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Lowering the reduction temperature of iron oxide is of great significance in applied engineering, but challenging to achieve in a hydrogen tube furnace as the partial pressure of hydrogen is limited to 1 ​atm. In this study CaH2 was used as a drying agent to control the partial pressure of water vapor to lower the reduction potential of iron oxide. By comparing the extent of formation of the reduction product α-Fe in Fe3O4 reduced under hydrogen with and without CaH2 at various temperatures, the presence of CaH2 was shown to lower the temperature required for complete reduction from 400 ​°C to 300 ​°C accompanied by an increase in the H2/H2O ratio of the outlet gas. Thermodynamic calculations indicated that the addition of CaH2 increases the reduction potential, causing a higher production ratio of α-Fe. These findings indicate that CaH2 promotes reduction by efficiently absorbing the water vapor generated during reduction.

The α′′-Fe16N2 has attracted much interest as a candidate for semi-hard magnetic materials. As reported coercivity of α′′-Fe16N2 nanoparticles so far were not high, it is necessary to improve magnetocrystalline anisotropy of α′′-phase to be used practically. Since theoretical calculation suggests a possibility of the improvement of magnetocrystalline anisotropy by substituting of Fe with Co, we challenged to make α′′-(Fe1-xCox)16N2 nanoparticles by hydrogen reduction of α-(Fe1-xCox)OOH as a starting material changing X from 0 to 0.1. We were able to produce α-(Fe1-xCox) nanoparticles through (Fe0.98Co0.02)OOH, and (Fe0.95Co0.05)OOH and (Fe0.95Co0.05)2O3. Sintering occurred during reduction and crystallite diameter D increased with increasing reduction temperature. α′′-(Fe1-xCox)16N2 phase containing α-(Fe,Co) nanoparticles were obtained only at reduction of 340 °C for 4 h and nitridation of 170 °C for 5 h for X = 0.02. It has been revealed that α′′-(Fe1-xCox)16N2 or α′′-Fe16N2 could be formed below D = 50 nm of α-(Fe,Co) or α-Fe. And containing Co make it more difficult to produce α′′-phase. It can be said that the formation of α′′-(Fe1-xCox)16N2 is subject to a limit of D and Co content. Long time nitridation is only way to increase the formation yield of α′′-(Fe1-xCox)16N. High Hc = 2000 Oe was obtained for α′′-(Fe0.98Co0.02)16N2 by changing nitridation time 10 hours from 5 hours. Further long nitradation is expected to increase in Hc of α′′-(Fe0.98Co0.02)16N2.

The metastable $\alpha^{\prime\prime}-\text{Fe}_{16}\mathrm{N}_{2}$ with b.c.t structure has been paid much attention as a new candidate for isotropic hard magnetic material exhibits high $M_{\mathrm{s}}$ of 234 emu/g and relativerly high $K_{\mathrm{u}}\ \text{of}\ \simeq 10^{7}\text{erg}/\text{cm}^{3}$ [1].

In the course of a study on microstructural changes in Sm 2 Fe 17 during a hydrogenation-disproportionation-desorption-recombination process, a peculiar microstructure has been observed just after the hydrogenation-disproportionation processing. SmH 2 crystals, formed as a result of decomposition of the Sm 2 Fe 17 compound, are present with a fibrous shape, about 7 nm in diameter and 1 μm in length. These SmH 2 fibres, all with the same orientation, are arranged at nearly regular intervals of about 11 nm and with a definite orientation relationship to the α-Fe matrix, Fe// SmH 2 .

The structures of Sm8.3Fe85.2B2.0Ti4.5 and Sm9.4Fe84.1B2.0Ti4.5 alloys, which show superior properties as isotropic permanent magnets after a hydrogenation–disproportionation–desorption–recombination (HDDR) process followed by a nitridation, have been investigated by transmission electron microscopy, and electron and X-ray diffraction, paying particular attention to the structural changes induced by the HDDR process. It is found that a hexagonal Th2Ni17-type structure, observed in both alloys, with an approximate composition Sm(Fe,Ti)9.5 before the HDDR process, transforms to a rhombohedral Th2Zn17-type structure with a composition Sm(Fe,Ti)8.5 after the HDDR process. The Ti content in the hexagonal Th2Ni17-type structure is higher than that in the rhombohedral structure. The hexagonal Th2Ni17-type and rhombohedral Th2Zn17-type structures in the Sm9.4Fe84.1B2.0Ti4.5 alloy have lattice parameters a=0.85103(3) nm and c=0.83820(5) nm, and a=0.85549(3) nm and c=1.24826(9) nm, respectively, and show the relationship ahex 1/3crhomb.

Quantitative measurements of the (00 · 2) pole density distribution (PDD) of hexagonal CoCrTa alloy thin films on different kinds of substrates under different sputtering conditions have been performed using the X-ray diffraction method. The sputtering conditions, e.g. the ultimate vacuum pressure, and the kind of substrate, influence the preferred orientation (PO) of the Cr underlayer and the (00 · 2) PDD of CoCrTa. It is also proposed that to form films with a high coercive force, the suppression of the normal component of (00 · 2) PDD is important.

Thermal stability of HDDR processed Sm-Fe-Ti-B-N bonded magnets is investigated in comparison with HDDR processed Sm-Fe-N bonded magnets. Temperature coefficients of Br and iHc of Sm-Fe-Ti-B-N bonded magnet are -0.06%//spl deg/C and -0.43%//spl deg/C, respectively, in the temperature range of 25 to 100/spl deg/C range. Irreversible loss of Sm-Fe-Ti-B-N bonded magnet at 100/spl deg/C is -2.1% and -2.5% respectively after exposure for 2 hrs and 300 hrs. This irreversible loss of Sm-Fe-Ti-B-N is lower than that of Sm-Fe-N which has coercivity 16 kOe. The corrosion resistance of Sm-Fe-Ti-B-N powder is evaluated by measuring increase in oxygen content after exposure at 120/spl deg/C. It is compared with Sm-Fe-N and Nd-Fe-Co-B powders. Sm-Fe-Ti-B-N powder shows slight increase in oxygen content after exposure at 120/spl deg/C in air for 300 hrs. It is also found to have good thermal stability and corrosion resistance.

A scheme for the speed control of rolling mill drives is presented. The proposed speed controller is based on a two degree of freedom (TDF) structure and uses an observer-based state feedback compensator for the major control loop. The control method yields a robust system with respect to system uncertainties and modeling errors and is very effective for vibration suppression. Experimental verification is carried out on a prototype rolling mill mini-model system. The experimental drive system has a three-mass-model structure (motor-gear-load) connected by low stiffness shafts. The mechanical resonances and the inertia ratios between the motor, gear, and load are comparable to those of an actual rolling mill system (resonant frequencies are at 17.4 Hz and 51.32 Hz). The proposed scheme is compared to the conventional proportional plus integral controller, and the performance of each scheme is presented. A high closed loop speed bandwidth was obtained with the proposed TDF speed controller. >

This paper proposes a fast and robust speed controller for electric motor drive systems having torsional loads and containing a gear backlash. The controller is designed using the state feedback technique combined with state variable observers and is implemented on a digital signal processor. Analysis, simulation and experimental results of a prototype variable speed drive system are presented and discussed. It is shown that the proposed speed controller yields a robust system with respect to system uncertainties and modeling errors and is very effective for the suppression of mechanical vibrations. >

The authors describe the control problems associated with rolling mill drive systems and propose a robust speed controller for the suppression of the torsional vibrations. The undesirable mechanical vibrations inherent in a rolling mill drive system impose severe limitations on the dynamic performance of the speed control loop. Plant parameter variations uncertain dynamics, and load torque disturbances are among the major factors which must be addressed to guarantee the system stability and the high-performance operation of the system. To solve these problems, a robust speed controller based on a state feedback control structure is developed. The control law is derived using the loop transfer recovery design methodology, where plant and disturbance uncertainties are incorporated in the design to achieve a robust speed control loop. The design steps of the state controller and the state observer are described, and the constraints imposed on the system are discussed. Analysis and simulation results of the total speed drive system are presented. >

In an asynchronous pulsewidth modulation (PWM) method, the ratio of the carrier frequency to the fundamental frequency must be at least 15-20 in order to suppress the beat phenomenon. However, it is impossible to achieve this condition for large-capacity inverters (e.g., gate-turn-off thyristor inverters), when the fundamental frequency is high. Assuming that the beat phenomenon is caused by an error generated in the PWM process, the authors have introduced a compensator to reduce the error. As a result, beat phenomenon can be decreased for a low carrier frequency. Effectiveness of the proposed method is shown by experimental results.