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The misalignment between degradation rate and mechanical integrity of Mg-Zn-Y-Nd alloy during the degradation evaluation in modified Hanks’solutions
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作者 Di Mei Qingyuan Zhang +7 位作者 Yaqian Li Mengyao Liu Wenkai Li Pingli Jiang Ruiqing Hou Shijie Zhu Liguo Wang Shaokang Guan 《Journal of Magnesium and Alloys》 SCIE EI CAS CSCD 2024年第9期3661-3674,共14页
The degradation behavior of biodegradable Mg alloys has become a research hotspot in the fields about biodegradable metallic materials.While the most of the related publications mainly focused on the degradation rate ... The degradation behavior of biodegradable Mg alloys has become a research hotspot in the fields about biodegradable metallic materials.While the most of the related publications mainly focused on the degradation rate of Mg-based materials,but rare to care about the changes of their mechanical properties during the immersion period,which can significantly affect their service performance.The link between residual strength and Mg degradation is not appreciated enough.In this work,a series media were constructed based on Hanks’solution,the effects of inorganic ions on the degradation rate and mechanical integrity of Mg-Zn-Y-Nd alloy were investigated.The results indicated that the degradation behavior of Mg alloy was mainly controlled by degradation products and there is no direct correspondence between the degradation rate change and mechanical integrity of Mg alloy.The relevant findings are beneficial for selecting the monitoring index in Mg corrosion tests and evaluating the service reliability of Mg alloys for biomedical applications. 展开更多
关键词 Magnesium alloy degradation rate mechanical integrity Hanks’solution
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Unraveling the degradation mechanism of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) at the high cut-off voltage for lithium ion batteries 被引量:3
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作者 Liming Wang Qingmei Su +10 位作者 Bin Han Weihao Shi Gaohui Du Yunting Wang Huayv Li Lin Gu Wenqi Zhao Shukai Ding Miao Zhang Yongzhen Yang Bingshe Xu 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2023年第2期428-437,I0011,共11页
LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)layered oxides have been regarded as promising alternative cathodes for the next generation of high-energy lithium ion batteries(LIBs)due to high discharge capacities and energy ... LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)layered oxides have been regarded as promising alternative cathodes for the next generation of high-energy lithium ion batteries(LIBs)due to high discharge capacities and energy densities at high operation voltage.However,the capacity fading under high operation voltage still restricts the practical application.Herein,the capacity degradation mechanism of NCM811 at atomic-scale is studied in detail under various cut-off voltages using aberration-corrected scanning transmission electron microscopy(STEM).It is observed that the crystal structure of NCM811 evolution from a layered structure to a rock-salt phase is directly accompanied by serious intergranular cracks under 4.9 V,which is distinguished from the generally accepted structure evolution of layered,disordered layered,defect rock salt and rock salt phases,also observed under 4.3 and 4.7 V.The electron energy loss spectroscopy analysis also confirms the reduction of Ni and Co from the surface to the bulk,not the previously reported only Li/Ni interlayer mixing.The degradation mechanism of NCM811 at a high cut-off voltage of4.9 V is attributed to the formation of intergranular cracks induced by defects,the direct formation of the rock salt phase,and the accompanied reduction of Ni^(2+)and Co^(2+)phases from the surface to the bulk. 展开更多
关键词 Ni-rich layered cathode Electrochemical performance degradation mechanism Crack Atomic scale
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Investigation of photoelectrocatalytic degradation mechanism of methylene blue by a-Fe_(2)O_(3) nanorods array 被引量:1
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作者 Yaqiao Liu Shuozhen Hu +1 位作者 Xinsheng Zhang Shigang Sun 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2023年第5期162-172,共11页
Efficiently and thoroughly degrading organic dyes in wastewater is of great importance and challenge.Herein,vertically oriented mesoporous a-Fe_(2)O_(3)nanorods array(a-Fe_(2)O_(3)-NA)is directly grown on fluorine-dop... Efficiently and thoroughly degrading organic dyes in wastewater is of great importance and challenge.Herein,vertically oriented mesoporous a-Fe_(2)O_(3)nanorods array(a-Fe_(2)O_(3)-NA)is directly grown on fluorine-doped tin oxide(FTO)glass and employed as the photoanode for photoelectrocatalytic degradation of methylene blue simulated dye wastewater.The Ovsites on the a-Fe_(2)O_(3)-NA surface are the active sites for methylene blue(MB)adsorption.Electrons transfer from the adsorbed MB to Fe-O is detected.Compared with electrocatalytic and photocatalytic degradation processes,the photoelectrocatalytic(PEC)process exhibited the best degrading performance and the largest kinetic constant.Hydroxyl,superoxide free radicals,and photo-generated holes play a jointly leading role in the PEC degradation.A possible degrading pathway is suggested by liquid chromatography-mass spectroscopy analysis.This work demonstrates that photoelectrocatalysis by a-Fe_(2)O_(3)-NA has a remarkable superiority over photocatalysis and electrocatalysis in MB degradation.The in-depth investigation of photoelectrocatalytic degradation mechanism in this study is meaningful for organic wastewater treatment. 展开更多
关键词 a-Fe_(2)O_(3)nanorods array Methylene blue Photoelectrocatalytic degradation mechanism Free radicals Photo-generated holes
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Research and experimental analysis of precision degradation method based on the ball screw mechanism
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作者 孔德顺 GAO Xiangsheng JIANG Huizeng 《High Technology Letters》 EI CAS 2023年第3期247-256,共10页
As a key transmission component in computer numerical control(CNC) machine tools,the ball screw mechanism(BSM) is usually investigated under working load conditions. Its accuracy degradation process is relatively long... As a key transmission component in computer numerical control(CNC) machine tools,the ball screw mechanism(BSM) is usually investigated under working load conditions. Its accuracy degradation process is relatively long,which is not conducive to the design and development of new products. In this paper,the normal wear depth of the BSM nut raceway is calculated under the variable speed operation condition using the fractal wear analysis method and the BSM’s accelerated degradation proportional wear model. Parameters of the acceleration degradation model of the double-nut preloaded ball screw pair are calculated based on the physical simulation results. The accelerated degradation test platform of the BSM is designed and manufactured to calculate the raceway wear model when the lubrication condition is broken under the variable-speed inertial load and the boundary lubrication condition under the uniform speed state. Three load forces and two samples are selected for the accelerated degradation test of the BSM. The measured friction torque of the BSM is employed as the evaluation index of the accuracy degradation test. In addition,the life cycle of the accuracy retention is accurately calculated by employing the parameters of the physical simulation model of the BSM. The calculations mentioned above can be used to estimate BSM’s accuracy performance degradation law under normal operating conditions. The application of the proposed model provides a new research method for researching the precision retention of the BSM. 展开更多
关键词 ball screw mechanism(BSM) fractal theory wear model accelerated degradation method friction torque precision retention
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Achieving high strength and rapid degradation in Mg-Gd-Ni alloys by regulating LPSO phase morphology combined with extrusion
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作者 Kai Ma Jingfeng Wang +7 位作者 Yinhong Peng Chaoneng Dai Yuanlang Pan Ye Wang Danqian Wang Jinxing Wang Yanlong Ma Fusheng Pan 《Journal of Magnesium and Alloys》 SCIE EI CAS CSCD 2024年第6期2312-2326,共15页
In this study,Mg-13.2Gd-4.3Ni alloys containing continuous bulk-shaped long-period stacking ordered(LPSO),lamellar LPSO,and a small amount of eutectic phase were prepared,and the evolution of microstructure at differe... In this study,Mg-13.2Gd-4.3Ni alloys containing continuous bulk-shaped long-period stacking ordered(LPSO),lamellar LPSO,and a small amount of eutectic phase were prepared,and the evolution of microstructure at different extrusion temperatures and its influence on mechanical and degradation properties as well as corrosion mechanism were investigated.Preheating before extrusion can effectively promote the precipitation of lamellar LPSO in matrix.EX400 with higher volume fraction of non-DRXed grains exhibited higher strength,which was mainly due to strong texture,high dislocation density,and high volume fraction of lamellar LPSO.The EX420 with higher volume fraction of DRXed grains showed higher degradation rate,which was mainly due to the higher density of grain boundary.The EX400 exhibited excellent comprehensive properties with tensile yield strength(TYS)of 334 MPa,ultimate tensile strength(UTS)of 484 MPa and elongation(EL)of 7.4%,ultimate compressive strength(UCS)of 638 MPa and compressive yield strength(CYS)of 443 MPa,degradation rate of 86.1 mg/cm^(2)/h at 93℃in 3 wt.%KCl solution. 展开更多
关键词 Mg-Gd-Ni alloys LPSO mechanical properties degradation rate
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Microwave photocatalytic degradation of Rhodamine B using TiO_2 supported on activated carbon:Mechanism implication 被引量:23
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作者 HE Zhong,YANG Shaogui,JU Yongming,SUN Cheng State Key Laboratory of Pollution Control and Resource Reuse,School of the Environment,Nanjing University,Nanjing 210093,China. 《Journal of Environmental Sciences》 SCIE EI CAS CSCD 2009年第2期268-272,共5页
The photocatalytic degradation of Rhodamine B (RhB) was carried out using TiO2 supported on activated carbon (TiO2-AC) under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X... The photocatalytic degradation of Rhodamine B (RhB) was carried out using TiO2 supported on activated carbon (TiO2-AC) under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET). In the process of microwave-enhanced photocatalysis (MPC), RhB (30 mg/L) was almost completely decoloured in 10 min, and the mineralization efficiency was 96.0% in 20 min. The reaction rate constant of RhB in MPC using TiO2-AC by pseudo first-order reaction kinetics was 4.16 times of that using Degussa P25. Additionally, according to gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) identification, the major intermediates of RhB in MPC included two kinds of N-de-ethylation intermediates (N,N-diethyl-N'-ethyl-rhodamine (DER)), oxalic acid, malonic acid, snccinic acid, and phthalic acid, maleic acid, 3-nitrobenzoic acid, and so on. The degradation of RhB in MPC was mainly attributed to the destruction of the conjugated structure, and then the intermediates transformed to acid molecules which were mineralized to water and carbon dioxide. 展开更多
关键词 microwave photocatalytic WiO2 activated carbon Rhodamine B degradation mechanism
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Degradation mechanism of 2,4,6-trinitrotoluene in supercritical water oxidation 被引量:15
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作者 CHANG Shuang-jun LIU Yu-cun 《Journal of Environmental Sciences》 SCIE EI CAS CSCD 2007年第12期1430-1435,共6页
The 2,4,6-trinitrotoluene (TNT) is a potential carcinogens and TNT contaminated wastewater, which could not be effectively disposed with conventional treatments. The supercritical water oxidation (SCWO) to treat T... The 2,4,6-trinitrotoluene (TNT) is a potential carcinogens and TNT contaminated wastewater, which could not be effectively disposed with conventional treatments. The supercritical water oxidation (SCWO) to treat TNT contaminated wastewater was studied in this article, The TNT concentration in wastewater was measured by high-performance liquid chromatograph (HPLC) and the degraded intermediates were analyzed using GC-MS. The results showed that SCWO could degrade TNT efficiently in the presence of oxygen. The reaction temperature, pressure, residence time and oxygen excess were the main contributing factors in the process. The decomposition of TNT was accelerated as the temperature or residence time increased. At 550℃, 24 MPa, 120 s and oxygen excess 300%, TNT removal rate could exceed 99.9%. Partial oxidation occured in SCWO without oxygen. It was concluded that supercritical water was a good solvent and had excellent oxidation capability in the existence of oxygen. The main intermediates of TNT during SCWO included toluene, 1,3,5-trinitrobenzene, nitrophenol, naphthalene, fluorenone, dibutyl phthalate, alkanes and several dimers based on the intermediate analysis. Some side reactions, such as coupled reaction, hydrolysis reaction and isomerization reaction may take place simultaneously when TNT was oxidized by SCWO. 展开更多
关键词 supercritical water oxidation TNT degradation mechanism wastewater treatment
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Reaction site and mechanism in the UV or visible light induced TiO2 photodegradation of Orange G 被引量:8
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作者 YANG Shi-ying LOU Li-ping +1 位作者 WU Xiao-na CHEN Ying-xu 《Journal of Environmental Sciences》 SCIE EI CAS CSCD 2006年第1期180-183,共4页
For TiO2 heterogeneous reaction, the reaction site and the detailed mechanism are interesting and controversy topics. In this paper, effects of surface fluorination of TiO2 on the photocatalytic degradation of an azo ... For TiO2 heterogeneous reaction, the reaction site and the detailed mechanism are interesting and controversy topics. In this paper, effects of surface fluorination of TiO2 on the photocatalytic degradation of an azo dye, Orange G(OG) under UV or visible light irradiation were investigated, and the possible reaction site and mechanism were elucidated. The adsorption of OG on TiO2 was nearly inhibited by fluoride but its UV light induced photodegradation rate was greatly increased by a factor of about 2.7, which was due to the more generated free hydroxyl radicals. It supported the views that fluoride could desorb the oxidant species from surface and that the reaction sites could move to the bulk solution. In TiO2/Vis system, the observed inhibition effects of fluorination could be interpreted by the competitive adsorption, which provided additional evidences that the visible light sensitized photodegradation of dye pollutants on the catalyst surface. 展开更多
关键词 photocatalytic degradation mechanism ADSORPTION FLUORINATION dye pollutants
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Thermal degradation of diethanolamine at stripper condition for CO2 capture: Product types and reaction mechanisms 被引量:3
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作者 Idris Mohamed Saeed Brahim Si Ali +3 位作者 Badrul Mohamed Jan Wan Jefrey Basirun Shaukat Ali Mazari Ibrahim Ali Obid Birima 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2019年第12期2900-2908,共9页
Amine-based absorption/stripping is one of the promising technology for CO2 capture from natural and industrial gas streams.During the process,amines and CO2 undergo irreversible reactions to produce undesired compoun... Amine-based absorption/stripping is one of the promising technology for CO2 capture from natural and industrial gas streams.During the process,amines and CO2 undergo irreversible reactions to produce undesired compounds,which cause corrosion,foaming,increased viscosity and breakdown of equipment,ultimately contributing to the economic loss and environmental pollution.In this study,the thermal degradation of aqueous diethanolamine in the presence and absence of dissolved CO2 was investigated.The experiments were performed in stainless steel cylinders.The results show that thermal degradation in the absence of CO2 was a slow process;triethanolamine,and tris(2-aminoethyl)amine were only the degradation products identified in the mixture In addition,the rate of degradation was very low,only 3%degradation was observed after 4 weeks.But in the presence of CO2,sixteen degradation products were identified,nine of which were new degradation products reported for the first time in this study.The 3-(2-hydroxyethyl)-2-oxazolidinone,1,4-bis(2-hydroxyethyl)piperazine and triethanolamine were the most abundant degradation products.The remaining DEA concentration after 4 weeks was about 20%of the total amine concentration.The most probable degradation reactions and their mechanisms are also proposed. 展开更多
关键词 DIETHANOLAMINE CO2 CAPTURE degradation mechanism
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The Mechanism of Carotenoid Degradation in Flue-Cured Tobacco and Changes in the Related Enzyme Activities at the Leaf-Drying Stage During the Bulk Curing Process 被引量:6
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作者 SONG Zhao-peng LI Tong-shuai +3 位作者 ZHANG Yong-gang CAO Hui-jing GONG Chang-rong ZHANG Wei-jian 《Agricultural Sciences in China》 CSCD 2010年第9期1381-1388,共8页
The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical b... The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components (β-carotene, lutein, neoxanthin, and violaxthin) decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing (T1) were relatively higher than the rapid heating curing (T2) accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments (P〉 0.05). The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes' activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma. 展开更多
关键词 bulk curing leaf-drying stage carotenoids mechanism of degradation enzyme
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Priori information analysis of optocoupler accelerated degradation experiment based on failure mechanism verification test 被引量:2
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作者 Xuan-gong Zhang Xi-hui Mu +1 位作者 Jing Feng Hui-zhi Li 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2020年第2期392-400,共9页
The optocoupler is a weak link in the inertial navigation platform of a kind of guided munitions.It is necessary to use accelerated storage test to verify the storage life of long storage products.Especially for small... The optocoupler is a weak link in the inertial navigation platform of a kind of guided munitions.It is necessary to use accelerated storage test to verify the storage life of long storage products.Especially for small sample products,it is very important to obtain prior information for the design and implementation of accelerated degradation test.In this paper,the optocoupler failure mechanism verification test is designed and the experimental results are analyzed and the prior information is obtained.The results show that optocouplers have two failure modes,one is sudden failure and the other is degradation failure;the maximum temperature stress of optocoupler can’t exceed 140℃;the increase of leakage current of optocoupler is caused by movable ions contaminating the LED chip.The surface leakage current is proportional to the adsorption amount.The increase of leakage current makes p-n junction tunneling effect occur which LEDs the failure of the optocoupler.The lifetime distribution model of the optocoupler is determined by the failure physics.The lifetime of the optocoupler is subject to the lognormal distribution.The degeneracy orbit of the optocoupler leakage current is described by a power law model.The estimated values of the orbital parameters are initially calculated and the parameters of its life distribution function are deduced.The above information lays a good foundation for the optimization design and data processing of the accelerated degradation experiment. 展开更多
关键词 Priori information FAILURE mechanism FAILURE mechanism VERIFICATION TEST ACCELERATED degradation
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The degradation mechanism of an AlGaN/GaN high electron mobility transistor under step-stress 被引量:1
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作者 陈伟伟 马晓华 +3 位作者 侯斌 祝杰杰 张进成 郝跃 《Chinese Physics B》 SCIE EI CAS CSCD 2013年第10期508-511,共4页
Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor (HEMT). It is found that the stress current shows a recoverable decrease... Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor (HEMT). It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT. 展开更多
关键词 A1GaN/GaN HEMT RELIABILITY degradation mechanism inverse piezoelectric effect
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Degradation of Spent Radioactive Ion Exchange Resins and Its Mechanisms by Fenton Process 被引量:1
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作者 Wendong Feng Jian Li +1 位作者 Hongxiang An Yunhai Wang 《Journal of Renewable Materials》 SCIE EI 2020年第10期1283-1293,共11页
Spent IERs are released during the operation and decommissioning of nuclear facilities.The safe and efficient treatment of spent IERs is an emergent problem in nuclear industry.IRN77 is a typical ion exchange resin wi... Spent IERs are released during the operation and decommissioning of nuclear facilities.The safe and efficient treatment of spent IERs is an emergent problem in nuclear industry.IRN77 is a typical ion exchange resin widely used in many nuclear power plants.Fenton process can degrade organic resins and reduce the radioactive residues volume and the disposal cost significantly.In this work,the IRN77 resin was selected as a model ion exchange resin and its treatment via Fenton process was investigated.The influencing factors for resin degradation,including catalyst dosage,reaction time,initial pH,temperature and oxidant dosage were investigated and optimized via the single-factor experimental method.Under the reaction temperature of 100℃ and reaction time of 120 min at initial pH of 2,more than 97%COD was removed with 1.66 g H_(2)O_(2) and 32 mg FeSO_(4)·7H_(2)O added to per gram of wet resin.The catalyst dosage and H_(2)O_(2) dosage can decrease 78%and 50%respectively compared to previous results.SEM,FT-IR and ion chromatograph were employed to characterize the resin beads,soluble organics and intermediates during the degradation reaction.Based on the characterization results,the resin degradation pathway was discussed in detail and it is proposed to three stages including beads dissociation,styrene and divinylbenzene decomposition and carboxylic acids mineralization.During the IERs degradation,formic acid,acetic acid,propionic acid and oxalic acid were quantitatively monitored as main intermediates,and oxalic acid accounted for over 90%of COD in the final residue solution.Fenton process is suggested as a promising resin degradation method. 展开更多
关键词 FENTON RESIN degradation mechanism
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Formation of active radicals and mechanism of photocatalytic degradation of phenol process using eosin sensitized TiO_2 under visible light irradiation 被引量:1
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作者 宋琳 张鑫 +2 位作者 马云坤 李明玉 曾小龙 《Journal of Central South University》 SCIE EI CAS 2013年第2期495-500,共6页
The role of oxygen and the generation of active radicals in the photocatalitic degradation of phenol were investigated using the eosin sensitized TiO2 as photocatalyst under visible light irradiation. Diffuse reflecta... The role of oxygen and the generation of active radicals in the photocatalitic degradation of phenol were investigated using the eosin sensitized TiO2 as photocatalyst under visible light irradiation. Diffuse reflectance spectra show that the absorbancy range of eosin/TiO2 is expanded from 378 nm (TiO2 ) to about 600 nm. The photocatalitic degradation of phenol is almost stopped when the eosin/TiO2 system is saturated with N2 , which indicates the significance of O2 . The addition of NaN 3 (a quencher of single oxygen) causes about a 62% decrease in the phenol degradation. The phenol degradation ratio is dropped from 92% to 75% when the isopropanol (a quencher of hydroxyl radical) is present in the system. The experimental results show that there are singlet oxygen and hydroxyl radical generated in the eosin/TiO2 system under visible light irradiation. The changes of absorbancy indicate that the hydrogen peroxide might be produced. Through the analysis and comparison, it is found that the singlet oxygen is the predominant active radical for the degradation of phenol. 展开更多
关键词 eosin sensitized TiO2 visible light photocatalytic degradation reaction mechanism
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Mechanisms of Accelerated Degradation in the Front Cells of PEMFC Stacks and Some Mitigation Strategies
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作者 LI Pengcheng PEI Pucheng +3 位作者 HE Yongling YUAN Xing CHAO Pengxiang WANG Xizhong 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2013年第6期1250-1258,共9页
The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell(PEMFC) stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and... The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell(PEMFC) stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and configuration of the gas intake manifold, which may lead to the maldistribution of flow and pressure. In order to find out the mechanisms of the accelerated degradation in the front cells, an extensive program of experimental and simulation work is initiated and the results are reported. It is found that after long-term lifetime tests the accelerated degradation in the front cells occurs in all three fuel cell stacks with different flow-fields under the U-type feed configuration. Compared with the rear cells of the stack, the voltage of the front cells is much lower at the same current densities and the membrane electrode assembly(MEA) has smaller active area, more catalyst particle agglomeration and higher ohmic impedance. For further investigation, a series of three dimensional isothermal numerical models are built to investigate the degradation mechanisms based on the experimental data. The simulation results reveal that the dry working condition of the membrane and the effect of high-speed gas scouting the MEA are the main causes of the accelerated degradation in the front cells of a PEM fuel cell stack under the U-type feed configuration. Several mitigation strategies that would mitigate these phenomena are presented: removing cells that have failed and replacing them with those of the same aging condition as the average of the stack; choosing a Z-type feed pattern instead of a U-type one; putting several air flow-field plates without MEA in the front of the stack; or exchanging the gas inlet and outlet alternately at a certain interval. This paper specifies the causes of the accelerated degradation in the front cells and provides the mitigation strategies. 展开更多
关键词 Proton exchange membrane fuel cell degradation mechanism Mitigation strategy
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Insight into the degradation mechanism of cefixime under crystallization condition
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作者 Lingyu Wang Xiaona Li +5 位作者 Yumin Liu DANDan Han Shiyuan Liu Teng Zhang Bo Yu Junbo Gong 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2018年第7期1458-1467,共10页
The chemical stability of cefixime was determined by high-performance liquid chromatography (HPLC) under different conditions, including factors such as pH, solvents, initial concentration, temperature and additives... The chemical stability of cefixime was determined by high-performance liquid chromatography (HPLC) under different conditions, including factors such as pH, solvents, initial concentration, temperature and additives. The degradation process follows the first-order kinetics. A pH-rate profile exhibits the U-shape and shows the maximum stability of cefixime at pH = 6. The stability in different pure solvents is ranked as acetone 〉 ethanol 〉 methanol 〉 water, while the degradation rate of cefixime exists a maximum at the ratio of 0.6 in water + methanol mixtures. In addition, the degradation rate increases with the temperature increasing and the activation energy of degradation was found to be 27.078 kJ. mol- 1 in acetone + water mixed solvents. The addition of different additives was proven to either inhibit or accelerate the degradation. The degradation products were analyzed using HPLC, LC-MS and infrared spectroscopy, and the possible degradation pathways in acid as well as alkaline environment were proposed to help us understand the degradation behavior of cefixime. 展开更多
关键词 Chemical stability degradation kinetics degradation mechanism Cefixime Additives
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STUDY OF DEGRADATION MECHANISM AND PACKAGING OF ORGANIC LIGHT EMITTING DEVICES
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作者 Gu Xu Materials Science and Engineering McMaster University Hamilton, Ontario, L8S 4L7 Canada 《Chinese Journal of Polymer Science》 SCIE CAS CSCD 2003年第5期527-531,共5页
Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to the... Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation. 展开更多
关键词 Organic light emitting devices degradation mechanism Dark spots Cathode rebuilding Polymer composites Heat dissipation and moisture resistance
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Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures
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作者 张进成 郑鹏天 +2 位作者 张娟 许志豪 郝跃 《Chinese Physics B》 SCIE EI CAS CSCD 2009年第7期2998-3001,共4页
This paper finds that the two-dimensional electron gas density in high Al-content A1GaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was inv... This paper finds that the two-dimensional electron gas density in high Al-content A1GaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements,high resolution x-ray diffraction,scanning electron microscopy,x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy.The results reveal that the formation of surface oxide is the main reason for the degradation,and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures. 展开更多
关键词 degradation mechanism two-dimensional electron gas AlGaN/GaN heterostructures surface oxidation
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Electrode degradation mechanism during resistance spot welding of zinc coated steel using Cu-TiB_2 electrodes 被引量:7
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作者 董仕节 ZHOU Norman +2 位作者 程长坤 史耀武 常保华 《中国有色金属学会会刊:英文版》 EI CSCD 2005年第6期1219-1225,共7页
The TiB2 dispersion-reinforced copper-matrix composite used as electrode material in resistance spot welding of zinc coated steels was studied. The service life of the composite electrode reaches (7700) welds, whi... The TiB2 dispersion-reinforced copper-matrix composite used as electrode material in resistance spot welding of zinc coated steels was studied. The service life of the composite electrode reaches (7700) welds, which is 4 times that of the conventional Cu-Cr-Zr electrode. Little gross deformation is observed on the composite (electrodes) because of the higher thermal strength; therefore, it is believed that wear is the only mechanism for the composite (electrode) deterioration. However, both wear and plastic deformation are responsible for the large increase in the tip diameter of the Cu-Cr-Zr electrodes. Moreover, the large deformation of the Cu-Cr-Zr electrodes may contribute to the increased wear rate of the tips. 展开更多
关键词 Cu-TiB2电极 退化机理 镀锌钢 电阻点焊 电极材料
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Efficiency and mechanism of degradation of alachlor in water by O_3/H_2O_2 catalyst system
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作者 高金胜 于颖慧 +1 位作者 孙志忠 马军 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2003年第2期208-213,共6页
Alachlor is used widely as a herbicide,but is an environmental endocrine disruptor. O 3/H 2O 2 system is used as catalyst to delve on the degradation efficiency of alachlor. The amount of the catalyst H 2O 2,the pH va... Alachlor is used widely as a herbicide,but is an environmental endocrine disruptor. O 3/H 2O 2 system is used as catalyst to delve on the degradation efficiency of alachlor. The amount of the catalyst H 2O 2,the pH value of the soluble, the temperature and quality of water sample are changed to investigate the effect of these factors on the degradation of alachlor. The degradation of alachlor is qualitatively analyzed through their GS MS spectra and the possible mechanism of the degradation of alachlor is discussed as well. 展开更多
关键词 ALACHLOR OZONE hydrogen peroxide degradation compound oxide mechanism
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