em meio aquoso neutro. Neste trabalho, são apresentados as condições de eletrossíntese das polianilinas, a caracterização preliminar das polianilinas por UV-visível, FTIR e MEV, ensaios de polarização potenciodinâmica e impedância eletroquímica do aço inox 304 sem e com filmes das polianilinas para avaliar a resistência à corrosão em meio aquoso de NaCl 0,5 mol/L. O trabalho mostrou que a eletrossíntese das polianilinas em meio aquoso neutro é viável. Além disso, foi verificada a seguinte ordem do potencial de corrosão, do menor para o maior: aço inox 304 puro, aço inox 304 com PAni e aço inox 304 com PAni/MM. / Polyaniline is one of the most studied conducting polymers and with various applications, including use on steels for corrosion protection. This work aimed to find the conditions for electrosynthesis of polyanilines in neutral aqueous media and to evaluated the corrosion protection of 304 stainless steel. The electrosynthesizeds polyanilines were one pure form (PAni) and one with the addition of melamine (PAni/MM). One of the justifications of this work is the need to deepen the scarce studies in electrosynthesis in neutral aqueous media. In this work, we will see the conditions for electrosynthesis of polyanilines, the UV-visible, FTIR and SEM polyanilines preliminary characterization, the potentiodynamic polarization experiments and impedance spectroscopy of 304 stainless steel without and with films from polyanilines for evaluate the corrosion resistance in NaCl 0,5 mol/L aqueous media. This work showed that electrosynthesis of polyanilines is feasible in neutral aqueous media. In addition, it was verified the following order of corrosion potencial, from lowest to highest: pure 304 stainless steel, 304 stainless steel with PAni and 304 stainless with PAni/MM.
|
126 |
Nitreta??o em plasma com gaiola cat?dica: investiga??o do mecanismo e estudo comparativo com a nitreta??o em plasma de tens?o cont?nuaSousa, R?mulo Ribeiro Magalh?es de 18 December 2007 (has links)
Made available in DSpace on 2014-12-17T14:06:57Z (GMT). No. of bitstreams: 1
RomuloRMS.pdf: 3055902 bytes, checksum: 75eaf485a85529179129dd468ccfc772 (MD5)
Previous issue date: 2007-12-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The ionic plasma nitriding is one of the most important plasma assisted treatment technique for surface modification, but it presents some inherent problems mainly in nitriding
pieces with complex geometries. In the last four years has appeared a plasma nitriding technique, named ASPN (Active Screen Plasma Nitriding) in which the samples and the
workload are surrounded by a metal screen on which the cathodic potential is applied. This new technique makes possible to obtain a perfect uniform nitrided layer apart from the shape of the samples. The present work is based on the development of a new nitriding plasma technique named CCPN (Cathodic Cage Plasma Nitriding) Patent PI 0603213-3 derived from ASPN, but utilizes the hollow cathode effect to increase the nitriding process efficiency. That technique has shown great improvement on the treatment of several types of steels under different process conditions, producing thicker and harder layers when compared with both, ASPN and ionic plasma nitriding, besides eliminating problems associated with the later technique. The best obtained results are due to the hollow cathode effect on the cage holes. Moreover, characteristic problems of ionic plasma nitriding are eliminated due to the fact that the luminescent discharge acts on the cage wall instead of on the samples surface, which
remains under a floating potential. In this work the enhancement of the cathodic cage nitriding layers proprieties, under several conditions for some types of steels was investigated, besides the mechanism for nitrides deposition on glass substrate, concluding that the CCPN is both a diffusion and a deposition process at the same time / A nitreta??o i?nica ? um dos processos de revestimento superficial dos mais importantes, mas apresenta alguns problemas inerentes, principalmente, na nitreta??o de pe?as com geometria complexa. Nos ?ltimos quatro anos surgiu uma nova t?cnica de nitreta??o a plasma, denominada de ASPN (Active Screen Plasma Nitriding), na qual as amostras s?o envolvidas por uma tela polarizada catodicamente e com ela ? poss?vel obter uma camada nitretada, perfeitamente uniforme, independente da forma da amostra. O nosso trabalho
baseia-se no desenvolvimento, no ?mbito do LabPlasma, de uma nova t?cnica de nitreta??o em plasma, denominada nitreta??o em gaiola cat?dica (NGC) dep?sito de patente PI 0603213-3 derivada da ASPN, mas que utiliza o efeito de c?todo oco para aumentar a efici?ncia do processo de nitreta??o. Esta t?cnica apresentou bastante efic?cia na nitreta??o de v?rios tipos de a?os, nas mais variadas condi??es de tratamento, proporcionando a obten??o
de camadas mais espessas e de maior dureza, quando comparada com a ASPN e com a nitreta??o i?nica convencional, al?m de eliminar problemas de irregularidades associados ? t?cnica convencional. Sua maior efici?ncia deve-se ? utiliza??o do efeito de c?todo oco estabelecido nas paredes dos furos da gaiola, enquanto que a elimina??o dos problemas inerentes ? t?cnica convencional, deve-se ao fato do plasma atuar na gaiola e n?o nas amostras, as quais permanecem em potencial flutuante. Neste trabalho, foram avaliadas as condi??es de otimiza??o da nitreta??o, realizada com esta t?cnica, para diferentes tipos de a?os, al?m de investigarmos os mecanismos que atuam, quando da deposi??o de nitretos em substratos de vidro, observando que a NGC ? um processo misto de difus?o e deposi??o
|
127 |
Influ?ncia dos par?metros de processo na deposi??o de nitreto de tit?nio por plasma em gaiola cat?dicaDaudt, Natalia de Freitas 27 February 2012 (has links)
Made available in DSpace on 2014-12-17T14:07:01Z (GMT). No. of bitstreams: 1
NataliaFD_DISSERT.pdf: 4136751 bytes, checksum: 47b384d6442f251d58542735c23ae300 (MD5)
Previous issue date: 2012-02-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Titanium nitride films were grown on glass using the Cathodic Cage Plasma Deposition
technique in order to verify the influence of process parameters in optical and structural
properties of the films. The plasma atmosphere used was a mixture of Ar, N2 and H2,
setting the Ar and N2 gas flows at 4 and 3 sccm, respectively and H2 gas flow varied
from 0, 1 to 2 sccm. The deposition process was monitored by Optical Emission
Spectroscopy (OES) to investigate the influence of the active species in plasma. It was
observed that increasing the H2 gas flow into the plasma the luminescent intensities
associated to the species changed. In this case, the luminescence of N2 (391,4nm)
species was not proportional to the increasing of the H2 gas into the reactor. Other
parameters investigated were diameter and number of holes in the cage. The analysis
by Grazing Incidence X-Ray Diffraction (GIXRD) confirmed that the obtained films are
composed by TiN and they may have variations in the nitrogen amount into the crystal
and in the crystallite size. The optical microscopy images provided information about the
homogeneity of the films. The atomic force microscopy (AFM) results revealed some
microstructural characteristics and surface roughness. The thickness was measured by
ellipsometry. The optical properties such as transmittance and reflectance (they were
measured by spectrophotometry) are very sensitive to changes in the crystal lattice of
the material, chemical composition and film thicknesses. Therefore, such properties are
appropriate tools for verification of this process control. In general, films obtained at 0
sccm of H2 gas flow present a higher transmittance. It can be attributed to the smaller
crystalline size due to a higher amount of nitrogen in the TiN lattice. The films obtained
at 1 and 2 sccm of H2 gas flow have a golden appearance and XRD pattern showed
peaks characteristics of TiN with higher intensity and smaller FWHM (Full Width at Half
Maximum) parameter. It suggests that the hydrogen presence in the plasma makes the
films more stoichiometric and becomes it more crystalline. It was observed that with
higher number of holes in the lid of the cage, close to the region between the lid and the
sample and the smaller diameter of the hole, the deposited film is thicker, which is
justified by the most probability of plasma species reach effectively the sample and it
promotes the growth of the film / Filmes finos de nitreto de tit?nio foram crescidos sobre vidro utilizando a t?cnica de
deposi??o por descarga em gaiola cat?dica a fim de averiguar a influ?ncia das vari?veis
de processo nas propriedades ?pticas e estruturais do filme. Como atmosfera do
plasma foi utilizada a mistura de gases Ar, N2 e H2, fixando o fluxo de Ar e N2 em 4 e 3
sccm, respectivamente, e usando fluxos de 0, 1 e 2 sccm de H2. O processo de
deposi??o foi monitorado por Espectroscopia de Emiss?o ?ptica (OES) para
investiga??o das esp?cies ativas no plasma. Observou-se que com o aumento fluxo de
H2 as intensidades das esp?cies luminescentes no plasma sofrem altera??es e que a
esp?cie N2 (391,4 nm) n?o teve um crescimento proporcional ao fluxo de H2. Outros
par?metros investigados foram o di?metro e o n?mero de furos da gaiola. As an?lises
de difra??o de raios X com ?ngulo de incid?ncia rasante (GIXRD) comprovaram que os
filmes obtidos s?o compostos por TiN, podendo ter varia??es quanto a quantidade de
nitrog?nio na rede e o tamanho de cristalito; a microscopia ?ptica forneceu dados sobre
a homogeneidade, a partir da microscopia de for?a at?mica (AFM) observou-se
algumas caracter?sticas microestruturais do filme e a rugosidade. A espessura foi
quantificada atrav?s das an?lises de elipsometria. As propriedades ?pticas como
reflet?ncia e transmit?ncia (medidas por espectrofotometria) s?o bastante sens?veis a
altera??es na rede cristalina do material, composi??o qu?mica e espessura, sendo,
portanto, uma boa ferramenta para verifica??o do controle do processo. De maneira
geral, os filmes obtidos com fluxo de 0 sccm de H2 possuem uma maior transmit?ncia
atribu?da ao menor cristalinidade decorrente da maior quantidade de nitrog?nio na rede
cristalina do TiN. Os filmes obtidos nos fluxos de 1 e 2 sccm de H2 obtiveram um
aspecto dourado e o difratograma apresentou picos caracter?sticos do TiN com maior
intensidade e menor largura a meia altura, sugerindo que com a presen?a de hidrog?nio
na atmosfera do plasma os filmes s?o mais estequiom?tricos e com maior
cristalinidade. Quanto ? configura??o da gaiola observou-se que com maior quantidade
de furos na tampa, maior a proximidade da tampa com a amostra e menor o di?metro
do furo, maior ? a espessura do filme, o que ? justificado pela maior probabilidade das
esp?cies do plasma atingirem efetivamente o substrato e promoverem o crescimento do
filme
|
128 |
Estudo da viabilidade t?cnica para obten??o de superf?cie duplex em a?o inoxid?vel martens?tico AISI 410 atrav?s do processo de deposi??o a plasma por gaiola cat?dica / Technique feasibility study for obtaining duplex surface in AISI 410 martensitic stainless steel through the plasma deposition process by cathodic cageSantos, Poliana Rochele F?lix dos 01 March 2013 (has links)
Made available in DSpace on 2014-12-17T14:07:06Z (GMT). No. of bitstreams: 1
PolianaRFS_DISSERT.pdf: 3998823 bytes, checksum: e0480a4a5d6b04450e748434898535a9 (MD5)
Previous issue date: 2013-03-01 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The technique of plasma nitriding by the cathode cage mainly stands out for its ability
to produce uniform layers, even on parts with complex geometries. In this study, it
was investigated the efficiency of this technique for obtaining duplex surface, when
used, simultaneously, to nitriding treatment and thin film deposition at temperatures
below 500?C. For this, were used samples of AISI 41 0 Martensitic Stainless Steel
and performed plasma treatment, combining nitriding and deposition of thin films of Ti
and/or TiN in a plasma atmosphere containing N2-H2. It was used a cathodic cage of
titanium pure grade II, cylindrical with 70 mm diameter and 34 mm height. Samples
were treated at temperature 420?C for 2 and 12 hours in different working pressures.
Optical Microscopy (OM), Scanning Electron Microscopy (SEM) with micro-analysis
by Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Atomic Force
Microscopy (AFM) and analysis of Vickers Microhardness were used to investigate
coating properties such as homogeneity and surface topography, chemical
composition, layer thickness, crystalline phase, roughness and surface
microhardness. The results showed there is a direct proportionality between the
presence of H2 in plasma atmosphere and the quantity of titanium in surface
chemical composition. It was also observed that the plasma treatment at lowpressure
is more effective in formation of TiN thin film / A t?cnica de nitreta??o a plasma por gaiola cat?dica vem se destacando,
principalmente, pela sua capacidade de produzir camadas uniformes mesmo em
pe?as com geometria complexa. Neste trabalho, investigou-se a efici?ncia desta
t?cnica para obten??o de superf?cie duplex, quando utilizada, simultaneamente, para
tratamento de nitreta??o e deposi??o de filmes finos em temperaturas inferiores a
500?C. Para tal, foram utilizadas amostras do a?o inoxid?vel martens?tico AISI 410 e
realizados tratamentos a plasma, combinando a nitreta??o e deposi??o de filmes
finos de Ti e/ou TiN, em uma atmosfera contendo N2-H2. Foi utilizada uma gaiola
cat?dica de tit?nio puro grau II em forma cil?ndrica, com 70 mm de di?metro e 34 mm
de altura. As amostras foram tratadas numa temperatura de 420?C, com dura??o de
2 e 12 horas e em diferentes press?es de trabalho. Microscopia ?ptica (MO),
Microscopia Eletr?nica de Varredura (MEV) com microan?lise por Espectroscopia de
Energia Dispersiva (EDS), Difra??o de Raios-X (DRX), Microscopia de For?a
At?mica (MFA) e ensaio de Microdureza Vickers foram empregados para investigar
as propriedades do revestimento, tais como homogeneidade e topografia superficial,
composi??o qu?mica, espessura da camada, fases cristalinas, rugosidade e
microdureza superficial. Os resultados mostraram existir uma proporcionalidade
direta entre a presen?a de H2 na atmosfera do plasma e a quantidade do elemento
qu?mico tit?nio na composi??o qu?mica superficial. Observou-se, tamb?m, que o
tratamento a plasma em baixa press?o ? mais eficaz na forma??o do filme fino de
nitreto de tit?nio
|
129 |
Desenvolvimento e teste de um prot?tipo de reator de plasma com gaiola cat?dica rotat?ria para nitreta??o em lote de pequenas pe?asAra?jo Filho, Lino 09 August 2013 (has links)
Made available in DSpace on 2014-12-17T14:58:23Z (GMT). No. of bitstreams: 1
LinoAF_DISSERT.pdf: 8452397 bytes, checksum: f4854ebf6942546ff7bf8e8e0a4689c4 (MD5)
Previous issue date: 2013-08-09 / The technique of ion nitriding, despite being fully consolidated in the industry, has
great limitations when applied to the treatment of small parts. This is because effects
that occur due to non-uniformity of the electric field, generate localized heating in
parts, damaging the uniformity of nitrided layer. In addition, because the samples are
treated static parts thereof are untreated. To expand the use of plasma nitriding, this
work presents the development, assembly and testing of a prototype plasma reactor
with rotatory cathodic cage [patent pending], able to meet these needs, giving the
material a uniform treatment and opening doors to industrial scale production. The
samples tested with hexagonal nuts are 6.0 mm in diameter, made of stainless steel
AISI 304 nitrided at a pressure of 1 mbar in an atmosphere of 20% H2 + 80% N2 for
1 h. After treatment, testing visual inspection, optical microscopy and microhardness
were carried out to check the effectiveness of the process for uniformity and
hardness of the parts. All samples exhibited uniform color, and matte brownish,
unlike the untreated samples, silver color and gloss. The hardness of the surface (top
and sides) was 65% and even higher than the original hardness. The nitrided layer
showed great uniformity in microstructure and thickness. It is concluded, therefore,
that the unit was effective constructed for the purposes for which it was designed / A t?cnica de nitreta??o i?nica, apesar de estar plenamente consolidada na ind?stria,
possui grande limita??o quando aplicada ao tratamento de pe?as pequenas. Isso
acontece porque efeitos que ocorrem devido a n?o uniformidade do campo el?trico,
geram aquecimentos localizados nas pe?as, prejudicando a uniformidade da
camada nitretada. Al?m disso, pelo fato das amostras serem tratadas de maneira
est?tica, partes das mesmas ficam sem tratamento. Para ampliar o uso da nitreta??o
a plasma, este trabalho apresenta o desenvolvimento, montagem e teste de um
prot?tipo de reator de plasma com gaiola cat?dica rotat?ria [patente requerida],
capaz de atender a essas necessidades, conferindo ao material um tratamento
uniforme e abrindo portas ? produ??o em escala industrial. As amostras submetidas
ao teste s?o porcas sextavadas de 6,0 mm de di?metro, fabricadas em a?o
inoxid?vel AISI 304, nitretadas numa press?o de 1 mbar em atmosfera de 20%H2 +
80%N2, durante 1 h. Ap?s o tratamento, ensaios de inspe??es visuais, microscopia
?tica e microdureza foram realizadas a fim de conferir a efic?cia do processo quanto
? uniformidade e dureza das pe?as. Todas as amostras apresentaram cor uniforme,
amarronzada e fosca, ao contr?rio das amostras sem tratamento, de cor prata e
brilhosas. A dureza da superf?cie (topo e lateral) mostrou-se uniforme e 65% superior
? dureza original, considerado o tempo de tratamento. A camada nitretada
apresentou grande uniformidade na microestrutura e espessura. Conclui-se,
portanto, que o equipamento constru?do mostrou efic?cia para os fins a que foi
designado
|
130 |
Desenvolvimento de um equipamento para avaliação da susceptibilidade à fragilização por hidrogênio / Development of an equipment to evaluate the susceptibility to hydrogen assisted crackingMartiniano, Guilherme Antonelli 28 December 2016 (has links)
FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / A fragilização por hidrogênio tem sido um problema constante em diferentes setores da indústria. Por ser o menor átomo existente, o hidrogênio difunde-se na microestrutura dos materiais metálicos, inserindo tensões mecânicas internas que podem, eventualmente, levar a uma falha catastrófica. Atualmente, os métodos mais comuns existentes para analisar este fenômeno são lentos e caros, configurando-se assim a necessidade de desenvolver um método de ensaio que não possua tais desvantagens. No presente trabalho, apresenta-se o desenvolvimento de um equipamento cuja função é avaliar de forma rápida a susceptibilidade à fragilização por hidrogênio (SFH) dos materiais metálicos através de ensaios de carregamento progressivo em meio assistido (RSL). Este equipamento apresenta uma grande vantagem em relação aos outros métodos avaliação da SFH, que é o menor tempo de ensaio para se ter resultados representativos. Na presente dissertação foram realizadas a concepção, projeto, simulação em elementos finitos, construção e validação do equipamento. Sua validação foi realizada ensaiando-se uma amostra sem entalhe,cuja tensão mecânica medida foi comparada com aquela retornada pelo software do RSL. Além disso, foi calculada a incerteza de medição relacionada ao cálculo da tensão mecânica na amostra. Os ensaios de verificação do desempenho do RSL foram realizados em amostras de aço AISI 4140 beneficiado com dureza de 40HRC, onde foi avaliada a relação entre o nível de potencial catódico aplicado e a SFH do material das amostras. Os resultados obtidos na validação do equipamento mostraram erros inferiores a 1%. Os resultados mostraram um aumento da SFH com o aumento da dureza indicando que há uma elevada sensibilidade da SFH em relação à dureza da amostra. Os ensaios com variação do potencial catódico mostraram uma relação direta entre esse parâmetro e a SFH da amostra, havendo uma saturação na SFH a partir de -1,1 VAg/AgCl. / Hydrogen embrittlement of metallic materials has been a frequent problem in different
industry sectors. Because it is the smallest existing atom, hydrogen diffuses into the
microstructure of metallic materials, resulting in internal mechanical stresses that may
eventually lead to a catastrophic failure. The most common methods available to analyze this
phenomenon are time consuming and expensive. For this reason, it is desired to develop a
test method that does not have such disadvantages. In this work it is presented the
development of an equipment to rapidly evaluate the susceptibility to hydrogen embrittlement
(SHE) of the metallic materials using the rising step load (RSL) bend testing in assisted
environment. This equipment has a great advantage over the other evaluation methods of
SHE, which is the shortest test time to have representative results. The validation of the
infrastructure was performed by testing bars without notches to, whose measured
mechanical stress was compared with that returned by the RSL software. In addition, the
measurement uncertainty related to the calculation of the mechanical stress in the sample
was calculated. The tests to verify the performance of the RSL equipment were carried out
on samples of steel AISI 4140 heat treated to a hardness of 40HRC. The effect of the
cathodic potential applied to notched bars of AISI 4140 on the SHE was evaluated. The
results obtained in the validation phase of the equipment showed errors lower than 1%. The
results showed also an increase in SHE with increasing material hardness indicating that
there is a high sensitivity to the SHE with respect to the hardness of the sample. The tests
carried out using cathodic potential variation showed a direct relationship between this
parameter and the SHE of the sample, with saturation of the SHE at -1.1 VAg/AgCl. / Dissertação (Mestrado)
|
Page generated in 0.0457 seconds