Norazharuddin Shah Abdullah

Phase Evolution of Yttrium Iron Garnet (YIG) Made by Solid State Sintering: Particle Size Effect

The phase evolution of yttrium iron garnet (YIG) during reaction 3Y2O3-5Fe2O3 was investigated by modifying Fe2O3 particle sizes (FPS). Five different sizes of Fe2O3, (d50) are used to prepare YIG powder. Solid state reaction (SSR) was applied at 1200 °C in order to gain insight on the effect of FPS towards the YIG formation. Rietveld refinement method was used to quantify the amount of YIG yielded (%). Larger FPS (> 50 μm) initiates only 5Fe2O3 + 3Y2O3 à 3YFeO3 + Fe2O3 + Y3Fe5O12.. However, when the fine FPS (5 μm) is used, the reaction pathway was changed into 5Fe2O3 + 3Y2O3 à 6YFeO3 + 2Fe2O3 à 2Y3Fe5O12. These behaviors is explained that the smaller FPS consumed quickly to form YIG due to the smaller particle distance between Fe2O3 and Y2O3. This shall be leading to higher reaction rates (mass-transfer kinetics).

Tetragonal and Monoclinic Phase Transformation of ZTA-MgO Ceramic Cutting Tool by Machining Process

The purpose of this study is to investigate the phase transformation route of ZTA-MgO ceramic cutting tool in raw powder form, after sintering process and after machining process. This is to evaluate the effect of phase transformation to the properties of the cutting tool i.e hardness and fracture toughness. Samples of ZTA-MgO ceramic cutting insert were fabricated by wet mixing the materials, and then dried at 100°C before crushed into powder. The powder was pressed into rhombic shape and sintered at 1600°C at 4 hours soaking time to yield dense body. To study the effect of the phase transformation of the fabricated tool, machining was performed on the stainless steel 316L at 2000 rpm cutting speed. XRD analysis were performed on three type of ZTA-MgO samples which were the raw powder, the sintered samples and also the samples after machining process. Results shows that the m-ZrO2 reduced to 0% when sintering process take place and reappear at 12% when the machining process take place proving the occurrence of transformation toughening during the machining process. The consequence of this condition is the hardness of the samples increased by 22% while the fracture toughness decreased by 21.1%.

Why a Comprehensive Physical Characterization Effort of Microdialysis Membranes is Imperative for Computational Mass Transfer Studies

Microdialysis, being a well-established sampling technique, still suffers from mass transfer limitations. Arguably, the biggest contributor to mass transfer limitation in this case is the membrane layer. To reduce limitations to mass transfer, and at the same time, increasing the performance of microdialysis probes, a concise mass transfer analysis must be done. For microdialysis probes, being relatively small in size and operating under possibly stringent biological conditions, an experimental route of analysis is less preferred compared to a computational route. This paper looks at the needs of computational mass transfer studies, and provides an idea why a comprehensive physical characterization effort is imperative for computational mass transfer studies.

Studies on Alkaline Pretreatment of Sugarcane Bagasse and Rice Straw Hydrolysis for the Recovery of Reducing Sugar

Preliminary screening was performed to investigate the effects of different types of alkaline solution (2%, w/v NaOH and Ca(OH)2) on total reducing sugar (TRS) recovery. The results showed that usage of Ca(OH)2 yields higher TRS as compared to NaOH. Therefore, Ca(OH)2 was chosen for further studies in this effort. One-Factor-A-Time (OFAT) approach was employed to determine possible optimum ranges of chosen independent variables (i.e., pre-treatment temperature, concentration of Ca(OH)2 and reaction time). It is found that for both biomasses, rice straw gives the higher yield of TRS. The optimum temperature for rice straw and sugarcane bagasse are 70 °C and 80 °C, respectively. Increasing the concentration of Ca(OH)2 and reaction time gives an overall negative effect on the yield of TRS.

Structural Evolution of YIG during Microwave and Conventional Sintering at 1000 ºC

Microwave heating(MH) has emerged in recent years as a new method for sintering a variety of materials against conventional sintering (CH) procedure. However,the phenomenon of microwave-materials interaction is still under debate. In this work,the effect of microwave heating on YIG phase formation was investigated at 1000oC under the electromagnetic field(2.4GHz). The phase stability fired samples were qualitative and quantitative analyzed using X-ray diffraction(XRD)techniques. The obtained data were compared with CH to track the phase evolution. XRD revealed MHhas produced, YIG with 94% faster than CS. The calculated activation energy at this temperature via diffusion control model shows that MH(39.20kJ/mol)can effectively promote the phase growth rather than CH(90.96 kJ/mol).

Mineralogical Characteristics and Quantification of Mineral Phases in Malaysian Low Grade Manganese Ore

The aim of this work is to study the quantification of crystalline and amorphous content of manganese ore. The mineralogical characteristics and mineral phases of Malaysian low grade manganese ore are investigated using spiking method technique. Manganese ore was mixed with an internal standard of rutile and analyzed by Rietveld refinement with SIROQUANT. The refinement qualification and quantification indicated three phases which are pyrolusite (MnO2) with 1.1%, goethite (α-FeOOH) with 0.5% and quartz (SiO2) with 30.9%. From the calculation, sample consisted more amorphous content which is 0.6 compared to crystalline (0.4). This revealed that the ore is in amorphous form.

Investigation of YIG’s active site using density functional theory

Numerous materials characteristic including yttrium iron garnet (YIG) are directly dependent on its crystal structure; phase diversity. However, only a few examination of energy and its mechanism at atomistic scales was reported. In this article, a density functional theory (DFT) based calculations have been carried out to study electronic properties of cubic Y3Fe5O12 (YIG) at its known active sites; (0,0,4), (2,2,4) and (2,2,4). The density of state (DOS) these sites were presented at-19 eV to-14 eV for lower valance band and-6 eV to 0 for upper valance band. Both (0,0,4) and (0,2,4) planes shows highest possibility of cation substitution since the energy substitution are the lowest (~40 KeV). (2,2,4) plane composed of O-O interaction in which would contribute to the oxygen vacancy.

Chemical and Mineralogical Characterization of Malaysian Low Grade Manganese Ore

This paper aims to chemically and mineralogically characterize the Malaysian low grade manganese ore (LGMO). The optical microscope, and scanning electron microscope (SEM) fitted with an energy-dispersive x-ray analyzer (EDX) were used for ore morphology assessment, mineral liberation analysis, particle texture studies, grain size distribution and mineral association assessment. X-ray fluorescence (XRF) and X-ray diffraction (XRD) were used to determine the LGMO’s composition and to identify mineral phases, respectively. SEM images with EDX analysis revealed various optical characteristics of the ore, while XRF results showed that the major elements present in this LGMO are Si, (16.95%), followed by Mn, Fe and Al (at 13.17%, 4.63% and 4.70%, respectively). Phase analysis by XRD meanwhile, revealed the presence of α-quartz, pyrolusite and aluminum-substituted goethite. The natural grain-size distribution and texture (observed using optical and backscattered image analysis) revealed that manganese liberation was observed at particle sizes below 150 µm. This indicates that particle size has a significant effect in the recovery of the manganese oxide. The data and information obtained from this characterization study will aid in the identification and the design of a suitable treatment method for this local LGMO, and with that, the possibility of exploiting this deposit as a local source of manganese.

The Cutting Speed Influences on Tool Wear of ZTA Ceramic Cutting Tools and Surface Roughness of Work Material Stainless Steel 316L during High Speed Machining

The purpose of this research is to find the effects of cutting speed on the performance of the ZTA ceramic cutting tool. Three types of ZTA tools used in this study which are ZTA-MgO(micro), ZTA-MgO(nano) and ZTA-MgO-CeO2. Each of them were fabricated by wet mixing the materials, then dried at 100°C before crushed into powder. The powder was pressed into rhombic shape and sintered at 1600°C at 4 hours soaking time to yield dense body. To study the effect of the cutting speed on fabricated tool, machining was performed on the stainless steel 316L at 1500 to 2000 rpm cutting speed. Surface roughness of workpiece was measured and the tool wears were analysed by using optical microscope and Matlab programming where two types of wear measured i.e. nose wear and crater wear. Result shows that by increasing the cutting speed, the nose wear and crater wear increased due to high abrasion. However, surface roughness decreased due to temperature rise causing easier chip formation leaving a good quality surface although the tool wear is increased.

On Using Factorial Fractional Design to Fabricate Porous Alumina Scaffolds for Bone Tissue Engineering (BTE)

The porous scaffold has a weakness in terms of compressive strength. This is due to the porosity that is inversely proportional to the strength of the porous scaffold. Greater the percentage of porosity will decreasing the compressive strength. However, this compressive strength can be improve by controlling several factors (i.e., number of PU pores, composition ratio of slurry, percentage of binder and number of coating process). In general, fabrication porous alumina by conventional process was takes a longer time and consuming high cost. In addition, the conventional process could not explain the interaction relationship between all factors. Therefore, experimental design using Minitab 16 is applied to investigate the factors’ interaction. From the analysis, a combination of composition ratio and number of coating were found to have a significant impact to increase the compressive strength (> 2MPa) while others are less significant.