Advanced Materials Research Vol. 545

Abstract: Hydroxyapatite (HA) is by far the closest match to the human bone in terms of chemical composition. Furthermore, HA boasts excellent biocompatibility thus earning its reputation for human bone replacement. However, HA lacks desirable mechanical properties (i.e. hardness, fracture toughness, etc.). Due to the poor heat conductivity of ceramics, it is hypothesized that HA when sintered via conventional pressureless sintering, smaller ramp rates are advantageous as oppose to larger ramp rates. These advantages can be observed as improved densification along with improved mechanical properties. In the present work, the sintering profile for the HA green bodies were held at 1 minute in comparison to the usual 2 hours holding time. The applied ramp rates were 2 °C/min, 5 °C/min and 10 °C/min. Sintering temperatures were set to 1000, 1100, 1200, and 1300 °C. Sample characterization was then reviewed in the aspects of phase stability, % shrinkage, bulk and relative density, Young’s modulus, Vickers hardness, as well as fracture toughness. The results revealed that sintering with shorter holding time yielded an improvement in the mechanical properties of HA. It was observed that sintering HA with a 2 °C/min ramp rate does not result in the formation of extrageneous phases even when sintered to 1300 °C. Similarly at 2 °C/min and 1300 °C, densification was observed to be 99.05 %. In addition, Young’s modulus recorded its highest value (117.03 GPa) when sintered with a ramp rate of 2°C/min. It was also observed that sintering HA at a ramp rate of 2°C/min produced a hardness value of 5.88 GPa (improvement of 0.68 GPa when compared with 2 hours holding time).

Abstract: In this study, hydroxyapatite (HAp) was extracted from freshwater fish scales and saltwater fish scales using thermal decomposition method at various temperatures. The percentages of HAp in each species of raw fish scales were analysed using thermogravimetry analysis (TGA) whereas Fourier transform infrared (FTIR) was used to confirm the present of HA. The crystallinity of the HAp was studied using x-ray diffractometer (XRD). TGA and FTIR are found to be useful techniques to predict the composition of the HAp present in the fish scales. The results show that the composition of HAp in the fish scales was not significantly dependent on the species of the fish. The percentage of HAp in the fish scales ranged from 40 to 45 wt%. The heating temperature had an effect on the crystallinity and colour of the HAp produced. Results from FTIR and XRD confirmed that the HAp extracted from fish scales was similar to the HAp standard. However, the natural HAp produced from saltwater fish scales was more crystalline than that produced from freshwater fish scales. The HAp produced from this study is relatively cheap and more importantly they are HALAL for four billion Muslims population around the world.

Abstract: Reverse micelle extraction has received considerable attention in recent years due to its ability to selectively solubilise solutes from an aqueous phase, and in the case of biomolecules to maintain their biological activities. The apparent success of research on protein extraction from the aqueous phase using reverse micelle provides motivation to study the solubilisation of antibiotic. The objective of this study is to investigate the extraction of antibiotic (penicillin G is chosen as model antibiotic) from aqueous solution (forward extraction) and from the reverse micelle to a new aqueous solution (backward extraction). Sodium di(2-ethylhexyl)sulfosuccinate (AOT) is chosen as the surfactant and isooctane as the organic solvent. The UV-Vis spectrophotometer is used to determine the mass of penicillin G in solution after the extraction process. The extraction is expected to be influenced by the initial penicillin G concentration, the salt type and concentration in the aqueous phase, pH, and surfactant concentration. It is expected that as penicillin is an interfacially active compound that will interacts with AOT surfactant, the interfacial association will be dependent on both pH and surfactant concentration.

Abstract: Magnesium alloys are the lightest structural materials known that are increasingly replacing steel and aluminium. However, due to its flammable nature, protective atmospheres are employed during Mg-alloy production. In this novel work, Mg-Al alloys with ~3 and ~5 wt.% Al were processed in CO₂ atmosphere, so as to utilize the CO₂ during the melting process. The cast Mg-Al alloys were extruded and studied for their structural, physical and mechanical properties. Results showed improvements in mechanical properties such as hardness, tensile strength and compressive yield strength. The improvement in properties was attributed to the in situ formation of Al₄C₃ arising due to molten metal-carbon interaction. It is noteworthy that the incorporation of CO₂ during processing did not adversely affect the mechanical properties of the alloys. Further, the process is eco-friendly as it not only utilized CO₂, but also eliminates use of harmful cover gases.

Abstract: When the use of lead was banned, the development of lead-free solders began to rise and was greatly explored. Presently, majority of the eutectic Pb-free solders are Sn-based and the most promising is ternary SnAgCu (SAC) solder. However, SnAgCu solder tends to become brittle in nature and excessive solder interfacial reactions. An attractive approach is by introducing alloying elements such as Ce, Fe and Zn into the SnAgCu solder, which allows for an increase of the mechanical properties and refine the solder microstructure as well as improve the wetting properties. The present work focuses on the effects of a series of elemental additions of 0.5% Ce, Fe and Zn into the basic Sn_3.0Ag_0.5Cu solder, in attempt to reduce the intermetallic compound (IMC) growth as well as joint reliability and reflow properties of the solder on Ni-P surface finish. The intermetallic compound Cu₆Sn₅, containing a small amount of dissolved Ni, was found to form preferentially on the Ni coating. This compound layer served as a barrier for direct reaction of Sn with the Ni-P coating. The P-rich Ni layer acts as a good diffusion barrier layer, which decreases the dissolution rate of the Ni-P layer hence decreases the growth of IMC thickness layer. It is also expected that with the addition of alloying elements, the wetting properties will be further enhanced.

Abstract: In this work, the polymethylmethacrylate (PMMA) based gel polymer electrolyte samples have been prepared by the solution casting technique. The composition range of the salt was from 3 wt% to 35 wt%. The ionic conductivity of the samples was measured using a.c. impedance technique. The highest room temperature conductivity was obtained from the sample containing 30 wt% of NaCF₃SO₃ salt, i.e. 5.31 x 10^-3 S cm^-1. The increase in the ionic conductivity with increasing salt concentrations is due to the increase in both concentration and mobility of charge carriers. The decrease in ionic conductivity at higher salt concentrations can be explained by aggregation of the ions, leading to the formation of ion-pair, thus decreasing the number of charge carriers and hence the ionic mobility. The conductivity-temperature dependence obeys the Arrhenius rule from which the activation energy was evaluated. The ionic transference number estimated by dc polarization method revealed that the conducting species are predominantly ions.

Abstract: In this study, the two systems of polymethylmethacrylate (PMMA) based polymer electrolyte films have been prepared by the solution casting technique. Lithium iodide (LiI) and ethylene carbonate (EC) were used as inorganic salt and plasticizer, respectively. The highest room temperature conductivity for the plasticized system and unplasticized system is 4.42 x 10^-5 Scm^-1 and 4.37 x 10^-6 Scm^-1, respectively. The conductivity-temperature dependence studies have been performed on these films in the temperature range of 303 K to 373 K. It can be observed that the log σ versus 1000/T plots obey the Arrhenius rule and VTF rule for the plasticized film and unplasticized film, respectively [1-3]. The surface morphology of the plasticized and unplasticized films was observed by using scanning electron microscope (SEM).

Abstract: A new perovskite based titano-manganite (La_0.5-xPr_xBa_0.5)(Mn_0.5Ti_0.5)O₃ at x concentration 0, 0.01, 0.03, 0.05, 0.07 and 0.09 has been successfully prepared by ceramic solid-state technique at sintering temperature of 1300 °C. Dielectric electrical properties of the synthesized materials at frequency ranging from 5 Hz to 1 MHz and magnetic properties have been studied at room temperature. Analyses have been carried out to determine the structural, magnetic and dielectric properties of the synthesized material as a candidate of multiferroic material.

Abstract: A ceramics sample of LiTaO3 was prepared using a sol-gel method. The sample is annealed at 750 °C for 48 hours. X-ray diffraction analysis indicate the formation of single phase, rhombohedral structure. An ac impedance study was used to analyse the conductivity of LiTaO3 at room temperature and at various temperatures.

Abstract: This paper elucidates the structural and electrical properties of Bi₄Ti₃O₁₂ (BIT), Bi_3.25Nd_0.75Ti₃O₁₂ (BNT075) and Bi_3.25La_0.75Ti₃O₁₂ (BLT075) compounds that were primarily prepared by a novel combustion route at temperature as low as 300°C. Single crystalline phase of bismuth-layered perovskite structure was obtained directly after combustion without calcination. X-ray diffraction and Raman spectra analysis showed the phase transition from orthorhombic to tetragonal symmetry with substituting compounds. Compared to BIT, the Curie temperature at maximum dielectric peak of BNT075 and BLT075 decreased to lower values of 434°C and 365°C, respectively. The loss tangen for corresponding substitution compounds were 5 times lower than that of BIT. Besides, BNT075 resulted in large remanent polarization (2P_r) and coercive field (E_c) values of 19µC/cm² and 45kV/cm, respectively, while 17.6µC/cm² and 42kV/cm for BLT075.