Solid State Phenomena Vol. 307

Abstract: Conventionally, chromium is deposited from hexavalent chromium baths containing extremely toxic compounds of Cr (VI). Due to serious health and environmental concerns of Cr (VI), trivalent chromium bath is proposed as a counter approach towards greener and safer chromium plating. In the present work, chromium coatings were electrodeposited onto copper substrate using a modified trivalent chromium electroplating bath with addition of polyethylene glycol (PEG 1500). The effects of PEG on the Cr coating were investigated. The crystalline structure, composition and surface morphology of the deposits were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The surface roughness of the coatings were characterized by atomic force microscopy (AFM). With addition of PEG, the surface roughness of Cr coating decreased by 44.5 % and the corrosion rate decreased by 23.3 % compared to that of without PEG. Meanwhile, the hardness increased by 22.7 %.

Abstract: Preparation of MgO and Mg_0.95Zn_0.05O nanomaterials using self-propagating combustion method are done to investigate the effect of doping on the band gap energy. The synthesis condition has been optimized to obtain pure MgO and Mg_0.95Zn_0.05O materials which confirmed by XRD. FESEM results shows agglomeration of crystallite with average crystallite size of samples between 30 nm to 125 nm. The band gap obtained from the measurement of UV-Vis NIR spectrophotometer for MgO nanostructure is 6.36 eV which is lower than bulk MgO of 7.8 eV. The presence of Zn in Mg_0.95Zn_0.05O sample causes the narrowing of band gap to 5.33 eV.

Abstract: Copper nanoparticles were synthesized using laser ablation method by the reduction of copper plate in the presence of distilled water. Effects of time as the laser hits on the copper target were increased, the amount of Cu NPs in the distilled water also increased. EDAX confirms the existence of Cu NPs. The metallic nanoparticles have a unique optical property known as Surface Plasmon Resonance (SPR) which can be utilized to enhance the light harvesting performance in many applications. The noble metals of copper have the ability to support surface plasmon resonance which can be used to enhance the efficiency of any device.

Abstract: Metal corrosion generally refers to metal deterioration process that is caused by electrochemical reactions between the metallic substrate with corrosive environment. Marine grade stainless steel type 316L (SS 316L) is a premium material for marine applications. Prolonged exposure to chloride-containing environments increases the susceptibility of unprotected SS 316L to localized corrosion namely pitting and crevice corrosion. In this study, the potential protective coating comprising of the epoxy matrix with ZnO nanoparticles combination was formulated and its anticorrosive properties on SS 316L substrate were analyzed. Variation in corrosion behaviour of SS 316L coated with a series of epoxy coating solution containing 1, 3, 5, 7 and 10 wt % ZnO nanoparticles were thoroughly observed. The coating formulations were characterised by using X-ray Diffraction (XRD) spectroscopy and Scanning Electron Microscope (SEM). Meanwhile, the corrosion performance testing was measured by using Potentiodynamic Polarization (PP) technique. The results revealed that epoxy coating incorporated with 3 wt % of ZnO nanoparticles provided the best corrosion protection on SS 316L as the corrosion rate for the metal substrate has been minimized from 0.05268 mm/year to as low as 0.00047 mm/year after coating. Dispersion of ZnO nanoparticles in epoxy matrix increases the barrier properties of the coating and impeded corrosion process on SS 316L through suppression of anodic reaction.

Abstract: A micro-perforated panel (MPP) works as a Helmholtz-type resonance absorber formed by an air-gab cavity in order to minimize the reflected sound effectively at a selective resonance frequency. Furthermore, the use of natural fibers as sound absorbing materials recently has attracted more attention because it is completely biodegradable, environmental friendly and more economical. In this paper, the combination of MPP and natural fiber as sound absorptive material is investigated. The MPP is made of a transparent acrylic board with 1.5 mm thickness and backed by a coconut fiber panel. The effect of the fiber panel that inserted in the air-gab cavity to the sound absorption characteristic of a single leaf MPP is observed. Sound absorption coefficient is measured by transfer function method using two microphones-impedance tube. It is found that the sandwich model of MPP backed by a coconut fiber changes the sound absorption characteristics of MPP by shifting the maximum absorption coefficient into the lower frequency and making a wider band of frequency absorption. Moreover, the air-gab cavity between MPP and fiber panel give fewer contribution to construct the MPP frequency resonant than the natural fiber panel one.

Abstract: Solar thermal energy is one of the promising renewable and sustainable energy that have gain research interest. However, the nature of intermittent solar irradiation limits the usage of this energy. Phase change material (PCM) are substance that has the property of absorbing and releasing thermal energy through phase transformation. Combination of graphene foam/PCM composite will be able to absorb heat from solar thermal energy and sustain energy release to thermoelectric generator (TEG) for electrical conversion. Two different PCM material were tested which are petroleum-based paraffin wax and bio-based PCM beeswax. Thermal properties of both materials were measured using DSC and heat absorption were tested under real solar irradiation. This solar-thermal converter showed that graphene/paraffin/beeswax composite is more effective than the paraffin wax or beeswax alone. The recorded results also showed that combination of these petroleum based and bio-based PCM with added graphene foam could retain longer heat than graphene/paraffin wax and individual PCM. The longer heat can be stored in solar-thermal converter device may sustain electricity generation even with absence of solar energy.

Abstract: A series of (74.4-x) TeO₂ – (4.3) LiO₂ – (21.3) LiCl – (x) Eu₂O₃ with 0.0 ≤ x ≤ 2.0 mol % has been made using melt-quenching technique and their optical characteristic has been studied. The present works cover the preparation of the glass sample and the effects of Eu³⁺ on the physical properties, absorption and photoluminescence behaviour of the lithium chloride tellurite glass. The physical properties such as density and molar volume are determined. It is found that the density and molar volume presents fluctuation trends. As the samples are excited at 393 nm, six emission peaks have been observed at 532, 552, 586, 613, 649, and 697 nm indicating the transitions of ⁵D₁ → ⁷F₁, ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃ and ⁵D₀ → ⁷F₄ respectively. It is observed that transition ⁵D₀ → ⁷F₂ shows the highest intensity. The emission intensity increases with the increment of Eu₂O₃ concentration. The high-intensity ratios of 1.88 observed for glass sample contain 2.0 mol % Eu₂O₃ concentrations indicate a greater degree of Eu-O-covalency and possess the better quality of host matrix.

Abstract: The luminescence properties Dy³⁺, Eu³⁺ and Sm³⁺ doped magnesium sodium borate glasses were investigated. The glasses samples containing the composition 30MgO-70Na2B4O7.10H2O-xRE₂O₃ (where RE = Dy³⁺, Eu³⁺, and Sm³⁺, x = 0.1, 0.5, and 1.0 mol %) are prepared by the conventional melt quenching technique. The optical properties have been evaluated using Ultraviolet-Visible Spectroscopy and Photoluminescence Spectroscopy. The X-ray Diffraction pattern was studied to confirm the amorphous nature of the prepared glass. The absorption spectra yield the most intense absorption bands and transition energy levels for Dy³⁺, Eu³⁺, and Sm³⁺ located at 347 nm (⁶H_15/2 → ⁶P_7/2), 393 nm (⁷F₀ → ⁵L₆), and 403 nm (⁶H_5/2 →⁶P_5/2) respectively. The emission spectra demonstrate the highest emission intensity centered at 463 nm (⁴F_9/2 → ⁶F_11/2 + ⁶H_9/2), 612 nm (⁵D₀ → ⁷F_J), and 599 nm (⁴G_5/2 → ⁶H_7/2) for Dy³⁺, Eu³⁺, and Sm³⁺ respectively. Dy³⁺ emits combination of blue, yellow, and red light, Eu³⁺ emits red light and Sm³⁺ emits orange to red light. The higher the content of Dy³⁺, Eu³⁺, and Sm³⁺, the higher the spectral or peak intensity for both absorption and emission. The findings could be useful for development of laser, light emitting diode (LED), and color displays applications. KEY WORDS: Luminescence, Borax glass, Magnesium, Dysprosium, Europium, Samarium.

Abstract: Silica borotellurite glasses doped with different molar fraction of V₂O₅ have been prepared by melt quenching technique. The elastic properties of {[(TeO₂)_0.7 (B₂O₃)_0.3]_0.8(SiO₂)_0.2}_(1-x)(V₂O₅)_x glasses are investigated using ultrasonic pulse echo measurements and their elastic properties have been characterized at room temperature. The density of the glasses was measured by Archimedes method using distilled water as buoyant liquid. The ultrasonic wave velocities (longitudinal, v_l and shear, v_S) were recorded at 5 MHz. Elastic moduli, Poisson’s ratio (σ) and microhardness (H) were then calculated to obtain quantitative analysis regarding the structure of these glasses. The results obtained showed that the doping of V₂O₅ with silica borotellurite enhances the strengthening of glass network. Glass with 0.03 molar fraction of V₂0₅ shows low ultrasonic velocities and low elastic moduli. The variation of elastic properties is related to the change of structure in the vanadium doped silica-borotellurite glass system.

Abstract: In this project, the nominal glass composition with the form of (55-x) H₃BO₃-45ZnO-xY₂O₃ (x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) are synthesized by melt quenching techniques. The effect of Y₂O₃ on physical, mechanical and structural properties of glasses have been investigated using different characterization techniques. The parameters like density, molar volume and oxygen packing density have been calculated. Based on the micro hardness study, it has showed the decreasing trend from 518.80 N.mm^-2 to 453.13 N.mm^-2 with an increasing of Y₂O₃ content from 0.0 mol% to 2.5 mol%. The structural features of the yttrium oxide doped zinc borate glass were studied via X-Ray Diffraction (XRD) to confirm the amorphous nature of glass and Fourier Transforms Infrared Spectroscopy (FTIR) has been done to obtain the band positions and functional groups. FTIR spectral studies were recorded in the 400-4000 cm^-1 wavenumber range at room temperature.