Applied Mechanics and Materials Vol. 761

Abstract: Despite the rapid increase in the utilization of reinforced nanomaterials composites, micromaterials may also have the potential to be utilized as filler in polymer composites. In this study, the activated carbon (AC) filled epoxidized natural rubber (ENR) composite was fabricated using the solvent casting method. AC was used as the filler at different filler addition in range from 0 to 7 parts per hundred rubbers (phr). The intention was to investigate the effect of AC filled ENR on mechanical properties and interaction between AC and ENR matrix. Overall, the result shows high improvement in mechanical properties. At 7 phr, the tensile strength was 7.0 MPa compared to 2.6 MPa for 0 phr, which indicates the increase by almost 2 times. The elongation also increases for all phr, which indicates the good filler effect.

Abstract: A nanocomposite TiAlBN (n-TiAlBN) coating has been successfully deposited via RF magnetron sputtering by varying the nitrogen-to-total gas flow ratio (R_N) at a substrate temperature of 300 °C. The coating was deposited on AISI 316 substrates using a single Ti-Al-BN hot-pressed target. The crystal phases, grain size and chemical composition of the coatings were measured using the glancing angle X-ray diffraction analysis (GAXRD) and X-ray photoelectron spectroscopy (XPS). The grains size of the n-TiAlBN coating was found to be within the range of 3.5 to 5.7 nm calculated using Scherrer’s formula. The n-TiAlBN coating reached a nitride saturated state at a higher R_N (e.g >15%) with the amount of boron concentration to be around 9 at. %. Further, reducing the R_N (e.g. 5%) has increased the boron concentration to 16.17 at. %. This paper shows that by carefully control the nitrogen-to-total gas flow ratio (R_N) in the n-TiAlBN coating, it indeed gives a significant effect on its crystallographic structure, grain size, and chemical compositions.

Abstract: Ceramics are increasingly popular in dental restoration after metal restoration has been found to be less esthetic. One such example is yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP). However, one of the challenges of this application is its insufficient translucency to ensure high esthetic restoration. This study reviews the effect of sintering parameters, primary particle size, microstructure homogeneity, and thickness of zirconia on its translucency. Several studies remarked that the thickness of the framework had the greatest effect on zirconia translucency. Thus, a rigorous thickness control is necessary. The consideration for optimal sintering parameters (sintering temperature and holding time) and the use of smaller particle sizes help in the densification and elimination of porosity in zirconia, which, consequently, improve its translucency. Finally, a homogeneous microstructure can reduce the light scattering effect in zirconia and increase its translucency. Identifying the factors that influence zirconia translucency can contribute to future research in improving the esthetic dental restoration.

Abstract: Natural Rubber/EPDM blends were successfully prepared by direct melt compounding method using an internal mixer. The significance of MAH grafted EPM (MAH-g-EPM) and compounding parameters were studied via the response surface methodology (RSM) using the two-level full factorial design. The MAH-g-EPM loading, mixing temperature, rotor speed and mixing time were selected as four independent variables. Cure characteristics of scorch time, cure time and maximum torque were selected as the responses. The statistical significance of all variables and their interactions during compounding were analysed using ANOVA. The degree of agreement between experimental results with those predicted by the statistical model was confirmed using constant of determination, R² with values approaching ~0.99. It was observed in the results, that the incorporation of high loading (10 phr) of MAH-g-EPM has predominantly enhanced the scorch safety time of NR/EPDM blends, as well as increased the modulus of NR/EPDM blends to some extent compared to low loading (5 phr and 7.5 phr). These finding were further supported by the Differential Scanning Calorimetry (DSC) analysis.

Abstract: 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.

Abstract: In this study, a mixture of activated carbon (AC) and graphene (G) was coated onto the stainless steel (SS) mesh to produce an electrode for the electrochemical capacitor (EC). Different materials, such as carbon nanotube (CNT) mixed with G, were also used in this experiment to compare the electrochemical properties of both electrodes. The electrochemical properties of the electrode were determined by using cyclic voltammetry (CV). The CV curves of the AC/G electrodes showed good capacitive behaviour, and the highest capacitance values obtained for AC/G and CNT/G electrodes in 1M H₂SO₄ at 1 mVs^-1 were 13 Fg^-1 and 4.34 Fg^-1, respectively. Meanwhile, the highest capacitance values obtained in 6M KOH at 1 mVs^-1 were 14 Fg^-1 and 12.07 Fg^-1 for AC/G and CNT/G electrodes, respectively.

Abstract: NiAl is widely used for elevated temperature application because it gives better properties, especially in the gas turbine application. This study was done in order to investigate the effects of calcination temperature on NiAl and α-Al₂O₃ formation using gel combustion synthesis method. This method used fatty alcohol and fatty acid ester for producing NiAl powders. X-Ray diffraction patterns of calcined samples exhibited NiAl and α-Al₂O₃ at temperature 1050°C. Therefore, nanostructured NiAl-α- Al₂O₃ can be successfully produced with the gel combustion method using less expensive and more environmental friendly fatty alcohol and fatty acid ester as fuels.

Abstract: The artificial basilar membrane has been developed to mimic the mechanical performance of the basilar membrane in the cochlea. The artificial basilar membrane consists of an array of microbridgeresonators that are mechanically sensitive to the perceived audible frequency range between 20 Hz to 20 kHz. In this work, the finite element (FE) model of the microbridge resonators have been designed in Comsol Multiphysics 4.3 to work close to the audible frequency range. The lumped element (LE) model of the microbridge resonators have been calculated and compared to the simulated FE model. The microbridge resonators array with 0.5 μm thickness, 20 μm width and length varying from 275 μm up to 7700 μm have been designed using two different materials, i.e., platinum (Pt) and aluminium (Al). The microbridge resonators have been found to mimic closely the tonotopicorganisation characteristics of the basilar membrane. From the FE and LE models of the Pt and Almicrobridge resonators, Pt has been found to be a better material than Alfor the artificial basilar membrane design. For the same geometrical dimensions, the Ptmicrobridge resonatorsoperate within the audible frequency range while the Almicrobridge resonatorsoperate approximately 43%-53% above the audible frequency range.

Abstract: 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.

Abstract: SBA-15 mesoporous silica was directly synthesised under difference acidic conditions by a “pH modification method” using hexamethylenetetramine (HMTA) as an internal pH-modifier. The synthesised material has been characterised by XRD, Nitrogen adsorption–desorption, and TEM. The characterisation results showed that mesoporous silica lead to high-ordered hexagonal mesoporous morphology by TEM at high acidity compared to low acidity condition. In addition, the physical properties of SBA-15 showed a decrease of surface area and pore size due to the increase in the pH. Use of HMTA as pH modifier is suitable, due to pH value increases occurred in the hydrothermal processes only. This is because during the hydrothermal process at a temperature of 100°C, HMTA decomposes to NH₃ which in turn increase of the pH value in the silica gel. It can be concluded that the formation of mesoporous silica SBA-15 to some extent been influenced by the pH value. This can be seen from the results of the study show that mesoporous silica type SBA-15 lead to well-ordered hexagonal mesoporous at high acidity and poor order hexagonal pore structure was formed in low acidity condition.