Day :
- Physics and Chemistry of Materials | Materials Science and Engineering
Location: Webinar
Session Introduction
Rohin Sharna
Kathmandu University, Nepal
Title: Electronic structure calculation of graphene by formulating a relativistic tight-binding approximation model
Biography:
Rohin Sharma is a graduate student of physics at Kathmandu University who recently graduated with a MSc. degree in Physics. He has a research background and interest in condensed matter theory and computational material science. He has done several research involving investigating materials properties using first principle calculation methods, namely the plane wave dft codes of Quantum espresso. The work presented here is his most recent work which was part of his thesis work for the achievement of the master’s degree. The work presents a theoretical framework that is used to accurately build the Hamiltonian matrix of the system. He is currently working as a research assistant in Phutung Research Institute doing experimental optical research on the nano-photonic waveguides and Raman scattering.
Abstract:
A non-perturbative relativistic Tight-Binding (TB) approximation method applicable to crystalline material immersed in a magnetic field was developed in 2015. To apply this method to any material in a magnetic field, the electronic structure of the material in absence of the magnetic field must be calculated. In this study, we present the relativistic TB approximation method for graphene in a zero magnetic field. The Hamiltonian and overlap matrix is constructed considering the nearest neighbouring atomic interactions between the s and p valence orbitals, where the relativistic hopping and overlap integrals are calculated using the relativistic version of the Slater-Koster table. The method of constructing the Hamiltonian and overlap matrix and the resulting energy-band structure of graphene in the first Brillouin zone is presented in this paper. It is found that there is an appearance of a small band-gap at the k points (also known as the spin-orbit gap) due to the relativistic effect, whose magnitude is 25 $mu$eV.
Shrishma Paik
Bhabha Atomic Research Centre, India
Title: Process intensification and optimization for sonocrystallisation of uranium peroxide
Biography:
Shrishma Paik is currently working in the field of nuclear technology on separation and recovery of uranium from different sources. Her development area involves intensification of process of uranium by precipitation as well as solvent extraction by novel techniques and minimization of waste volume during uranium refining process.
Abstract:
Peroxide precipitation is an emerging process in nuclear technology and one of the well-known methods for production of first intermediate uranium compound before uranium bearing fuel production. Though the conventional method of precipitation is practiced worldwide, it suffers from the limitation of non-uniform particle formation and lesser control over particle growth and size. Hence there is always a scope to study the effect of novel technique for process intensification. Application of ultrasound or sonochemical technique is one of the techniques which can intensify the crystallization event to a large extent by the impact of its cavitational process imparting micro mixing, enhanced mass transfer and the effect of additional spontaneous nucleation. It also facilitates in enhancing the crystal shape and size with better consistency and can control physical and morphological characteristics of the powder in several ways. Here, study was carried out for establishing important process parameters namely uranium cocn and temperature for ultrasonic precipitation compared to conventional methods in laboratory scale with an ultrasound horn at 35 KHz. Uranyl nitrate with 30% hydrogen peroxide was used for the reaction in 1 liter scale. No appreciable difference in the phases has been found from the XRD study. However a more homogeneous, regular and smooth crystalline appearance is observed in sonochemical precipitation route compared to conventional route under SEM study at 100 g/L uranium with 60ºC temperature. The crystal shape is rhombohedra with a spherical aggregation in comparison to needle shaped crystals in conventional route. Significant improvement is also seen in specific surface area and tap density of the prepared powder in sononchemical route. The powders obtained from this novel technique are having recovery more than 99.9% w.r.t. uranium. The purity of the synthesized powder also meets the specification of nuclear grade quality. Overall, the sonochemical method of precipitation of uranium peroxide is a fast, simple, convenient and intensifying technique imparting appreciable morphology and physical characteristics over the conventional precipitation process.