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Jitendra S Sangwai - One of the best experts on this subject based on the ideXlab platform.
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synergistic effect of lactam ammonium and hydroxyl ammonium based ionic liquids with and without nacl on the Surface Phenomena of crude oil water system
Fluid Phase Equilibria, 2015Co-Authors: Sivabalan Sakthivel, Pratap K Chhotaray, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Abstract Typical surfactants have been found to be less efficient in harsh conditions of temperature and salinity. The need for alternatives is in great demand which is expected to be resolved through the use of ionic liquids, being the area of the present research. In the present investigation, eleven different ionic liquids (ILs) from three various families, namely, lactam, ammonium and hydroxyl ammonium based ionic liquids with various anions, such as, [HCOO]−, [CH3COO]−, [C6H13COO]− and [CF3COO]− are studied to understand the Surface phenomenon of water and crude oil–water system. In addition, the synergistic effects of NaCl on the Surface tension (SFT) and interfacial tension (IFT) are also investigated in the presence of ionic liquid. The impacts of the ring size, alkyl chain length, temperature, concentration of ILs, the nature of cation and anions on the SFT/IFT are evaluated in the temperature range of 288.15–318.15 K with various concentrations of ILs. In addition, the electrical conductivity of aqueous solution of ILs are also presented to understand the critical aggregation concentration (cac) range of studied ILs. The exploration of SFT/IFT of water and crude oil–water systems divulge the fact that the ILs with NaCl are useful in minimizing the Surface forces and thus, it could assist in impressively augmenting oil recovery, flow assurance and oil/gas production operations as well as being environment friendly.
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use of aromatic ionic liquids in the reduction of Surface Phenomena of crude oil water system and their synergism with brine
Industrial & Engineering Chemistry Research, 2015Co-Authors: Sivabalan Sakthivel, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil–water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil–water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]− in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of Surface tension (SFT) of water and interfacial tension of crude oil–water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperatu...
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Use of Aromatic Ionic Liquids in the Reduction of Surface Phenomena of Crude Oil–Water System and their Synergism with Brine
2015Co-Authors: Sivabalan Sakthivel, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil–water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil–water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]− in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of Surface tension (SFT) of water and interfacial tension of crude oil–water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperature and concentration of ILs. The study reveals that these ILs are effective in reducing the SFT and IFT of water and crude oil–water systems at high salinity and temperature conditions. In the IFT measurements, a linear decrement with increase in temperature is observed for crude oil–water in the presence of ILs. The interfacial tension of the various imidazolium-based ionic liquids with the crude oil–water system has been measured as a function of temperature by means of the Wilhelmy plate method. The influence of the nature of cation and anion of ionic liquids and of the chain length on the cationic head of the ILs on interfacial tension is also discussed in detail. At increased salinity conditions, unlike classical surfactants, these ILs are found to be more successful. Enhanced efficiency of the drop in IFT using NaCl and IL mixture has been confirmed by measuring the IFT between crude oil and the aqueous solution of IL. The synergism of salt and IL mixture on the reduction of IFT has been observed
Sefer Birhan - One of the best experts on this subject based on the ideXlab platform.
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Environment Related Surface Phenomena and their Influence on Properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : Oxidation at Elevated Temperature and Corrosion During Chemical Treatment
Luleå tekniska universitet Materialvetenskap, 2016Co-Authors: Sefer BirhanAbstract:This doctoral thesis covers investigation of the Surface Phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion duringchemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored Phenomenaare related to manufacturing and service conditions of aero-engine components. Duringmanufacturing and operation, the alloys are running at elevated temperatures in oxygencontaining environment. Under these conditions there are formations of an oxide on the Surfaceand an oxygen enriched layer below the oxide, commonly referred as alpha-case. The alpha-caseis a hard and brittle layer that is detrimental to the mechanical properties and must therefore beminimized or completely eliminated. A conventional method for elimination of alpha-case ischemical processing in HF/HNO3 solutions, known as chemical milling.Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carriedout in this study. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Moexhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linearoxidation rate was observed at 700 ºC and ≥ 200 hours for both alloys. The difference in theoxidation kinetics of the two alloys is suggested to be related with the chemical composition ofthe alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thicknesswas measured using conventional metallographic and microscopic techniques. Parabolicrelationship of the alpha-case layer growth rate with time was observed for both alloys. Theoxygen diffusion parameters and activation energies were estimated in the temperature range of500-700 ºC. Additionally, the oxidation at 700 ºC for 500 hours resulted in microstructuralchanges and element re-distribution. The bulk and alpha-case layer hardness at micro- and nanoscalewere measured using microhardness and nanoindentation techniques. The alpha-case layerhad higher hardness due to the solid solution strengthening effect of the diffused oxygen.The effect of chemical milling in 1:11 HF/HNO3 solution on the Surface integrity, and theinfluence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy wasinvestigated. Short and long chemical processing times (5 and 60 minutes) and three imposedtotal strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observedfor the samples etched before LCF testing, as compared to the non-etched samples. The influencefrom etching was found to be most detrimental for fatigue samples tested at the lowest strainranges. The fatigue life reduction was correlated with the number of crack initiation sites.Multiple crack initiation sites were observed for the etched samples, whereas only one crackinitiation site was discerned in the non-etched samples. Inspection of the Surface of the etchedsamples revealed selective and severely etched prior β grain boundaries and pit formation at thetriple joints of the prior β grain boundaries. These Surface defects were considered as stressraisers promoting an earlier fatigue crack initiation.The influence of two different molar concentration ratios (1:3 and 1:11) of HF and HNO3acids on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigatedusing electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the twoalloys was a function of the HF/HNO3 concentration ratio and also of the alloys’ chemicalcompositions. The AFM measurements revealed selective and faster dissolution rate of the α-phase than the β-phase in the Widmanstätten microstructure. It was considered that the reason forselective dissolution was the formation of local micro-galvanic cells between the α-phase and theβ-phase. Moreover, the Volta-potential was measured using scanning Kelvin probe forcemicroscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential betweenvithe α-laths and the β-laths in both alloys. This observation strengthened the likelihood forformation and operation of micro-galvanic cells between the α-phase and the β-phase when thealloys were in contact with HF/HNO3 solution.Keywords: Titanium alloys, oxidation, oxide, alpha-case, chemical milling, corrosion
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Environment related Surface Phenomena and their influence on properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : oxidation at elevated temperature and corrosion during chemical treatment
Universitat Politècnica de Catalunya, 2016Co-Authors: Sefer BirhanAbstract:Cotutela Universitat Politècnica de Catalunya i Luleå University of TechnologyThis thesis covers investigation of the Surface Phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion during chemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored Phenomena are related to manufacturing and service conditions of aero-engine components. During manufacturing and operation, the alloys are sunjected to elevated temperatures in oxygen environment. In such conditions an oxide on the Surface and an oxygen enriched layer below the oxide, commonly referred as alpha-case is formed. Alpha-case is a hard and brittle layer that is detrimental to the mechanical properties and must therefore be completely eliminated. A conventional method for elimination of alpha-case is chemical processing in HF/HNO3 solutions, i.e. chemical milling. Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carried out in this thesis. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Mo exhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linear oxidation rate was observed at 700 ºC and = 200 hours for both alloys. The difference in the oxidation kinetics of the two alloys is suggested to be related with the chemical composition of the alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thickness was measured using conventional metallographic and microscopic techniques. The parabolic rate constants, the oxygen diffusion parameters and activation energies were estimated in the temperature range of 500-700 ºC for both alloys. Moreover, the oxidation for 500 hours at 700 ºC resulted in microstructural changes and element re-distribution. The bulk and alpha-case layer hardness at micro- and nano-scale were measured using microhardness and nanoindentation techniques. The alpha-case layer had higher hardness due to the solid solution strengthening effect of the diffused oxygen. The effect of chemical milling in 1:11 HF/HNO3 solution on the Surface integrity, and the influence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy was investigated. Five and sixty minutes chemical processing times and three imposed total strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observed for the samples etched before LCF testing, as compared to the non-etched samples. The influence from etching was found to be most detrimental for fatigue samples tested at the lowest strain ranges. The fatigue life reduction was correlated with the number of crack initiation sites. Multiple crack initiation sites were observed for the etched samples, whereas only one crack initiation site was discerned in the non-etched samples. Inspection of the Surface of the etched samples revealed selective and severely etched prior ß grain boundaries and pit formation at the triple joints of the prior ß grain boundaries. These Surface defects were considered as stress raisers promoting an earlier fatigue crack initiation. The influence of two molar concentration ratios of HF and HNO3 acids (1:3 and 1:11) on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigated by electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the two alloys was a function of the concentration ratio of the acids and also of the alloys¿ chemical compositions. The AFM measurements showed faster dissolution rate of the a-phase than the ß-phase in the Widmanstätten microstructure. It was considered that the reason for this is formation of local micro-galvanic cells between the phases. Moreover, the Volta-potential was measured using scanning Kelvin probe force microscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential between the a- and the ß-laths in both alloys. This observation strengthened the likelihood for formation and operation of micro-galvanic cells between the phases.En esta tesis doctoral se estudian los fenómenos superficiales relacionados con la oxidación a alta temperatura y la corrosión producidos durante el tratamiento químico en soluciones de ácido fluorhídrico-nítrico (HF-HNO3) en las aleaciones Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo. Estos fenómenos se producen durante la fabricación y el servicio de componentes para motores aeronáuticos, pues se dan condiciones de elevada temperatura en un ambiente rico en oxígeno, las cuales favorecen la formación de óxido en la superficie y también de una capa enriquecida en oxígeno debajo del óxido, comúnmente conocida como alpha-case o capa alfa. La alpha-case es una capa dura y frágil, perjudicial para las propiedades mecánicas, por lo que debe ser minimizada o totalmente eliminada. Un método convencional para eliminar la capa alfa es el procesado químico en soluciones de ácido fluorhídrico-nítrico, conocido como chemical milling. En este estudio se han efectuado tratamientos isotérmicos en aire a 500, 593 y 700 °C, con duración máxima de 500 horas. Ambas aleaciones desarrollaron óxido tipo rutilo, en tanto que la Ti-6Al-2Sn-4Zr-2Mo mostró mejor resistencia a la oxidación que la Ti-6Al-4V. Se observó una transición de la velocidad de oxidación de parabólica a lineal a 700 °C y tiempos = 200 horas, para ambas aleaciones. Las diferencias en la cinética de oxidación entre ambas aleaciones se han relacionado con su composición química. La capa rica en oxígeno, i.e. alpha-case, fue caracterizada y su espesor medido mediante técnicas metalográficas. Se observó que la velocidad de crecimiento de la capa alfa seguía una relación parabólica con el tiempo para ambas aleaciones. La difusión del oxígeno y la energía de activación se estimaron en el rango de temperaturas de 500-700 °C. Adicionalmente, se comprobé que el tratamiento isotérmico a 700 °C durante 500 horas dio lugar a cambios microestructurales y a la redistribución de elementos. Las durezas del interior y de la capa alfa se midieron a escalas micro- y nano- mediante técnicas de microdureza y nanoindentación. La capa alfa mostró mayor dureza debido al efecto de endurecimiento por solución sólida debido al oxígeno difundido. El efecto de la solución 1:11 HF-HNO3 en la integridad superficial y en la resistencia a fatiga en el régimen de oligofatiga (LCF = Low Cycle Fatigue) de la aleación Ti-6Al-2Sn-4Zr-2Mo fue investigado. Se evaluaron tiempos de procesado químico cortos y largos (5 y 60 minutos) y tres valores de amplitud de deformación total. Se observó una significativa disminución de la vida a fatiga para las muestras atacadas antes de los ensayos LCF, en comparación con las muestras no atacadas. La influencia del ataque se mostró más perjudicial a bajos valores de deformación impuesta. La reducción en la vida a fatiga se correlacionó con el número de zonas de iniciación de grietas. Múltiples zonas se observaron para las muestras atacadas, mientras que solo un lugar de nucleación de grieta se detectó para las no atacadas. La inspección de las superficies de las muestras atacadas reveló un ataque selectivo y severo en los bordes de grano prior beta y la formación de picaduras en los puntos triples de los bordes de grano prior beta. Estos defectos superficiales fueron considerados como exaltadores de tensiones que promueven la temprana nucleación de las grietas de fatiga. Se investigó la influencia en el comportamiento a corrosión de Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo de dos diferentes relaciones de concentración (1:3 y 1:11) de los ácidos HF y HNO3. Se emplearon para ello técnicas electroquímicas y microscopía de fuerza atómica (AFM). La corrosión de las dos aleaciones depende de la concentración de HF-HNO3 y posiblemente también de sus composiciones químicas. Las medidas de AFM revelaron una velocidad de disolución mayor de la fase alfa que de la beta en la microestructura tipo Widmanstätten. Se considera que la razón de esta disolución selectiva es la formación de celdas micro-galvánicas
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Environment related Surface Phenomena and their influence on properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : oxidation at elevated temperature and corrosion during chemical treatment
Universitat Politècnica de Catalunya, 2016Co-Authors: Sefer BirhanAbstract:This thesis covers investigation of the Surface Phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion during chemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored Phenomena are related to manufacturing and service conditions of aero-engine components. During manufacturing and operation, the alloys are sunjected to elevated temperatures in oxygen environment. In such conditions an oxide on the Surface and an oxygen enriched layer below the oxide, commonly referred as alpha-case is formed. Alpha-case is a hard and brittle layer that is detrimental to the mechanical properties and must therefore be completely eliminated. A conventional method for elimination of alpha-case is chemical processing in HF/HNO3 solutions, i.e. chemical milling. Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carried out in this thesis. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Mo exhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linear oxidation rate was observed at 700 ºC and = 200 hours for both alloys. The difference in the oxidation kinetics of the two alloys is suggested to be related with the chemical composition of the alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thickness was measured using conventional metallographic and microscopic techniques. The parabolic rate constants, the oxygen diffusion parameters and activation energies were estimated in the temperature range of 500-700 ºC for both alloys. Moreover, the oxidation for 500 hours at 700 ºC resulted in microstructural changes and element re-distribution. The bulk and alpha-case layer hardness at micro- and nano-scale were measured using microhardness and nanoindentation techniques. The alpha-case layer had higher hardness due to the solid solution strengthening effect of the diffused oxygen. The effect of chemical milling in 1:11 HF/HNO3 solution on the Surface integrity, and the influence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy was investigated. Five and sixty minutes chemical processing times and three imposed total strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observed for the samples etched before LCF testing, as compared to the non-etched samples. The influence from etching was found to be most detrimental for fatigue samples tested at the lowest strain ranges. The fatigue life reduction was correlated with the number of crack initiation sites. Multiple crack initiation sites were observed for the etched samples, whereas only one crack initiation site was discerned in the non-etched samples. Inspection of the Surface of the etched samples revealed selective and severely etched prior ß grain boundaries and pit formation at the triple joints of the prior ß grain boundaries. These Surface defects were considered as stress raisers promoting an earlier fatigue crack initiation. The influence of two molar concentration ratios of HF and HNO3 acids (1:3 and 1:11) on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigated by electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the two alloys was a function of the concentration ratio of the acids and also of the alloys¿ chemical compositions. The AFM measurements showed faster dissolution rate of the a-phase than the ß-phase in the Widmanstätten microstructure. It was considered that the reason for this is formation of local micro-galvanic cells between the phases. Moreover, the Volta-potential was measured using scanning Kelvin probe force microscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential between the a- and the ß-laths in both alloys. This observation strengthened the likelihood for formation and operation of micro-galvanic cells between the phases.En esta tesis doctoral se estudian los fenómenos superficiales relacionados con la oxidación a alta temperatura y la corrosión producidos durante el tratamiento químico en soluciones de ácido fluorhídrico-nítrico (HF-HNO3) en las aleaciones Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo. Estos fenómenos se producen durante la fabricación y el servicio de componentes para motores aeronáuticos, pues se dan condiciones de elevada temperatura en un ambiente rico en oxígeno, las cuales favorecen la formación de óxido en la superficie y también de una capa enriquecida en oxígeno debajo del óxido, comúnmente conocida como alpha-case o capa alfa. La alpha-case es una capa dura y frágil, perjudicial para las propiedades mecánicas, por lo que debe ser minimizada o totalmente eliminada. Un método convencional para eliminar la capa alfa es el procesado químico en soluciones de ácido fluorhídrico-nítrico, conocido como chemical milling. En este estudio se han efectuado tratamientos isotérmicos en aire a 500, 593 y 700 °C, con duración máxima de 500 horas. Ambas aleaciones desarrollaron óxido tipo rutilo, en tanto que la Ti-6Al-2Sn-4Zr-2Mo mostró mejor resistencia a la oxidación que la Ti-6Al-4V. Se observó una transición de la velocidad de oxidación de parabólica a lineal a 700 °C y tiempos = 200 horas, para ambas aleaciones. Las diferencias en la cinética de oxidación entre ambas aleaciones se han relacionado con su composición química. La capa rica en oxígeno, i.e. alpha-case, fue caracterizada y su espesor medido mediante técnicas metalográficas. Se observó que la velocidad de crecimiento de la capa alfa seguía una relación parabólica con el tiempo para ambas aleaciones. La difusión del oxígeno y la energía de activación se estimaron en el rango de temperaturas de 500-700 °C. Adicionalmente, se comprobé que el tratamiento isotérmico a 700 °C durante 500 horas dio lugar a cambios microestructurales y a la redistribución de elementos. Las durezas del interior y de la capa alfa se midieron a escalas micro- y nano- mediante técnicas de microdureza y nanoindentación. La capa alfa mostró mayor dureza debido al efecto de endurecimiento por solución sólida debido al oxígeno difundido. El efecto de la solución 1:11 HF-HNO3 en la integridad superficial y en la resistencia a fatiga en el régimen de oligofatiga (LCF = Low Cycle Fatigue) de la aleación Ti-6Al-2Sn-4Zr-2Mo fue investigado. Se evaluaron tiempos de procesado químico cortos y largos (5 y 60 minutos) y tres valores de amplitud de deformación total. Se observó una significativa disminución de la vida a fatiga para las muestras atacadas antes de los ensayos LCF, en comparación con las muestras no atacadas. La influencia del ataque se mostró más perjudicial a bajos valores de deformación impuesta. La reducción en la vida a fatiga se correlacionó con el número de zonas de iniciación de grietas. Múltiples zonas se observaron para las muestras atacadas, mientras que solo un lugar de nucleación de grieta se detectó para las no atacadas. La inspección de las superficies de las muestras atacadas reveló un ataque selectivo y severo en los bordes de grano prior beta y la formación de picaduras en los puntos triples de los bordes de grano prior beta. Estos defectos superficiales fueron considerados como exaltadores de tensiones que promueven la temprana nucleación de las grietas de fatiga. Se investigó la influencia en el comportamiento a corrosión de Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo de dos diferentes relaciones de concentración (1:3 y 1:11) de los ácidos HF y HNO3. Se emplearon para ello técnicas electroquímicas y microscopía de fuerza atómica (AFM). La corrosión de las dos aleaciones depende de la concentración de HF-HNO3 y posiblemente también de sus composiciones químicas. Las medidas de AFM revelaron una velocidad de disolución mayor de la fase alfa que de la beta en la microestructura tipo Widmanstätten. Se considera que la razón de esta disolución selectiva es la formación de celdas micro-galvánicas
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Environment related Surface Phenomena and their influence on properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : oxidation at elevated temperature and corrosion during chemical treatment
Universitat Politècnica de Catalunya, 2016Co-Authors: Sefer BirhanAbstract:Cotutela Universitat Politècnica de Catalunya i Luleå University of TechnologyThis thesis covers investigation of the Surface Phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion during chemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored Phenomena are related to manufacturing and service conditions of aero-engine components. During manufacturing and operation, the alloys are sunjected to elevated temperatures in oxygen environment. In such conditions an oxide on the Surface and an oxygen enriched layer below the oxide, commonly referred as alpha-case is formed. Alpha-case is a hard and brittle layer that is detrimental to the mechanical properties and must therefore be completely eliminated. A conventional method for elimination of alpha-case is chemical processing in HF/HNO3 solutions, i.e. chemical milling. Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carried out in this thesis. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Mo exhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linear oxidation rate was observed at 700 ºC and = 200 hours for both alloys. The difference in the oxidation kinetics of the two alloys is suggested to be related with the chemical composition of the alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thickness was measured using conventional metallographic and microscopic techniques. The parabolic rate constants, the oxygen diffusion parameters and activation energies were estimated in the temperature range of 500-700 ºC for both alloys. Moreover, the oxidation for 500 hours at 700 ºC resulted in microstructural changes and element re-distribution. The bulk and alpha-case layer hardness at micro- and nano-scale were measured using microhardness and nanoindentation techniques. The alpha-case layer had higher hardness due to the solid solution strengthening effect of the diffused oxygen. The effect of chemical milling in 1:11 HF/HNO3 solution on the Surface integrity, and the influence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy was investigated. Five and sixty minutes chemical processing times and three imposed total strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observed for the samples etched before LCF testing, as compared to the non-etched samples. The influence from etching was found to be most detrimental for fatigue samples tested at the lowest strain ranges. The fatigue life reduction was correlated with the number of crack initiation sites. Multiple crack initiation sites were observed for the etched samples, whereas only one crack initiation site was discerned in the non-etched samples. Inspection of the Surface of the etched samples revealed selective and severely etched prior ß grain boundaries and pit formation at the triple joints of the prior ß grain boundaries. These Surface defects were considered as stress raisers promoting an earlier fatigue crack initiation. The influence of two molar concentration ratios of HF and HNO3 acids (1:3 and 1:11) on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigated by electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the two alloys was a function of the concentration ratio of the acids and also of the alloys¿ chemical compositions. The AFM measurements showed faster dissolution rate of the a-phase than the ß-phase in the Widmanstätten microstructure. It was considered that the reason for this is formation of local micro-galvanic cells between the phases. Moreover, the Volta-potential was measured using scanning Kelvin probe force microscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential between the a- and the ß-laths in both alloys. This observation strengthened the likelihood for formation and operation of micro-galvanic cells between the phases.En esta tesis doctoral se estudian los fenómenos superficiales relacionados con la oxidación a alta temperatura y la corrosión producidos durante el tratamiento químico en soluciones de ácido fluorhídrico-nítrico (HF-HNO3) en las aleaciones Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo. Estos fenómenos se producen durante la fabricación y el servicio de componentes para motores aeronáuticos, pues se dan condiciones de elevada temperatura en un ambiente rico en oxígeno, las cuales favorecen la formación de óxido en la superficie y también de una capa enriquecida en oxígeno debajo del óxido, comúnmente conocida como alpha-case o capa alfa. La alpha-case es una capa dura y frágil, perjudicial para las propiedades mecánicas, por lo que debe ser minimizada o totalmente eliminada. Un método convencional para eliminar la capa alfa es el procesado químico en soluciones de ácido fluorhídrico-nítrico, conocido como chemical milling. En este estudio se han efectuado tratamientos isotérmicos en aire a 500, 593 y 700 °C, con duración máxima de 500 horas. Ambas aleaciones desarrollaron óxido tipo rutilo, en tanto que la Ti-6Al-2Sn-4Zr-2Mo mostró mejor resistencia a la oxidación que la Ti-6Al-4V. Se observó una transición de la velocidad de oxidación de parabólica a lineal a 700 °C y tiempos = 200 horas, para ambas aleaciones. Las diferencias en la cinética de oxidación entre ambas aleaciones se han relacionado con su composición química. La capa rica en oxígeno, i.e. alpha-case, fue caracterizada y su espesor medido mediante técnicas metalográficas. Se observó que la velocidad de crecimiento de la capa alfa seguía una relación parabólica con el tiempo para ambas aleaciones. La difusión del oxígeno y la energía de activación se estimaron en el rango de temperaturas de 500-700 °C. Adicionalmente, se comprobé que el tratamiento isotérmico a 700 °C durante 500 horas dio lugar a cambios microestructurales y a la redistribución de elementos. Las durezas del interior y de la capa alfa se midieron a escalas micro- y nano- mediante técnicas de microdureza y nanoindentación. La capa alfa mostró mayor dureza debido al efecto de endurecimiento por solución sólida debido al oxígeno difundido. El efecto de la solución 1:11 HF-HNO3 en la integridad superficial y en la resistencia a fatiga en el régimen de oligofatiga (LCF = Low Cycle Fatigue) de la aleación Ti-6Al-2Sn-4Zr-2Mo fue investigado. Se evaluaron tiempos de procesado químico cortos y largos (5 y 60 minutos) y tres valores de amplitud de deformación total. Se observó una significativa disminución de la vida a fatiga para las muestras atacadas antes de los ensayos LCF, en comparación con las muestras no atacadas. La influencia del ataque se mostró más perjudicial a bajos valores de deformación impuesta. La reducción en la vida a fatiga se correlacionó con el número de zonas de iniciación de grietas. Múltiples zonas se observaron para las muestras atacadas, mientras que solo un lugar de nucleación de grieta se detectó para las no atacadas. La inspección de las superficies de las muestras atacadas reveló un ataque selectivo y severo en los bordes de grano prior beta y la formación de picaduras en los puntos triples de los bordes de grano prior beta. Estos defectos superficiales fueron considerados como exaltadores de tensiones que promueven la temprana nucleación de las grietas de fatiga. Se investigó la influencia en el comportamiento a corrosión de Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo de dos diferentes relaciones de concentración (1:3 y 1:11) de los ácidos HF y HNO3. Se emplearon para ello técnicas electroquímicas y microscopía de fuerza atómica (AFM). La corrosión de las dos aleaciones depende de la concentración de HF-HNO3 y posiblemente también de sus composiciones químicas. Las medidas de AFM revelaron una velocidad de disolución mayor de la fase alfa que de la beta en la microestructura tipo Widmanstätten. Se considera que la razón de esta disolución selectiva es la formación de celdas micro-galvánicas.Postprint (published version
Sivabalan Sakthivel - One of the best experts on this subject based on the ideXlab platform.
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synergistic effect of lactam ammonium and hydroxyl ammonium based ionic liquids with and without nacl on the Surface Phenomena of crude oil water system
Fluid Phase Equilibria, 2015Co-Authors: Sivabalan Sakthivel, Pratap K Chhotaray, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Abstract Typical surfactants have been found to be less efficient in harsh conditions of temperature and salinity. The need for alternatives is in great demand which is expected to be resolved through the use of ionic liquids, being the area of the present research. In the present investigation, eleven different ionic liquids (ILs) from three various families, namely, lactam, ammonium and hydroxyl ammonium based ionic liquids with various anions, such as, [HCOO]−, [CH3COO]−, [C6H13COO]− and [CF3COO]− are studied to understand the Surface phenomenon of water and crude oil–water system. In addition, the synergistic effects of NaCl on the Surface tension (SFT) and interfacial tension (IFT) are also investigated in the presence of ionic liquid. The impacts of the ring size, alkyl chain length, temperature, concentration of ILs, the nature of cation and anions on the SFT/IFT are evaluated in the temperature range of 288.15–318.15 K with various concentrations of ILs. In addition, the electrical conductivity of aqueous solution of ILs are also presented to understand the critical aggregation concentration (cac) range of studied ILs. The exploration of SFT/IFT of water and crude oil–water systems divulge the fact that the ILs with NaCl are useful in minimizing the Surface forces and thus, it could assist in impressively augmenting oil recovery, flow assurance and oil/gas production operations as well as being environment friendly.
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use of aromatic ionic liquids in the reduction of Surface Phenomena of crude oil water system and their synergism with brine
Industrial & Engineering Chemistry Research, 2015Co-Authors: Sivabalan Sakthivel, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil–water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil–water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]− in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of Surface tension (SFT) of water and interfacial tension of crude oil–water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperatu...
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Use of Aromatic Ionic Liquids in the Reduction of Surface Phenomena of Crude Oil–Water System and their Synergism with Brine
2015Co-Authors: Sivabalan Sakthivel, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil–water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil–water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]− in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of Surface tension (SFT) of water and interfacial tension of crude oil–water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperature and concentration of ILs. The study reveals that these ILs are effective in reducing the SFT and IFT of water and crude oil–water systems at high salinity and temperature conditions. In the IFT measurements, a linear decrement with increase in temperature is observed for crude oil–water in the presence of ILs. The interfacial tension of the various imidazolium-based ionic liquids with the crude oil–water system has been measured as a function of temperature by means of the Wilhelmy plate method. The influence of the nature of cation and anion of ionic liquids and of the chain length on the cationic head of the ILs on interfacial tension is also discussed in detail. At increased salinity conditions, unlike classical surfactants, these ILs are found to be more successful. Enhanced efficiency of the drop in IFT using NaCl and IL mixture has been confirmed by measuring the IFT between crude oil and the aqueous solution of IL. The synergism of salt and IL mixture on the reduction of IFT has been observed
Natalie A Krivova - One of the best experts on this subject based on the ideXlab platform.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of solar Surface Phenomena
Astronomy and Astrophysics, 2014Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:Aims. We present a point spread function (PSF) for the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and discuss the effects of its removal on the apparent properties of solar Surface Phenomena in HMI data. Methods. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the Venusian disc and solar background with a guess PSF. We described the PSF as the sum of five Gaussian functions, the amplitudes of which vary sinusoidally with azimuth. This relatively complex functional form was required by the data. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. We also examined the variation in the shape of the solar aureole in daily data, as an indication of PSF changes over time. Results. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 6173 A line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the solar disc. The shape of the solar aureole varied, with time and between the two CCDs. There are also indications that the PSF varies across the FOV. However, all these variations were found to be relatively small, such that a single PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Conclusions. Restoring HMI observations with the PSF presented here returns a reasonable estimate of the stray light-free intensity contrast. Image restoration affects the measured radiant, magnetic and dynamic properties of solar Surface Phenomena sufficiently to significantly impact interpretation.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of solar Surface Phenomena
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:We present a PSF for SDO/HMI and discuss the effects of its removal on the apparent properties of solar Surface Phenomena in HMI data. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the venusian disc and solar background with a guess PSF. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 617.3 nm line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the solar disc. There are indications that the PSF varies across the FOV, with time and between the two CCDs. However, all these variations were found to be relatively small, such that the derived PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Image restoration affects the measured radiant, magnetic and dynamic properties of solar Surface Phenomena sufficiently to significantly impact interpretation.
Sugirtha Velusamy - One of the best experts on this subject based on the ideXlab platform.
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synergistic effect of lactam ammonium and hydroxyl ammonium based ionic liquids with and without nacl on the Surface Phenomena of crude oil water system
Fluid Phase Equilibria, 2015Co-Authors: Sivabalan Sakthivel, Pratap K Chhotaray, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Abstract Typical surfactants have been found to be less efficient in harsh conditions of temperature and salinity. The need for alternatives is in great demand which is expected to be resolved through the use of ionic liquids, being the area of the present research. In the present investigation, eleven different ionic liquids (ILs) from three various families, namely, lactam, ammonium and hydroxyl ammonium based ionic liquids with various anions, such as, [HCOO]−, [CH3COO]−, [C6H13COO]− and [CF3COO]− are studied to understand the Surface phenomenon of water and crude oil–water system. In addition, the synergistic effects of NaCl on the Surface tension (SFT) and interfacial tension (IFT) are also investigated in the presence of ionic liquid. The impacts of the ring size, alkyl chain length, temperature, concentration of ILs, the nature of cation and anions on the SFT/IFT are evaluated in the temperature range of 288.15–318.15 K with various concentrations of ILs. In addition, the electrical conductivity of aqueous solution of ILs are also presented to understand the critical aggregation concentration (cac) range of studied ILs. The exploration of SFT/IFT of water and crude oil–water systems divulge the fact that the ILs with NaCl are useful in minimizing the Surface forces and thus, it could assist in impressively augmenting oil recovery, flow assurance and oil/gas production operations as well as being environment friendly.
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use of aromatic ionic liquids in the reduction of Surface Phenomena of crude oil water system and their synergism with brine
Industrial & Engineering Chemistry Research, 2015Co-Authors: Sivabalan Sakthivel, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil–water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil–water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]− in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of Surface tension (SFT) of water and interfacial tension of crude oil–water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperatu...
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Use of Aromatic Ionic Liquids in the Reduction of Surface Phenomena of Crude Oil–Water System and their Synergism with Brine
2015Co-Authors: Sivabalan Sakthivel, Sugirtha Velusamy, Ramesh L Gardas, Jitendra S SangwaiAbstract:Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil–water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil–water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]− in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of Surface tension (SFT) of water and interfacial tension of crude oil–water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperature and concentration of ILs. The study reveals that these ILs are effective in reducing the SFT and IFT of water and crude oil–water systems at high salinity and temperature conditions. In the IFT measurements, a linear decrement with increase in temperature is observed for crude oil–water in the presence of ILs. The interfacial tension of the various imidazolium-based ionic liquids with the crude oil–water system has been measured as a function of temperature by means of the Wilhelmy plate method. The influence of the nature of cation and anion of ionic liquids and of the chain length on the cationic head of the ILs on interfacial tension is also discussed in detail. At increased salinity conditions, unlike classical surfactants, these ILs are found to be more successful. Enhanced efficiency of the drop in IFT using NaCl and IL mixture has been confirmed by measuring the IFT between crude oil and the aqueous solution of IL. The synergism of salt and IL mixture on the reduction of IFT has been observed
