Mg3Sb1.5Bi0.5-based alloys have received much attention,and current reports on this system mainly focus on the modulation of doping.However,there lacks the explanation for the choice of Mg3Sb1.5Bi0.5 as matrix.Here in...Mg3Sb1.5Bi0.5-based alloys have received much attention,and current reports on this system mainly focus on the modulation of doping.However,there lacks the explanation for the choice of Mg3Sb1.5Bi0.5 as matrix.Here in this work,the thermoelectric properties of Mg3Sb2-xBix(0.4≤x≤0.55)compounds are systematically investigated by using the first principles calculation combined with experiment.The calculated results show that the band gap decreases after Bi has been substituted for Sb site,which makes the thermal activation easier.The maximum figure of merit(ZT)is 0.27 at 773 K,which is attributed to the ultra-low thermal conductivity 0.53 W·m-1·K-1 for x=0.5.The large mass difference between Bi and Sb atoms,the lattice distortion induced by substituting Bi for Sb,and the nanoscale Bi-rich particles distributed on the matrix are responsible for the reduction of thermal conductivity.The introduction of Bi into Mg3Sb2-based materials plays a vital role in regulating the transport performance of thermoelectric materials.展开更多
Highly efficient removal of impurity Bi element from scrap brass can facilitate the recycling process of brass.The effects of melting temperature,holding time and Mg-Ca alloy content on the removal effect of impurity ...Highly efficient removal of impurity Bi element from scrap brass can facilitate the recycling process of brass.The effects of melting temperature,holding time and Mg-Ca alloy content on the removal effect of impurity Bi element were investigated by compound-separation method.The mechanism of the compound-separation method was revealed for removing the Bi element from a thermodynamic point of view.The results showed that the Bi content was decreased from 1.95 wt.%to 0.178 wt.%at the optimum process parameters of melting temperature of 980°C,holding time of 20 min,and Mg-Ca alloy content of 6 wt.%,achieving a removal rate of 90.9%.A small amount of Ca-Bi compound remained in the brass matrix after refining.NaF flux can effectively wet and adsorb Ca-Bi compounds due to its low viscosity and the function of lowering the surface tension,which facilitate the agglomeration and flotation of Ca-Bi compounds to the melt surface,thereby ensuring the sufficient removal of Bi element.展开更多
Recently,Mg_(3)Sb_(2)-xBixalloys have attracted intensive attention,with the aim of maximizing the electrical transport performance via donor element doping,increasing the grain size,as well as electronic band structu...Recently,Mg_(3)Sb_(2)-xBixalloys have attracted intensive attention,with the aim of maximizing the electrical transport performance via donor element doping,increasing the grain size,as well as electronic band structure engineering.However,less attention has been paid to other significant factors,like how these intrinsic point defects and accompanied secondary phases influence thermoelectric properties.In this study,the microstructure and thermoelectric transport properties of Mg_(3.2)Sb_(0.5)Bi_(1.495-x)Te_(0.005)(x=0~0.2)compounds were systematically investigated,where tuning the Bi content shows the counter-intuitive impact on the thermoelectric properties.It was found that the Bipoor environment associated with Bi impurities facilitated the increment of cation vacancy formation energy and then increased the carrier concentration,leading to the enhancement of power factor.Simultaneously,the reduction of Bi-rich second phase content weakened the carrier scattering by grain boundaries whereas high carrier mobility was maintained.Moreover,the bipolar thermal conductivity decreased obviously due to the increased majority carrier concentration to suppress the intrinsic excitation.The synergistic optimization pushes the average ZT value(300-573 K)up to 0.95 in the Mg_(3.2)Sb_(0.5)Bi_(1.295)Te_(0.005)sample.Moreover,the calculated single-leg conversion efficiency is increased up to 9.7%with the hot-side temperature of 573 K,as the record-high value in this system.展开更多
Recently, Sn-Zn-Bi alloys have been reported to be the sheath material for miniature detonating cords,due to appropriate mechanical properties, ease of manufacturing, and low cost. Bi addition was found beneficial to ...Recently, Sn-Zn-Bi alloys have been reported to be the sheath material for miniature detonating cords,due to appropriate mechanical properties, ease of manufacturing, and low cost. Bi addition was found beneficial to the mechanical performance of Sn-Zn. However, limited information about the influence of Bi on the corrosion properties of Sn-Zn alloys has been provided. In this work, electrochemical corrosion behaviours of Sn-3Zn-xBi(x=0, 1, 3, 5, 7 wt%) alloys were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) techniques, to explore the effects of Bi on the corrosion performance of Sn-Zn alloys. The corrosion mechanism of Sn-Zn-Bi alloys was analysed through microstructure examination on the surface of alloys after corrosion measurements. Results indicated that the addition of 1 wt% Bi increased the corrosion susceptibility of the Sn-3Zn alloy, mainly attributed to the coarsened and more uniformly distributed corrosion-vulnerable Zn-rich precipitates, while further increasing the Bi contents decreased the corrosion susceptibility of Sn-3Zn-xBi alloys due to the higher fraction of nobler Bi particles serving as anodic barriers. The Sn-3Zn-7Bi possessed the best corrosion resistance among all Sn-Zn-Bi alloys investigated. The role of Bi on corrosion was considerably discussed.展开更多
A series of 1,3-bis（2-alkyltetrazol-5-yl）triazenes have been synthesized in high yields by treatment of sodium nitrite and hydrochloric acid with substituted-5-aminotetrazoles. All compounds were fully characterized...A series of 1,3-bis（2-alkyltetrazol-5-yl）triazenes have been synthesized in high yields by treatment of sodium nitrite and hydrochloric acid with substituted-5-aminotetrazoles. All compounds were fully characterized using IR spectroscopy,~1H NMR and^（13） C NMR spectroscopy and high resolution mass spectrometer（HRMS）. Most of these triazenes exhibit good detonation performance comparable with TNT and low melting points ranging from 81°C to 106°C, which are suitable for melt-cast explosives.Among these compounds, 1,3-bis（2-azidoethyltetrazol-5-yl）triazene（2g） displays a low melting point（106°C）, moderate onset decomposition temperature（183°C） and good detonation performance（D：7087 m/s; P： 17.6 GPa）.展开更多
基金National Natural Science Foundation of China(Grant Nos.51371010,51572066,and 50801002)the Beijing Municipal Natural Science Foundation,China(Grant No.2112007)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.PXM2019-014204-500032)the Science Fund from the Advanced Space Propulsion Laboratory of BICE and Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology,China(Grant No.LabASP-2018-09).
文摘Mg3Sb1.5Bi0.5-based alloys have received much attention,and current reports on this system mainly focus on the modulation of doping.However,there lacks the explanation for the choice of Mg3Sb1.5Bi0.5 as matrix.Here in this work,the thermoelectric properties of Mg3Sb2-xBix(0.4≤x≤0.55)compounds are systematically investigated by using the first principles calculation combined with experiment.The calculated results show that the band gap decreases after Bi has been substituted for Sb site,which makes the thermal activation easier.The maximum figure of merit(ZT)is 0.27 at 773 K,which is attributed to the ultra-low thermal conductivity 0.53 W·m-1·K-1 for x=0.5.The large mass difference between Bi and Sb atoms,the lattice distortion induced by substituting Bi for Sb,and the nanoscale Bi-rich particles distributed on the matrix are responsible for the reduction of thermal conductivity.The introduction of Bi into Mg3Sb2-based materials plays a vital role in regulating the transport performance of thermoelectric materials.
基金the financial supplies supported by the National Natural Science Foundation of China(Nos.U2202255,52371038)the Science and Technology Innovation Program of Hunan Province,China(No.2023RC1019)。
文摘Highly efficient removal of impurity Bi element from scrap brass can facilitate the recycling process of brass.The effects of melting temperature,holding time and Mg-Ca alloy content on the removal effect of impurity Bi element were investigated by compound-separation method.The mechanism of the compound-separation method was revealed for removing the Bi element from a thermodynamic point of view.The results showed that the Bi content was decreased from 1.95 wt.%to 0.178 wt.%at the optimum process parameters of melting temperature of 980°C,holding time of 20 min,and Mg-Ca alloy content of 6 wt.%,achieving a removal rate of 90.9%.A small amount of Ca-Bi compound remained in the brass matrix after refining.NaF flux can effectively wet and adsorb Ca-Bi compounds due to its low viscosity and the function of lowering the surface tension,which facilitate the agglomeration and flotation of Ca-Bi compounds to the melt surface,thereby ensuring the sufficient removal of Bi element.
基金National Natural Science Foundation of China(Nos.52130106)Heilongjiang Touyan Innovation Team ProgramFundamental Research Funds for the Central Universities(FRFCU5710053021 and HIT.OCEF.2021014)。
文摘Recently,Mg_(3)Sb_(2)-xBixalloys have attracted intensive attention,with the aim of maximizing the electrical transport performance via donor element doping,increasing the grain size,as well as electronic band structure engineering.However,less attention has been paid to other significant factors,like how these intrinsic point defects and accompanied secondary phases influence thermoelectric properties.In this study,the microstructure and thermoelectric transport properties of Mg_(3.2)Sb_(0.5)Bi_(1.495-x)Te_(0.005)(x=0~0.2)compounds were systematically investigated,where tuning the Bi content shows the counter-intuitive impact on the thermoelectric properties.It was found that the Bipoor environment associated with Bi impurities facilitated the increment of cation vacancy formation energy and then increased the carrier concentration,leading to the enhancement of power factor.Simultaneously,the reduction of Bi-rich second phase content weakened the carrier scattering by grain boundaries whereas high carrier mobility was maintained.Moreover,the bipolar thermal conductivity decreased obviously due to the increased majority carrier concentration to suppress the intrinsic excitation.The synergistic optimization pushes the average ZT value(300-573 K)up to 0.95 in the Mg_(3.2)Sb_(0.5)Bi_(1.295)Te_(0.005)sample.Moreover,the calculated single-leg conversion efficiency is increased up to 9.7%with the hot-side temperature of 573 K,as the record-high value in this system.
基金Financial support from the National Aerospace Technology Exploitation Programme (NATEP)Chemring Energetics UK [grant number WEAF058]
文摘Recently, Sn-Zn-Bi alloys have been reported to be the sheath material for miniature detonating cords,due to appropriate mechanical properties, ease of manufacturing, and low cost. Bi addition was found beneficial to the mechanical performance of Sn-Zn. However, limited information about the influence of Bi on the corrosion properties of Sn-Zn alloys has been provided. In this work, electrochemical corrosion behaviours of Sn-3Zn-xBi(x=0, 1, 3, 5, 7 wt%) alloys were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) techniques, to explore the effects of Bi on the corrosion performance of Sn-Zn alloys. The corrosion mechanism of Sn-Zn-Bi alloys was analysed through microstructure examination on the surface of alloys after corrosion measurements. Results indicated that the addition of 1 wt% Bi increased the corrosion susceptibility of the Sn-3Zn alloy, mainly attributed to the coarsened and more uniformly distributed corrosion-vulnerable Zn-rich precipitates, while further increasing the Bi contents decreased the corrosion susceptibility of Sn-3Zn-xBi alloys due to the higher fraction of nobler Bi particles serving as anodic barriers. The Sn-3Zn-7Bi possessed the best corrosion resistance among all Sn-Zn-Bi alloys investigated. The role of Bi on corrosion was considerably discussed.
基金Financial support of this work from the National Natural Science Foundation of China(No.21372027)
文摘A series of 1,3-bis（2-alkyltetrazol-5-yl）triazenes have been synthesized in high yields by treatment of sodium nitrite and hydrochloric acid with substituted-5-aminotetrazoles. All compounds were fully characterized using IR spectroscopy,~1H NMR and^（13） C NMR spectroscopy and high resolution mass spectrometer（HRMS）. Most of these triazenes exhibit good detonation performance comparable with TNT and low melting points ranging from 81°C to 106°C, which are suitable for melt-cast explosives.Among these compounds, 1,3-bis（2-azidoethyltetrazol-5-yl）triazene（2g） displays a low melting point（106°C）, moderate onset decomposition temperature（183°C） and good detonation performance（D：7087 m/s; P： 17.6 GPa）.
