Advanced Materials Research Vols. 123-125

Abstract: In order to develop an effective near-field electromagnetic (EM) wave absorber, we have fabricated polymeric thin films including hollow metallic microfibers. Hydrolyzed polymer micro fibers (~2.5 ㎛) were used as a substrate material for the electroless metal plating. Nickel and subsequent Fe-Co metal layers were coated on the surface of activated polymer fibers and then heat treatment for the hollow structure as well as the densification of metallic layers was performed under the Argon atmosphere. Unlike conventional particulate or flaky metal powders, these fibers can play a significant role in elevating the magnetic property of polymer films, resulting in the increased efficiency of EM absorbing properties. In addition, their hollow structure can also lower their apparent density. SEM and EDS analysis were carried out to verify the morphology and metal compositions. Polymeric thin films containing hollow Ni/Fe-Co micro fibers were prepared to investigate the effect of metal compositions, filler distribution and heat treatment conditions on not only the near-field absorbing performance, but also magnetic properties such as permeability and magnetization. For the measurement of near-field EM absorbance in the frequency range of ~6GHz, micro strip line and network analyzer were used.

Abstract: LiFePO4 is one of the most promising cathode materials for lithium ion battery, especially those used in electrical vehicles and hybrid electrical vehicles. However, its very poor rate performance caused by its low electronic and ionic conductivity limits the wide utilization in high power lithium ion battery. Iron phosphides, such as FeP and Fe2P, were reported to have positive effect on the improvement of the rate performance. In order to improve the electrochemical properties, LiFe1+xPO4/C (x = 0-0.1) composite with various contents of iron phosphides was synthesized by adding different amount of iron source during a sol-gel process. The amount of iron phosphides increased with the increase of iron source. Electrochemical performance showed that the samples with 1% iron source in excess had better rate performance than the LiFePO4/C sample synthesized with stoichiometric iron source. However, the overall samples with excessive iron source showed relatively low specific discharge capacity. Hence, some balance between the rate capability and discharge capacity should be found and the amount of the in-situ formed iron phosphides should be optimized.

Abstract: The extruded poly ether ether ketone (PEEK) and glass fibre were used to obtain the co-woven hybrid fibre fabrics and converted into composites using compression moulding technique. The effect of shear stress and shear rate on the shear viscosity of PEEK was investigated to optimise the process conditions for converting hybrid fabrics into composites. The mechanical properties such as flexural strength and inter laminar shear strength (ILSS) as a function of number of layers of fabric have been evaluated. Low velocity (2.1 m/s) repeated drop weight impact tests were carried out on the fabricated composites at 5 and 10 J incident energy. Dielectric properties as a function of temperature and frequency have been carried out. Flammability behaviour of composites has been carried out using cone calorimeter. The data generated shows that glass-PEEK based composites are excellent potential materials for advanced structural composites.

Abstract: Calcium fluoroborate glasses doped with trivalent praseodymium ions have been prepared using melt quenching technique with the molar composition (42-x) B2O3 + 20 CaF2 + 15 CaO + 15 BaO + 8 Al2O3 + x PrF3 (x = 0.05, 0.1, 0.5, 1.0, 2.0 and 4.0). Absorption, fluorescence and lifetime spectra were recorded for the title glasses. Judd-Ofelt intensity parameters Ωt (t = 2, 4 and 6) have been determined for the measured oscillator strengths of the absorption bands by including and excluding the 3H4 → 3P2 hypersensitive transition. From the intensity parameters spontaneous emission probabilities (AR), excited state radiative lifetimes (τR) and branching ratios (βR) were calculated. Fluorescence quenching is observed in all the peaks and is explained by energy transfer mechanisms. Using the fluorescence spectra stimulated emission cross section (σe) for all emission transitions have been estimated. Energy transfer processes were also explained to emphasize the quenching of fluorescence intensity of certain emission transition. Based on the results, the utility of Pr3+ doped calcium fluoroborate glasses as laser active materials as well as wave guides in the visible region is discussed.

Abstract: Fractal carbon films deposited on copper plate by ethanol chemical vapor deposition are reported. In order to prepare fractal carbon films, iron nitrate was employed as catalyst precursor, copper plate as substrate, and ethanol as carbon source materials. The as-prepared carbon films were characterized by employing scanning electron microscopy and Raman spectroscopy. The thickness of the film was a few micrometers. According to Raman spectrum, we know the films exhibit low graphitization. According to SEM observation, we find that there are many protuberances with nanometer scale tips on the film surface. Due to direct growth on metal substrate and many nanometer scale tips, it has potential application that is fit for electron source in vacuum devices.

Abstract: In this paper, a simple and controllable method to fabricate - and -PbO is reported. Lead nitrate as precursor was dissolved in 50ml distilled water, and was heated to 80oC. Sodium chloride was added into the lead nitrate aqueous solution. During the process, -PbO deposition will be obtained when we add lead nitrate solutions with KOH pellets without chloride anion. When we add lead nitrate solutions with KOH pellets with a little chloride anion, there will produce -PbO deposition. Our results indicate that the concentration of chloride anion and temperature of reaction solution affects the crystal morphologies and modifications of lead monoxide plate precipitates from lead nitrate solution and we can selectively and controllably produce - or -PbO by this way.

Abstract: Blends of wool and moisture management fibres such as Coolmax and Finecool have been prepared to produce innovative yarns with specific functionalities. These yarns have been used to produce knitted fabrics and their performance was evaluated, including vertical and horizontal wicking. The influence of wool fibre proportion on the performance of each blend is analyzed. It is observed that the Coolmax based fabrics show the best capillarity performance, and the wool fibre based fabrics show lower water absorption performance.

Abstract: An attempt has been made in this study to modify the crumb rubber powder (CRP) surface with maleic anhydride (MA) and thereby improving its adhesion with waste polypropylene (WPP) after melt blending. The modification results in grafting of CRP onto the WPP matrix. The mechanical strength properties of the surface modified CRP-WPP blends increased. This implied improved interaction between WPP and CRP. The increase in decomposition rate as well as the decrease in viscosity under processing conditions for the blends indicates the formation of a copolymer interface between WPP and CRP as a result of CRP modification. A smooth and stable morphology was also found in case of blends of WPP with modified CRP.

Abstract: Electroactive polyurethane (EPU) containing conjugated segments of electroactive amino-capped aniline trimer (ACAT) has been successfully synthesized and characterized through Fourier-Transformation infrared and UV–visible absorption spectroscopy. Subsequently, electroactivity (i.e., redox capability) of as-prepared EPU was investigated by electrochemical cyclic voltammetry (CV) studies. It was noticed that the as-prepared EPU exhibited reversible redox capability was found to reveal better corrosion protection effect on cold-rolled steel (CRS) electrodes than that of non-electroactive polyurethane based on a series of electrochemical measurements such as corrosion potential, polarization resistance, corrosion current and electrochemical impedance spectroscopy (EIS) studies in 5 wt-% NaCl electrolyte. This significant enhancement of corrosion protection on CRS electrodes as compared to non-electroactive polyurethane might be probably ascribed to the redox catalytic property of as-prepared EPU coatings inducing the formation of passive layer of metal oxide, as evidenced by the SEM and ESCA studies.

Abstract: Polypropylene (PP) has the disadvantage of flammability and easy dripping, flame retardant was incorporated into polymer to improve the thermal and flame retardant property. Conventional flame retardant containing halogen would release toxic gases when the materials got fire and let the people died in the fire and destroy the environment. Intumenscent flame retardant consists of three key components: acid source, carbon source and blowing agent. Acid source is phosphoric acid, which can dehydrate the materials. Carbon source can form char layer to prevent further thermal degradation. The blowing agent can swell the carbon layer to avoid heat and mass transfer during material get fire. Novel intumenscent flame retardant which contains phosphorus and nitrogen was successfully prepared. FTIR, TGA, LOI and UL-94 were used to characterize the structure, flame retardant mechanism and thermal property of the composites. LOI and UL-94 data showed the composites possess excellent flame retardant property. For kinetic of thermal degradation.