Presented herein is an experimental study on the combustion of B4C/KNO3 binary pyrotechnic system.Combustion products were tested using X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive sp...Presented herein is an experimental study on the combustion of B4C/KNO3 binary pyrotechnic system.Combustion products were tested using X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometer(EDS).According to the results of tests and CEA calculation,the combustion reaction equation was established.The flames and burning rates were recorded by a high speed camera and a spectrophotometer.The effect of B4C particle size on the thermal sensitivity of B4C/KNO3 was investigated by differential scanning calorimetry(DSC)techniques.In addition,a reliable method for calculating the flame temperature was proposed.Based on the results of experiments,the combustion reaction mechanism was briefly analyzed.The burning rate,flame temperature and thermal sensitivity of B4C/KNO3 increase with the decrease of B4C particle size.The mass ratio of B4C/KNO3 has a great effect on combustion properties.Oxidizer-rich compositions have low flame temperatures,low burning rates,and provide green light emission.The combustion reactions of fuel-rich compositions are vigorous,and the B4C/KNO3 with mass ratio of 25:75 has the highest burning rate and the highest flame temperature.展开更多
Energetic metal-organic complexes have been involved in nanothermites as novel oxidants.However,the existing preparation methods often lead to mixing inhomogeneity and small contact area of ingredients,the reactivity ...Energetic metal-organic complexes have been involved in nanothermites as novel oxidants.However,the existing preparation methods often lead to mixing inhomogeneity and small contact area of ingredients,the reactivity and functionality of the novel energetic nanocomposites are still limited.In this work,spray crystallization(SC)method was used to prepare novel energetic nanocomposites,the high-energy metal-organic complex[Ni(CHZ)_(3)](ClO_(4))_(2)(CHZ=1,3-diaminourea)was composited with nanoaluminum(n-Al).Results showed that n-Al/[Ni(CH_(2))_(3)](ClO_(4))_(2)energetic nanocomposites prepared by SC method increased heat release to 2977.6 J/g and peak pressure to 3.91 MPa with higher pressurization rate(1324.06 MPa/s),decreased sensitivity thresholds(>100 mJ)to electrostatic discharge(ESD)and enhanced detonation ability compared with[Ni(CHZ)_(3)](ClO_(4))_(2)alone and physically mixed(PM)n-Al/[Ni(CHZ)_(3)](ClO_(4))_(2).These results proved that it is significant to introduce energetic metal-organic complexes with inherent high energy in new-concept n-Al/energetic metal-organic complexes nanocomposites through SC method for a better performance of its application.展开更多
Monolayer transition metal dichalcogenides favor the formation of a variety of excitonic quasiparticles,and can serve as an ideal material for exploring room-temperature many-body effects in two-dimensional systems.He...Monolayer transition metal dichalcogenides favor the formation of a variety of excitonic quasiparticles,and can serve as an ideal material for exploring room-temperature many-body effects in two-dimensional systems.Here,using mechanically exfoliated monolayer WS;and photoluminescence(PL)spectroscopy,exciton emission peaks are confirmed through temperature-dependent and electric-field-tuned PL spectroscopy.The dependence of exciton concentration on the excitation power density at room temperature is quantitatively analyzed.Exciton concentrations covering four orders of magnitude are divided into three stages.Within the low carrier concentration stage,the system is dominated by excitons,with a small fraction of trions and localized excitons.At the high carrier concentration stage,the localized exciton emission from defects coincides with the emission peak position of trions,resulting in broad spectral characteristics at room temperature.展开更多
It is a valuable issue to explore whether a flame can radiate microwaves,in spite of the electric field formed in the flame.Presented herein is an experimental study on a series of flames with millimeterwave radiation...It is a valuable issue to explore whether a flame can radiate microwaves,in spite of the electric field formed in the flame.Presented herein is an experimental study on a series of flames with millimeterwave radiation in the combustion of pyrotechnic films.The pyrotechnic films were composed of ultrafine red phosphorus(P),sodium nitrate(NaNO_3),Polyvinyl Alcohol(PVA) and some additives such as chopped carbon fibers(CFs) and aluminized glass fibers(GFs).The combustion temperatures and millimeter-wave radiation signals of the flames were measured,the millimeter-wave emissivity and spectral radiant exitance were calculated to describe the millimeter-wave radiation intensity.The results demonstrate that the flame of the pyrotechnic films based on P/NaNO_3/CFs can radiate millimeter waves,and different materials and their proportion have a great effect on the millimeter-wave radiation intensity.展开更多
A projectile with exotic wraparound wings( WAW) configuration is designed to improve the finstabilized projectile shooting quality. Two fin-stabilized projectiles with the same body with and without exotic WAW configu...A projectile with exotic wraparound wings( WAW) configuration is designed to improve the finstabilized projectile shooting quality. Two fin-stabilized projectiles with the same body with and without exotic WAW configuration are simulated numerically by applying the Roe scheme. The shear-stress transport turbulence models and the lower-upper symmetric Gauss-Seidel implicit method are used to solve 3D Reynoldsaveraged Navier—Stokes equations. The differences in aerodynamic coefficients and aerodynamic characteristics of the projectiles when the Mach number varies from 0. 35 to 0. 95 are obtained,and the cause of these differences is analyzed. The calculation results indicate that the lift-to-drag ratio of the projectile significantly increases,the rolling moment decreases,and the position of the pressure center of the projectile shows relatively small changes when the exotic WAW configuration is used. Therefore,this projectile can obviously reduce rolling effect,enlarge range and improve flying stability.展开更多
基金The support for this work was provided by the National Natural Science Foundation of China(Project No.51676100).
文摘Presented herein is an experimental study on the combustion of B4C/KNO3 binary pyrotechnic system.Combustion products were tested using X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometer(EDS).According to the results of tests and CEA calculation,the combustion reaction equation was established.The flames and burning rates were recorded by a high speed camera and a spectrophotometer.The effect of B4C particle size on the thermal sensitivity of B4C/KNO3 was investigated by differential scanning calorimetry(DSC)techniques.In addition,a reliable method for calculating the flame temperature was proposed.Based on the results of experiments,the combustion reaction mechanism was briefly analyzed.The burning rate,flame temperature and thermal sensitivity of B4C/KNO3 increase with the decrease of B4C particle size.The mass ratio of B4C/KNO3 has a great effect on combustion properties.Oxidizer-rich compositions have low flame temperatures,low burning rates,and provide green light emission.The combustion reactions of fuel-rich compositions are vigorous,and the B4C/KNO3 with mass ratio of 25:75 has the highest burning rate and the highest flame temperature.
基金supported by National Natural Science Foundation of China(project no.51676100)。
文摘Energetic metal-organic complexes have been involved in nanothermites as novel oxidants.However,the existing preparation methods often lead to mixing inhomogeneity and small contact area of ingredients,the reactivity and functionality of the novel energetic nanocomposites are still limited.In this work,spray crystallization(SC)method was used to prepare novel energetic nanocomposites,the high-energy metal-organic complex[Ni(CHZ)_(3)](ClO_(4))_(2)(CHZ=1,3-diaminourea)was composited with nanoaluminum(n-Al).Results showed that n-Al/[Ni(CH_(2))_(3)](ClO_(4))_(2)energetic nanocomposites prepared by SC method increased heat release to 2977.6 J/g and peak pressure to 3.91 MPa with higher pressurization rate(1324.06 MPa/s),decreased sensitivity thresholds(>100 mJ)to electrostatic discharge(ESD)and enhanced detonation ability compared with[Ni(CHZ)_(3)](ClO_(4))_(2)alone and physically mixed(PM)n-Al/[Ni(CHZ)_(3)](ClO_(4))_(2).These results proved that it is significant to introduce energetic metal-organic complexes with inherent high energy in new-concept n-Al/energetic metal-organic complexes nanocomposites through SC method for a better performance of its application.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61635001,52072117,and 51972105)。
文摘Monolayer transition metal dichalcogenides favor the formation of a variety of excitonic quasiparticles,and can serve as an ideal material for exploring room-temperature many-body effects in two-dimensional systems.Here,using mechanically exfoliated monolayer WS;and photoluminescence(PL)spectroscopy,exciton emission peaks are confirmed through temperature-dependent and electric-field-tuned PL spectroscopy.The dependence of exciton concentration on the excitation power density at room temperature is quantitatively analyzed.Exciton concentrations covering four orders of magnitude are divided into three stages.Within the low carrier concentration stage,the system is dominated by excitons,with a small fraction of trions and localized excitons.At the high carrier concentration stage,the localized exciton emission from defects coincides with the emission peak position of trions,resulting in broad spectral characteristics at room temperature.
基金support for this work was provided by the National Natural Science Foundation of China(Project No.51676100)。
文摘It is a valuable issue to explore whether a flame can radiate microwaves,in spite of the electric field formed in the flame.Presented herein is an experimental study on a series of flames with millimeterwave radiation in the combustion of pyrotechnic films.The pyrotechnic films were composed of ultrafine red phosphorus(P),sodium nitrate(NaNO_3),Polyvinyl Alcohol(PVA) and some additives such as chopped carbon fibers(CFs) and aluminized glass fibers(GFs).The combustion temperatures and millimeter-wave radiation signals of the flames were measured,the millimeter-wave emissivity and spectral radiant exitance were calculated to describe the millimeter-wave radiation intensity.The results demonstrate that the flame of the pyrotechnic films based on P/NaNO_3/CFs can radiate millimeter waves,and different materials and their proportion have a great effect on the millimeter-wave radiation intensity.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51076066)
文摘A projectile with exotic wraparound wings( WAW) configuration is designed to improve the finstabilized projectile shooting quality. Two fin-stabilized projectiles with the same body with and without exotic WAW configuration are simulated numerically by applying the Roe scheme. The shear-stress transport turbulence models and the lower-upper symmetric Gauss-Seidel implicit method are used to solve 3D Reynoldsaveraged Navier—Stokes equations. The differences in aerodynamic coefficients and aerodynamic characteristics of the projectiles when the Mach number varies from 0. 35 to 0. 95 are obtained,and the cause of these differences is analyzed. The calculation results indicate that the lift-to-drag ratio of the projectile significantly increases,the rolling moment decreases,and the position of the pressure center of the projectile shows relatively small changes when the exotic WAW configuration is used. Therefore,this projectile can obviously reduce rolling effect,enlarge range and improve flying stability.
