Advanced Materials Research Vol. 1058

Abstract: An aqueous deposited polymerization method to fabricate PAN based composite sheet films after multiwall carbon nanotubes (CNTs) modified with concentrated nitric acid was presented. This paper disscussed the effect of CNTs modified with concentrated nitric acid on the thermal and the crystal properties of PAN based composite sheet films. The results indicated that the normal process of multiwall CNTs treated with concentrated nitric acid can change the crystallization properties of polymers but not change the basic structure of polymers. The crystallinity of pure PAN at 2θ≈17° was strengthened after preoxidation. With the addition of CNTs, the crystallization peak of composite sheet films at 2θ≈17° became weaker, and a sharp crystallization peak appeared at 2θ≈25°, as showed that the composite sheet films could carry out the cyclization at low preoxidation temperature. During their process of preoxidation and carbonization, modified CNTs could promote the formation of cyclization and cause the formation of aromatic ring structure, and the cyclization efficiency increased from 20.24% to 70.41%. TEM analysis indicated that the modified CNTs existed in the composite sheet films in two forms: the dispersion and reunite of the single state. The test results of the surface resistivity of the composite sheet films showed that when the CNT content was lower, the surface resistivity of film was very large. When the CNT content was 5% and 10%, the surface resistivity of the film was 5.74 MΩ and 0.15 MΩ, respectively. It was obvious that once the continuous conductive network of CNTs was formed, the surface resistivity of composite sheet films hardly changed.

Abstract: Recently, noble metal nanoparticles (Au or Ag NPs) decorated graphene (GE) sheets are used as good surface-enhanced Raman scattering (SERS) substrates for detection of molecules. Ultrathin GE film covered by Ag NPs has been designed for the SERS substrate in this paper. The films were prepared firstly by dip-coating method with graphene oxide (GO) and AgNO₃ or Ag NPs colloid as raw materials and secondly reduced by thermal annealing at 600 °C in H₂/Ar atmosphere. The structure and SERS activity of the obtained films have been investigated in detail. Results indicated that Ag NPs can be decorated on graphene sheets through the electrostatic adsorption between the GO sheets and positively charged Ag⁺ or Ag NPs. Compared with the film obtained with AgNO₃, Ag NPs/GE film prepared with Ag NPs colloid showed the higher SERS sensitivity with rhodamine 6G (R6G) as the probing molecules, the enhanced factor for 1×10^-5 M of R6G adsorbed on the surface of Ag NPs/GE substrate is about 9.1×10⁷.

Abstract: Materials used on exterior spacecraft surfaces are subjected to many environmental threats which can cause degradation, atomic oxygen is one of the most threats. We prepared organic silicon atomic-oxygen-protection film using method of polymerization. This paper presented the effects on the film structure and its durability of the preparation processing, and analyzed the polymerization theory, the film structure and composition of the film. At last, we tested the film in our ground based atomic oxygen simulator, and indicated that the film worked well.

Abstract: Li_1+xMn_2-x-yAl_yO₄cathode materials were prepared via co-precipitation route; and the crystalline structures, morphologies and electrochemical performance of the prepared powder samples are characterized by XRD, SEM, Galvanostatic charge–discharge cycling. Experimental results show that Li, Al co-substitution significantly enforces the crystalline structures and improves the cycle stability of LiMn₂O₄ materials, and Li_1.1Mn_1.805Al_0.095O₄ exhibits promising electrochemical performance.

Abstract: Coprecipitation method is adopted to prepare LiNi0.8Co0.1Mn0.1O2, to discuss the factors of affecting electrochemical properties and structure at lithium ion battery cathode material LiNi0.8Co0.1Mn0.1O2. In order to improve the electrochemical properties of materials, LiNi0.8Co0.1Mn0.1O2 materials were modified by doping the cation of Li or Mg or Al. Through the charge-discharge tests in the range of 2.5~4.3V, the result show that doped Mg samples with a discharge capacity and high efficiency as well as the lowest capacity loss, the initial discharge capacity is 205.9mA.h/g, after 20 cycles the discharge capacity reached 142.4mA.h/g.

Abstract: A spinel-structured LiNi_0.5-xCr_2xMn_1.5-xO₄(x=0, 0.05) were prepared via co-precipitation routes. The experiment results from XRD, SEM and electrochemical analyses show that the substitutions of Ni and Cr for Mn in LiMn₂O₄can not prevent Mn²⁺from being oxidized into Mn³⁺ in solution process, however,Mn²⁺ oxidation does not change their final crystal structures of spinel phase, but do influence the Li/Ni²⁺ cation mixing and Mn³⁺occurrence in lattice. After substitution the first charge and discharge capacities decrease but its cycleability is improved significantly, especially for the Ni and Cr co-substitution

Abstract: A LiNi_0.4Co_0.2Mn_0.4O₂ material was prepared via the co-precipitation in solution and ensuing solid reaction of the prepared precursors with LiOH.H₂O, investigating the influence of solid reaction temperature on the cation mixing and electrochemical performance of the materials as a cathode. The results show that Li⁺/Ni²⁺ cation mixing decreases with the increase of calcination temperature in the range of 700-900°C, and the lower degree of cation mixing can improve 2D layered structure and make the material more stable. The discharge capacity and the capacity retention rate of the material is strongly impacted by the reaction temperature.The powders calcined at 900°C show the best electrochemical performance and the initial discharge capacity is 163.1mA·h/g, after 40 cycles, the capacity retention rate is 93.9%.

Abstract: LiNi_0.8Co_0.15Al_0.05O₂, as the cathode materials for lithium ion battery, were prepared from the precursors, Ni_0.8Co_0.15Al_0.05(OH)₂ which were synthesized by chemical co-precipitation method. LiNi_0.8Co_0.15Al_0.05O₂ particles are modified with AlF₃ and AlPO₄. Even though the initial discharge capacity of the coated LiNi_0.8Co_0.15Al_0.05O₂ was decreased that of the pristine material, the capacity retention and the thermal stability, in a highly oxidized state are both significantly improved. This effect is attributed to the thin coating layer protecting the oxidized cathode particles from being attacked by hydrogen fluoride in the electrolyte. The cycling behavior of the AlF₃-coated LiNi_0.8Co_0.15Al_0.05O₂ is quite stable showing good capacity retention (96.3% of its initial capacity after 30 cycles).

Abstract: Purpose To investigate the cariostatic effect of six restorative materials in vitro. Method Enamel blocks of bovine incisors were restored with six restorative materials (a conventional GIC, FujiIILC, Compoglass F, BeautifilII,Charisma and an experimental fluoride releasing resin composite) respectively with a gap of 270μm in width between each filling material and enamel. Then all restorations were immersed in a partially saturated acidic buffer solution at 37C for 3days. The surface enamel microhardness of the enamel blocks were measured before and after demineralization and the depth of enamel demineralization was measured using polarization microscope for each restoration.Results Enamel surface hardness of all restorations demonstrated significant reduced after demineralization ( p<0.05), and the order of hardness reduction is as follows: Charisma >BeautifilII≈Compoglass F≈Experimental Resin>FujiIILC>GIC ( p> 0.05). The order of the depth of enamel demineralization along the surface and the interface near the gap for the 5 materials is as follows: Charisma >BeautifilII≈Compoglass F ≈Experimental Resin>FujiIILC>GIC (P > 0.05). Conclusion The new fluoride releasing and recharging composite resin has the ability to prevent recurrent caries around the restoration and its ability is comparable to compomer materials.

Abstract: The objectives of this in vitro study is to display the overall planar morphology of leakage at resin-dentin interface using ammoniacal silver nitrate as tracer. Twelve human extracted third molars were used and the occlusal enamel of each tooth was removed. All teeth were divided into four groups of three teeth each and bonded with one of four adhesives (Prime&Bond NT, Adper Prompt, Xeno III, Clearfil S³ Bond) and then a composite resin crown was built up. After storage in water (37°C) for 24 h, all teeth were vertically serially sectioned into stick-shaped specimens the bond interfaces. All specimens were immersed in ammoniacal silver nitrate solution, followed by developing solution and subjected to tensile test and the fracture surface were observed with a SEM. The overall planar morphology of leakage at resin-dentin interface appeared to be various tree-like figures, with character of stem-like portion in the periphery and extending from the periphery to the center of the fractured surface and stretching out a lot of branches. Prim&bond NT presented a couple of big tree-like silver deposition extending to center besides many short tree-like figures located along the periphery. Adper Prompt showed short tree-like figures with many branches. Xeno III displayed tree-like figures with thinner stem portion and more branches. Clearfil S³ Bond presented many short shrub-like figures with fewer branches.