Advanced Structural and Functional Materials for Protection, 2008

Volume 136

doi: 10.4028/

Paper Title Page

Authors: Ramaseshan Ramakrishnan, Ying Jun Liu, Sundarrajan Subramanian, Seeram Ramakrishna
Abstract: For ages, activated carbon has been unarguably the most preferred material for chemical warfare protective clothing by armies across the globe. Although the morphology in which it is used has changed from granular form to fiber form, there has not been much change in the chemical composition or functionality (ASZM-TEDA grade). In this paper we investigate to find out if there is a possibility of replacement of the activated carbon by other materials. Before we find the answer to this question, it is important to reason out why replacement is thought of in the first place. Activated carbon is a versatile material that brings with it several good qualities like large surface area, adsorptive nature, fire-resistant, robustness and availability of aplenty. Some of its disadvantages include heavy weight and low breathability (moist activated carbon will adsorb oxygen from the environment causing breathing difficulties). One other disadvantage which is often overlooked by the user is the disposal of the suits after usage. Activated carbon merely adsorbs the nerve and mustard agents and once they become saturated, they are classified as hazardous materials necessitating safe disposal. The used wear is normally sent back to the supplier of manufacturer where it would be essentially decontaminated by bleaching and then disposed by incineration or landfill. Thus, if there is a material that can ensure breathability is of light weight and has the capacity to decontaminate the adsorbed warfare agents in situ, it would be ideal for use in the protective clothing. In this paper novel electrospun ceramic nanostructures are introduced which are capable of reactive decontamination of nerve and mustard agents. The decontamination efficiencies of the ceramic nanofibers are presented as tested against simulants of nerve and mustard agents. Electrospinning was chosen as the fabrication method because it is a simple traditional technique that is capable of manufacturing nano sized structures in a large scale. Moreover, electrospun materials possess more activity due to their surface charge density. The contribution of nano-size scale to the reactivity of the fibers is shown. All these project the electrospun nanostructured ceramics as the best possible substitutes to activated carbon.
Authors: S.W. Du, Alfred Ling Yoong Tok, F.Y.C. Boey
Abstract: Boron carbide is one of the hardest materials known. The research on the synthesis of nano-sized boron carbide is of great importance. RF plasma synthesis of B4C nanoparticle was carried out by powder feeder using micro-sized commercial boron carbide powder as the stating material. Different plasma energy and powder feeder probe position was used to find out the optimum condition to achieve nanoparticles. Powders were collected from Chamber 1, 2 and 3. fine particles can be achieved, but the decomposition and oxidation of B4C powder during the high temperature plasma spray was detected. Boron oxide was found in the sprayed powder, and the powder was purified by washing and heat treatment. XRD, SEM and TEM was used to for characterization of the particles.
Authors: Willy C.K. Tan, J.C. Kiew, K.Y. Siow, Z.R. Sim, H.S. Poh, M.D. Taufiq
Abstract: When one cut himself, it's amazing to watch how quickly the body acts to mend the wound. Immediately, the body works to pull the skin around the cut back together. The concept of repair by bleeding of enclosed functional agents serves as the biomimetric inspiration of synthetic self repair systems. Such synthetic self repair systems are based on advancement in polymeric materials; the process of human thrombosis is the inspiration for the application of self healing fibres within the composite materials. Preliminary results based on flexural 3 point bend test on prepared samples have shown the healed hollow fibre laminate has a healed strength increase of 47.6% compared to the damaged baseline laminate. These results gave us confidence that there is a great potential to adopt such self healing mechanism on actual composite parts like in aircraft’s composite structures.
Authors: Christian N. Della, Dong Wei Shu
Abstract: Carbon nanotubes (CNT) have been shown to enhance the engineering properties of plastic fibers in ballistic-resistant garments enabling the garments to withstand very high impact forces while remaining to be lightweight. Previous study shows that by reinforcing ultra high molecular weight polyethylene (UHMWPE) fibers with a small amount of carbon nanotubes, the fibers are simultaneously toughened and strengthened. In this paper, we study the mechanical properties of carbon nanotube reinforced ultra high molecular weight polyethylene (UHMWPE) by using micromechanics-based Mori-Tanaka model. Results show that the addition of small amount of carbon nanotubes as reinforcement can substantially improve the mechanical properties of the UHMWPE fibers.
Authors: Zhi Fei Li, Guo Hua Luo, Wei Ping Zhou, Fei Wei
Abstract: Multi-walled carbon nanotube (MWNT) was filled into poly (ethylene terephthalate) (PET) matrix and MWNT/PET composite was prepared by injection molding process. The microstructure and electrical conductive property were investigated carefully. After injection molding, the electrical conductivity of injected sample decreased sharply because of the orientation of CNT due to strong shearing force. The electrical conductive network of CNT had been destroyed after orientation of CNT. Because of the difference of shearing rate between the surface and the body center during the injection molding process, a skin-core structure emerged. Near the surface, the injected sample has higher degree of orientation of CNT and higher electrical resistance.
Authors: L. Yang, H.H. Hng, T. Sun, H. Cheng, Jan Ma
Abstract: Skutterudite materials have received great attention because their promising properties for thermoelectric (TE) applications. Among the family of skutterudites, CoSb3 has been intensively investigated due to its large electrical conductivity and Seebeck coefficient. However, its thermal conductivity is too high to make it an effective TE material. Nanostructuring of CoSb3 has the desirable effects of reducing its lattice thermal conductivity as the point imperfections or grain boundaries can scatter phonons (heat carrier) more effectively than electrons (charge carrier). In this study, nanostructured CoSb3 was synthesized by solvothermal routes using CoCl2·6H2O and SbCl3 as precursors dissolved in anhydrous ethanol with the reaction temperature kept at 240°C. In addition to the CoSb3 phase, other Co-Sb compounds were also formed during the reaction process. In this paper, we investigated the effects of processing parameters, such as concentration of CoCl2·6H2O, SbCl3 and NaBH4 in ethanol and thermal duration of solvothermal synthesis, on the yield of CoSb3 phase.
Authors: N.T. Chua, J. Wang, Jan Ma
Abstract: Lead-based piezoceramic, such as lead zirconate titanate (PZT), is widely used because it has excellent piezoelectric properties near the morphotropic phase boundary (MPB). However, because of environmental issues associated with lead, the development of lead-free piezoceramics has attracted much attention recently. Solid solution of (K,Na)NbO3 (KNN), (K,Na)TaO3 (KNT) and LiNbO3 (LN) is one of the leading candidates. An MPB was formed at composition [(K0.5Na0.5)0.97Li0.03](Nb0.8Ta0.2)O3(KNN-KNT-L0.03N). Its piezoelectric response has been shown to be comparable to that of PZT system. However, complex texturing process is required to achieve the desired property. In this project, we investigated the KNN-KNT-LN system using conventional solid state reaction. The effects of increasing lithium, sintering process and the addition of CuO on the sample structure and electrical properties were studied. Remanent polarization of 28.39 μC/cm 2 was observed for the 0.1 wt% CuO added ceramic, which was sintered under pressureless condition.
Authors: Z.H. Du, T.S. Zhang, H.M. Shang, X.L. Chen, Jan Ma
Abstract: PLZT9/65/35 thick films were prepared from the solution containing PVP360 (polyvinylpyrrolidone, with average molecular weight of 360000). With the solutions, the critical thickness of a single PLZT layer could increase to ~624nm compared with 77nm-thick films prepared without PVP360. Furthermore, by adding 20~35% excess of Pb to the precursor solutions, the nano-porous rosette-like structures and a small amount of pyrochlore remnant, which were found very common in the PVP-modified films, could be eliminated. 35% Pb excess was also found to initiate liquid-phase sintering, leading to dense and crack-free films. The effect of Pb excess on the rosette removal and densification behavior of the films was discussed. Moreover, the optical and electrical properties of the PLZT films with 35% Pb excess were also studied.
Authors: H. Cheng, H.H. Hng, Jan Ma
Abstract: Thermoelectric (TE) materials are attracting renewed attention for clean energy conversion. Reducing the dimension of materials to 2D/1D (e.g. thin film and nanowire) is one major approach to achieve high figure of merit (ZT) in the existing TE materials system. Electrodeposition has been widely used in fabricating various low dimensional TE materials. However, electrodeposition behavior of CoSb3 skutterudites is rarely reported. In this work, we report the co-deposition behavior of cobalt and antimony in citric based solutions by electrodeposition. The effects of deposition potential and concentration of cobalt and antimony containing precursors were studied. The focus of the study will be on the crystalline properties and chemical composition of the deposited films.

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