The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of h...The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration;although a new in-situ two-step sintering process can solve the above problems to some extent,yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process.In this paper,an in-situ one-step synthesis technology is proposed,which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace.A kind of Ti（C,N）-based ceramic cutting tool material synergistically toughened by TiB_2 particles and whiskers is fabricated with this new process.The phase compositions,relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The composite which is sintered under a pressure of 32 MPa at a temperature of 1700℃in vacuum holding for 60 min can get the optimal mechanical properties.Its flexural strength,fracture toughness and Vickers hardness are 540 MPa,7.81 MPa·m（1/2）and 20.42 GPa,respectively.The composite has relatively high density,and the in-situ synthesized TiB_2 whiskers have good surface integrity,which is beneficial for the improvement of the fracture toughness.It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers,crack bridging by whiskers/particles and multi-scale particles synergistically toughening.This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.展开更多
CONSPECTUS:Macrocycles play pivotal roles in supramolecular chemistry and materials science because of their distinctive molecular recognition capabilities and versatile applications in selfassembly.However,traditiona...CONSPECTUS:Macrocycles play pivotal roles in supramolecular chemistry and materials science because of their distinctive molecular recognition capabilities and versatile applications in selfassembly.However,traditional macrocycles,such as cyclodextrins,calixarenes,cucurbiturils,and pillararenes,have inherent limitations in terms of cavity size and structural variety,which restrict their ability to encapsulate vip molecules of varying sizes and their potential in constructing multifunctional materials.展开更多
Electrochemical nitrate reduction reaction(NO_(3)RR)represents a prospective approach to convert the hazardous NO_(3)-waste into valuable NH_(3)product.Yet,designing highly efficient and durable catalyst with high NH_...Electrochemical nitrate reduction reaction(NO_(3)RR)represents a prospective approach to convert the hazardous NO_(3)-waste into valuable NH_(3)product.Yet,designing highly efficient and durable catalyst with high NH_(3)formation selectivity is still challenging.Herein,we report a catalyst of Ru SAs/Co-NC with Ru single atoms(Ru SAs)anchored on Co,N co-doped carbon materials(Co-NC)for efficient NO_(3)RR catalysis to generate NH_(3).The Ru single atoms were prepared through in-situ transformation of metal nodes in metal-organic frameworks(MOFs),and the confinement in MOFs ensured the atomical dispersion of Ru atoms.The Ru SAs/Co-NC catalyst exhibited excellent catalytic performance toward NO_(3)RR,evidenced by a NH_(3)Faradaic efficiency of 96.3%and yield rate of 1.12 mmol·h^(-1)·cm^(-2)at-0.5 V vs.reversible hydrogen electrode(RHE),as well as good cycling stability.The density functional theory calculations revealed a Ru-Co synergistic catalytic effect,where the Co site promotes H_(2)O dissociation to supply sufficient^(*)H for continuous hydrogenation/deoxygenation,and the Ru site is able to achieve enhanced NO_(3)-adsorption and accelerated hydrogenation process to form NH_(3)eventually.展开更多
An abrasive free chemical mechanical planarization（AFCMP） of semi-polar（1122） Al N surface has been demonstrated. The effect of slurry p H, polishing pressure, and platen velocity on the material removal rate（MRR...An abrasive free chemical mechanical planarization（AFCMP） of semi-polar（1122） Al N surface has been demonstrated. The effect of slurry p H, polishing pressure, and platen velocity on the material removal rate（MRR） and surface quality（RMS roughness） have been studied. The effect of polishing pressure on the AFCMP of the（1122） Al N surface has been compared with that of the（1122） Al Ga N surface. The maximum MRR has been found to be 562 nm/h for the semi-polar（1122） Al N surface, under the experimental conditions of 38 k Pa pressure,90 rpm platen velocity, 30 rpm carrier velocity, slurry p H 3 and 0.4 M oxidizer concentration. The best root mean square（RMS） surface roughness of 1.2 nm and 0.7 nm, over a large scanning area of 0.70×0.96 mm^2, has been achieved on AFCMP processed semi-polar（1122） AlN and（AlGaN） surfaces using optimized slurry chemistry and processing parameters.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51175305)Key Special Project of Numerical Control Machine Tool of China(Grant No.2012ZX04003-051)China Postdoctoral Science Special Foundation(Grant No.2012T50610)
文摘The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration;although a new in-situ two-step sintering process can solve the above problems to some extent,yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process.In this paper,an in-situ one-step synthesis technology is proposed,which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace.A kind of Ti（C,N）-based ceramic cutting tool material synergistically toughened by TiB_2 particles and whiskers is fabricated with this new process.The phase compositions,relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The composite which is sintered under a pressure of 32 MPa at a temperature of 1700℃in vacuum holding for 60 min can get the optimal mechanical properties.Its flexural strength,fracture toughness and Vickers hardness are 540 MPa,7.81 MPa·m（1/2）and 20.42 GPa,respectively.The composite has relatively high density,and the in-situ synthesized TiB_2 whiskers have good surface integrity,which is beneficial for the improvement of the fracture toughness.It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers,crack bridging by whiskers/particles and multi-scale particles synergistically toughening.This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.
基金supported by the National Natural Science Foundation of China(22471195,22201212)Natural Science Foundation of Tianjin City(23JCZDJC00660).
文摘CONSPECTUS:Macrocycles play pivotal roles in supramolecular chemistry and materials science because of their distinctive molecular recognition capabilities and versatile applications in selfassembly.However,traditional macrocycles,such as cyclodextrins,calixarenes,cucurbiturils,and pillararenes,have inherent limitations in terms of cavity size and structural variety,which restrict their ability to encapsulate vip molecules of varying sizes and their potential in constructing multifunctional materials.
基金the Research Grant Council of Hong Kong for financial support through the projects(Nos.GTF21EG07,16201622,and 16201820)acknowledge Hong Kong University of Science and Technology(HKUST)Fok Ying Tung Research Institute and Guangzhou Nansha subcenter of National Supercomputing Center for offering high-performance computational resources+1 种基金F.C.appreciates the start-up funds from the University of Bayreuth.Z.H.Tsupport from Guangdong Natural Science Funds(No.2023A0505050107).
文摘Electrochemical nitrate reduction reaction(NO_(3)RR)represents a prospective approach to convert the hazardous NO_(3)-waste into valuable NH_(3)product.Yet,designing highly efficient and durable catalyst with high NH_(3)formation selectivity is still challenging.Herein,we report a catalyst of Ru SAs/Co-NC with Ru single atoms(Ru SAs)anchored on Co,N co-doped carbon materials(Co-NC)for efficient NO_(3)RR catalysis to generate NH_(3).The Ru single atoms were prepared through in-situ transformation of metal nodes in metal-organic frameworks(MOFs),and the confinement in MOFs ensured the atomical dispersion of Ru atoms.The Ru SAs/Co-NC catalyst exhibited excellent catalytic performance toward NO_(3)RR,evidenced by a NH_(3)Faradaic efficiency of 96.3%and yield rate of 1.12 mmol·h^(-1)·cm^(-2)at-0.5 V vs.reversible hydrogen electrode(RHE),as well as good cycling stability.The density functional theory calculations revealed a Ru-Co synergistic catalytic effect,where the Co site promotes H_(2)O dissociation to supply sufficient^(*)H for continuous hydrogenation/deoxygenation,and the Ru site is able to achieve enhanced NO_(3)-adsorption and accelerated hydrogenation process to form NH_(3)eventually.
基金financial support from the Department of Science and Technology(DST),Government of India(No,SR/S2/Cmp-0009/2011)partial support from the Board of Research in Nuclear Sciences(BRNS),Department of Atomic Energy(DAE),Government of India(No.-34/14/43/2014-BRNS)with ATC
文摘An abrasive free chemical mechanical planarization（AFCMP） of semi-polar（1122） Al N surface has been demonstrated. The effect of slurry p H, polishing pressure, and platen velocity on the material removal rate（MRR） and surface quality（RMS roughness） have been studied. The effect of polishing pressure on the AFCMP of the（1122） Al N surface has been compared with that of the（1122） Al Ga N surface. The maximum MRR has been found to be 562 nm/h for the semi-polar（1122） Al N surface, under the experimental conditions of 38 k Pa pressure,90 rpm platen velocity, 30 rpm carrier velocity, slurry p H 3 and 0.4 M oxidizer concentration. The best root mean square（RMS） surface roughness of 1.2 nm and 0.7 nm, over a large scanning area of 0.70×0.96 mm^2, has been achieved on AFCMP processed semi-polar（1122） AlN and（AlGaN） surfaces using optimized slurry chemistry and processing parameters.
