摘要:

The high (BH)maxpotential of Nd‐Fe‐B materials make them excellent candidates for bonded magnets. We have previously shown that anisotropic bonded magnets can be made from hot deformed rapidly solidified materials. The purpose of this paper is to show how hot deformed materials can be pulverized into desired particle size ranges by using specific hydrogen decrepitation (HD) cycles. Specific temperatures for hydriding and desorbing cycles to achieve desired particle size ranges and magnetic values are given. The data shows that there are optimum times and temperatures to achieve the desired magnetic properties. TEM and SEM photomicrographs of mechanically and HD pulverized materials are shown. TEM studies show that stacking faults generated during HD are relieved after desorption. With proper control of HD and desorption, bonded magnets have been produced having (BH)maxvalues as high as 18.9 MGOe.

ISSN:0021-8979    

DOI:10.1063/1.349871

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The aging behaviors of Nd16.4Fe75.7B7.9, Nd16Fe76.3Nb0.3B7.4, and Nd14.5Dy1.5Fe76Nb1B7magnets were investigated. The magnets were quenched and then aged at 500 °C to establish whether recovery of coercivity was possible below the melting point of the grain boundary. The samples were cooled and measured magnetically after 10‐ or 20‐min intervals before being heated again for another interval. After aging at 500 °C for 55 min there was a dramatic increase in coercivity in the Nd‐Dy‐Fe‐Nb‐B samples, whereas the coercivity of the Nd‐Fe‐B samples remained unaltered. The results from thermomagnetic analysis on Nd‐Dy‐Fe‐Nb‐B show that an extra ferromagnetic phase is present in the magnets that had been aged for over 55 min and in the magnets that had full magnetic properties, but not in the quenched magnets. The Nd‐Fe‐B samples did not show any additional ferromagnetic phase. The experiments were repeated with Nd‐Fe‐Nb‐B magnets and the results followed the same trend to those observed in the Nd‐Dy‐Fe‐Nb‐B magnets. The difference in coercivity between the aged and the initial‐state magnets, for all types, was recovered upon heating at 650 °C.

ISSN:0021-8979    

DOI:10.1063/1.349872

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

NdFeB is an important class of new magnetic materials, however corrosion resistance is a serious concern and literature on the electrochemical behavior of NdFeB is scarce. This paper reports the results of an electrochemical investigation of the corrosion behavior of sintered NdFeB magnets obtained from three manufacturers. Linear polarization (cyclic voltammetry) experiments were conducted in aqueous solutions ranging inpH from 0.7 to 13.5. A limited degree of passivation was observed in all solutions which is believed to be due to the formation of a complex Fe‐Nd oxide and/or hydroxide film. The presence of a small amount of chloride ion, 10 to 100 ppm, shows only a slight effect, but higher concentrations (1000 ppm) cause a total breakdown in passivity and a dramatic increase in anodic current. The cathodic potential sweep shows an abrupt and unusual oxidation process, giving rise to an oxidation peak not commonly seen. This peak may result from dissolution of the film or preferential attack of intergranular phases.

ISSN:0021-8979    

DOI:10.1063/1.349873

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of partial substitution NdX3(X=F or Cl) for Nd2O3on the reduction–diffusion (R/D) process of Nd–Fe–B powders has been investigated. NdX3reacts with Ca in the R/D process to produce CaX2. CaCl2is distributed uniformly around the Nd2Fe14B grains after reaction. During water washing, CaCl2reacts quickly with water. This improves the disintegration of compacts and facilitates the removal of Ca. The best results with residual Ca content of 400 ppm and oxygen content of 3000 ppm were obtained. In the case of fluoride, however, a negative result was found. There was no improvement in the disintegration of fluoride compact. This was due to the poor water affinity of CaF2.

ISSN:0021-8979    

DOI:10.1063/1.349874

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This paper describes the fabrication, testing, and analysis of epoxy‐bonded neodymium–iron–boron (Nd–Fe–B) magnetic rollers used in electrophotographic copiers. The theoretical analysis gives a closed‐form approximation for the magnetic field that agrees well with experimental measurements and is useful for design purposes.

ISSN:0021-8979    

DOI:10.1063/1.349875

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Magnetic rollers have been widely used in xerographic processes to transport the toners. Conventionally, magnetic rollers were made from extruded Ba‐ (or Sr‐) ferrite with energy product 1.4–1.8 MGOe. Recently, a magnetic roller with stronger field and smaller size is required by some laser printers or copiers. The MQ1 powder was used in designing a new bonded Nd–Fe–B magnetic roller with energy product about 3 MGOe. The distribution of the radial magnetic field of the quadrupole magnetic roller was measured by a Hall probe over the surface. The theoretical simulation was calculated by using the ANSYS Version 4.4 software. The error of the peak positions and the wave widths of the quadrupoles between the theoretical and experimental data is within 5°. The error of the peak value between theoretical analysis and experimental measurement is within 10%. The theoretical analysis of the magnetic roller is very useful for designing a new magnetic roller.

ISSN:0021-8979    

DOI:10.1063/1.349876

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High magnetic fields (≊20 kG) are realizable from spherical and cylindrical transverse field sources in relatively small structures (∼10 cm). In some applications where the working space is cylindrical and long compared to its diameter, these fields can be augmented by about 5 kOe without an increase in the outer dimensions of the original structures. In spherical sources, a similar procedure yields a field increase of approximately 3 kOe. A method is described whereby field distortions arising from access holes to the interiors of such magnet structures can be greatly reduced. Such options considerably enhance the range of applicability to millimeter/microwave and optical devices.

ISSN:0021-8979    

DOI:10.1063/1.349877

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A major part of the bulk and mass of an extended interaction amplifier resides in its magnetic field source. Both can be considerably reduced by application of novel designs made possible by high‐energy product permanent magnet materials such as the samarium–cobalts and neodymium–iron–borides. We compare a structure derived from a hemispherical source design (‘‘magic igloo’’) with several more conventional permanent magnet and electromagnet configurations and find that mass reductions of 50% to 80% are often realized when the hemispherical source replaces any of the others. Such reductions afford considerable performance improvement in radars, radios, and jammers, especially in airborne and ballistic devices. Further compaction results from closer packing of field‐sensitive instruments afforded by leakage field reduction in the hemispherical source. Other advantages of the latter as well as drawbacks, are discussed.

ISSN:0021-8979    

DOI:10.1063/1.349878

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Efforts were made to obtain anisotropic thin‐film magnets at low substrate temperature. This is an important criterion for practical applications such as to build motors. The influence of substrate materials as well as film thickness on thec‐axis orientation were studied. It has been shown that thin‐film magnets with the easy axis of magnetization normal to the film plane could be deposited at a substrate temperature of around 450 °C by choosing the composition near the line from Nd13Fe76B11to Nd13Fe70B17in the ternary phase diagram. It was found that the anisotropic film magnets could be also deposited on the metallic substrate. Thec‐axis orientation tended to be isotropic with an increase in film thickness. The obtained results were used to fabricate a milli‐size motor by depositing 20‐&mgr;m‐thick Nd–Fe–B films on a silicon steel disk substrate of 5‐mm diam. The milli‐size motor exhibited a torque of 0.8 g mm at a rotational speed of 3000 rpm.  

ISSN:0021-8979    

DOI:10.1063/1.349879

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This paper presents an original torque sensor structure using the properties of magnetic circuits, including permanent magnets. The torque is measured through the torsion of the transmitting shaft. The torsion is proportional to the torque. Considering two points of the shaft on the same line in absence of torque, the information is given by the twisting angle in the presence of a torque. A rotating magnetic circuit yields an angle representative signal. This circuit is deformed by the shaft torsion. The reluctance varies and so does the magnet operating point. The induction is measured in an airgap by a statoric galvanomagnetic device. The magnetic field source is an axial permanent magnet ring. Two iron‐toothed rings, fixed to the driving and driven part of the shaft, respectively, and separated by an airgap make up the variable part of the magnetic circuit. The teeth get out of line whenever a torque is applied. The galvanomagnetic device measures an uniform induction and so delivers a modulation free signal, i.e., rotation independent. Because of the periodic toothed structure, the induction varies periodically with the twisting angle. The sense of the variation is the same over half a period or half a pitch. The variation form depends on the teeth design. Operating interval is to be chosen equal to or smaller than the half pitch.

ISSN:0021-8979    

DOI:10.1063/1.349880

出版商:AIP    

年代:1991

数据来源: AIP