Nurul Hidayat

Thermal expansion coefficient prediction of fuel-cell seal materials from silica sand

This study is focused on the prediction of coefficient of thermal expansion (CTE) of silica-sand-based fuel-cell seal materials (FcSMs) which in principle require a CTE value in the range of 9.5–12 ppm/°C. A semi-quantitative theoretical method to predict the CTE value is proposed by applying the analyzed phase compositions from XRD data and characterized density-porosity behavior. A typical silica sand was milled at 150 rpm for 1 hour followed by heating at 1000 °C for another hour. The sand and heated samples were characterized by means of XRD to perceive the phase composition correlation between them. Rietveld refinement was executed to investigate the weight fraction of the phase contained in the samples, and then converted to volume fraction for composite CTE calculations. The result was applied to predict their potential physical properties for FcSM. Porosity was taken into account in the calculation after which it was directly measured by the Archimedes method.

Studies on Nanostructure and Magnetic Behaviors of Mn-Doped Black Iron Oxide Magnetic Fluids Synthesized from Iron Sand

Manganese (Mn)-doped black iron oxide (Fe3O4) magnetic fluids in the system of MnxFe3−xO4 were successfully synthesized from natural magnetite (iron sand) by using co-precipitation method at room temperature. The analyses of the small angle neutron scattering (SANS) data by applying a log-normal sphere with a mass fractal models for x=0 and x=0.25 and two log-normal spheres with a single mass fractal models for x=0.5, 0.75 and 1 revealed that the primary particles of the MnxFe3−xO4 fluids tended to decrease from 3.8nm to 1.5nm along with the increasing fraction of Mn contents. The fractal dimension (D) increased from about 1.2 to 2.7 as the Mn contents were increasing; which physically represents an aggregation of the MnxFe3−xO4 particles in the fluids growing up from 1 to 3 dimensions to consolidate a more compact structure. The magnetization curves of the fluids exhibited an increasing saturation magnetization from x=0 to x=0.25, and a decreasing on x=0.5 and 0.75, with the maximum achievement of x=1. T...

Synthesis and Characterization of γ-Al2O3/SiO2 Composite Materials

This article reports the synthesis process of γ-alumina/SiO2 composite from aluminium powders and amorphous nanosilica through the means of tetra-methyl-ammonium hydroxide (TMAH) as the mixing medium which produced aluminium hydroxide Al(OH)3 in the form of white powders. The crystal structures, microstructures, and mapping of the atomic constituent of γ-Al2O3 and γ-Al2O3/SiO2 samples were respectively analyzed via X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray SEM-EDX. At the calcination temperature to 300 °C, the samples still had boehmite phase, and the boehmite phase transformation to γ-alumina phase occurred at temperature of 700-900 °C. The γ-alumina phase began to form at the calcination temperature of 500-700 °C with the crystal structure of (440), (511), (400), (222), (311), and (111). The similar diffraction pattern was also shown by the γ-Al2O3/SiO2 composite for the calcination temperature of 700 °C and 900 °C. The microstructure analysis of the γ-Al2O3/SiO2 showed that SiO2 particles were smaller and round while the γ-Al2O3 particles were bigger and elongated. Additionally, the mapping results showed SiO2 and γ-Al2O3 particles were homogenously distributed.

Crystalline Phase Analysis and Thermal Expansion Coefficient Calculation of Quartz-Sand/Corundum Composites

Quartz-sand/corundum composites have been successfully produced by a simple solid-state reaction approach. The composites with corundum weight fractions of 10%, 20%, and 30% were prepared through grinding mixtures of purified Indonesian quartz sand and commercial high purity corundum for a half-hour with an addition of 3% polyvinyl alcohol. The composites were shaped into discs and pressed prior to the sintering at 950 °C and 1050 °C to form compact ceramic composites. The crystalline phase verification within the samples was conducted by means of X-ray diffraction (XRD). The coefficient of thermal expansion (CTE) of the composites was semi-theoretically evaluated, after being taken into consideration the XRD data analysis results, by means of Halpin-Tsai formula. The detected major crystalline phases within the sintered samples, based on the XRD profiles analysis, were quartz-SiO2 and corundum-Al2O3. Meanwhile, the minor crystalline phases were wollastonite-CaSiO3 (below 7%) for all samples and cristobalite-SiO2 (around 1%) for the composite with 1050 °C sintering temperature. Generally, the addition of corundum into the quartz-sand/corundum composites reduced the CTE, having the value from 10.5 to 11.5 ppm/°C.