Yuchong Ding

The preparation of sintered NdFeB magnet with high-coercivity and high temperature-stability

The NdFeB magnets with high intrinsic coercivity have been produced by using the conventional powder metallurgy method (including SC, HD and JM) of sintered NdFeB magnets. The effects of grain boundary phases on the microstructure and magnetic properties of as-sintered and annealed magnets have been tried to investigate. Also the Curie temperature of the magnets was studied. By adopting suitable component ratio of some heavy rare-earth atoms and some micro-quantity additives, we have prepared high-coercivity sintered NdFeB magnets with magnetic properties of jHc=36.3kOe, Br=11.7kGs and (BH)max=34.0MGOe. The temperature coefficient of residual magnetic flux of the magnets (between 20 and 200°C) is -0.113%/°C, while the temperature coefficient of intrinsic coercivity -0.355%/°C. The Curie temperature of the magnets is about 342°C.

Coercivity enhancement of sintered Nd14.4Fe78.4Co1.3B5.9 magnets by dysprosium diffusion in grain boundaries of rapidly solidified strips

A new coercivity enhancement process using dysprosium diffusion in grain boundaries of rapidly solidified strips was developed. The effects of the dysprosium diffusion on microstructure and magnetic properties of sintered Nd14.4Fe78.4Co1.3B5.9 magnets have been investigated. The transmission electron microscope observation showed that the intergranular phases of rapidly solidified strips were optimized through the grain boundary diffusion process of strips. From the mapping distribution of dysprosium atoms in sintered magnets and the fact that remanence almost kept constant, one could suppose that dysprosium element preferred the interface of the matrix grains, which was probably a reason of coercivity enhancement. The coercivity of the magnets made from diffusion heat treatment strips was increased by 1100 Oe, while the remanence was almost kept constant. Reduction in remanence is from 14.1 to 13.92 kG. The energy product of the magnets was slightly increased from 46.4 to 47.4 MGOe.

Phase structure, magnetic properties, and magnetization behavior of Sm (Co,Zr) 7/α- (Fe-Co) nanocomposite made by mechanical alloying

The Sm(Co,Zr)7/α-(Fe–Co) nanocomposite permanent magnets are produced by mechanical alloying and subsequent annealing. The soft magnetic phases were introduced by two different processes. In the first process, the crushed as-cast SmCo6.8Zr0.2 powders were blended and milled with different weight percent of fine iron powders (SCZ+Fe) and in the second process, the crushed as-cast (SmCo6.8Zr0.2)1−xFex (x=0,0.1,0.25,0.5,0.75) powders (SCZF) were milled directly. XRD analysis showed that the phase structure of annealed SCZ+Fe are consisted of SmCo7 phase and α-(Fe,Co) phase, while the composites of annealed SCZF are composed of α-(Fe,Co) and SmCo hard phases that varied with different Fe content. The best energy product of the annealed SCZF and SCZ+Fe are 11.3 MGOe (SCZF-3) and 10 MGOe (SCZ+Fe-1), respectively, resulting from the very strong exchange coupling between the hard phase and the soft phase. According to the Henkel-plots of SCZF-3 and SCZ+Fe-1, a stronger intergrain exchange coupling effect was obse...

Growth and anisotropic thermal properties of biaxial Ho:YAlO3 crystal

Ho:YAlO3 (YAP) crystal with large size and good optical quality has been grown by the Czochralski method. Thermal properties of the as-grown Ho:YAP crystal have been investigated by measuring the temperature-dependent, anisotropic thermal expansion, specific heat, thermal diffusion, and thermal conductivity. The results show that Ho:YAP crystal possesses a large anisotropic thermal expansion and good thermal conductivity. The calculated average thermal expansion coefficients along a, b, and c axis are αa=9.18×10−6/K, αb=1.94×10−6/K, and αc=7.61×10−6/K from 293.15 to 770.15 K. The thermal conductivities along a, b, and c axis are up to 11.6, 9.9, and 12.3 W m−1 K−1 at 298.15 K. Compared with Ho: Y3Al5O12 (YAG), Ho:YAP crystal has a larger thermal conductivity along a axis from 298.15 to 568.15 K.

Effect of DyHx addition on the magnetic properties and microstructure of Nd14.1Co1.34Cu0.04FebalB5.84 magnets

The sintered Nd14.1Co1.34Cu0.04FebalB5.84 permanent magnets with DyHx addition have been prepared by powder-blending technique. The magnetic properties and microstructures of the magnets were investigated. It was found that Dy element is enriched in the intergranular phase, being evenly distributed throughout the grain boundary and improving the orientation of magnets as a lubricant, and 1.2% to 2% DyHx additions are proved to be very effective in improving the permanent magnetic properties of Nd14.1Co1.34Cu0.04FebalB5.84 magnets. Further analysis revealed that the increase of coercivity and slight decrease of remanence due to DyHx addition can be attributed to the reduction of the primary phase volume, formation of the (NdDy)-rich phase and grain refinement of the main phase.

Temperature effect on emission spectra and fluorescence lifetime of the 4I13=2 state of Er3+-doped Gd2SiO5 crystal

By measuring the emission spectra and the fluorescence lifetime of the 4I13=2 state of Er3+ ions in Gd2SiO5 crystal at different temperatures, the effects of temperature on the spectra and the lifetime of the 4I13=2 state are investigated. When the temperature increases, the emission line width for the 4I13=2 -> 4I15=2 transition is broadened, and the main emission lines at 1 596, 1 609, and 1 644 nm shifte toward shorter wavelengths. The measured lifetime of the 4I13=2 state decreases from 13.2 to 8.4 ms with temperature increase from 13 to 300 K, which is mainly due to the temperature dependence of multiphonon relaxation between the 4I13=2 and 4I15=2 states and the changing population distribution among the Stark levels within the 4I13=2 state. The experimental results imply that low temperature condition is better for the ~1.6- \mu m laser output.

Effects of annealing on luminescence efficiency of large-size YAG：Ce crystal grown by temperature gradient techniques

YAG:Ce crystal with a diameter of 110 mm is successfully grown by the temperature gradient technique (TGT). The effects of annealing on the luminescence efficiency of YAG:Ce crystal are investigated, and the optimal annealing temperature and atmosphere are obtained. The mechanism of variation behavior of the luminescence efficiency of YAG:Ce under different annealing conditions is discussed and some details on the luminescence associated with color centers are analyzed.