87 research outputs found
Bio-bibliometric Study of Prof. P Balaram contributions in the field of Bio-organic Chemistry and Molecular Biophysics
No full textThe present study uses Bio-Bibliometrics to examine the contributions made by Prof P Balaram renowned scientists in the field of Bio-organic chemistry and molecular biophysics from Indian Institute of Science (IISC) in India. It is important to study the contributions made by him to understand magnitudes and nature of contribution in a particular domain. The data was collected using Scopus database. Further the paper highlights on the contributions of P Balaram author productivity, Collaborations magnitude, Productivity of year wise distribution, collaboration coefficient, channels of communications, most used author keywords and high cited papers
Synthesis and development of multifunctional carbonaceous nanostructures for magnetic, optical and catalytic applications
No full textOwing to the ease of functionalization, low synthesis-cost and polymorphism,
carbonaceous nanostructures such as carbon globules, nanotubes (CNTs) and graphene sheets
emerged technologically as one of the most important class of multifunctional materials. In this
thesis a wide variety of carbon based nanostructures were synthesized by the simple pyrolysis
method, characterized and their applicabilities are demonstrated. Among the synthesized
materials, metallic particles embedded amorphous carbon globules, CNTs of different
morphologies such as spiralling tendrils, cup and box type bamboos, hollow and filled onions
etc. are the exotic ones. We also demonstrated a way to synthesize nanoscale particles of various
metallic alloys, which can be useful for any structural design in powder metallurgy. These
carbon coated metallic particles, which protect themselves against any environmental corrosion,
are otherwise, difficult to synthesize by any other conventional method. The structure,
morphology, size distribution of the dispersed metallic particles in carbon nanostructures were
investigated and correlated with their optical, magnetic, electronic and chemical properties.
We have demonstrated multifunctionality of our synthesized carbonaceous materials. Our
investigation highlights the non-linear absorption of laser beams in metallic nanoparticles
embedded carbon materials, making them potential candidates for optical limiters. Furthermore,
the dispersion of nano-sized metallic particles inside amorphous carbon matrix proves to be
microwave absorption enhancers, enabling their use as electromagnetic interference (EMI)
shields. In addition, the catalytic activity of most of our samples is excellent, but can be further
improved by controlling the amount of defects via nitrogen doping. The catalytic performance
for reduction of 4-nitrophenol by some selective samples exceeds many of the catalysts reported
earlier. The performance of some of our samples in electronic devices such as in infrared photodetectors
is exceptional. The use of the samples for magnetorheological applications for energy storage
and many other applications cannot be undermined. Hence, our work demonstrates that
our synthesized samples are versatile and truly multifunctiona
Mechanistic Insights for Controlling Electromagnetic Interference Shielding Through Microwave Absorption in Magnetic Composites
No full textExtensive use of electronic devices in daily communication and information technology causes high (microwave) frequency electromagnetic interference (EMI). This EMI often leads to noise, data misinterpretation or malfunctioning of electronic devices such as medical equipment. To protect the device from this unwanted EMI, a shield layer is essential, which can shield the device from the unwanted radiation via either reflection or absorption. As the reflected microwave may cause further EMI, the later phenomenon is advantageous, because it forbids any further interference with neighboring devices. This absorption-based shielding is also useful in stealth technology to design radar camouflage military aircraft. Metallic shields normally reflect the microwave and are heavy. To address this issue one requires shield layers with lightweight and conducting. In this respect, conducting polymer-based or metallic nanoparticles based composites seems handy. Hence, in this thesis work, we have adopted various strategies to design composites that can address the above limitations of metallic shields. We have demonstrated that the scattering, reflection and absorption of microwave depend upon the micro and macroscopic properties of the filler particles. Such properties include concentration, size, morphology, conductivity, defects and magnetism of the filler materials. We have systematically investigated their effect on EMI shielding to validate our strategies. We used composites of conducting polymer (Polyaniline), hard ferrimagnetic hexaferrites, soft magnetic Yttrium Iron Garnet (YIG), metallic iron particles, metal (Fe/Co/Ni) doped carbonaceous materials along with microwave transparent paraffin wax or PVDF. The effect of concentration, size, morphology, conductivity, defects and magnetic properties of these fillers in these composites on EMI shielding is studied. Furthermore, to understand the atomistic mechanism of shielding through light-matter interactions, complex permittivity and permeability of composites used to demonstrate the dielectric and magnetic loss contributing to the microwave absorption.
In this work, in particular, the mechanistic insight into the role of concentration of hexaferrite in hexaferrite-polyaniline-Wax composites, role of network structure of garnet particles in YIG-polyaniline-wax composite, the effect of size of carbon-coated iron/iron carbide particles and micron-sized iron particles in PVDF composite, the role of defects in carbon-coated cobalt and iron particles in scattering of microwave, the effect of improved graphitization and role of magnetism in carbon-coated cobalt and iron particles and the effect of morphology of bimetallic alloy doped carbonaceous materials in PVDF matrix, on
EMI shielding behavior is studied in detail. It is demonstrated that using different strategies, the designed composite specimens are very highly effective in attenuating the microwave radiation. The mechanistic insight into microwave absorption in designing highly absorbing EMI shield layer is the highlight of this thesis. The results can directly utilize for industrial applications
Investigation into the Synthesis, Structure and Dielectric Property of Lead-Free Double Perovskite Structured Materials
No full textLead based materials have shown to be important materials showing high
piezoelectricity, colossal dielectric constant, ferroelectricity along with their good mechanical
behaviour and resistance to corrosion. As a result, they have wide range of applications such
as sensors, actuators, detectors, batteries, lead-painting pigments etc. However, due to high
toxicity of lead and its nature to accumulate in the environment with gradually increasing
concentrations, increasingly more health hazards are encountered. In this regard, replacing
these lead based materials by lead free material with similar/higher level of dielectric
properties is the driving force for research on lead free dielectric materials. In this work, we
have studied few double perovskites structured dielectric materials and their solid solutions.
The present work attempts to understand synthesis, structure and dielectric property of
lead free double perovskite structure BaFe0.5Nb0.5O3, BaFe0.5Ta0.5O3 and solid solution of (x)
BaFe0.5Nb0.5O3–(1-x)KNbO3 (x= 0, 0.2, 0.4, 0.6, 0.8 and 1). This thesis work organized in
seven chapters as given below. First two chapters describe the motivation behind the work
and experimental technique used for synthesis and characterizes materials, chapter 3, 4, 5 and
6 described investigated material and chapter 7 summarizes the thesis. Details of chapters as
follows
Synthesis and Applications of Size and Shape Controlled Magnetic Oxide Particles for Magnetorheological Fluids
No full textMagnetorheological fluids (MRFs) are non-colloidal stable suspensions of polarizable mesoscale soft magnetic particles, usually metallic Fe-particles, in a carrier liquid such as oil or water; the solidity of which can be tuned by varying the applied magnetic field strength.
Magnetorheological fluids are agile candidates for impact mitigation due to their tunable “solidity”, quick and complete reversibility of physical states, durability and reusability in comparison to their mechanical counterparts. The highly desirable property of an MRF is its yield strength and hence the conventional MRFs are Fe-based. However, uncoated Fe-particles suffer from poor chemical and thermo-oxidative stabilities, poor sedimentation stability and redispersibilities necessitating the coatings / additives; which always lead to compromised performance when used in MRFs.
An alternative (to Fe) magnetic filler phase is the use of magnetic oxide particles. Soft magnetic spinel ferrites and garnets (though with moderate yield strength in an MRF) with their excellent chemical, thermo-oxidative and sedimentation stabilities, ready-redispersibility, less stringent synthesis and preservation conditions, lower cost, need no stabilizers and additives make them potential contenders for use in MRFs which can provide reliable MR performance.
As the microstructure and magnetic nature of particles have direct influence on the MR property, the effects of these were studied by preparing MRFs with magnetic oxide particles of different sizes and shapes. These MRFs were simple bi-phasic as magnetic oxide particles were dispersed in versatile carrier fluid (silicone oil) without any additives; where the magnetic fill fraction was decided based on off state viscosity and the wettability criteria.
As the MRFs in a device can undergo different stress / strain conditions of varying amplitudes and frequencies during their service, such a response was studied in laboratory using magnetorheometer via different modes of operation which mimic the service conditions. By varying the applied magnetic field strength and applied shear conditions, the performance of MRFs was evaluated and correlated to the physical and magnetic properties of the particles. Such a study provides a basis for the choice of magnetic phase in MRFs and their required concentration in the base fluid to provide highest efficiency.
The dynamic yield strengths (field dependent yield stress) of MRFs extracted from steady shear measurements showed that the yield strength was strongly dependent on the
saturation magnetization as well as on the microstructure of the particles used in MRF. The yield strength scaled with the saturation magnetization, magnetic fill fraction and applied magnetic field strength due to stronger magnetic column formation. The stability of MRFs (via the absence of wall slip) was found to depend predominantly on the microstructure of magnetic particles in the fluid such that MRFs containing structured particles showed the absence of wall slip while the MRFs containing irregular shaped powder particles showed poor stability via the occurrence of wall slip. The steady shear tests highlight the importance of using particles of definite shape with superior magnetic properties at a certain magnetic fill fraction for an efficient and reliable MR performance.
The MRFs subjected to different oscillatory shear conditions showed that sturdier structures form in-field (exhibited via high gain modulus or low loss factor) when the particles have certain shapes (and size distribution) which result in high surface contact and are highly magnetic. Hence, the MRF containing Fe3O4 micro-octahedrons with high magnetization and large surface area for contact with other octahedron showed the large value of gain modulus and low loss factor compared to all other MRF samples. Poly-dispersity in spheres was found to be advantageous over monodisperse spherical magnetic particles due to void-bridging effects that strengthen the magnetic structuration. The irregular shaped particles based MRFs showed lower gain (higher loss factor) due to weak structuration. Anomalously high loss factor observed for rod shaped LZFP particles based MRF at medium strains and low field strengths is attributed to the rotation hindrance and low density of particles. The polydisperse particles based MRFs showed need for higher applied field strengths to decrease the loss and irregular particles based MRFs showed noisy response. The magnetosweep results showed that shape anisotropic particles based MRFs respond faster to applied field manifested as a faster decrease in loss factor with field. With magnetorheological parameters showing high dependence on the physical and magnetic nature of particles, oscillatory shear tests can serve as a means to select and assess the suitability of these particles for magnetorheological fluid for specific applications.
The time dependent magneto-mechanical behaviour such as creep-recovery in MRFs showed that the strain recovery was dependent on the microstructure and magnetic nature of the particles such that fluids containing structured particles with high saturation magnetization showed higher recovery (due to better in-field structuration) compared to the irregular shaped and lower magnetization particles based MRF counterparts. The endurance of the MRFs
(sustenance of strength of the MRF) under sustained stress conditions were estimated by a novel method which showed that MRFs containing ‘structured’ particles with high saturation magnetization showed high creep strength. In case of spherical particles based MRFs, the polydispersity of particles was found to aid in better column strength due to void-filling. The high surface contact between rod-shaped particles in the fluid resulted in good creep-strength among all MRFs. Among all the particles, the octahedron shaped Fe3O4 particles with large surface contact coupled with high saturation magnetization makes the Fe3O4 micro-octahedron particles based MRF the best amongst all the MRFs studied in this work. In case of irregular shaped particles based MRFs, the creep strength lagged behind the yield strength suggesting that such MRFs are not suitable for applications which demand sustained strength over prolonged action of stresses. Thus, the present work highlights the importance of considering the physical and magnetic properties of magnetic particles while selecting them for application specific MRFs where high endurance is sought.
The stress relaxation behaviour of MRFs showed an overall high strength (via relaxation moduli) for MRFs containing particles with definite shape and high magnetization values (increased structure strength). However, the rod shaped particles based MRF did not witness increased strain limit with increased field strength, probably due to the mass flow in fluid due to higher inter-particle interaction than the interaction with applied field. The observation of increase in critical strain with increase in field for MRFs containing irregular shaped particles is only due to the higher number of particles resulting in overall increase in viscosity with field. Among all the MRFs, octahedron Fe3O4 particles with superior magnetic properties and large surface contact between facets showed highest critical strain for flow, which is in corroboration with other magnetorheological studies discussed so far.
The creep-recovery and stress relaxation behaviours of MRFs are rarely studied, yet very important when selecting an MRF for an application which seeks high retention of MR strength over prolonged action of stress or strains.
A comparison of particle shapes used in the MRFs suggests that although both octahedron shaped and rod shaped particles make high surface contact during structuration, the former is better due to lack of rotation hindrance, thus useful for preparing quickly responding MRFs.
The inadequacies in th e conventio nal FOMs are address ed by a new FOM which is based o n a wholistic approach formulated consideri ng all relev ant physical and magnetic paramete rs of the particles. Also, the individ ual terms of this FOM help in selecting a particular MRF for a specific application. The FOM is as follows: λ – sedimentation constant (time taken by the MRF to sediment to about 1/eth of its total volume)
With the MRFs containing octahedron shape d Fe3O4 pa rticles showing the highest FOM followed by s pheres (mod erate value ) which are succeeded by irregular powder samples based MRFs, the FO M observed in all MRF cases follow the same trend as observed by results from different magnetorheologi cal studies. Hence, the highest F4 (or FAB) observed for Fe3O4 octahedron particles based MR F in comparison to a ll other MR Fs (including Fe-based) is justified by the o
Mbserved large yield strength, creep-resistance, low density and ready-redispersibilities, validating the FOM.
The entire thesis is organized as follows.
Chapter 1 details the motivation for the present research work, introduction to the material of interest (Magnetorheological fluid) with overview of different areas of potential applications, important properties of MRF, the current status of MRF, the challenges / issues needed to be addressed followed by choice of alternate materials for addressal of these drawbacks faced by conventional (Fe based) MRFs.
Chapter 2 explains the synthesis of magnetic-oxide particles of different sizes and shapes by following different synthesis techniques. This is followed by the structural, microstructural and magnetic properties characterizations carried out by employing different, standard characterization techniques. The procedure for preparation of MRFs from the synthesized magnetic oxide particles is discussed. The basis of carrier fluid selection and magnetic particle concentration in MRF is explained.
Chapter 3 gives a background to magnetorheology, in terms of the instrumentation (magnetorheometer), the relation between the magnetorheological parameters and the instrumental parameters (conversion factors), the different operating modes and the relevance of characterization modes in terms of practical applications, the procedure of different characterizations and the standard response behavior of MRFs to the characterizations.
Chapter 4 is comprehensive characterization of all the MRFs subjected to steady shear conditions at various applied fields. The detailed analyses in terms of MR response are given with respect to the structure, microstructure, magnetic nature, and magnetic fill fraction of the magnetic particle in the fluid.
Chapter 5 is extensive study of all the MRFs subjected to dynamical shear conditions at various applied fields. The magnetorheological responses of MRFs under different dynamical conditions (amplitude sweep, frequency sweep and magnetosweep) are analyzed in regard to role of microstructure, magnetic nature and magnetic fill fraction of the magnetic particle in the fluid.
Chapter 6 explains the creep-recovery response of MRFs for the best magnetic fill fraction, decided from the steady and dynamical shear responses for all concentrations of MRFs. The recovered strain is analyzed with respect to a range of applied field strength and stress values. The creep strength determined from this study is correlated to the microstructure and magnetic nature of particles constituting the MRFs.
Chapter 7 elaborates the stress relaxation behaviour of MRFs for the best magnetic fill fraction, decided from the steady and dynamical shear responses for all concentrations of MRFs. The stress relaxation (plateau values) moduli for the MRFs extracted at various applied field strength and strain values are analyzed to estimate the critical stress for flow in MRFs. This relationship between the critical stress that an MRF can withstand and the microstructure and magnetic nature of the particles in the fluid are investigated.
Chapter 8 is about the study of sedimentation stability (and the redispersibility) of magnetic oxide particles based MRFs and the comparison of these properties with Fe- based MRFs. The role of mass-density and microstructure of particles in the fluid on sedimentation rate is briefly explained.
Chapter 9 compares the important outcome of all the magnetorheological characterizations for all the studied MRFs in terms of extent and speed of response, the sedimentation stability and eases of redispersibility, and relates the observations to the physical and magnetic properties of the magnetic particles. The method of developing a new figure of merit based on a wholistic approach for assessing the efficiency and reliability of MRF is discussed which overcomes the shortcomings of conventional figures of merit.
Chapter 10 summarizes the important findings of research work and highlights the validity of the new figure of merit in assessing ‘reliability and performance’ of MRFs
Structural and magnetic properties of Al-doped yttrium iron aluminum garnet and optical properties of Mn, Sr, Fe-doped ZnO prepared by solution combustion method
No full textThe structural and magnetic properties of Al substituted yttrium-iron garnet (Y3AlxFe5-xO12, x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 and 1.8) ceramic powders synthesized using solution combustion method were investigated. For low Al content, Al3+ ions have preference to occupy tetrahedral (Td) sites than the octahedral (Oh) sites. At higher Al content the distribution of Al tends towards a ratio of 3:2 at the tetrahedral:octahedral site. Increase in Al doping results in the decrease in the lattice parameter due to smaller size of Al3+ as compared to Fe3+ ion. All the studied samples show coral-network-like surface morphology. The saturation magnetization (MS) values decrease from ∼26.94 emu/g to ∼ 0.17 emu/g with increase in Al content from 0.0 to 1.8. Further addition of Al makes the sample paramagnetic at RT. Substitution of non-magnetic Al3+ reduces the saturation magnetization rapidly due to the decrease in the superexchange interaction in the crystal.
Furthermore, solution combustion synthesis of Mn, Sr or Fe-doped zinc oxide ceramic samples was carried out. All the samples were characterized by XRD, SEM and UV-DRS. The magnetic order of Fe in ZnO lattice of the Fe-doped ZnO samples was characterized by Mössbauer spectroscopy. The X-ray diffractograms determine the solubility limits of dopant in the host (ZnO) lattice. Electron micrographs confirmed the spongy network nanostructure of all the samples. The bandgap of the samples was estimated from Tauc plots of corresponding UV-DRS spectra. The spongy (high surface area) and low bandgap of Fe-ZnO renders it as an important candidate for photocatalytic applications. Our results show that among all these samples, Fe-doped zinc oxide nanoparticles can be the most suitable candidate for photocatalytic applications
Graphene based materials : Mechanistic insights into corrosion inhibition and supercapacitance
No full textIn the contemporary scenario, protecting metals and alloys from deterioration through the coating is the main concern that extracts worldwide attention. Although existing coating processes and methods such as epoxy coatings and polymer composite coating are already considerably invented and improved, further progress is still essential in terms of economical, nature-friendly, and long-term protection. So to overcome these issues, organic-based coatings have been drawn escalating consideration and became the most efficient ways to shield a metal substrate. Among them, Graphene Oxide (GO)-based functionalized hydrophobic coating materials have been extensively investigated in the last decades. This thesis demonstrates that a very thin sub-nanometric layer of GO on a metal surface has excellent long-term anti-corrosive properties against a very harsh saline environment. Furthermore, we have shown a direction to choose an organic grafting agent among para-aminobenzoic acid (PABA), alanine, and glycine in a very economical way to enhance the anti-corrosion behavior of GO.
In addition, recently, the derivatives of graphene have become the center of attraction among the materials used for supercapacitors. Graphene as electrode material in supercapacitors does not exhibit the required energy and power output when used in its ideal form. Earlier reports have shown that graphene necessitates the doping of heteroatoms such as N, S, B, P etc., to alter and amend its Physico-chemical and electrochemical behaviors. In most of those reports, merely a few milligrams of GO precursor were taken to get rid of the agglomeration problem in the dispersion medium. This is due to the fact that a greater amount of graphene oxide often leads to the poor reduction and exfoliation of GO. Thus, the up-scaling in the productivity of N-doped rGO (N-rGO) using such reported synthesis methods is quite challenging. Hence, efficient, straightforward, and inexpensive synthesis techniques for the synthesis of N-rGO are still not fully explored. Considering all the above drawbacks in mind, we have attempted a synthesis by ta= king GO, a comparatively large amount of precursor, to provide the roadmap for the up-scaled synthesis of N-rGO by solvothermal synthesis method, which is simple and more accessible.
In this thesis, we have demonstrated the synthesis, characterization, and anti-corrosive properties of GO/PABA thin coating on iron metal in 1 M KCl (aq. solution) saline medium. Furthermore, we investigated the non-expensive amino acids (Alanine and Glycine) as grafting agents to protect the iron metal by a thin layer of GO coating in a highly saline (3 M KCl aq. solution) medium. Furthermore, experimentally and theoretically, we illustrated the investigation of the role of oxygen functionality through GO/rGO/N-rGO coating to protect the iron metal from corrosion. For exploring the supercapacitors, we examined the role of N-doping in reduced graphene oxide to enhance the supercapacitance at different precursor ratios. Later on, we explored the role of precursor content, synthesis time, and dispersive solvent for maximizing the supercapacitance of N-rGO sheet.SP/ISTC-19-001
Spin Structure of Exchange Biased Heterostructures: Fe/MnF<sub>2 </sub>and Fe/FeF<sub>2 </sub>
No full textNeutron Diffraction, Mossbauer and Electron Paramagnetic Resonance Studies of Pb0.8Bi0.2Fe0.6Nb0.4O3 Multiferroic
No full textThe Pb0.8Bi0.2Fe0.6Nb0.4O3 (PFN-BFO) multiferroic solid solution was synthesized by single step solid state reaction method with low calcination (700 degrees C/2h) and sintering (800 degrees C/3h) temperatures. Single phase formation was confirmed through X Ray Diffraction (XRD) and Neutron Diffraction (ND) at room temperature (RT). The structural analysis was carried out by Rietveld refinement through the Fullprof program. Refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.6449(8) angstrom, b = 5.6536(5) angstrom, c = 4.0017(6) beta = 30(4). ND data at RT exhibits G-type antiferromagnetic structure. The Mossbauer and Electron Paramagnetic Resonance (EPR) spectroscopy studies were carried out at RT. The isomer shift and the quadrupole splitting of the Mossbauer spectra confirm the Fe in +3 states. An EPR spectrum shows a single broad slight asymmetric line, is an evidence of Fe in +3 states. ND, Mssbauer and EPR studies are the clear evidence of existence of antiferromagnetic ordering near room temperature
Approximate analytical method for porous stepped fins with temperature-dependent heat transfer parameters
No full textThis work presents the thermal investigation of a porous stepped fin made from different ceramic porous materials (Al and SiC) having temperature-dependent internal heat generation. The fin is dissipating heat to the environment by means of convection and radiation modes of heat transfer, which are further considered to be temperature dependent. The approximate analytical Adomian decomposing method is used to solve this nonlinear problem along with the Newton–Raphson method. The results obtained using the Adomian decomposing method are compared with relevant results available in literature. The effect of various thermophysical parameters on the thermal behavior of the fin is critically analyzed. An optimization study to maximize the heat transfer rate for a constant material volume has been also conducted. The performance of the porous stepped fin is compared with a porous straight fin and solid stepped fin, which proves that the porous stepped fin is a better alternative
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