Materials Science Forum Vol. 848

Abstract: Adulteration of polycarbonate (PC) drinking bottles with postconsumer recycled PC materials was considerably difficult to identify due to similar chemical compositions and minute differences between virgin and recycled PC materials. In the present study, UV/Vis spectroscopy coupled with GC-MS analysis was carried out to identify the adulteration with recycled materials in PC drinking bottles. The minimum adulterating level which could be detected was 20 %. This strategy represents a rapid and promising analytical method for screening the adulteration of PC drinking bottles with postconsumer recycled plastics.

Abstract: A new kind of structural damping composites was prepared by interleaving polyamide nonwoven fabrics (PNF) between the carbon fiber reinforced epoxy composite laminates. The damping behaviors of the composites made were experimentally investigated using cantilever beam test and dynamic mechanical analysis. The damping ratios of the nonwoven fabrics interleaved composites were compared with the ones of non-interleaved composites. In addition, the interlaminar shear strength and flexible modulus of the composites were also investigated, as well as the composite compression after impact (CAI), Mode I and Mode II interlaminar fracture toughness (G_IC and G_IIC), in order to evaluate the influence of the polyamide nonwoven fabric layers on the composite mechanical properties. It has been observed that the interleaved polyamide nonwoven fabric layers greatly improved the composite damping loss factors, and the composites containing 7 layers of PNF showed the best damping behavior. Meanwhile, the addition of PNF showed a negligible influence on the composite flexible strength and modulus and interlaminar shear strength. Most importantly, the CAI, G_IC and G_IIC tests indicated that the composite interlaminar toughness and impact resistance were significantly improved by the interleaved PNF. Finally, the reinforcing mechanism of this kind of composites is discussed.

Abstract: Laminated Ti-TiBw/Ti composites behave a moderate loading capacity and high fracture ductility with non-castropic failure stage under three-point bending test. Fracture characteristics of laminated composites reveal many extrinsic toughening behaviors, such as, interfacial delamination, bucking and crack deflection, and the interfacial delamination is attributed to the weak bonding strength. Many strengthening and toughening mechanisms are presented in the TiBw/Ti composite layer, such as de-bonding effects of TiB whiskers, multi-fracture of TiB whiskers, crack trapping effect and crack bridging effect.

Abstract: Energy harvesting from ambient environment vibration is a potential method to supply the low-power consumption devices. This paper demonstrates a new method to proceed energy harvesting using a piezoceramic. Both the mechanical and electrical excitations (hybrid stimulation) have been exerted on a piezoceramic. Current was measured though a current amplifier to calculate the induced polarization. By comparing the hybrid stimulation and the pure mechanical one, it can be found that the hybrid stimulation method enable to amplifier the harvested energy, which is promising to be used in energy harvesting and sensor applications.

Abstract: BaTiO₃/La₂O₃ nanopowders were synthesized by a low-temperature soft chemical method, and then the BaTiO₃/La₂O₃ composite ceramics were prepared. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the prepared powders and ceramics. And the dielectric properties of the BaTiO₃/La₂O₃ composite ceramics were studied. The results revealed that some of La³⁺ ions dissolved into the lattice of BaTiO₃ at Ba-site and the rest remained at grain boundaries in oxide form of La₂O₃. With the content of La₂O₃ increasing, Curie peak of the BaTiO₃/La₂O₃ composite ceramics moved to a lower temperature, and the dielectric loss of the BaTiO₃/La₂O₃ composite ceramics decreased significantly, while the dielectric tunability still kept a relatively high value. The dielectric permittivity and dielectric loss of BaTiO₃/La₂O₃ composite with 10 at.% La₂O₃ was 227 and 0.0026 at 25 ^oC and 10 kHz, meanwhile the tunability was up to 17.4% under the electric field of 20 kV/cm.

Abstract: In this study, cristobalite was used as the addition to prepare silica based ceramic cores, and then the effect of cristobalite content on the mechanical and chemical properties was investigated. The increasing of pre-added cristobalite content resulted in more crystallized cristobalite in the sintered samples and the variation of the linear shrinkage and mechanical properties. When pre-added cristobalite content was 6.0 wt%, the shrinkage of ceramic core was 0.42%, the creep at 1540°C for 30 min was 0.10 mm, and the flexural strength at room temperature and at 1550°C were 25.2 MPa and 28.7 MPa, respectively, which meets the need of ceramic cores of hollow turbine blades.

Abstract: Oxide ceramic is a kind of environmental friendly materials, which has attracted more and more interests for its bunch of advantages such as sound chemical, thermal stability, simple synthetic process, cheap price, harmless and safety. Therefore, Oxide ceramic will be a promising material in the future. In this work, polycrystalline samples of CuAlO₂ were prepared by a solid state reaction method. The mixture of pure CuO and Al₂O₃ powders was firstly pressed under the pressure of 60 MPa, and then 200 MPa to prepare pellets of 5 mm thick and 10 mm in diameter. The green compacts were sintered at five different temperatures (1273 K, 1323 K, 1373 K, 1423 K, 1473 K) for various holding times (5 h, 10 h and 15 h) in the air and then the furnace cooled. The crystalline and microstructures of the sintered CuAlO₂ bodies were detected by XRD and SEM. The properties of density, thermal conductivity were also investigated in detail. The experimental results show that CuAlO₂ bodies were rhombohedral, belonging to R3m space group. It is found that the density and the thermal conductivity of CuAlO₂ ceramics were significantly dependent on the sintering temperatures. The density and thermal conductivity increased with increasing the sintering temperatures. The thermal conductivity of samples sintered at 1273 and 1473 K with the same holding time (10 h) were 9.70 and 35.53 W/mk at the room temperature, 3.41 and 8.29 W/mk at 1100 K, respectively.

Abstract: Fused silica-based ceramics are often used as sacrificial cores in investment castings to produce hollow, precise, and complex-shaped blades. In this work, the content of mullite fiber and its effects on mechanical and dimension behavior of silica-based ceramic cores were investigated. In order to simulate the single crystal blades casting process, the sintered samples were also heated up to 1540°C and kept for 0.5 h. Flexural strength test at 1540°Cwas carried out for the samples. The shrinkage, creep behavior and erode behavior were characterized. The results showed that in the premise of maintaining strength of materials, mullite fiber could decrease significantly the shrinkage. Many gains appeared on the surface of fiber after creep test of the core samples at 1540°C.

Abstract: SiC porous ceramics were prepared by oxidation-bonding technique using SiC powder as main material and carbon black as pore former. The phase composition, surface morphologies, bulk densities, porosities, mass and linear changes of the samples were also investigated. The physical-chemical properties have been analyzed. The results indicate that the oxidation reaction of SiC ceramics was accelerated with the increase of temperatures. It displays undamaged surface after 1400°C treatment, as well as fused surface after 1450°C treatment. The latter is attributed to violent oxidation reaction of SiC. As C contents increase, the porosities of the samples increase and the infiltration of O₂ into interior of SiC ceramics was facilitated. The internal network microstructure is controlled by O₂ infiltration and SiO₂ coating.

Abstract: In order to improve the efficiency of solid-liquid separation, dewatering and filtration, as well as to reduce the loss of concentrate and production costs, silicon carbide porous ceramic filter plate with high porosity and high bending strength was prepared by using the particles close packing method adding proper amount of adhesives and sintering additives at 1450 ^oC. The porosity of the fired samples was evaluated by Archimedes law. The morphology and properties of the samples were characterized. Effects of SiC grains gradation, pore formers content, molding pressure and soaking time on the bending strength and porosity of ceramic filter plate was studied. SiC porous ceramic composition was prepared by mixing 90wt% and 10wt% SiC powders with D₅₀ of 200.7 μm and 312.6 μm, respectively, 4% walnut powder as pore former and 5% Kaolin clay as binder. The sample was pressured at 8 MPa and fired at 1450 ^oC for 30 min, and endowed with 6-8 μm of the average pore diameter, 41% of the porosity and 11 MPa of the bending strength, respectively, which is especially not easy to plug hole. The obtained results can be applied in ceramic filter core parts for heavy metal concentration.