Ziquan Li

Synthesis and characterization of magnetic nanocomposites with Fe3O4 core

To improve the infrared absorbing performance of the ferrite magnetic material which has good electromagnetic wave absorbing performance, the core-shell structured multilayer coating is introduced to achieve multiple wavelength range absorbing. Nanocomposites Fe3O4/SiO2/Al2O3 and Fe3O4/SiO2/TiO2 have been prepared using a series of chemical methods. The results of TEM and XRD analysis show that multilayer coated structures exit in both Fe3O4/SiO2/Al2O3 and Fe3O4/SiO2/TiO2 and that the core-double shell particles are all in nano-scale. The saturation magnetization and the coercivity of Fe3O4 at room temperature are 72 Am2/kg and 3.82 kA/m, respectively. Further coating of SiO2 and Al2O3 or TiO2 decreases the saturation magnetization and the coercivity while all nanocomposites remain ferromagnetic. There is no obvious improvement of the infrared absorbing ability of Fe3O4 nanoparticles in coating of SiO2 while further coating of Al2O3 or TiO2 reduces the infrared emissivity from 0.97 of Fe3O4 nanoparticles to about 0.83 of the core-double shell nanocomposites.

Ex-situ method for toughening glass/epoxy composites by interlaminar films made of polyetherketone cardo and calcium sulfate whisker

Epoxy matrix composites were toughened by introducing films into fiberglass fabric layers based on an ex-situ vacuum-assisted resin transfer molding technique. The mixture films were made of a certain polyetherketone cardo and calcium sulfate whiskers with different mass percent. The toughening mechanism was studied by dynamic mechanical thermal analysis and scanning electron microscopy. The addition of calcium sulfate whisker changed glass transition temperatures of Epoxy Resin (EP) and polyetherketone cardo, indicating that films with calcium sulfate whisker were melting during the curing of epoxy resin and forming the mixture of EP phase, polyetherketone cardo phase, and calcium sulfate whisker between the layers of composites. Meanwhile, the results indicated that calcium sulfate whiskers and fiberglass fabric formed three-dimensional structure between the layers of composites to toughen the composites. The results of the mechanical properties show that the interlaminar shear strength and fracture toughness (GIC) were obviously improved meanwhile tensile strength and flexural strength kept stable whether the addition of films or not. Maximum values of the interlaminar shear strength and fracture toughness (GIC) were 22% and 95% higher than that of the controlled specimens without films, respectively. The interlaminar mechanical properties improved with the addition of films made of polyetherketone cardo and calcium sulfate whisker, which is benefit for the improvement of whole mechanical properties and wide usage of laminate composites.

Effects of period number and sputtering time on optical properties of Si/Ge multilayer films deposited by magnetron sputtering

Si/Ge multilayer films were deposited by radio frequency magnetron sputtering method, and effects of period number and sputtering time on structure and optical absorption properties of the films were investigated by XP-1 profilometer, XRD, SEM, AFM, Ramman and UV–Vis techniques. Results indicated that the films exhibited the incomplete crystallization, and the appropriate period number benefited the ordering of the Si. Simultaneously, the films showed smooth growth, and the islands were spread all over the surface, and changing of the roughness was attributed to the interface effects. Strong absorption range in the UV–Vis spectra was enlarged with increasing period numbers, and there was a general trend for the band gaps to decrease with increasing period numbers, accompanied the gradually decreasing amplitude. Theoretical calculation and analysis displayed that the ECB value gradually increased and the EVB value gradually decreased with the increasing period number, eventually resulting in the decreasing band gap, and the corresponding values remained stable at different sputtering time when period number was 5.

Effect of Gd on microstructure, mechanical properties and wear behavior of as-cast Mg–5Sn alloy

Effect of minor Gd addition on the microstructure, mechanical properties and wear behavior of as-cast Mg–5Sn-based alloy was investigated by means of OM, XRD, SEM, EDS, a super depth-of-field 3D system, standard high-temperature tensile testing and dry sliding wear testing. Minor Gd addition has strong effect on changing the morphology of the Mg–5Sn binary alloy. Gd addition benefits the grain refinement of the primary α-Mg phase, as well as the formation and homogeneous distribution of the secondary Mg2Sn phase. The mechanical properties of the Mg–5Sn alloys at ambient and elevated temperatures are significantly enhanced by Gd addition. The wear behavior of the Mg–5Sn alloy is also improved with minor Gd addition. The alloy with 0.8% Gd addition exhibits the best ultimate tensile strength and elongation as well as the optimal wear behavior. Additionally, the worn surface of the Mg–5Sn–Gd becomes smoother in higher Gd-containing alloys. The best wear behavior of alloy was exhibited when Gd addition was up to 0.8%, showing a much smoother worn surface than that of control sample. The improvement of tensile properties is mainly attributed to the refinement of microstructure and the increasing amount and uniform distribution of Mg2Sn phase. The larger amount of Mg2Sn phase uniformly distributed at the grain boundary of Mg–Sn–Gd alloys act as a lubrication during sliding, and combined with smaller grain size improve wear behavior of the binary alloy.