The shaping quality of green ceramic balls is directly related to the efficiency and cost of later machining for the ceramic balls. Until now the shaping for green ceramic balls is still conducted by handwork. In this...The shaping quality of green ceramic balls is directly related to the efficiency and cost of later machining for the ceramic balls. Until now the shaping for green ceramic balls is still conducted by handwork. In this paper, a new shaping model for green ceramic balls was designed. In the new model, two grinding wheels with the same generator line as circular arc are mounted on symmetry, and their axes are parallel. The green ball can be put in the enveloping space formed by the two grinding wheels. The radius of generator line must be equal to or slightly greater than the final radius of the green balls, which can ensure that an ideal sphere can be enveloped by the generator of grinding wheel as grinding the green body surface with the wheels. One of the two wheels rotates in upward direction at high speed v 1, conversely, the other wheel rotates in downward direction at low speed v 2, and a cluster of compressed air is exerted on the green ball above for canceling out the force acting upon the green ball created by the action of the grinding wheel revolving at high speed and avoiding that the green ball jumps off its station. Because of the randomness of the distributions of abrasive grains on the surface of grinding wheels, the size and shape of the abrasive grains, and the posture of green body when falling into the grinding space, the values and directions of the resultant forces and torques exerted on the body, caused by the tow wheels, are random, the rotation of green body is irregular under the actions of the compressed air and the wheels. The irregularity of rotation can ensure an ideal sphere in theory. Experiment researches indicate that the new shaping model can improve the spherical deviations and the size distribution of the green ceramic balls, raise the production, and reduce the costs. The spherical deviations can be improved to 0.04 mm easily. It can be observed by SEM that there is no crack in the surface of sintered ceramic balls shaped with the new model in green blank.展开更多
The influence of the residual stress in surface of ceramic balls on the fatigue life is large, because the life of silicon nitride ball bearings is more sensitive to the load acted on the bearings than the life of all...The influence of the residual stress in surface of ceramic balls on the fatigue life is large, because the life of silicon nitride ball bearings is more sensitive to the load acted on the bearings than the life of all-steel ball bearings. In this paper, the influence of thermal stress produced in sintering and mechanical stress formed in lapping process on residual stress in surface of silicon nitride ceramic balls was discussed. The residual compress stress will be formed in the surface of silicon nitride ceramic balls after sintering. The residual tensile stress will be formed in surface of silicon nitride ceramic balls in lapping process, and the size of abrasive particle is smaller, such trend is stronger. In this paper the residual stress was measured by the xylometric measurement in which the material in surface was peeled with lapping. The distribution of residual stress in surface can be calculated with the variation in specific volume. The technological parameter with which the material was peeled by lapping was given, for minimizing the extra influence of the residual stress forming in peeling on the original residual stress in surface, the abrasive particle size would not be too small and the load impressed would not be too large. Some experimental researches on residual stress in surface of silicon nitride ceramic balls were made. The surface of silicon nitride ceramic balls presented residual compressive stress after sintering and the influence of the ball size on the residual stress is feeble. It is expected that the size of ball blank is same for achieving the same residual compressive stress in surface on balls after final machining. In lapping process, the surface of silicon nitride ceramic balls presented residual tensile stress, the larger the load which is impressed on single ball, the larger the amplitude of residual tensile stress is; the smaller the abrasive particle, the stronger the trend of plastic deformation is and the larger the amplitude of residual tensile stress is.展开更多
To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 wer...To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 were prepared, and the Al2O3 content of the prepared balls was 75%. It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one： the wear rate of the ceramic balls prepared in CaO-Al2O3-SiO2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al2O3-SiO2 is the highest. The main crystal phase of the ceramic ball is mullite and corundum. The ceramic ball granular is uniform and fine with 4-5 μm average size. The pore diameter is about 2 μm. The wear way of the ceramic balls is mainly transcrystalline fracture.展开更多
A new ball lapping method i s presented.By using the method , there is a distance be- tween the centre Iine of cireular groove and the rotating axis of lapping plate。 The proper dis-tance can make the lapped probabil...A new ball lapping method i s presented.By using the method , there is a distance be- tween the centre Iine of cireular groove and the rotating axis of lapping plate。 The proper dis-tance can make the lapped probability of each point on ball surfaee as consistent as possible。 This method is especially adapted for lapping high hardness ceramic balls due to its high material re- moval rate。展开更多
From the experimental data on ceramic/aluminum composite target, the mechanism of tungsten ball impacting a ceramic/aluminum composite target has been studied. By analyzing the transition of energy in the process of i...From the experimental data on ceramic/aluminum composite target, the mechanism of tungsten ball impacting a ceramic/aluminum composite target has been studied. By analyzing the transition of energy in the process of impact, a simple ballistic limit analytical model of tungsten ball impacting a ceramic/aluminum composite target has been proposed; and the result taken from this model is consistent with that of the experiment.展开更多
The influence of high energy ball milling on Al 30Si powder and ceramic particulate SiC was studied by means of SEM, XRD and DSC. The results show that Al 30Si powder and their microstructure are obviously refined aft...The influence of high energy ball milling on Al 30Si powder and ceramic particulate SiC was studied by means of SEM, XRD and DSC. The results show that Al 30Si powder and their microstructure are obviously refined after high energy ball milling process. The alloy powder and SiC p stick closely to each other without interfacial reaction. DSC results detect no reaction but relaxation of the samples. So high energy ball milling can be used as an effective method for ceramic particulate pre treatment in the fabrication of MMC.展开更多
Four process parameters, pad diameter, stencil thickness, ball diameter and stand-off were chosen as four control factors. By using an L25 （5^6 ） orthogonal array the ceramic ball grid array （ CBGA ） solder joints...Four process parameters, pad diameter, stencil thickness, ball diameter and stand-off were chosen as four control factors. By using an L25 （5^6 ） orthogonal array the ceramic ball grid array （ CBGA ） solder joints which have 25 different combinations of process parameters were designed. The numerical models of all the 25 CBGA solder joints were developed using the Sugrace Evolver. Utilizing the sugrace coordinate exported from the 25 CBGA solder joints numerical models, the finite element analysis models were set up and the nonlinear finite element analysis of the CBGA solder joints under thermal cycles were pegrormed by ANSYS. The thermal fatigue life of CBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results, the range analysis and the variance analysis were pegrormed. The results show that the fatigue life of CBGA solder joint is affected by the pad diameter, the stencil thickness, the ball diameter and the stand-off in a descending order, the best combination of process parameters results in the longest fatigue life is 0.07 mm stand-off, 0.125 mm stencil thickness of, 0.85 mm ball diameter and 0. 89 mm pad diameter. With 95% confidence the pad diameter has a significant effect on the reliability of CBGA solder joints whereas the stand-off, the stencil thickness and the ball diameter have little effect on the reliability of CBGA solder joints.展开更多
The critical speeds for a vehicle turbocharger with hybrid ceramic ball bearing are researched. The ball bearing-rotor system produces resonance when it working in critical speed and that makes the turbocharger injury...The critical speeds for a vehicle turbocharger with hybrid ceramic ball bearing are researched. The ball bearing-rotor system produces resonance when it working in critical speed and that makes the turbocharger injury working for a long time. The calculation and analysis methods of the critical speed for the vehicle turbocharger are described. The critical speed is computed by two methods including Riccati transfer matrix and DyRoBeS finite element method for a vehicle turbocharger with hybrid ceramic ball bearing. The vibration experiment had been taken to validate the calculating result, Comparison between the results by two calculation methods and the test results show that the first critical speed differences are 6.47 % and 5.66 %, the second critical speed differences are 2.87 % and 2.94 % respectively. And then, the primary factors which influence the critical speed are analyzed, the conclusions will be helpful for the vehicle turbocharger bearing-rotor system design.展开更多
The chemical composition, structure and thermal stability of the spent FCC equilibrium catalyst from an oil refinery were characterized by XRD, FT-IR, DTA-TG, BET, complete chemical analysis, SEM, and XRF. The spent F...The chemical composition, structure and thermal stability of the spent FCC equilibrium catalyst from an oil refinery were characterized by XRD, FT-IR, DTA-TG, BET, complete chemical analysis, SEM, and XRF. The spent FCC equilibrium catalyst, clay, barium carbonate, and talc were used as the main raw materials to prepare the alumina abrasion-resistant ceramic balls to be used in the powder grinding mill for manufacture of architecture tiles. The results showed that after proper formulation study, the spent FCC equilibrium catalyst could replace industrial alumina to prepare high performance grinding balls. Meanwhile, the various performance indices of the grinding ball could meet the quality standard for similar products, and additionally, the energy saving effect was achieved in the operation of the grinding section, resulting in a successful comprehensive utilization of solid wastes.展开更多
A ceramic ball is a basic part widely used in precision bearings.There is no perfect testing equipment for ceramic ball surface defects at present.A fast visual detection algorithm for ceramic ball surface defects bas...A ceramic ball is a basic part widely used in precision bearings.There is no perfect testing equipment for ceramic ball surface defects at present.A fast visual detection algorithm for ceramic ball surface defects based on fringe reflection is designed.By means of image preprocessing,grayscale value accumulative differential positioning,edge detection,pixel-value row difference and template matching,the algorithm can locate feature points and judge whether the spherical surface has defects by the number of points.Taking black silicon nitride ceramic balls with a diameter of 6.35 mm as an example,the defect detection time for a single gray scale image is 0.78 s,and the detection limit is 16.5μm.展开更多
MgTiO3 precursor was mechanochemically synthesized by high-energy ball milling of MgO and TiO2 . The sinteting characteristic of the resulted MgTiO3 precursor was investigated. The experirneatal resalts indicate that...MgTiO3 precursor was mechanochemically synthesized by high-energy ball milling of MgO and TiO2 . The sinteting characteristic of the resulted MgTiO3 precursor was investigated. The experirneatal resalts indicate that particles of both MgO and TiO2 powders become smaller rapidly, and then the costalline structures of MgO and TiO2 change significantly. MgTiO3 was observed by XRD after 30 hours of ball milling. Strong diffraction peaks of MgTiO3 were observed after 50 hours of ball milling. HRTEM observation proves that dense MgTiO3 ceramics with a compact crystalline structure can be sintered from rnechanochemically activated MgTiO3 precursor, the volume density of the resulting ceramie is as high aa 95% of the theoretical density, the porosity and average pore diameter of the ceramic are measured as 4.95% and 50 nm respectively, and the transverse strength exceeded 500 MPa.展开更多
We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With a...We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With an increasing milling time, this particle size of mixture is gradually reduced, thus, we have mostly an amorphous phase. The BIT ceramics were duly obtained by sintering the synthesized powders at temperatures ranging from 850°C to 1000°C. The BIT ceramics sintered at 1020°C for 1 h, exhibiting a density with 7.52 g/cm3 of a crystaline phase and a dielectric of K = 288.11 (100 Hz), as well as a dielectric loss of 0.05 (100 kHz). The High-energy ball milling process is a promising way to prepare BIT ceramics. After the preparation of the BIT, we doped it with the Multi-Walled Carbon Nanotubes which are properly obtained by a chemical vapour deposition (CVD), using nickel as a catalyst, as well as using acetilene at 720°C, and then proceeded with the dielectric and optical measurements.展开更多
A newly developed pure rolling fatigue test rig with three contact points for bearing bails was used to perform rolling contact fatigue （RCF） tests. The fatigue properties of GCrl5 steel bails and two kinds of Si3N4...A newly developed pure rolling fatigue test rig with three contact points for bearing bails was used to perform rolling contact fatigue （RCF） tests. The fatigue properties of GCrl5 steel bails and two kinds of Si3N4 ceramic balls （GSN-200 and NBD-200） produced with different technologies were compared. Ball surfaces were examined after failure with optical microscope and scanning electron microscope （SEM）. It was identified by tests that the failure mode of ceramic balls was surface spail. The main factor of ceramic bail failure was principal tensile stress. Life tests data, summarized in accordance with the Weibull theory, showed that the life of GSN-200 balls was close to that of GCrl5 balls, whereas the life of NBD-200 balls was much longer than those of GSN-200 and GCr15. Under the same working condition, the temperature rise of all ceramic bails was lower than that of steel balls, and their crack propagation rates were slower than that of steel balls.展开更多
Rare earth composite ceramic materials (RE/CM) were prepared by the method of firing the mixtures of the rare earth elements, polar crystal mineral materials and clays. The effects of processing method on the reducing...Rare earth composite ceramic materials (RE/CM) were prepared by the method of firing the mixtures of the rare earth elements, polar crystal mineral materials and clays. The effects of processing method on the reducing exhaust emissions were studied. The results show that after dealt with the ceramic balls, the surface tension of gasoline, and the CO concentration among exhaust emissions during combustion, decrease by 2.7% and 11.5%, respectively; however the temperature of the inner flue increases by 4.8%.展开更多
A research on fabrication of finegrained Al2O3 ceramic at lower sintering temperature was carried out. Al2O3 powder with 50 nm in diameter is compounded with 11.24%Al and 4.75%Fe（mass fraction） by high-energy ball-m...A research on fabrication of finegrained Al2O3 ceramic at lower sintering temperature was carried out. Al2O3 powder with 50 nm in diameter is compounded with 11.24%Al and 4.75%Fe（mass fraction） by high-energy ball-milling. Al is got from Al powder which is a component of the materials being milled and Fe from steel milling balls and milling jar during the milling. In this way, nearly no impurity is brought into the composite powder during milling. With hot pressing of the composite powder and pure Al2O3 powder, it is proved that Al2O3 powder can be densified at lower sintering temperature when the powder is compounded in this way. Al2OC and AlFe form during sintering process of the composite powder. With the reactive sintering and multiphase sintering mechanisms, finegrained Al2O3 ceramic is fabricated at low sintering temperature.展开更多
文摘The shaping quality of green ceramic balls is directly related to the efficiency and cost of later machining for the ceramic balls. Until now the shaping for green ceramic balls is still conducted by handwork. In this paper, a new shaping model for green ceramic balls was designed. In the new model, two grinding wheels with the same generator line as circular arc are mounted on symmetry, and their axes are parallel. The green ball can be put in the enveloping space formed by the two grinding wheels. The radius of generator line must be equal to or slightly greater than the final radius of the green balls, which can ensure that an ideal sphere can be enveloped by the generator of grinding wheel as grinding the green body surface with the wheels. One of the two wheels rotates in upward direction at high speed v 1, conversely, the other wheel rotates in downward direction at low speed v 2, and a cluster of compressed air is exerted on the green ball above for canceling out the force acting upon the green ball created by the action of the grinding wheel revolving at high speed and avoiding that the green ball jumps off its station. Because of the randomness of the distributions of abrasive grains on the surface of grinding wheels, the size and shape of the abrasive grains, and the posture of green body when falling into the grinding space, the values and directions of the resultant forces and torques exerted on the body, caused by the tow wheels, are random, the rotation of green body is irregular under the actions of the compressed air and the wheels. The irregularity of rotation can ensure an ideal sphere in theory. Experiment researches indicate that the new shaping model can improve the spherical deviations and the size distribution of the green ceramic balls, raise the production, and reduce the costs. The spherical deviations can be improved to 0.04 mm easily. It can be observed by SEM that there is no crack in the surface of sintered ceramic balls shaped with the new model in green blank.
文摘The influence of the residual stress in surface of ceramic balls on the fatigue life is large, because the life of silicon nitride ball bearings is more sensitive to the load acted on the bearings than the life of all-steel ball bearings. In this paper, the influence of thermal stress produced in sintering and mechanical stress formed in lapping process on residual stress in surface of silicon nitride ceramic balls was discussed. The residual compress stress will be formed in the surface of silicon nitride ceramic balls after sintering. The residual tensile stress will be formed in surface of silicon nitride ceramic balls in lapping process, and the size of abrasive particle is smaller, such trend is stronger. In this paper the residual stress was measured by the xylometric measurement in which the material in surface was peeled with lapping. The distribution of residual stress in surface can be calculated with the variation in specific volume. The technological parameter with which the material was peeled by lapping was given, for minimizing the extra influence of the residual stress forming in peeling on the original residual stress in surface, the abrasive particle size would not be too small and the load impressed would not be too large. Some experimental researches on residual stress in surface of silicon nitride ceramic balls were made. The surface of silicon nitride ceramic balls presented residual compressive stress after sintering and the influence of the ball size on the residual stress is feeble. It is expected that the size of ball blank is same for achieving the same residual compressive stress in surface on balls after final machining. In lapping process, the surface of silicon nitride ceramic balls presented residual tensile stress, the larger the load which is impressed on single ball, the larger the amplitude of residual tensile stress is; the smaller the abrasive particle, the stronger the trend of plastic deformation is and the larger the amplitude of residual tensile stress is.
基金the National Natural Science Fundation of China(No.50272016),Guangxi 2003 Degree Authorzation Office academic Construction Fun,and Natural Science Fund of Guangxi Education Department(No.[2004]4)
文摘To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 were prepared, and the Al2O3 content of the prepared balls was 75%. It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one： the wear rate of the ceramic balls prepared in CaO-Al2O3-SiO2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al2O3-SiO2 is the highest. The main crystal phase of the ceramic ball is mullite and corundum. The ceramic ball granular is uniform and fine with 4-5 μm average size. The pore diameter is about 2 μm. The wear way of the ceramic balls is mainly transcrystalline fracture.
文摘A new ball lapping method i s presented.By using the method , there is a distance be- tween the centre Iine of cireular groove and the rotating axis of lapping plate。 The proper dis-tance can make the lapped probability of each point on ball surfaee as consistent as possible。 This method is especially adapted for lapping high hardness ceramic balls due to its high material re- moval rate。
文摘From the experimental data on ceramic/aluminum composite target, the mechanism of tungsten ball impacting a ceramic/aluminum composite target has been studied. By analyzing the transition of energy in the process of impact, a simple ballistic limit analytical model of tungsten ball impacting a ceramic/aluminum composite target has been proposed; and the result taken from this model is consistent with that of the experiment.
文摘The influence of high energy ball milling on Al 30Si powder and ceramic particulate SiC was studied by means of SEM, XRD and DSC. The results show that Al 30Si powder and their microstructure are obviously refined after high energy ball milling process. The alloy powder and SiC p stick closely to each other without interfacial reaction. DSC results detect no reaction but relaxation of the samples. So high energy ball milling can be used as an effective method for ceramic particulate pre treatment in the fabrication of MMC.
基金This work was supported by Science Foundation of Guangxi Zhuang Autonomous Region (Contract No. 02336060).
文摘Four process parameters, pad diameter, stencil thickness, ball diameter and stand-off were chosen as four control factors. By using an L25 （5^6 ） orthogonal array the ceramic ball grid array （ CBGA ） solder joints which have 25 different combinations of process parameters were designed. The numerical models of all the 25 CBGA solder joints were developed using the Sugrace Evolver. Utilizing the sugrace coordinate exported from the 25 CBGA solder joints numerical models, the finite element analysis models were set up and the nonlinear finite element analysis of the CBGA solder joints under thermal cycles were pegrormed by ANSYS. The thermal fatigue life of CBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results, the range analysis and the variance analysis were pegrormed. The results show that the fatigue life of CBGA solder joint is affected by the pad diameter, the stencil thickness, the ball diameter and the stand-off in a descending order, the best combination of process parameters results in the longest fatigue life is 0.07 mm stand-off, 0.125 mm stencil thickness of, 0.85 mm ball diameter and 0. 89 mm pad diameter. With 95% confidence the pad diameter has a significant effect on the reliability of CBGA solder joints whereas the stand-off, the stencil thickness and the ball diameter have little effect on the reliability of CBGA solder joints.
文摘The critical speeds for a vehicle turbocharger with hybrid ceramic ball bearing are researched. The ball bearing-rotor system produces resonance when it working in critical speed and that makes the turbocharger injury working for a long time. The calculation and analysis methods of the critical speed for the vehicle turbocharger are described. The critical speed is computed by two methods including Riccati transfer matrix and DyRoBeS finite element method for a vehicle turbocharger with hybrid ceramic ball bearing. The vibration experiment had been taken to validate the calculating result, Comparison between the results by two calculation methods and the test results show that the first critical speed differences are 6.47 % and 5.66 %, the second critical speed differences are 2.87 % and 2.94 % respectively. And then, the primary factors which influence the critical speed are analyzed, the conclusions will be helpful for the vehicle turbocharger bearing-rotor system design.
基金the funding provided by the Fujian Provincial Education Department Project(JA09054)the Project administered by the Fujian Normal University(XG-004)+4 种基金the Fujian Provincial Eco- nomic and Trade Commission Project(HE0536)the Open Project of the MOE's Key Laboratory for Medical and Photoelectrical Science and Technology(JYG0821)the Open Project of Hubei Province,the State Nationalities Committee,and the MOE Joint Key Laboratory for Catalytic Material Science(CHCL08008)the Fujian Provincial Testing Fund Project for the Key Laboratory of Highmolecular Materials(FJKL-POLY2010-17)the Training for Excellence Youth Skeleton Teacher of Fujian Normal University(No.2008100228).
文摘The chemical composition, structure and thermal stability of the spent FCC equilibrium catalyst from an oil refinery were characterized by XRD, FT-IR, DTA-TG, BET, complete chemical analysis, SEM, and XRF. The spent FCC equilibrium catalyst, clay, barium carbonate, and talc were used as the main raw materials to prepare the alumina abrasion-resistant ceramic balls to be used in the powder grinding mill for manufacture of architecture tiles. The results showed that after proper formulation study, the spent FCC equilibrium catalyst could replace industrial alumina to prepare high performance grinding balls. Meanwhile, the various performance indices of the grinding ball could meet the quality standard for similar products, and additionally, the energy saving effect was achieved in the operation of the grinding section, resulting in a successful comprehensive utilization of solid wastes.
基金National Science and Technology Major Project of China(No.2016ZX04003001)。
文摘A ceramic ball is a basic part widely used in precision bearings.There is no perfect testing equipment for ceramic ball surface defects at present.A fast visual detection algorithm for ceramic ball surface defects based on fringe reflection is designed.By means of image preprocessing,grayscale value accumulative differential positioning,edge detection,pixel-value row difference and template matching,the algorithm can locate feature points and judge whether the spherical surface has defects by the number of points.Taking black silicon nitride ceramic balls with a diameter of 6.35 mm as an example,the defect detection time for a single gray scale image is 0.78 s,and the detection limit is 16.5μm.
文摘MgTiO3 precursor was mechanochemically synthesized by high-energy ball milling of MgO and TiO2 . The sinteting characteristic of the resulted MgTiO3 precursor was investigated. The experirneatal resalts indicate that particles of both MgO and TiO2 powders become smaller rapidly, and then the costalline structures of MgO and TiO2 change significantly. MgTiO3 was observed by XRD after 30 hours of ball milling. Strong diffraction peaks of MgTiO3 were observed after 50 hours of ball milling. HRTEM observation proves that dense MgTiO3 ceramics with a compact crystalline structure can be sintered from rnechanochemically activated MgTiO3 precursor, the volume density of the resulting ceramie is as high aa 95% of the theoretical density, the porosity and average pore diameter of the ceramic are measured as 4.95% and 50 nm respectively, and the transverse strength exceeded 500 MPa.
基金We would like to thank to the institution below:UFC,LOCEM,UECE,CNPq,CAPES,FUNCAP,G.D.Saraiva acknowledges the support from MCT/CNPqEdital 14/2010(process 476569/2010-9)FUNCAP/Edital 02/2010(process 10293648-0)+1 种基金 FUNCAP/Edital 05/2009(process 186.01.00/09)The other authors acknowledge CNPq and FUNCAP for partial financial support.
文摘We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With an increasing milling time, this particle size of mixture is gradually reduced, thus, we have mostly an amorphous phase. The BIT ceramics were duly obtained by sintering the synthesized powders at temperatures ranging from 850°C to 1000°C. The BIT ceramics sintered at 1020°C for 1 h, exhibiting a density with 7.52 g/cm3 of a crystaline phase and a dielectric of K = 288.11 (100 Hz), as well as a dielectric loss of 0.05 (100 kHz). The High-energy ball milling process is a promising way to prepare BIT ceramics. After the preparation of the BIT, we doped it with the Multi-Walled Carbon Nanotubes which are properly obtained by a chemical vapour deposition (CVD), using nickel as a catalyst, as well as using acetilene at 720°C, and then proceeded with the dielectric and optical measurements.
基金Project supported by the Science Foundation of Shanghai Municipal Commission of Science and Technology （Grant No.05KJB460106）, and the Provincial University Natural Science Foundation of Jiangsu, China （Grant No.0152nm031）
文摘A newly developed pure rolling fatigue test rig with three contact points for bearing bails was used to perform rolling contact fatigue （RCF） tests. The fatigue properties of GCrl5 steel bails and two kinds of Si3N4 ceramic balls （GSN-200 and NBD-200） produced with different technologies were compared. Ball surfaces were examined after failure with optical microscope and scanning electron microscope （SEM）. It was identified by tests that the failure mode of ceramic balls was surface spail. The main factor of ceramic bail failure was principal tensile stress. Life tests data, summarized in accordance with the Weibull theory, showed that the life of GSN-200 balls was close to that of GCrl5 balls, whereas the life of NBD-200 balls was much longer than those of GSN-200 and GCr15. Under the same working condition, the temperature rise of all ceramic bails was lower than that of steel balls, and their crack propagation rates were slower than that of steel balls.
文摘Rare earth composite ceramic materials (RE/CM) were prepared by the method of firing the mixtures of the rare earth elements, polar crystal mineral materials and clays. The effects of processing method on the reducing exhaust emissions were studied. The results show that after dealt with the ceramic balls, the surface tension of gasoline, and the CO concentration among exhaust emissions during combustion, decrease by 2.7% and 11.5%, respectively; however the temperature of the inner flue increases by 4.8%.
基金Project(2001AA421160) supported by the Hi tech Research and Development Program of China
文摘A research on fabrication of finegrained Al2O3 ceramic at lower sintering temperature was carried out. Al2O3 powder with 50 nm in diameter is compounded with 11.24%Al and 4.75%Fe（mass fraction） by high-energy ball-milling. Al is got from Al powder which is a component of the materials being milled and Fe from steel milling balls and milling jar during the milling. In this way, nearly no impurity is brought into the composite powder during milling. With hot pressing of the composite powder and pure Al2O3 powder, it is proved that Al2O3 powder can be densified at lower sintering temperature when the powder is compounded in this way. Al2OC and AlFe form during sintering process of the composite powder. With the reactive sintering and multiphase sintering mechanisms, finegrained Al2O3 ceramic is fabricated at low sintering temperature.
