This paper aims to investigate if the dental restoration of nickel-chromium based alloy(Ni-Cr) leads to the enhanced excretions of Ni and Cr in urine.Seven hundred and ninety-five patients in a dental hospital had sin...This paper aims to investigate if the dental restoration of nickel-chromium based alloy(Ni-Cr) leads to the enhanced excretions of Ni and Cr in urine.Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni-Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination.Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry.Compared to the control group,the urinary level of Ni was significantly higher in the patient group of < 1 month of the restoration duration,among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain.Urinary levels of Cr were significantly higher in the three patient groups of <1,1 to <3 and 3 to <6 months,especially in those with a higher metal crown exposure index.Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups.Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration.Potential short- and long-term effects of Ni-Cr alloy restoration need to be investigated.展开更多
Ni-Cr alloys with mass fraction of 1.4%23.9%Cr, 76.1%98.6%Ni, and hardness of 70.5 80.5HR were electrodeposited on aluminium substrate from the trivalent chromium sulphate-chloride solution using citric acid as comple...Ni-Cr alloys with mass fraction of 1.4%23.9%Cr, 76.1%98.6%Ni, and hardness of 70.5 80.5HR were electrodeposited on aluminium substrate from the trivalent chromium sulphate-chloride solution using citric acid as complexing agent. The aluminium was pretreated by means of degreasing and eroding, polishing and twice chemical immersion of zinc. The effects of electrodeposition parameters such as current density, temperature, pH value and bath concentration on the composition and hardness of deposits were investigated. The results show that the Cr content increases with the increase of current density and the decrease of temperature, and that it increases with the increase of pH value to a maximum and then decreases. The increase of Cr content leads to the increase of hardness of the Ni-Cr layers. The deposits with high Cr content are of good corrosion resistance. Good adherence of Ni-Cr deposits to aluminium substrate is obtained. The Ni-Cr alloys are the Ni-Cr solid solution with fcc crystalline structure. The Ni-Cr alloy deposits are fine, bright and smooth and compact.展开更多
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
Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures(350-500℃),strain rates(0.01...Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures(350-500℃),strain rates(0.01-5 s^(-1)),and strains(0.2,0.4,and 0.8).A strong dynamic softening is observed in all stress-strain curves,even at higher strain rates(1 and 5 s^(-1))due to an adiabatic heating effect.Various stress-strain curves are applied to construct a processing map and develop an Arrhenius-type constitutive equation.With the prediction of the processing map,an optimal processing domain has been determined to be the temperature range 450-500℃and strain rate range 0.01-0.1 s^(-1)at a strain of 0.8.The volume fraction of DRX grains is the largest in the corresponding domain of high temperature and low strain rate.For the effect of TMP parameters on the dynamic restoration,the discontinuous dynamic recrystallization(DDRX)and continuous DRX(CDRX)synergistic effect occur throughout the whole process at high temperature and high strain rate.In terms of high temperature and low strain rate,DDRX characteristics at a low strain and then the DDRX+CDRX synergistic effect is observed at a higher strain.Although the DRX process is weak at low temperature and low strain rate,deformation twins have occurred and provided nucleation sites for DRX grains.展开更多
Metastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density.Thermal-mechanical processing(TMP)is one of the most effective ways t...Metastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density.Thermal-mechanical processing(TMP)is one of the most effective ways to improve the mechanical properties of such alloys.This paper describes a systematic TMP investigation on a new metastableβtitanium alloy,including its dynamic mechanical behavior,and microstructure evolution,via isothermal compression tests and electron back‐scattered diffraction characterizations.The results show that the compression stress increases with an increase in the strain rate and a decrease in the temperature.After yielding,the compression stress-strain pattern shows flow‐softening behavior at a low temperature and a high strain rate,while sustaining a steady flow state at a high temperature and a low strain rate.The temperature‐rise effect contributes to a large degree of flow softening at high strain rates.After the correction for temperature rise,the stress-strain constitutive relationships are established,showing that the compression behavior varies in different phase regions.Based on the microstructure characterizations,it is found that the dynamic recovery and dynamic recrystallization dominate the hot deformations inβphase region and at low strain rates,while the deformation band as an additional product is found inα+βphase region and at high strain rates.The results contribute to a better understanding of the TMP for the considered alloy and may also represent a useful database forβ‐Ti alloy applications in lightweight mechanical systems.展开更多
基金supported by Open Fund of State Key Laboratory of Oral Diseases,Sichun University
文摘This paper aims to investigate if the dental restoration of nickel-chromium based alloy(Ni-Cr) leads to the enhanced excretions of Ni and Cr in urine.Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni-Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination.Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry.Compared to the control group,the urinary level of Ni was significantly higher in the patient group of < 1 month of the restoration duration,among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain.Urinary levels of Cr were significantly higher in the three patient groups of <1,1 to <3 and 3 to <6 months,especially in those with a higher metal crown exposure index.Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups.Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration.Potential short- and long-term effects of Ni-Cr alloy restoration need to be investigated.
基金Project (59674025) supported by the National Natural Science Foundation of China
文摘Ni-Cr alloys with mass fraction of 1.4%23.9%Cr, 76.1%98.6%Ni, and hardness of 70.5 80.5HR were electrodeposited on aluminium substrate from the trivalent chromium sulphate-chloride solution using citric acid as complexing agent. The aluminium was pretreated by means of degreasing and eroding, polishing and twice chemical immersion of zinc. The effects of electrodeposition parameters such as current density, temperature, pH value and bath concentration on the composition and hardness of deposits were investigated. The results show that the Cr content increases with the increase of current density and the decrease of temperature, and that it increases with the increase of pH value to a maximum and then decreases. The increase of Cr content leads to the increase of hardness of the Ni-Cr layers. The deposits with high Cr content are of good corrosion resistance. Good adherence of Ni-Cr deposits to aluminium substrate is obtained. The Ni-Cr alloys are the Ni-Cr solid solution with fcc crystalline structure. The Ni-Cr alloy deposits are fine, bright and smooth and compact.
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.
基金financially supported by the National Natural Science Foundation of China(No.51571084)financial support from the China Scholarship Council(No.201908410208)。
文摘Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures(350-500℃),strain rates(0.01-5 s^(-1)),and strains(0.2,0.4,and 0.8).A strong dynamic softening is observed in all stress-strain curves,even at higher strain rates(1 and 5 s^(-1))due to an adiabatic heating effect.Various stress-strain curves are applied to construct a processing map and develop an Arrhenius-type constitutive equation.With the prediction of the processing map,an optimal processing domain has been determined to be the temperature range 450-500℃and strain rate range 0.01-0.1 s^(-1)at a strain of 0.8.The volume fraction of DRX grains is the largest in the corresponding domain of high temperature and low strain rate.For the effect of TMP parameters on the dynamic restoration,the discontinuous dynamic recrystallization(DDRX)and continuous DRX(CDRX)synergistic effect occur throughout the whole process at high temperature and high strain rate.In terms of high temperature and low strain rate,DDRX characteristics at a low strain and then the DDRX+CDRX synergistic effect is observed at a higher strain.Although the DRX process is weak at low temperature and low strain rate,deformation twins have occurred and provided nucleation sites for DRX grains.
基金This study was supported by the National Natural Science Foundation of China(Nos.92163215,51731006,52174364,52101143,51771093,and 91860104)the Fundamental Research Funds for the Central Universities(Nos.30922010711 and 30922010202)+1 种基金the Natural Science Foundation of Jiangsu Province Major Project(No.BK20212009)the Open Project Program of Key Laboratory of China North Engine Research Institute(No.6142212210103)。
文摘Metastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density.Thermal-mechanical processing(TMP)is one of the most effective ways to improve the mechanical properties of such alloys.This paper describes a systematic TMP investigation on a new metastableβtitanium alloy,including its dynamic mechanical behavior,and microstructure evolution,via isothermal compression tests and electron back‐scattered diffraction characterizations.The results show that the compression stress increases with an increase in the strain rate and a decrease in the temperature.After yielding,the compression stress-strain pattern shows flow‐softening behavior at a low temperature and a high strain rate,while sustaining a steady flow state at a high temperature and a low strain rate.The temperature‐rise effect contributes to a large degree of flow softening at high strain rates.After the correction for temperature rise,the stress-strain constitutive relationships are established,showing that the compression behavior varies in different phase regions.Based on the microstructure characterizations,it is found that the dynamic recovery and dynamic recrystallization dominate the hot deformations inβphase region and at low strain rates,while the deformation band as an additional product is found inα+βphase region and at high strain rates.The results contribute to a better understanding of the TMP for the considered alloy and may also represent a useful database forβ‐Ti alloy applications in lightweight mechanical systems.
