Search

The hydrogenation disproportionation desorption recombination (HDDR) process can yield highly anisotropic and coercive NdFeB-type powders with energy densities in excess of [(BH).sub.max] = 340 kJ/[m.sup.3]. The elucidation of the very unusual phenomenon of texture inducement is of great scientific and technological interest. Here, [Nd.sub.12.5][Fe.sub.bal][B.sub.6.3] and [Nd.sub.12.5][Fe.sub.bal][Ga.sub.0.3][Nb.sub.0.3][B.sub.6.3] alloys have been processed and hydrogen partial pressures and dwell times during disproportionation and recombination have been varied systematically. The effect of these processing parameters on the microstructural and magnetic properties is described. Intermediate processing stages were characterized by Rietveld analysis, field emission gun scanning electron microscopy, transmission electron microscopy using EDX and diffraction modes. Crystallographic relationships between parent, disproportionated and recombined phases are described and it is suggested that the iron boride phase could act as the anisotropy-mediating phase throughout the different stages of the process. The nucleation and growth of the various phases are controlled by the hydrogen partial pressure during the exothermic disproportionation, thereby strongly effecting the final degree of texture. This d-HDDR (dynamic-) process yields a highly stable memory carrier, thus, allowing to maximize texture without Co addition. It is proposed that Nb is useful for the stabilization of the boride phase, whereas Ga is beneficial during initial recombination. Index Terms--Electron microscopy, HDDR, magnetic properties, NdFeB, polymer bonded permanent magnets, texture.

An anisotropic bonded magnet (MAGFINE25), is about to be applied to de motors for automobile use such as power seat motors and window motors. These de motors have achieved a 50% reduction in weight and in volume, with the heat resistance of 120 [degrees]C. However, the heat resistance of 150 [degrees]C is required for motors near the engine, such as fan motors and wiper motors. We improved the heat resistance of the bonded magnet by the addition of Dy element to magnet powder, and succeeded in developing a bonded magnet with the heat resistance of 150 [degrees]C. Index Terms--Anisotropic bonded magnet, d-HDDR, dysprosium, heat resistance.

The maximum energy product of bonded magnets is advancing every year. The highest maximum energy product of any bonded magnet achieved is 25 MGOe (200 kJ/[m.sup.3]) in the Nd--Fe--B system by d-HDDR treatment. There is a great demand for even higher energy bonded magnets with the desire for smaller, more efficient electric motors. Bonded magnets made from d-HDDR treated anisotropic magnet powder have low squareness due to low squareness of the powder. The authors developed a method to increase squareness of d-HDDR powder, and succeeded in developing the world's highest energy bonded magnet with 26.6 MGOe (213 kJ/[m.sup.3]). This was achieved through Dy-diffusion treatment followed by d-HDDR treatment, as well as an increase in the density of the bonded magnet. This magnet has little aging loss after being held at 393 K for 878 h. Index Terms--Anisotropic bonded magnet, d-HDDR treatment, dysprosium, NdFeB.

There is a need to reduce the weight and size of dc brush motors for automobile use. In the current study, sintered ferrite magnets were replaced by Nd-Fe-B anisotropic bonded magnets in an effort to reduce the size and weight of the motor. Finite-element analysis was carried out, and a four-pole anisotropic magnet was determined to be optimal. Based on these results, an actual 35-W brush motor for power automobile seats was test produced. A roughly 50% reduction of weight and volume was realized in this test-produced motor, which also maintained the same torque as the currently used ferrite motor. Index Terms--DC brush motor, four-pole, Nd-Fe-B anisotropic bonded magnet, volume reduction, weight reduction.

The NdFeB anisotropic bonded magnet produced by the HDDR method, which was developed in 1990, has not found general popularity due to its high cost and low serviceable temperature of 353 K. The authors have developed a new production method that overcomes these barriers to decrease the cost and increase the serviceable temperature. The use of the dynamic HDDR (d-HDDR) process eliminates the need for Co, thus greatly reducing the production cost of NdFeB anisotropic bonded magnets with a (BH)max of 159 kJ/[m.sup.3]. The anisotropy of the NdFeB magnetic powder is induced by the control of the reaction rate of the NdFeB alloy and hydrogen, by controlling the hydrogen pressure in the HDDR process. The serviceable temperature is increased by the addition of Dy after the application of the d-HDDR method. An increase in intrinsic coercivity, iHc, from 1.12 MA/m to 1.56 MA/m, corresponds to a proportional increase in the serviceable temperature to 413 K. Index Terms--Anisotropic bonded magnet, coercivity, Dy, HDDR, NdFeB, reaction rate.

A highly sensitive and quick response acceleration sensor has been constructed using the stress-impedance (SI) element of 20 [micro]m diameter CoSiB amorphous wires combined with a CMOS IC multivibrator. The resolution of the acceleration sensor is [10.sup.-3] Gal (= 0.01 m/[s.sup.2]) for repetitive vibration and 0.1 Gal for nonrepetitive motion. The high sensitivity is based on the ultra high values of the gauge factor of about 4000 in the CoSiB amorphous wire SI element. The power consumption is about 6 mW due to the pulse magnetization circuitry. Basic properties of the acceleration sensor and application to the sensing of road bridge seismovibration due to car passing are presented. Index Terms--Acceleration sensor, amorphous wire, CMOS IC multivibrator circuit, stress-impedance effect.