No description available.

The marine biofouling and corrosion of Kunifer 10 (10% Ni, 1. 5% Fe, copper alloy), was studied using a combination of analytical techniques including x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDXA) and electron microscopy. Particular emphasis was placed on the very early stages of fouling, although the study continued until a climax community of macrofouling organisms had become established. Dissolved organic matter (DOM), was successfully extracted from seawater by ultrafiltration and chloroform-emulsion separation. The collected materials were partially characterised using fourier transform infrared spectroscopy (FTIR) and standard chemical analyses. Extracted materials were found to be mainly carbohydrate in character, with lesser quantities of protein. The FTIR investigations indicated considerable seasonal variation in the extracted DOM. XPS proved to be a suitable technique to investigate the development of marine organic and inorganic films that form on the alloy. Adsorbed organic macromolecules exhibited a characteristic spectral "fingerprint". The effect of elevated DOM on the corrosion behaviour of the Kunifer 10 alloy was investigated, using DC and AC impedance electrochemistry. Studies indicated that a temporary loss of passivation occurred in the presence of DOM under transient oxygen conditions. The development of organic layers on the alloy was shown to influence subsequent stages of biofouling, Kunifer 10 coated with elevated levels' of organic extracts was less likely to become fouled by microorganisms, although certain extracts appeared to stimulate the settlement of marine protozoans. However, such effects were short lived due to the continual formation of bio/corrosion layers. An unusual form of corrosion, not previously documented, is reported and an explanation for the exfoliation of the bio/corrosion films on Kunifer 10 is suggested. A range of cupronickel-iron alloys were assessed for their short-term marine biofouling/corrosion performance. Of the alloys tested Kunifer 10 showed optimum resistance. The study includes a literature review on marine biofouling and corrosion.

<p> The present work is aimed at studying the oxidation of thin films of nickel, nichrome and nickel phosphorous in air and water vapour at temperatures ranging from 100°C to 500°C. The optical constants, i.e., refractive index n and extinction coefficient k for these materials have been determined and their variation with temperature has been studied using ellipsometric technique. It has been shown that nickel oxide (NiO) is the more predominant phase in the oxides formed on these materials. It has also been found that within experimental error, the water vapour does not play a vital role in the oxidation process.</p> / Thesis / Master of Science (MSc)

Zinc-nickel ?-phase silicate and copper-nickel silicate corrosion resistant coatings have been prepared via electrochemical methods to improve currently available corrosion resistant materials in the oil and gas industry. A layered silicate, montmorillonite, has been incorporated into the coatings for increased corrosion protection. For the zinc nickel silicate coatings, optimal plating conditions were determined to be a working pH range of 9.3 -9.5 with a borate based electrolyte solution, resulting in more uniform deposits and better corrosion protection of the basis metal as compared to acidic conditions. Quality, strongly adhering deposits were obtained quickly with strong, even overall coverage of the metal substrate. The corrosion current of the zinc-nickel-silicate coating is Icorr = 3.33E-6 for a borate based bath as compared to a zinc-nickel bath without silicate incorporation (Icorr = 3.52E-5). Step potential and direct potential methods were examined, showing a morphological advantage to step potential deposition. The effect of borate addition was examined in relation to zinc, nickel and zinc-nickel alloy deposition. Borate was found to affect the onset of hydrogen evolution and was examined for absorption onto the electrode surface. For copper-nickel silicate coatings, optimal conditions were determined to be a citrate based electrolytic bath, with pH = 6. The solutions were stable over time and strong adhering, compact particle deposits were obtained. The corrosion current of the copper-nickel-silicate coatings is Icorr = 3.86E-6 (copper-nickel coatings without silicate, Icorr = 1.78E-4). The large decrease in the corrosion current as the silicate is incorporated into the coating demonstrates the increase in corrosion resistance of the coatings with the incorporation of silicates.

As curvas de polarização potenciodinâmicas cíclicas da liga de níquel Inconel 625, em solução de NaCl 3,56 %, pH 7,5, desaerada e a temperatura ambiente, obtidas com base na metodologia descrita na norma ASTM G61, foram estudadas com o objetivo de interpretá-las, especialmente no trecho após a reversão da polarização. Para esse estudo, foram realizadas análises complementares por MEV/EDS e por espctroscopia Raman da superfície do eletrodo de trabalho e determinação qualitativa por EDS da composição do eletrólito coletado nas vizinhas do eletrodo de trabalho. Medidas de pH e determinação do teor de O2 do eletrólito junto ao eletrodo de trabalho também foram feitas. Os resultados obtidos mostraram que, entre o potencial de circuito aberto até potencial de quebra (Eb), da ordem de 0,600 V (ECS), a curva de polarização apresenta um comportamento passivo com tendência a atingir a densidade de corrente da ordem de 10-6 A/cm². Nessa região, ocorre o espessamento da camada devido à formação principalmente de Cr2O3. Após Eb, ocorre a mudança na inclinação da curva, devido à ocorrência da reação de oxidação da água, comprovada pela acidificação do eletrólito. No potencial de 0,750 V (ECS) ocorre uma inflexão na curva, causando a diminuição discreta da corrente, atribuída à formação de MoO42- (gel) que evita a incorporação de ânions como Cl- ou OH-, dificultando, porém não evitando, a oxidação/dissolução da camada passiva, comprovada pela presença de íons de Cr e de Ni no eletrólito, caracterizando uma região transpassiva. Após a reversão da polarização no potencial de 1,130 V (ECS), a curva apresenta uma histerese positiva, com valores de densidades de correntes menores em relação ao mesmo potencial aplicado durante a polarização direta, indicando a ocorrência de repassivação devido principalmente à formação de uma camada rica em Mo sobre a liga, cuja formação pode ser atribuída à transformação do molibdato para o óxido MoO3 decorrente da forte acidificação do eletrólito verificado nesse trecho da curva. Ainda, após a inversão da polarização, ocorre a transição da corrente anódica para catódica em um potencial próximo de 0,720 V (ECS). Do potencial de 0,600 V (ECS) até 0,200 V (ECS), observa-se uma região de passivação secundária, atribuída à formação do MoO3 de maneira mais significativa. Ao final a densidade de corrente volta a aumentar, indicando o início da oxidação/dissolução do MoO3 para Mo3+. / Cyclic potentiodynamic polarization curves of the nickel alloy Inconel 625 in 3.56 % NaCl solution, pH 7.5, deaerated and at ambient temperature, obtained according to the ASTM G61, were studied in order to interpret them, especially after the reversion of the scanning direction. For this study, complementary analyzes by MEV/EDS and by Raman spectroscopy of the working electrode surfaces as well as EDS analyses of the electrolyte collected near the working electrode were carried out. The pH values and O2 content of the electrolyte near the working electrode were also obtained. From the open circuit potential (OPC) up to breakdown potential (Eb), at about 0,600 V (ECS), the polarization curve presents a passive behavior with a tendency to reach the current density of 10-6 A/cm². In this region, the thickening of the passive film takes place mainly due to the formation of Cr2O3. After Eb, a change of the curve slope occurs due to the oxygen evolution reaction which is confirmed by the acidification of the electrolyte. At the 0,750 V (ECS) potential, an inflection of the curve is observed causing a discrete decrease in the current which was attributed to the formation of MoO42- (gel) which, in turn, avoids the incorporation of anions as Cl- or OH- in the passive film. This fact makes the oxidation/dissolution of the passive film difficult but does not avoid it since Cr and Ni ions were detected in the electrolyte after the inflection, characterizing a transpassive region. After the reversion of the scanning direction at the potential 1,130 V (ECS), the curve shows a positive hysteresis with lower current densities than the values obtained at the same potential applied during the direct polarization. This indicates the occurrence of repassivation mainly due to the formation of a Mo rich layer on the alloy whose formation can be attributed to the transformation of the molybdate to the MoO3 because of the strong acidification of the electrolyte. After the reversion of the polarization, a transition from the anodic current to cathodic occurs at a potential close to 0,720 V (ECS). From the potential of 0,600 V (ECS) up to 0,200 V (ECS), a secondary passivation region is observed which was attributed to the significant formation of MoO3. At the end of the reverse polarization, the current increases again, indicating the initiation of the oxidation/dissolution of MoO3 to Mo3+.

No description available.

As curvas de polarização potenciodinâmicas cíclicas da liga de níquel Inconel 625, em solução de NaCl 3,56 %, pH 7,5, desaerada e a temperatura ambiente, obtidas com base na metodologia descrita na norma ASTM G61, foram estudadas com o objetivo de interpretá-las, especialmente no trecho após a reversão da polarização. Para esse estudo, foram realizadas análises complementares por MEV/EDS e por espctroscopia Raman da superfície do eletrodo de trabalho e determinação qualitativa por EDS da composição do eletrólito coletado nas vizinhas do eletrodo de trabalho. Medidas de pH e determinação do teor de O2 do eletrólito junto ao eletrodo de trabalho também foram feitas. Os resultados obtidos mostraram que, entre o potencial de circuito aberto até potencial de quebra (Eb), da ordem de 0,600 V (ECS), a curva de polarização apresenta um comportamento passivo com tendência a atingir a densidade de corrente da ordem de 10-6 A/cm². Nessa região, ocorre o espessamento da camada devido à formação principalmente de Cr2O3. Após Eb, ocorre a mudança na inclinação da curva, devido à ocorrência da reação de oxidação da água, comprovada pela acidificação do eletrólito. No potencial de 0,750 V (ECS) ocorre uma inflexão na curva, causando a diminuição discreta da corrente, atribuída à formação de MoO42- (gel) que evita a incorporação de ânions como Cl- ou OH-, dificultando, porém não evitando, a oxidação/dissolução da camada passiva, comprovada pela presença de íons de Cr e de Ni no eletrólito, caracterizando uma região transpassiva. Após a reversão da polarização no potencial de 1,130 V (ECS), a curva apresenta uma histerese positiva, com valores de densidades de correntes menores em relação ao mesmo potencial aplicado durante a polarização direta, indicando a ocorrência de repassivação devido principalmente à formação de uma camada rica em Mo sobre a liga, cuja formação pode ser atribuída à transformação do molibdato para o óxido MoO3 decorrente da forte acidificação do eletrólito verificado nesse trecho da curva. Ainda, após a inversão da polarização, ocorre a transição da corrente anódica para catódica em um potencial próximo de 0,720 V (ECS). Do potencial de 0,600 V (ECS) até 0,200 V (ECS), observa-se uma região de passivação secundária, atribuída à formação do MoO3 de maneira mais significativa. Ao final a densidade de corrente volta a aumentar, indicando o início da oxidação/dissolução do MoO3 para Mo3+. / Cyclic potentiodynamic polarization curves of the nickel alloy Inconel 625 in 3.56 % NaCl solution, pH 7.5, deaerated and at ambient temperature, obtained according to the ASTM G61, were studied in order to interpret them, especially after the reversion of the scanning direction. For this study, complementary analyzes by MEV/EDS and by Raman spectroscopy of the working electrode surfaces as well as EDS analyses of the electrolyte collected near the working electrode were carried out. The pH values and O2 content of the electrolyte near the working electrode were also obtained. From the open circuit potential (OPC) up to breakdown potential (Eb), at about 0,600 V (ECS), the polarization curve presents a passive behavior with a tendency to reach the current density of 10-6 A/cm². In this region, the thickening of the passive film takes place mainly due to the formation of Cr2O3. After Eb, a change of the curve slope occurs due to the oxygen evolution reaction which is confirmed by the acidification of the electrolyte. At the 0,750 V (ECS) potential, an inflection of the curve is observed causing a discrete decrease in the current which was attributed to the formation of MoO42- (gel) which, in turn, avoids the incorporation of anions as Cl- or OH- in the passive film. This fact makes the oxidation/dissolution of the passive film difficult but does not avoid it since Cr and Ni ions were detected in the electrolyte after the inflection, characterizing a transpassive region. After the reversion of the scanning direction at the potential 1,130 V (ECS), the curve shows a positive hysteresis with lower current densities than the values obtained at the same potential applied during the direct polarization. This indicates the occurrence of repassivation mainly due to the formation of a Mo rich layer on the alloy whose formation can be attributed to the transformation of the molybdate to the MoO3 because of the strong acidification of the electrolyte. After the reversion of the polarization, a transition from the anodic current to cathodic occurs at a potential close to 0,720 V (ECS). From the potential of 0,600 V (ECS) up to 0,200 V (ECS), a secondary passivation region is observed which was attributed to the significant formation of MoO3. At the end of the reverse polarization, the current increases again, indicating the initiation of the oxidation/dissolution of MoO3 to Mo3+.

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / As ligas de nÃquel podem ser utilizadas na uniÃo de juntas dissimilares de aÃos carbono baixa liga. Uma das finalidades desta uniÃo à evitar a formaÃÃo de trincas induzidas pelo hidrogÃnio. Existe uma limitaÃÃo por norma que impÃe a temperatura de interpasse mÃxima de 150ÂC para soldagem com ligas de nÃquel. Contudo, a temperatura de interpasse baixa reduz a produtividade e consequentemente aumenta os custos de fabricaÃÃo. Um estudo que avalia como a temperatura de preaquecimento/interpasse na soldagem dissimilar influencia as alteraÃÃes metalÃrgicas e propriedades mecÃnicas à oportuno. Desta forma, o objetivo geral deste trabalho à avaliar o efeito do aumento da temperatura de interpasse nas alteraÃÃes metalÃrgicas e nas propriedades mecÃnicas de juntas dissimilares soldadas do aÃo ASTM A182-F22 com diferentes ligas de nÃquel. Foram realizadas soldagens MIG/MAG automÃtica em juntas do aÃo (ASTM A182-F22) utilizando diferentes ligas de nÃquel como metal de adiÃÃo e diferentes temperaturas de interpasse (35ÂC, 150ÂC e 350ÂC). A energia de soldagem foi mantida constante (1,0 kJ/mm). Baseado nos resultados obtidos o aumento da temperatura de preaquecimento tende a reduzir a fraÃÃo de precipitados, decorrente do aumento da diluiÃÃo. O coeficiente de distribuiÃÃo do Mo e Nb diminuem com o aumento do teor de ferro na solda. Isto, por sua vez, torna mais forte a segregaÃÃo destes elementos. A temperatura de interpasse tendeu a reduzir a dureza da (ZTA-GG), por conta da reduÃÃo da velocidade de resfriamento. Nos ensaios de traÃÃo os corpos de prova romperam na regiÃo referente ao metal de base. Houve uma reduÃÃo no limite de escoamento nas condiÃÃes soldadas com temperatura de 350ÂC, sendo uma possÃvel causa a precipitaÃÃo de carbonetos devido ao preaquecimento e aos multipasses. Os ensaios de Charpy-V indicaram que, de uma forma geral, o aumento da temperatura de interpasse reduziu a tenacidade na zona fundida. A energia absorvida na interface sofreu reduÃÃo com o aumento da temperatura de interpasse, decorrente do aumento da descarbonetaÃÃo. O tempo de soldagem foi reduzido de forma considerÃvel com o aumento de temperatura de interpasse, entretanto, deve-se avaliar as alteraÃÃes na ZTA e ZF. / Nickel alloys can be used to weld dissimilar joints of low alloy carbon steels. One of the purposes of this union is to avoid the formation of hydrogen induced cracking. According codes and standard there is a limitation that imposes the maximum interpass temperature at 150ÂC for welding using nickel alloys. However, the low interpass temperature reduces productivity and increases manufacturing costs. A study that evaluates effect of the preheating and interpass temperature of dissimilar welds on the metallurgical changes and mechanical properties is of great relevance. In this way, the general objective of this study is to assess the effect of interpass temperature on metallurgical changes and mechanical properties of dissimilar welded joints among ASTM A182-F22 steel and different nickel-based alloys. GMAW were carried out on joints of steel (ASTM A182-F22) using different nickel-based alloys as filler metal and different interpass temperatures (35ÂC, 150ÂC and 350ÂC). The heat input was kept constant (1.0 kJ/mm). Based on the results obtained it was observed that increasing preheating temperature there is a tends to reduce the precipitates content, because of dilution. The distribution coefficient of Mo and Nb decrease with the increase of iron content in the fusion zone, making stronger the segregation of these elements. Interpass temperature tend to reduce the HAZ hardness, due to the in cooling rate reduction caused by increase interpass temperature. In the tensile tests failure in the base metal. There was a reduction in yield strength for welds produced with 350ÂC preheat temperature, being a possible cause the precipitation of carbides due to preheating and multipasses. The Charpy-V tests indicated that, generally, the increase in interpass temperature reduced the toughness in the fusion zone. The absorbed energy by the interface dropped when interpass temperature increase. The welding time was considerably reduced with the interpass temperature increase, however, it should be to considerate changes in HAZ and fusion zone.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / As ligas de nÃquel sÃo de fundamental importÃncia para a indÃstria do PetrÃleo devido a suas propriedades mecÃnicas e a resistÃncia a corrosÃo. A liga Inconel 686 como soldada teve sua microestrutura e suas propriedades mecÃnicas estudadas em diversos trabalhos realizados no laboratÃrio de Engenharia de Soldagem da UFC (Universidade Federal do CearÃ), porÃm nÃo existe na literatura estudos sobre os efeitos do envelhecimento tÃrmico na microestrutura desta liga e na sua resistÃncia a corrosÃo. No presente estudo a liga AWS ER NiCrMo-14 (Inconel 686) foi soldada utilizando o processo TIG com alimentaÃÃo de arame frio e envelhecida em temperaturas de 650 ÂC e 950 ÂC por 10, 50, 100 e 200 horas, com o objetivo de analisar a microestrutura formada apÃs o envelhecimento tÃrmico e as suas consequÃncias na resistÃncia a corrosÃo. Os tratamentos de envelhecimento causaram uma intensa precipitaÃÃo em ambas as temperaturas. No tratamento a 650 ÂC ocorreu uma precipitaÃÃo agulhada, de fase P ou  ricas em molibdÃnio, em torno de precipitados maiores de fase P. Na amostra de 950 ÂC nÃo foi observada a precipitaÃÃo fina em torno da precipitaÃÃo maior, mas tambÃm apresentou-se uma intensa precipitaÃÃo, de atà 13,82 %. Os precipitados foram caracterizados por meio de difraÃÃo de raios X (DRX), anÃlises de microscopia eletrÃnica de varredura (MEV), microscopia eletrÃnica de transmissÃo (MET), difraÃÃo de elÃtrons de Ãrea selecionada (SAD), espectroscopia de energia dispersiva (EDS). Nas amostras de 650 ÂC foram identificados por difraÃÃo de raios X carbonetos do tipo M3C2, M7C3 e fase  e P e por difraÃÃo de elÃtrons foram identificadas fase P. Nas amostras tratadas a 950 ÂC foram identificadas por difraÃÃo de raios X e de elÃtrons as mesmas fases, com exceÃÃo do carboneto do tipo M23C6. Este formou-se em placas prÃximo a interface com o metal de base devido a migraÃÃo de carbono do metal de base (aÃo ASTM A36) para a liga de nÃquel e da alta temperatura que favoreceu sua formaÃÃo. A precipitaÃÃo teve uma grande influÃncia sobre a resistÃncia a corrosÃo das amostras. A liga foi submetida ao ensaio de corrosÃo por imersÃo seguindo a norma ASTM G48 mÃtodo C e algumas amostras apresentaram falhas a temperatura de 40 ÂC. / Nickel based alloys are highly recommended to oil industry due to its mechanical properties and corrosion resistance. The Inconel 686 alloy as-welded had its microstructure and mechanical properties studied in several works in Welding Engineering Laboratory of the UFC (Federal University CearÃ). However, there is no known scientific studies regarding to the effects of thermal aging on the microstructure of this given alloy and its corrosion resistance. This study examines the AWS ER NiCrMo-14 (Inconel 686) alloy in a way that it was TIG welded using cold wire feed and aged at temperatures of 650  C and 950  C for 10, 50, 100 and 200 hours, with the objective to analyze the microstructure formed after aging treatment and its consequences in corrosion resistance. The ageing treatments caused a significant precipitation at both temperatures. In the treatment at 650  C there was a needled precipitation, of P or  phases rich in molybdenum, around larger precipitates. In the sample of 950  C it was not observed the same precipitation as cited above, however, also presented an intense precipitation up to 13.82%. The precipitates were characterized by X-Ray diffraction (XRD) and Scanning Electronic Microscopic (SEM), Transmission Electronic Microscope (TEM), selected area electrons diffraction (SAD) and Energy Dispersive Spectroscopy (EDS). At the 650ÂC samples, it could be possible to identify, by using X-Ray diffraction, both M3C2 and M7C3 type carbides, &#956; and P phase. By using electron diffraction P phase was identified. At the 950ÂC treated samples, it could be possible to identify, by using X-ray diffraction and electron, the same stages that has been told above, except for the carbide M23C6 type. At this type, plaques were formed close to the interface with the base metal due to carbon migration from base metal (ASTM A36 Steel) to the nickel alloy and to the high temperature, which favors its formation. The precipitation had a great influence on the corrosion resistance of the samples. The alloy has been subjected to the immersion corrosion test according to ASTM G48 C method and anything samples had fail in temperature of 40 ÂC.