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EFFECTS OF TREATMENT TIME ON CORROSION OF DIFFUSION-ALLOYED COATINGS OF PURE MAGNESIUM

Acta Metallurgica Sinica(English Letters) 2007年第1期20卷 72-78页

作者： Y.P. Ma j. li j. Zhu L. Yang Y.G. liu Z.Y. li F. Zhao School of Metallurgic Engineering Xi＇an University of Architecture ＆ Technology Xi＇an 710055 China

The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480℃ for different solid diffusion time （8, 16, and 24h）. The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test （in 3.0% NaCl solution, temperature is （28±1）℃, and time is 96h）. Optical microscopy （OM） and EDS （energy dispersive spectrum） composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones （especially the samples treated for 24h at 480℃）, was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of Al5Mg11Zn4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous Al5Mg11Zn4 phase （WP-zone） of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.

关键词： pure magnesium solid diffusion treatment time microstructure corrosion

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Doubly periodic patterns of modulated hydrodynamic waves:exact solutions of the Davey-Stewartson system

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Acta Mechanica Sinica 2011年第5期27卷 620-626页

作者： j.-H. li S.-Y. Lou K.-W. Chow Department of Mechanical Engineering University of Hong Kong Pokfulam Road Hong Kong China Department of Physics Shanghai Jiao Tong University200030 Shanghai China

Exact doubly periodic standing wave patterns of the Davey-Stewartson （DS） equations are derived in terms of rational expressions of elliptic *** fluid mechanics,DS equations govern the evolution of weakly nonlinear,free surface wave packets when long wavelength modulations in two mutually perpendicular,horizontal directions are *** functions with two different moduli （periods） are necessary in the two *** relation between the moduli and the wave numbers constitutes the dispersion relation of such *** the long wave limit,localized pulses are recovered.

关键词： Free surface waves · Periodic patterns · DaveyStewartson equations

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COUPLED SIMULATION OF 3D ELECTRO-MAGNETO-FLOW FIELD IN HALL-HEROULT CELLS USING FINITE ELEMENT METHOD

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Acta Metallurgica Sinica(English Letters) 2006年第2期19卷 105-116页

作者： j. li W. liu Y.Q. Lai Q.Y. li Y.X. liu School of Metallurgy Science and Engineering Central South University Changsha 410083 China Chemistry Department Guangxi Normal University Guilin 531400 China

Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.

关键词： coupled simulation electromagnetic field flow field aluminum reduction cell finite element analysis

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Revealing the high-frequency attenuation mechanism of polyurea-matrix composites

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Acta Mechanica Sinica 2020年第1期36卷 130-142页

作者： j.Cheng Z.L.liu C.C.Luo T.li Z.j.li Y.Kang Z.Zhuang Applied Mechanics Laboratory School of Aerospace EngineeringTsinghua UniversityBeijing100084China Key Laboratory of Advanced Materials of Ministry of Education Department of Chemical EngineeringTsinghua UniversityBeijing100084China School of Materials Science and Engineering Tsinghua UniversityBeijing100084China

In this paper,a method for analyzing the high-frequency attenuation property of polyurea-matrix composites is developed by combining experimental,computational and theoretical ***,the ultrasonic experimental platform is established by solving the difficulties of high-frequency ultrasonic testing as high-frequency signal distortion,insufficient driving voltage and sampling rate failure,to study the dynamic mechanical properties(1-5 MHz)of pure polyurea and polyurea-matrix ***,the influences of composite parameters including the size and volume fraction of inclusions on wave attenuation performance under different frequencies are obtained and further verified by numerical ***,the contribution of inclusions to the wave attenuation performance is also theoretically *** is found that the increase of inclusion volume fraction and inclusion diameter will increase the attenuation coefficient of the *** the attenuation of composites with the inclusions of a 150-μm diameter and 30%as volume fraction can be 82%higher than pure *** amplifying attenuation effect of inclusions is mainly attributed to the scattering effect,which is verified by comparing numerical and theoretical results.

关键词： Polyurea Viscoelastic Dynamic mechanical properties Ultrasound

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EFFECT OF Cu-Ni CONTENT ON THE CORROSION RESISTANCE OF(Cu-Ni)/(10NiO-90NiFe_2O_4)CERMET INERT ANODE FOR ALUMINUM ELECTROLYSIS

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Acta Metallurgica Sinica(English Letters) 2008年第1期21卷 72-78页

作者： Z.L. Tian Y.Q. Lai j. li Y.X. liu School of Metallurgical Science and Engineering Central South University Changsha 410083 China

（Cu-Ni）/（10NiO-90NiFe204） cermet inert anodes containing metal Cu-Ni0, 5, 10, 15 and 20 wt pct were prepared and their corrosion resistance to Na3AlF6-Al2O3 melts was investigated. The results indicate that the content of metal Cu-Ni has little effect on the steady-state concentration of Ni in the electrolyte and the values could not be used to effectively differentiate their corrosion resistance. The steady-state concentration of Fe decreases from 304×10^-6 to 168×10^-6 and that of Cu increases from 21×10^-6 to 71×10^-6 with the content of metal Cu-Ni increasing from 0 to 20 wt pct. Post-examination shows that metallic phase Cu-Ni is corroded preferentially during electrolysis and many pores are left at the anode surface. Considering the corrosion resistance and electrical conductivity, the cermet containing metal Cu-Ni 5 wt pct should be selected and studied further.

关键词： Aluminum electrolysis Inert anode NiFe2O4 based cermet Corrosion resistance

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Properties of oscillatory neuronal activity in the basal ganglia and thalamus in patients with Parkinson’s disease

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Translational Neurodegeneration 2018年第1期7卷 154-166页

作者： G.Du P.Zhuang M.Hallett Y.-Q.Zhang j.-Y.li Y.-j.li Beij.ng Institute of Functional Neurosurgery Xuanwu HospitalCapital Medical UniversityNo.45 Changchun StreetXicheng DistrictBeijing 100053China Human Motor Control Section Medical Neurology BranchNINDSNIHBethesdaMDUSA Center of Parkinson’s disease Beijing Institute for Brain DisordersBeijingChina Key Laboratory of Neurodegenerative Diseases(Capital Medical University) Ministry of EducationBeijingChina

Background:The cardinal features of Parkinson’s disease(PD)are bradykinesia,rigidity and rest *** activity in the basal ganglia is predicted to underlie the mechanism of motor *** study aims to characterize properties of oscillatory activity in the basal ganglia and motor thalamus in patients with ***:Twenty-nine patients with PD who underwent bilateral or unilateral electrode implantation for subthalamic nucleus(STN)DBS(n=11),unilateral pallidotomy(n=9)and unilateral thalamotomy(n=9)were *** recordings in the STN,globus pallidus internus(GPi)and ventral oral posterior/ventral intermediate of thalamus(Vop/Vim)were *** of the contralateral limbs was *** unit characteristics including interspike intervals were *** and coherence analyses were *** spontaneous firing rate(MSFR)of neurons was *** of variance and χ^(2) test were ***:Of 76 STN neurons,39.5% were 4–6 Hz band oscillatory neurons and 28.9% were β frequency band(βFB)oscillatory *** MSFR was 44.2±7.6 *** 62 GPi neurons,37.1% were 4–6 Hz band oscillatory neurons and 27.4% were βFB *** MSFR was 80.9±9.6 *** 44 Vop neurons,65.9% were 4–6 Hz band oscillatory neurons and 9%were βFB *** MSFR was 24.4±4.2 *** 30 Vim oscillatory neurons,70% were 4–6 Hz band oscillatory neurons and 13.3% were β FB *** MSFR was 30.3±3.6 *** analysis indicated that proportion of βFB oscillatory neurons in STN and GPi was higher than that of similar neurons in the Vop and Vim(Plia play a critical role in generation of parkinsonism.β os

关键词： Parkinson’s disease Basal ganglia The subthalamic nucleus The globus pallidus internus The ventrolateral thalamus Oscillatory activity Microelectrode recordings

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EFFECT OF STRUCTURAL PARAMETERS ON THE THERMAL STRESS OF A NiFe_(2)O_(4)-BASED CERMET INERT ANODE IN ALUMINUM ELECTROLYSIS

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Acta Metallurgica Sinica(English Letters) 2007年第2期20卷 139-147页

作者： j. li Z.G. Wang Y.Q. Lai Y.Y. Wu S.L. Ye School of Metallurgy Science and Engineering Central South University Changsha 410083 China

Inert anode has been a hot issue in the aluminum industry for many decades. With the help of FEA （finite element analysis） software ANSYS, a model was developed to simulate the thermal stress distribution working condition of an inert anode. To reduce its thermal stress, the effect of some parameters on the thermal stress distribution was investigated, including the anode height, the anode radius, the hole depth, the hole radius, and the radius of inner chamfer and outer chamfer. The results showed that in the actual working condition of an inert anode, there existed a large axial tensile stress near the tangent interface between the anode and bath, which was the maj.r cause of anode breaking. Increasing the anode height and reducing the hole depth properly seemed to be beneficial for the stress distribution. With the increase of anode radius, the stress distribution became better first and then deteriorated, the reasonable value was between 0.045 to 0.06m. The hole radius had a significant effect on the stress and a smaller radius would reduce the thermal stress. The effect of the radius of the inner chamfer and the outer chamfer was less than other parameters.

关键词： inert anode thermal stress structural parameter aluminum electrolysis

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THERMAL STRESSES RELAXATION DESIGN OF Ni/NiFe_(2)O_(4) SYSTEM FUNCTIONALLY GRADED CERMET INERT ANODE

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Acta Metallurgica Sinica(English Letters) 2005年第5期18卷 635-641页

作者： j. li Q.S. Zhang Y.Q. Lai S.L. Ye Y.X. liu School of Metallurgy Science and Engineering Central South University Changsha 410083 China

The thermal stresses relaxation of Ni/NiFe2O4 system functionally graded cermet inert anode for aluminum electrolysis was optimally designed. The transient thermal stresses of the inert anode under complex boundary condition during high-temp （955℃） electrolysis were calculated using the finite-element software ANSYS, the influence of different parameters on the distribution of the thermal stresses were analyzed. The results showed that, during the process of thermal shock, the thermal hoop tensile stress on the surface of the anode is very large, which is possibly the maj.r cause of anode crack; when the radius of the anode is between 0.05-0.15m, a range that can be realized by recent manufacturing technology, the optimum composition distribution exponent p is 0.25; The hoop tensile stresses reduce with the decrease of anode scale and also decrease with the decrease of the convection coefficient between the electrolyte and the anode.

关键词： functionally graded material (FGM) transient thermal stresses ANSYS inert anode aluminum electrolysis

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THE EFFECT OF POWERFUL OXYGEN EVOLUTION METAL-OXIDE ON THE ELECTROOXIDATION OF METHANOL

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Acta Metallurgica Sinica(English Letters) 2001年第2期14卷 103-108页

作者： X.C. Chen, Y.X. liu, j. li, j.j. Chen and H.Z. liu (Department of Metallurgy Science and Engineering, Central South University, Changsha 410083, China) Department of Metallurgy Science and Engineering Central South University

An improved thermal decomposition method is used to prepare modified titanium base anodes. Some researches have been carried out to learn about the oxygen evolution properties of RuMn, RuCo and RuEu etc. in H2SO4 solution and their effect on the electrooxidation of methanol if they are added into the catalytic layers of Pt/Ti electrodes. The result indicates that the Pt/Ti electrodes containing RuMn, RuCo, RuCe and RuEu, etc. metal oxide catalysts with the powerful evolution property exhibit a higher electro-catalytic activity towards methanol electrooxidation than Pt/Ti electrodes without composite metal oxide catalysts.

关键词： Anodes Decomposition Methanol Oxidation Titanium

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FREEZE PROFILE AND HEAT BALANCE CALCULATION OF THE 160kA DRAINED CELL

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Acta Metallurgica Sinica(English Letters) 2004年第2期17卷 215-220页

作者： X.P. li j. li Y.Q. Lai H.Q.Zhao Y.X.liu School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China School of Metallurgical Science and Engineering Central South UniversityChangsha 410083China

A 2D full cell thermo-electric model of 160kA drained cell was set up using finiteelement code to calculate its freeze profile, then the drained cell model was modifiedaccording to the freeze profile computed and its heat balance was calculated. Comparedwith that of a 160kA conventional Hall-Heroult cell (H-H cell), though the melts vol-ume of the drained cell reduced greatly, the whole heat loss from it didn't drop downapparently, and an analysis was presented in the paper. On the other hand, the anode-cathode distance (ACD) of a drained cell was much less than that of a H-H cell, sothe voltage drop on it and heat produced decreased too, steps should be taken to keepa workable heat balance on a drained cell.

关键词： drained cell freeze profile heat balance finite element code

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