Rajashekhara Shabadi

Interfacial Structure and Photocatalytic Activity of Magnetron Sputtered TiO2 on Conducting Metal Substrates

The photocatalytic behavior of magnetron sputtered anatase TiO2 coatings on copper, nickel, and gold was investigated with the aim of understanding the effect of the metallic substrate and coating-substrate interface structure. Stoichiometry and nanoscale structure of the coating were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscope, and scanning and transmission electron microscopy. Photocatalytic behavior of the coating was explored by using optical spectrophotometry and electrochemical methods via photovoltage, photocurrent, and scanning kelvin probe microscopy measurements. The nature of the metal substrate and coating-substrate interface had profound influence on the photocatalytic behavior. Less photon energy was required for TiO2 excitation on a nickel substrate, whereas TiO2 coating on copper showed a higher band gap attributed to quantum confinement. However, the TiO2 coating on gold exhibited behavior typical of facile transfer of electrons to and from the CB, therefore requiring only a small amount of photon energy to make the TiO2 coating conductive.

Characterization of Joints Between Aluminum and Galvanized Steel Sheets

Sound joints between an AA6016 aluminum sheet of 1.2-mm thickness and a low-carbon galvanized steel sheet of 0.77-mm thickness are obtained using the laser pseudo-brazing method. A zinc-based aluminum alloy is used as a filler wire with optimized process parameters for laser pseudo-brazing. Metallurgical investigation of the joint is carried out using a scanning electron microscope and energy-dispersive X-ray analysis. Joints produced using Al-Zn filler wire showed a moderate strength and quality with a layer containing principally Fe2Al5Znx type intermetallics of ~10-μm thickness. Failure in the heat-affected zone of aluminum is found to be dominative, while in some cases, fracture along the interface between the intermetallic layer and the steel sheet is observed.

Powder metallurgy hollow fly ash cenospheres’ particles reinforced magnesium composites

This study reports for the first time the synthesis of syntactic composite foams based on magnesium matrix and hollow fly ash cenosphere particles using the powder metallurgy technique involving hybrid microwave sintering. The effects of varying amounts of hollow cenosphere particle addition on the density, microstructure, thermomechanical and mechanical properties of pure magnesium were investigated. Density measurements indicated up to 18% reduction in density with the highest quantity of cenospheres (15%) addition to the magnesium. Microstructural examination demonstrated evenly distributed, intact and a few broken cenosphere particles with good interfacial integrity. Phase analysis showed finely distributed intermetallic phases such as MgO and Mg2Si due to the reaction between Mg matrix and the hollow cenosphere reinforcement. Mechanical property measurements showed retention/slight improvement in specific mechanical properties of magnesium due to hollow fly ash cenosphere particles. However, the tensile ductility was marginally affected.

Nanoscale surface potential imaging of the photocatalytic TiO2 films on aluminum

The change in the surface potential of TiO2 coatings upon UV-illumination was investigated on the nanoscale using Scanning Kelvin Probe Force microscopy and on the micro-scale using photo-electrochemical measurements. A good correlation between the two techniques was obtained. The changes in the surface potential of TiO2 coatings upon UV-illumination are closely correlated to the band gap and thickness of the coatings. The inhomogeneity surface potential distribution of a 100 nm TiO2 film indicates a heterogeneous coating. Transition to a homogeneous surface potential distribution was observed with increasing thickness of the TiO2 coating.

Effect of Mn on the Nanoprecipitation in Binary Fe-Cu alloys

Effect of the third alloying element Mn on Cu-precipitation was studied in a binary Fe-1.3% Cu alloy. Precipitation in both the alloys was investigated after homogenization treatment and subsequent artificial aging. Advanced characterization techniques such as Positron Annihilation Spectroscopy (PAS) and Tomographic Atom Probe (TAP) were used to establish the chemical composition, morphology, size and number density of the Cu-rich phases. Combined results of PAS and TAP were particularly useful in order to follow the Cu precipitation in the binary alloy. At short aging times, addition of Mn significantly increased the kinetics of hardening while its effect on the magnitude of precipitation strengthening is only marginal. It further increases the over-aging kinetics.

Strength of Mg–3%Al alloy in presence of graphene nano-platelets as reinforcement

ABSTRACT Bulk Mg–3%Al alloy-based nanocomposites containing graphene nano-platelets (GNPs) were synthesised using the powder metallurgy technique incorporating energy efficient hybrid microwave sintering and hot extrusion. GNPs in amounts of 0.1, 0.3 and 0.5 wt-% were investigated as reinforcements. Microstructural characterisation accomplished using optical, scanning and transmission electron microscopy revealed the presence of minimal porosity (<1%), a uniform distribution of GNPs in the matrix and a reduced grain size as a result of the presence of GNPs. The results of mechanical property characterisation revealed an overall improvement in micro-hardness and compressive response, due to the presence of GNPs, with best results exhibited by the Mg–3Al/0.3% GNPs composite. The ductility under compressive loading for composite samples remained higher than 20%.

Effect of Aging at 700°C on Ferrite Transformation in a 316L/308L Weldment

This article deals with the study carried out on the 316L steel plates welded using a 308L filler material of less stable microstructure than the base plate. The phase transformations in these welds aged at 700°C were investigated by means of optical metallography (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). It was found that the σ-phase forms even at isothermal holding time less than 140 h. During aging, the growth of σ-phase occurs continuously within δ-ferrite grains. After 1,000 h aging, all of delta-ferrite was decomposed and transformed into σ-phase and secondary austenite. EDX revealed that the σ-phase was enriched in Cr and Mo. The molybdenum content of the weld originated from the regions of the base metal adjacent to the fusion line. It exerted a prevailing effect on the σ-phase precipitation.

Star-shaped sucrose-capped CaO nanoparticles from Azadirachta indica: A novel green synthesis

ABSTRACT Calcium oxide (CaO) is an essential compound because of its application as catalyst and as effective chemisorbent for toxic gases. In this research, sucrose-capped CaO nanoparticles (S-CaO NPs) were prepared via simple eco-friendly green synthesis method at room temperature. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM images showed that calcium oxide nanoparticles (CaO NPs) were nanoscale in morphology. TEM images illustrated that produced CaO nanoparticle are semicylindrical star-shaped particles that had a mean particle diameter of about 100 nm with a length of 500 nm. Further, the prepared CaO NPs were tested for their antimicrobial activity. Overall studies indicated that this method could be used for the production of CaO NPs on large scale as a cheap and convenient way, without using any surfactant, organic medium, or complicated instrumental procedure. These bioactive nanoparticles also inhibit the biofilm formation and may have future applications as a cheap and non-toxic antimicrobial drug for skin care products and biomedical applications.