Advanced Materials Research Vol. 410

Abstract: Crosslinking of UHMWPE by gamma irradiation has been the prime choice to improve the wear resistance of the polymer. However, it is always associated with few setbacks like degradation of material properties during the shelf ageing period. In the present work, nanocomposites were prepared using ball milling process and then compression moulding process where UHMWPE was reinforced by MWCNTs with 0.20 and 0.40 wt. %. The samples were gamma irradiated using ⁶⁰Co at 25 and 50 kGy sterilizing doses in air without any post irradiative treatments and then shelf aged for 240 days. The mechanical properties of the composites were studied using small punch technique according to ASTM F2183 standards. Both toughness and hardness of the composites were found to be improved with an increase of irradiation dosage and MWCNT concentration. It is observed that the percentage reduction in Young’s modulus, yield stress and % strain at fracture of 0.4% composite at 50 kGy dose are 6.4%, 8.8% and 12.7%, respectively compared to that of virgin UHMWPE irradiated at same dosage. It is concluded that presence of MWCNTs in UHMWPE prevents the degradation of material properties during the shelf ageing period after irradiation.

Abstract: PS/LDH nanocomposites were synthesized via in-situ polymerization technique using styrene monomer with toluene as a solvent. A series of LDHs (Mg-Al, Co-Al, Ni-Al, Cu-Al, Cu-Fe and Cu-Cr LDHs) was first prepared from their nitrate salts by co-precipitation method. The above prepared, pristine LDHs were organically modified using sodium dodecyl sulfate (SDS) to obtain organomodified LDHs (OLDH). Then, PS nanocomposites containing 5 wt.% OLDHs were prepared by in-situ polymerization method. The structural and thermal properties of LDHs and corresponding nanocomposites were characterized by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA). The absence of OLDH peak (003) in the XRD patterns of PS/OLDH nanocomposite confirms the formation of exfoliated nanocomposites. The presence of sulfate groups in the modified LDHs is confirmed by FTIR analysis. The appearance of new peaks in the FTIR spectra in the region of 3400-3500 cm^-1, 1670-1680 cm^-1 and 1200-1260 cm^-1 for O-H stretching, H-O-H vibration and stretching vibration of sulfate, respectively indicate the existence of LDHs in the PS/OLDH nanocomposites. The entire exfoliated PS/OLDH nanocomposites exhibit enhanced thermal stability relative to the pure PS. When 50% weight loss is selected as point of comparison, the decomposition temperature of nanocomposites is about 3-5^o C higher than that of pure PS.

Abstract: This work highlights the fabrication of multiwalled carbon nanotube (MWCNT)-TiO₂ nanocomposite for use in dye-sensitized solar cells (DSSCs) to improve the photovoltaic conversion efficiency. Morphology of the MWCNT-TiO₂ film was investigated by field emission scanning electron microscopy (FESEM). FESEM images demonstrated that MWCNTs were dispersed homogeneously in TiO₂ matrix. MWCNT acted as an efficient conduit for electron transfer that can enhance the photovoltaic conversion efficiency of the DSSC. The proposed MWCNT-TiO₂ nanocomposite photoelectrode might be beneficial to develop high photovoltaic conversion efficiency of DSSCs.

Abstract: In this paper, the specific influence of quasi-isostatic forging and rolling of cryomilled powder on microstructural development and resultant tensile deformation and fracture behavior of aluminum alloy 5083 is highlighted and comparison made with the coarse grained counterpart. The specific influence and contribution of strain hardening to enhancing strength of the ultra-fine grain microstructure of the aluminum alloy is presented and discussed. It is shown that the capability of the ultra fine grain microstructure to recover strength through the mechanism of work hardening is quite similar to the conventionally processed counterpart. The influence and role of intrinsic microstructural features in governing tensile deformation and fracture behavior is elaborated upon. The viable microscopic mechanisms governing final fracture behavior is discussed in light of the competing and mutually interactive influences of nature of loading, intrinsic microstructural effects, and deformation kinetics. Key Words: aluminum alloy 5083, processing, microstructure, tensile properties, fracture

Abstract: A novel approach of brazing porous W and Mo using three clad Ti-Ni-Nb foils has been performed in the experiment. Clad Ti-Ni-Nb filler foils are featured with low brazing temperature of below 1350°C. Both W and Mo are completely soluble with β-Ti and Nb, and the Ni addition into the braze alloy is served as a melting point depressant (MPD). Decreased brazing temperature and/or time are necessary in order to minimize infiltration of the molten braze into the porous W substrate. According to the experimental results, Ti-Ni-Nb ternary alloys are promising filler metals in low-temperature brazing porous W and Mo.

Abstract: The manufacturing of plate heat exchangers is much more difficult than that of making traditional heat exchangers. The demand of increased corrosion resistance, avoiding Cu ion contamination, resisting to high-temperature resulting from various applied environments makes the traditional Cu brazed 316 stainless steel (316SS) plate heat exchanger fail to satisfy certain applications. Corrosion-resistant brazed 316SS plate heat exchangers are successfully developed using two commercially available Ni-based brazing foils, and they are valuable for industrial applications.

Abstract: The technique of friction stir welding (FSW) does offer several advantages over conventional welding techniques. In this paper is presented the results of an investigation aimed at understanding the effect of tool angle on welding of sheets of commercially pure aluminum and aluminum alloy AA5052-H32 having different thickness. The present study demonstrates the feasibility of using friction stir welding (FSW) for joining two different thickness sheets of commercially pure aluminum (t = 1.5 mm and t = 2.0) with sheets of aluminum alloy 5052-H32 having thickness of 1.6 mm and 2 mm. It was found that the tool angle does play a major role in the welding of sheets having different thickness. Formation of the FSW zone was analyzed both macroscopically and microscopically. The tensile properties of the joints were evaluated and correlated with the formation and presence of the FSW zone. From this study it was found that the tool angle for commercially pure aluminum having a thickness of 1.5 mm and 2.0 mm is 2.58⁰. The tool angle is 1.91⁰ for the sheets of AA 5052-H32 having a thickness of 1.6 mm and 2 mm. The joint efficiency of the friction stir welded AA 5052-H32 was 87.5 pct. when compared to the base material. The hardness was also observed to drop in the region of the weld. Key words: Friction stir welding, tool angle, aluminum alloy (AA5052-H32), Hardness, macrostructure, microstructure.

Abstract: The axial force during friction stir welding is sensitive to plunge depth of the tool and is one of the prime factors, which exercises control over heat generation during welding. Consequently, the plunge depth for a given tool rotation speed, traverse speed, material and test machine needs to be optimized so as to get a defect-free weld. In this paper, we present and briefly discuss the results of an elaborate and enriching investigation aimed at understanding the extrinsic influence of plunge depth of the tool on weld formation in aluminium alloy 7020-T6 for a range of rotation rate and traverse speed and using two different tools. The critical need for use of a scientific approach to optimize plunge depth for a given tool material and test machine in fewer number of steps is emphasized. Key Words: Friction Stir Welding, Tool Plunge, Rotation speed, Traverse speed, Aluminium Alloy 7020

Abstract: In this work, the three compositions of hexagonal boron nitride (10, 15 and 20 vol. %)-embedded 316L stainless steel (SS316L/h-BN) composites were prepared by a conventional powder metallurgy technique and then sintered at varying temperatures of 1100 to 1250°C for 60 min in H₂ atmosphere. The h-BN content and sintering temperature were found to affect the microstructure and hardness of the composites. The hardness decreased with increasing h-BN content and was improved by increasing the sintering temperature. Microstructure results revealed that the boride phase was formed at the grain boundary at the sintering temperature higher than 1150°C and the boride phase formation was observed to transform the h-BN in the composites.

Abstract: This work studied an adsorption of ammonium sulfate (NH₄)₂SO₄ from synthesized zeolite, with 3M NaOH at temperature of 90°C for 9 h, from waste sludge of water treatment plant. The scanning electron microscopic analysis revealed that the synthesized zeolite was observed to be cubic in shape. For adsorption capacity, the pH was varied at 4, 5, 6, 7 and 8, the contact times used were 0, 5, 10, 15, 30, 45 and 60 min, and the initial (NH₄)₂SO₄ concentrations used ranged from 60-120 mg/L. The recommended pH and contact time were 8 and 15 min, respectively. Adsorption isotherm for synthesized zeolite was fitted to Langmuir model more effectively than Freundlich model. The K values for Langmuir and Freundlich isotherm was 0.061 and 1.751 L/mg with R² values of 0.989 and 0.965, respectively. The maximum adsorption capacity was 9.597 mg/g obtained by the Langmuir isotherm. The work has concluded that the fabricated zeolite could successfully be used for adsorption of ammonium sulfate.