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Masakazu Aono - One of the best experts on this subject based on the ideXlab platform.
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Structural studies of Copper Sulfide films: effect of ambient atmosphere
Science and Technology of Advanced Materials, 2008Co-Authors: Manisha Kundu, Tsuyoshi Hasegawa, Kazuya Terabe, Kazuhiro Yamamoto, Masakazu AonoAbstract:We examined the structural properties of Copper Sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper Sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the Copper Sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of Copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films.
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Effect of sulfurization conditions on structural and electrical properties of Copper Sulfide films
Journal of Applied Physics, 2008Co-Authors: Manisha Kundu, Tsuyoshi Hasegawa, Kazuya Terabe, Masakazu AonoAbstract:We examined the structural and electrical properties of Copper Sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper Sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and mixed roxbyite-covellite phases were formed with increasing sulfurization time. The Cu∕S atomic percentage ratio of the films decreased with increasing sulfurization time, and films with various compositions such as Cu-rich and stoichiometric Copper Sulfide with underlying unreacted Cu as well as pure stoichiometric and S-rich Copper Sulfide were obtained. The surface morphology and the electrical resistivity of the films depended on the chemical phase and composition of the films. The resistivity decreased with increasing Cu deficiency in the films. Distinct switching of the resistance from high to low-state, and vice versa, with the reversal of the bias polarity of the film was observed only for the mixed metallic Cu-chalcocite phased film with underlying Cu. H...
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nanometer scale switches using Copper Sulfide
Applied Physics Letters, 2003Co-Authors: Toshitsugu Sakamoto, Hiroshi Sunamura, Hisao Kawaura, Tsuyoshi Hasegawa, Tomonobu Nakayama, Masakazu AonoAbstract:We describe a nanometer-scale switch that uses a Copper Sulfide film and demonstrate its performance. The switch consists of a Copper Sulfide film, which is a chalcogenide semiconductor, sandwiched between Copper and metal electrodes. Applying a positive or negative voltage to the metal electrode can repeatedly switch its conductance in under 100 μs. Each state can persist without a power supply for months, demonstrating the feasibility of nonvolatile memory with its nanometer scale. While biasing voltages, Copper ions can migrate in Copper Sulfide film and can play an important role in switching.
S. Toyama - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen generation by adding passivator for suppressing Copper-Sulfide deposition in transformers
IEEE Transactions on Dielectrics and Electrical Insulation, 2017Co-Authors: F. Kato, T. Amimoto, R. Nishiura, K. Mizuno, S. ToyamaAbstract:Generation of hydrogen from oils with the addition of passivators such as 1, 2, 3-benzotriazole (BTA) and Irgamet® 39 for suppressing Copper Sulfide deposition was investigated by heating tests. Large amounts of hydrogen were generated from the oils with the addition of Irgamet® 39 compared to the oils with the addition of BTA. BTA is suitable in terms of less generation of hydrogen. For Irgamet® 39 added oils, the amounts of hydrogen increase with an increase in oxygen concentration. Irgamet® 39 was consumed by thermal decomposition and oxidation. Consumption by oxidation of Irgamet® 39 is considered to be affected to the hydrogen generation. Amounts of hydrogen increase with increase in heating temperature for a certain period of time. After conducting heating test, Irgamet® 39 was remained in oil. Total amount of hydrogen, which is defined by sum of the amount of hydrogen generated by consumed Irgamet® 39 and the amount of hydrogen generated by residual Irgamet® 39, are considered to be independent of heating temperature. Effects of additives such as dibenzyl diSulfide, which is one of the prime compounds that cause the Copper Sulfide deposition, and 2, 6 ditertiary-butyl paracresol as antioxidant on hydrogen generation were significant. Consequently, in case of adding Irgamet® 39 for the purpose of suppressing Copper Sulfide deposition, installation of a conservator system and rubber bag which reduces the dissolution of oxygen into the oil is effective to minimize the amount of hydrogen.
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Suppressive effect and its duration of triazole-based passivators on Copper Sulfide deposition on kraft paper in transformer
IEEE Transactions on Dielectrics and Electrical Insulation, 2013Co-Authors: F. Kato, K Mizuno, T. Amimoto, R. Nishiura, S. ToyamaAbstract:The suppressive effect of triazole-based passivators such as 1,2,3-benzotriazole (BTA) and Irgamet 39 and duration of the suppressive effect on Copper Sulfide deposition are investigated by changing the time when passivators are added to oil. All corrosive sulfur tests were performed by the method stipulated by IEC 62535. In order to simulate the timing for adding passivators into actual transformers, preheated and non-preheated oils were used for corrosive sulfur test. Adding a passivator into preheated oil simulates the condition where a passivator is added into the transformer after a period of operation, and adding a passivator into non-preheated oil simulates the condition where a passivator is added before operation. Although the deposition rate of Copper Sulfide in preheated oil with the addition of passivator was lower in preheated oil without passivator, Copper Sulfide deposition still continued even while the passivator was detected in the oil. The result suggests that the precursors of Copper Sulfide have been already generated in preheated oil before adding a passivator. After the passivator was depleted in the oil, the period until onset of Copper Sulfide deposition in the preheated oil was shorter than in non-preheated oil since a protective complex layer was created on the Copper surface and reaction with the passivator continued to prevent the deposition of Copper Sulfide precursors.
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Influences of oxygen and 2,6-di-tert-butyl-p-cresol on Copper Sulfide deposition on insulating paper in oil-immersed transformer insulation
IEEE Transactions on Dielectrics and Electrical Insulation, 2012Co-Authors: H. Kawarai, Y. Uehara, S. Toyama, E. Nagao, N. Hosokawa, K Mizuno, T. AmimotoAbstract:Copper Sulfide deposition on cellulosic insulating materials in oil-immersed transformers was investigated by heating tests stipulated by IEC 62535 with controlled atmospheres to which mineral insulating oils were exposed. Both oxygen in the atmosphere and 2,6-di-tert-butyl-p-cresol (DBPC) in the oil were found to accelerate the Copper Sulfide deposition on the insulating paper when the oil contains dibenzyl diSulfide (DBDS). The weight of Copper Sulfide deposition on the insulating paper was found to increase when the oxygen concentration was increased up to 20 volume %. X-ray absorption near edge structure (XANES) analysis was applied to study the chemical bonding state of Copper atoms in Copper deposits on the insulating paper for the first time. It can be clarified the Copper deposits on the insulating paper are mainly Cu2S and small amounts of CuO are contained.
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Influence of inhibitor and oil components on Copper Sulfide deposition on kraft paper in oil-immersed insulation
IEEE Transactions on Dielectrics and Electrical Insulation, 2011Co-Authors: S. Toyama, E. Nagao, T. Amimoto, K Mizuno, F. Kato, N. HosokawaAbstract:Copper Sulfide deposition on Kraft paper in oil-immersed transformers is found to be accelerated by di-tert-butyl p-cresol (DBPC), which is widely used as an antioxidant, and paraffinic hydrocarbons in their oils, which is verified in laboratory experiments. DBPC can prolong the lifetime of precursors of the Copper Sulfide deposition by reacting decomposition products of Copper dibenzyl diSulfide (Cu-DBDS) complex and by creating the Cu-DBPC complex. Because the lifetime of the Cu-DBPC complex is far longer than that of the Cu-DBDS complex, considerable amounts of Copper Sulfide are deposited on Kraft paper instead of being formed on the surface of Copper. A good correlation is obtained between the concentration of paraffinic hydrocarbons and the amount of Copper Sulfide deposited on Kraft paper in the three commercial oils.
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Effect of DBDS concentration and heating duration on Copper Sulfide formation in oil-immersed transformer insulation
IEEE Transactions on Dielectrics and Electrical Insulation, 2011Co-Authors: F. Kato, S. Toyama, E. Nagao, N. Hosokawa, T. Amimoto, J. TanimuraAbstract:Copper Sulfide is found to be more likely formed on Kraft paper in oil-immersed transformers with an increase in either dibenzyl diSulfide (DBDS) concentration or heating duration, which is verified by heating tests stipulated by IEC 62535. Two effects of DBDS concentration on the formation rates of Copper Sulfide were obtained. The formation rates of investigated oils are proportional to the DBDS concentration when the concentration is low. However, the amounts of Copper on the Kraft papers are constant when the DBDS concentrations are more than certain values, which is considered to reflect the saturation of dissolving DBDS-Cu complex in the oil. These concentrations depend on oil brand. Copper Sulfide begins to form after some duration of heating and the duration decreases with an increase in the DBDS concentration. Copper Sulfide formed on the Kraft paper is a portion of the total Copper reacted with DBDS by comparing the amount of Copper formed on the Kraft paper with the total amount of reacted Copper calculated from the amount of consumed DBDS.
T. Amimoto - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen generation by adding passivator for suppressing Copper-Sulfide deposition in transformers
IEEE Transactions on Dielectrics and Electrical Insulation, 2017Co-Authors: F. Kato, T. Amimoto, R. Nishiura, K. Mizuno, S. ToyamaAbstract:Generation of hydrogen from oils with the addition of passivators such as 1, 2, 3-benzotriazole (BTA) and Irgamet® 39 for suppressing Copper Sulfide deposition was investigated by heating tests. Large amounts of hydrogen were generated from the oils with the addition of Irgamet® 39 compared to the oils with the addition of BTA. BTA is suitable in terms of less generation of hydrogen. For Irgamet® 39 added oils, the amounts of hydrogen increase with an increase in oxygen concentration. Irgamet® 39 was consumed by thermal decomposition and oxidation. Consumption by oxidation of Irgamet® 39 is considered to be affected to the hydrogen generation. Amounts of hydrogen increase with increase in heating temperature for a certain period of time. After conducting heating test, Irgamet® 39 was remained in oil. Total amount of hydrogen, which is defined by sum of the amount of hydrogen generated by consumed Irgamet® 39 and the amount of hydrogen generated by residual Irgamet® 39, are considered to be independent of heating temperature. Effects of additives such as dibenzyl diSulfide, which is one of the prime compounds that cause the Copper Sulfide deposition, and 2, 6 ditertiary-butyl paracresol as antioxidant on hydrogen generation were significant. Consequently, in case of adding Irgamet® 39 for the purpose of suppressing Copper Sulfide deposition, installation of a conservator system and rubber bag which reduces the dissolution of oxygen into the oil is effective to minimize the amount of hydrogen.
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Suppressive effect and its duration of triazole-based passivators on Copper Sulfide deposition on kraft paper in transformer
IEEE Transactions on Dielectrics and Electrical Insulation, 2013Co-Authors: F. Kato, K Mizuno, T. Amimoto, R. Nishiura, S. ToyamaAbstract:The suppressive effect of triazole-based passivators such as 1,2,3-benzotriazole (BTA) and Irgamet 39 and duration of the suppressive effect on Copper Sulfide deposition are investigated by changing the time when passivators are added to oil. All corrosive sulfur tests were performed by the method stipulated by IEC 62535. In order to simulate the timing for adding passivators into actual transformers, preheated and non-preheated oils were used for corrosive sulfur test. Adding a passivator into preheated oil simulates the condition where a passivator is added into the transformer after a period of operation, and adding a passivator into non-preheated oil simulates the condition where a passivator is added before operation. Although the deposition rate of Copper Sulfide in preheated oil with the addition of passivator was lower in preheated oil without passivator, Copper Sulfide deposition still continued even while the passivator was detected in the oil. The result suggests that the precursors of Copper Sulfide have been already generated in preheated oil before adding a passivator. After the passivator was depleted in the oil, the period until onset of Copper Sulfide deposition in the preheated oil was shorter than in non-preheated oil since a protective complex layer was created on the Copper surface and reaction with the passivator continued to prevent the deposition of Copper Sulfide precursors.
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Influences of oxygen and 2,6-di-tert-butyl-p-cresol on Copper Sulfide deposition on insulating paper in oil-immersed transformer insulation
IEEE Transactions on Dielectrics and Electrical Insulation, 2012Co-Authors: H. Kawarai, Y. Uehara, S. Toyama, E. Nagao, N. Hosokawa, K Mizuno, T. AmimotoAbstract:Copper Sulfide deposition on cellulosic insulating materials in oil-immersed transformers was investigated by heating tests stipulated by IEC 62535 with controlled atmospheres to which mineral insulating oils were exposed. Both oxygen in the atmosphere and 2,6-di-tert-butyl-p-cresol (DBPC) in the oil were found to accelerate the Copper Sulfide deposition on the insulating paper when the oil contains dibenzyl diSulfide (DBDS). The weight of Copper Sulfide deposition on the insulating paper was found to increase when the oxygen concentration was increased up to 20 volume %. X-ray absorption near edge structure (XANES) analysis was applied to study the chemical bonding state of Copper atoms in Copper deposits on the insulating paper for the first time. It can be clarified the Copper deposits on the insulating paper are mainly Cu2S and small amounts of CuO are contained.
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Influence of inhibitor and oil components on Copper Sulfide deposition on kraft paper in oil-immersed insulation
IEEE Transactions on Dielectrics and Electrical Insulation, 2011Co-Authors: S. Toyama, E. Nagao, T. Amimoto, K Mizuno, F. Kato, N. HosokawaAbstract:Copper Sulfide deposition on Kraft paper in oil-immersed transformers is found to be accelerated by di-tert-butyl p-cresol (DBPC), which is widely used as an antioxidant, and paraffinic hydrocarbons in their oils, which is verified in laboratory experiments. DBPC can prolong the lifetime of precursors of the Copper Sulfide deposition by reacting decomposition products of Copper dibenzyl diSulfide (Cu-DBDS) complex and by creating the Cu-DBPC complex. Because the lifetime of the Cu-DBPC complex is far longer than that of the Cu-DBDS complex, considerable amounts of Copper Sulfide are deposited on Kraft paper instead of being formed on the surface of Copper. A good correlation is obtained between the concentration of paraffinic hydrocarbons and the amount of Copper Sulfide deposited on Kraft paper in the three commercial oils.
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Effect of DBDS concentration and heating duration on Copper Sulfide formation in oil-immersed transformer insulation
IEEE Transactions on Dielectrics and Electrical Insulation, 2011Co-Authors: F. Kato, S. Toyama, E. Nagao, N. Hosokawa, T. Amimoto, J. TanimuraAbstract:Copper Sulfide is found to be more likely formed on Kraft paper in oil-immersed transformers with an increase in either dibenzyl diSulfide (DBDS) concentration or heating duration, which is verified by heating tests stipulated by IEC 62535. Two effects of DBDS concentration on the formation rates of Copper Sulfide were obtained. The formation rates of investigated oils are proportional to the DBDS concentration when the concentration is low. However, the amounts of Copper on the Kraft papers are constant when the DBDS concentrations are more than certain values, which is considered to reflect the saturation of dissolving DBDS-Cu complex in the oil. These concentrations depend on oil brand. Copper Sulfide begins to form after some duration of heating and the duration decreases with an increase in the DBDS concentration. Copper Sulfide formed on the Kraft paper is a portion of the total Copper reacted with DBDS by comparing the amount of Copper formed on the Kraft paper with the total amount of reacted Copper calculated from the amount of consumed DBDS.
Lijun Yang - One of the best experts on this subject based on the ideXlab platform.
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Corrosion Mechanisms for Electrical Fields Leading to the Acceleration of Copper Sulfide Deposition on Insulation Windings
Industrial & Engineering Chemistry Research, 2017Co-Authors: Lijun Yang, Bangfei Deng, Zhidong ChengAbstract:Numerous failures of high-voltage transformers and reactors are caused by Copper Sulfide formation in oil-immersed insulations. This study explored the effect of electrical fields on Copper Sulfide formation. Accelerated aging experiments were conducted for mineral oil that contains dibenzyl diSulfide, which was aged along with insulation windings under different conditions, including single thermal aging and electrical–thermal aging. The corrosive sulfur deposits were quantified using SEM/EDX and ICP-AES. The properties of the insulation oils were also measured and analyzed. Corrosion mechanisms for electrical fields leading to the acceleration of Copper Sulfide deposition on the oil-immersed insulation were proposed.
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Corrosion Mechanisms for Electrical Fields Leading to the Acceleration of Copper Sulfide Deposition on Insulation Windings
Industrial and Engineering Chemistry Research, 2017Co-Authors: Lijun Yang, Sihang Gao, Bangfei Deng, Zhidong ChengAbstract:© 2017 American Chemical Society. Numerous failures of high-voltage transformers and reactors are caused by Copper Sulfide formation in oil-immersed insulations. This study explored the effect of electrical fields on Copper Sulfide formation. Accelerated aging experiments were conducted for mineral oil that contains dibenzyl diSulfide, which was aged along with insulation windings under different conditions, including single thermal aging and electrical-thermal aging. The corrosive sulfur deposits were quantified using SEM/EDX and ICP-AES. The properties of the insulation oils were also measured and analyzed. Corrosion mechanisms for electrical fields leading to the acceleration of Copper Sulfide deposition on the oil-immersed insulation were proposed.
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Effects of electric fields on Copper Sulfide deposition and the properties of insulating oils in oil-immersed transformers
IEEE Transactions on Dielectrics and Electrical Insulation, 2017Co-Authors: Lijun Yang, Bangfei Deng, Jie Tang, Jia-jia HuangAbstract:The failures of high-voltage transformers and reactors can result from the deposition of Copper Sulfide on the oil-impregnated paper insulation. This study explored the influence of electric fields on Copper Sulfide deposition and the properties of insulating oils as a result of the reaction of dibenzyl diSulfide (DBDS) with Copper in oil-immersed transformers. Accelerated aging experiments were conducted for pig-tail windings under two sets of conditions, namely, thermal aging only at 140 °C and AC/DC electrical and thermal aging at 5 kV/140 °C under low oxygen condition. This was combined with oil containing dibenzyl diSulfide (DBDS) added to the non-corrosive oil to a concentration of 200 mg/kg. The corrosive sulfur deposits were examined by observing the surface morphology of the windings and measuring the Copper and sulfur contents on the windings via inductively coupled plasma-atomic emission spectrometry and a precipitation method. The properties of the insulating oils were measured and analyzed at intervals. The results indicate that electric fields increased the amount of deposited Copper Sulfide on the windings. The higher the electric field strength, the higher the amount of deposited Copper Sulfide on the insulating paper surface. Subjecting the oil-paper insulation to electric field and elevated temperature generates dissolved Copper in the insulating oil. The electric field can promote the dissolution of Copper in oil. The ageing oil under thermal and electrical stresses promote Copper dissolution and increase corrosion rate.
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Influence of wrapped paper and atmosphere on the deposition of Copper Sulfide induced by the dibenzyl diSulfide in oil-immersed insulation
2016 IEEE Electrical Insulation Conference (EIC), 2016Co-Authors: Lijun Yang, Yuan Yuan, Jiang Zhang, Bangfei DengAbstract:Many failures of high-voltage transformers and reactors occurred because of Copper Sulfide formation and deposition, this study aims to explore the influence of the insulating paper and atmosphere on the deposition of Copper Sulfide on the insulating windings as a result of the reaction of dibenzyl diSulfide (DBDS) with Copper in oil-immersed insulation. The accelerated thermal aging experiments under atmosphere (Nitrogen and air) conditions at 130°C were conducted by adding 1000mg/L dibenzyl diSulfide (DBDS) and the insulation windings which half of Copper strip were wrapped insulating paper to the mineral insulation oil. The deposition of Copper Sulfide were studied by observing the surface morphology of windings and analyzing the surface components of the windings by EDX. The results indicate that Copper Sulfide is prone to deposition on the Copper strip surface which is wrapped by the insulating paper. Few Copper Sulfide is deposited on the bare Copper strip under nitrogen, but Copper Sulfide is deposited on the Copper strip under air. Meanwhile, the sediments of Copper Sulfide deposition on the Copper strip under air are much higher than that under nitrogen, and more sediments of Copper Sulfide are deposited on the insulating paper under air than on the insulating paper under nitrogen. Moreover, the effect of wrapped paper and atmosphere on the mechanism of Copper Sulfide deposition will be discussed.
Paul Jarman - One of the best experts on this subject based on the ideXlab platform.
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Tracking Copper Sulfide formation in corrosive transformer oil
Electrical Insulation and Dielectric Phenomena (CEIDP), 2013 IEEE Conference on, 2013Co-Authors: P. Amaro, R. C. D. Brown, J. A. Pilgrim, A. F. Holt, Paul L. Lewin, M. Facciotti, G Wilson, Paul JarmanAbstract:Corrosive sulfur in the last decade has been recognized as a major risk to high voltage transformers. An initial study undertaken by CIGRE on Copper Sulfide in transformer insulation investigated possible sources, i.e. Dibenzyl DiSulfide (DBDS), it also looked at possible mitigating techniques, i.e. passivation, environmental influences, i.e. temperature, and improvement to oil corrosion standards, i.e. EN 62535. Although there was significant volume of research undertaken the high voltage industry still felt there is a lack of understanding in the process of Copper Sulfide formation and long-term effects of mitigation techniques. Hence a new CIGRE transformer working group, A2.40, was created. The identification of techniques with the ability to track the mechanism of Copper Sulfide (Cu2S) formation is fundamental to the current research objectives. The technique suggested in this paper involves the use of X-ray fluorescence (XRF), which is used for elemental analysis, to track the quantity of sulfur in the oil. As the deposits of Cu2S form in the conductors and paper insulation the amount of sulfur in the oil decreases. By using a series of laboratory experiments is possible to investigate how the rate of formation of Cu2S changes with time, suggesting that there is an initial chemical reaction needed for the Cu2S deposits to form. Scanning Electron Microscopy with Energy-dispersive X-ray spectroscopy (SEM-EDX) has been used to investigate the surface of Copper at several different stages of the Copper Sulfide formation. By manipulating variables, i.e. temperature, it is possible to map their influence and provide a more precise risk assessment of transformer with corrosive oil to electrical utility companies. The experimental results suggest the possibility of developing a method to indirectly measure Cu2S deposition on conductors and insulation paper by tracking sulfur concentration changes in the transform- r oil.
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Tracking Copper Sulfide formation in corrosive transformer oil
2013 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2013Co-Authors: P. Amaro, R. C. D. Brown, J. A. Pilgrim, A. F. Holt, Paul L. Lewin, M. Facciotti, G Wilson, Paul JarmanAbstract:Corrosive sulfur in the last decade has been recognized as a major risk to high voltage transformers. An initial study undertaken by CIGRE on Copper Sulfide in transformer insulation investigated possible sources, i.e. Dibenzyl DiSulfide (DBDS), it also looked at possible mitigating techniques, i.e. passivation, environmental influences, i.e. temperature, and improvement to oil corrosion standards, i.e. EN 62535. Although there was significant volume of research undertaken the high voltage industry still felt there is a lack of understanding in the process of Copper Sulfide formation and long-term effects of mitigation techniques. Hence a new CIGRE transformer working group, A2.40, was created. The identification of techniques with the ability to track the mechanism of Copper Sulfide (Cu2S) formation is fundamental to the current research objectives. The technique suggested in this paper involves the use of X-ray fluorescence (XRF), which is used for elemental analysis, to track the quantity of sulfur in the oil. As the deposits of Cu2S form in the conductors and paper insulation the amount of sulfur in the oil decreases. By using a series of laboratory experiments is possible to investigate how the rate of formation of Cu2S changes with time, suggesting that there is an initial chemical reaction needed for the Cu2S deposits to form. Scanning Electron Microscopy with Energy-dispersive X-ray spectroscopy (SEM-EDX) has been used to investigate the surface of Copper at several different stages of the Copper Sulfide formation. By manipulating variables, i.e. temperature, it is possible to map their influence and provide a more precise risk assessment of transformer with corrosive oil to electrical utility companies. The experimental results suggest the possibility of developing a method to indirectly measure Cu2S deposition on conductors and insulation paper by tracking sulfur concentration changes in the transformer oil.