Advanced Materials Research Vols. 29-30

Abstract: We have reported that development of texture can be controlled by colloidal processing in a strong magnetic field followed by heating even for diamagnetic ceramics such as alumina, titania and so on. We demonstrate in this study that alumina/alumina laminar composites with different crystalline-oriented layer are produced by electrophoretic deposition (EPD) in a strong magnetic field. This composite was fabricated by alternately changing the angle between the directions of the magnetic and electric fields layer by layer during EPD in 12T. The grains in alternate layers are aligned differently.

Abstract: Cathodic electrophoretic deposition of bimodal alumina suspension was performed using conductive polypyrrole (Ppy) film as an electrode. The coating of the Ppy on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The relative green density of the deposits measured by Archimedes’ method was 68 %. Alumina ceramics were obtained by sintering the deposits together with the Ppy coated ceramic substrates in air.

Abstract: In the present work the behaviour of HAp extracted from pig bones at elevated temperatures up to 1000oC in O2 and CO2 atmospheres has been studied. It has been found that CO2 atmosphere arrests HAp decomposition. Chemical analysis and infrared spectroscopy reveal that no free CaO appears and no decrease of CO3 -2 concentration groups occurs in the material calcined in CO2 atmosphere. In the O2 atmosphere at elevated temperatures CaO and CO2 are emitted from the samples, although the remaining material retains the HAp structure as indicated by the X-ray diffraction.

Abstract: Alumina–zirconia composites Al2O3–20 vol. % yttria stabilized zirconia containing two types of yttria stabilized zirconia: 3mol% yttria doped ZrO2 and 8mol% yttria doped ZrO2 were consolidated very rapidly to full density by high frequency induction heating sintering (HFIHS). A comparison between 3YSZ and 8YSZ as a second phase toughening alumina has been made. Effects of sintering temperature on the mechanical properties have been studied. The consolidated samples were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The microhardness, strength and toughness of the composites are determined. The results showed that, 3YSZ is most effective as a second phase toughening alumina then 8YSZ. Al2O3-3YSZ composites with higher mechanical properties and small grain size were successfully developed at relatively low temperatures through this technique.

Abstract: Vinyl ester BisGMA [Bisphenol-A-glycidyldimethacrylate] resin has been modified by incorporating Titanium dioxide(TiO2)nanoparticles (0.5%-2% by weight). An ultrasonic mixing process was employed to disperse the particles into the resin system prior to casting and curing test specimens. From TEM investigation, it is found that the particles are nano size (5-60nm) and dispersed throughout the entire volume of the resin. Dynamic mechanical analysis was conducted for both the neat resin and nanocomposite. In dynamic mechanical analysis, nanocomposite shows increase in storage modulus (6%), and glass transition temperature (5.8%) from neat resin system. Thermogravimetric analysis shows 7.5% better thermal stability. In addition, the nanocomposite shows enhance in the stiffness by 5% in flexural loading. The Tg and flexural modulus of the nanocomposites were enhanced as the particle volume fraction was enhanced and than decreased.

Abstract: An ultrafine-grained Al-5083 alloy reinforced with 5 vol.% nano-sized β-SiC particles was fabricated with a powder cryomilling and consolidation technique. Tensile tests were conducted at temperatures from 298 to 773 K for this composite. The mechanisms for deformation and fracture of this nanostructured composite at various temperatures are discussed.

Abstract: The displacement reaction (in situ reaction) is an effective process to solve the interfacial problem between Al matrix and ceramic particles in Al alloy matrix composites. In this study, an Al alloy matrix composite powder containing nanometer was produced by using high energy ball milling, and a bulk Al alloy matrix composite reinforced with nanometer and submicrometer sized Al2O3 particles was obtained by sintering the ball milled composite powder at 950 °C for 2h. It was found that the Al2O3 particles were homogeneously distributed in the Al matrix after sintering. Some of the Si particles have lots of fine Al2O3 particles distributed homogeneously in the Al matrix. The hardness of the sintered specimen produced using as-milled composite powder is higher than that of the sintered specimen produced using as-mixed powder.

Abstract: Composites made from wood residues and biomasses, together with either conventional polymers such as polypropylene (PP) and their recyclate streams or with the new emerging biopolymers such as polylactic acid (PLA), were compounded and injection moulded. Mechanical properties and biodegradation analyses were undertaken. The addition of wood flour/sander dust (SD) and wood fibres (WF), to the PP, with suitable compatibilizer, increased the flexural and tensile modulus and strength, indicating a good bond between the fibres and matrix. The tensile and flexural strengths were decreased with the addition of wood fillers, additives and biomasses to a PLA biopolymer blend. Such biomasses and additives increased the biodegradation of the PLA blend, and some control over biodegradation rates was achievable.

Abstract: Particulate composites prepared by sintering compacts of Al2O3 and TZP powders, in air at 1500 and 1600 oC have been characterized in terms of microstructure and mechanical properties. The mechanical properties of the composites appear to be controlled by three main factors: the grain size of major phase, type of intergranular TZP, and presence of residual stress.

Abstract: Four types of yarns were made from flax sliver (Linum usitatissimum) as reinforcements in composites: (1) twist-less, (2) two-fold, (3) high-twist singles and (4) medium-twist singles yarns. Flexural, compressive and tensile properties of the epoxy composites were compared.