Silver and silver alloys usually tarnish,which causes some changes in their aesthetic appearance and electrical properties,due to their exposure to sulphide environments(H2S),and this is a problem in the field of corr...Silver and silver alloys usually tarnish,which causes some changes in their aesthetic appearance and electrical properties,due to their exposure to sulphide environments(H2S),and this is a problem in the field of corrosion and conservation of cultural heritage metallic artefacts.In this study,the role of copper content in the tarnishing process of 0.925,0.800 and 0.720 silver alloys in a 0.07 vol.%ammonium sulphide solution for different immersion periods was analyzed by electrochemical impedance spectroscopy(EIS)and scanning electron microscopy(SEM).The polarisation curves showed that the copper content and sulphide increased the corrosion current density and delayed the passivation of silver alloys.The impedance spectra collected at the open circuit potential(OCP)showed a single capacitive,incomplete and depressed loop,indicating that the charge transfer resistance decreased as the copper content increased in the alloys.In contrast,the double-layer capacitance increased as the copper content increased.The SEM-EDS analysis confirmed that the copper-rich phase in the silver alloys was selectively dissolved due to the preference of S to react with Cu,resulting in a localised attack,thus delaying the formation of a passive film.A marked localised attack was observed in alloys with lower copper content.The mechanism for the tarnishing of silver alloys in sulphide media was dependent on the nature of the alloy and the greater affinity of copper for sulphur.The dissolution of Ag and Cu to form corrosion products was proposed as the rate determining step.展开更多
In natural environment, tarnish was observed on the surface of historic and contemporary gold coins in several countries. Few years after the emergence of panda gold coins, several red spots were appeared on the surfa...In natural environment, tarnish was observed on the surface of historic and contemporary gold coins in several countries. Few years after the emergence of panda gold coins, several red spots were appeared on the surface. To identify the stains and to examine the spots, optical microscope （OM）, scanning electron microscope （SEM）, electron microprobe analysis （EMPA）, X-ray photoelectron spectroscopy （XPS）, and X-ray diffraction （XRD） were used. It was found by microscopic observation that the stain has a dark blue central area surrounded by a large area with a nuance of colors from brown to red. Red spots usually contain holes in the center, which are distributed along the forging stress zones formed in the struck process. From the surface analyses using EMPA, sulfur and silver are detected besides gold, and the contents of Ag and S at the tarnish part are higher than those at the other part. Furthermore, distributions of Ag and S are correlated with the morphology of stains. XPS shows that components of stains are Ag2S and Ag2SO4 and the former is much predominant. These results are confirmed using XRD analysis. Accelerated tarnish test of gold in an atmosphere containing sulfur compound proves that the similar phenomenon appears when a small amount of silver is present on the surface of gold. It can be concluded that the occurrence of tarnish stains is caused by the presence of Ag and S.展开更多
It has been demonstrated that sterling silver alloy is a widely used material in the jewelry industry. The anti-tarnish property is one of the most important properties of this material. In this work, the effect of yt...It has been demonstrated that sterling silver alloy is a widely used material in the jewelry industry. The anti-tarnish property is one of the most important properties of this material. In this work, the effect of yttrium on the corrosion resistance, and tarnish resistance properties of sterling silver alloy were investigated with the use of CIE-LAB uniform color scale, which gained acceptance as an effective way to assess color. To better understand the mechanism of the effect, the distribution of yttrium in the alloy was analyzed by mainly segregating in gaps among dendrite crystals and grain boundary. An increase in yttrium content in sterling silver alloy resulted in a decrease in the amount of eutectic structure. The tarnish and corrosion resistance of sterling silver were improved with yttrium content increase. However, too high yttrium content will lead to poor anti-tarnish properties.展开更多
The effect of Sn on the color and tarnishing of Cu-Mn-Zn alloys is investigated quantitatively. Using the CIE LAB color system, color parameters such as L*, a* and V are selected to describe the surface color of atloy...The effect of Sn on the color and tarnishing of Cu-Mn-Zn alloys is investigated quantitatively. Using the CIE LAB color system, color parameters such as L*, a* and V are selected to describe the surface color of atloys while the color difference (AB*) is used to evaluate the color stability. The results show that with the increase of Sn, the color change of Cu-Mn-Zn alloys is greatly reduced and the corrosion resistance in the synthetic sweat is improved dramatically. However, up to 4.4 wt pct Sn does not change the color of Cu-Mn-Zn alloys much. XPS and AES are employed to analyze the tarnished surface. It is proved that a Sn enriched film is formed and Sn takes the form of Sn oxide. This thin and protective oxide film can prevent alloy from further tarnishing.展开更多
The tarnishing test in the presence of hydrogen sulfide（H2S） vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with Si02-like films by means of plasma-enhanced chemi...The tarnishing test in the presence of hydrogen sulfide（H2S） vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with Si02-like films by means of plasma-enhanced chemical vapor deposition（PECVD） fed with a tetraethoxysilane/oxygen mixture.The chemical and morphological properties of the films have been characterized by using infrared absorption spectroscopy（IR） and scanning electron microscopy（SEM）with energy disperse spectroscopy（EDS）.The corrosion products of the samples after the tarnishing test have been identified by X-ray diffraction analysis（XRD）.It has been found that SiO2-like films formed via PECVD with a high O2 flow rate could protect copper-based alloys from H2S vapor tarnishing.The alloys coated at the O2 flow rate of 20 sccm remain uncorroded after 54days of H2S vapor tarnish testing.The corrosion products for the alloys deposited at a low O2flow rate after 54 days of tarnish testing are mainly composed of brochantite.展开更多
This work is a study of effect of laser ablation in different medium on silver artifacts. The effectiveness of laser ablation cleanness methods was evaluated in air, water and vacuum condition. The samples were subjec...This work is a study of effect of laser ablation in different medium on silver artifacts. The effectiveness of laser ablation cleanness methods was evaluated in air, water and vacuum condition. The samples were subjected to HC1 treatment for several hours to simulate the formation of chloride patina on marine archeological artifacts. Laser ablation removes the patina in all medium, reducing its thickness from 300 to few microns in air and water and eliminating completely the chlorine in vacuum conditions. However, it was observed the formation, during cleanness of a white patina in air and water and an increasing of oxygen amount on surface. This indicate that in ambient reach in oxygen laser ablation favorite the oxygen absorbance on surface and the formation of a thin layer of AgO which dulls the surface. This hypothesis is confirmed by the results of laser ablation in vacuum conditions where surface tarnishing was not observed. So, laser ablation in vacuum condition was indicated as the most effective procedure to clean silver artifacts.展开更多
The mechanism of tarnish caused by exposure to light and Na_2S solution treatment on silver-electroplated deposit and the antitarnish effects of various antitarnish agents have been investigated in this paper. The res...The mechanism of tarnish caused by exposure to light and Na_2S solution treatment on silver-electroplated deposit and the antitarnish effects of various antitarnish agents have been investigated in this paper. The results showed that 1-phenyl-5-mercaptotetrazole (PMTA) has excellent antitarnish effect for UV light and H_2S tests.The studies of XPS and AES and UV absorption spectra showed that PMTA can absorb effectively UV light and form a dense surface film which can prevent effectively the reactions between silver deposit with corrosive media.Antitarnish surface film could be composed of a polynuclear coordination polymeric compound with structure unit approximate to [Ag_3(PMTA)]. according to the depth dependence of percent component (C%) and sputtering time.展开更多
Insect source-sink dynamics are vital to ecologically intensive pest management. Maintaining sink plant hosts,or "trap crops",and destroying alternate hosts or breeding places adjacent to the field crop are ...Insect source-sink dynamics are vital to ecologically intensive pest management. Maintaining sink plant hosts,or "trap crops",and destroying alternate hosts or breeding places adjacent to the field crop are effective pest management strategies for some arthropods. However,determining whether a host acts as a source or a sink is challenging, especially when the pest species is highly mobile and polyphagous. The western tarnished plant bug,Lygus hesperus,is highly polyphagous,and can utilize >300 hosts. Its presence has been documented in 26 roadside weed hosts in the Texas High Plains.Previous studies demonstrated that L. hesperus prefer alfalfa over cotton and several alternate weed hosts.A four-year project involved surveying and sampling for L. hesperus in the agricultural landscapes of several sub-regions of the southwestern United States,including the Texas High Plains. In Texas,geographic information of the landscape vegetation complex was compiled from a 150 km radius in the Texas High Plains. In one study,fifty irrigated cotton fields representing the crop diversity within this region were sampled via sweep-net for 10 weeks. This effort also included sampling of up to six noncotton insect habitats within a 3 km radius of each field. Seasonal average L. hesperus abundance data were regressed with 27 field characteristics( variables),including habitat-specific land cover,distance between focal cotton fields and non-cotton habitats,longitude,latitude,elevation,habitat heterogeneity index,and several environmental / ecological variables. Significant variables were selected using a stepwise regression at 15% probability rate. A 10-parameter linear model explained 93% of the variation in the data. Major parameters contributing significantly to variation in L. hesperus abundance in cotton were corn and sunflower acreages,focal cotton field distances from several non-cotton hosts,and habitat heterogeneity index. In addition,field marking-and-capture studies were conducted using protein markers and enzyme-linked immunosorbent assays to characterize L. hesperus intercrop movement behavior. The field marking-and-capture approach can be used to study the effects of various crop management practices on L. hesperus intercrop movement and can potentially be applied to other pests and cropping systems.展开更多
Due to rapidly developed resistance,pest management relies less on pyrethroids to control economically damaging infestations of the tarnished plant bug(TPB),Lygus lineolaris(Palisot de Beauvois)in cotton fields of Mis...Due to rapidly developed resistance,pest management relies less on pyrethroids to control economically damaging infestations of the tarnished plant bug(TPB),Lygus lineolaris(Palisot de Beauvois)in cotton fields of Mississippi.Yet,pyrethroid resistance remains prevalent in TPB populations.This study assessed the resistance levels in adult TPB to six common pyrethroids and acephate.Resistant TBPs were collected from wild host plants in late October after harvest in the Mississippi Delta region of the United States.Based on LCso values,the field-resistant TPBs displayed higher resistance to permethrin,esfenvalerate,and bifenthrin(approximately 30 fold)and moderate resistance toα-cyhalothrin,β-cyfluthrin,5-cypermethrin,and acephate(approximately 15 fold).Further investigations showed that the inhibitors of three detoxification enzyme,triphenyl phosphate(TPP),diethyl maleate(DEM),and piperonyl butoxide(PBO)had synergistic effects on permethrin,γ-cyhalothrin,and bifenthrin in resistant TPBs.Furthermore,elevated esterase,GST,and P450 activities were significantly expressed in fieldresistant TPBs.Additionally,GST and esterase were reduced after 48 h exposure to certain pyrethroids at LCso dose.The synergistic and biochemical assays consistently indicated that P450 and esterase were involved in pyrethroid detoxification in TPBs.This study provides valuable information for the continued use of pyrethroids and acephate in controlling TPBs in cotton fields in the Mississippi Delta region of the United States.展开更多
基金CONACyT for their support:scholarship to JOC 45653 and the Basic Science Projects 239938LANCIC CONACyT LN 232619,260779 and 271614the Chemistry School at UNAM for the financial support given for this work through the Program for Research and Graduate Studies Sponsorship(PAIP)
文摘Silver and silver alloys usually tarnish,which causes some changes in their aesthetic appearance and electrical properties,due to their exposure to sulphide environments(H2S),and this is a problem in the field of corrosion and conservation of cultural heritage metallic artefacts.In this study,the role of copper content in the tarnishing process of 0.925,0.800 and 0.720 silver alloys in a 0.07 vol.%ammonium sulphide solution for different immersion periods was analyzed by electrochemical impedance spectroscopy(EIS)and scanning electron microscopy(SEM).The polarisation curves showed that the copper content and sulphide increased the corrosion current density and delayed the passivation of silver alloys.The impedance spectra collected at the open circuit potential(OCP)showed a single capacitive,incomplete and depressed loop,indicating that the charge transfer resistance decreased as the copper content increased in the alloys.In contrast,the double-layer capacitance increased as the copper content increased.The SEM-EDS analysis confirmed that the copper-rich phase in the silver alloys was selectively dissolved due to the preference of S to react with Cu,resulting in a localised attack,thus delaying the formation of a passive film.A marked localised attack was observed in alloys with lower copper content.The mechanism for the tarnishing of silver alloys in sulphide media was dependent on the nature of the alloy and the greater affinity of copper for sulphur.The dissolution of Ag and Cu to form corrosion products was proposed as the rate determining step.
文摘In natural environment, tarnish was observed on the surface of historic and contemporary gold coins in several countries. Few years after the emergence of panda gold coins, several red spots were appeared on the surface. To identify the stains and to examine the spots, optical microscope （OM）, scanning electron microscope （SEM）, electron microprobe analysis （EMPA）, X-ray photoelectron spectroscopy （XPS）, and X-ray diffraction （XRD） were used. It was found by microscopic observation that the stain has a dark blue central area surrounded by a large area with a nuance of colors from brown to red. Red spots usually contain holes in the center, which are distributed along the forging stress zones formed in the struck process. From the surface analyses using EMPA, sulfur and silver are detected besides gold, and the contents of Ag and S at the tarnish part are higher than those at the other part. Furthermore, distributions of Ag and S are correlated with the morphology of stains. XPS shows that components of stains are Ag2S and Ag2SO4 and the former is much predominant. These results are confirmed using XRD analysis. Accelerated tarnish test of gold in an atmosphere containing sulfur compound proves that the similar phenomenon appears when a small amount of silver is present on the surface of gold. It can be concluded that the occurrence of tarnish stains is caused by the presence of Ag and S.
基金supported by the National Nature Science Foundation of China (No.51003060)Shenzhen Science & Technology Research (Nos. JC200903130261A, CXB200903090012A)Open Foundation of Shenzhen Key Laboratory of Special Functional Materials (No. T201110)
文摘It has been demonstrated that sterling silver alloy is a widely used material in the jewelry industry. The anti-tarnish property is one of the most important properties of this material. In this work, the effect of yttrium on the corrosion resistance, and tarnish resistance properties of sterling silver alloy were investigated with the use of CIE-LAB uniform color scale, which gained acceptance as an effective way to assess color. To better understand the mechanism of the effect, the distribution of yttrium in the alloy was analyzed by mainly segregating in gaps among dendrite crystals and grain boundary. An increase in yttrium content in sterling silver alloy resulted in a decrease in the amount of eutectic structure. The tarnish and corrosion resistance of sterling silver were improved with yttrium content increase. However, too high yttrium content will lead to poor anti-tarnish properties.
基金The authors acknowledge the financial support by Shanghai Science Council (grant No. 99JC14021 and OOZE14035), China.
文摘The effect of Sn on the color and tarnishing of Cu-Mn-Zn alloys is investigated quantitatively. Using the CIE LAB color system, color parameters such as L*, a* and V are selected to describe the surface color of atloys while the color difference (AB*) is used to evaluate the color stability. The results show that with the increase of Sn, the color change of Cu-Mn-Zn alloys is greatly reduced and the corrosion resistance in the synthetic sweat is improved dramatically. However, up to 4.4 wt pct Sn does not change the color of Cu-Mn-Zn alloys much. XPS and AES are employed to analyze the tarnished surface. It is proved that a Sn enriched film is formed and Sn takes the form of Sn oxide. This thin and protective oxide film can prevent alloy from further tarnishing.
基金supported by the Special Fund for Talent of Wuhan Institute of Technology,China(No.237127)the"Fellowship for Junior Researchers"from Politecnico di Torino and Regione Piemonte,Italy
文摘The tarnishing test in the presence of hydrogen sulfide（H2S） vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with Si02-like films by means of plasma-enhanced chemical vapor deposition（PECVD） fed with a tetraethoxysilane/oxygen mixture.The chemical and morphological properties of the films have been characterized by using infrared absorption spectroscopy（IR） and scanning electron microscopy（SEM）with energy disperse spectroscopy（EDS）.The corrosion products of the samples after the tarnishing test have been identified by X-ray diffraction analysis（XRD）.It has been found that SiO2-like films formed via PECVD with a high O2 flow rate could protect copper-based alloys from H2S vapor tarnishing.The alloys coated at the O2 flow rate of 20 sccm remain uncorroded after 54days of H2S vapor tarnish testing.The corrosion products for the alloys deposited at a low O2flow rate after 54 days of tarnish testing are mainly composed of brochantite.
文摘This work is a study of effect of laser ablation in different medium on silver artifacts. The effectiveness of laser ablation cleanness methods was evaluated in air, water and vacuum condition. The samples were subjected to HC1 treatment for several hours to simulate the formation of chloride patina on marine archeological artifacts. Laser ablation removes the patina in all medium, reducing its thickness from 300 to few microns in air and water and eliminating completely the chlorine in vacuum conditions. However, it was observed the formation, during cleanness of a white patina in air and water and an increasing of oxygen amount on surface. This indicate that in ambient reach in oxygen laser ablation favorite the oxygen absorbance on surface and the formation of a thin layer of AgO which dulls the surface. This hypothesis is confirmed by the results of laser ablation in vacuum conditions where surface tarnishing was not observed. So, laser ablation in vacuum condition was indicated as the most effective procedure to clean silver artifacts.
文摘The mechanism of tarnish caused by exposure to light and Na_2S solution treatment on silver-electroplated deposit and the antitarnish effects of various antitarnish agents have been investigated in this paper. The results showed that 1-phenyl-5-mercaptotetrazole (PMTA) has excellent antitarnish effect for UV light and H_2S tests.The studies of XPS and AES and UV absorption spectra showed that PMTA can absorb effectively UV light and form a dense surface film which can prevent effectively the reactions between silver deposit with corrosive media.Antitarnish surface film could be composed of a polynuclear coordination polymeric compound with structure unit approximate to [Ag_3(PMTA)]. according to the depth dependence of percent component (C%) and sputtering time.
文摘Insect source-sink dynamics are vital to ecologically intensive pest management. Maintaining sink plant hosts,or "trap crops",and destroying alternate hosts or breeding places adjacent to the field crop are effective pest management strategies for some arthropods. However,determining whether a host acts as a source or a sink is challenging, especially when the pest species is highly mobile and polyphagous. The western tarnished plant bug,Lygus hesperus,is highly polyphagous,and can utilize >300 hosts. Its presence has been documented in 26 roadside weed hosts in the Texas High Plains.Previous studies demonstrated that L. hesperus prefer alfalfa over cotton and several alternate weed hosts.A four-year project involved surveying and sampling for L. hesperus in the agricultural landscapes of several sub-regions of the southwestern United States,including the Texas High Plains. In Texas,geographic information of the landscape vegetation complex was compiled from a 150 km radius in the Texas High Plains. In one study,fifty irrigated cotton fields representing the crop diversity within this region were sampled via sweep-net for 10 weeks. This effort also included sampling of up to six noncotton insect habitats within a 3 km radius of each field. Seasonal average L. hesperus abundance data were regressed with 27 field characteristics( variables),including habitat-specific land cover,distance between focal cotton fields and non-cotton habitats,longitude,latitude,elevation,habitat heterogeneity index,and several environmental / ecological variables. Significant variables were selected using a stepwise regression at 15% probability rate. A 10-parameter linear model explained 93% of the variation in the data. Major parameters contributing significantly to variation in L. hesperus abundance in cotton were corn and sunflower acreages,focal cotton field distances from several non-cotton hosts,and habitat heterogeneity index. In addition,field marking-and-capture studies were conducted using protein markers and enzyme-linked immunosorbent assays to characterize L. hesperus intercrop movement behavior. The field marking-and-capture approach can be used to study the effects of various crop management practices on L. hesperus intercrop movement and can potentially be applied to other pests and cropping systems.
文摘Due to rapidly developed resistance,pest management relies less on pyrethroids to control economically damaging infestations of the tarnished plant bug(TPB),Lygus lineolaris(Palisot de Beauvois)in cotton fields of Mississippi.Yet,pyrethroid resistance remains prevalent in TPB populations.This study assessed the resistance levels in adult TPB to six common pyrethroids and acephate.Resistant TBPs were collected from wild host plants in late October after harvest in the Mississippi Delta region of the United States.Based on LCso values,the field-resistant TPBs displayed higher resistance to permethrin,esfenvalerate,and bifenthrin(approximately 30 fold)and moderate resistance toα-cyhalothrin,β-cyfluthrin,5-cypermethrin,and acephate(approximately 15 fold).Further investigations showed that the inhibitors of three detoxification enzyme,triphenyl phosphate(TPP),diethyl maleate(DEM),and piperonyl butoxide(PBO)had synergistic effects on permethrin,γ-cyhalothrin,and bifenthrin in resistant TPBs.Furthermore,elevated esterase,GST,and P450 activities were significantly expressed in fieldresistant TPBs.Additionally,GST and esterase were reduced after 48 h exposure to certain pyrethroids at LCso dose.The synergistic and biochemical assays consistently indicated that P450 and esterase were involved in pyrethroid detoxification in TPBs.This study provides valuable information for the continued use of pyrethroids and acephate in controlling TPBs in cotton fields in the Mississippi Delta region of the United States.
