Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leachin...Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.展开更多
Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal s...Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles.Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements,was favorable for the formation of in-situ synthesized carbide particles.In this paper,rare earth oxide(RE2O3) was added into t...展开更多
The large particle CeO2 and Y2O3 were prepared using oxalic acid as precipitator. The effects of operational parameters such as stirring velocity, precipitation temperature, feeding speed, aging time, precipitation me...The large particle CeO2 and Y2O3 were prepared using oxalic acid as precipitator. The effects of operational parameters such as stirring velocity, precipitation temperature, feeding speed, aging time, precipitation method, and calcination temperature on particle size and loose density of CeO2 were studied. Under the particular conditions, particle median size of D50≥30μm, loose density of ≥2.0 g/mlof CeO2, and particle median size of D50≥20 μm of Y2O3 were prepared. This technology had advantages of simple process, less equipment investment, ease of use, and suitability for industrialization products.展开更多
The rare earth based hydrogen storage alloys Ml_ 0.7Mm_ 0.3(Ni_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3) were chosen as objects of investigation in this paper. The effects of particle size on electrochemical properties of the allo...The rare earth based hydrogen storage alloys Ml_ 0.7Mm_ 0.3(Ni_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3) were chosen as objects of investigation in this paper. The effects of particle size on electrochemical properties of the alloy were investigated. The results indicate that the alloy with particle size of 100 and 150 mesh shows good activation behavior and high discharge capacity (the first discharge capacity and the maximum discharge capacity), but poor cycling stability, low capacity retention and high discharge capacity rate. The Ml_ 0.7Mm_ 0.3(Ni_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3) alloy with particle size of 150 mesh shows excellent electrochemical properties.展开更多
Spherical YAG:Ce^3+ phosphor particles with narrow size distribution were prepared by spray pyrolysis. The effects of the concentration of solution, the flow rate of cartier gas and the annexing temperature on the p...Spherical YAG:Ce^3+ phosphor particles with narrow size distribution were prepared by spray pyrolysis. The effects of the concentration of solution, the flow rate of cartier gas and the annexing temperature on the phosphor morphology were studied. The productivity of precursor particles shows a trend of drop after rising with the increase of concentration Raising the flow rate of nitrogen can improve the productivity of the precursor particles. Phosphor prepared by spray pyrolysis has obviously higher emission intensity than that synthesized by solid state reaction, spray pyrolysis makes Ce^3+ ions well distributed in the crystal lattice as the luminescent centers, and phosphor particles have regular sphericity and narrow size distribution.展开更多
Cerium dioxide(CeO2) has attracted much attention and has wide applications such as automotive exhaust catalysts,polishing materials for optical glasses and additives for advanced glasses,as well as cosmetic materials...Cerium dioxide(CeO2) has attracted much attention and has wide applications such as automotive exhaust catalysts,polishing materials for optical glasses and additives for advanced glasses,as well as cosmetic materials.The particle size and its distribution are key factors to the performance of the materials in the functional applications.However,control of particle size is still a challenge in materials synthesis.Therefore,continuous precipitation of cerium oxalate(precursor of ceria) was carried out at dif...展开更多
Ce0.6Zr0.4O2 solid solution ultrafine particle was prepared in the cyclohexane/water/OP-10/n-hexanol reversed microemulsion. The quasi-ternary phase diagram investigations showed that the system has narrow W/O type mi...Ce0.6Zr0.4O2 solid solution ultrafine particle was prepared in the cyclohexane/water/OP-10/n-hexanol reversed microemulsion. The quasi-ternary phase diagram investigations showed that the system has narrow W/O type microemulison region, so it is the proper system to prepare Ce0.6Zr0.4O2 solid solution ultrafine particle. Some physical-chemical techniques such as TG/DTA, XRD, BET, and HRTEM are used to characterize the resultant powders. The results show that the fluorite cubic Ce0.6Zr0.4O2 solid solution is obtained at 400 ℃. The surface area is (146.7 m^2·g^-1), which is higher than the surface area for sol-gel prepared sample (59.5m^2·g^-1). HRTEM images indicated that the Ce0.6Zr0.4O2 solid solution ultrafine particle is well-crystallized, narrow size distribution, less agglomeration, within mean size of 5 -7 nm.展开更多
Cerium is one of the most abundant rare earth elements in both bastnasite and monazite. Ceria has been widely used in optical, catalytic, electrolyte, and sensor materials, with unique performances. With the developme...Cerium is one of the most abundant rare earth elements in both bastnasite and monazite. Ceria has been widely used in optical, catalytic, electrolyte, and sensor materials, with unique performances. With the development of functional materials, great interest has been focused on the synthesis and characterization of specific fine/mesoporous ceria powder. In this study, the modified precipitation and recrystallization processes combined with a controlled calcination process for fabricating the ceria with large particle size and high appearance density was reported. During precipitation, a certain amount of mineral acid such as nitric acid served as an additive, to adjust the precipitation and crystallization processes of cerium oxalates. An appropriate acidic condition could lead the process into the Oswald ripening stage and made the particles become bigger. Thus, the appearance density of powder was increased. The optimized conditions, such as the temperature, feeding speed, type and concentration of mineral acids, and the concentration of cerium-contained stock solution, were investigated and evaluated.展开更多
We present how the luminescence of europium RR-2-P-oxides complexes can be increased by interaction of electronic levels of the complex with the radiation field of silver nanoparticles (NPs). The procedure by which ...We present how the luminescence of europium RR-2-P-oxides complexes can be increased by interaction of electronic levels of the complex with the radiation field of silver nanoparticles (NPs). The procedure by which silver NPs are formed in a sol-gel polyurethane matrix precursor was elaborated. The formed Ag NPs were combined with Eu complex incorporated in ormocer matrix. The emission spectra of the complexes without silver NPs were compared with spectra of the same complexes with addition of silver NPs. As the result of the interaction of the electronic levels of lanthaaide ligands with silver plasmons, dramatic increase of luminescence was observed.展开更多
Fine spherical particle sized ceria (CeO_2) was prepared by homogeneous precipitation method with ammonium bicarbonate as precipitant. The prepared CeO_2 has the primary particle size of 10~50 nm when calcined betwee...Fine spherical particle sized ceria (CeO_2) was prepared by homogeneous precipitation method with ammonium bicarbonate as precipitant. The prepared CeO_2 has the primary particle size of 10~50 nm when calcined between 400~700 ℃ analyzed by XRD and the aggregated particle size is about 300 nm measured by LASER particle sizer. SEM, TG-DTA and Zeta-potential analyzer were employed individually to study the morphology and the formation of CeO_2 product. It was found that excess NH_4NO_3 can serve as an sphericallization agent to prepare spherical CeO_2 powder by precipitation method.展开更多
The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na2CO3, S, NaCl or their combination, were introduced into the precursor to prepare Y2O3 :Eu^3+ red phosphors at 10...The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na2CO3, S, NaCl or their combination, were introduced into the precursor to prepare Y2O3 :Eu^3+ red phosphors at 1000 1300 ℃ for 2 h. The effect of molten salts on particle size and luminescent intensity was studied. The experimental results showed that the complex molten salt (Na:CO3 + S + NaCl) was conductive to enhance the luminescent intensity of Y2O3 :Eu^3+. The emission intensity of the phosphor prepared with these additives at 1300 ℃ was about 45% higher than that of the one prepared without molten salt, and about 11% higher than that of the corresponding commercial phosphor. Meanwhile, the particle size of Y2O3 :Eu^3+ phosphor was controlled effectively with the molten salt.展开更多
The effect of particle size and distribution of rapidly quenching NdFeB magnetic powder on the magnetic properties of polymerbonded NdFeB permanent magnet was studied. The results show that the particle size and the d...The effect of particle size and distribution of rapidly quenching NdFeB magnetic powder on the magnetic properties of polymerbonded NdFeB permanent magnet was studied. The results show that the particle size and the distribution of rapidly quenching NdFeB magnetic powder have significant effects on the magnetic properties of polymerbonded NdFeB permanent magnet. As long as the size and the distribution of rapidly quenching NdFeB powder are within the right range, high magnetic properties of polymerbonded NdFeB permanent magnet can be obtained. This is mainly because the rapidly quenching NdFeB magnetic powder has high hardness and is scaleshaped. The larger the size of rapidly quenching NdFeB particles is, the more difficult it is to obtain high density of bonded NdFeB magnet. However the structure will be destroyed if the size is too small. It results in the deterioration of magnetic properties. The mechanism is also discussed.展开更多
The SiO 2 adsorbing YF 3, Y 2(CO 3) 3, Y 2(C 2O 4) 3 and YPO 4, respectively, formed four systems of particle materials: SiO 2·YF 3, SiO 2·Y 2(CO 3) 3 , SiO 2·Y 2(C 2O 4) 3 and SiO ...The SiO 2 adsorbing YF 3, Y 2(CO 3) 3, Y 2(C 2O 4) 3 and YPO 4, respectively, formed four systems of particle materials: SiO 2·YF 3, SiO 2·Y 2(CO 3) 3 , SiO 2·Y 2(C 2O 4) 3 and SiO 2·YPO 4. The electrorheological(ER) behavior of the electrorheological fluids (ERF) prepared by dispersing them in silicone oil was tested at 20 ℃ under d.c. field. The results show that the system of SiO 2·YF 3 does not display ER activity, and the ER performance of the particle materials of SiO 2·Y 2(CO 3) 3 is the best among them. The shearing stress of ERF with SiO 2·Y 2(CO 3) 3 particles is 1.644 KPa and the relative viscosity η r(=η E/η 0) is 20.3 (under field strength E=4200 V·mm -1) while the adsorbed content of Y 2(CO 3) 3 in the SiO 2 particle materials is 12.4%(mass fraction).展开更多
The SiO_2 particle material has weak electrorheological (ER) activity. The ER performance of the SiO_2 particles can be ameliorated after adsorbing Y_2(CO_3)_3. In this paper, the effect of Y_2(CO_3)_3 and different s...The SiO_2 particle material has weak electrorheological (ER) activity. The ER performance of the SiO_2 particles can be ameliorated after adsorbing Y_2(CO_3)_3. In this paper, the effect of Y_2(CO_3)_3 and different surfactants on the ER performance of the SiO_2 particle materials is investigated. The results show that anionic or cationic surfactants maybe enhance the ER activity of SiO_2 material, and nonionic surfactants cannot when surfactants are added during the process of the SiO_2 particle preparation, only the anionic surfactant, AES, can enhance markedly the ER performance of the material. The surface area, pore volume and pore diameter of the particles were measured. The effect of Y_2(CO_3)_3 and the surfactants on the microstructure of SiO_2 materials and the relationship between ER effect and the microstructure are described.展开更多
Heterogeneous photocatalysed reduction of aqueous Na_2CO_3 was carried out by using nano LaCoO_3 semiconductor powders. Formic acid and formaldehyde were identified as photoproducts,and were measured spectrophotometri...Heterogeneous photocatalysed reduction of aqueous Na_2CO_3 was carried out by using nano LaCoO_3 semiconductor powders. Formic acid and formaldehyde were identified as photoproducts,and were measured spectrophotometrically using Nash reagent. The effect of different parameters such as sodium carbonate concentration,amount of photocatalyst and different light sources on the yield of photoproducts was also investigated. It shows that nano LaCoO_3 has photocatalytic activity. Irradiation leads to the production of electrons in the conduction band of the LaCoO_3 semiconductor. It is likely that the photoproduced electrons initially reduce CO_3 (2-) to HCOO -,and then to HCHO and CH_3OH.展开更多
A technique for preparing perovskite type oxides was developed. By this technique, ultra fine particles of La 0.9 RE 0.1 MnO 3 (RE: Y, Ce, Pr, Sm, Gd,or Dy) with high surface area and single perovskite stru...A technique for preparing perovskite type oxides was developed. By this technique, ultra fine particles of La 0.9 RE 0.1 MnO 3 (RE: Y, Ce, Pr, Sm, Gd,or Dy) with high surface area and single perovskite structure were prepared, and the series of La 0.9 RE 0.1 MnO 3 catalysts were studied experimentally. The so prepared ultra fine particles exhibites high catalytic activity for CH 4 total oxidation. The ultra fine particles of La 0.9 RE 0.1 MnO 3 (except for La 0.9 Pr 0.1 MnO 3) prepared by this method are thermally much more stable than LaMnO 3. Of the La 0.9 RE 0.1 MnO 3 series, La 0.9 Y 0.1 MnO 3 is most thermally stable, and La 0.9 Y 0.1 MnO 3 or La 0.9 Gd 0.1 MnO 3 (varies with calcination temperature) exhibits the highest catalytic activity for total oxidation of methane. The specific surface area of La 0.9 Y 0.1 MnO 3 calcined at 1000 ℃ reaches 14.9 m 2·g -1 , while the specific surface area of LaMnO 3 calcined at the same temperature is only 1.8 m 2·g -1 .展开更多
The influence of mean particle size on magnetic properties ofSm ( Co0.72Fe0. 15 Cu0. 1Zr0. 03 ) 7.5 sintered magnets, prepared by the conventional powder metallurgy method, was studied. With increasing ballmilling t...The influence of mean particle size on magnetic properties ofSm ( Co0.72Fe0. 15 Cu0. 1Zr0. 03 ) 7.5 sintered magnets, prepared by the conventional powder metallurgy method, was studied. With increasing ballmilling time, mean particle size decreases, specific surface increases, and sintering temperature decreases. The optimum sintering temperature of powders fabricated by baH-milling for 5, 7, 9 and 11 h are 1225, 1225, 1215 and 1215℃ respectively. The optimum value of Br, (BH)max, Hob and Hci of Sm ( Co0.72Fe0. 15 Cu0. 1Zr0. 03 ) 7.5 sintered magnets with powders ball-milling for 9 h and sintering at 1215 ℃ can reach 0.94 T, 708.4 kA·m^-1, 171.9 kJ·m^-3 and 2276.6 kA·m^-1 respectively, and the irreversible flux loss is less than 5 % after the sample ageing at 550 ℃ for 2 h, so the temperature stability improves and the magnets may be expected to be applied in the circumstances of 550 ℃.展开更多
基金the National Natural Science Foundation of China(Nos.52174258,92162109,52222405 and 52004184).
文摘Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.
文摘Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles.Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements,was favorable for the formation of in-situ synthesized carbide particles.In this paper,rare earth oxide(RE2O3) was added into t...
基金National Key Basic Research Program (NKBRP 2004CCA03900) the National Natural Science Foundation of China (50662002)
文摘The large particle CeO2 and Y2O3 were prepared using oxalic acid as precipitator. The effects of operational parameters such as stirring velocity, precipitation temperature, feeding speed, aging time, precipitation method, and calcination temperature on particle size and loose density of CeO2 were studied. Under the particular conditions, particle median size of D50≥30μm, loose density of ≥2.0 g/mlof CeO2, and particle median size of D50≥20 μm of Y2O3 were prepared. This technology had advantages of simple process, less equipment investment, ease of use, and suitability for industrialization products.
文摘The rare earth based hydrogen storage alloys Ml_ 0.7Mm_ 0.3(Ni_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3) were chosen as objects of investigation in this paper. The effects of particle size on electrochemical properties of the alloy were investigated. The results indicate that the alloy with particle size of 100 and 150 mesh shows good activation behavior and high discharge capacity (the first discharge capacity and the maximum discharge capacity), but poor cycling stability, low capacity retention and high discharge capacity rate. The Ml_ 0.7Mm_ 0.3(Ni_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3) alloy with particle size of 150 mesh shows excellent electrochemical properties.
基金Project supported by National "The Tenth Five-Year"plan (2003BA316A01-03-05) and "The Tenth Five-Year"Plan(BE2004021) of Jiangsu provicce
文摘Spherical YAG:Ce^3+ phosphor particles with narrow size distribution were prepared by spray pyrolysis. The effects of the concentration of solution, the flow rate of cartier gas and the annexing temperature on the phosphor morphology were studied. The productivity of precursor particles shows a trend of drop after rising with the increase of concentration Raising the flow rate of nitrogen can improve the productivity of the precursor particles. Phosphor prepared by spray pyrolysis has obviously higher emission intensity than that synthesized by solid state reaction, spray pyrolysis makes Ce^3+ ions well distributed in the crystal lattice as the luminescent centers, and phosphor particles have regular sphericity and narrow size distribution.
基金supported by the National Natural Science Foundation of China (2056601, 50662002)
文摘Cerium dioxide(CeO2) has attracted much attention and has wide applications such as automotive exhaust catalysts,polishing materials for optical glasses and additives for advanced glasses,as well as cosmetic materials.The particle size and its distribution are key factors to the performance of the materials in the functional applications.However,control of particle size is still a challenge in materials synthesis.Therefore,continuous precipitation of cerium oxalate(precursor of ceria) was carried out at dif...
文摘Ce0.6Zr0.4O2 solid solution ultrafine particle was prepared in the cyclohexane/water/OP-10/n-hexanol reversed microemulsion. The quasi-ternary phase diagram investigations showed that the system has narrow W/O type microemulison region, so it is the proper system to prepare Ce0.6Zr0.4O2 solid solution ultrafine particle. Some physical-chemical techniques such as TG/DTA, XRD, BET, and HRTEM are used to characterize the resultant powders. The results show that the fluorite cubic Ce0.6Zr0.4O2 solid solution is obtained at 400 ℃. The surface area is (146.7 m^2·g^-1), which is higher than the surface area for sol-gel prepared sample (59.5m^2·g^-1). HRTEM images indicated that the Ce0.6Zr0.4O2 solid solution ultrafine particle is well-crystallized, narrow size distribution, less agglomeration, within mean size of 5 -7 nm.
基金Project supported by the Ministry of Science and Technology of China (2006BAC02A06)
文摘Cerium is one of the most abundant rare earth elements in both bastnasite and monazite. Ceria has been widely used in optical, catalytic, electrolyte, and sensor materials, with unique performances. With the development of functional materials, great interest has been focused on the synthesis and characterization of specific fine/mesoporous ceria powder. In this study, the modified precipitation and recrystallization processes combined with a controlled calcination process for fabricating the ceria with large particle size and high appearance density was reported. During precipitation, a certain amount of mineral acid such as nitric acid served as an additive, to adjust the precipitation and crystallization processes of cerium oxalates. An appropriate acidic condition could lead the process into the Oswald ripening stage and made the particles become bigger. Thus, the appearance density of powder was increased. The optimized conditions, such as the temperature, feeding speed, type and concentration of mineral acids, and the concentration of cerium-contained stock solution, were investigated and evaluated.
基金supported by the Institute of Physical Chemistry of the Polish Academy of Sciences
文摘We present how the luminescence of europium RR-2-P-oxides complexes can be increased by interaction of electronic levels of the complex with the radiation field of silver nanoparticles (NPs). The procedure by which silver NPs are formed in a sol-gel polyurethane matrix precursor was elaborated. The formed Ag NPs were combined with Eu complex incorporated in ormocer matrix. The emission spectra of the complexes without silver NPs were compared with spectra of the same complexes with addition of silver NPs. As the result of the interaction of the electronic levels of lanthaaide ligands with silver plasmons, dramatic increase of luminescence was observed.
基金Project supported by Rare Earth Department of National Development Committee Preparation of High Quality Polishing Powder
文摘Fine spherical particle sized ceria (CeO_2) was prepared by homogeneous precipitation method with ammonium bicarbonate as precipitant. The prepared CeO_2 has the primary particle size of 10~50 nm when calcined between 400~700 ℃ analyzed by XRD and the aggregated particle size is about 300 nm measured by LASER particle sizer. SEM, TG-DTA and Zeta-potential analyzer were employed individually to study the morphology and the formation of CeO_2 product. It was found that excess NH_4NO_3 can serve as an sphericallization agent to prepare spherical CeO_2 powder by precipitation method.
基金Project supported by the National Natural Science Foundation of China (50372086)the Ministry of Science and Technology of Chi-na (2006CB601104)
文摘The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na2CO3, S, NaCl or their combination, were introduced into the precursor to prepare Y2O3 :Eu^3+ red phosphors at 1000 1300 ℃ for 2 h. The effect of molten salts on particle size and luminescent intensity was studied. The experimental results showed that the complex molten salt (Na:CO3 + S + NaCl) was conductive to enhance the luminescent intensity of Y2O3 :Eu^3+. The emission intensity of the phosphor prepared with these additives at 1300 ℃ was about 45% higher than that of the one prepared without molten salt, and about 11% higher than that of the corresponding commercial phosphor. Meanwhile, the particle size of Y2O3 :Eu^3+ phosphor was controlled effectively with the molten salt.
文摘The effect of particle size and distribution of rapidly quenching NdFeB magnetic powder on the magnetic properties of polymerbonded NdFeB permanent magnet was studied. The results show that the particle size and the distribution of rapidly quenching NdFeB magnetic powder have significant effects on the magnetic properties of polymerbonded NdFeB permanent magnet. As long as the size and the distribution of rapidly quenching NdFeB powder are within the right range, high magnetic properties of polymerbonded NdFeB permanent magnet can be obtained. This is mainly because the rapidly quenching NdFeB magnetic powder has high hardness and is scaleshaped. The larger the size of rapidly quenching NdFeB particles is, the more difficult it is to obtain high density of bonded NdFeB magnet. However the structure will be destroyed if the size is too small. It results in the deterioration of magnetic properties. The mechanism is also discussed.
文摘The SiO 2 adsorbing YF 3, Y 2(CO 3) 3, Y 2(C 2O 4) 3 and YPO 4, respectively, formed four systems of particle materials: SiO 2·YF 3, SiO 2·Y 2(CO 3) 3 , SiO 2·Y 2(C 2O 4) 3 and SiO 2·YPO 4. The electrorheological(ER) behavior of the electrorheological fluids (ERF) prepared by dispersing them in silicone oil was tested at 20 ℃ under d.c. field. The results show that the system of SiO 2·YF 3 does not display ER activity, and the ER performance of the particle materials of SiO 2·Y 2(CO 3) 3 is the best among them. The shearing stress of ERF with SiO 2·Y 2(CO 3) 3 particles is 1.644 KPa and the relative viscosity η r(=η E/η 0) is 20.3 (under field strength E=4200 V·mm -1) while the adsorbed content of Y 2(CO 3) 3 in the SiO 2 particle materials is 12.4%(mass fraction).
文摘The SiO_2 particle material has weak electrorheological (ER) activity. The ER performance of the SiO_2 particles can be ameliorated after adsorbing Y_2(CO_3)_3. In this paper, the effect of Y_2(CO_3)_3 and different surfactants on the ER performance of the SiO_2 particle materials is investigated. The results show that anionic or cationic surfactants maybe enhance the ER activity of SiO_2 material, and nonionic surfactants cannot when surfactants are added during the process of the SiO_2 particle preparation, only the anionic surfactant, AES, can enhance markedly the ER performance of the material. The surface area, pore volume and pore diameter of the particles were measured. The effect of Y_2(CO_3)_3 and the surfactants on the microstructure of SiO_2 materials and the relationship between ER effect and the microstructure are described.
文摘Heterogeneous photocatalysed reduction of aqueous Na_2CO_3 was carried out by using nano LaCoO_3 semiconductor powders. Formic acid and formaldehyde were identified as photoproducts,and were measured spectrophotometrically using Nash reagent. The effect of different parameters such as sodium carbonate concentration,amount of photocatalyst and different light sources on the yield of photoproducts was also investigated. It shows that nano LaCoO_3 has photocatalytic activity. Irradiation leads to the production of electrons in the conduction band of the LaCoO_3 semiconductor. It is likely that the photoproduced electrons initially reduce CO_3 (2-) to HCOO -,and then to HCHO and CH_3OH.
文摘A technique for preparing perovskite type oxides was developed. By this technique, ultra fine particles of La 0.9 RE 0.1 MnO 3 (RE: Y, Ce, Pr, Sm, Gd,or Dy) with high surface area and single perovskite structure were prepared, and the series of La 0.9 RE 0.1 MnO 3 catalysts were studied experimentally. The so prepared ultra fine particles exhibites high catalytic activity for CH 4 total oxidation. The ultra fine particles of La 0.9 RE 0.1 MnO 3 (except for La 0.9 Pr 0.1 MnO 3) prepared by this method are thermally much more stable than LaMnO 3. Of the La 0.9 RE 0.1 MnO 3 series, La 0.9 Y 0.1 MnO 3 is most thermally stable, and La 0.9 Y 0.1 MnO 3 or La 0.9 Gd 0.1 MnO 3 (varies with calcination temperature) exhibits the highest catalytic activity for total oxidation of methane. The specific surface area of La 0.9 Y 0.1 MnO 3 calcined at 1000 ℃ reaches 14.9 m 2·g -1 , while the specific surface area of LaMnO 3 calcined at the same temperature is only 1.8 m 2·g -1 .
文摘The influence of mean particle size on magnetic properties ofSm ( Co0.72Fe0. 15 Cu0. 1Zr0. 03 ) 7.5 sintered magnets, prepared by the conventional powder metallurgy method, was studied. With increasing ballmilling time, mean particle size decreases, specific surface increases, and sintering temperature decreases. The optimum sintering temperature of powders fabricated by baH-milling for 5, 7, 9 and 11 h are 1225, 1225, 1215 and 1215℃ respectively. The optimum value of Br, (BH)max, Hob and Hci of Sm ( Co0.72Fe0. 15 Cu0. 1Zr0. 03 ) 7.5 sintered magnets with powders ball-milling for 9 h and sintering at 1215 ℃ can reach 0.94 T, 708.4 kA·m^-1, 171.9 kJ·m^-3 and 2276.6 kA·m^-1 respectively, and the irreversible flux loss is less than 5 % after the sample ageing at 550 ℃ for 2 h, so the temperature stability improves and the magnets may be expected to be applied in the circumstances of 550 ℃.