Key Engineering Materials Vol. 636

Abstract: Simultaneous determination of Pb²⁺ and Co²⁺ without separation has been successfully achieved by a bicolor quantumn dots mixture. This method takes advantage of the different degrees of the fluorescence quenching effects of Pb²⁺ and Co²⁺ to the bio-color quantum dots. Chemometrical approaches were applied to assist the discrimination and detection process. The construction of the multivariate calibration models, based on partial least squares (PLS), orthogonal projections to latent structures least squares (O-PLS) and kenel based orthogonal projections to latent structures (K-OPLS), allowed the simultaneous determination of Pb²⁺ (in the concentration range of 0-120 mM) and Co²⁺ (0-300 mM). The optimal number of factors in PLS and the optimal number of orthogonal components in O-PLS and K-OPLS were carefully selected. A comparison of prediction performances between these results was performed by relative prediction errors, square of the correlation coefficient and root mean squares error of prediction.

Abstract: Considering that nanosized LaB₆ has unique optical properties and ITO has been widely applied for low-emission window glass, LaB₆/ITO composite films were designed and prepared on SiO₂ glass substrates by DC magnetron sputtering method in this paper. AFM and HRTEM methods were used for microstructure evolution analysis, and their IR and UV spectra were measured. Results proved that dense LaB₆/ITO films with amorphous structure were deposited on the substrate with strong interface bonding. Crystallizing occurred during annealing of amorphous films, and the nanosized grains formed. Compared with the as-deposited films, the annealed films showed improved optical properties. Generally, the glass with the annealed film was available with more than 80% visible light transmittance, and good reflectance on UV light range.

Abstract: To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4 V class lithium ion batteries, spinel were successfully prepared using the sol-gel method. The dependence of the physicochemical properties of the spinel LiCr_xMn_2-xO₄ (x=0,0.05,0.1,0.2,0.3,0.4) powders powder has been extensively investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), charge-discharge test and electrochemical impedance spectroscopy (EIS). The results show that as Mn is replaced by Cr, the initial capacity decreases, but the cycling performance improves due to stabilization of spinel structure. Of all, the LiCr_0.2Mn_1.8O₄ has best electrochemical performance, 107.6 mAhg^-1 discharge capacity, 96.1% of the retention after 50 cycles.

Abstract: Dense BaCe_1-xMo_xO_3-δ ceramics were fabricated by sintering at 1450°C for 7h. All samples were characterized by XRD, SEM. All samples were orthorhombic structure. Electrical conductivities of all samples were measured by AC impedance. Electrical conductivity of Mo-doped samples reaches maximum value when doping content of Mo is 5%, which is one order of magnitude greater than that of BaCeO₃. Chemical stability of BaCe_1-xMo_xO_3-δ samples was investigated by immersing samples into the boiling water for 12h. The doping of Mo can partially inhibit the reaction between BaCeO₃ and H₂O.

Abstract: The mechanic properties mainly the room temperature bending strength and the creep of the Al₂O₃ ceramic specimens which were prepared by cold isostatic pressing and had undergone different thermal histories have been measured and compared. The results suggest that the bending strength of the ceramic increases after high temperature soaking. The ceramic can withstand cyclic rapid cooling with an initial temperature of 200 °C. The sample has shown a very good dimensional stability after a long service time (50h) at 1550 °C.

Abstract: The modified sands compared with plain quartz sands possessed larger surface area and higher specific affinity towards heavy metal ions in waste water. Methods to synthesize modified sands have been briefly reviewed. Emphasis has been on the adsorption mechanisms and the characteristics of the modifying coatings which influence the absorbents’ efficiency and speciality.

Abstract: The crystallization activation energies and crystalline phases of lithium-iron-phosphate (LIP) glasses with alkali and alkali-earth metal oxides have been studied and compared. The results indicate that the alkali and alkali-earth metal oxides reduce the glass crystallization. Moreover, the alkali metal oxides result in the changes in the crystalline phase, while the alkali-earth metal oxides make the glass crystallization more sensitive to the thermal treatment conditions.

Abstract: Microencapsulated E-51 epoxy resin healing agent and phthalic anhydride latent curing agent were incorporated into E-44 epoxy matrix to prepare self-healing epoxy composites. When cracks were initiated or propagated in the composites, the microcapsules would be damaged and the healing agent released. As a result, the crack plane was healed through curing reaction of the released epoxy latent curing agent. In the paper, PUF/E-51 microcapsules were prepared by in-situ polymerization. The mechanical properties of the epoxy composites filled with the self-healing system were evaluated. The impact strength and self-healing efficiency of the composites are measured using a Charpy Impact Tester. Both the virgin and healed impact strength depends strongly on the concentration of microcapsules added into the epoxy matrix. Fracture of the neat epoxy is brittle, exhibiting a mirror fracture surface. Addition of PUF/E-51 microcapsules decreases the impact strength and induces a change in the fracture plane morphology to hackle markings. In the case of 8.0 wt% microcapsules and 3.0 wt% latent hardener, the self-healing epoxy exhibited 81.5% recovery of its original fracture toughness.

Abstract: The polytetrafluoroethylene (PTFE) matrix composites reinforced by polyphenylene sulfide (PPS) fiber and poly-p-phenelenferephthalamide (PPTA) fiber were prepared by the processes of mechanical blending, compression molding and sintering. The fractured surfaces of impacting specimens were examined by scanning electron microscopy (SEM). The tribological properties of the composites were investigated on M-2000 wear tester at dry friction condition. The wear mechanism was also discussed and the wear surfaces were examined by SEM. The result indicates that fibers which diffused in PTFE matrix wind with PTFE molecule chain, and then form grid structure. The load-bearing capacity of composites can be obviously enhanced and the trend of block fragmentation’s slide is inhibited, so that the tribological properties are improved markedly. The friction coefficient of composites is reduced by adding graphite which also prevents fibers leaving. The tribological properties of PTFE matrix composites is greatly improved because of the synergistic effect between fibers and graphite, which has good prospect for low loading application.

Abstract: Using methyl triethoxysilane, tetrabutyl titanate and ethyl acetoacetate as raw materials, the Si-Ti polymer was synthesized to prepare Si-Ti polymer/montmorillonite nanocomposites. The effects of OMMT content on the impact properties and barrier performance of nanocomposites were investigated. The results show that with the increasing of OMMT content, the impact properties of nanocomposites are improved significantly. The impact strength of nanocomposite with 10wt% OMMT is about twice times than that without OMMT. The gas barrier properties of nanocomposites are also improved significantly. Compared with pure Si-Ti polymer, the water absorption of nanocomposite with 6wt% OMMT is decreased by 60.3%.