Song Ji

The Effect of B2O3–Li2CO3 Addition on Sintering Behavior and Dielectric Properties of Ba 0.6Sr0.4TiO3 Ceramics

Barium strontium titanate (Ba0.6Sr0.4TiO3: BST) powders were prepared by the oxalate co-precipitation method. The ceramics from thus obtained BST powders with B2O3-Li2CO3 addition were prepared by conventional oxide mixing method. The powders and the ceramics were observed and analyzed by SEM and X-ray diffraction. The effects of B2O3-Li2CO3 addition and powder properties on the sintering behavior and the dielectric properties of BST-based ceramics were investigated. SEM results revealed that the BST powders are micron-sized with cauliflower-shaped rough surface leading the specific surface area reaches 18.52m2/g. In dilatometric studies, the ceramics without B2O3-Li2CO3 addition didn’t produce the desired shrinkage and dense microstructure at relative low temperatures (<1000°C). However, the sintering temperature is decreased to 850°C by addition of small amount (≤3wt %) of B2O3 and Li2CO3. This was also verified in sintered microstructures. The XRD results showed that the main phase of the ceramics was BST without any other crystalline phases of remarkable extent. With increasing of B2O3-Li2CO3 content, the permittivity and the tunability of the ceramics were decreased.

Effect of Microstructure on Magnetic Properties of Nd-Fe-B Permanent Magnet

The new Nd-Fe-B magnets were prepared by powder metallurgical processing. The thermal stability and magnetic properties were found to be remarkably improved after annealing at 680 °C for 2 h. The Br, and Hc, BH of annealed magnets were improved by-0.04 T, 132 KA·m-1, 22 KJ·m-3, from 1.25 T, 882 KA·m-1, 286 KJ·m-3 of the as-sintered magnets, respectively. The losses and average temperature coefficients of magnetic properties were very low at 373 K. Compare with the as-sintered magnets, the magnetic property losses of the annealed magnets decreased by half at different temperature. Scanning electron microscopy on magnets did reveal a noticeable difference in phase morphology, and found that the improvements of thermal stability and magnetic properties can be attributed to the change of magnetic domain wall motion, composition, stray demagnetizing fields, and microstructure. The new Nd-Fe-B preferment magnets are promising to use in the all-electric bus hub direct drive motor.

Production, Characterization, and Flowability of Assemblies Consisting of Highly Active Aluminum Nanoparticles

Highly active aluminum nanoparticles are currently needed as a component in propellants. A hybrid spray method was used the HT (stating in this paper that the HT was cured in a 1.05∶1.00 mass ratio of hydroxyl-terminated polybutadiene to 2’4-toluene diisocyanate) to coat the surface of highly active aluminum nanoparticles, as accomplished in a xylene suspension. As indicated, HT coating can be completely carried out to form high-quality assemblies in micrometer scale, which can prevent circumambient oxygen from infiltrating and reacting with the active aluminum nanoparticles while favoring the preservation of the assemblies for a long term. The existence of voids or holes in the assembled aluminum nanoparticles could reduce density and improve the combustion thermal efficiency in a propellant. The flowability of the HT-coated assemblies evidently increases in comparison to that of original aluminum nanoparticles. Related mechanisms have been investigated and discussed. In terms of quality and content of h...

The GMI-Hysteresis of Co67Fe4.5Cu1Si12.5B15 Amorphous Thin Strip

This paper presents the results of investigations recently done by our research group that improve the properties stability of GMI sensors by exploring the giant magneto-impedance (GMI) and the GMI-hysteresis of Co67Fe4.5Cu1Si12.5B15 amorphous thin strips, which was the most promising soft magnetic material could be used in the weak magnetic transducers. The amorphous thin strips were prepared by the so-called planar flow casting technology. With the circumferential driving mode, the changes of the GMI on the frequency of the ac current under different external magnetic field were measured on Agilent 4294A precision impedance analyzer. The maximum GMI ratio of 201.4% was observed. The field sensitivity, (δZ/Z)/δH, has reached 413.2%. Additionally, the ratio of GMI changes of the CoFeCuSiB amorphous thin strips could be control under 1%, by the optimum parameters of this amorphous strip, such as the DC current and the time of joule current annealing, the dc level and frequency of the excitation current, the driving method.

Study on Two Plasma Physical Vapor Deposition Methods for Preparing Ultrafine Al Powders

Plasma physical vapor deposition method was most widely used to prepare ultrafine Al powders. Direct Current Arc Plasma (DCAP) and Radio Frequency Induction Plasma (RFIP) were adopted individually to produce Al powders with different particle size. The micro structure such as grain size, morphology and crystal phase was examined by SEM, TEM and XRD methods. The results show that the Al production by RFIP was better than by DCAP. DCAP has outstanding advantages in producing nanoAl powders with the particle size below 300nm while the RFIP is better to produce Al powders with the particle size 300nm to 1 μm.

Preparation and Characterization of Silver Powders with Spheric Shape and Different Sizes

The preparation and characterization of silver powders with spheric shape and different sizes by chemical reduction of silver ions in the presence of ethanol amine using hydrochinone (C6H6O2) as the reducing agent are described. The size distribution, microstructure, and the phase composition of the obtained Ag Powders were characterized by the Laser Particle Size Analyzer, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and the X-ray diffraction (XRD). The Ag powder was in face-centered cubic crystal structure with spheric morphology. The average tap density of silver powders is up to 4.0g/cm3. It was also found that the size of the Ag particles can be adjusted conveniently to a certain degree by varying the silver ions content, the addition amount of dispersing agent, the aging time, the temperature of the reaction, and the concentration ratio of hydrochinone to Ag+.