Shaifulazuar Rozali

Oxidation of nanodiamonds and modulation of their assembly in polymer-based nanohybrids by field-inducement

Linear assembly of densely packed oxidized nanodiamonds (OxNDs) was performed in polymer-based nanohybrid films. A homogeneous suspension of the pre-polymer polyepoxide and OxNDs was placed onto a polyamide spacer and subjected to an electric field in order to induce the relocation and assembly of the fillers before the mixture became cross-linked. The OxNDs suspended readily, forming linear assemblies of OxNDs (LAOxNDs) of varying thicknesses, aligned perpendicular to the film surfaces. Nanohybrid films with linear assemblies of LAOxNDs exhibited a moderate increase in thermal conductivity while maintaining the electrical insulation properties of the polyepoxide. Mechanisms for the field-induced fabrication and the structural variation of LAOxNDs in the pre-polymer matrix are elucidated in relation to the variations in physical properties. The present air oxidation process and field-induced application are simple but effective in enhancing the physical properties of polymer-based hybrids, and hence, has the potential for applying in the fabrication and modulation of nanocomposite materials.

Toward improved heat transfer performance of annular heat exchangers with water/ethylene glycol- based nanofluids containing graphene nanoplatelets

A novel synthesis procedure is presented for preparing functionalized graphene nanoplatelets (GNPs). Using sonication method, the functionalized GNPs are dispersed in water-ethylene glycol to prepare water–ethylene glycol-based functionalized GNP nanofluids. Meanwhile, the thermophysical properties of the prepared nanofluids, i.e., thermal conductivity, specific heat capacity, and rheological properties are investigated. As the second phase of study, the heat transfer performance of an annular channel is simulated and measured in the presence of the prepared nanofluids. To this end, a computational fluid dynamics study has been carried out to calculate the heat transfer rate as well as pressure drop of the well-dispersed nanofluids. Meanwhile, the effects of concentration and Reynolds number on the convective heat transfer coefficient have been investigated at constant wall temperature boundary condition under turbulent flow regime. Consist with the results, the convective heat transfer coefficient of nanofluids are significantly higher than that of the base-fluid. The novel type of nanofluid reveals promising potential for use as an advanced working fluid in future heat transfer applications.

Effect of temperature and alloying elements (Fe and Bi) on the electrical resistivity of Sn–0.7Cu solder alloy

In this paper, we investigated the electrical resistivity as a function of temperature of the Sn–0.7Cu solder alloy with the addition of Fe and Bi. The electrical resistivity were characterized by the four-point probe method. Apparent change in electrical resistivity was witnessed by the addition of both Fe and Bi. At room temperature, the electrical resistivity was found to be increased with the addition of Fe, as well as a further increase with the addition of Bi. Fe and Bi modified Sn–0.7Cu alloys also experienced the similar increasing trend when they were subjected to higher temperatures within the range of 300–423 K. Chemical state of Sn was analyzed by means of X-ray photoelectron spectroscopy (XPS). The results revealed the presence of Sn in Sn2+, Sn4+ and state of metallic Sn. With the addition of Fe & Bi, a substantial decrease was observed in the atomic percent of the Sn4+ chemical state. X-ray diffraction (XRD) was performed on the alloys. The XRD pattern showed disturbance in the 2 theta values with the addition of Bi. The disturbance confirmed the presence of stress and imperfections in the crystal lattice. Field emission scanning electron microscope (FESEM) micrographs revealed the formation of the FeSn2 intermetallic compound with the addition of Fe. However, the addition of Bi promotes the formation of solid solution and goes into primary β-Sn dendrites. Microstructural changes, shifts in the chemical state of Sn and a disturbance in the XRD peaks resulting from the addition of Fe and Bi have been correlated to the variation in electrical resistivity.

Effect of Powder Particle Sizes on the Development of Ultra Hard Surface through Superplastic Boronizing of Duplex Stainless Steel

In this work, a further study on boronizing using compression method called superplastic boronizing (SPB) was conducted. This process was conducted on duplex stainless steel (DSS) that exhibited superplasticity. Efforts were being put in obtaining ultra hard surface through SPB by focusing on the boron powder particle size. The microstructure, hardness, and layer thickness of the boronized materials were investigated. Comparison using as-received DSS with coarse microstructure also was performed. The overall results from the study showed that the SPB process can produced a very hard surface of close to 4000 HV and significantly improved the surface properties of the DSS.