Iskandar Idris Yaacob

Polymer matrix templated synthesis: Cobalt ferrite nanoparticles preparation

Cobalt ferrite (CoFe 2 O 4 ) nanoparticles were successfully synthesized by polymer matrix templated synthesis. Synthetic ion-exchange resins were used as hosts for the coprecipitation of cobalt ferrite where the nanopores of the resin acted as the constrained environment. The weight fraction of the particles within the resin was roughly 16%. X-ray diffraction analysis indicated that cobalt ferrite crystallites were about 1-7 nm in diameter. Magnetic properties measured using an alternating gradient magnetometer showed the particles (prepared using initial salt solution ratio of Fe 3 + :Co 2 + of 1.5:1.0) were superparamagnetic with magnetization M (of the particle-resin system) in the range of 3.0 to 4.4 emu/g at 10 kOe of applied field. The least upper bound of the magnetic size was about 3 nm in diameter. Ratios of Fe 3 + to Co 2 + within the matrix of the resin before and after precipitation were investigated by x-ray fluorescence spectrometry and were found to be sensitive to the initial salt solution mixture. The ratio Fe 3 + :Co 2 + of 1.5:1.0 was found to be a better mixture in terms of magnetization value. Spherical shape cobalt ferrite particles 2-8 nm in diameter were observed using transmission electron microscopy. The close agreement between the physical and crystallite size indicated that the particles are largely monocrystals.

Room temperature synthesis of copper pyrovanadate; the effect of stirring time

Abstract Copper pyrovanadate was successfully prepared at ambient temperature and pressure by mixing copper monoxide Cu 2 O with a solution of vanadium oxide xerogel, V 2 O 5 .2H 2 O. By stirring, Cu 2 O progressively dissolves and reacts with xerogel of vanadium oxide solution. After 2 days of stirring, although the reaction is not complete, the precipitate is mainly composed of copper pyrovanadate Cu 3 (OH) 2 V 2 O 7 ·2H 2 O. With prolonged stirring, a pure copper pyrovanadate is obtained.

Melting of multipass surface tracks in steel incorporating titanium carbide powders

Abstract Overlapping tracks were processed by melting preplaced titanium carbide (TiC) powder on steel surfaces using a tungsten inert gas torch. The tracks produced ∼1·0 mm melt depth free from cracks, but occasional pores were observed. The microstructure consisted of unmelted and partially melted TiC particulates together with reprecipitated TiC particles, which were prominent in tracks processed in the initial stage. A greater number of reprecipitated globular and cubic TiC particles were observed in tracks processed in the later stages, indicating more dissolution of TiC particulates from the overlapping operation. Those multitracks processed in the initial stage developed a maximum hardness of 850–1000 HV, which was lower in most other tracks, although comparable hardness values were recorded in the last track.

Effect of polyurethane/nanosilica composite coating on thermomechanical properties of polyethylene film

Abstract Polyurethane (PU)/nanosilica composite was fabricated and then coated on polyethylene (PE) film using a rod Mayer technique. The silica nanoparticles used have an average particle size of 16 nm, and their weight fractions varied from 0 to 14%. Two different thicknesses of PU/nanosilica coating layer were fabricated, which were 4 and 8 μm. The morphology and thermal mechanical properties of the nanocomposite coated PE film were characterised using scanning electron microscope, dynamic mechanical analyser, thermogravimetric analyser as well as tensile tests. The results showed that a thin layer coating of PU/nanosilica composite has a slightly reduced tensile strength of the PE substrate. However, the nanocomposite coating of up to 8 μm reduced the elongation of PE substrate significantly. The PU/nanosilica composite coating layer increased the tensile modulus and stiffness of the PE substrate. There was no influence of PU/nanosilica composite coating on the thermal degradation rate of the PE film.

Synthesis, characterisation and stability of superparamagnetic maghemite nanoparticle suspension

Abstract Maghemite nanoparticles were synthesised using the co-precipitation method and characterised by various techniques, including X-ray diffraction, transmission electron microscopy, alternating gradient magnetometry, dynamic light scattering and zeta potential. The stability of the suspension was monitored by measuring the particle size distribution and zeta potential using dynamic light scattering over a period of few months. The pattern obtained from X-ray diffraction confirmed that the particles were maghemite with crystallite size of 9·4 nm. Transmission electron microscopy observations and analyses showed that the mean physical size of the nanoparticles was 9·5 nm. The nanoparticles show superparamagnetic behaviour with magnetisation value at ±10 kOe of 32·18 emu g−1. The intensity averaged particle size of as-synthesised maghemite nanoparticles was 45·3 nm. The suspension was stored for periods of 2, 4 and 8 months. The intensity averaged sizes were 47·1, 50·5 and 52·1 nm respectively. No sedimentation was observed. The suspensions zeta potential value was 44·6 mV for as-synthesised sample and 43·3, 42·7 and 41·8 mV for sample after storage period of 2, 4 and 8 months, respectively. This indicated that the suspension was very stable.

Effect of Nitric Acid Concentrations on Synthesis and Stability of Maghemite Nanoparticles Suspension

Maghemite (γ-Fe2O3) nanoparticles have been synthesized using a chemical coprecipitation method at different nitric acid concentrations as an oxidizing agent. Characterization of all samples performed by several techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM), thermogravimetric analysis (TGA), dynamic light scattering (DLS), and zeta potential. The XRD patterns confirmed that the particles were maghemite. The crystallite size of all samples decreases with the increasing concentration of nitric acid. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with decreased magnetization values at the increasing concentration of nitric acid. TGA measurement showed that the stability temperature decreases with the increasing concentration of nitric acid. DLS measurement showed that the hydrodynamic particle sizes decrease with the increasing concentration of nitric acid. Zeta potential values show a decrease with the increasing concentration of nitric acid. The increasing concentration of nitric acid in synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability, and more stable maghemite nanoparticles suspension.

Weathering Effect on PE Coated with Thin Layer of PU/Nanosilica Composite

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.

Preparation of maghemite-silica nanocomposites using sol-gel technique

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.

Synthesis and Characterization of Nickel-Iron-Silicon Nitride Nanocomposite

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.

Synthesis and Characterization of Iron Oxides Nanoparticles

Magnetic iron oxides nanoparticles were synthesized at room temperature using water in oil microemulsion process. This microemulsion system was prepared using HTAB (surfactant), noctane (oil), 1-butanol (cosurfactant) and aqueous salt solution of Fe2+ and OH-. The microemulsions were used as microreactors for controlling the growth of the particles. The nanoparticles were characterized using TGA, XRD, TEM, BET, DLS and AGM. X-ray diffraction analysis revealed that the magnetic nanoparticles could be directly formed at room temperature. It also showed that the particles were either maghemite (γ-Fe2O3) or magnetite (Fe3O4). TGA thermogram showed two significant weight losses at around 100°C and 250° C, which were caused by dehydration and burn off of the surfactant. The surface area of the magnetic particles measured using gas absorption and desorption technique was 105.43m2/g, which indicated the presence of particles of 21nm in length. The size measured by TEM and DLS was 105nm and 107.9nm respectively due to the formation of large aggregated clusters. The sample also showed strong magnetic properties with the value of Ms of 11.2 emu/g.