JunhHua WU
材料科学技术（英文）
Microwave dielectric measurements over the broad bandwith of 10 MHz to 20 GHz were conducted on composites comprising bundles of single-walled carbon nanotubes (SWNT) embedded in an epoxy matrix, in comparison to the nano-graphite and MWNT. It is found that both relative real and imaginary permittivity of the nanocomposites are strong functions of the SWNT concentration, showing large, wide dielectric and electrical response. Distinct resonance around 1.5 GHz is observed at high SWNT concentrations, accompanied by the downshift of the resonance frequency with increasing concentration. Largely, the SWNT-epoxy composites share the behavior of the MWNT owing to structural similarity, much more effective than the nano-graphite. The remarkable, broadband dielectric and electrical properties of the nanotubes acquired in the work originate from their unique seamless graphene architectures, modeled by two major contributions, dielectric relaxation/resonance and electronic conduction, which is substantiated by the agreement between theoretical analysis and experimental results. The carbon nanotube composites are prospective for microwave applications and offer experimental evidence for fundamental studies in low-dimensional systems.
关键词:
Single-walled carbon nanotube
,
carbon
,
nanotube
,
Dielectric
Peng QI
,
Jinfeng WANG
,
Baoquan MING
,
Juan DU
,
Xinghua LIANG
,
Limei ZHENG
材料科学技术（英文）
Lead-free piezoelectric ceramics (Na0.5K0.5-xLix)NbO3 (x=0.057–0.066) were synthesized by an ordinary sintering technique. Substituting Li for K can lead to structural distortion, which improves the Curie temperature (TC) greatly. By adding appropriate LiNbO3 content, piezoelectric constant d33 values reach 202–212 pC/N. Electromechanical coefficients of the planar mode reach 44.4%–46.8%. The dielectric loss is below 2.6%, which is much lower than reported (about 50%). The TC of (Na0.5K0.5-xLix)NbO3 (x=0.057–0.066) is in the range of 490–510oC, at least 70oC higher than that of pure (Na0.5K0.5)NbO3 ceramics. The results show that (Na0.5K0.5-xLix)NbO3 ceramic is a kind of good lead-free high-temperature piezoelectric material.
关键词:
Lead-free
,
null
,
null
,
null
Azizah Shaaban
,
Sian-Meng Se
,
Imran Mohd Ibrahim
,
Qumrul Ahsan
新型炭材料
doi:10.1016/S1872-5805(15)60182-2
采用 ZnCl2对橡胶木屑进行化学活化制备出活性炭。 ZnCl2与橡胶木屑的浸渍质量比为1.0-2.0,活化温度为500℃,时间为60 min。通过扫描电镜、X射线衍射和BET比表面分析仪探讨浸渍比例对活性炭孔结构的影响。结果表明,当浸渍比为1.5：1时,样品的比表面积和孔径分别为1301 m2/g 和0.37 cm3/g。通过化学发泡工艺将不同质量分数(1%,2%,3%,5%,8%)的活性炭填充至聚氨酯中制备出聚氨酯复合材料。在1-5 GHz频率范围内,复合材料吸收微波。随着活性炭含量增加,在1-3 GHz范围内,介电常数(ε’)和回波损耗增加。活性炭含量为8%时复合材料的介电常数达到最大值3.0。在1.8 GHz时,复合材料的回波损耗为10 dB。在-2.5 GHz,电磁屏蔽效率大于3 dB。与传统聚合物材料如填加金属的聚氨酯和聚酯相比,所制复合材料呈微波段吸收,可作为电磁屏蔽材料。
关键词:
橡胶木屑
,
化学活化
,
活性炭
,
微波吸收材料
,
介电常数
,
回波损耗
