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Current understanding of the origin of equiaxed grains in pure metals during ultrasonic solidification and a comparison of grain formation processes with low frequency vibration,pulsed magnetic and electric-current pulse techniques

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Journal of Materials Science & Technology 2021年第6期65卷 38-53页

作者： Nagasivamuni Balasubramani gui Wang David h.St John Matthew S.Dargusch Centre for Advanced Materials Processing and Manufacturing(AMPAM) School of Mechanical and Mining EngineeringUniversity of QueenslandSt Lucia

The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(i.***.independent of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electric current pulse techniques.The dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites(ultrasonic field),wall crystals arising from the cold surface of the mould(electric current pulse,magnetic and pulsed magnetic fields).In all these cases fluid flow provides an additional contribution(e.***.reduced temperature gradients,growth rate and remelting of dendrites)to maintaining an equiaxed grain structure.The origin of equiaxed grains under an external field also depends on the casting conditions(volume and shape of casting)and the type of alloy other than the mechanisms specific to a particular technique.The current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals(magnesium and zinc)subjected to Ultra Sonic Treatment(UST).The role of the temperature range of UST application,time duration and an unpreheated sonotrode are examined with respect to the origin,evolution of equiaxed grain structure,morphology and the columnar to equiaxed transition.The origin of grains was analysed from three fundamental aspects that contribute to refinement(i)heterogeneous nucleation(ii)fragmentation of existing dendrites and(iii)grains produced from the colder surfaces(arising from mould walls or vibrating surfaces as wall crystals).A comparison of UST refinement with mechanical,low-frequency vibration,electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces(sonotrode and mould wall)in influencing grain refinement.

关键词： Ultrasonic treatment Grain refinement Equiaxed grains Magnesium Zinc Solidification

Catalytic performance and reaction mechanisms of NO removal with Nh_(3) at low and medium temperatures on Mn-W-Sb modified siderite catalysts

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Journal of Environmental Sciences 2022年第5期34卷 126-139页

作者： guihuan Yao Yuliang Wei Keting gui Xiang Ling School of Mechanical and Power Engineering Nanjing Tech UniversityNanjing 211816China School of Energy and Environment Southeast UniversityNanjing 210096China

Iron-based catalysts have been explored for selective catalytic reduction(SCR)of NO due to environmentally benign characters and good SCR activity.Mn-W-Sb modified siderite catalysts were prepared by impregnation method based on siderite ore,and SCR perfor-mance of the catalysts was investigated.The catalysts were analyzed by X-ray diffrac-tion,h_(2)-temperature-programmed reduction,Brunauer-Emmett-Teller,Thermogravimetry-derivative thermogravimetry and in-situ diffused reflectance infrared Fourier transform spectroscopy(DRIFTS).The modified siderite catalysts calcined at 450℃ mainly consist of Fe_(2)O_(3),and added Mn,W and Sb species are amorphous.3Mn-5W-1.5Sb-siderite catalyst has a wide temperature window of 180-360℃ and good N_(2) selectivity at low temperatures.In-situ DRIFTS results show Nh_(4)^(+),coordinated Nh_(3),Nh_(2),NO_(3)^(-)species(bidentate),NO_(2)-species(nitro,nitro-nitrito,monodentate),and adsorbed NO_(2) can be discovered on the sur-face of Mn-W-Sb modified siderite catalysts,and doping of Mn will enhance adsorbed NO_(2) formation by synergistic catalysis with Fe^(3+).In addition,the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO_(2) and h_(2)O.Time-dependent in-situ DRIFTS studies also indicate that both of Lewis and Br?nsted acid sites play a role in SCR of NO by ammonia at low temperatures.The mechanism of NO removal on the 3Mn-5W-1.5Sb-siderite catalyst can be discovered as a combination of Eley-Rideal and Langmuir-hinshelwood mechanisms with three reaction pathways.The mechanism of NO,oxidized by synergistic catalysis of Fe^(3+)and Mn^(4+/3+)to form NO_(2) among three pathways,reveals the reason of high NO_(x) conversion of the catalyst at medium and low temperatures.

关键词： Iron-based catalysts Mn-W-Sb In-situ diffused reflectance infrared Fourier transform spectroscopy Reaction mechanism Siderite Low and medium temperature

A comparative study of the role of solute,potent particles and ultrasonic treatment during solidification of pure Mg,Mg-Zn and Mg-Zr alloys

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Journal of Magnesium and Alloys 2021年第3期9卷 829-839页

作者： Nagasivamuni Balasubramani gui Wang Mark A.Easton David h.St John Matthew S.Dargusch Centre for Advanced Materials Processing and Manufacturing(AMPAM) School of Mechanical and Mining EngineeringThe University of QueenslandBrisbane 4072Australia School of Engineering RMIT UniversityCarlton3053 VICAustralia

Ultrasonic treatment(UST)applied during the solidification of pure Mg,eutectic(Mg-Zn)and peritectic(Mg-Zr)alloys was investigated in order to explore the grain refinement mechanisms.Temperature dependent grain refinement is observed in pure Mg where decreasing the superheat temperature(at which UST is applied from above the melting temperature,TM)from 100℃to 40℃produces significant refinement with a uniform grain structure.The presence of solute reduces the temperature dependence of the UST refinement and excellent grain refinement is obtained regardless of the superheat temperature(100℃or 40℃)and even with the use of preheated sonotrode in the Mg-6 wt.%Zn alloy.A further improvement in grain refinement is achieved when the alloy contains potent particles that introduce additional nucleation of grains in Mg-0.5 and 1.0 wt.%Zr alloys(producing an average grain size of≤100μm).At 40℃superheat,UST of Mg-Zn alloys produces excellent refinement(average grain sizeh non-dendritic grains,which is normally achieved only with the addition of grain refining master alloy in the as-cast condition.The enhanced refinement observed in the eutectic alloy is explained through the undercooling imposed by a relatively cold sonotrode combined with high frequency vibrations and acoustic streaming.The advantages of using a cold sonotrode,a low superheat and solute are demonstrated for achieving significant refinement during solidification of Mg alloys under UST without or with a lower addition of grain refining master alloys.

关键词： Grain refinement Mg-Zn alloy Mg-Zr alloy Ultrasonic treatment Interdependence Model Solidification

Photochemical multicomponent transformation of acceptor-only diazoalkanes by merging their cycloaddition and carbene reactivities

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中国化学快报:英文版 2023年第9期34卷 138-142页

作者： Bao-gui Cai Guo-Yong Xu Jun Xuan Anhui Province Key Laboratory of Chemistry for Inorganic/Organic hybrid Functionalized Materials College of Chemistry&Chemical EngineeringAnhui UniversityHefei 230601China Key Laboratory of Structure and Functional Regulation of hybrid Materials Ministry of EducationHefei 230601China Institute of Physical Science and Information Technology Anhui UniversityHefei 230601China

herein,we report an efficient photochemical method for the synthesis of poly-substituted pyrazoles through a multicomponent reaction of acceptor-only diazoalkanes,alkynes,and solvents(cyclic ethers or nitriles).The key to this success was driven by the photolysis of acceptor-only diazoalkanes to form free carbene species and the fast in situ[3+2]-cycloaddition formation of nucleophilic N–h pyrazole derivatives.This work also serves as an entry to allow future reaction design on the combination of carbene reactivity of diazoalkanes with their other reaction modes.

关键词： Photochemical synthesis Multicomponent reaction Diazoalkanes Carbene Pyrazoles

Regional coupled C-N-h2O cycle processes and associated driving mechanisms

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Science China Earth Sciences 2020年第9期63卷 1227-1236页

作者： Yang GAO gui-Rui YU Key Laboratory of Ecosystem Network Observation and Modeling Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijing 100101China College of Resources and Environment University of Chinese Academy of SciencesBeijing 100049China

From a molecular level to an ecosystem scale,different coupling mechanisms take place during coupled carbonnitrogen-water(C-N-h2O)cycle,of which essential are water flux and related biogeochemical processes through physicochemical reactions associated with terrestrial and aquatic ecosystems.Meanwhile,regional coupled C-N-h2O cycle will subsequently impact regional gross primary productivity(GPP)and C and N exchanges during air-water interactions that occur downstream of watersheds.This study aimed to first synthetically analyze the regional dynamics of C,N and h2O cycles in ecosystems and determine their interactional relationships;second,to specify regional C-N-h2O coupled relationships of ecosystems and their theoretical ecological principles;third,to classify coupled regional response and adaptation of the C-N-h2O cycle to climatic and environmental changes under anthropogenic activities,providing a theoretical basis to fully understand and make adjustments to interactional C,N and h2O cycling relationships at different ecosystem scales and under associated coupling processes.

关键词： Regional C-N-h2O cycle Coupled relationship C cycle N cycle Water cycle Driving mechanisms

Thermodynamics of Cascaded Waste heat Utilization from Flue Gas and Circulating Cooling Water

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Journal of Thermal Science 2023年第6期32卷 2166-2178页

作者： LI Yuanyuan ChEN Xin JIANG Shan LU gui State Key Laboratory of New Energy Power Systems North China Electric Power UniversityBeijing102206China Department of Water Resources China Institute of Water Resources and Hydropower ResearchBeijing100038China School of Energy Power and Mechanical Engineering North China Electric Power UniversityBeijing102206China

A detailed thermal power plant model was developed to evaluate power plant waste heat usage in terms of the operating parameters,energy consumption,water consumption,and pollutant emissions.This model was used to analyze the bypass flue gas energy cascade utilization design which provides excellent energy savings and emission reductions.This paper then presents a design to use the low-temperature waste heat and to extract water from the flue gas.The low-grade heat can be recovered from a coal-fired unit using absorption heat pumps to increase the air preheating.This method significantly reduces the turbine steam extraction in the low pressure stages which increases the turbine power and reduces the coal consumption.This design has a small heat transfer temperature difference between the air preheater and the air warmer,resulting in a smaller exergy loss.The power output of the present design was 1024.28 MW with a coal consumption savings of 3.69 g·(kWh)^(−1).In addition,the present design extracts moisture out of the flue gas to produce 46.48 t·h^(−1)of water.The main goal of this work is to provide a theoretical analysis for studying complex thermal power plant systems and various energy conservation and CO_(2)reduction options for conventional power plants.

关键词： integrated thermal power plant model low-grade waste heat energy cascade utilization exergy losses absorption heat pumps

Automated Dimensioning Method of Engineering Drawings for Mechanical Products Based on Curve Chain

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Computers, Materials & Continua 2020年第10期65卷 847-863页

作者： gui Li Peng Yang Key Laboratory of Metallurgical Equipment and Control Technology Ministry of EducationWuhan University of Science and TechnologyWuhan430081China hubei Key Laboratory of Mechanical Transmission and Manufacturing Engineering Wuhan University of Science and TechnologyWuhan430081China

An automated method based on the curve chain was proposed for dimensioning of engineering drawings for the mechanical products.According to the internal relation between the features of 3D model feature and elements of 2D drawing,the curve chain was established to reflect the geometric topological structure between the elements.It divides the dimensions into the absolute dimensions within the cure chain and the relative dimensions between the curve chains.The parallel and lengthy relationship between the drawing elements of the constructed X and Y parallel matrix was solved to remove redundant elements in the curve chain and labeled the absolute dimensions of the remaining valid elements.The average minimum weight coefficient was introduced to judge the dependence on the relative dimensions between curve chains.Through the analysis of the overlap between the circular rectangular areas,including all the absolute dimensions of the curve chains,overlapping curve chains were merged,and their dimensions were rearranged to avoid the cross interference between them.The method was seamlessly integrated into the drafting module of product design software NX,and it developed an automated dimensioning system.The examples show that the system has excellent interactivity and robustness in the dimensioning of product engineering drawings.The dimension information is complete,accurate and reliable.

关键词： Automated dimensioning engineering drawing curve chain mechanical product weight coefficient

Effect of Ti and Ta content on the oxidation resistance of Co-Ni-based superalloys

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International Journal of Minerals,Metallurgy and Materials 2024年第2期31卷 351-361页

作者： Yuheng Zhang Zixin Li Yunwei gui huadong Fu Jianxin Xie Beijing Advanced Innovation Center for Materials Genome Engineering University of Science and Technology BeijingBeijing 100083China Institute of Materials Intelligent Technology Liaoning Academy of MaterialsShenyang 110004China Key Laboratory for Advanced Materials Processing(MOE) University of Science and Technology BeijingBeijing 100083China Beijing Laboratory of Metallic Materials and Processing for Modern Transportation University of Science and Technology BeijingBeijing 100083China

Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature structural materials for aeroengine and gas turbine hot-end components.Our previous work elucidated the influence of Ti and Ta on the high-temperature mechanical properties of alloys.however,the intricate interaction among elements considerably affects the oxidation resistance of alloys.In this paper,Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5−x)Ta alloys(x=1,2,3,4)with varying Ti and Ta contents were designed and compounded,and their oxidation resistance was investigated at the temperature range from 800 to 1000℃.After oxidation at three test conditions,namely,800℃for 200 h,900℃for 200 h,and 1000℃for 50 h,the main structure of the oxide layer of the alloy consisted of spinel,Cr_(2)O_(3),and Al_(2)O_(3)from outside to inside.Oxides consisting of Ta,W,and Mo formed below the Cr_(2)O_(3)layer.The interaction of Ti and Ta imparted the highest oxidation resistance to 3Ti2Ta alloy.Conversely,an excessive amount of Ti or Ta resulted in an adverse effect on the oxidation resistance of the alloys.This study reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloys with a high Al content for the first time and explains the formation mechanism of holes in the oxide layer.The results provide a basis for gaining insights into the effects of the interaction of alloying elements on the oxidation resistance of the alloys they form.

关键词： Co-Ni-based superalloys high-temperature oxidation Ti and Ta elements formation mechanism of holes

Structures of Interaction of Non-selfsimilar Elementary Waves for 2D Scalar Conservation Law with Two Initial Discontinuities

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Acta Mathematicae Applicatae Sinica 2023年第3期39卷 465-490页

作者： gui-qin QIU Gao-wei CAO Xiao-zhou YANG University of Chinese Academy of Sciences Beijing 100049China Wuhan Institute of Physics and Mathematics Innovation Academy for Precision Measurement Science and TechnologyCASWuhan 430071China

In this paper,we investigate the global solution and the structures of interaction between two dimensional non-selfsimilar shock wave and rarefaction wave of general two-dimensional scalar conservation law in which flux functions f(u)and g(u)do not need to be convex,and the initial value contains three constant states which are respectively separated by two general initial discontinuities.When initial value contains three constant states,the cases of selfsimilar shock wave and rarefaction wave had been studied before,but no results of the cases of neither non-selfsimilar shock wave or non-selfsimilar rarefaction wave.Under the assumption that Condition h which is generalization of one dimensional convex condition,and some weak conditions of initial discontinuity,according to all the kinds of combination of elementary waves respectively staring from two initial discontinuities,we get four cases of wave interactions as S+S,S+R,R+S and R+R.By studying these interactions between non-selfsimilar elementary waves,we obtain and prove all structures of non-selfsimilar global solutions for all cases.

关键词： Riemann problem shock wave rarefaction wave wave interaction