Theses & Dissertations

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Now showing 1 - 5 of 293
  • Publication
    Microstructure and properties of sintered Co-Cr-Mo alloy powder under different processing conditions (Restricted)
    (Universiti Malaysia Perlis (UniMAP), 2011)
    Zuraidawani Che Daud
    Co-Cr-Mo (ASTM F-75) alloy is one of the most important metallic biomaterials that are commonly used for surgical implant due to its mechanical properties, good wear resistance and biocompatibility. This study has focused on the effect of sintering time and sintering temperature on the microstructure development and properties of sintered Co-Cr-Mo alloy powder, sintering mechanism and activation energy, and corrosion behaviour. In the fabrication of PM Co-Cr-Mo alloy, five weight percentages (wt. %), 1.0, 1.5, 2.0, 2.5 and 3.0 of binder (stearic acid) were studied to determine the optimum amount of binder content based on the results of linear shrinkage, bulk density, apparent porosity and Vickers microhardness of the sintered samples. Then the Co-Cr-Mo alloy powder were blended with the selected amount of optimum binder (2wt. % of stearic acid) using a rotation mill at 16SRPM for 30 minutes, uniaxially pressing at SOOMPa and sintering in a furnace at three different sintering temperatures (12S0°C, 1300°C and 13S0°C) for five sintering times (30, 60, 90, 120 and 150 minutes) in argon atmosphere. The characterisation on sintered samples were carried out based on microstructure, grain size, bulk density and apparent porosity, Vickers microhardness test and followed by compressive strength. The study of sintering mechanism was carried out in order to determine the activation energy of Co-CrMo alloy. The corrosion behaviour of selected samples was analysed based on the minimum value of compressive strength. For corrosion test, the selected samples were immersed in simulated body fluid, 0.9% sodium chloride (NaCt) solution at 37°C for 90 days. From this study, the values of bulk density and grain size increased with increasin~ sintering temperature and sintering time. The bulk density values are in the range 7.04g/cm to 7.21 g/cm3 , 7.16 g/cm3 to 7.28 g/cm3 and 7.45 g/cm3 to 7.54 g/cm3 for sintering temperature of 1250°C, 1300°C and 1350°C, respectively for five sintering times. Meanwhile, the grain sizes for five sintering times are 25.6~m to 37.7~m, 36.6~m to 44.5~m and 80.4~m to 89.9~m respectively for the three sintering temperatures. However, opposite results were obtained for apparent porosity, hardness and compressive strength. The samples sintered at 13S0°C have the highest values of hardness (303HV -294HV) and compressive strength (329MPa-206MPa) for 30 to 150 minutes of sintering times. Based on the fracture mode, all samples show the fracture with a shear mode and occurred close to an angle of 45° from the compressive axis. The samples sintered at 12S0°C and 1300°C exhibited smooth transgranular fracture mode. Meanwhile, the step-like transgranular fracture mode was observed in the samples sintered at 1350°C. The results of corrosion test showed that sample sintered at 1300°C gives the highest value of corrosion rate (0.07Smpy) meanwhile sample sintered at 1350°C has the lowest corrosion rate (0.006mpy). From this study, the samples sintered at 13S0°C with 120 minutes of sintering times showed the compressive strength close to the bone strength and better corrosion properties.
  • Publication
    Development and characterization of Co-Cr-Mo (F-75 alloy)/hydroxyapatite composites fabricated by powder metallurgy for biomedical applications (Restricted)
    (Universiti Malaysia Perlis (UniMAP), 2013)
    Nur Maizatul Shima Adzali
    Co-Cr-Mo (F-75) alloy is known to be used in biomedical field because of their excellent biocompatibility when implanted to human or animal body. Hydroxyapatite (HAP) powders have been used as filler because HAP is the one of the most effective biocompatible materials with similarities to mineral constituents of bones and teeth. This research reported the fabrication and characterization of F-75 alloy filled with HAP which have been prepared by powder metallurgy method. This study has focused on the effect of HAP addition into F-75 alloy and sintering temperature on the physical and mechanical properties of the F-75/HAP composites, its microstructure, and also its corrosion and bioactivity behaviour. In fabrication of the F-75/HAP composite, 2, 4, 6, 8 and 10 wt. % of HAP have been added to F-75 alloys. The reference samples of F-75 alloy (with no addition of HAP) also have been prepared for all sintering temperatures. The mixtures were milled on a rotation mill for 20 minutes at 154 rpm before cold compacted at 550 MPa using an uniaxial press machine. The samples then have been sintered at three different sintering temperatures (11000C, 11500C and 12000C) in a tube furnace for 2 hours. Physical properties were measured by means of bulk density and apparent porosity while mechanical property was measured in term of compressive strength. The corrosion behaviour of the F-75/HAP composite has been analysed using electrochemical test controlled by Gamry G300 potentiostat. Bioactivity test for the composite was conducted in-vitro by immersing the composite into simulated body fluid for 18 days. XRD, SEM, FTIR and pH analyses had been done in order to observe the presence of the apatite layer on the surface of F-75/HAP composites. From this study, the values of bulk density decreased as the HAP content increased. The highest value of bulk density was gained by the composite with 2 wt. % of HAP with value 6.6217 g/cm3 with sintering temperature 12000C, while the lowest bulk density value was given by the composite with 10 wt. % of HAP after sintered at 11500C (4.3915 g/cm3). The apparent porosity was increased in the range of 13.13% (for 2 wt. % HAP) to 37.58% (for 10 wt. % HAP). Compressive strength was decreased by the additional of HAP. The sample with 2 wt. % of HAP addition with sintering temperature 12000C gave the highest compressive strength (341.81 MPa). The microstructure of F-75/HAP composites after sintering at three different sintering temperatures showed that porosity and HAP agglomeration increased with HAP content and sintering temperature. The results of corrosion test showed that the samples with 8 wt. % HAP addition gave the lowest value for corrosion rate (16.59 x 10-6 mpy for F-75/8% HAP sintered at 11500C). From bioactivity test results, the carbonated apatite layer was formed on the surfaces of the composite. According to the results for physical and mechanical properties testing of the composites, the optimum HAP addition to F-75 alloy was 2 wt. %, while samples that have been sintered at higher temperature (12000C), showed good physical and mechanical properties and also corrosion behavior. From corrosion test, F-75/6% HAP and F-75/8% HAP composites that have been sintered at higher temperature showed good corrosion resistance. Bioinert F-75 alloys can be converted into F-75 bioactive type by adding up to 10 wt. % of HAP.
  • Publication
    Gold leaching process and recovery from gold scraps using ascorbic acid (Restricted)
    (Universiti Malaysia Perlis (UniMAP), 2010)
    Sharizan Ibrahim
    A new process of gold leaching which involves the use of hydrochloric acid, sulphuric acid and sodium nitrate was studied. A series of screening study was conducted to identify the most suitable of these acids that capable of dissolving gold completely. This was achieved by altering the concentration of hydrochloric acid and sulphuric acid while the amount of sodium nitrate was remained constant. It is concluded that the optimal dissolving condition depends on the concentration of the acids which was between 1 M to 6 M and 6 M to 11.5 M for sulphuric acid and hydrochloric acid, respectively and the dissolution rate depends on temperature of the solution and it is found that the optimum temperature is between 90°C to 150°C. The reaction order is second order with respect to the concentration of hydrochloric acid and sodium nitrate respectively. The reaction order for the sulphuric acid concentration is zero order. From the temperature dependence of rate measurement, the values of activated energy, entalphy and entrophy are -4.6k.Jmor1, -3.90 kJ mol1 and -291 J mol"1 K"1, respectively. The amount of dissolved gold was determined gravimetrically and the recovery of gold was achieved by precipitation with ascorbic acid. The study showed that ascorbic acid is capable to recover gold up to 99.9%. Analysis by cupellation method found that the fineness of refined gold is 998 fine or 99.8% of purity. Finally a brief comparison of this dissolution system and aqua regia method was reviewed and it is concluded that this method is suitable for small and medium scale refining.
  • Publication
    A study on nanostructured of anodised aluminium template synthesised by the mixture of phosphoric acid and acetic acid (Restricted)
    (Universiti Malaysia Perlis (UniMAP), 2010)
    Juyana A. Wahab
    The formation of anodic aluminium oxide (AAO) film in anodising process has been studied. The anodising process was done in a mixture of phosphoric acid and acetic acid. The purpose of mixed acid solution as electrolyte is to increase the efficiency of AAO film formation. This study was performed to determine optimum parameter of anodising process in order to develop AAO film with diverse application in electronic field. The studies were focused on the influence of anodising parameters which are anodising temperature and anodising voltage on the growth of AAO film. The anodising temperature was controlled in the range of 5°C to 25°C and the anodising voltage was controlled from 70V to 130V respectively. The electrical properties of AAO film also studied via impedance measurement. The growth, morphology and composition analysis of AAO film were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. The results showed that the formation of AAO film was strictly influenced by the anodising parameter. The average pore diameter of AAO film was larger at temperature 15°C which is 87nm and the pores have more ordered arrangement. Meanwhile, the AAO film was shown have large pore diameter around 92nm at higher anodising voltage at 130V. The pore diameter of AAO film was gradually increased as the anodising voltage increase. The AAO film was shown to have highly ordered arrangement of pores at 130V of anodising voltage. The kinetic reaction of AAO film formation was expressed as percentage of mass change and AAO film thickness. At 15°C, the percentage of mass change showed a greater change which is 0.21% compared to the other anodising temperature. However, by increasing the anodising voltage, the percentage of mass change increased. Besides, the AAO film also showed greater thickness at 15°C which is 2.82μm. The thickness of AAO film decreased as the anodising temperature increased to 20°C and 25°C. At lower temperature, the thickness of AAO film is decreased. Meanwhile, the thickness of AAO film is strongly influenced by anodising voltage. Higher anodising voltage showed higher thickness of AAO film which is 2.8μm. The impedance measurement of AAO film revealed that the resistance of AAO film increased and the capacitance decreased as the thickness of AAO film increased. According to the results of this study, the optimum parameter of anodising should be in the range of 130V and the anodising temperature is about 15°C in order to obtain best characteristic of AAO film that can be related to the requirement of electronic applications.
  • Publication
    Phase equilibrium studies for the development of fuel systems and LPG fuel mixture using regular solution theory (Restricted)
    (Universiti Malaysia Perlis (UniMAP), 2011)
    Mario Kabbour
    The objective of this work is the assessment of the feasibility studies of phase equilibria mutual solubility process utilizing subcritical propane. A thermodynamic model based on regular solution theory studies to evaluate activity coefficients expression to each the heavy compound such as (propane and hexane) and the solvent such as propane in order to predict mutual solubility data. The use of equations derived from thermodynamic of the regular solution theory for collecting and predicting mutual solubility discussed with reference to binary pairs (propane / hexane and propane / decane systems). It is concluded that the calculation of some of the parameters required for these calculation would be difficult if the solute or heavy component hexane or decane in LPG or LNG were sensitive to temperature or complex substance about which little was known apart for its structural formula. An alternative procedure is to apply activity coefficients expression of the regular solution theory from which is called Universal Functional Activity Coefficient theory (UNIFAC) to each phase. Calculation along these lines described and the physical basis for applying this method under the relevant condition discussed. The UNIFAC theory approach in particular has been found to be in good estimation for the present studies of these systems LNG and LPG composition.