Magnetic materials with ingeniously designed structure may be utilized as highly efficient microwave absorbing materials (MAMS) working at ultralow matching thickness. However, it remains a challenge to decrease the matching...
Regulating phase composition and dispersion state of oxide particles inside metal-organic frameworks-derived carbon composite holds enormous potential in enhancing dielectric property and microwave absorption performance. Herein, solid state reaction between Fe-bdc nanorod and TiO2 shell has been used to synthesize a series of Fe-Ti oxides/carbon (FTO/C) composites at different annealing temperatures. The results show that with the increase of temperature, the grain size of oxide particles, which tend to distribute in the center of carbon rod, has increased, resulting in the formation of continuous conductive surface caron layer. Meanwhile, the aspect ratio of carbon rod would decrease, which would hinder the construction of conductive path in paraffin matrix. At lower temperature, internal oxide particles are less crystallized (Fe2.5Ti0.5)1.04O4, which may induce obvious dipole polarization. While at higher temperature, phase conversion from (Fe2.5Ti0.5)1.04O4 to Fe2TiO4 and FeTiO3 would bring about more interfaces, which generate strong interfacial polarization. Therefore, dielectric loss of as-prepared FTO/C composites would be enhanced with rising temperature until 700 oC, and impedance matching condition would always be improved with increasing temperature, in terms of lowest matching thickness in whole Ku or X bands. Consequently, S-700 owns a broad effective absorption bandwidth (EAB) of 6.84 GHz at 2.2 mm, covering whole Ku band and S-800 owns a large EAB of 4.16 GHz at 2.8 mm, covering whole X band. This work may provide novel insights into the design of metal-organic frameworks-derived carbon composite with desired dielectric properties through controlling the composition and dispersion of inner oxide particles.
The difficulty of short-process bonded Nd–Fe–B
magnet
waste recycling lies in the effective removal of the cured polymer
matrix while protecting the magnetic powder. In this study, the polymer
matrix in bonded Nd–Fe–B magnet waste was destroyed
using sodium hydroxide ethanol solution, and the effect of the recycling
process on the magnetic powders was studied. The nonmagnetic polymer
matrix was removed, while the magnetic phase was not destroyed. The
carbon and oxygen contents of the recycled magnetic powders decreased
by 92.96 and 89.30%, respectively, while the M
S (saturation magnetization), M
r (remanence), and H
cj (coercivity) values
of the recycled magnetic powders were 99.8, 98.5, and 95.9% of the
original magnetic powders, respectively. The curing and decomposition
processes of the polymer matrix were also analyzed. During the curing
process, dicyandiamide and bisphenol A epoxy resin acted as bridges
and skeletons, respectively, finally forming a thermosetting three-dimensional
network structure. In the alkaline alcohol solution, the bridges and
skeletons were destroyed by the free hydroxyl groups and free hydrogen
radicals in ethanol, and small molecular products were dissolved in
the solution.
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