Volume 20 (2020): Issue 3 (September 2020)

Poly(vinyl alcohol) (PVA) has been considered as an important commercial synthetic thermoplastic polymer. PVA is a low cost, reasonably processable, optically transmitting, heat stable, and mechanically robust plastic. PVA-based nanomaterials usually comprise of the nanocomposites (PVA/graphene, PVA/carbon nanotube, PVA/nanodiamond, PVA/metal nanoparticle) and nanofibers. The structural, optical, mechanical, and electrical properties of the PVA-based nanomaterials have been enhanced with nanofiller addition or nanostructuring. This review offers fundamentals and advanced aspects of poly(vinyl alcohol) and the derived nanomaterials. It highlights recent advances in PVA nanocomposites and nanofibers for potential applications. The PVA-based nanomaterials have been successfully employed in fuel cells, sensors, batteries, membranes, electronics, and drug delivery relevances. The challenges and opportunities to strengthen the research fields of PVA-based nanomaterials have also been presented.

Ba_0.85(La,Y)_0.15Fe₁₂O₁₉ hexaferrite magnets were produced using the powder metallurgy method. The phase analysis of the ferrite magnets was carried out by X-ray diffraction (XRD) technique. A single hexaferrite phase was present in both samples as revealed by XRD patterns. The microstructural evolution in the hexaferrite samples was examined using Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). The grain morphology altered with the sintering temperature. Room temperature ferrimagnetic hysteresis curves were obtained by Vibrating Sample Magnetometer (VSM). The crystallite size and the lattice parameters (a,c) were also calculated after sintering at 1150ºC and 1250ºC. Saturation magnetizations, Ms were determined to be 48.60 emu/g and 52.95 emu/g for the samples sintered at 1150ºC and 1250ºC, respectively whereas the remanent magnetizations, Mr were 29.26 emu/g and 31.17 emu/g. The coercivity, Hc decreased from 3.95 kOe to the value of 2.44 kOe with the sintering temperature due to the increase of the crystallite size. The squareness ratios (Mr/Ms) of the ferrimagnetic samples were different because the uniaxial anisotropies altered after sintering at 1150ºC and 1250ºC. The maximum energy product, (BH)max dropped from 35.81 kJ/m³ to 27.38 kJ/m³ when the sintering temperature increased. This result can be attributed to a combination of higher magnetization and the lower coercivity.

In this work, we have prepared new materials of the nickel sulfide thin films by using the spray pyrolysis technique for promising co-catalyst to improve the photocatalytic performance or superconductivity. The effect of deposition temperature (523, 573 and 623 K) on structural, optical and electrical properties was investigated. The XRD diffraction shows that the prepared nickel sulfide at 523, 573 and 623 K having an orthorhombic, hexagonal and hexagonal structure, which were Ni₃S₂, Ni₁₇S₁₈ and NiS₂, respectively. The minimum value of crystallite size (45,9 nm) was measured of deposited film at 573K. The thin films prepared at 523 and 573 K have an average transmittance is about 20 %. The prepared Ni₁S₂ thin film at T=623 K has the lowest calculated optical band gap and Urbach energy. The Ni₁S₂ thin film also has the best calculated of the refractive index and the extinction coefficient. The FTIR spectrums of the nickel sulfide have various bands such as Ni-S, C-H, O-H, N–H and C-S. The maximum electrical conductivity is 4,29x10⁵ (Ω.cm)⁻¹ was obtained at 573K of the Ni₁₇S₁₈. The nickel sulfide thin films sprayed at 573K have good structural, optical and electrical properties.

The purpose of this study is to elucidate the flow features of the dissimilar Al-Cu welded plates. The welding method used is Bobbin Friction Stir Welding (BFSW), and the joint is between two dissimilar materials, aluminium alloy (AA6082-T6) and pure copper. Weld samples were cut from along the weld line, and the cross-sections were polished and observed under an optical microscope (OM). Particular regions of interest were examined under a scanning electron microscope (SEM) and analysed with Energy Dispersive X-ray Spectroscopy (EDS) using the AZtec software from Oxford Instruments. The results and images attained were compared to other similar studies. The reason for fracture was mainly attributed to the welding parameters used; a higher rotational speed may be required to achieve a successful BFSW between these two materials. The impact of welding parameters on the Al-Cu flow bonding and evolution of the intermetallic compounds were identified by studying the interfacial microstructure at the location of the tool action. The work makes an original contribution to identifying the solid-phase hybrid bonding in Al-Cu joints to improve the understanding of the flow behaviours during the BFSW welding process. The microstructural evolution of the dissimilar weld has made it possible to develop a physical model proposed for the flow failure mechanism.

In this work, nickel oxide was deposited on a glass substrate at by spray deposition technique; the structural, optical and electrical properties were studied at different NiO concentrations (0.05, 0.10 and 0.15 mol.l⁻¹). Polycrystalline NiO films with a cubic structure with a strong (111) preferred orientation were observed at all sprayed films with minimum crystallite size of 11.97 nm was attained of deposited film at 0.1 mol.l⁻¹. However, α-Ni(OH)₂ was observed at 0.15 mol.l⁻¹. The NiO thin films have good transparency in the visible region, the band gap energy varies from 3.54 to 376 eV was affected by NiO concentration, it is shown that the NiO thin film prepared at 0.05 mol.l⁻¹ has less disorder with few defects. The NiO film deposited at 0.15 mol.l⁻¹ has the electrical conductivity was 0.169 (Ω.cm)⁻¹.