Lakshminath Bezbaroa Central Library Digital Repository

Welcome to the Institutional Digital Repository of Lakshminath Bezbaroa Central Library.

  • This digital archive comprised of the Institutes' intellectual output.
  • It manages, preserves & makes available the academic works of faculty and research scholars.
  • It is established to facilitate deposit of digital content of scholarly or heritage nature.
  • Allowing academics & their departments to share & preserve contents in a managed environment.
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Recent Submissions

Valorization of Rice-Husk for Optimal Production of Bio-Oil, Bio-Char, And Silica Nanoparticles
(2022) Das, Sutapa
Rice husk is an agricultural waste-product whose management has yet not been standardized on a commercial-scale following sustainable norms. Ineffective waste management of this abundant biomass often leads to large amounts of rice husk being decomposed via means such as open-pit incineration. This severely impacts the environment and is one of the leading causes of air pollution, notable mostly in the region of North India. Over the decades, different processes have been adapted to tackle this issue. One of the thermochemical techniques, pyrolysis, offers immense potential towards converting this biomass to several value-added products. This thesis employs the usage of slow pyrolysis to achieve the conversion of rice husk to bio-oil, bio-char and silica nanoparticles. In order to optimize the overall process towards maximizing the product yield, an optimization scheme, namely, Response Surface Methodology (RSM) has been employed which helps determine the ranges for the different process variables - temperature, gas holding time and gas flow rate. Extensive characterization of the process and the products have been carried out. Slow pyrolysis has been performed under inert (N2) and reactive environments (CO2) to understand the effect of ambient conditions of the product profile. For instance, bio-char, displayed adsorbent features such as high porosity, surface area, and hydrophilicity when generated under CO2 environment, while under N2 environment, it possessed a high carbon content, thus highlighting its usage as a soil conditioner for improving soil fertility. Bio-oil, on the other hand, was also obtained and its physico-chemical characterization revealed potential for usage as a fuel. It was subjected to different upgradation techniques such as solvent-exchange and catalytic-upgradation in presence of bio-char. Thus, the latter technique also presented itself as another route towards utilization of organic modifiers for improving bio-oil properties. Silica nanoparticles (SI NP), were also generated using the rice husk as a feedstock. These particles were obtained as a result of calcination process involving bio-char. SI NP could themselves be modified and applied as a membrane, using natural cotton substrate, for effectively separating oil from an oil-water mixture. Thus, in a nutshell, this thesis aims to highlight the effectiveness of the slow pyrolysis process by utilizing the abundant biomass for obtaining the diverse collection of valuable products.
Magnetic Field Induced Transitions and Exchange Interactions in Columbites
(2023) Maruthi, R
The studies on strongly correlated aspects of the Columbite family of compounds have become more intense in recent years because of their novel magnetic and electronic properties which provide impetus to the scientific community in searching for practical systems in the field of ‘Quantum Magnets’ that can be used to test the predictions of theoretically solvable models. Columbites are generally complex transition metal oxides with the chemical formula AB2O6, where both A and B site atoms are transition metal cations with divalent and pentavalent oxidation states, respectively. These systems are unique in the sense that they exhibit quantum critical behavior, magneto-electric coupling, tri-critical behavior, field-induced metamagnetic transitions, etc. The exotic physical properties of Columbites have been utilized in various industrial applications and they have huge commercial demand. In this thesis, we tried to establish the complete H-T phase diagram and understand the magnetic ground spin configuration of magnetic ions in the Columbite family of compounds. Nonetheless, we also focused on the determination of exchange constants between the magnetic cations by using different experimental results and theoretical models which is the strongest point of the current thesis. Also, the research work related to the dielectric response of columbites, mainly the analysis pertaining to the temperature and frequency dependence of ac-conductivity by using different theoretical models is unique. Magnetic measurements on MnNb2O6 reveal the robust anti-ferromagnetic ordering below TN = 4.33 K which is further confirmed by heat capacity measurements (TN = 4.36 K). The high-temperature paramagnetic susceptibility is fitted with modified Curie-Weiss law (χ = χ0 + C/(T-ϴ)) which yields ϴ = -17 K and C = 4.38 emu K mol-1Oe-1. Using these magnitudes, we further estimated the magnitude of effective magnetic moment μ which is ~ 5.920 μB per Mn2+ ion in MnNb2O6 system, and the corresponding g-factor 2.001 for Mn2+. Moreover, this compound shows magnetic field-induced spin-flop transition at Hsf = 18 kOe. We provide a clear and vivid picture of the H-T phase diagram of the MnNb2O6 system which shows the triple point at TTP (H, T) = (18 kOe, 4.06 K). Next, we employed the molecular field theory (MFT) and estimated the intrachain and interchain exchange constants whose magnitudes turn out to be J0/kB = -1.08 K and J┴/kB = -0.61 K, respectively. Furthermore, we presented the ac-conductivity (σ(ω,T)) analysis exhibiting the thermally driven, Arrhenius-like behavior which is predominant at temperatures above 300 K. However the Double power law-based explanation of the dispersive behavior of electrical conductivity σ(ω,T) studies provide evidence for the correlated-barrier hopping (CBH) conduction mechanism of charge carriers for temperatures between 173 K and 473 K. Moreover, the dynamical response of complex electric modulus spectra (M*(ω,T)) and the corresponding analysis using the Kohlrausch-Williams-Watts method shows the non-Debye type relaxation process is prevalent in the MnNb2O6 system with decay function exponent β lying between 0.794 and 0.840. Besides we presented the magnetic properties of tantalite Columbite MnTa2O6 which provide evidence of the AFM ordering with Néel temperature TN = 5.97 K consistent with the TN = 6.00 K determined from the peak in the Cp vs. T data. Further we estimated the critical exponents α = 0.10(0.13) for T > TN (T < TN) from experimental data of Cp vs. T near TN through the mathematical fits to the equation: Cp = A|T-TN|-α. Magnetic studies reveals μeff = 5.96 μB per Mn2+ ion and yields the effective spin S = 5/2 with g = 2.015. Finally, we mapped the H-T phase diagram using the M-H isotherms and M-T data measured at different H yielding the tricritical point TTP (H, T) = (17.0 kOe, 5.69 K) for MnTa2O6. Using the magnitudes of ϴ and TN and molecular field theory, the antiferromagnetic exchange constants J0/kB = -1.5 ± 0.2 K and J┴/kB = -0.85 ± 0.05 K are determined for the MnTa2O6 system. Further, we explored the magnetic ground state properties of CoNb2O6 which shows that the ground state of Co2+ has the effective spin S = 1/2 and not S = 3/2 expected from Hund’s rules, the S = 1/2 ground state resulting from the combined effects of non-cubic crystalline field and spin-orbit coupling. On the other hand, by means of the experimentally obtained g value with S =1/2 and the experimental critical fields for spin flips we calculated the interchain antiferromagnetic exchange constants J1/kB (= -0.42 K) and J2/kB (= -0.67K) along with intrachain ferromagnetic exchange constant Jo/kB = 6.2 K. Next, we further explored the rich magnetic properties of the NiNb2O6 system.
Shaping Emotions: An Emotive Form Design Framework for Emotional Disconnect Identification and Creativity Enhancement
(2023) Vaidya, Gaurav Vinod
The prime aim of this research is to formulate a framework for emotional disconnect identification and creativity enhancement during the product form ideation phase of the design process. Contemporary trends in design show consumer inclination towards objects which motivate them, improve their quality of life and spark emotions. Consequently, along with the functionality requirements, a product needs to serve consumers' emotional needs, and for that, the product must relate to them at their emotional level. Previous research suggests that the emotional element of design could be more crucial in deciding the success of the product than the functional aspect, as it affects consumers' decision-making in choosing a product. Thus, designers must possess the necessary knowledge and skills to deal with this design paradigm of product emotions. Moreover, designers should know whether their intended emotions are conveyed to the consumers. These issues are addressed in the current research with a systematic approach in a phase-wise manner that has resulted in proposing the Shaping Emotions Framework. The proposed framework has been experimented with and successfully demonstrated with a case of form ideation of Bluetooth Speakers.
Prosodic Aspects of Sylheti
(2023) Raychoudhury, Priti
This dissertation discusses the nature of prosodic features of Sylheti, an Indo-Aryan language (ISO 15924), also debatably a dialect of Bengali. It aims to present the correlation between components of the prosodic hierarchy in the language and the components of its grammar. It is an attempt to present a typological study of Sylheti that evolved into a tone language, independently from the group of the language family to which it genetically belongs. It presents an overall view of tone and intonation in the language and shows how these connect to sound systems and grammar. The language exhibits a three-way tonal contrast, distinguishing the High, Mid, and Low lexical tones. The tonogenetic factors contributed by the instability of the diachronic four-way laryngeal contrast conditioned a three-way tonal contrast in Sylheti depending on the voicing and syllabic position of the sound. Tonogenesis is one of the central aspects of the phonology of the language, as a detailed study on the phonetics and phonology of the three-way tonal system of the language reveals the factors behind the difference in the tonal behaviour at the post-lexical level such as the difference between the complex morphemes and compounds in the language.
Geometrical Frustration in Jahn-Teller Active Spinel Pyrochlores
(2023) Jena, Suchit Kumar
Geometrical frustration (GF) in magnetic materials has attracted researchers of current era owing to their unusual physical properties, in which the origin of frustration is two-fold. The first and foremost requirement is the peculiar arrangement of the crystal lattice, while the second most important requirement is the nature of the magnetic ions occupying the specific lattice sites. Such GF phenomena is inherent in the specific lattice having corner-shared tetrahedral geometry, commonly known as the ‘Pyrochlore lattice’, where the fragile magnetic ground state leads to novel physical phenomena such as: Reentrant spin-glass state, Quantum spin-liquid/ice nature, Bipolar exchange-bias, and giant magneto-caloric-effect. In this context, spinel oxides (AB2O4) are considered to be the well-known systems which are prone to exhibit unusual magnetic properties because of their special features like competing exchange interactions (JAB, JAA and JBB) and the topology of B sublattice. However, in the spinel-Pyrochlores only the B sublattice formulates a pyrochlore arrangement whereas A forms a diamond lattice. Therefore, tuning the magnetic interaction on the B site have shown much higher degrees of magnetic frustration. The GF phenomena in the spinel-Pyrochlore ZnFe2O4 (ZFO) was first predicted by Anderson in 1956, which was then experimentally unveiled to exhibit magnitude of frustration index f = |ΘCW|/TN as high as 12 (where the antiferromagnetic Néel temperature TN ≃ 10 K). In this research work, we attempt to lift the GF in cubic ZFO by compelling it to stabilize in the lower crystal structural symmetry (tetragonal) with incorporation of the Jahn-Teller (JT) active spin‒1 Mn3+ on B site and additional dilution effect from another JT active spin‒1/2 Cu2+. Here the divalent Cu is capable of occupying both A and B sites and is expected to alter the exchange coupling significantly. The role of weakly magnetic Ru3+ substitution on the magnetic exchange interactions of ZFO has also been investigated. A systematic comparison of the change in magnetic ordering with the substitution of Ru3+ and Cu2+ are thoroughly studied in terms of the associated exchange interactions (J) along with the magnetic Field-Temperature (H‒T) phase diagrams. Alongside, this work aims to probe the variations occurring in JAA, JAB and JBB with increasing the Cu content in ZFO. Such Cu substitution in ZFO introduces complexity in the cationic distribution which leads to very high ferrimagnetic (FiM) ordering TFiM ~ 743 K in the tetragonal CuFe2O4. Further, a comprehensive study of the magnetic and dielectric properties of the investigated systems are discussed considering their importance in the field of microwave and spintronic devices.