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In this investigation, hybrid laser-arc welding was performed on 6-mm thick ultrahigh-strength quenched and tempered steel plates. Laser-arc welds were characterized for hardness and metallurgical properties in three defined cooling cycles. Destructive tests of the joints revealed that the joints were characterized by tensile strength similar to that of the base material. Microstructural characterization was made by optical microscopy, scanning electron microscopy and X-ray diffraction. It was revealed that the weld beads consist of lath martensitic structure with small percentage of retained austenite. Quantitative analysis of mixed mi crostructures of the heat affected zone (HAZ) revealed 0%, 38% and 62% of the upper bainite for the cooling cycles- cycles A, B and C respectively. In addition, the hardness profile of the cross-section of the weld was characterized by Vicker’s microhard ness test. The hardness fluctuation values within the HAZ for the cycles A, B and C are 450-510, 370-425 and 320-375 HV respectively, thus increasing as the upper bainite percentage increases with each cycle.

Abstract

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Tin oxide nanoparticles has been synthesized via green route using SnCl .2H O and Euphorbia trigona (African 2 2 cactus) plant extract as precursors. In this green route process parameters such as, solution pH, precursor concentration and synthesis temperature were optimized to produce nanoparticles with smaller size. The degree of sensitivity of the process parameters vis-a-viz towards optimization were carried out by applying the Box-Behnken Design from Response Surface Methodology (RSM). The Box-Behnken Design was designated as a statistical prediction technique with the goal of decreasing the number of possible experimental outcomes, which would invariably reduced time and quantity of reagents, by this means plummeting the general cost of the production process. The particle size of the nanoparticles was chosen as the response factor for the green synthesis. The optimal predicted conditions obtained tetragonal cassiterite phase of SnO were at a solution pH of 10, precursor concentration of 0.40 M and synthesis 2 ο temperature of 57.5 C. From the optimized experimental conditions, the particle size was found to be 6.71 nm which , was also found to be in accordance with predicted value of 6.73 nm from the developed model. These results were 2 substantiated by the comparatively high correlation coefficients of SnO NPs (R = 99.96, R = 99.87, R =99.28) 2 2 adj obtained from the statistical prediction after the Analysis of Variance (ANOVA).

Abstract

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Copper doped tin oxide thin film was synthesised by electrodeposition technique. Film growth was maintained at cathodic potential of 1.60 V at a varied deposition time. Surface morphological studies of the deposited films were achieved by field emission scanning electron microscopy (FE-SEM). The scanning electron microscopy image revealed evenly distributed films, across the substrate with rice-like or dome-like particles, depending on the deposition time. Post-annealing enhanced films crystallinity and particles agglomeration. Energy disperse X-ray spectra revealed the elemental constituents present in the film. The results obtained from electrical characterisation of the samples showed the ohmic properties of the deposited sample. X-ray diffraction results indicated that samples are polycrystalline in nature with tetragonal rutile structure. The average interplanar spacing and crystallite size of the samples were estimated as 2.93 Å and 202.5 Å respectively. Optical characterisation of the samples showed that absorption and transmittance across the ultraviolet-visible spectrum range depend on deposition time. The estimated energy band gaps of 3.06 eV suggested the films as good candidates for transparent contact electrodes in optoelectronic applications.

Abstract

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TiO was synthesized by Sol-gel method and doped by Impregnation of Nitrogen from Ammonium Chloride to obtain 5% 2 N-TiO . The undoped TiO and N-doped TiO photocatalysts were characterized by Fourier Transform Infrared (FTIR) 2 2 Spectroscopy, X-Ray Diffraction (XRD) Crystallography and Scanning Electron Microscopy (SEM). Investigation of the activities of the photocatalysts for degradation of Indigo carmine dye in aqueous solution was carried out at different operating conditions of pH, temperature, catalyst concentration and dye concentration under aeration and UV- irradiation using a 20 Watt UV lamp in a specially constructed reactor made up of four compartments. The dye degradation reaction was monitored on a N4S UV-Spectrophotometer at 290 nm. The FTIR results attested the presence of N-H, Ti-O-Ti, Ti O, H-O-H, O-H functional groups in the catalysts. The XRD Crystallography results show that 5% N- TiO catalyst 2 contains a mixture of anatase and rutile phase compared to undoped TiO which contains pure anatase phase. The SEM 2 results show decrease in particle size when TiO was doped with Nitrogen. The degradation rate was found to comply 2 2 o with first order kinetics and optimum degradation was attained at the same pH and temperature of 3 and 40 C respectively for both photocatalysts. However, the dye and catalyst concentrations where optimum degradation was observed for 5 % N-TiO and undoped TiO were found to be 20 ppm, 0.025 g/l and 12.5 ppm, 0.05 g/l respectively. Percent degradation in 2 the presence of both UV- Irradiation and catalyst was calculated to be 28.5 % and 34.14% for TiO and 5% N- TiO 2 2 respectively. The percent degradation result shows a higher efficiency on 5% N- TiO than undoped TiO

Abstract

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The properties of surfaces in contact are known to have significant influence on the tribological behavior of any tribosystem in different contact situations. In the present work, the effect of using different ball counterface material on the tribological behavior of AISI 340L stainless steel under marginally lubricated contact was studied. The frictional behavior was evaluated using a ball-on-flat configuration in reciprocating sliding under marginally lubricated contact condition. 440C stainless steel, Al (2017) alloy and bronze were used as the ball counterface while base-stock synthetic polyalfaolefin oil (PAO10) without additives was used as lubricant. After the friction test, flats and balls surfaces were examined by optical profilometer and optical microscope in order to assess the wear dimension and mechanism. In all the sliding pairs tested at different loads, an initial rapid increase in friction coefficient and a period of transition to a lower steady state friction coefficient were observed. In SS304L-440C pair, wear proportional to applied load occurred in the AISI 340L stainless steel flat by a combination of gross plasticity and abrasion. For both SS304L-Al (2017) and SS304L bronze pairs, severe wear proportional to applied load, which occurred predominantly by abrasive mechanism was observed in the different ball counterface. The study concluded that the types of materials in contact have significant influence on the tribological property of any tribosystem.

Abstract

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The study investigated the physicochemical properties and heavy metal contents of water samples from three major sources; river (sample A), borehole (sample B), and well (sample C), in Usen using standard procedures. The heavy metal content was analyzed using Atomic Absorption Spectrometer. The results obtained were compared to permissible limits based on WHO standard. The pH of the water samples ranged from 6.80 to 7.00. The nitrate content varied from 2.30 to 2.40 mg/L, which was lower than the maximum limit of 10 mg/L. The conductivity was from 36.52 to 64.61 us/cm. Copper was not detected in all the water sources investigated. There was significant difference in the contents of other metals investigated. The concentration of other metals ranged from 1.84 – 9.12, 0.002 – 0.035, 0.001 – 0.061, 0.074 – 0.263, and 0.055 – 0.243 mg/kg for iron, cadmium, lead, zinc and manganese respectively. The metal contents were in the order: Fe> Zn> Mn> Pb > Cd > Cu. The results of this study also revealed that the water samples under study are contaminated by heavy metals and therefore unfit for human consumption. Thus, it becomes very important to treat these waters to make it safe for the populace.

Abstract

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Nanocrystalline BaTiO (BT) powder was synthesized by a combination of the solid-state and mechanochemical method. X-ray diffraction, field emission scanning electron microscopy, and impedance spectroscopy utilised appropriately to characterize the BT sample (ceramic). The X-ray diffraction confirmed a single-phase perovskite compound of cubic symmetry with space group Pm-3m. The crystallite size and crystal cell volumes were found to be 3 25.7 nm and 64.250 Å respectively. The average grain size estimated from FE-SEM was found to be 144.5 nm by using intercept technique. Electrical parameters like impedance, modulus, and electrical conductivity of the ceramic were obtained from AC complex impedance spectroscopy technique in the frequency and temperature range of 40Hz – o 1MHz and 30 to 150 C, respectively. Both impedance and modulus plots showed the negative temperature coefficient of o resistance (NTCR) character in the sample at 70, 110, 130, and 150 C with are similar to a semiconductor. This can be used for the fabrication of highly sensitive thermistors. The Cole-Cole (Nyquist) plot represents the grain and grain boundary conduction which indicates the ideal non-Debye type dielectric relaxation. The modulus analysis suggested the temperature-dependent relaxation process in the BT ceramic. A positive temperature coefficient of resistance o (PTCR) character was observed at 90, 50, and 30 C. The activation energy values are found to be 1.12 eV and 1.07 eV for Z″, and M” while it's 0.46 eV and 0.12 eV for t and t respectively. g , gb A possible suggestion is due to hopping conduction. The AC and DC conductivity spectra were found to rise with increasing temperature and frequency obey the Jonscher's power law. The conduction process was observed to be thermally activated and followed by Arrhenius law. that the carrier transport