Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 （mass fraction）, which were reconstituted into micrometer-sized granu...Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 （mass fraction）, which were reconstituted into micrometer-sized granules by spray drying, subsequently sintering at different temperatures to form nanostructured feedstock for thermal spraying, and then A1203-13%TiO2 nanocoatings were deposited by plasma spraying. The evolution of morphology, microstructure, and phase transformation of the agglomerated powder and as-sprayed coatings were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that A1203 retains the same a phase as the raw material during sintering, while TiO2 changes from anatase to futile. During plasma spraying, some a-A1203 phases solidify to form metastable y-A1203, and the volume fraction of a-A1203 decreases as CPSP increases. However, peaks of the TiO2 phase are not observed from the as-sprayed coatings except for the coatings sprayed at the lower CPSP. As the CPSP increases, nanostructured TiO2 is dissolved easily in y-A1203 or z-A1203＇TiO2 phase. After heat treatment, y-A1203 in the coatings transforms to a-A1203, and rutile is precipitated.展开更多
Nano-sized Er^(3+)∶Y_(3)Al_(5)O_(12)powders was successfully prepared via a simple sol-gel route at as low a temperature at 800℃whereas a temperature much higher is necessary to obtain this compound by solid state s...Nano-sized Er^(3+)∶Y_(3)Al_(5)O_(12)powders was successfully prepared via a simple sol-gel route at as low a temperature at 800℃whereas a temperature much higher is necessary to obtain this compound by solid state synthesis(about 1500℃).The phase purity,composition and microstructural features of the materials were analyzed by means of X-ray diffraction(XRD),infrared spectroscopy(IR)and transmission electron microscopy(TEM),and no other intermediate phase were observed to form in the range of 700~1000℃.The luminescence spectra of Er^(3+)substituted for Y^(3+)in YAG in 1%content was characterized on samples at different temperature.展开更多
Combustion of nitrate-citrate gel was employed to prepare REFeO3(RE=Y,La and Gd) nanocrystalline powders.The samples were characterized with X-ray diffraction(XRD) analysis,thermal analysis(TG/DTA) and transmission el...Combustion of nitrate-citrate gel was employed to prepare REFeO3(RE=Y,La and Gd) nanocrystalline powders.The samples were characterized with X-ray diffraction(XRD) analysis,thermal analysis(TG/DTA) and transmission electron microscopy(TEM).LaFeO3 crystallites were directly obtained by the sol-gel combustion process,and orthorhombic YFeO3 and GdFeO3 were formed when annealed at 800 oC.The investigation of magnetic properties showed that YFeO3 and LaFeO3 exhibited ferromagnetic behavior,while GdFeO3 presented...展开更多
Fe73. 5 Cu1 Nb3 Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 9m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P cv and decreased ini...Fe73. 5 Cu1 Nb3 Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 9m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P cv and decreased initial permea- bility μi with addition of fine powders below 50 μm in size, and the content should be less than 40 mass%. It was thought to be closely related to the high coercive force H c due to the stresses generated during the crushing process and high demagnetization fields of small powders. Furthermore, modifying the alloy compositions by adding defined amount of Ni could improve the soft magnetic properties, including superior characteristics of permeability under high direct current （DC） bias field and comparable low core loss at high frequency.展开更多
Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change...Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change slightly with the dopant concentrations. The the of the dopants on the sintering of the compacted powders was investigated during heating at a constant rate of 10℃/min. The elemental composition and the concentration of the dopant has significant efFect on the densification and grain growth. Compared to undoped CeO2, the dopants produce a shift in the densification curve to higher temperatures. For the same dopant concentration and under identical sintering conditions, the Ca doped samples reach nearly full density with the smallest grain size (≈50 nm), however, the Mg doped sample has the lowest density (≈95% of the theoretical) with the largest grain size (≈1 μm)展开更多
In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distributi...In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.展开更多
The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ra...The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ray diffraction, transmission electron microscopy, plasma emission spectroscopy and infrared spectrum were used to analyze the prepared samples, and density functional theory was used to investigate the cryomilling process. For nanocrystalline silicon powder cryomilled with liquid N2, the amorphous outer layer with N element is formed On the surface, and chemisorption caused by the formation of Si-N-Si bond leads to the surface passivation; although physisorpfion also he confirmed, the Si-N bond is steady after exploded in air for 30 days and no new bond is observed. For nanocrystalline silicon powder cryomilled with liquid At, no new chemical bond is Observed, Ar element absorbs on the surface of the prepared powder only through physisorption, and after exploded in air for 30 days, a Si-O bond can be observed obviously.展开更多
Nanocrystalline WC-Co composite powder and coated tungsten diamond by using vacuum vapor deposition were consolidated by the spark plasma sintering （SPS） process to prepare diamond-enhanced WC-Co cemented carbide co...Nanocrystalline WC-Co composite powder and coated tungsten diamond by using vacuum vapor deposition were consolidated by the spark plasma sintering （SPS） process to prepare diamond-enhanced WC-Co cemented carbide composite materials. The interface microstructures between coated tungsten diamond and WC-Co cemented carbide matrix were investigated by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）. The results showed that there is a transitional layer between the diamond and the matrix, in which the carbon content is 62.97wt.%, and the content of cobalt in the transitional zone is 6.19wt.%; the content of cobalt in the WC-Co cemented carbide matrix is 6.07wt.%, in which the carbon content is 15.95wt.%, and the content of cobalt on the surface of diamond is 7.30wt.%, in which the carbon content is 80.38wt.%. The transitional zone prevents the carbon atom of the diamond from spreading to the matrix, in which the carbon content does coincide with the theoretical value of the raw nanocomposite powders, and the carbon content forms a graded distribution among the matrix, transitional zone, and the surface of diamond; after the 1280℃ SPS consolidated process the diamond still maintains a very good crystal shape, the coated tungsten on the surface of the diamond improves thermal stability of the diamond and increases the bonding strength of the interface between the diamond and the matrix.展开更多
The hot-deformed magnets processed from nanocrystalline/amorphous Nd-Fe-B powders were preparedunderdifferenthot-pressingtemperatures(600-750℃,at intervals of 25℃)by the self-made hotpressing equipment.The microstru...The hot-deformed magnets processed from nanocrystalline/amorphous Nd-Fe-B powders were preparedunderdifferenthot-pressingtemperatures(600-750℃,at intervals of 25℃)by the self-made hotpressing equipment.The microstructure and magnetic properties of hot-deformed magnets prepared at different temperatures were also investigated.When the temperature is above 650℃,the density of magnet reaches 7.5 g·cm^(-3).The optimum magnetic properties of magnetic induction intensity of B_(r)=1.3 T,optimum energy product of(BH)_(max)=282.5 kJ·m^(-3),intrinsiccoercivityof H_(cj)=1130.0 kA·m-1 of hot-deformed magnets are obtained at hot-pressing temperature of 650℃.X-ray diffractometer pattern shows that the(00 L)texture has been obtained.For the microstructural characteristic,on the one hand,the good magnetic performance is attributed to the fine platelet-like grains with an average length of 410-440 nm at the hot-pressing temperature range from625 to 675℃.On the other hand,the unaligned coarse grains are observed in all the samples.And the areal fraction of those is gradually increasing with the rise of the hot-pressing temperature,which tends to deteriorate the magnetic properties.The composition map shows the accumulation of Nd/Pr-rich phase in the coarse grains’region.展开更多
WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing （HIP）. Influences of carbo...WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing （HIP）. Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength （TRS） was higher than 3 890 MPa, Rockwell A hardness （HRA） was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained.展开更多
基金Projects(51072045,51102074)supported by the National Natural Science Foundation of China
文摘Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 （mass fraction）, which were reconstituted into micrometer-sized granules by spray drying, subsequently sintering at different temperatures to form nanostructured feedstock for thermal spraying, and then A1203-13%TiO2 nanocoatings were deposited by plasma spraying. The evolution of morphology, microstructure, and phase transformation of the agglomerated powder and as-sprayed coatings were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that A1203 retains the same a phase as the raw material during sintering, while TiO2 changes from anatase to futile. During plasma spraying, some a-A1203 phases solidify to form metastable y-A1203, and the volume fraction of a-A1203 decreases as CPSP increases. However, peaks of the TiO2 phase are not observed from the as-sprayed coatings except for the coatings sprayed at the lower CPSP. As the CPSP increases, nanostructured TiO2 is dissolved easily in y-A1203 or z-A1203＇TiO2 phase. After heat treatment, y-A1203 in the coatings transforms to a-A1203, and rutile is precipitated.
基金Project supported by the National Natural Science Foundation of China(50372034)
文摘Nano-sized Er^(3+)∶Y_(3)Al_(5)O_(12)powders was successfully prepared via a simple sol-gel route at as low a temperature at 800℃whereas a temperature much higher is necessary to obtain this compound by solid state synthesis(about 1500℃).The phase purity,composition and microstructural features of the materials were analyzed by means of X-ray diffraction(XRD),infrared spectroscopy(IR)and transmission electron microscopy(TEM),and no other intermediate phase were observed to form in the range of 700~1000℃.The luminescence spectra of Er^(3+)substituted for Y^(3+)in YAG in 1%content was characterized on samples at different temperature.
基金supported by the National High Technology Research and Development Program of China (2006AA03Z419)Project of Shanghai Insti-tute of Technology(YJ2009-31)Shanghai Science and Technology Committee (08520513100)
文摘Combustion of nitrate-citrate gel was employed to prepare REFeO3(RE=Y,La and Gd) nanocrystalline powders.The samples were characterized with X-ray diffraction(XRD) analysis,thermal analysis(TG/DTA) and transmission electron microscopy(TEM).LaFeO3 crystallites were directly obtained by the sol-gel combustion process,and orthorhombic YFeO3 and GdFeO3 were formed when annealed at 800 oC.The investigation of magnetic properties showed that YFeO3 and LaFeO3 exhibited ferromagnetic behavior,while GdFeO3 presented...
基金Sponsored by National High-tech Research and Development Program(863 Program)of China(2013AA030802)
文摘Fe73. 5 Cu1 Nb3 Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 9m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P cv and decreased initial permea- bility μi with addition of fine powders below 50 μm in size, and the content should be less than 40 mass%. It was thought to be closely related to the high coercive force H c due to the stresses generated during the crushing process and high demagnetization fields of small powders. Furthermore, modifying the alloy compositions by adding defined amount of Ni could improve the soft magnetic properties, including superior characteristics of permeability under high direct current （DC） bias field and comparable low core loss at high frequency.
文摘Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change slightly with the dopant concentrations. The the of the dopants on the sintering of the compacted powders was investigated during heating at a constant rate of 10℃/min. The elemental composition and the concentration of the dopant has significant efFect on the densification and grain growth. Compared to undoped CeO2, the dopants produce a shift in the densification curve to higher temperatures. For the same dopant concentration and under identical sintering conditions, the Ca doped samples reach nearly full density with the smallest grain size (≈50 nm), however, the Mg doped sample has the lowest density (≈95% of the theoretical) with the largest grain size (≈1 μm)
基金This work was financially supported by the Postdoctoral Science Foundation of China (No.2003034504),the Open Foundation ofState Key Laboratory of Advanced Technology for Materials Synthesis & Processing, Wuhan University of Technology (2004-2005)and the National High-Tech Research and Development Program of China (No.2002AA302504).
文摘In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.
基金Supported by the National Natural Science Foundation of China(No.51202171)the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20120143120004)the"111"Project(No.B13035)
文摘The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ray diffraction, transmission electron microscopy, plasma emission spectroscopy and infrared spectrum were used to analyze the prepared samples, and density functional theory was used to investigate the cryomilling process. For nanocrystalline silicon powder cryomilled with liquid N2, the amorphous outer layer with N element is formed On the surface, and chemisorption caused by the formation of Si-N-Si bond leads to the surface passivation; although physisorpfion also he confirmed, the Si-N bond is steady after exploded in air for 30 days and no new bond is observed. For nanocrystalline silicon powder cryomilled with liquid At, no new chemical bond is Observed, Ar element absorbs on the surface of the prepared powder only through physisorption, and after exploded in air for 30 days, a Si-O bond can be observed obviously.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50502026), the Chinese 863 Program (No. 2002AA302504), the Science Foundation of Wuhan University of Technology (No. xjj2005166), and the Key Project for Science and Technology Development of Wuhan City (No. 20041003068-04)
文摘Nanocrystalline WC-Co composite powder and coated tungsten diamond by using vacuum vapor deposition were consolidated by the spark plasma sintering （SPS） process to prepare diamond-enhanced WC-Co cemented carbide composite materials. The interface microstructures between coated tungsten diamond and WC-Co cemented carbide matrix were investigated by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）. The results showed that there is a transitional layer between the diamond and the matrix, in which the carbon content is 62.97wt.%, and the content of cobalt in the transitional zone is 6.19wt.%; the content of cobalt in the WC-Co cemented carbide matrix is 6.07wt.%, in which the carbon content is 15.95wt.%, and the content of cobalt on the surface of diamond is 7.30wt.%, in which the carbon content is 80.38wt.%. The transitional zone prevents the carbon atom of the diamond from spreading to the matrix, in which the carbon content does coincide with the theoretical value of the raw nanocomposite powders, and the carbon content forms a graded distribution among the matrix, transitional zone, and the surface of diamond; after the 1280℃ SPS consolidated process the diamond still maintains a very good crystal shape, the coated tungsten on the surface of the diamond improves thermal stability of the diamond and increases the bonding strength of the interface between the diamond and the matrix.
基金financially supported by the National Key Research and Development Program(No.2016YFB0700902)。
文摘The hot-deformed magnets processed from nanocrystalline/amorphous Nd-Fe-B powders were preparedunderdifferenthot-pressingtemperatures(600-750℃,at intervals of 25℃)by the self-made hotpressing equipment.The microstructure and magnetic properties of hot-deformed magnets prepared at different temperatures were also investigated.When the temperature is above 650℃,the density of magnet reaches 7.5 g·cm^(-3).The optimum magnetic properties of magnetic induction intensity of B_(r)=1.3 T,optimum energy product of(BH)_(max)=282.5 kJ·m^(-3),intrinsiccoercivityof H_(cj)=1130.0 kA·m-1 of hot-deformed magnets are obtained at hot-pressing temperature of 650℃.X-ray diffractometer pattern shows that the(00 L)texture has been obtained.For the microstructural characteristic,on the one hand,the good magnetic performance is attributed to the fine platelet-like grains with an average length of 410-440 nm at the hot-pressing temperature range from625 to 675℃.On the other hand,the unaligned coarse grains are observed in all the samples.And the areal fraction of those is gradually increasing with the rise of the hot-pressing temperature,which tends to deteriorate the magnetic properties.The composition map shows the accumulation of Nd/Pr-rich phase in the coarse grains’region.
基金the National Natural Science Foundation of China (No.50502026)the Youth Science Plan for Light of the Morning Sun of Wuhan City(No.200750731270)Key Project for the Science & Technology Research Department,Chinese Ministry of Education (No.105123)
文摘WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing （HIP）. Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength （TRS） was higher than 3 890 MPa, Rockwell A hardness （HRA） was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained.
