Papers by Author: Iskandar Idris Yaacob

Abstract: Polyethylene (PE) film coated with polyurethane/nanosilica composite with varying composition were prepared and then exposed to ultraviolet radiation for accelerated weathering studies. The chemical and physical changes on nanocomposite coated PE film induced by UV exposure were studied by monitoring the changes in tensile strength, tensile modulus, elongation, carbonyl index, and visible light transmission. The effect of polyurethane/nanosilica composite coating on the durability and optical properties of polyethylene substrate was determined after 200 hrs and 500 hrs of ultraviolet exposure. There is no significant change was observed on visible light transmission for nanocomposite coated PE film after 500 hrs UV weathering. The mechanical properties of coated and uncoated PE were tremendously affected by UV exposure. PE coated with 4 µm of nanocomposite containing 6 wt% nanosilica showed less tensile properties deterioration compared to uncoated PE film after UV weathering. The surface protective coating of polyurethane/nanosilica composite with 6 wt% nanosilica content reduced the photodegradation rate of PE due to its excellent thermal stability compared to PE.

Abstract: Intermetallic nanocomposites of nickel aluminide (Ni3Al) alloy and nanosized zirconia (ZrO2) were fabricated using combined powder metallurgy technique and reaction synthesis. Nanosized zirconia as dispersed phase at 2 and 5 weight percent were pre-mixed with nickel, aluminum powders and other alloying elements in a planetary ball mill for 18 hours at 175 rpm to achieve mechanical alloying effect. The mixture was then compacted using a hydraulic press at 400MPa for 15 minutes. Sintering was done under inert condition (flowing Argon gas) in a tube furnace at 850oC with 3 hours holding time. The saturation magnetization (Ms) values of nickel aluminide nanocomposites containing 2wt% ZrO2 (ICZ2) and 5wt% ZrO2 (ICZ5) were 7.94 and 3.65 emu/g respectively. Reduced elastic modulus (Er) for ICZ5 was lower than ICZ2. Isothermal oxidation/sulfidation test in 1%SO2/air gas mixture at 800 and 1000oC were performed using a thermogravimetric analyzer (TGA) for up to 24 hours duration. The isothermal kinetic results for ICZ2 and ICZ5 are parabolic indicating rate limiting step. Reaction rates increased with increasing temperature. At this low concentration of sulfur, the test specimen only exhibited adsorption of sulfur in the vicinity of the surface region and no sulfide phase was observed.

Abstract: Nickel-iron nanocrystalline alloy films were prepared on copper substrates by electrochemical deposition at various current densities of 6, 9.7, 11.5 and 15.2 A dm-2. X-ray diffraction measurements confirmed that all nickel-iron alloy films formed have face-centered cubic structure. The structural parameters such as the lattice constant, crystallite size, microstrain and dislocation density were determined for the nickel-iron alloy films. The crystallite size of the films reduced from 17 to 12.9 nm when the current densities were decreased. The reduction in crystallite size increased the dislocation density. Magnetic property measurements using alternating gradient magnetometer indicated that these alloys were ferromagnetic. The saturation magnetization Ms of nickel-iron alloy films increased with decreasing deposition current density, which was attributed to the increase of iron content. Nickel-iron alloy film prepared at deposition current density of 6 A dm-2 showed the maximum value of Ms. The coercivity of nickel-iron alloy films increased with decreasing current density, which was likely caused by reduction in crystallite size.

Abstract: Iron-Platinum (Fe-Pt) and Cobalt-Iron-Platinum (Co-Fe-Pt) nanocrystalline thin films were deposited on brass substrates using a single bath electrodeposition system. The effects of addition of various concentrations of cobalt towards the composition, crystallographic structure, microstructure and magnetic properties of the Fe-Pt alloy films were investigated. Ammonium tartrate and ammonia solution were used as complex forming additives to stabilize the Fe2+ and Co2+ ions and to enhance co-deposition with platinum complexes. The as-synthesized thin films were characterized by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and alternating gradient magnetometry (AGM). EDS results showed that cobalt was preferentially deposited compared to iron during Co-Fe-Pt film electrodeposition. SEM results showed that the microstructure of the films consisted of spherical granules. XRD showed formation of disordered face-centered cubic (fcc) Fe-Pt phase and all peaks were shifted to slightly higher diffraction angles with increasing cobalt content. The average crystallite size calculated from XRD peak broadening varied from 2.33nm to 6.54nm. The saturation magnetization and coercivity increased with increasing cobalt content.

Abstract: MnxZn1-xFe2O4 nanoparticles with x = 0, 0.2, 0.4, 0.5, 0.6 and 1.0 were synthesized by polymer matrix templated synthesis. Ion exchange resins in a form of spherical beads that contained nanopores were used to precipitate the nanoparticles. The synthesized nanoparticles were characterized using several characterization techniques including X-ray diffractometry, transmission electron microscopy and alternating gradient magnetometry. XRD patterns showed that only manganese zinc ferrite nanoparticles were formed. Calculation of crystallite size from x-ray peak broadening showed that the crystallite sizes were within the range 5-11 nm. The crystallite size increased with increasing Mn concentration. TEM images showed that the particles were almost spherical with diameters ranging from 8-19 nm. Magnetization curves passed through the origin and showed no hysteresis indicated that the particles are superparamagnetic. The magnetization value at 10kOe applied magnetic field increased with increasing particle size which was mainly due to the effect of manganese content of the nanoparticles.

Abstract: Superparamagnetic maghemite nanoparticles were successfully produced using Massart’s procedure. Nanocomposites consisting of the synthesized maghemite nanoparticles and silica were produced by dispersing the as-synthesized maghemite nanoparticles into the silica xerogel, which was prepared by sol-gel technique. The system was then heated for 3 days at 140oC. A variety of weight ratios of Fe2O3/SiO2 was investigated. The nanocomposites were characterized using TGA, XRD, TEM and AGM. TGA thermogram showed one significant weight loss at around 250oC. It was caused by dehydration and evaporation of solvent from sol-gel process. XRD showed that the dispersed particles were still maghemite. TEM micrographs showed that the maghemite nanoparticles were in spherical shape and they were homogeneously incorporated in the silica matrix. The values of magnetization at 10kOe applied field were in the range of 1.79emu/g to 9.53emu/g depending of the Fe2O3/SiO2 ratio. Reduction of average crystallite size of dispersed maghemite particles was observed after encapsulation process. Increasing weight ratio of Fe2O3/SiO2 caused increase of the average crystallite size of maghemite nanoparticles.

Abstract: Polyethylene (PE) film was coated with nanosilica-polyurethane layer using rod Mayer process. The nanosilica-polyurethane system was prepared by dispersing nanosilica (SiO2) powder into solvent borne polyurethane (PU) binder under vigorous stirring. Various compositions of nanosilica-polyurethane slurry were prepared. A battery of characterization procedures were used to study the properties of the nanocomposite coating. ATR FTIR confirmed the presence of functional groups of silica and polyurethane. The uniformity of silica dispersion was probed using scanning electron microscopy (SEM). With the introduction of nanosilica to polyurethane binder, the visible light transmittance and ultra-violet (UV) radiation of nanosilica-polyurethane system reduced with increasing nanosilica content and coating layer thickness. The PE coated with nanocomposite containing 14wt% nanosilica and with 8 µm coating thickness showed >88% transmittance in the visible light region. Infrared (IR) effectiveness (between 7 μm to 13 μm wavelengths) measurements by FTIR also showed that nanosilica/polyurethane system coating on PE film surface greatly improved the infrared opacity properties of PE film.

Abstract: Nickel-iron-silicon nitride nanocomposite thin films were prepared by electrodeposition technique. The deposition was performed at current density of 11.5 A dm-2. Nano-size silicon nitride was mixed in the electrolyte bath as dispersed phase. The effects of silicon nitride nanoparticulates in the nickel-iron nanocomposite thin films were investigated in relation to the amount of silicon nitride in the plating bath. X-ray diffraction (XRD) analysis showed that the deposited nickel iron film has face-centered cubic structure (FCC). However, a mixture of body-centered cubic (BCC) and face-centered cubic (FCC) phases were observed for nickel iron-silicon nitride nanocomposite films. The crystallite size of Ni-Fe nanocomposite coating decreased with increasing amount of silicon nitride in the film. From elemental mapping procedure, Si3N4 nanopaticles were uniformly distributed in the Ni-Fe film. The presence of silicon nitride increased the hardness of the film. The microhardness of the nickel-iron nanocomposite increased from 495 HV for nickel-iron film to 846 HV for nickel-iron nanocomposite film with 2 at. % Si. The coercivity of Ni-Fe nanaocomposite films increases with decreasing crystallite size.

Abstract: Two different methods were utilized to synthesize intermetallic nickel aluminide alloy. The first method was combination of powder metallurgy and reaction synthesis (IMC_RS) and the second method was plasma melting to form homogenous plasma melted samples (IMC_PM). XRD patterns for both samples showed complete formation of single phase Ni3Al. Saturation magnetization value for IMC_RS was 0.445 emu/g and IMC_PM was 0.157 emu/g. This was comparable with Ms value of commercial Ni3Al from Alfa Aeser (0.398 emu/g). The reduced elastic modulus, Er value of IMC_PM and IMC_RS were 441.09 MPa. 408.2 MPa respectively. Both samples were exposed to 1%SO2/air gas mixture at 1000oC for 24-hour duration. The isothermal kinetic results for both samples were parabolic indicating rate limiting step. The oxide scales consisted of NiO, NiAl2O4 and Al2O3.

Abstract: Fe/Pt bimetallic nanoparticles at various molar ratios have been prepared by simultaneous reduction of FeCl2 and H2PtCl6 with hydrazine hydrate in water/Triton X- 100/cyclohexane/pentanol microemulsions at room temperature. The size, structure, composition and the magnetic properties of the resultant nanoparticles were characterized by XRD, EDX, TEM and AGM. XRD patterns indicated the formation of face centered cubic FePt nanoparticles with crystallite size in the range of 4 nm to 8 nm. Higher content of iron resulted in larger FePt nanoparticles. EDX analyses on the samples confirmed the presence of Fe and Pt elements in the particle. The composition for each particle was roughly consistent with the Fe2+ to Pt 4+ ratio of initial solution. TEM micrograph showed homogeneous fine spherical particles. The physical sizes were similar to the crystallite sizes of FePt nanoparticles calculated from XRD. The Fe/Pt molar ratio of 1 to 1 showed optimum magnetic properties with coercivity (Hc) of 68.67 Oe .