Papers by Author: Abdul Rahman Mohamed

Abstract: The reduction of ilmenite by a gas comprising of CNG, hydrogen and nitrogen mixture was investigated by experimental and kinetic modeling in MATLAB. The CNG flow time was varied from 15 to 45 minutes at the temperatures of 1100-1200°C for 1-3 hours. In order to predict the extent of reduction, a shrinking core model (SCM) and crackling core model (CCM) were employed for the kinetic modeling. The results showed that the extent of reduction of 80% was achieved by using a CNG flow time of 45 minutes at 1200°C for 1 hour. The kinetic modeling for non-isothermal SCM at the same conditions gave a predicted value of 87%. The CCM gave a predicted value of about 100% at the same conditions. The non-isothermal SCM showed a closer trend to the experimental results. The deviation between SCM and CCM with the experimental data was attributed to porosity, thermodynamic properties and minute thermal fluctuations within the sample during the reduction process.

Abstract: Micro end milling is one of the most important micromachining process and widely used for producing miniaturized components with high accuracy and surface finish. This paper present the influence of three micro end milling process parameters; spindle speed, feed rate, and depth of cut on surface roughness (R_a) and material removal rate (MRR). The machining was performed using multi-process micro machine tools (DT-110 Mikrotools Inc., Singapore) with poly methyl methacrylate (PMMA) as the workpiece and tungsten carbide as its tool. To develop the mathematical model for the responses in high speed micro end milling machining, Taguchi design has been used to design the experiment by using the orthogonal array of three levels L₁₈ (2¹×3⁷). The developed models were used for multiple response optimizations by desirability function approach to obtain minimum R_a and maximum MRR. The optimized values of R_a and MRR were 128.24 nm, and 0.0463 mg/min, respectively obtained at spindle speed of 30000 rpm, feed rate of 2.65 mm/min, and depth of cut of 40 μm. The analysis of variance revealed that spindle speeds are the most influential parameters on R_a. The optimization of MRR is mostly influence by feed rate. Keywords: Micro milling, surface roughness, MRR, PMMA

Abstract: Free-standing carbon nanotubes (CNTs) film known as buckypaper is a method used to address dispersion problems of CNTs. Unique properties of CNTs made the CNTs buckypaper to be considered as promising reinforcement materials in development of high-performance of nanocomposites. Buckypaper was fabricated by dispersing multi-walled carbon nanotubes (MWCNTs) in two different types of solution namely Triton X-100 and ethanol then followed by filtration process. In this study, MWCNTs loading and pressure used during filtration process were manipulated. The morphology, thermal and electrical conductivity of the buckypaper produced was studied.

Abstract: Graphene nanoplatelets (GNP)/epoxy and multi-walled carbon nanotube (MWCNTs)/epoxy thin film composites were fabricate by ultrasonication and spin coating technique. The tensile properties of epoxy containing (0.2, 0.6 and 1 vol%) of GNP sonicated at different duration (10, 20 and 30 min) or MWCNTs sonicated at 20 min only have been studied. It was found that the addition of GNP was decrease the tensile strength and modulus. However, among all samples, GNP/epoxy produced by 20 min sonication time showed slightly higher tensile strength and modulus. The effect of sonication time was supported by morphological analysis, which showed an improvement of GNP dispersion with increased sonication time. However, GNP deformation was observed with long sonication time. Compared with MWCNTs/epoxy sonicated at 20 min at different filler loadings, GNP/epoxy shows lower tensile properties. This can attribute to the two dimensional GNP are more easier to aggregate than MWCNTs.

Abstract: Polymer ceramic composite materials are candidate material for capacitor application. In this research, MWCNT and BaTiO₃ were used as fillers in epoxy thin film composites where the filler loading was in the range of 0 to 2.0 vol%. The thin film composites were fabricated by using spin coating method. The dielectric constant and dielectric loss were measured at 100 Hz to 1 MHz. The dielectric constant of CNT was in the range of 3.5 to 243.7 whereas the dielectric constant of BaTiO₃ was 3.5 to 33.7 at 1 kHz. Meanwhile the dielectric loss of MWCNT was 0.009 to 6.83 while dielectric loss of BaTiO₃ was 0.009 to 0.016 at 1 kHz. In general, it was found that MWCNT filler provide high dielectric constant value compare to BaTiO₃ this is because MWCNT is more conductive than BaTiO₃. However MWCNT/epoxy composites exhibit higher dielectric loss compare to BaTiO₃/epoxy composites.

Abstract: Carbon dioxide (CO2) is considered to be the main greenhouse gas contributing to global warming and climate change. Therefore, the present paper investigates the CO2-capture performance of synthesized calcium hydroxides, Ca(OH)2 sorbent at different temperatures which are 350, 450, 550 and 650°C. The CO2 adsorption of the materials synthesized was studied in a thermo-gravimetric analyzer (TGA). The CO2 adsorption temperature strongly influenced the capture performance of the absorbent. The Ca(OH)2 sorbent are prepared by hydrolysis of calcium alkoxides, NaOH as precipitating agent and mixed solvent of ethanol with deionized (DI) water as medium at 35°C. X- ray diffraction (XRD) result showed 40 nm crystallite size of Ca(OH)2 hexagonal crystal structures. The Ca(OH)2 particle size and morphological properties before and after CO2 adsorption are studied by Field Emission Scanning Electron Microscopy (FESEM). The FESEM image indeed showed the rod like shape of Ca(OH)2 structures with rod length increased from 765 to 893 nm while the diameter is between 140 to 160 nm. When Ca(OH)2 sorbent adsorbed CO2, the structures are rigid interconnected each others like a lump shaped. The prepared Ca(OH)2 sorbent possesses a great potential to capture CO2 when increased temperature. Nevertheless, at intermediate temperatures (350-450°C), Ca(OH)2 sorbent still demonstrates a higher CO2 capture capacity than other intermediate temperature adsorbents such as layered double hydroxides (LDHs), lithium zirconates (LiZrO3) and hydrotalcites.

Abstract: Morphological evolution and phase transformations of copper ion doped TiO₂nanotubes after being calcined at different temperatures were studied by field emission scanning electronmicroscopy, transmission electron microscopy, and X-ray diffraction. After calcination at 300°C, the nanotubes with uniform diameter and length wereobtained. At 400°C, the nanotube structures were maintained. Nevertheless the inner tube diameter became narrower, and in same instances disappeared due to aggregation of nanotubes. The copper ion doped TiO₂nanotubes then transformed to nanorodsat 500°C and the length of the nanorodsshortens after calcination at 600 °C. When the calcination temperature was further increased to 700°C, the nanorodsdisintegrate to form nanoparticles. On the other hand the phase structures of copper ion doped TiO₂ nanotubes calcined at 300 and 400 °C were TiO₂ hexagonal. After calcined at higher temperature (600 and 700°C) they transformed to anatase TiO₂ (tetragonal).

Abstract: In this paper, one dimensional nanorod CaCO₃ adsorbents were synthesized via hydrothermal method by varying the amount of polyacrylamide (PAM). The XRD results indicated that all of the characteristic peaks of synthesized adsorbents were matched well with the aragonite CaCO₃ phase. FE-SEM analysis showed one dimensional nanorod structures with diameter of 40 - 70 nm and lengths up to micrometer. TG results exhibited CaCO₃ adsorbents synthesized with 0.4 and 0.6 g of polyacrylamide possessed high CO₂ adsorption capacities for first carbonation/calcination cycle (0.86 and 0.79 g-CO₂/g-sorbent) which were higher than the theoretical CO₂ adsorption capacity (0.78 g-CO₂/g-sorbent) of calcium oxide based adsorbents.

Abstract: Copper doped titanium dioxide (Cu-TiO₂) nanotubes were synthesised by hydrothermal method. The samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and nitrogen gas adsorption. The photocatalytic activity of the copper doped titanium dioxide nanotubes was investigated by photodegradation of methyl orange under UV light. The structural and morphological studies showed that, the copper was incorporated into interstitial positions of the TiO₂ lattice to form a new phase of TiO₂ (hexagonal). The copper doped TiO₂ nanotubes possessed high surface area and pore volume, results high photocatalytic activity for degradation of methyl orange (MO).

Abstract: CO₂ is the major anthropogenic greenhouse gas which contributes to the increasing atmospheric CO₂ concentration, leading to serious global warming and climate change. Thus, the present paper investigates the CO₂-capture performance of synthesized calcium hydroxides, Ca (OH)₂nanosorbent at intermediate-high temperatures which are 350, 450, 550 and 650oC. CO₂ adsorption performance was analysed by thermo-gravimetricanalyser (TGA).The CO₂ adsorption temperature strongly influenced the capture performance of the sorbent.Facile wet chemical technique was utilized to synthesize Ca (OH)₂ nanorod sorbent structures using calcium nitrate tetrahydrate, Ca (NO₃)₂.4H₂O as the calcium precursor, and precipitated with sodium hydroxides (NaOH) in N,N-Dimethylformamide (DMF) mixed deionized (DI) water media at 55 oC. X-ray diffraction (XRD) result exhibitedCa (OH)₂hexagonal crystal structures. The Ca (OH)₂ particle size and morphological properties before and after CO₂ adsorption are studied by Field Emission Scanning Electron Microscopy (FESEM). The FESEM image indeed showed the rod like shape of Ca (OH)₂nanosorbent with rod length approximately700 nm while the diameter 140nm. When CO₂ molecules were adsorbed by Ca (OH)₂nanosorbent, the nanorodstructures are changed to rigid interconnected each other like a lump shaped. Ca (OH)₂nanosorbentseems to be a potentially good absorbent for capturing CO₂when increased temperatures. However, at intermediate temperature 350 and 450oC, the synthesized Ca (OH)₂nanosorbent demonstrated higher CO₂ adsorption (141 to 220 mg/g CO₂) than others intermediate temperature CO₂ sorbent such as layer double hydroxides (LDH), lithium zirconates (LiZrO₃) and hydrotalcite.