In Alnico 5, cooling rate c in a magnetic field from 900°C to 600°C and optimum aging time t at 600°C have the relation of log(t) = 0.417 log (c) + 0.884. However the final magnetic properties are highly dependent on the cooling rate. Spinodally decomposed structures of this alloy show that the faster the cooling rate the smaller the size of the FeCo-rich precipitates and the larger the aspect ratio without change of the volume fraction of the precipitates. The length of the long axis of the FeCo-rich precipitates at a given cooling rate is not uniform due to the interconnection of the subsequent precipitates by the magnetic field effect, and this tendency seems to be stronger when the cooling rate is slower. However the length of the short axis of the precipitates is almost the same at a given cooling rate. The length of the short axis l and the cooling rate c in a magnetic field have the relation oflog (l) = 2.385 - 0.317 log (c). Optimum solution treatment temperature of the low-temperature treatment method was 860°C. This method has higher coercive force than that of the high-temperature treatment method. The FeCo-rich precipitates of the specimen were aligned more parallel to the applied magnetic field with little interconnection of the precipitates and have a higher aspect ratio than that of the high temperature treatment specimen. 相似文献
The thermodynamic cycle performance of Gadolinium (Gd) and Gd0.87Dy0.13 used as the working substance in regeneration magnetic Brayton and Ericsson refrigeration cycles are investigated under different external magnetic field conditions. Based on the experimental iso-field heat capacities of Gd with different magnetic fields, the effects of magnetic field change on thermodynamic performances including the magnetic entropy change, cooling quantity, non-perfect regeneration, net cooling quantity, and coefficient of performance (COP) are analyzed and discussed. The present work shows the possibility of reducing the regenerative losses and thereby improving the net cooling quantity for a given field change by selecting optimal initial and final magnetic field values. The similar analysis and calculation of the related thermodynamic performances are further applied to the magnetic material Gd0.87Dy0.13 which exhibits better net cooling quantities when compared to Gd at low temperature. 相似文献
The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20-40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5-20%. An increase of the magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by 30-50% but the maximum temperature span by only 20-30%. Finally, it was seen that the influence of changing the magnetic field was more or less the same for the different regenerator geometries and operating parameters studied here. This means that the design of the magnet can be done independently of the regenerator geometry. 相似文献
We have conducted to develop an axial-gap type synchronous propulsion motor with Gd-bulk HTS field pole magnets. It has been established on the fundamental technology upon the liquid nitrogen cooling. In the present study, we aimed an output improvement of the motor by the magnetic flux density enhancement of the bulk HTS, in a word, the trapped magnetic flux density on the HTS bulk. The output of the motor depends on the physics of the motor, the magnetic flux density, and the electric current density flowing through the armature. We have employed a condensed neon with a helium GM refrigerator. The bulk HTS placed on the rotor disk inside the motor frame was successfully cooled down with circulating condensed neon. The temperature at the bulk HTS surface reached 38 K. Upon magnetization, we developed controlled magnetic field density distribution coil (CMDC) composed of a couple of pulsed copper armature coil. In the magnetization procedure, with decreasing magnetization temperature, minute by minute, after Sander and Kamijyo that the step cooling magnetization method was used. In addition, the CMDC coil has enabled to control the applied flux distribution. Three parameters as the temperature, the applied magnetic field, and the effective applied flux density distribution were changed within eight times pulsed magnetizations in total. Up to 4th pulsed magnetization, we kept (1st step) high temperature, and subsequent pulsed magnetizations were done at low temperature. As a result, the highest maximum trapped magnetic flux density was reached 1.31 T, about 2.5 times compared to the value obtained upon cooling with liquid nitrogen. Consequently, the output of the motor has been enhanced to 25 kW from 10 kW taken in the previous operation. 相似文献
Effects of a steady magnetic field on the laser-induced breakdown spectroscopy of certain elements (Mn, Mg, Cr, and Ti) in aqueous solution were studied, in which the plasma plume expanded across an external steady magnetic field (approximately 6 kilogauss). Nearly 1.6 times enhancement in the line emission intensity was observed in the presence of the magnetic field. The temporal evolution of the line emission showed a significant enhancement in plasma emission between 2- and 7- micro(s) gate delays for Mg in the presence of the magnetic field (5-30 micro(s) for Mn). This enhancement in the emission is attributed to an increase in the rate of recombination because of an increase in plasma density due to a magnetic confinement after cooling the plasma. The increase in the optical line emission due to magnetic confinement was absent when the plasma was hot with a dominant background (continuum) emission. The limits of detection of Mg and Mn were reduced by a factor of two in the presence of a steady magnetic field of 5 kilogauss. 相似文献
We have designed and operated a rotating-magnet type AMR (active magnetic regeneration) refrigerator that uses water as a heat transfer fluid. Four kinds of gadolinium-based alloy are used as magnetic materials. A magnetic field of 0.77 T is applied by neodymium permanent magnets. The refrigerator produces a maximum cooling power of 60 W around 10 °C. An optimal time for one cycle exists, and it depends on the water flow rate and the frequency of magnetization and demagnetization. Enhancement of the water flow rate and the frequency is known to be essential for increasing the cooling power of this refrigerator. 相似文献
For research in the highest continuous and pulsed magnetic fields large, complex and powerful installations are needed. This paper describes the new 20 MW installation for continuous high magnetic fields that has been built at the University of Nijmegen. The ultra-low ripple power converter provides the capability to perform experiments up to 33 T with resistive magnets (up to 40 T with the hybrid magnet system under construction) and will be of great value for investigations in physics, chemistry and biology at the forefront of fundamental and applied research. Typically during experiments, the magnetic field is slowly varied or held constant for a period lasting from a few minutes to an hour. The cooling installation is designed to allow uninterrupted operation at maximum power for 3 hours, and when the magnetic field is being swept between zero and full field the cooling plant does not pose limits to the operation. When much higher fields are required, there is the option to go to pulsed magnetic fields with duration in the tens of milliseconds. 相似文献
AC magnetic susceptibility of Rb3C60 superconductor as a function of temperature was measured in an applied static magnetic field perpendicular to the AC magnetic field. The peaks in real part of AC susceptibility curves located in the transitional temperature indicate that there may exist the differential paramagnetic effect χ′(T) = dM/dH > 0 in the specimen. The amplitude of the peak and the temperature of diamagnetic onset are proportional to intensity of the applied field, and upon cooling the peaks occur before the transition temperature of zero field. Through discussing and comparing our experimental result with those reported previously, we have put forward a new opinion on producing condition of the differential paramagnetic effect (DPE). 相似文献
Perpendicular magnetic field dependences of the Josephson current through tunnel junction were first measured. Niobium/aluminum-oxide/niobium (200/5/150 nm in thickness) superconducting tunnel junctions were fabricated by DC-magnetron apparatus with a load-lock chamber. Josephson current Ic through the superconducting junction is usually changed by the external magnetic field in one direction to check the barrier uniformity. To obtain more information of the barrier uniformity, we have changed the external magnetic field in two directions (Hx and Hy: parallel field to the junction plane) parallel to the junction plane. The shape of Ic-Hx curve and Ic-Hy curve were the Fraunhofer pattern in the Ic-Hx-Hy dependence of the junction with uniform barrier. This Ic-Hx-Hy dependence has no hysteresis. In this study, we have first applied the external magnetic field Hz perpendicular to the junction plane and have obtained Ic-Hz characteristics using three pairs of Helmholtz coils. In the case that the perpendicular field Hz < 2400 A/m, the Ic-Hz characteristics have a little hysteresis. The shape of Ic-Hz characteristics was similar to the Fraunhofer pattern. In the case that the perpendicular field Hz > 2400 A/m, the Ic-Hz characteristics have strong hysteresis. The Josephson current Ic always disappeared in the case that Hz > 7000 A/m. Two recovering methods of this current Ic were (a) alternating Hz field and (b) heating the sample to the room temperature and again cooling to the liquid He temperature. 相似文献
The separation of magnetic microparticles was achieved by on-chip free-flow magnetophoresis. In continuous flow, magnetic particles were deflected from the direction of laminar flow by a perpendicular magnetic field depending on their magnetic susceptibility and size and on the flow rate. Magnetic particles could thus be separated from each other and from nonmagnetic materials. Magnetic and nonmagnetic particles were introduced into a microfluidic separation chamber, and their deflection was studied under the microscope. The magnetic particles were 2.0 and 4.5 microm in diameter with magnetic susceptibilities of 1.12 x 10(-4) and 1.6 x 10(-4) m(3) kg(-1), respectively. The 4.5-microm particles with the larger susceptibility were deflected further from the direction of laminar flow than the 2.0-microm magnetic particles. Nonmagnetic 6-microm polystyrene beads, however, were not deflected at all. Furthermore, agglomerates of magnetic particles were found to be deflected to a larger extent than single magnetic particles. The applied flow rate and the strength and gradient of the applied magnetic field were the key parameters in controlling the deflection. This separation method has a wide applicability since magnetic particles are commonly used in bioanalysis as a solid support material for antigens, antibodies, DNA, and even cells. Free-flow magnetophoretic separations could be hyphenated with other microfluidic devices for reaction and analysis steps to form a micro total analysis system. 相似文献
The effects of high magnetic fields on the solidification microstructure of Al–Si alloys were investigated. Al–7.2 wt%Si and
Al–11.8 wt%Si alloys were solidified in various high magnetic fields at different cooling rates. The secondary dendrite arm
spacing (SDAS) of the primary Al dendrites and the lamellar spacing (LS) of the eutectics were measured. It was found that
the application of a high magnetic field could decrease the SDAS of the primary Al dendrites in Al–7.2 wt%Si alloys and the
LS of the eutectics in Al–11.8 wt%Si alloys. The effects of the high magnetic field on the SDAS decreased with increasing
cooling rate. The decrease in the SDAS and LS can be attributed to the decrease of the solute diffusivity in the liquid ahead
of the solid/liquid interface during the growth of the dendrite and eutectic. This decrease is caused by the high magnetic
field which can damp the convection and avoid its contributions to the diffusion. 相似文献
In this second part of a two-part paper, a mathematical model of active magnetic regenerators is applied to identify and quantify the main losses taking place in the AMR evaluated experimentally in Part I. Among those losses, the heat interaction with the external environment and the presence of dead (void) volumes between each end of the regenerator and the hot and cold heat exchangers were found to be the main factors that affect the AMR performance. Demagnetizing losses were considered as a function of the matrix geometry, temperature and applied magnetic field. In addition to predicting the time-dependent behavior of the fluid temperature exiting the regenerator during each blow and the cycle average cooling capacity, the model was able to quantify the impact of each loss mechanism on the thermal performance of the AMR. 相似文献
The caloric effects under combined applications of magnetic field and hydrostatic pressure to a MnCoSi meta-magnet were investigated. Under a magnetic field change of 0–5 T, the maximum magnetic entropy change was enhanced by 35.7% when a 3.2kbar hydrostatic pressure was applied, and the cooling temperature span was extended by 60 K when a hydrostatic pressure of 9.7 kbar was applied. The coupled caloric entropy change, which originates from the coupling between the magnetism and volume, was calculated and accounted for the enhanced entropy change of MnCoSi. The present work facilitates the use of MnCoSi as a solid-state refrigerant and also enriches the investigation of the multicaloric effect under multiple external fields.
We report magnetic studies of the paramagnetic effect observed in the superconducting nano-structured opal-lead system. Positive
magnetization is clearly observed when the sample is cooled in field. The paramagnetic effect is strongly dependent on the
applied field and the cooling rate. The results suggest that the paramagnetic moment is due to flux trapping and the competition
between the positive and negative moments due to the temperature dependence of the penetration depth. 相似文献