A wide-spectrum pulsed magnetic field(WSPMF)was obtained by adjusting the number of current pulses and the pulse interval between adjacent pulses.The effect of WSPMF on the grain refinement of pure aluminium was studi...A wide-spectrum pulsed magnetic field(WSPMF)was obtained by adjusting the number of current pulses and the pulse interval between adjacent pulses.The effect of WSPMF on the grain refinement of pure aluminium was studied.The distribution of electromagnetic force and flow field in the melt under the WSPMF was simulated to reveal the grain refining mechanism.Results show that the grain refinement is attributed to the combined effect of the melt flow and oscillation under a WSPMF.When the pulse interval is 5 ms,the extreme value of electromagnetic force is the highest,and the size of the crystal nucleus is 0.35 mm.In the case of similar flow rates,the grain size gradually decreases as the pulse interval increases.The range of the harmonic frequency of the magnetic field gradually expands with the increase of the pulse interval,which can provide more energy for nucleation at the solid-liquid interface and promote nucleation.展开更多
The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC ...The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.展开更多
The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pul...The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.展开更多
The combined effects of direct current pulsed magnetic field (DC-PMF) and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental resul...The combined effects of direct current pulsed magnetic field (DC-PMF) and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% (mass fraction) Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.展开更多
We present a scheme to control the generated ultrafast magnetic field in H_(3)^(2+)molecules using multi-frequency tricircular pulses composed of co-and counter-rotating bicircular pulses.Simulations show that the fie...We present a scheme to control the generated ultrafast magnetic field in H_(3)^(2+)molecules using multi-frequency tricircular pulses composed of co-and counter-rotating bicircular pulses.Simulations show that the field amplitude and the wavelength are two significant factors for magnetic field generation by tricircular pulses.Specifically,the strength of the magnetic field is linearly related to the field amplitude atλ_(0)=50 nm,while atλ_(0)=70 nm,the strength first increases and then decreases with the amplitude,this can be attributed to the resonance between the ground and excited states.Moreover,the phase and helicity of bicircular pulses are shown to have important effects on the magnetic field.The dependence of the magnetic field on the phase arises from the interference effect between multiple ionization pathways.These findings illustrate a guiding principle for controlling the magnetic field in molecular systems for future research in ultrafast magneto-optics.展开更多
The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidifi...The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidification structures of 2124 Al-alloy under pulsed magnetic field. The eutectic phase at grain boundaries change from thick continuous eutectic network to thin discontinuous one, and the distribution of solute elements was also homogenized. The typical negative segregation phenomenon of Cu in common solidification condition was restrained, and the segregation of Mg decreased.展开更多
To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidifica...To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.展开更多
The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coli cells suspended in phosphate buffer s...The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coli cells suspended in phosphate buffer solution Na 2HPO 4/NaH 2PO 4(0 334/0 867 mmol/L). Experimental results indicated that the survivability(N/N 0; where N 0 and N are the number of cells survived per mill il iter before and after electromagnetic pulses application, respectively) of E. coli decreased with magnetic field intensity B and treatment time t. It was also found that the medium temperatures, the frequencies of pulse f, and the initial bacterial cell concentrations have determinate influences in destruction of E. coli cells by the application of magnetic pulses. The application of an magnetic intensity B=160 mT at pulses frequency f=62 kHz and treatment time t=16 h result in a considerable destruction levels of E. coli cells (N/N 0=10 -4 ). Possible mechanisms involved in sterilization of the magnetic field treatment were discussed. In order to shorten the treatment time, many groups of parallel inductive coil were used. The practicability test showed that the treatment time was shortened to 4 h with the application of three groups of parallel coil when the survivability of E.coli cells was less than 0 01%; and the power consumption was about 0 2 kWh /m 3.展开更多
The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cul alloy are studied. Amorphous Fe52Co34Hf7B6Cul alloys are first treated by a pulsed magnetic field with a medium frequency, and then...The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cul alloy are studied. Amorphous Fe52Co34Hf7B6Cul alloys are first treated by a pulsed magnetic field with a medium frequency, and then annealed at 100 ℃-400 ℃ for 30 min in a vacuum. The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer. The soft magnetic properties of specimens are measured by a vibrating sample magnetometer (VSM). The microstructure changes of specimens are observed by a MSssbauer spectroscopy and transmission electron microscope (TEM). The results show the medium-frequency pulsating magnetic field will pro- mote nanocrystallization of the amorphous alloy with a lower temperature rise. The nanocrystalline phase is (α-Fe(Co) with bcc crystal structure, and the grain size is about 10 nm. After vacuum annealing at 100 ℃ for 30 min, scattering nanocrystalline phases become more uniform, the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.展开更多
Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturba...Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr(CO3)2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.展开更多
The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pu...The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.展开更多
For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification struc...For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification structure of AZ80 magnesium alloy.The numerical simulation was simultaneously conducted to investigate the refinement mechanisms.The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field.Meanwhile,finer grains were obtained with the higher current intensity.However,the increase of current intensity could only refine the grains to about 0.5 mm.Furthermore,compared to a single pulsed magnetic field(PMF)and alternating series of OPPMF(Connection II),a finer structure was observed when the consecutive series of OPPMF(Connection I)was imposed.In contrast with a single PMF and Connection II,the numerical results showed that the greater axial Lorentz force was obtained under the Connection I,generating the stronger forced flow in the melt.It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow;besides,the lower superheat and greater temperature uniformity in bulk melt were realized,accounting for the finest structures under the Connection I.展开更多
Wuhan National High Magnetic Field Center(WHMFC)at Huazhong University of Science and Technology is one of the top-class research centers in the world,which can offer pulsed fields up to 90.6 T with different field wa...Wuhan National High Magnetic Field Center(WHMFC)at Huazhong University of Science and Technology is one of the top-class research centers in the world,which can offer pulsed fields up to 90.6 T with different field waveforms for scientific research and has passed the final evaluation of the Chinese government in 2014.This paper will give a brief introduction of the facility and the development status of pulsed magnetic fields research at WHMFC.In addition,it will describe the application development of pulsed magnetic fields in both scientific and industrial research.展开更多
The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pu...The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260?? under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and then it is substituted into the magnetic field model.The fluid flow model was solved with the acquired electromagnetic force.The effects of pulse voltage frequency on the current wave and on the distribution of magnetic and flow fields were numerically studied.The pulsed magnetic field increases melt convection,which stirs and fractures the dendritic arms into pieces.These broken pieces are transported into the bulk liquid by the liquid flow and act as nuclei to enhance grain refinement.The Joule heat effect produced by the electric current also participates in the microstructural refinement.展开更多
The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pu...The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.展开更多
Dielectric barrier discharge (DBD) for SOs removal from indoor air is investigated. In order to improve the removal efficiency, two novel methods are combined in this paper, namely by applying a pulsed driving volta...Dielectric barrier discharge (DBD) for SOs removal from indoor air is investigated. In order to improve the removal efficiency, two novel methods are combined in this paper, namely by applying a pulsed driving voltage with nanosecond rising time and applying a magnetic field. For SOs removal efficiency, different matches of electric field and magnetic field are discussed. And nanosecond rising edge pulsed power supply and microsecond rising edge pulsed power supply are compared. It can be concluded that a pulsed DBD with nanosecond rising edge should be adopted, and electrical field and magnetic field should be applied in an appropriate match.展开更多
A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (-230 ns), 55 kA current pulse into ...A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (-230 ns), 55 kA current pulse into a single-turn coil surrounding the laser target, using a capacitor bank of 200 nF, a laser-triggered switch and a low-impedance strip transmission line. A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter. The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam, a femtosecond probing laser beam and an optical Intensified Charge Coupled Device (ICCD) detector. The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field.展开更多
A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath.Taking the typical parameters of plasma sheath at th...A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath.Taking the typical parameters of plasma sheath at the height of 71 km as an example,the distribution characteristics and time evolution characteristics of plasma density in the flow field under the action of pulsed magnetic field,as well as the effect of self-electric field on the distribution of plasma density,are studied.The simulation results show that pulsed magnetic field can effectively reduce the density of plasma sheath.Meanwhile,the simulation results of three-dimensional plasma density distribution show that the size of the density reduction area is large enough to meet the communication requirements of the Global Position System(GPS)signal.Besides,the location of density reduction area provides a reference for the appropriate location of antenna.The time evolution of plasma density shows that the effective density reduction time can reach 62%of the pulse duration,and the maximum reduction of plasma density can reach 55%.Based on the simulation results,the mechanism of the interaction between pulsed magnetic field and plasma flow field is physically analyzed.Furthermore,the simulation results indicate that the density distributions of electrons and ions are consistent under the action of plasma self-electric field.However,the quasi neutral assumption of plasma in the flow field is not appropriate,because the self-electric field of plasma will weaken the effect of the pulsed magnetic field on the reduction of electron density,which cannot be ignored.The calculation results could provide useful information for the mitigation of communication blackout in hypersonic vehicles.展开更多
A pulsed transverse magnetic field with pulse width of 12 ms and magnitude of 2 T was used to modify the density distribution of a weakly-ionized plasma flow with strong collisions between the charged particles and ne...A pulsed transverse magnetic field with pulse width of 12 ms and magnitude of 2 T was used to modify the density distribution of a weakly-ionized plasma flow with strong collisions between the charged particles and neutrals.The morphology of the plasma is changed substantially,with the density increased upstream and decreased downstream.Meanwhile,the plasma toward the axis contracts laterally and gradually converges to a collimated flow.In addition,a drift wave is observed to be excited in the inhomogeneous plasma by the magnetic field.展开更多
In this paper,the principle of Pulsed Magnetic Field(PMF) force was analyzed through mathematical analyses.By theoretical analysis and calculation,the results show that the great electromagnetic force is made in the m...In this paper,the principle of Pulsed Magnetic Field(PMF) force was analyzed through mathematical analyses.By theoretical analysis and calculation,the results show that the great electromagnetic force is made in the melt under pulsed magnetic field,as well as changing its direction in different places of melt at the same time.It enforces the crystallizing nucleus and brittle crystallite to fragment in the solidification processing.From the point of view,one of the main factors of grain refinement is that the fragmentations occur under a pulsed magnetic field by preliminary judgement. The feasibility of application in the metallurgical industry under PMF was discussed through comparing the results of grain refinement under EMS.According to the theoretic calculation,the power consumption under EMS is 5 -8 times the amount under PMF,when both of magnetic flux density B are 0.07T.That is to say,the better effect on grain refining can be obtained under PMF,compared with EMS,even in the lower power consumption.The solidification experiments of Sn-20%Pb alloy are conducted under the same experimental conditions that the magnetic intensity is 0.07T in the center of the crucible,it also shows that PMF has a better effect on grain refining than EMS. Combined with the continuous casting process,the influence of pulsed parameters and the metallurgical effects with applying PMF at different solidification stages was investigated.There are different grain refining effects under PMF in different solidification stages,and there are different grain refining effects under PMF in different PMF parameters.For the Sn-20%Pb alloy or silicon steel,it is more effective during the initial stage,in which the pulse frequency is 5Hz.For the Sn-20%Pb alloy,the average grain size ofβphase is the smallest,when applying the PMF during the temperature of melt decreasing from 201℃to 184℃.Further investigation of the specified technique parameters for industrial applications are required.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52071194,U1760204)the National Key Research Program of China(Grant Nos.2020YFB2008401 and 2017YFB0701800)。
文摘A wide-spectrum pulsed magnetic field(WSPMF)was obtained by adjusting the number of current pulses and the pulse interval between adjacent pulses.The effect of WSPMF on the grain refinement of pure aluminium was studied.The distribution of electromagnetic force and flow field in the melt under the WSPMF was simulated to reveal the grain refining mechanism.Results show that the grain refinement is attributed to the combined effect of the melt flow and oscillation under a WSPMF.When the pulse interval is 5 ms,the extreme value of electromagnetic force is the highest,and the size of the crystal nucleus is 0.35 mm.In the case of similar flow rates,the grain size gradually decreases as the pulse interval increases.The range of the harmonic frequency of the magnetic field gradually expands with the increase of the pulse interval,which can provide more energy for nucleation at the solid-liquid interface and promote nucleation.
基金Project(51034012)supported by the the National Natural Science Foundation of ChinaProject(2013CB632205)supported by the National Basic Research Program of China
文摘The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.
基金Project(2010CB631205)supported by the National Basic Research Program of ChinaProject(51034012)supported by the National Natural Science Foundation of China
文摘The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.
基金Projects(51074031,51271042,50874022)supported by the National Natural Science Foundation of ChinaProject(2013M530913)supported by the China Postdoctoral Science FoundationProject(DUT12RC(3)35)supported by the Fundamental Research Funds for the Central Universities of China
文摘The combined effects of direct current pulsed magnetic field (DC-PMF) and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% (mass fraction) Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.
基金the National Natural Science Foundation of China(Grant No.12074146).
文摘We present a scheme to control the generated ultrafast magnetic field in H_(3)^(2+)molecules using multi-frequency tricircular pulses composed of co-and counter-rotating bicircular pulses.Simulations show that the field amplitude and the wavelength are two significant factors for magnetic field generation by tricircular pulses.Specifically,the strength of the magnetic field is linearly related to the field amplitude atλ_(0)=50 nm,while atλ_(0)=70 nm,the strength first increases and then decreases with the amplitude,this can be attributed to the resonance between the ground and excited states.Moreover,the phase and helicity of bicircular pulses are shown to have important effects on the magnetic field.The dependence of the magnetic field on the phase arises from the interference effect between multiple ionization pathways.These findings illustrate a guiding principle for controlling the magnetic field in molecular systems for future research in ultrafast magneto-optics.
基金This research was supported by National Key Basic Research and Development Programme of China "973" (No. G19990649051).
文摘The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidification structures of 2124 Al-alloy under pulsed magnetic field. The eutectic phase at grain boundaries change from thick continuous eutectic network to thin discontinuous one, and the distribution of solute elements was also homogenized. The typical negative segregation phenomenon of Cu in common solidification condition was restrained, and the segregation of Mg decreased.
基金Item Sponsored by National Natural Science Foundation of China (50274050) and Shanghai Baoshan Iron and Steel Group
文摘To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.
文摘The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coli cells suspended in phosphate buffer solution Na 2HPO 4/NaH 2PO 4(0 334/0 867 mmol/L). Experimental results indicated that the survivability(N/N 0; where N 0 and N are the number of cells survived per mill il iter before and after electromagnetic pulses application, respectively) of E. coli decreased with magnetic field intensity B and treatment time t. It was also found that the medium temperatures, the frequencies of pulse f, and the initial bacterial cell concentrations have determinate influences in destruction of E. coli cells by the application of magnetic pulses. The application of an magnetic intensity B=160 mT at pulses frequency f=62 kHz and treatment time t=16 h result in a considerable destruction levels of E. coli cells (N/N 0=10 -4 ). Possible mechanisms involved in sterilization of the magnetic field treatment were discussed. In order to shorten the treatment time, many groups of parallel inductive coil were used. The practicability test showed that the treatment time was shortened to 4 h with the application of three groups of parallel coil when the survivability of E.coli cells was less than 0 01%; and the power consumption was about 0 2 kWh /m 3.
基金Project supported by the National Natural Science Foundation of China(Grant No.50771025)
文摘The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cul alloy are studied. Amorphous Fe52Co34Hf7B6Cul alloys are first treated by a pulsed magnetic field with a medium frequency, and then annealed at 100 ℃-400 ℃ for 30 min in a vacuum. The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer. The soft magnetic properties of specimens are measured by a vibrating sample magnetometer (VSM). The microstructure changes of specimens are observed by a MSssbauer spectroscopy and transmission electron microscope (TEM). The results show the medium-frequency pulsating magnetic field will pro- mote nanocrystallization of the amorphous alloy with a lower temperature rise. The nanocrystalline phase is (α-Fe(Co) with bcc crystal structure, and the grain size is about 10 nm. After vacuum annealing at 100 ℃ for 30 min, scattering nanocrystalline phases become more uniform, the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.
基金This work was financially supported by the Foundation for Key Program of the Ministry of Education of China (No.207038)the Technological Achievement Conversion Program of Jiangsu Province in China (No.BA2005054)+1 种基金the High Technology Research Program of Jiangsu Province (No.BG2005026)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province, China (No. 05KJD450043).
文摘Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr(CO3)2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.
基金Project(ZC304009103) supported by the Doctoral Fund of Zhejiang Normal University,ChinaProject(KYJ06Y09157) supported by School-level Project of Zhejiang Normal University,China
文摘The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.
基金This work was supported by the National Key Re-search and Development Program of China(Grant No.2016YFB0301101)the National Natural Science Foundation of China(Grant No.51971054)the Fundamental Research Funds for the Central Universities(Grant No.N180904006 and N2009006).
文摘For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification structure of AZ80 magnesium alloy.The numerical simulation was simultaneously conducted to investigate the refinement mechanisms.The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field.Meanwhile,finer grains were obtained with the higher current intensity.However,the increase of current intensity could only refine the grains to about 0.5 mm.Furthermore,compared to a single pulsed magnetic field(PMF)and alternating series of OPPMF(Connection II),a finer structure was observed when the consecutive series of OPPMF(Connection I)was imposed.In contrast with a single PMF and Connection II,the numerical results showed that the greater axial Lorentz force was obtained under the Connection I,generating the stronger forced flow in the melt.It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow;besides,the lower superheat and greater temperature uniformity in bulk melt were realized,accounting for the finest structures under the Connection I.
基金We gratefully acknowledge the financial support of the National Key Research and Development Program of China(2016YFA0401700).
文摘Wuhan National High Magnetic Field Center(WHMFC)at Huazhong University of Science and Technology is one of the top-class research centers in the world,which can offer pulsed fields up to 90.6 T with different field waveforms for scientific research and has passed the final evaluation of the Chinese government in 2014.This paper will give a brief introduction of the facility and the development status of pulsed magnetic fields research at WHMFC.In addition,it will describe the application development of pulsed magnetic fields in both scientific and industrial research.
基金Project(50774075)supported by the National Natural Science Foundation of ChinaProject(2006BAE04B01-4)supported by Key Technologies R&D Program,China
文摘The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260?? under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and then it is substituted into the magnetic field model.The fluid flow model was solved with the acquired electromagnetic force.The effects of pulse voltage frequency on the current wave and on the distribution of magnetic and flow fields were numerically studied.The pulsed magnetic field increases melt convection,which stirs and fractures the dendritic arms into pieces.These broken pieces are transported into the bulk liquid by the liquid flow and act as nuclei to enhance grain refinement.The Joule heat effect produced by the electric current also participates in the microstructural refinement.
基金Project(50774075) supported by the National Natural Science Foundation of ChinaProject(2006BAE04B01-4) supported by the Key Technologies R&D Program of Ministry of Science and Technology of China
文摘The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.
基金the Sci.& Tech.research key project of Ministry of Education and National Natural Science Foundation of China (Nos.50477025 and 50537050)
文摘Dielectric barrier discharge (DBD) for SOs removal from indoor air is investigated. In order to improve the removal efficiency, two novel methods are combined in this paper, namely by applying a pulsed driving voltage with nanosecond rising time and applying a magnetic field. For SOs removal efficiency, different matches of electric field and magnetic field are discussed. And nanosecond rising edge pulsed power supply and microsecond rising edge pulsed power supply are compared. It can be concluded that a pulsed DBD with nanosecond rising edge should be adopted, and electrical field and magnetic field should be applied in an appropriate match.
基金supported by National Natural Science Foundation of China(Nos.11105147,11375197 and 11175179)the Ministry of Education of China(No.IRT1190)
文摘A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (-230 ns), 55 kA current pulse into a single-turn coil surrounding the laser target, using a capacitor bank of 200 nF, a laser-triggered switch and a low-impedance strip transmission line. A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter. The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam, a femtosecond probing laser beam and an optical Intensified Charge Coupled Device (ICCD) detector. The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field.
基金supported by the Innovation Fund for TT&C and Measurement of Near Space Vehicles(No.20180102).
文摘A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath.Taking the typical parameters of plasma sheath at the height of 71 km as an example,the distribution characteristics and time evolution characteristics of plasma density in the flow field under the action of pulsed magnetic field,as well as the effect of self-electric field on the distribution of plasma density,are studied.The simulation results show that pulsed magnetic field can effectively reduce the density of plasma sheath.Meanwhile,the simulation results of three-dimensional plasma density distribution show that the size of the density reduction area is large enough to meet the communication requirements of the Global Position System(GPS)signal.Besides,the location of density reduction area provides a reference for the appropriate location of antenna.The time evolution of plasma density shows that the effective density reduction time can reach 62%of the pulse duration,and the maximum reduction of plasma density can reach 55%.Based on the simulation results,the mechanism of the interaction between pulsed magnetic field and plasma flow field is physically analyzed.Furthermore,the simulation results indicate that the density distributions of electrons and ions are consistent under the action of plasma self-electric field.However,the quasi neutral assumption of plasma in the flow field is not appropriate,because the self-electric field of plasma will weaken the effect of the pulsed magnetic field on the reduction of electron density,which cannot be ignored.The calculation results could provide useful information for the mitigation of communication blackout in hypersonic vehicles.
基金supported by National Natural Science Foundation of China (Nos. 11975086, 51577043)
文摘A pulsed transverse magnetic field with pulse width of 12 ms and magnitude of 2 T was used to modify the density distribution of a weakly-ionized plasma flow with strong collisions between the charged particles and neutrals.The morphology of the plasma is changed substantially,with the density increased upstream and decreased downstream.Meanwhile,the plasma toward the axis contracts laterally and gradually converges to a collimated flow.In addition,a drift wave is observed to be excited in the inhomogeneous plasma by the magnetic field.
文摘In this paper,the principle of Pulsed Magnetic Field(PMF) force was analyzed through mathematical analyses.By theoretical analysis and calculation,the results show that the great electromagnetic force is made in the melt under pulsed magnetic field,as well as changing its direction in different places of melt at the same time.It enforces the crystallizing nucleus and brittle crystallite to fragment in the solidification processing.From the point of view,one of the main factors of grain refinement is that the fragmentations occur under a pulsed magnetic field by preliminary judgement. The feasibility of application in the metallurgical industry under PMF was discussed through comparing the results of grain refinement under EMS.According to the theoretic calculation,the power consumption under EMS is 5 -8 times the amount under PMF,when both of magnetic flux density B are 0.07T.That is to say,the better effect on grain refining can be obtained under PMF,compared with EMS,even in the lower power consumption.The solidification experiments of Sn-20%Pb alloy are conducted under the same experimental conditions that the magnetic intensity is 0.07T in the center of the crucible,it also shows that PMF has a better effect on grain refining than EMS. Combined with the continuous casting process,the influence of pulsed parameters and the metallurgical effects with applying PMF at different solidification stages was investigated.There are different grain refining effects under PMF in different solidification stages,and there are different grain refining effects under PMF in different PMF parameters.For the Sn-20%Pb alloy or silicon steel,it is more effective during the initial stage,in which the pulse frequency is 5Hz.For the Sn-20%Pb alloy,the average grain size ofβphase is the smallest,when applying the PMF during the temperature of melt decreasing from 201℃to 184℃.Further investigation of the specified technique parameters for industrial applications are required.