Multi-Functional Materials and Structures II

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Authors: Dong Xu, Xiao Nong Cheng, Ming Song Wang, Li Yi Shi
Abstract: La2O3-doped ZnO-Bi2O3-based varistor ceramics were obtained by a solid reaction route, and the microstructure and electrical properties of the varistor ceramics were studied in this paper. The results showed with addition of 0-1.00mol% La2O3, La2O3-doped ZnO-based varistor ceramics were prepared in this paper with the voltage gradient of 77-503V/mm, the nonlinear coefficient of 2.4-36.8, and the leakage current of 0.09-494μA. The results also showed with addition of 0.08mol% La2O3, La2O3-doped ZnO-based varistor ceramics exhibit comparatively ideal comprehensive electrical properties. Such as the threshold voltage was 320V/mm, the nonlinear coefficient was 36.8 and the leakage current was 0.29μA. The doping of La2O3 affects the form and decomposition of the pyrochlore.
Authors: Hai Tang Wu, Wei Gang Zhang
Abstract: ZrB2-SiC-BN ultrahigh-temperature ceramic (UHTC) was fabricated by hot-pressing at 1800°C under 23MPa pressure of argon. Compared to ZrB2-SiC, the flexural strength of ZrB2-SiC-BN composite material was enhanced by adding 30% BN, and the fracture toughness showed a slight decrease, while the hardness decreased sharply. The addition of 30% BN also noticeably improved the machinability of the composites. Furthermore, ablation resistance tests were carried out using an oxyacetylene torch under subsonic conditions. Results indicated that a coherent compact scale of zirconium silicate was formed, which acted as an effective barrier against the inward diffusion of oxygen.
Authors: Shao Qing Wang, Hua Shun Yu, Zhen Ya Zhang, Guang Hui Min, Hui Yu
Abstract: In this study, an ultrastrength Al-10Zn-3.2Mg-2.3Cu alloy was fabricated by powder hot extrusion technique. The microstructures of powder, extruded and subsequently heat treated rods were investigated by means of X-ray diffractometer (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) for compositional analysis. During extrusion, more MgZn2 compounds were precipitated from the supersaturated Al matrix and observed on the grain boundaries and in the grain interiors. The microstructure of as-extruded alloy is composed of Al matrix and MgZn2 phases in different shapes. After solution treating, the MgZn2 phases were mostly dissolved into matrix and the major constituent are Al7Cu2Fe phase as well as oxides. The mean size of grains was controlled to 2.5μm, and the major precipitates were GP zones and/or η’(MgZn2) phases in the Al matrix after peak-aging (T6) treatment (120°C for 20h). The ultimate tensile strength (σb), yield strength (σ0.2) and elongation (δ) are 745Mpa, 690MPa and 9.0%, respectively.
Authors: Xue Ma, Xiao Yao, Su Dong Hua
Abstract: The study provides a novel way for the utilization of coal fly ash, and enriches the sintering mechanism in preparation of low-cost, high performance mullite based ceramic. The phase evolution, microstructure, densification behavior and flexural strength as a function of the sintering temperatures, were investigated by XRD, SEM and evaluated by density, open porosity and shrinkage and three point bending method, respectively. Secondary mullite nucleates from the dissolution of alumina in transient liquid phase at 1300°C. Above 1400°C, mullite content increases and the densification is promoted with increasing temperature. Fast densification takes place and high flexural strength of 149MPa is achieved at 1600°C.
Authors: De Gao Zhong, Bing Teng, Ming Li, Qing Guo Wang, Yan Shuai Zhao, Fei You, Hui Xu, Shi Ming Zhang
Abstract: A kind of in-situ crystal growth observation system for solution temperature reduction method was designed. The growth surface morphology of KDP crystal was observed by this system. Dislocation hillocks with elliptical shape were clearly distinguished on the {100} face. The dynamics process of morphology evolvement on growth surface of KDP crystals was recorded and analyzed. The growth velocity of the step trains generated from dislocation hillocks was about ~10-4.
Authors: Poonsub Threepopnatkul, Chanin Kulsetthanchalee, K. Bunmee, N. Kliaklom, W. Roddouyboon
Abstract: This research was to study the related mechanical and thermal properties of recycled polypropylene from post consumer containers reinforced with coir fiber. Surface of coir fiber was treated with sodium hydroxide to remove lignin and hemicelluloses and likely to improve the interfacial adhesion in the composites. The composites of treated coir fiber and recycled polypropylene were prepared by varying the coir fiber contents at 5%, 10% and 20% by weight using a twin screw extruder. The thermal properties were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC). The results from TGA showed that thermal stability of the composites was lower than that of recycled polypropylene resin and thermal stability decreased with increasing coir fiber content. From DSC results, it indicated that the crystallinity of treated coir fiber composites increased as a function of fiber content. The mechanical properties of injection-molded samples were studied by universal testing machine. The treated coir fiber composites produced enhanced mechanical properties. The tensile strength, tensile modulus and impact strength of modified coir fiber/recycled polypropylene composites increased as a function of coir fiber content.
Authors: Chee Kiong Soh, Yee Yan Lim
Abstract: In this paper, the feasibility of damage detection and characterization using the EMI technique on high cycles fatigue induced damage is investigated. Cyclic tensile load is applied on a lab sized aluminium beam up to failure. Piezo-impedance transducer in the form of PZT patch (lead zirconate titanate) is surface bonded on the specimen for crack detection. Progressive shift in admittance signatures measured by the PZT patch corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression.
Authors: Zhi Hong Ji, Yan Bin Jiang, Hao Li, Li Ye, Wei Jian Han, Tong Zhao
Abstract: A Pt-containing ordered mesoporous carbon with a high specific surface area was synthesized through evaporation-induced multi-constituent co-assembly method, wherein soluble resol polymer is used as the carbon precursor, silicate oligomers as the inorganic precursor, triblock copolymer as the template, and H2PtCl6•6H2O as the Pt precursor. After thermopolymerization, the template was removed by calcinations, and silica was removed by NaOH solutions. The resultant sample was characterized by X-ray diffraction, nitrogen sorption and transmission electron microscopy. The results showed that the carbon material exhibited highly ordered mesoporous structure, with a high specific surface area of 1560 m2/g, and the pore size distributions of the sample are very narrow, centering at around 6 nm; and the platinum particles with sizes of less than 8 nm were highly distributed in the carbon matrix. The high specific surface area may be ascribed to plenty of small pores inside carbon walls caused by the removal of silica from the composites. Interaction between the Pt4+ and the resin caused the Pt species to be incorporated into the framework of the resin, which was self-assembled into an ordering structure under the direction of the surfactant. After being subjected to pyrolysis at a high temperature, the Pt4+ ions were gradually reduced to form Pt nanoparticles, which were strongly imbedded in the carbon substrate and thereby thermally stable. The removal of silica may result in the exposure of Pt nanoparticles, which render Pt nanoparticles to contact easily with reactant molecules.
Authors: Li Ye, Wei Jian Han, Zhi Hong Ji, Ji Dong Hu, Tong Zhao
Abstract: A series monolithic silica aerogels modified by amino-substituted organic groups were synthesized by sol-gel processing of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) mixtures, followed by drying of the wet gels with supercritical carbon dioxide (SCCO2). The molar ratios of EtOH/TEOS and DMF/ (TEOS+APTES) were fixed at 5 and 0.4, respectively, and APTES/TEOS ratio was varied between 1:9 and 3:7. HCl was added to obtain a narrow pore distribution, and the ratio of HCl/ (TEOS+APTES) was varied between 0 and 0.004. When APTES/TEOS ratio was kept at constant, gelling of the precursor mixtures was accelerated with an increasing ratio of HCl/ (TEOS+APTES). The physical properties of the aerogels have been investigated in detail by the bulk density, porosity, nitrogen sorption measurements and scanning electron microscopic (SEM). The results showed that adding HCl did increase the specific surface areas of the aerogels and make the aerogels have narrow pore distributions, but also resulted in some increase in bulk densities and decrease in porosities. The bulk density of the aerogels was 0.13-0.32 g/cm3, the corresponding porosity between 80% and 92%. Microscopically, the framework of the functional aerogels consists of spherical secondary nano-particles, which stack into grape-like aggregate and interconnect in different directions into a network. The specific surface area of the aerogels were in the range of 362-1044 m2/g, and uniform pore distribution aerogels were obtained when the molar ratio of APTES/ (TEOS+APTES)/HCl at 1/10/0.002 and 1/10/0.004.
Authors: Shan Shan Li, Fu Tian Liu, Qun Wang, Xiu Xiu Chen, Ping Yang
Abstract: Cu2+-doped ZnSe quantum dots (ZnSe:Cu) were prepared via a green and simple route, namely the chemical coprecipitation method. Under 365 nm UV excitation, green emission is observed. X-ray powder diffraction (XRD) shows that ZnSe:Cu nanoparticle is cubic zinc blende structure; the transmission electron microscopy (TEM) exhibits that the average diameter of ZnSe:Cu nanocrystals is less than 10 nm. UV-vis spectrophotometer and fluorescence spectrophotometer indicate that ZnSe:Cu nanocrystals have good fluorescence effects.

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