In this paper, single-phase and fine-grain hexagonal barium ferrite powder was prepared based on the optimal calcination condition. The influence of calcination conditions including temperature and holding time on microstructure and magnetic properties of powder were studied in detail. Firstly, θ –2 θ scan X-ray diffraction (XRD) results reveal that it is hard to obtain single phase of powder when the calcination temperature is lower than 850 °C. In addition, the calcination time for single phase of barium ferrite powder was reduced with the increase in calcination temperature. Scanning electron microscopy (SEM) images and magnetic hysteresis loops show that the condition of low temperature and long holding time is beneficial for obtaining homogeneous size of grain and excellent magnetic properties. Consequently, hexagonal barium ferrite powder with uniform grain size of ~ 180 nm, high purity and excellent magnetic properties is obtained at optimal calcination condition of 850 °C–10.0 h.
Liu Sining,Yan Xin,Tian Xinru,Li Sinan,Luo Shao-hua
To meet the development needs of high-performance and low-cost lithium-ion batteries, lithium-rich Co-free manganese-based cathode materials have become the primary choice for future power batteries based on the advantages of low cost and improved battery performance. Herein, Li 1.2 Mn 0.6 Ni 0.2 O 2 is prepared by the high-temperature solid-state method. The impacts of calcination temperature, holding time, and heating rate on the microstructure and properties of cathode materials are systematically studied via orthogonal experiments. Results revealed that Li 1.2 Mn 0.6 Ni 0.2 O 2 prepared by the high-temperature solid-state method at a calcination temperature of 900 °C, holding time of 12 h, and heating rate of 15 °C/min is ideal, with a smaller particle size and uniform particle distribution and a lower agglomeration degree, and the initial discharge specific capacity reaches 148.4 mAh·g −1 at 0.1 C. The discharge specific capacity of 102.8 mAh·g −1 is still maintained after 100 charge–discharge cycles. Among the various factors, holding time has the greatest influence on the lithium-rich Co-free manganese-based cathode material. The crystallinity, electrochemical properties, and microstructure of the material prepared at 12 h were considerably better than those prepared under other conditions. Test findings show that with a small particle size and uniform distribution, the synthesized cathode material has better rate and cycle performances.
Cui Yongping,Shang Yaru,Shi Ruixia,Che Quande,Wang Yingzi,Yang Ping
The effects of calcination temperature, precursor content, holding time and heating rate on the morphology of WO 3 nanofibers (NFs) prepared by electrospinning technology have been investigated systematically. The X-ray diffraction (XRD) patterns using Rietveld method indicated that average crystalline sizes of nanoparticles of WO 3 NFs increase with increasing calcination temperature. Also, the crystallinity of the nanofibers increases with the rise of calcination temperature. The suitable precursor contents and holding time facilitate the formation of continuous and uniform NFs. The samples prepared by different heating rates showed that the WO 3 NFs fabricated with heating rate of 5 °C/min possess the smallest and uniform nanoparticle sizes. The X-ray diffraction (XRD) patterns using Rietveld method exhibited that different heating rate had no significant influence on the crystallinity of WO 3 NFs. Additionally, the experimental results of photocurrent responses and electrochemical impedance indicate that the WO 3 NFs prepared by different heating rate have different photoelectrochemical performances.
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