β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanica...β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanical properties of the materials was展开更多
The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite ...The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature展开更多
The green specimens of nano-size Y-TZP are formed by gelcasting method. Using polymer electrolytes NaPAA and NH_4PAA, we have studied the rheological properties of slurry.The optimum pH range is between 8 to 10. The p...The green specimens of nano-size Y-TZP are formed by gelcasting method. Using polymer electrolytes NaPAA and NH_4PAA, we have studied the rheological properties of slurry.The optimum pH range is between 8 to 10. The proper amount of dispersant changes with the solid content.The rheological measurements of suspension containing NH_4PAA show lower viscosity.The theoretical green density has been calculated.展开更多
Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)acti...Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)activities of fluid catalytic cracking(FCC)diesel.They were characterized by SEM,BET,XRD,H2-TPR,NH3-TPD and HRTEM.The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter,higher pore volume,weaker and lesser acid sites,more easily reducible metal phases,shorter MoS2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y.The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed.The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.展开更多
Nano-sized yttria particles were synthesized via a non-aqueous sol-gel process based on hydrated yttrium nitrate and ethylene glycol. The effects of the molar ratio of ethylene glycol to yttrium ion and calcination te...Nano-sized yttria particles were synthesized via a non-aqueous sol-gel process based on hydrated yttrium nitrate and ethylene glycol. The effects of the molar ratio of ethylene glycol to yttrium ion and calcination temperature on crystallite size of the products were studied. The catalytic performance of the as-prepared yttria for the ammonium perchlorate (AP) decomposition was investigated by differential scanning calorimetry (DSC). The results indicate that the nano-sized cubic yttria particles with less than 20 nm in average crystallite size can be obtained after 2 h reflux at 70℃, dried at 90 ℃, forming xerogel, and followed by annealing of xerogel for 2 h, and that the addition of the nano-sized yttria to AP incorporates two small exothermic peaks of AP in the temperature ranges of 310 - 350 ℃ and 400 - 470 ℃ into a strong exothermic peak of AP and increases the apparent decomposition heat from 515 to over 1110 J·g^- 1. It is also clear that the temperature of AP decomposition exothermic peak decreases and the apparent decomposition heat of AP increases with the increase of the amount of nano-sized yttria. The fact that the addition of the 5 % nano-sized yttria to AP decreases the temperature of AP exothermic peak to 337.7℃ by reduction of 114.6℃ and increases the apparent decomposition heat from 515 to 1240 J·g^-1, reveals that nano-sized yttria shows strong catalytic property for AP thermal decomposition.展开更多
Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4....Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5:1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and inductively coupled plasma - mass spectrometry (ICP-MS), inductively coupled plasma - atomic emission spectrometry (ICP-AES), inductive combustion infrared absorption (ICIA) and infrared thermal conductivity of oxygen and nitrogen analyzer (ITCA). The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.展开更多
The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffracti...The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.展开更多
Coal dust explosion accidents often cause substantial property damage and casualties and frequently involve nano-sized coal dust.In order to study the impact of nano-sized coal on coal dust and methane–coal dust expl...Coal dust explosion accidents often cause substantial property damage and casualties and frequently involve nano-sized coal dust.In order to study the impact of nano-sized coal on coal dust and methane–coal dust explosions,a pipe test apparatus was used to analyze the explosion pressure characteristics of five types of micro-nano particle dusts(800 nm,1200 nm,45μm,60μm,and 75μm)at five concentrations(100 g/m3,250 g/m3,500 g/m3,750 g/m3,and 1000 g/m3).The explosion pressure characteristics were closely related to the coal dust particle size and concentration.The maximum explosion pressure,maximum rate of pressure rise,and deflagration index for nano-sized coal dust were larger than for its micro-sized counterpart,indicating that a nano-sized coal dust explosion is more dangerous.The highest deflagration index Kst for coal dust was 13.97 MPa/(m·s),indicating weak explosibility.When 7%methane was added to the air,the maximum deflagration index Kst for methane–coal dust was 42.62 MPa/(m·s),indicating very strong explosibility.This indicates that adding methane to the coal dust mixture substantially increased the hazard grade.展开更多
The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as ...The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and hard agglomerates brought by the chemical precipitation method. The powders were characterized by TG-DTA, XRD, FT-IR, TEM respectively and the photoluminescence (PL) spectra of (Nd0.01Y0.99)3Al5O12 green and sintered ceramic disks were measured. The results show that the forming temperature of YAG crystal phase is 850 ℃ and YAP crystal phase appearing during the calcinations transforms to pure YAG at 1050 ℃. The particle size of the powders synthesized by the LCS is in a range of 20~50 nm depending on the thermal treatment temperatures. The effectively induced cross section (σin) with the value 4.03×10-19 cm2 of (Nd0.01Y0.99)3Al5O12 ceramics is about 44% higher than that of single crystal.展开更多
Nano-sized aluminum(Nano-Al)powders hold promise in enhancing the total energy of explosives and the metal acceleration ability at the same time.However,the near-detonation zone effects of reaction between Nano-Al wit...Nano-sized aluminum(Nano-Al)powders hold promise in enhancing the total energy of explosives and the metal acceleration ability at the same time.However,the near-detonation zone effects of reaction between Nano-Al with detonation products remain unclear.In this study,the overall reaction process of 170 nm Al with RDX explosive and its effect on detonation characteristics,detonation reaction zone,and the metal acceleration ability were comprehensively investigated through a variety of experiments such as the detonation velocity test,detonation pressure test,explosive/window interface velocity test and confined plate push test using high-resolution laser interferometry.Lithium fluoride(LiF),which has an inert behavior during the explosion,was used as a control to compare the contribution of the reaction of aluminum.A thermochemical approach that took into account the reactivity of aluminum and ensuing detonation products was adopted to calculate the additional energy release by afterburn.Combining the numerical simulations based on the calculated afterburn energy and experimental results,the parameters in the detonation equation of state describing the Nano-Al reaction characteristics were calibrated.This study found that when the 170 nm Al content is from 0%to 15%,every 5%increase of aluminum resulted in about a 1.3%decrease in detonation velocity.Manganin pressure gauge measurement showed no significant enhancement in detonation pressure.The detonation reaction time and reaction zone length of RDX/Al/wax/80/15/5 explosive is 64 ns and 0.47 mm,which is respectively 14%and 8%higher than that of RDX/wax/95/5 explosive(57 ns and 0.39 mm).Explosive/window interface velocity curves show that 170 nm Al mainly reacted with the RDX detonation products after the detonation front.For the recording time of about 10 ms throughout the plate push test duration,the maximum plate velocity and plate acceleration time accelerated by RDX/Al/wax/80/15/5 explosive is 12%and 2.9 ms higher than that of RDX/LiF/wax/80/15/5,respectively,indicating that the aluminum reaction energy significantly increased the metal acceleration time and ability of the explosive.Numerical simulations with JWLM explosive equation of state show that when the detonation products expanded to 2 times the initial volume,over 80%of the aluminum had reacted,implying very high reactivity.These results are significant in attaining a clear understanding of the reaction mechanism of Nano-Al in the development of aluminized explosives.展开更多
A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and pr...A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), O2 temperature-programmed desorption (O2-TPD), and inductively coupled with plasma atomic emission spectroscopy (ICP-AES) techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO (Mg/SiO2 weight ratio) shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.展开更多
Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide(CTAB)through a facile one-step crystallization process.Commercial ZSM...Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide(CTAB)through a facile one-step crystallization process.Commercial ZSM-5 zeolites with a SiO2/Al2O3 ratio comparable to that of ZSM-5 products were treated with alkali and used as the seed particles.The influences of crystallization conditions were investigated,and the possible synthesis mechanism was proposed.ZSM-5 zeolites with diff erent amounts of CTAB added were characterized using many techniques and evaluated in toluene alkylation with methanol.The results showed that a trace amount of CTAB signifi cantly promoted the crystallization of ZSM-5 zeolite,with the morphology changing from hexagonal-shape crystals to uniform spherical aggregates.CTAB may act as the structure-directing agent and assemble the primary crystallites to generate hierarchical ZSM-5 aggregates.The ZSM-5 zeolite with the smallest primary particles of 50-80 nm exhibited large specific surface area,abundant mesopores,and the greatest microporosity.The hierarchical nano-sized ZSM-5 aggregate showed higher toluene conversion and a longer lifetime without compromising the selectivity to xylene and p-xylene in toluene alkylation with methanol.展开更多
The desulfurizer research is focused on transition-metal oxide.The paper had discussed in depth the desulfurization activity of nano-size ZnO doped with metallic elements.In order to improve the desulfurization activi...The desulfurizer research is focused on transition-metal oxide.The paper had discussed in depth the desulfurization activity of nano-size ZnO doped with metallic elements.In order to improve the desulfurization activity of nano-desulfurizer,we prepared the nano-size ZnO desulfurizer doped with iron,nickel and copper ionic respectively,using homogeneous precipitation.At the same time,the effects of different doped elements on the desulfurization activity of nano-size ZnO were compared by removing the pollutant of H2S.The experimental results showed that the desulfurization activity of metallic elements-doped nano-size ZnO increased significantly.When the molar ratio of Fe/Zn is 5:100(FZ5.0) and Cu/Zn is 2:100(CuZ2.0),their sulfur contents are 5.3% and 5.6% respectively.These desulfurizers can reach better desulfurization activity than that doped with nickel.Further research showed that,for CuZ2.0,the primary desulfurization activity is better than that of FZ5.0,but the regeneration temperature is as high as 570 ℃,and after three times regeneration/sulfuration cycle tests,the desulfurization activity decreases obviously.However,FZ5.0 can be recycled 5 times continuously at 370℃ with a stable desulfurization activity.In view of the better regeneration/sulfuration performance of FZ5.0,the dynamics of the removing H2S process by FZ5.0 were further studied.The result showed that the reaction order of removing H2S by FZ5.0 is 0.96385 at 25 ℃.展开更多
Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering ( LPS ). The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 ( s ) + 1.5 02 ( g...Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering ( LPS ). The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 ( s ) + 1.5 02 ( g ) = 3 Si2 N2O ( s ) + N2 ( g ) . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition : amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa (Vickers) at 1 600 ℃ .展开更多
Fluoride mediated nano-sized ZSM-5 (ZSM-5-F) with a high Si/AI ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene (MTP) reaction. High propylene sele...Fluoride mediated nano-sized ZSM-5 (ZSM-5-F) with a high Si/AI ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene (MTP) reaction. High propylene selectivity (45%) was similar to ZSM-5-OH synthesized via a hydroxide route. However, ZSM- 5-F showed much longer lifetime (305 h) compared with ZSM-5-OH (157 h) in spite of similar crystal size and aluminum content. Characterization by NH3-TPD. Py-IR, OH-IR, SEM, TG-DTA, XRD and 1H MAS NMR techniques indicated that the enhanced catalytic performance of ZSM-S-F is attributed to the fewer structural defects in the form of internal silanol groups and silanol nests.展开更多
文摘β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanical properties of the materials was
文摘The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature
文摘The green specimens of nano-size Y-TZP are formed by gelcasting method. Using polymer electrolytes NaPAA and NH_4PAA, we have studied the rheological properties of slurry.The optimum pH range is between 8 to 10. The proper amount of dispersant changes with the solid content.The rheological measurements of suspension containing NH_4PAA show lower viscosity.The theoretical green density has been calculated.
基金financially supported by the Basic Research Program'Green Chemistry and Engineering of Heavy Oil Conversion with High Efficiency' and the National Key Fundamental Research Development Project(973 Project:No.2010CB226905)
文摘Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)activities of fluid catalytic cracking(FCC)diesel.They were characterized by SEM,BET,XRD,H2-TPR,NH3-TPD and HRTEM.The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter,higher pore volume,weaker and lesser acid sites,more easily reducible metal phases,shorter MoS2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y.The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed.The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.
基金Project supported by the National Natural Science Foundation of China (50306008)Advance Research Foundation forGeneral Equipment Department (41328030507)
文摘Nano-sized yttria particles were synthesized via a non-aqueous sol-gel process based on hydrated yttrium nitrate and ethylene glycol. The effects of the molar ratio of ethylene glycol to yttrium ion and calcination temperature on crystallite size of the products were studied. The catalytic performance of the as-prepared yttria for the ammonium perchlorate (AP) decomposition was investigated by differential scanning calorimetry (DSC). The results indicate that the nano-sized cubic yttria particles with less than 20 nm in average crystallite size can be obtained after 2 h reflux at 70℃, dried at 90 ℃, forming xerogel, and followed by annealing of xerogel for 2 h, and that the addition of the nano-sized yttria to AP incorporates two small exothermic peaks of AP in the temperature ranges of 310 - 350 ℃ and 400 - 470 ℃ into a strong exothermic peak of AP and increases the apparent decomposition heat from 515 to over 1110 J·g^- 1. It is also clear that the temperature of AP decomposition exothermic peak decreases and the apparent decomposition heat of AP increases with the increase of the amount of nano-sized yttria. The fact that the addition of the 5 % nano-sized yttria to AP decreases the temperature of AP exothermic peak to 337.7℃ by reduction of 114.6℃ and increases the apparent decomposition heat from 515 to 1240 J·g^-1, reveals that nano-sized yttria shows strong catalytic property for AP thermal decomposition.
基金supported in part by the National Centre of Analysis and Testing for Nonferrous Metal & Electronic Material for Elementary Analysis, Beijing, China
文摘Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5:1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and inductively coupled plasma - mass spectrometry (ICP-MS), inductively coupled plasma - atomic emission spectrometry (ICP-AES), inductive combustion infrared absorption (ICIA) and infrared thermal conductivity of oxygen and nitrogen analyzer (ITCA). The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.
文摘The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.
基金This research was supported by the National Key Research and Development Program of China(2016YFC0801800)the National Nature Science Foundation of China(51774291,51864045).
文摘Coal dust explosion accidents often cause substantial property damage and casualties and frequently involve nano-sized coal dust.In order to study the impact of nano-sized coal on coal dust and methane–coal dust explosions,a pipe test apparatus was used to analyze the explosion pressure characteristics of five types of micro-nano particle dusts(800 nm,1200 nm,45μm,60μm,and 75μm)at five concentrations(100 g/m3,250 g/m3,500 g/m3,750 g/m3,and 1000 g/m3).The explosion pressure characteristics were closely related to the coal dust particle size and concentration.The maximum explosion pressure,maximum rate of pressure rise,and deflagration index for nano-sized coal dust were larger than for its micro-sized counterpart,indicating that a nano-sized coal dust explosion is more dangerous.The highest deflagration index Kst for coal dust was 13.97 MPa/(m·s),indicating weak explosibility.When 7%methane was added to the air,the maximum deflagration index Kst for methane–coal dust was 42.62 MPa/(m·s),indicating very strong explosibility.This indicates that adding methane to the coal dust mixture substantially increased the hazard grade.
文摘The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and hard agglomerates brought by the chemical precipitation method. The powders were characterized by TG-DTA, XRD, FT-IR, TEM respectively and the photoluminescence (PL) spectra of (Nd0.01Y0.99)3Al5O12 green and sintered ceramic disks were measured. The results show that the forming temperature of YAG crystal phase is 850 ℃ and YAP crystal phase appearing during the calcinations transforms to pure YAG at 1050 ℃. The particle size of the powders synthesized by the LCS is in a range of 20~50 nm depending on the thermal treatment temperatures. The effectively induced cross section (σin) with the value 4.03×10-19 cm2 of (Nd0.01Y0.99)3Al5O12 ceramics is about 44% higher than that of single crystal.
基金The authors would like to acknowledge National Natural Science Foundation of China(Grant No.11832006)Open Project of State Key Laboratory of Explosion Science and Technology in Beijing Institute of Technology(Grant No.KFJJ20-04 M)to provide fund for conducting experiments.
文摘Nano-sized aluminum(Nano-Al)powders hold promise in enhancing the total energy of explosives and the metal acceleration ability at the same time.However,the near-detonation zone effects of reaction between Nano-Al with detonation products remain unclear.In this study,the overall reaction process of 170 nm Al with RDX explosive and its effect on detonation characteristics,detonation reaction zone,and the metal acceleration ability were comprehensively investigated through a variety of experiments such as the detonation velocity test,detonation pressure test,explosive/window interface velocity test and confined plate push test using high-resolution laser interferometry.Lithium fluoride(LiF),which has an inert behavior during the explosion,was used as a control to compare the contribution of the reaction of aluminum.A thermochemical approach that took into account the reactivity of aluminum and ensuing detonation products was adopted to calculate the additional energy release by afterburn.Combining the numerical simulations based on the calculated afterburn energy and experimental results,the parameters in the detonation equation of state describing the Nano-Al reaction characteristics were calibrated.This study found that when the 170 nm Al content is from 0%to 15%,every 5%increase of aluminum resulted in about a 1.3%decrease in detonation velocity.Manganin pressure gauge measurement showed no significant enhancement in detonation pressure.The detonation reaction time and reaction zone length of RDX/Al/wax/80/15/5 explosive is 64 ns and 0.47 mm,which is respectively 14%and 8%higher than that of RDX/wax/95/5 explosive(57 ns and 0.39 mm).Explosive/window interface velocity curves show that 170 nm Al mainly reacted with the RDX detonation products after the detonation front.For the recording time of about 10 ms throughout the plate push test duration,the maximum plate velocity and plate acceleration time accelerated by RDX/Al/wax/80/15/5 explosive is 12%and 2.9 ms higher than that of RDX/LiF/wax/80/15/5,respectively,indicating that the aluminum reaction energy significantly increased the metal acceleration time and ability of the explosive.Numerical simulations with JWLM explosive equation of state show that when the detonation products expanded to 2 times the initial volume,over 80%of the aluminum had reacted,implying very high reactivity.These results are significant in attaining a clear understanding of the reaction mechanism of Nano-Al in the development of aluminized explosives.
基金supported by the Youth Fund Project(2002B25)of Sichuan Department of Educationthe Scientific Research Foundation for Doctor from Yibin College of China(2010B12)
文摘A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), O2 temperature-programmed desorption (O2-TPD), and inductively coupled with plasma atomic emission spectroscopy (ICP-AES) techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO (Mg/SiO2 weight ratio) shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.
基金supported by the National Natural Science Foundation of China(No.21276183).
文摘Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide(CTAB)through a facile one-step crystallization process.Commercial ZSM-5 zeolites with a SiO2/Al2O3 ratio comparable to that of ZSM-5 products were treated with alkali and used as the seed particles.The influences of crystallization conditions were investigated,and the possible synthesis mechanism was proposed.ZSM-5 zeolites with diff erent amounts of CTAB added were characterized using many techniques and evaluated in toluene alkylation with methanol.The results showed that a trace amount of CTAB signifi cantly promoted the crystallization of ZSM-5 zeolite,with the morphology changing from hexagonal-shape crystals to uniform spherical aggregates.CTAB may act as the structure-directing agent and assemble the primary crystallites to generate hierarchical ZSM-5 aggregates.The ZSM-5 zeolite with the smallest primary particles of 50-80 nm exhibited large specific surface area,abundant mesopores,and the greatest microporosity.The hierarchical nano-sized ZSM-5 aggregate showed higher toluene conversion and a longer lifetime without compromising the selectivity to xylene and p-xylene in toluene alkylation with methanol.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50978073)China Postdoctoral Science Foundation (Grant No.20090450982)the Postdoctoral Research Foundation of Heilongjiang Province(Grant No.LBH-Z08171)
文摘The desulfurizer research is focused on transition-metal oxide.The paper had discussed in depth the desulfurization activity of nano-size ZnO doped with metallic elements.In order to improve the desulfurization activity of nano-desulfurizer,we prepared the nano-size ZnO desulfurizer doped with iron,nickel and copper ionic respectively,using homogeneous precipitation.At the same time,the effects of different doped elements on the desulfurization activity of nano-size ZnO were compared by removing the pollutant of H2S.The experimental results showed that the desulfurization activity of metallic elements-doped nano-size ZnO increased significantly.When the molar ratio of Fe/Zn is 5:100(FZ5.0) and Cu/Zn is 2:100(CuZ2.0),their sulfur contents are 5.3% and 5.6% respectively.These desulfurizers can reach better desulfurization activity than that doped with nickel.Further research showed that,for CuZ2.0,the primary desulfurization activity is better than that of FZ5.0,but the regeneration temperature is as high as 570 ℃,and after three times regeneration/sulfuration cycle tests,the desulfurization activity decreases obviously.However,FZ5.0 can be recycled 5 times continuously at 370℃ with a stable desulfurization activity.In view of the better regeneration/sulfuration performance of FZ5.0,the dynamics of the removing H2S process by FZ5.0 were further studied.The result showed that the reaction order of removing H2S by FZ5.0 is 0.96385 at 25 ℃.
基金Funded by the National Science Foundation of China ( No.50375037)
文摘Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering ( LPS ). The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 ( s ) + 1.5 02 ( g ) = 3 Si2 N2O ( s ) + N2 ( g ) . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition : amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa (Vickers) at 1 600 ℃ .
文摘Fluoride mediated nano-sized ZSM-5 (ZSM-5-F) with a high Si/AI ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene (MTP) reaction. High propylene selectivity (45%) was similar to ZSM-5-OH synthesized via a hydroxide route. However, ZSM- 5-F showed much longer lifetime (305 h) compared with ZSM-5-OH (157 h) in spite of similar crystal size and aluminum content. Characterization by NH3-TPD. Py-IR, OH-IR, SEM, TG-DTA, XRD and 1H MAS NMR techniques indicated that the enhanced catalytic performance of ZSM-S-F is attributed to the fewer structural defects in the form of internal silanol groups and silanol nests.