Advanced Materials Research Vols. 535-537

Abstract: The PA66-based composites containing dispersible nano-SiO₂ (DNS) were prepared in a twin-screw extruder by melt compounding. The microstructures of dispersible nano-SiO₂/PA66 composites were investigated by means of TEM and XRD, and the non-isothermal crystallization behavior was studied through Jeziorny method and Mo method based on DSC analysis. The results showed that the dispersion of DNS was uniform in PA66 matrix, which could be related to surface structure of dispersible nano-SiO₂. It was found from the study of the non-isothermal crystallization kinetics that dispersible nano-SiO₂ possessed a heterogeneous nucleation capability in PA66 matrix, and its addition could hinder the motion of PA66 molecular chain, lower the crystallization temperature, and prolong the crystallization time of PA66. In addition, the activation energies for non-isothermal crystallization of neat PA66 and composites were also evaluated by the Kissinger method. The result showed that the activation energies of dispersible nano-SiO₂/PA66 composites were higher than that of neat PA66.

Abstract: The polyoxymethylene-based composites containing reactable nano-SiO₂ were prepared in a twin-screw extruder by melt compounding, and mechanical and thermal properties of pure polyoxymethylene (POM) and composites were investigated. The results showed that reactable nano-SiO₂ could reinforce the tensile strength and Young’s modulus of composites. To the impact strength of composites, there was obvious improvement when a small amount of silica was added into POM. With the increase of silica content, the impact strength of composites showed a gradually decrease trend. It was worthy to note that reactable nano-SiO₂ could significantly increase the decomposition temperature of POM. When the content of reacta_{Subscript text}ble nano-SiO₂ was up to 5 wt%, the degradation temperature of composites could increase about 38.3°C under n_{Subscript text}itrogen atmosphere and 43.8°C under air atmosphere, respectively, compared with pure POM. Furthermore, the differential scanning calorimetry (DSC) analysis showed that reactable nano-SiO₂ had a good heterogeneous nucleation capability in POM, and could increase crystallization temperature of POM, but surface structure of reactable nano-SiO₂ was not propitious to the growth of POM crystals, accordingly leading to the decreasing crystallinity of composites.

Abstract: Particles size grading method was employed to fabricate aluminum matrix composites reinforced with 75% volume fraction B4C particles by squeeze casting. Dynamic behaviors of the composite was investigated and compared with 55 vol. % composite which were reinforced with particles of uniform size. The results showed that the flow stress increased but the fracture strain decreased with increasing reinforcement volume fraction. Furthermore, the dynamic behaviors of 55 vol. % composite were significantly affected by adiabatic heating softening which was demonstrated by the local melted matrix on the fracture surface and an increase-decrease tendency on flow stress and failure strain was obtained with increasing impact velocity. However, due to load redistribution caused by particles size grading, no melted region was found on the fracture surface and no increase-decrease tendency on flow stress and failure strain was observed for 75 vol. % composites under the same impact loading.

Abstract: A facile hydrothermal method has been developed for synthesis of nanocapsual-shaped α-Fe₂O₃ using FeCl₃•6H₂O as iron source, 4, 4–bipyridine and thiourea as surfactant, and then the above α-Fe₂O₃ sample’s outer surface were coated with TiO₂ and obtained nanocomposite of α-Fe₂O₃@TiO₂. Magnetic nanocomposite (Fe₃O₄@ TiO₂) were obtained by a reduction process with the above α-Fe₂O₃@ TiO₂ products as starting materials by hydrothermal synthesis method using hydrazine hydrate as reductant. The as-prepared Fe₃O₄@TiO₂ samples have good photocatalytic activity and it can photocatalyze RhB at the condition of the external magnetic field

Abstract: Abstract. Ballistic impact tests were preformed on triaxial braided composite panels using blade-like projectile in a way that approximates the impact velocity, deformation modes, and strain energy density at failure for composite fan case material during blade-out event. The failure modes are identified from impact test results. The main failure modes are fiber shear failure and matrix crush failure in the impact surface and fiber tensile failure, fiber pull-out, matrix cracking and delamination in the exit surface. Finite element model is developed to analyze the damage evolution of penetration process. It is found that the penetration process can be subdivided into 3 stages based on different damage mechanisms and the energy absorption mechanism in each phase is illustrated too.

Abstract: 2D-C/C composites with the dimension of Φ80mm×400mm were prepared rapidly by thermal gradient CVI within 104 hours. Their density reached 1.74g/m³ and the density difference was less than 0.04g/cm³. The pyrocarbon microstructure changed from RL to RL+SL, and then to SL along radial direction. These changes were attributed mainly to the difference of gas concentration and temperature gradient at every micro-zone during chemical vapor infiltration. After heat-treatment at high temperature, the space among layers of pyrocarbon enlarged and residual thermal stress was freed, which could lead to cracks formed in matrix. The flexural property of composites decreased with increasing heat-treatment temperature and the fracture mode changed from the brittleness to pseudo-plastic. Carbon particulars between pyrocarbon laminas can increase the flexural strength by particular reinforcement.

Abstract: Five commercial PTFE based self-lubricating composites were selected for candidates in space. The hardness was measured by depth-sensing indentation in CMC mode. The tribological properties of composites sliding against a 440C steel balls were investigated using a vacuum rotational ball-on-disc apparatus. The result show the hardness of Rulon 945, Rulon XL, GR 0348, D 5813 and LW 155 are about 62.01 MPa, 45.42 MPa, 84.62 MPa, 116.59 MPa and 569.40 MPa, which are higher than pure PTFE composite. The friction coefficient of Rulon 945, Rulon XL,GR 0348, D 5813, LW 155 obtained in vacuum are, 0.08 to 0.20, 0.06 to 0.10, 0.05 to 0.10, 0.06 to 0.10 and 0.05 to 0.15. Rulon XL, GR 0348 and D 5813 show very stable friction level around 0.08. For volumetric wear rate, D 5813 have the biggest volumetric wear rate of 2.36×10-7mm3/mm, which is twelve times of Rulon 945 and nearly five times of Rulon XL, GR 0348 and LW 155. Rulon XL and GR 0348 have the best friction and wear properties.

Abstract: Polyaniline/SiO2 composites were prepared by the SiO2 particles whose surface character was modified by succinic acid. The composites were characterized by Fourier transform infrared (FT–IR) spectroscopy, X–ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM). The results demonstrated that the thermal stability of PANI had improved.

Abstract: Hybrid composites were prepared by incorporating oil palm fruit bunch (OPFB) fibre in the mixture of clay and polypropylene as secondary filler. OPFB and MAPP loadings were varied to investigate it effects on the performance. Tensile and impact tests were performed on the hybrid composites to evaluate their mechanical performances. Water absorption and thermal degradation tests were also conducted on the hybrid composites. Results indicated that the incorporation of OPFB in PP/PPnanoclay has decreased the thermal stability of hybrid composites. Tensile modulus of hybrid composites increased as the OPFB loading increases and further increased with the increasing of MAPP loading. Generally the tensile strength has decreased with the addition of OPFB, however slight increased was observed when the MAPP loading was increased. The impact strength has also increased with the increasing of OPFB for higher MAPP loading.