Papers by Author: Othman Mamat

Abstract: Tronohs raw sand was converted into fine silica particles via a series of milling process. Addition of these fine particles into iron composite was found to modify its mechanical properties. The composite was prepared using powder metallurgy technique with varying percentage of silica particles; 5, 10, 15, 20 and 25wt%. The composites were sintered at three different temperatures; 1000° C, 1100° C and 1200° C to find the most suitable sintering temperature. Changes in density and hardness were observed. The results showed that composite consist of 20wt% silica particles and sintered at 1100° C exhibits best improvement.

Abstract: Silica sand nanoparticles are widely used as filler, coating and reinforcer to increase materials strength and durability. The objective of the research is to design a new technique of converting Tronoh silica sand to silica sand nanoparticles by using ingenious combination of milling process and heating mechanism. Raw Tronoh silica sand was milled for 10 hours with heating process after every 2 hours of milling and the results are analyzed using particle size analyzer. Particles size of less than 100 nm has been repeatedly achieved in this research. Findings from this research provide a simple and low cost alternative method of producing silica sand nanoparticles.

Abstract: Analysis of structural and mechanical properties of cubic zirconia was conducted using a simulation code (GULP) that is based on the concept of energy minimization. Some mechanical properties of zirconia were computed such as elastic constant tensors, shear modulus, bulk modulus, Youngs modulus and others along the lattice planes. The stiffness constants obtained (C₁₁, C₂₂ and C₃₃) were equal, implying that zirconia is flexible in all directions of the lattice plane. The predicted bulk modulus was 285 GPa with the shear modulus ranging between 78 and 105 GPa. The Youngs modulus of 577 GPa indicates higher ductile behavior as confirmed by the compressibility of 0.0035. The Poissons ratio with values ranging from 0.16 to 0.31 may indicate high anisotropy. Other acoustic features related to mechanical properties of zirconia such as velocity wave ratio, stress matrix dielectric constants and others were also analyzed. All estimations obtained show good agreement to recent measured properties of zirconia.

Abstract: An Oxide Ceramic-Based Composite in the Al₂o₃-Sio₂-Zro₂ (ASZ) System Was Developed and Investigated Using a Pressureless Sintering Route. the Effect of the Content of each Component and Sintering Temperature upon the Microstructure, Density, Hardness and Strength Was Studied. X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) Were Used to Investigate the Phase Transformation Sequences of the ASZ Composite System. the Flexural Strength Was Measured Using Three-Point Bending Method on a Universal Testing Machine, while the Indentation Fracture (IF) Method Was Used to Determine the Fracture Toughness of the Composite. the Results Showed that, with Varying Zro₂ Content, Keeping the Silica Content Constant and the Alumina as a Matrix, Densification Tends to Decrease as the Content of Zirconia Increases from 20 Wt. % of the Composition. X-Ray Diffraction Peaks Indicated Fully Developed Alumina, Mullite and Zirconia Phases due to Solid-Phase Reaction and Liquid-Phase Sintering of the System. the Experimental Results Also Revealed that, for a Sintering Temperature of 1500°C, the Hardness Value Ranged from 12 Gpa to 14 Gpa and the Flexural Strength Was 420±31MPa.The Fracture Toughness (K_Ic) Was Also Reported to Be between 4.5 and 5.1 Mpa.m^1/2, for Samples Sintered at a Temperature of 14500C.

Abstract: This research presents the effects of temperature and cooling rate on mechanical properties of powder injection molded 316L Stainless steel. Steel powder and binder were mixed together to produce the feedstock. The green samples were produced by injection molding and debinded. Brown test samples were sintered in vacuum at 1325°C, 1360°C and 1380°C for 2h with two heating and cooling rates 5°C/min and 10°C/ min. The test samples sintered at 1325°C achieved maximum sintered density. The higher cooling rate improved the strength of the sintered test samples. The maximum sintered density of 96% and tensile strength of 503MPa was achieved and these results are comparable to the wrought 316L stainless steel (according to ASTM standard).

Abstract: Several processing methods have been used to obtain silica from rice husk with a persistent problem of lack of scalability from laboratory scale to levels of production necessary for commercial or industrial applications, at low cost. To address this draw-back, a novel method- hydro thermo-baric process, was developed and used to process high purity silica from rice husk. Since the suitability of rice husk silica in a given application is dependent on the nature of its structure and morphology and the two parameters are affected by the processing methods used in obtaining the silica, this paper reports the preliminary studies done on the silica obtained from this novel method using XRF, XRD, FESEM and EDX. XRD results show that the silica produced, which by XRF analysis had purity approaching 98%, is amorphous in nature. FESEM images showed that the particles have nanometric size. However, EDX results show an increase in residual carbon in the silica, with increase in the processing temperature. BET analysis showed an increased surface area from 21.42m2/g to 133.94m2/g for the untreated and treated samples, respectively.