There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by... more There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by public concern over traditional waste handling methodologies, to identify safe and efficient alternative technologies. One very effective process for the destruction of such waste is supercritical water oxidation (SCWO). By capitalizing on the properties of water above its critical point (374 C and 22.4 MPa for pure water), this technology provides rapid and complete oxidation with high destruction efficiencies at typical operating temperatures. Nevertheless, corrosion of the materials of fabrication is a serious concern. While nickel and nickel-based alloys are generally considered important for severe service applications, results from laboratory and pilot-scale SCWO systems presently in operation indicate that they will not withstand some aggressive feeds. Significant weight loss and localized effects, including stress corrosion cracking (SCC) and dealloying, are seen in chlorinated environments. The current paper assesses the corrosion characteristics of various alloys exposed to high supercritical temperatures in a chlorinated feed stream containing salts.
For corrosion to occur on a coated metal surface, an electrochemical double layer must be establi... more For corrosion to occur on a coated metal surface, an electrochemical double layer must be established. Hence, the adhesion between the substrate and the coating must be weakened to enable a separate thin layer of water to be formed at the interface from water that has permeated the coating. To prevent the failure of a painted coating, we applied a cathodic protection method. This method has been controversial for a few years because cathodic protection can induce cathodic delamination of the entire surface, especially near the anode, and also because it is not effective on a not-wetted surface from the anode. We therefore evaluated the efficiency of cathodic protection for 700 days in an atmospheric environment and performed surface observation, AC impedance measurements and corrosion tests. In the case of a noncathodic protected painted steel specimen, blisters formed after 100 days and grew in number for the remainder of the test. However, cathodic protection of the painted steel increased the coating resistance and extended the lifetime of the coating. According to our calculation with the BEASY program, the thickness of the water film under a rain condition barely influenced the protection potential. The high voltage of the cathodic protection and the subsequent cathodic delamination caused the paint to peel off near the anode. Hence, the protection voltage should be controlled in accordance with changes to the environmental condition.
There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by... more There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by public concern over traditional waste handling methodologies, to identify safe and efficient alternative technologies. One very effective process for the destruction of such waste is supercritical water oxidation (SCWO). By capitalizing on the properties of water above its critical point (374 C and 22.4 MPa for pure water), this technology provides rapid and complete oxidation with high destruction efficiencies at typical operating temperatures. Nevertheless, corrosion of the materials of fabrication is a serious concern. While nickel and nickel-based alloys are generally considered important for severe service applications, results from laboratory and pilot-scale SCWO systems presently in operation indicate that they will not withstand some aggressive feeds. Significant weight loss and localized effects, including stress corrosion cracking (SCC) and dealloying, are seen in chlorinated environments. The current paper assesses the corrosion characteristics of various alloys exposed to high supercritical temperatures in a chlorinated feed stream containing salts.
The hot corrosion behaviors of several alloys and Al diffusion coatings were evaluated by electro... more The hot corrosion behaviors of several alloys and Al diffusion coatings were evaluated by electrochemical impedance technique under molten sulfate film with a special designed electrochemical cell. It was found that corrosion resistance of alloys changed greatly with the changing of atmosphere. For alloys, the atmosphere has much greater effect on corrosion behavior under molten salt film than in bulk molten salt. Meanwhile, Atmosphere did not have significant effect on corrosion behavior of Al diffusion coatings probably due to the instant formation of protective aluminum oxide film under any atmosphere tested. More information about changes in aluminum oxide film properties was also obtained by impedance monitoring. Electrochemical technique was proved to be very useful for the evaluation of hot corrosion resistance of both alloys and protective coatings under molten salt film condition.
Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conduct... more Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conducted. The credibility of HAp coatings on SUS316L stainless steel and the effect of heat treatment were assessed by electrochemical impedance monitoring in physiological saline. The adhesion of HAp coating on SUS316L was evaluated by three-point bending test. It was found that post heat treatment improves not only crystallinity but also the credibility of HAp coatings on SUS316L stainless steel. Also, the corrosion resistance of HAp coating on SUS316L was improved by lowering the cooling or heating rate during post heat treatment process. It was found that plasma titanium intermediate layer played an important role both in improving corrosion resistance of HAp coating on SUS316L stainless steel and in increasing the adhesion of HAp coating layer to the metallic substrate. Zn doped HAp plasma spray coatings was prepared and its credibility was evaluated by electrochemical impedance measurements.
In a super-aged society such as Japan, needs for new type implants which has both excellent bioco... more In a super-aged society such as Japan, needs for new type implants which has both excellent biocompatibility and high functionality are increasing. Hydroxyapatite (HAp) is known to be very biocompatible since it is the main inorganic content of human tooth and bones. The development of HAp plasma spray coating on metallic substrate has been engaged by our lab and other researchers. In this study, Zn doped HAp plasma coatings on Ti and SUS316L were prepared by using Zn doped HAp powder obtained by high temperature sintering of the mixture of ZnO and HAp. The credibility, the functionality and the adhesion were investigated by electrochemical impedance measurements, ICP analysis and two types of adhesion tests. After the mixture of ZnO and HAp was sintered at 1150˚C for 10 hours, ZnO X-ray diffraction peaks reduced greatly. Also, the lattice constants of HAp changed with the change of ZnO percentage in the mixture meaning most Zn2+ ions were embedded into the crystal structure of HAp. Long-term credibility evaluation for Zn doped HAp plasma spray coatings in SUS316L was conducted by electrochemical impedance measurements. The results of impedance results showed that corrosion resistance for coatings with post heat treatment kept in a very high value during 12 weeks immersion in Hanks solution, indicating the post heat treatment improved the stability of Zn doped HAp coatings in SUS316L by changing the coating from amorphous structure to a crystalized one. The results from ICP analysis also proved the higher stability achieved by post heat treatment. The dissolution of Zn2+ ions was detected in Hanks solution which implies the possibility of stimulation to the bone growth. The adhesion evaluation was done by three-points bending test and a standard ASTM adhesion test for Zn doped HAp plasma spray coatings on Ti. Zn doped HAp coatings showed strong adhesion to the metallic substrate. The residual stress in coatings was investigated by x-ray diffraction for understanding the mechanism of strong adhesion.
e c h n o l o g y Possibility of the application of the electrochemial noise analysis to aluminum... more e c h n o l o g y Possibility of the application of the electrochemial noise analysis to aluminum crevice corrosion was studied. Anodic polarization curves with various scanning rates of potential were measured for the aluminum electrode in the artificial crevice. Current noises were measured for the aluminum artificial crevice electrode at various anodic potentials. On the other hand, current noises were measured for the platinum artificial crevice electrode at various cathodic potentials. The short-circuited current noise and the potential noise of the aluminum artificial crevice e l e ctrode coupled with an external aluminum electrode were measured. Any current noises were not obserbed in the region of the potential less noble than crevice potential (Ec), above which the noises were generated due to the hydrogen evolution. This was verifyed by the fact for the hydrogen e v olution on the platinum crevice electrode. Notable noises of synchronized short-circuited current and potential appeared after 50 minutes of immersion being due to the hydrogen evolution. Thus, the natural crevice corrosion was simulated with this short-circuited coupling cell. The potential noise will be considerd as an easy monitoring tool for these crevice corrosion detection, because the potential noise was changed with the current noise in the same period.
The application of electrochemical noise (Fluctuation) analysis for localized corrosion have been... more The application of electrochemical noise (Fluctuation) analysis for localized corrosion have been studied. Foils of zinc, aluminum and magnesium were used as specimens for electrochemical cell simulating localized corrosion. Time variations of short circuited potential and current were measured in these solutions, and simultaneously the surfaces of specimens were observed using microscope with television monitor. Two types fluctuation were detected. In the case of aluminum and magnesium, It was seemed that the fluctuations result from hydrogen evolution on the active site in the crevice. In the case of magnesium, fluctuations appeared on the trendy component of the corrosion potential. And that was random one. It was seemed that these fluctuations result from the hydrogen evolution on the active site in the crevice of magnesium from the microscopic observation. In the case of zinc, It was seemed that the fluctuations result from the dissolution on the active site in the crevice and generation of corrosion products on the cathodic site on the outer site.
Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conduct... more Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conducted. The credibility of HAp coatings on SUS316L stainless steel and the effect of heat treatment were assessed by electrochemical impedance monitoring in physiological saline. The adhesion of HAp coating on SUS316L was evaluated by three-point bending test. It was found that post heat treatment improves not only crystallinity but also the credibility of HAp coatings on SUS316L stainless steel. Also, the corrosion resistance of HAp coating on SUS316L was improved by lowering the cooling or heating rate during post heat treatment process. It was found that plasma titanium intermediate layer played an important role both in improving corrosion resistance of HAp coating on SUS316L stainless steel and in increasing the adhesion of HAp coating layer to the metallic substrate. Zn doped HAp plasma spray coatings was prepared and its credibility was evaluated by electrochemical impedance measureme...
In a super-aged society such as Japan, needs for new type implants which has both excellent bioco... more In a super-aged society such as Japan, needs for new type implants which has both excellent biocompatibility and high functionality are increasing. Hydroxyapatite (HAp) is known to be very biocompatible since it is the main inorganic content of human tooth and bones. The development of HAp plasma spray coating on metallic substrate has been engaged by our lab and other researchers. In this study, Zn doped HAp plasma coatings on Ti and SUS316L were prepared by using Zn doped HAp powder obtained by high temperature sintering of the mixture of ZnO and HAp. The credibility, the functionality and the adhesion were investigated by electrochemical impedance measurements, ICP analysis and two types of adhesion tests. After the mixture of ZnO and HAp was sintered at 1150˚C for 10 hours, ZnO X-ray diffraction peaks reduced greatly. Also, the lattice constants of HAp changed with the change of ZnO percentage in the mixture meaning most Zn2+ ions were embedded into the crystal structure of HAp. Long-term credibility evaluation for Zn doped HAp plasma spray coatings in SUS316L was conducted by electrochemical impedance measurements. The results of impedance results showed that corrosion resistance for coatings with post heat treatment kept in a very high value during 12 weeks immersion in Hanks solution, indicating the post heat treatment improved the stability of Zn doped HAp coatings in SUS316L by changing the coating from amorphous structure to a crystalized one. The results from ICP analysis also proved the higher stability achieved by post heat treatment. The dissolution of Zn2+ ions was detected in Hanks solution which implies the possibility of stimulation to the bone growth. The adhesion evaluation was done by three-points bending test and a standard ASTM adhesion test for Zn doped HAp plasma spray coatings on Ti. Zn doped HAp coatings showed strong adhesion to the metallic substrate. The residual stress in coatings was investigated by x-ray diffraction for understanding the mechanism of strong adhesion.
There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by... more There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by public concern over traditional waste handling methodologies, to identify safe and efficient alternative technologies. One very effective process for the destruction of such waste is supercritical water oxidation (SCWO). By capitalizing on the properties of water above its critical point (374 C and 22.4 MPa for pure water), this technology provides rapid and complete oxidation with high destruction efficiencies at typical operating temperatures. Nevertheless, corrosion of the materials of fabrication is a serious concern. While nickel and nickel-based alloys are generally considered important for severe service applications, results from laboratory and pilot-scale SCWO systems presently in operation indicate that they will not withstand some aggressive feeds. Significant weight loss and localized effects, including stress corrosion cracking (SCC) and dealloying, are seen in chlorinated environments. The current paper assesses the corrosion characteristics of various alloys exposed to high supercritical temperatures in a chlorinated feed stream containing salts.
For corrosion to occur on a coated metal surface, an electrochemical double layer must be establi... more For corrosion to occur on a coated metal surface, an electrochemical double layer must be established. Hence, the adhesion between the substrate and the coating must be weakened to enable a separate thin layer of water to be formed at the interface from water that has permeated the coating. To prevent the failure of a painted coating, we applied a cathodic protection method. This method has been controversial for a few years because cathodic protection can induce cathodic delamination of the entire surface, especially near the anode, and also because it is not effective on a not-wetted surface from the anode. We therefore evaluated the efficiency of cathodic protection for 700 days in an atmospheric environment and performed surface observation, AC impedance measurements and corrosion tests. In the case of a noncathodic protected painted steel specimen, blisters formed after 100 days and grew in number for the remainder of the test. However, cathodic protection of the painted steel increased the coating resistance and extended the lifetime of the coating. According to our calculation with the BEASY program, the thickness of the water film under a rain condition barely influenced the protection potential. The high voltage of the cathodic protection and the subsequent cathodic delamination caused the paint to peel off near the anode. Hence, the protection voltage should be controlled in accordance with changes to the environmental condition.
There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by... more There is a need to destroy both military and civilian hazardous waste and an urgency, mandated by public concern over traditional waste handling methodologies, to identify safe and efficient alternative technologies. One very effective process for the destruction of such waste is supercritical water oxidation (SCWO). By capitalizing on the properties of water above its critical point (374 C and 22.4 MPa for pure water), this technology provides rapid and complete oxidation with high destruction efficiencies at typical operating temperatures. Nevertheless, corrosion of the materials of fabrication is a serious concern. While nickel and nickel-based alloys are generally considered important for severe service applications, results from laboratory and pilot-scale SCWO systems presently in operation indicate that they will not withstand some aggressive feeds. Significant weight loss and localized effects, including stress corrosion cracking (SCC) and dealloying, are seen in chlorinated environments. The current paper assesses the corrosion characteristics of various alloys exposed to high supercritical temperatures in a chlorinated feed stream containing salts.
The hot corrosion behaviors of several alloys and Al diffusion coatings were evaluated by electro... more The hot corrosion behaviors of several alloys and Al diffusion coatings were evaluated by electrochemical impedance technique under molten sulfate film with a special designed electrochemical cell. It was found that corrosion resistance of alloys changed greatly with the changing of atmosphere. For alloys, the atmosphere has much greater effect on corrosion behavior under molten salt film than in bulk molten salt. Meanwhile, Atmosphere did not have significant effect on corrosion behavior of Al diffusion coatings probably due to the instant formation of protective aluminum oxide film under any atmosphere tested. More information about changes in aluminum oxide film properties was also obtained by impedance monitoring. Electrochemical technique was proved to be very useful for the evaluation of hot corrosion resistance of both alloys and protective coatings under molten salt film condition.
Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conduct... more Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conducted. The credibility of HAp coatings on SUS316L stainless steel and the effect of heat treatment were assessed by electrochemical impedance monitoring in physiological saline. The adhesion of HAp coating on SUS316L was evaluated by three-point bending test. It was found that post heat treatment improves not only crystallinity but also the credibility of HAp coatings on SUS316L stainless steel. Also, the corrosion resistance of HAp coating on SUS316L was improved by lowering the cooling or heating rate during post heat treatment process. It was found that plasma titanium intermediate layer played an important role both in improving corrosion resistance of HAp coating on SUS316L stainless steel and in increasing the adhesion of HAp coating layer to the metallic substrate. Zn doped HAp plasma spray coatings was prepared and its credibility was evaluated by electrochemical impedance measurements.
In a super-aged society such as Japan, needs for new type implants which has both excellent bioco... more In a super-aged society such as Japan, needs for new type implants which has both excellent biocompatibility and high functionality are increasing. Hydroxyapatite (HAp) is known to be very biocompatible since it is the main inorganic content of human tooth and bones. The development of HAp plasma spray coating on metallic substrate has been engaged by our lab and other researchers. In this study, Zn doped HAp plasma coatings on Ti and SUS316L were prepared by using Zn doped HAp powder obtained by high temperature sintering of the mixture of ZnO and HAp. The credibility, the functionality and the adhesion were investigated by electrochemical impedance measurements, ICP analysis and two types of adhesion tests. After the mixture of ZnO and HAp was sintered at 1150˚C for 10 hours, ZnO X-ray diffraction peaks reduced greatly. Also, the lattice constants of HAp changed with the change of ZnO percentage in the mixture meaning most Zn2+ ions were embedded into the crystal structure of HAp. Long-term credibility evaluation for Zn doped HAp plasma spray coatings in SUS316L was conducted by electrochemical impedance measurements. The results of impedance results showed that corrosion resistance for coatings with post heat treatment kept in a very high value during 12 weeks immersion in Hanks solution, indicating the post heat treatment improved the stability of Zn doped HAp coatings in SUS316L by changing the coating from amorphous structure to a crystalized one. The results from ICP analysis also proved the higher stability achieved by post heat treatment. The dissolution of Zn2+ ions was detected in Hanks solution which implies the possibility of stimulation to the bone growth. The adhesion evaluation was done by three-points bending test and a standard ASTM adhesion test for Zn doped HAp plasma spray coatings on Ti. Zn doped HAp coatings showed strong adhesion to the metallic substrate. The residual stress in coatings was investigated by x-ray diffraction for understanding the mechanism of strong adhesion.
e c h n o l o g y Possibility of the application of the electrochemial noise analysis to aluminum... more e c h n o l o g y Possibility of the application of the electrochemial noise analysis to aluminum crevice corrosion was studied. Anodic polarization curves with various scanning rates of potential were measured for the aluminum electrode in the artificial crevice. Current noises were measured for the aluminum artificial crevice electrode at various anodic potentials. On the other hand, current noises were measured for the platinum artificial crevice electrode at various cathodic potentials. The short-circuited current noise and the potential noise of the aluminum artificial crevice e l e ctrode coupled with an external aluminum electrode were measured. Any current noises were not obserbed in the region of the potential less noble than crevice potential (Ec), above which the noises were generated due to the hydrogen evolution. This was verifyed by the fact for the hydrogen e v olution on the platinum crevice electrode. Notable noises of synchronized short-circuited current and potential appeared after 50 minutes of immersion being due to the hydrogen evolution. Thus, the natural crevice corrosion was simulated with this short-circuited coupling cell. The potential noise will be considerd as an easy monitoring tool for these crevice corrosion detection, because the potential noise was changed with the current noise in the same period.
The application of electrochemical noise (Fluctuation) analysis for localized corrosion have been... more The application of electrochemical noise (Fluctuation) analysis for localized corrosion have been studied. Foils of zinc, aluminum and magnesium were used as specimens for electrochemical cell simulating localized corrosion. Time variations of short circuited potential and current were measured in these solutions, and simultaneously the surfaces of specimens were observed using microscope with television monitor. Two types fluctuation were detected. In the case of aluminum and magnesium, It was seemed that the fluctuations result from hydrogen evolution on the active site in the crevice. In the case of magnesium, fluctuations appeared on the trendy component of the corrosion potential. And that was random one. It was seemed that these fluctuations result from the hydrogen evolution on the active site in the crevice of magnesium from the microscopic observation. In the case of zinc, It was seemed that the fluctuations result from the dissolution on the active site in the crevice and generation of corrosion products on the cathodic site on the outer site.
Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conduct... more Biocompatible plasma spray hydroxyapatite (HAp) coatings on metallic substrates have been conducted. The credibility of HAp coatings on SUS316L stainless steel and the effect of heat treatment were assessed by electrochemical impedance monitoring in physiological saline. The adhesion of HAp coating on SUS316L was evaluated by three-point bending test. It was found that post heat treatment improves not only crystallinity but also the credibility of HAp coatings on SUS316L stainless steel. Also, the corrosion resistance of HAp coating on SUS316L was improved by lowering the cooling or heating rate during post heat treatment process. It was found that plasma titanium intermediate layer played an important role both in improving corrosion resistance of HAp coating on SUS316L stainless steel and in increasing the adhesion of HAp coating layer to the metallic substrate. Zn doped HAp plasma spray coatings was prepared and its credibility was evaluated by electrochemical impedance measureme...
In a super-aged society such as Japan, needs for new type implants which has both excellent bioco... more In a super-aged society such as Japan, needs for new type implants which has both excellent biocompatibility and high functionality are increasing. Hydroxyapatite (HAp) is known to be very biocompatible since it is the main inorganic content of human tooth and bones. The development of HAp plasma spray coating on metallic substrate has been engaged by our lab and other researchers. In this study, Zn doped HAp plasma coatings on Ti and SUS316L were prepared by using Zn doped HAp powder obtained by high temperature sintering of the mixture of ZnO and HAp. The credibility, the functionality and the adhesion were investigated by electrochemical impedance measurements, ICP analysis and two types of adhesion tests. After the mixture of ZnO and HAp was sintered at 1150˚C for 10 hours, ZnO X-ray diffraction peaks reduced greatly. Also, the lattice constants of HAp changed with the change of ZnO percentage in the mixture meaning most Zn2+ ions were embedded into the crystal structure of HAp. Long-term credibility evaluation for Zn doped HAp plasma spray coatings in SUS316L was conducted by electrochemical impedance measurements. The results of impedance results showed that corrosion resistance for coatings with post heat treatment kept in a very high value during 12 weeks immersion in Hanks solution, indicating the post heat treatment improved the stability of Zn doped HAp coatings in SUS316L by changing the coating from amorphous structure to a crystalized one. The results from ICP analysis also proved the higher stability achieved by post heat treatment. The dissolution of Zn2+ ions was detected in Hanks solution which implies the possibility of stimulation to the bone growth. The adhesion evaluation was done by three-points bending test and a standard ASTM adhesion test for Zn doped HAp plasma spray coatings on Ti. Zn doped HAp coatings showed strong adhesion to the metallic substrate. The residual stress in coatings was investigated by x-ray diffraction for understanding the mechanism of strong adhesion.
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Papers by Seisho Take