Band 114, Heft 3

Spinel nano-ferrite compounds have attracted significant interest in industrial, scientific and technological communities as a result of their promising and unique features especially at nano-scale range. The present and future potentials of spinel nano-ferrite materials cut across several applications such as biotechnology, magnetic storage, sensors, magnetic hyperthermia, microwave absorbance and photo-catalysis. Enhancing the photocatalytic application of spinel nano-ferrite materials involves accommodation of foreign materials into the parent compound as well as appropriate fabrication technique which respectively alter the crystal structure and nano-size of the spinel nano-ferrite materials. This work implements the crystal lattice distortion and the size of nano-particles to develop, for the first time, hybridization of a support vector regression algorithm with a genetic algorithm for estimating the energy gap of doped spinel nano-ferrite materials. The developed hybrid genetic algorithm based support vector regression model was built using two hundred different spinel nano-ferrite materials doped with varieties of materials and synthesized through various methods. The developed genetic algorithm based support vector regression model that is characterized by low root mean square error and mean squared error of 0.3075 eV and 0.095 eV respectively, was further validated using eighteen different spinel nano-ferrite materials and the estimated energy gaps agree excellently with the experimental values. The influence of magnesium, aluminum and lanthanum on the band gap of spinel ferrite nanoparticles was investigated and studied using the developed genetic algorithm based support vector regression model. The developed model in this work ultimately provides a quick, accurate and precise method of characterizing the band gap of spinel nano-ferrite materials while circumventing experimental stress with conservation of appreciable time and other valuable resources.

In this study, Ni–SiO 2 nanocomposite coatings were deposited on the surface of X70 steel by performing direct current electrodeposition. The effect of different concentrations of cetyltrimethylammonium bromide surfactant (0.3, 0.5, 1, and 2 g L −1 ) on particle distribution and corrosion behaviour of the coatings was analysed. The structural properties of the obtained coatings were evaluated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis, X-ray diffraction, and atomic force microscopy. The corrosion behaviour of the coatings was tested by potentiodynamic polarisation and electrochemical impedance spectroscopy. The results showed that the electrodeposited coatings obtained from the electroplating bath with 1 g L −1 of surfactant modified the surface morphology of the Ni–SiO 2 nanocomposite coating and presented a finer and more uniform microstructure. The results of the phase structure analysis showed that the addition of the surfactant in the electrodeposition process changed the preferred orientations for the coatings from (111) to (220) and (200) planes. The anti-corrosion performance of the resulting coating produced in the presence of 1 g L −1 of surfactant was significantly higher than the anti-corrosion performance of the other coatings and showed a lower corrosion rate.

Reduced graphene oxide/maghemite (RGO/γ-Fe 2 O 3 ) material was successfully synthesized by combining the modified Hummers method with co-precipitation (RGO 10 wt.%). γ-Fe 2 O 3 nanoparticles with a particle size of ∼14.8 nm were distributed on the surface of RGO sheets. Results of Brunauer–Emmett–Teller analysis showed that RGO/γ-Fe 2 O 3 had a mesoporous structure and a narrow capillary size distribution curve at about 13 nm. The specific surface area of the RGO/γ-Fe 2 O 3 was 168 m 2 ·g −1 . The RGO/γ-Fe 2 O 3 nanocomposite was used to adsorb arsenic As(V) and a mixture of heavy metals (As(V), Cr(VI), Pb(II), and Fe(III)) in water. The maximum adsorption efficiency of As(V) reached 98.9% after 45 min with an adsorption capacity of 5.93 mg·g −1 , higher than the simultaneous adsorption of the four metal ions. Competitive adsorption decreased in the order As(V), Cr(VI), Pb(II), and Fe(III). Therefore, RGO/γ-Fe 2 O 3 could be used as an effective adsorbent to remove heavy metals from aqueous solutions.

In this paper, a nickel complex with the general formula [Ni(HST)(OAc)] (HST: 1-salicylaldehydethiosemicarbazone, OAc: acetate) was subjected to thermal decomposition to produce nanoparticles at three different temperatures. The semiconductor nanoparticles have a particle size of 22.18 nm and a band gap of 2.68 eV. Furthermore, it was observed that the nanoparticles exhibiting a zeta-potential value of −26.1 are stable in colloidal media. The produced nanoparticles have the potential to be used as wastewater treatment agents under optimized conditions, as evidenced by the photocatalytic activity on methylene blue degradation with a 69.30% decomposition. Although all the synthesized compounds exhibit high antibacterial activity with low minimal inhibitory concentration values, the nanoparticles obtained by calcination at 400 °C had the highest activity, which is consistent with the literature.

Bi 2 O 3 /Dy 2 O 3 nanoflakes with triclinic Bi 2 O 3 and cubic Dy 2 O 3 phases were synthesized by a hexadecyl trimethyl ammonium bromide (CTAB)-assisted hydrothermal route. The Bi 2 O 3 /Dy 2 O 3 nanoflakes were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy and electrochemical impedance spectroscopy. The size of the Bi 2 O 3 /Dy 2 O 3 nanoflakes with curled surface is about 2 μm and thickness is about 25 nm. X-ray photoelectron spectroscopy confirms the chemical composition of the Bi 2 O 3 /Dy 2 O 3 nanoflakes. The formation process of the Bi 2 O 3 /Dy 2 O 3 nanoflakes was investigated by controlling the CTAB concentration, reaction temperature and reaction time. The formation of the Bi 2 O 3 /Dy 2 O 3 nanoflakes depends on CTAB. The results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy demonstrate good electro-catalytic activity of the Bi 2 O 3 /Dy 2 O 3 nanoflakes towards L-cysteine with a pair of quasi-reversible CV peaks at +0.01 V and –0.68 V, respectively. Bi 2 O 3 /Dy 2 O 3 nanoflakes modified electrode detects L-cysteine linearly over a concentration ranging from 0.001 to 2 mM with a detection limit of 0.32 μM. The proposed nanocomposites modified electrode possesses good reproducibility and stability which can be used as a promising candidate for L-cysteine detection.

In the present work, finite element simulations were performed to capture the influence of friction and temperature gradient on the local strain distribution across the cross-section of a hot compressed specimen. The finite element predicted deformation histories for different regions of the hot compressed sample were exported to the viscoplastic self-consistent model to perform texture simulations in the variable velocity gradient mode and to capture the texture heterogeneity. Differences in texture intensity as well as characteristics were observed depending upon the distance from the central region of the hot compressed sample. It was observed that a double fiber texture with {110} and {100} parallel to the compression direction evolved in the central region of the specimen, which accommodates the highest amount of local plastic strain. On the other hand, only {110} fiber evolved in the region close to the dead zone, which accommodates the least amount of local plastic strain. Furthermore, volume fraction of the {100} fiber was observed to be sensitive towards strain rate sensitivity, where a higher rate sensitivity enhances the shear rates on the non-octahedral slip systems resulting in strengthening of {100} texture fiber.

The mechanical performance of AZ31, a popular aerospace structural material, manufactured using CMT-WAAM was studied in this paper. A wall of 70 × 200 × 4 mm was built by layer-by-layer deposition of 4 mm thick beads. The influence of rolling along the direction of welding on hardness, tensile strength and residual stress was investigated and compared with the control build fabricated using “synergic” parameters recommended by Fronius, Austria. The specimens extracted from the AM (Additive Manufacturing) built walls were subjected to cross-section reduction up to 22.5% compared to control specimens. The rolled specimens displayed up to 10% increase in the tensile strength values compared to control specimens and a generally lower elongation value. A similar trend was observed in the hardness examination as well. A peak hardness of 77 HV0.5 was observed in the specimen subjected to 22.17% reduction. The rolled samples exhibit a 14.32% reduction in residual stresses.