• MANOJ KUMAR

Articles written in Bulletin of Materials Science

• CO2 laser processing for reducing core loss of cold-rolled grain-oriented silicon steel

Non-contact processing technique involving the use of CW and pulsed CO2 laser irradiation has been used for reducing the core loss of cold-rolled grain-oriented silicon steel. Laser scribing perpendicular to the rolling direction resulted in a refinement of domain wall spacing which subsequently reduced the loss of silicon steel. It was found that laser irradiation was more effective in a specimen with higher magnetic induction (Hi-B) and the loss was reduced by more than 10% under optimum conditions of the laser irradiation and the scribing speed. Since laser processing is a non-contact technique, it can be easily applied to the production line of the silicon steel.

• Optical absorption and fluorescent behaviour of titanium ions in silicate glasses

Titanium in normal melting conditions in air atmosphere present as Ti4+ ion in basic silicate glasses exhibited an ultra-violet cut-off in silicate glasses, viz. soda–magnesia–silica, soda–magnesia–lime–silica and soda–lime–silica glasses. This indicates that Ti4+ ion can be a good replacement for Ce4+ ion in producing UV-absorbing silicate glasses for commercial applications. The wavelength maxima at which the infinite absorption takes place in glasses was found to be around 310 nm against Ti-free blank glass in UV-region. The mechanism of electronic transition from O2- ligands to Ti4+ ion was suggested as L $\rightarrow$ M charge transfer. The low energy tails of the ultra-violet cut-off were found to obey Urbach’s rule in the optical range 360–500 nm. The fluorescence spectra of these glasses were also studied and based on the radiative fluorescent properties it was suggested that the soda–lime–silica glass containing Ti4+ ion with greater emission crosssection would emit a better fluorescence than the corresponding soda–magnesia–lime–silica and soda–magnesia–silica glasses. The shift of emission wavelengths maxima towards longer wavelength in titania introduced silicate glasses was observed on replacement of MgO by CaO which may be attributed due to an increase in basicity of the glass system.

• Pyrolysis of petroleum asphaltenes from different geological origins and use of methylnaphthalenes and methylphenanthrenes as maturity indicators for asphaltenes

Asphaltenes separated from two different crude oils from upper Assam, India, having different geological origins, viz. DK (Eocene) and JN (Oligocene–Miocene) were pyrolysed at 600°C and the products were analysed by gas chromatography–mass spectrometry (GC/MS) especially for the generated alkylnaphthalenes and alkylphenanthrenes. Both the asphaltenes produced aliphatic as well as aromatic compound classes. Alkylnaphthalenes and alkylphenanthrenes were identified by using reference chromatograms and literature data and the distributions were used to assess thermal maturity of the asphaltenes. The ratios of 𝛽-substituted to α-substituted isomers of both alkylnaphthalenes and alkylphenanthrenes revealed higher maturity of the JN asphaltenes than the DK asphaltenes. For both the asphaltenes the abundance of 1-methylphenanthrene dominated over that of 9-methylphenanthrene showing the terrestrial nature of the organic matter.

• Pyrolysis of petroleum asphaltenes from different geological origins and use of methylnaphthalenes and methylphenanthrenes as maturity indicators for asphaltenes

Asphaltenes separated from two different crude oils from upper Assam, India, having different geological origins, viz. DK(eocene) and JN (oligocene–miocene) were pyrolysed at 600 °C and the products were analysed by gas chromatography–mass spectrometry (GC/MS) especially for the generated alkylnaphthalenes and alkylphenanthrenes. Both the asphaltenes produce aliphatic as well as aromatic compound classes. Alkylnaphthalenes and alkylphenanthrenes were identified by using reference chromatograms and literature data and the distributions used to assess thermalmaturity of the asphaltenes. The ratios of 𝛽-substituted to 𝛼-substituted isomers of both alkylnaphthalenes and alkylphenanthrenes revealed higher maturity of the JN asphaltenes than the DK asphaltenes. For both the asphaltenes, the abundance of 1-methylphenanthrene dominates over that of 9-methylphenanthrene showing the terrestrial nature of the organic matter.

• Gallium nitride nanocrystal formation in Si$_3$N$_4$ matrix by ion synthesis

Synthesis of nanoparticles in insulators attracts tremendous attention due to their unique electrical and optical properties. Here, the gallium (Ga) and gallium nitride (GaN) nanoclusters have been synthesized in the silicon nitridematrix by sequential ion implantation (gallium and nitrogen ions) followed by either furnace annealing (FA) or rapid thermal annealing (RTA). The presence of Ga and GaN nanoclusters has been confirmed by Fourier-transform infrared,Raman and X-ray photoelectron spectroscopy. Thereafter, the effect of RTA and FA on the conduction of charge carriers has been studied for the fabricated devices. It is found from the current–voltage measurements that the carrier transport is controlled by the space charge limited current conduction mechanism, and the observed values of parameter $m$ (trap density and the distribution of localized state) for the FA and RTA devices are $\sim$2 and $\sim$4.1, respectively. This reveals that more defects are formed in the RTA device and that FA provides better performance than RTA from the viewpoint ofopto- and nano-electronic applications.

• Material-specific properties and applications of additive manufacturing techniques: a comprehensive review

Additive manufacturing (AM) has emerged as a powerful tool of manufacturing over conventional manufacturing techniques due to its customization features, design flexibility, waste minimization and ability to create intrinsic shapes. This technology involves the fabrication of parts by layer-by-layer printing and thus offers robust mechanical properties. This study aims to provide a comprehensive overview of distinct AM processes, history, materials, comparison and their applications in different fields. In addition, this study also summarizes the mechanical properties of distinct parts fabricated by distinct AM methods, so that this research could become the torch bearer for the futuristic researchers working in this area.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020