http://localhost:8081/jspui/handle/123456789/35 2025-07-01T00:28:33Z http://localhost:8081/jspui/handle/123456789/15565 Title: ENERGY STORAGE CERAMICS: SYNTHESIS AND CHARACTERIZATION Authors: GUPTA, ABHISHEK KUMAR Abstract: In today’s era, where the world is moving towards miniaturization, light weight, cheaper electronics, easy integration etc., high energy density dielectric capacitors are essential to increase its volumetric efficiency. If the energy density of dielectric capacitors come at par with electrochemical capacitors or even batteries, the diversity of energy storage applications will increase dramatically. Lead zirconate titanate (Pb(Zr1−xTix)O3 or PZT) ferroelectric ceramics exhibit high dielectric and piezoelectric properties and are widely used in many applications such as sensors, actuators, transducers, ceramic capacitors, FRAM chips etc. The sintering of PZT ceramics has been challenging due to the volatile nature of PbO at temperatures >600℃ which is detrimental to dielectric and energy storage performance. Spark plasma sintering (SPS) technique has been successfully used for sintering ceramics to high density at lower sintering temperature than required for conventional sintering process. The tetragonal, rhombohedral, orthorhombic and MPB phase composition of PZT ceramics are synthesized by using SPS technique. Each sintered specimen showed density greater than 98% of theoretical density. The effect of SPS temperature (800, 850, 900, 950℃) on phase composition, phase constitution, grain size and permittivity was investigated for MPB phase composition of PZT ceramics. It was observed that the rapid sintering technique causes compositional fluctuation and optimization of SPS temperature is essential. Rietveld refinement was carried out to identify the phases in the sintered specimens. The PZT specimens sintered at or above 900℃ showed presence of multiple phases instead of single tetragonal phase. It was proposed that the highest permittivity observed for 900℃ sintered specimen was due to the presence of monoclinic phase resulting in enhanced polarization in PZT. 2021-03-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/15520 Title: SYNTHESIS AND CHARACTERIZATION OF LiFePO4/CPOLYMER CATHODE MATERIAL FOR Li-ION BATTERY Authors: Sehrawat, Rajeev Abstract: Due to the economic liability of fossil fuels and increasing global warming concerns, it is required to develop alternative renewable and clean energy sources (such as solar, wind, and hydroelectric power) intensively at wide scale. These developments have raised a strong demand of high capacity energy storage systems with lower production costs and safety requirements. Li-ion batteries (LIBs) have been considered as one of the most promising energy storage system to meet these requirements. The first commercial Li-ion battery was developed by Sony Company in 1991. The ever increasing demand of producing a high energy storage system at lower cost drives the continuous research on various components of LIB. There are three key components in a LIB system: cathode, anode and electrolyte. The modern cathode materials have been prepared in their lithiated (discharged) state so that they can be paired with delithiated anode with a minimum possibility of accidental short-circuiting during the assembling of a battery. Hence, cathode materials always have a keen interest in research to enhance the storage capacity and fast charging of a LIB. The commonly used cathode materials are based on transition metals oxides or phosphates active material like LiCo02, LiMn204, and LiFePO4 etc. LiFePO4 is a potential material for the cathode of Li-ion battery because it possesses superior performance as it has high discharge capacity of 170 mAhlg, flat discharge voltage (3.4 V) profile, excellent thermal stability both at the charged and discharged states, high cyclability, low cost and is environmental friendly. 1-lowever, a few limitations such as nominal discharge voltage of 3.4 V vs Li/Li-ion, low electronic conductivity (10 S/cm), lower Li-ion diffusion coefficient and poor performance at low temperature restrict LiFePO4 material from being used as cathode in commercial applications. The limitation of low redox voltage of 3.4 V for Fe2 /Fe3 couple can be solved by substituting Fe with the transition metals such as Ni, Co and Mn in the structure of LiFePO4. The issues related to conductivity and diffusivity can be solved by 1) powder particles size reduction, 2) doping and 3) conductive surface coating such as with carbon and/or conducting polymers. The reduced particle size of powder offers several advantages such as short diffusion length, improved electron propagation, large electrolyte/electrode interface area and modified chemical potential. In view of the above advantages the particles size reduction can improve the highrate capability and cycling stability of LiFePO4 material. - The coating with conducting materials of carbon and polymers improves the electrical conductivity and Li-ion diffusivity of LiFePO4 resulting in its improved capacity and rate capabiliy. The carbon coating is a potential approach to meet the theoretical capacity of LiFePO4 at a nominal current rate. The effect of carbon coating is to impart high electronic conductivity, enhance the Li-ion diffusion in LiFePO4/C composite. Despite of many advantages carbon coating decreases tap density and volumetric density of cathode, and form inactive Fe2P layer on LiFePO4 active particles. Substituting the inactive carbon and binder with electrochemically active polymer can enhance the electrochemical performance of LiFePO4. The conducting polymers viz. polypyrrole, polythiophene and polyaniline are electrochemically active in the range of 2.2 - 3.8 V which overlaps with the redox range (3.4 V for Fe2 /Fe3 ) for LiFePO4. Therefore, these conducting polymers can act not only as conducting agent but also as host material for Li-ion insert io n/ext ract ion. This PhD thesis aims at exploring and investigating different polymers coated LiFePO4/C cathode materials for lithium ion battery. Systematic studies on the synthesis, characterization, cell fabrication and electrochemical testing have been performed. The thesis has been presented in six chapters. Chapter 1 presents a brief overview on non-conventional and conventional energy sources, history of batteries development, and working principle of the lithium ion battery. This chapter also introduces several advantages of lithium ion battery over the other type of secondary batteries. Chapter 2 presents a brief description of the various components of Lithium ion battery. The present status of various anode materials has been summarized. The detailed survey on cathode materials with main emphasis on LiFePO4 has been conducted. The factors affecting the carbon coating on LiFePO4 have been described. The promising methods of synthesis of electrochemically active polymers have been discussed. Finally the recent development on electrochemically active polymer coatings on the potential cathode materials has been - summarized. Chapter 3 deals with the synthesis and characterization of LiFePO4/C and polymers coated LiFePO4/C. The LiFePO4/C nano-particles were synthesized by chemical precipitation method and the in-situ polymer coatings on LiFePO4/C were developed by oxidation polymerization method. Three types of electrochemically active polymer viz. polyaniline, polypyrrole and polythiophene have been used to coat LiFePO4/C material. Chapter 4 presents the process of LiFePO4 synthesis. The effects of 0.5 ml and 1.0 ml aniline monomers on structure and thickness of carbon coating as well as on the particle size of LiFePO4 have been investigated. The decomposition of the polymer coatings has resulted in good graphitized carbon coating on the LiFePO4 particles. The electrochemical study shows that discharge capacity of LiFePO4/C powder synthesized using I.0m1 aniline is higher than the powder synthesized using 0.5m1 aniline. The higher rate capability and cyclability of LiFePO4 synthesized using 1.Oml aniline were attributed to the smaller particle size, higher Li-ion - diffusion coefficient and higher electronic conductivity. Chapter 5 is broadly divided into three sections and presents the detailed investigation on mechanism of formation of polymer coatings viz, of polypyrrole, polythiophene and polyaniline on LiFePO4/C particles. In section-I, the Polypyrrole coating on LiFePO4/C (LiFePO4/C-PPy) particles has been discussed. The XRD pattern of the polypyrrole coated LiFePO4/C composite confirms the formation of two electrochemically active phases of LiFePO4 and Lioo5FePO4. The less porosity in the polypyrrole coating grown in ACN solvent produces good connectivity of the core particles resulting in higher electrical conductivity and Li-ion diffusivity. The composite LiFePO4/C-PPy polymerized in ACN shows appreciable rate capability of 82 mAh g 1 compared to 40 mAh g for sample LiFePO4/C at higher current rate of 20C. The better rate - capability of LiFePO4/C-PPy polymcrizcd in ACN was due to the higher electrical conductivity and higher Li-ion diffusivity as confirmed by electrochemical impedance spectroscopy (EIS) measurements. itt The section-Il presents the investigation on polythiophene coated LiFePO4/C material. To suppress the growth of Li3PO4 impurity phases, polythiophene coating was developed on Lideficient and Li-excess samples of LiFePO4. It has been observed that only the polythiophene coated Li-deficient Lio95FePO4 material was capable of suppressing the Li3PO4 impurity phase. Polythiophene with different quantities of 4, 6, 8 and 12 wt% were deposited on Li095FePO4 material and the resultant materials are designated as Li0 95FePO4/C-PTh(4), Li095FePO4/CPTh( 6), Lio 95FePO4/C-PTh(8) and Lio.95FePO4/C-PTh(12) respectively. The EIS measurements show that all the polythiophene coated L1095FePO4/C materials exhibit higher Li-ion diffusivity and low charge transfer resistance (Rd). As the quantity of polythiophene increases in composites the conductivity also increase. The improved rate capability of Li095FePO4/CPTh( 8) composite was due to optimum quantity of polythiophene covering and interconnecting the LiFePO4/C particles. In section-Ill detailed investigations on the polyaniline coated LiFePO4/C composite has been presented. The in-si/u polyaniline coating on LiFePO4 particles was done using three different oxidizing agents viz. (NH4)2S208, KMn04 and K2Cr207. Polyaniline (PANI) samples have been - grown separately by self oxidation process using the above oxidizing agents. XRD analysis reveals the formation of single phase pure active material LiFePO4IC and mixed phase containing LiFePO4 and FePO4 for polymer coated LiFePO4/C composite. The amounts of polymer in the polyaniline coated LiFePO4/C composites synthesized using (NH4)2S208, KMn04 and K2Cr207 are 14, 15 and 17 wt% respectively. Electrical conductivities of the composite materials were determined by Impedance spectroscopy method. The composite material synthesized with (NH4)2S208 has higher conductivity compared to those synthesized with KMn04 and KCr,07. Chapter 6 presents the major conclusions of the present study and scope of the future work. 2015-07-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/15519 Title: BENEFICIATION STUDIES OF BANDED IRON ORES Authors: Rayapudi, Veeranjaneyulu Abstract: The present work investigates the utilization/beneficiation of low-grade iron ores to meet the steel vision 2030 of 300MT steel production. Due to limited rate of crude steel production and depletion of high-grade iron ores, processing of alternative iron resources such as low-grade iron ores is inevitable. The low-grade iron ores do not respond to conventional beneficiation techniques because of their complex chemical association. In this study detailed study of low-grade iron ores i.e., banded iron ores were carried out such as mineral identification, characterization studies, magnetic property studies, and wet chemical analysis to develop suitable beneficiation process. The processing of banded iron ores include first part deals with comminution studies (breakage rate characteristics through ball mill /Compression mode breakage) and second part deals with up-gradation (iron grade, yield, and iron recovery) of banded iron ores. In comminution studies, BHJ ore was found harder than BHQ and BMQ. Thermal treatment of banded iron ores causes massive random micro-cracks which enhances breakage kinetics. Compression testing of banded iron ores yielded finer size reduction than ball mill due to induced microcracks. But the introduction of compression comminution could not lead to any improvement in the concentrate through the downstream magnetic separation process. The up-gradation of banded iron ores included physical separation, microwave exposure, and carbothermal reduction (conventional/microwave). It was found that BHJ/BMQ can be upgraded and the concentrate can be used as feed for pellet making for blast furnace through microwave processing. The microwave exposed BMQ, produced a concentrate under optimal condition with 60.1% Fe grade, 99% Fe recovery at 71% yield in a single step. Whereas microwave exposed BHJ under optimal conditions, yielded an iron- concentrate with 61% Fe, 85% Fe recovery at 50% yield and BHQ yielded concentrate with FeG of 56.30%, FeR of 50.68% and a yield of ~27%. Effective conversion of the hematite phase to magnetite phase was observed in conventional carbothermal reduction process which helped ineffective separation of iron values from gangue. Carbothermal reduction was evaluated using Box Behnken statistical design and was found effective for iron enrichment. Under optimal condition, carbothermal reduction of BHQ produced a concentrate of FeG of 57.6%, FeR of 68% and a yield of 35.7%. Where as in BHJ concentrate enriched to FeG of 61.2%, FeR of 82% and a yield of 52% and coarser particle size produced the fused fraction consisting of ̴85%Fe with retained austenite and martensitic iron phases. In microwave carbothermal reduction the formation of spheroidal ferrite ball was observed within 10 min with the addition of a minimal amount of charcoal dosage at a microwave power of 900 W. Microwave carbothermal reduction of BHJ under optimal condition yielded a magnetic vi concentrate having ~61.6% Fe, ~73.4% recovery at a yield of 44% and can be used for blast furnace feedstock. Similarly, other experimental condition yielded a magnetic concentrate with ~49.1% Fe, ~89.3% recovery at a yield of 59.7% with significant amount of ferrite balls. The microwave carbothermal reduction of BHQ yielded FeG of 57.6%, FeR of 47% and a yield of 24% at optimum condition and other optimal condition yielded a less grade with a significant amount of ferrite balls. It was found that a small fraction of microwave irradiated ore-charcoal mixture was rapidly melted to produce pure ferrite balls with Fe ~93 %. The iron grade deteriorated at prolonged exposure due to the formation of fayalite phase. The optical micrograph of the ferrite ball reveals the presence of retained austenite and martensitic iron phase with a saturation magnetization of ~200 emu/g. 2019-08-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/15518 Title: PHASE TRANSFORMATIONS IN INTERSTITIAL FREE AND LOW DENSITY STEELS Authors: Sinha, Mrinmoy Abstract: The interstitial-free (IF) steel is extremely soft and ductile. The strengthening is the key focus of the present study by heat treatment. The samples have been soaked in the austenitic temperature domain followed by different rates of cooling (furnace cooling, air cooling and water quenching) in a Gleeble 3800® thermo-mechanical simulator. The outcome exhibits a dramatic improvement in strength as compared to reported conventional techniques. The electron microscopy along with EBSD has characterized lath martensite in this commercial grade steel. The hot deformation of austenite to martensite has also been investigated to study constraints in the martensite formation with variant selection in the present alloy system as well for a comparative study. The structure-property correlation is the key ingredient to address the role of the hierarchical structure (block and sub-block boundaries) against microstructural morphology for the obtained mechanical properties. In the additional part of the present work, some calculation with Dictra simulation has been performed to study phase transformations in low density steel. It is known that Al as the alloying element is inevitable for density reduction of steels. It in turns produces δ-ferrite in the system. The consequence of δ-ferrite to the austenite formation is the key theme in this part of work 2019-08-01T00:00:00Z