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Behavior of phase transformation of Baotou mixed rare earth concentrate during oxidation roasting

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Journal of Rare Earths 2022年第6期40卷 981-987,I0005页

作者： Deliang Meng Meng Wang Zongyu Feng Chao Xia Yanyan Zhao xiaowei Huang School of Metallurgy Northeastern UniversityShenyang 110819China National Engineering Research Center for Rare Earth Materials GRINM Group Co.Ltd.Beijing 100088China General Research Institute for Nonferrous Metals Beijing 100088China GRIREM Advanced Materials Co. Ltd.Beijing 100088China

Based on the new process named "Combination Method" for metallurgy and separation of Baotou mixed rare earth concentrate(BMREC),the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450-800℃.The results indicate that the bastnaesite in BMREC is decomposed at 450-550℃,the weight loss is about 10.3 wt%,and the activation energy(E) is 144 kJ/mol.The bastnaesite in BMREC is decomposed into rare earth fluoride,rare earth oxides(La_(2)O_(3),Ce_(7)O_(12),Pr_(6)O_(11) and Nd_(2)O_(3)),and CO_(2),particularly,with the increase of roasting temperature,bastnaesite in BMREC is more completely decomposed into LaF_(3),which causes a decrease in leaching rate of La during the HCI leaching process.Additionally,the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500℃,and the oxidation reaction rate of cerium increases with the increasing roasting temperature.

关键词： Phase change Combination method Oxidation roasting Cerium oxidation efficiency Rare earths

Investigations of entrainment characteristics and shear-layer vortices evolution in an axisymmetric rear variable area bypass injector

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Chinese Journal of Aeronautics 2022年第4期35卷 230-244页

作者： Guoping HUANG chao LI Chen xia Qian LI College of Energy and Power Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

In this study,firstly,for the axisymmetric RVABI,the change-rule of adverse pressure gradient caused by radial velocity during the transition of internal flow mode in variable geometry is summarized,and a Bypass Ratio(BR) iterative algorithm based on the empirical correlation of non-equilibrium pressure is proposed.The algorithm can estimate the nonlinear relationship between area ratio and BR,with an error range falling below 6.5%.Then,we discuss the favorable effect of uniform mixing on the thrust augmentation of mixed exhaust under variable BR conditions.From this point of view,the characteristics of vortices evolution in different shear strength jets are compared,to clarify the effect of variable cycle parameters on jet mixing.As the results suggest,when ■ is as low as 0.22,the K-H disturbance is of high-frequency wavelet property,and it is difficult to induce large-scale spanwise vortices.The macro migrations of fluid elements in span wise vortices and the diffusion effect caused by edge tearing is weak,which is not conducive to the energy exchange between the two streams.However,the low ■ jet will also correspondingly weaken the viscous dissipation effect of vortices.It is concluded that the dissipation level is proportional to the 2.31 power of the ■.

关键词： Variable cycle engine Rear variable area bypass injector Bypass ratio adjustment Mixed exhaust Thermal mixing Spanwise vortex

Sharp Bounds on the A_(α)-index of Graphs in Terms of the Independence Number

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Acta Mathematicae Applicatae Sinica 2023年第3期39卷 656-674页

作者： Wan-ting SUN Li-xia YAN Shu-chao LI Xue-chao LI Faculty of Mathematics and Statistics Central China Normal UniversityWuhan 430079China School of Information Eigeneering Wuhan Business UniversityWuhan 430056China The University of Georgia AthensGA 30602United States

Given a graph G,the adjacency matrix and degree diagonal matrix of G are denoted by A(G)and D(G),respectively.In 2017,Nikiforov~([24])proposed the A_(α)-matrix:A_α(G)=αD(G)+(1-α)A(G),whereα∈[0,1].The largest eigenvalue of this novel matrix is called the A_(α)-index of G.In this paper,we characterize the graphs with minimum A_(α)-index among n-vertex graphs with independence number i forα∈[0,1),where i=1,[n/2],[n/2],[n/2]+1,n-3,n-2,n-1,whereas for i=2 we consider the same problem forα∈[0,3/4].Furthermore,we determine the unique graph(resp.tree)on n vertices with given independence number having the maximum A_(α)-index withα∈[0,1),whereas for the n-vertex bipartite graphs with given independence number,we characterize the unique graph having the maximum A_α-index withα∈[1/2,1).

关键词： independence number spectral radius A_(α)-index bipartite graph

Tuning heat transport via coherent structure manipulation:recent advances in thermal turbulence

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National Science Review 2023年第6期10卷 245-257页

作者： Ke-Qing xia Shi-Di Huang Yi-chao Xie Lu Zhang Center for Complex Flows and Soft Matter Research and Department of Mechanics and Aerospace Engineering Southern University of Science and Technology State Key Laboratory for Strength and Vibration of Mechanical Structures and School of Aerospace Xi'an Jiaotong University

Tuning transport properties through the manipulation of elementary structures has achieved great success in many areas,such as condensed matter physics.However,the ability to manipulate coherent structures in turbulent flows is much less explored.This article reviews a recently discovered mechanism of tuning turbulent heat transport via coherent structure manipulation.We first show how this me chanism can be realized by applying simple geometrical confinement to a classical thermally driven turbulence, which leads to the condensation of elementary coherent structures and significant heat-transport enhancement,despite the resultant slower flow.Some potential applications of this new paradigm in passive heat management are also discussed.We then explain how the heat transport behaviors in seemingly different turbulence systems can be understood by this unified framework of coherent structure manipulation.Several future directions in this research area are also outlined.

关键词： coherent structure turbulent flow heat transport geometrical confinement dynamical constraint

Theoretical and Experimental Analysis of Heat Transfer and Condensation in Micro-Ribbed Tubes

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Fluid Dynamics & Materials Processing 2023年第6期19卷 1411-1424页

作者： Daoming Shen Jinhong xia chao Gui Songtao Xue Xinxiang University Xinxiang453000China Department of Architecture Tohoku Institute of TechnologySendai982-8577Japan

The thermal transmission coefficient for a micro-ribbed tube has been determined using theoretical relationships and the outcomes of such calculations have been compared with experiments conducted using a R1234yf refrigerant undergoing condensation.In particular four theoretical single-phase flow and three multi-phase flow models have been used in this regard.The experimental results show that:the Oliver et al.criterion equation overestimates the experimental results as its accuracy is significantly affected by the specific conditions realized inside micro-fin tubes;the Miyara et al.criterion equation prediction error is less than 15%;the Cavallini et al.approach gives the highest prediction accuracy;the Goto et al.model overestimates the test data.Such results are critically discussed and some indications for the improvement of such models are provided.

关键词： Micro-ribbed tube flow condensation thermal transmission coefficient dimensionless criterion equation

Effect of cold stratification on the temperature range for germination of Pinus koraiensis

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Journal of Forestry Research 2023年第1期34卷 221-231页

作者： Yuan Song Xinghuan Li Mingyi Zhang Guowei xia chao Xiong College of Eco-Environmental Engineering Guizhou Minzu UniversityGuiyangPeople’s Republic of China Qingyuan Forest CERN Chinese Academy of SciencesShenyang 110016People’s Republic of China Karst Environmental Geological Hazard Prevention Laboratory of Guizhou Minzu University GuiyangPeople’s Republic of China Guiyang Institute of Information Science and Technology GuiyangPeople’s Republic of China

Germination at low spring temperatures may offer a competitive advantage for the growth and survival of plant species inhabiting temperate forest ecosystems.Pinus koraiensis is a dominant species in temperate forests of northeastern China.Its seeds exhibit primary morphophysiological dormancy following dispersal in autumn,limiting natural or artificial regeneration:direct seeding and planting seedlings in spring.The aim of this study was to determine the optimum cold stratification temperature that induces germination to increase towards lower temperatures.Seeds from two populations(Changbaishan and Liangshui)were cold stratified at 0,5 and 10℃.Germination to incubation temperatures(10/5,20/10,25/15 and 30/20℃;14/10 h day/night)were determined after 2 and 4 weeks,and 5.5 and6.5 months of cold stratification.After 5.5 months,approximately 68-91%of seeds from both populations germinated at incubation temperatures of 25/15℃and 30/20℃,regardless of cold stratification temperatures.When the cold stratification temperature was reduced to 0℃and the period increased to 6.5 months,germination at 10/5℃significantly improved,reaching 37%and 64%for the Changbaishan and Liangshui populations,respectively.After 6.5 months of cold stratification,there was a significant linear regression between cold stratification temperatures and germination at10/5℃.The range in temperatures allowing for germination gradually expanded to include lower temperatures with decreasing cold stratification temperatures from 10 to 5℃and further to 0℃.

关键词： Cold Stratification temperatures Pinus koraiensis Seed germination Germination temperature range

A Study on the Current Situation, Problems and Responsive Measures of Building China's National Carbon Market

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Chinese Journal of Urban and Environmental Studies 2022年第3期10卷 7-16页

作者： xia Yingzhe FENG chao YUAN xiaohua China Clean Development Mechanism Fund Management Center

Carbon emissions trading is a major innovation in the practice of using market mechanism to control and reduce greenhouse gas(GHG) emissions and promote green and low-carbon development. It is an important way to achieve China’s carbon peaking and carbon neutrality goals(the“dual carbon” goals) at a relatively low cost. Starting late and having gone through three development stages, China’s national carbon market has entered a new stage. However, given the problems such as incomplete institutional, regulatory and carbon emissions verification systems,less balanced and vibrant market, limited transaction entities and trading products, and lack of voice due to insufficient participation in relevant international affairs, continuous efforts are still required to further improve this market by deepening reform, strengthening capacity building and increasing international cooperation.

关键词： Climate change carbon neutrality carbon market MRV

Mechanism and control technology of strong ground pressure behaviour induced by high-position hard roofs in extra-thick coal seam mining

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International Journal of Mining Science and Technology 2022年第3期32卷 499-511页

作者： chao Pan Binwei xia Yujun Zuo Bin Yu Changnan Ou Mining College Guizhou UniversityGuiyang 550025China National&Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam Chongqing UniversityChongqing 400044China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing 400044China

This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for HHR was established by considering the gangue support coefficient,through which the modified expressions of limit breaking span and breaking energy of HHR were deduced.Combined with the relationship between the dynamic-static loading stress of supporting body(hydraulic support and coal wall)and its comprehensive supporting strength,the criteria of ground pressure behaviour(GPB)induced by HHR were discussed.The types of Ⅰ_(1),Ⅰ_(2),Ⅱ_(1),andⅡ_(2) of GPB were interpreted.Results showed that types Ⅰ_(1) and Ⅰ_(2) were the main forms of SGPB in extra-thick coal seam mining.The main manifestation of SGPB was static stress,which was mainly derived from the instability of HHR rather than fracture.Accordingly,an innovative control technology was proposed,which can weaken static load by vertical-well separated fracturing HHR.The research results have been successfully applied to the 8101 working face in Tashan coal mine,Shanxi Province,China.The results of a digital borehole camera observation and stress monitoring proved the rationality of the GPB criteria.The control technology was successful,paving the way for new possibilities to HHR control for safety mining.

关键词： Extra thick coal seam High-position hard roof Strong ground pressure behaviour Supporting structures Criteria of ground pressure behaviour Controlling effects

Behavior of sulfate in preparation of single light rare earth carbonate by Mg(HCO_(3))_(2) precipitation method

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Journal of Rare Earths 2021年第7期39卷 850-857,I0004页

作者： Meng Wang xiaowei Huang Zongyu Feng Chao Xia Deliang Meng Zonghe Yu National Engineering Research Center for Rare Earth Materials GRINM Group Co.Ltd.Beijing 100088China GRIREM Advanced Materials Co. Ltd.Beijing 100088China General Research Institute for Nonferrous Metals Beijing 100088China Rare Earth Functional Materials(Xiong'an)Innovation Center Co. Ltd.Baoding 071700China

The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_(4)^(2-)<1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_(4)^(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_(3))_(2) as a precipitant.The results indicate that the contents of SO_(4)^(2-) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La_(2)(CO_(3))2.15(-SO_(4))0.85·4 H_(2)O and Ce_(2)(CO_(3))_(2).15(SO_(4))0.85·3H_(2)O,while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_(4)^(2-) enclosed in the precipitation.The content of SO_(4)^(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_(4)^(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_(4)^(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.

关键词： Rare earth sulfate Magnesium bicarbonate Rare earth carbonate Sulfate ion Complex salt