Advanced Materials Research Vols. 264-265

Abstract: Since the discovery of carbon nanotubes (CNT) and subsequent Carbon Nanomaterials (CNMs), there has been an ever increased academic and industrial interest on there various fields of application due to their exceptional mechanical and electrical properties. In this work, granular activated carbon (GAC) made from palm Kernel shell (PKS) of mesh size 8x12 was impregnated with nickel as substrate catalyst for the growth of Carbon Nanomaterials (CNMs) in a chemical decomposition (CVD) reactor. Various percentages by weight of the nickel (1%, 3%, 5% and 7%) were impregnated on the GAC surface for CNM growth. The CNM growth took place at a fixed reaction temperature and gas flow rates for both the hydrogen gas and carbon source. Characterization of the novel composite material was carried out by using SEM, FESEM and TEM. The results show that growth was successful as at 1% nickel impregnation, while a denser network distribution and rougher surface of CNM was observed at 7% nickel. The growth of CNMs on a larger substrate GAC should make handling of the CNMs easier and it is expected to also open new doors of application in water treatment and oil refining.

Abstract: The assembly of plastic electronic package requires a sequence of process steps. Every process step induces thermal residual deformation and stresses on the assembled components, which cause mechanical effects on the subsequent process step. Processing model with considering the effect of chemical shrinkage on molding compound is built to simulate the package warpage and stresses in assembly. The processing model, a nonlinear model with element birth and death used to activate and deactivate the processing materials, can more realistically simulate a series of assembly processes in a plastic package. The stresses in package components are primary factor for the damage of package. The induced package stresses can cause the delamination between die/die attach interface or die attach/die pad interface. In this study, effects of material properties as well thickness of die attach on warpage and stresses of TSOP (Thin Small Outline Package) during assembly are discussed.

Abstract: Semi-active control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magneto-rheological (MR) dampers are semi-active control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take maximum advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper’s intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a model is proposed that can effectively portray the behavior of a typical magneto-rheological damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design and analysis.

Abstract: The influence of a binder system to the rheological behavior of a Metal Injection Molding (MIM) feedstock is presented in the paper. The binder systems used are: a) PEG & PMMA b) Palm stearin & LLDPE and, c) Tapioca starch & LLDPE. The viscosity and shear rate of the feedstocks were measured at various range of temperature and shear rate across the L/D = 10 capillary rheometer. The flow behavior index, n and activation energy, E of each feedstock were measured to show its significance as MIM feedstock. Generally, the result indicates all feedstock exhibits a shear thinning behavior and the binders are suitable as MIM binder. Additionally, the present paper has discovered that the binder system does not have much influence to the activation energy. In order to show the relevance of the rheological behavior to the actual injection molding performance, green parts has been injection molded and the result shows an agreement with the rheological behavior result.

Abstract: Electrical properties of carbon nanotubes-based epoxy nanocomposites for high electrical conductive plate were investigated. Dispersion and incorporation mechanism between two conductive fillers with different sizes (CNTs and Graphite) in the polymer matrix are the key factors in the fabrication of high electrical conductivity plate. Different variation of carbon nanotubes (CNTs) (1~10 wt %) and Graphite (G) (60 ~ 69 wt %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by the internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in terms of variation of G and CNTs concentration were measured by the four point probe for in a plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are effective ways to produce high electrical conductive nanocomposites. The highest electrical conductivity was reached on 104.7 S/cm by addition 7.5 wt% of CNTs. Dispersion quality of G and CNTs in the epoxy matrix was observed on the fractured surface by scanning electron microscopic.

Abstract: Highly crosslinked epoxy resin for engineering applications is normally stiff but brittle. Therefore, many attempts have been made to improve its toughness. Nowadays, several studies have been done on toughening epoxy resin using natural rubber (NR) because it is abundant and comes from renewable resource. In the present work, NR was subjected to depolymerize in order to achieve molecular dispersion of NR in epoxy matrix. Depolymerized natural rubber (DNR) was prepared by adding a carbonyl compound to natural rubber latex solution and subjecting the mixture to air oxidation in the presence of a radical forming agent at 70°C. In addition, the interfacial adhesion between rubber and matrix must be present to achieve a significant increase in toughness. Hence, DNR was further functionalized by grafting with monomer mixture of methyl methacrylate (MMA)/glycidyl methacrylate (GMA) (90/10 wt/wt%) in an amount of 50% based on rubber content. Solution polymerization was used to graft such monomers using 2 hours reaction times at a reaction temperature of 80oC. Two types of initiator used were benzoyl peroxide (BPO) and azo-bisisobutyronitrile (AIBN). The amounts of initiator in the grafting process were 1, 2, and 3 parts per hundred of DNR. Effects of type and concentration of initiator on grafting efficiency of MMA/GMA monomer mixture onto depolymerized natural rubber were studied by proton nuclear magnetic resonance (1H-NMR) analysis. The molecular weight of DNR was characterized by gel permeation chromatography (GPC). The results indicated good evidence for the formation of graft co-polymers in the presence of both initiators, AIBN or BPO. However, the amounts of grafted MMA/GMA on DNR backbone using BPO was higher than those on DNR backbone using AIBN.

Abstract: This paper presents an in-vitro evaluation of compressive strength of a locally produced hydroxyapatite from eggshell. Hydroxyapatite (HA) is a mineral that naturally occur in form of calcium apatite with the formula Ca5 (PO4)3(OH) but it is usually written as Ca10(PO4)6(OH). Hydroxyapatite (HA) is an example of bioactive ceramics that most commonly used in the bone implantation, as coating on prostheses or as bone filling material. Eggshell waste is available in huge quantity from food processing, egg breaking and hatching industries. This material goes as waste products and leads to pollution since it is microbial action in the environment and it is simply burned as organic waste that releasing CO2. By utilizing this organic waste that has high content of calcium carbonate, the cost of high quality of calcium source for preparation of hydroxyapatite can be reduced. At the same time, recycling of eggshell can be done. Many methods have been introduced to convert the calcium carbonate of eggshell to hydroxyapatite. Hydrothermal method technique has been selected to convert the calcium carbonate obtained from the eggshell since the procedure to transform it is simple and straight forward. An addition, the material that been used is not so expensive as compared to other method. Mechanical properties such as compression strength will be done to compare the synthetic hydroxyapatite in the market and hydroxyapatite from the hen’s eggshell.

Abstract: The findings for strengthening and repair of implant materials are stepping up to ensure better protection of the patients. The utilization of composite resin is favourable to combat this challenge. However, it being a brittle material does not entitle it to be used in the design. Hence, epoxy resin combining with silicon oxide filler from the rice husk; is a relatively new material in biomedical engineering, enable it to meet its fullest strength and flexibility. Work was performed at laboratory to extract the silicone compound from rice husk and as well investigate the compressive strength of rice husk filled resin material. Initially the rice husk was experimented by undergoing pre-treatment, chemical treatment and incineration process to obtain silicone compound. The silicone compound was later mixed with epoxy resin at different percentage of filler. In the final stage, the compressive strength of rice husk filled resin was analyzed and affirmed experimentally based on the ASTM standards. The results obtained were then analyzed using analytical software SPSS. Epoxy resin filled with 20% silica from rice husk gave the optimum compressive strength of 90 Mpa.

Abstract: Based on the pseudopotential scheme, the electronic and positron properties of zinc-blende compounds MgTe, CdTe and their alloy MgxCd1-xTe alloy have been studied. The agreement between our calculated electronic band parameters and the available experimental data is reasonable. For the ternary alloy MgxCd1-xTe, the virtual crystal approximation is coupled with the pseudopotential method. The energies at Γ, X and L points of MgxCd1-xTe alloy as a function of the alloy concentration are calculated. The electronic and positron band structures derived from pseudopotential calculations are also reported. Other quantity such as ionicity factor by means of our model with respect to the alloy concentration is discussed.

Abstract: Metal injection moulding (MIM) is a cost-effective technique for producing small, complex, precision parts in high volume. Each step in MIM process plays a vital role in order to achieve high quality final product. To have a good understanding of the MIM process and successful in manufacturing, characterisation of the material feedstock is essential. This paper presents the characterization of MIM feedstock consisting titanium alloy (Ti-6Al-4V) powder mix with binder 60 wt% of palm stearin and 40 wt% polyethylene. The characterisation of Ti-6Al-4V alloy powder, binders and feedstock includes scanning electron micrograph (SEM), thermo gravimetric analysis (TGA), differential scanning calorimeter (DCS) and rheological test were established. Rheological results exhibited pseudoplastic or shear thinning flow behaviour, where its viscosity decreased with increasing shear rate. The feedstock viscosity also decreased with increasing temperature and was found to be suitable for moulding.