Kok Tee Lau

Substrate-Free Thick-Film Lead Zirconate Titanate (PZT) Performance Measurement Using Berlincourt Method

Lead Zirconate Titanate or PZT is a high performance piezoelectric material which is able to generate charges when a proportional amount of stress is applied on the material. It has the potential to be used to fabricate micro-power generator for powering low power electronic devices, on top of already existence sensors and actuators. One of the indicators for comparing the performance of the smart materials is the piezoelectric charge coefficient, d33. In this paper, the actual d33 of PZT fabricated in the form of substrate-free thick-films were measured using Berlincourt Method whereby a standard dynamic force is applied to the materials and the resultant value of charges is recorded and compared over a period of time after the thick-films were polarized. The d33 values are compared between substrate-based and substrate-free specimens show a difference of about 45 % as a result of clamping effect contributed by d31. The experiment results also show that the thick-film PZT processed at 950 °C and polarized at 220 V with a thickness of about 120 μm has a piezoelectric charge coefficient of 82 pC/N.

Non-Covalent Polymeric Wrapping of IGEPAL C0890 for Graphene Nanoplatelets (GNPs-C0890) Filled NR/EPDM Rubber Blend Nanocomposites

Graphene nanoplatelets (GNPs) surface modification was performed by using a simplified dual-action of ultrasonication and high speed mechanical shearing. This approach induced a non-covalent polymeric wrapping interaction between GNPs surfaces with IGEPAL-C0890 (ethoxylated nonyl phenol with 40 moles ethylene oxide). Various characterization tools like FTIR, Raman spectroscopy, FESEM and TEM were utilized to confirm the success of the surface treatment. The efficacy and suitability of non-covalent treated GNPs-C0890 as nanofiller reinforcement and inorganic compatibilizer in NR/EPDM rubber blends were evaluated. Effects of GNPs-C0890 loading variation to the mechanical tensile properties and fracture morphologies of NR/EPDM nanocomposites rubber blend were studied. It is interesting to note that the GNPs-C0890 was not able to reinforce NR/EPDM blend at a higher loading addition (≥ 3.00 wt.%) due to the agglomeration and crosslinking retardation phenomena by phase separation. However, at a lower loading (≤ 1.00 wt.%), the blend strengthening effects promise the improvement at about 64.55% of tensile strength and 14.20% of elongation percentage as compared than unfilled NR/EPDM blend. Obvious fractured morphological changes due to the absence and presence of GNPs provide hints on the role of GNPs treatment in effecting the NR/EPDM rubber blend mechanical properties.

Stitch Bonding Strength of Cu Wire on AuAg/Pd/Ni Preplated Cu Leadframes: Influence of AuAg Thickness

Copper (Cu) wire bonding on the pre-plated leadframes with Ni/Pd/AuAg plating has been applied extensively in the semiconductor industry for the interconnection of integrated-circuit (IC) packaging due to the lower material cost of Cu and its excellent electrical properties. Furthermore, the Cu wire bonding on the preplated leadframe has advantages, such as the tin whisker prevention and the robust package for automotive application. Nevertheless, a stitch bondability of Cu wire-preplated leadframe is facing several challenges, such as the Cu oxidation, the high hardness of Cu wire and the very thin AuAg plating on the leadframes. This paper discusses the effect of AuAg plating thickness in roughened pre-plated leadframe on the stitch bonding of Cu wires with the leadframe. The stitch bonding integrity was assessed using Dage 4000 shear/pull tool at a key wire bond responses of stitch pull at time zero (T0). Results show that the stitch pull strength of the Cu-leadframe stitch bonding increases with the increase thickness of AuAg layer. FESEM images of the stitch bonding between the Cu wires and the pre-plated leadframes of different AuAg plating thickness did not show any defect in microstructures, thus it suggests that the bonding property is determined by diffusion mechanism at the Cu wire/AuAg stitch bonding interface. Finally, a brief discussion is provided on the stitch bondability of high performance Au-flashed palladium-coated copper wires on the pre-plated leadframe with different AuAg thickness.

Electrochemical Performance of Multi Walled Carbon Nanotube and Graphene Composite Films Using Electrophoretic Deposition Technique

This study aims to investigate multi-walled carbon nanotube and graphene composite thin films fabricated using cathodic electrophoretic deposition in aqueous solution. The deposition mechanism and films microstructure were investigated using the cyclic voltammetry (CV) and field emission scanning electron microscope. The depositions yield varied by the deposition time and deposition voltage. The composite films were studied for its application in the electrochemical capacitor. The electrochemical performance showed the capacitive behavior of the films in 6 M potassium hydroxide electrolyte. CV scans were verified from 0 to 1 V at different scan rates. The specific capacitance of 29 Fg-1 was achieved at the scan rate of 1 mVs-1.

Effect of Different Types of Pore-Forming Agent on the Macro Pore Size of Ceramic

The aim of this study is to determine the effect of different types of pore-forming agent and sintering temperature on the pore size of ceramics. The porous ceramic material was developed by mixing of alumina, zeolite and calcium oxide (CaO) as the main materials and ethylene glycol as the binder. Meanwhile, two types of pore-forming agent were used, i.e., yeast and a mixture of aluminium powder and expandable polymeric spheres (EPS). The content of pore-forming agent was at 10 wt% of the mixture and the samples were shaped by using plaster of paris mould. After being dried, the samples were sintered at temperature range of 1000 up to 1500 °C for two hours. Microstructural analysis and pores size measurement were performed to determine the effect of pore-forming agent and sintering temperature on the ceramic. The result showed that yeast yielded larger pore sizes in the porous ceramic upon being sintered at 1400 °C for two hours, which were up to 402 μm. Therefore, yeast has the potential to be utilized as pore-forming agent in development of filter and wall insulation material.

Electrophoretic Deposition and Heat Treatment of Steel-Supported PVDF-Graphite Composite Film

Polymeric poly (vinyliden fluoride) (PVDF) is nontoxic. It possesses a better mechanical flexibility and requires a lower synthesis temperature, as compared to the piezoceramic counterparts. In order to achieve a competitive advantage against the current piezoelectric sensor, graphite could replace a more expensive silver-palladium as the electrodes for the piezoelectric PVDF. This paper reports the preliminary results on the synthesis of steel-supported graphite-PVDF/PVDF/graphite-PVDF composite films using the two-step process, consisted of the electrophoretic deposition (EPD) and heat treatment. The composite films were characterized by means of the optical microscopy, scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. The heat treated graphite-PVDF electrode deposited by EPD provides adequate mechanical strength for the subsequent depositions of pure PVDF layer and the second layer of graphite-PVDF composite electrode. However, the final heat treatment stage did not eliminate the fine and large cracks of the composite film, which might be attributed to high residue stresses and weak bonding between graphite and PVDF particles in the post-heat treated composite films. Nevertheless, the increase in final heat treatment temperature of the composite film at Stage 3 improved the graphite and PVDF grain alignment, as well as its crystallinity.

Development of Green Composite: Pineapple Leaf Fibers (PALF) Reinforced Polylactide (PLA)

Green composite material has become the most desired material to replace polymer composites made from fossil oil. Besides having advantages over its biodegradability and quality performances, the material sources are abundant and renewable. Therefore, this research focused on developing green composite which is derived from a combination of pineapple leaf fibers (PALF) and Polylactide (PLA). PALF is extracted from pineapple leaves which are easily found during harvesting pineapple plantation. In order to study the influences of different fibres characterization, the fibres were extracted from different types of pineapple available in Malaysia, namely Moris Gajah, Jasopine, Maspine, and N36. The main objective of this study was to investigate the physical and mechanical properties of this green composite. The physical testing was carried out to determine water absorption while the tensile and bending tests were conducted for mechanical testing. For the purpose of comparing the material properties, PALF reinforced polypropelene (PP) was developed too. Based on the result, Jasopine fibre shows the highest tensile and flexural strength for the combination of both polymers in comparison to the other types of PALF.

Dispersion Stability of Graphene Nanoplatelets (GNPs) and Noncovalent-Functionalization of GNPs with Chitosan in Ethanol

A facile method for surface modification of graphene nanoplatelets (GNPs) in the presence of chitosan was developed to improve their interfacial interaction and dispersion within polymer matrix. The selection of a suitable organic dispersant for GNPs was performed using a sedimentation test of the GNPs in different organic media. GNPs exhibited the highest stability in ethanol dispersant after 3 weeks sedimentation test, and this was supported by TEM observation, which shows that GNPs dispersed well and fully exfoliated into individual sheets in ethanol. The dispersed GNPs in the ethanol dispersion were then functionalized with chitosan-acid solution, filtered and oven-dried into powder form for further characterization. FTIR spectra further verified that the formation of amide linkage between hydroxyl and carboxylic groups of GNP with the amide group of chitosan. The possible functionalization mechanism of GNPs with chitosan was also proposed.