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Studies on Dynamics of Wind Turbine Rotor Blade System
No full textThe use of wind turbines offers a pollution-free, sustainable, and economically workable alternative to the provision of energy. Though substantial progress has already been made in the area of the wind industry, the performances of small wind harvesters can still be enhanced. It is essential to conduct additional research on the aerodynamics of wind turbines and their interaction with fluid flow. It is thus necessary to know various methods that can enhance the potential of a wind turbine. Over the last three decades, the size of the wind turbine blades has increased significantly. This growing size along with the associated mechanical behaviour, results in the generation of aeroelastic effects caused by the fluid-structure interaction (FSI). Effective FSI modelling of rotor blades is highly essential for the research of large-scale wind turbines. These large-scale wind turbines, on the other hand, are incapable of powering small devices, especially in remote locations where such small devices are used to monitor temperature, traffic, cyber security, etc. A small-scale energy harvester that can be used effectively in low-power devices must be investigated. Accommodating the aforementioned statements, this research work has implemented a numerical technique to enhance wind turbine output using different modifications and configurations. The fluid-structure interaction (FSI) analysis is also performed for wind turbine blades using composite materials. Furthermore, an attempt has been made to examine the functioning of a small lab-scaled wind turbine experimentally inside the wind tunnel. To execute these techniques, the fluent solver has been used with the help of the finite-volume method. In this work, four different types of airfoils were investigated, i.e., NREL (National Renewable Energy Laboratory) S809, S818, S825, and S826. Moreover, this work covers two configurations of a wind turbine: one the two-bladed turbine and the other the three-bladed turbine. For the two-bladed turbine NREL phase VI model has been considered to carry out the numerical investigation. For a three-bladed turbine, three kinds of the turbine have been designed and are listed below. 1) Design of the turbine by changing the two-bladed NREL phase VI to the three-bladed turbine. 2) Design of the turbine by using the dimension of GE 1.5 MW and considering S818 airfoil, S825 airfoil, and S826 airfoil. 3) Design of in-house laboratory-scale wind turbine by considering S818 airfoil, S825 airfoil, and S826 airfoil. An FSI simulation was performed for a blade by taking four composite materials in turns. CFD is used to compute the aerodynamic loads, whereas FEA is used to determine the blade structural reactions. The investigation was conducted using commercially available ANSYS packages. The performance of the turbine has been studied in terms of power, torque, deformation, and Von-Mises stress under varying conditions, and the most efficient conditions are outlined. Experiments on small-sized wind turbines have been executed inside the subsonic wind tunnel. Performance parameters are checked by varying wind speeds and loads. An electromechanical model has been developed. The results of the experiments have been compared with the electromechanical model. The experimental outcomes indicate that the designed wind turbine is capable of powering micro-devices
Computational Study of Magnetohydrodynamics-Based Heat and Mass Transfer Inside Enclosed Systems by Lattice Boltzmann Method
No full textDouble diffusive convection (DDC) is a form of heat convection that occurs due to two different density gradients (temperature and concentration), which vary under the effect of gravity (Huppert and Turner, 1981). DDC is essential in understanding several systems. Thermal and concentration gradients diffuse with time (may be at the same or different rates), lowering the aptness to propel the convection and also spread these gradients further along the flow regions (Radko, 2013). This phenomenon can be noticed in several broad fields, such as oceanography (salt-fingers), geology (flow of magma), astrophysics (solarcorona), metallurgy (solidification, crystallography) (Huppert and Sparks, 1984). A practical example of DDC is in metallurgical industries. In particular, the solidification of two alloys in which the solute region brings to density difference in the liquid melt, which, jointly with the temperature gradient in the system, develops DDC phenomena (Verhaeghe et al., 2007). The interaction of DDC and the effect of the magnetic field has the potency to modify the fluid circulation, which may be relevant in many instances, like electromagnetic casting and other metal manufacturing processes, cooling of magnetic storage media or electronic devices under magnetic field, geothermal reservoirs, crystal growth, electromagnetic stirring, etc. These types of fluid convection are popularly known as Magneto hydrodynamic convection (Reddy and Murugesan, 2017; Sheikholeslami et al., 2013c; Borjini et al., 2005; Borhan Uddin et al., 2015; Tagawa et al., 2002). Moreover, magnetohydrodynamics (MHD) is the analysis of the interaction of the magnetic field with the electrically conducting fluids, such as plasma, liquid metals, salt water or electrolytes, etc., (Alcala et al., 2015; Manna and Biswas, 2021). The fundamental behind MHD is that the magnetic field induces currents in a moving conductive fluid, creating forces on the fluid and changing the magnetic field. MHD flow has seen an extensive range of applications in the modern past and has gained significant interest owing to geophysical and cosmic fluid dynamics (Hasanuzzaman et al., 2012; Gangawane, 2017a; Gangawane and Bharti, 2018).The application span of MHD for an electrically conducting fluid involves electrical power generation, astrophysical flows, solar power technology, and space vehicle re-entry (Gangawane and Bharti, 2018). Applying a magnetic field to convection processes plays a controlling factor in the convection by damping the flow and temperature oscillations in material manufacturing fields (Sheikholeslami et al., 2013a, 2014b). On the other side, natural convective heat transfer within the enclosure has received considerable attention because of its relevance in various applications, such as thermal insulation, cooling of nuclear reactors, solar panels, ventilation of houses, and petroleum reservoirs, cooling of electronic devices, etc., (Al-Balushi et al., 2019; Ostrach, 1972) more citations. In the last couple of decades, the lattice Boltzmann method (LBM) has evolved into an alternating and promising numerical tool for illustrating the transport processes in various systems and for single and multiphase flows. Rather than solving the mass, momentum, and energy equations, the LBM seeks a solution of the Boltzmann method. LBM was derived from Boolean variables based on lattice gas automata (LGA). The discrete particle kinetics utilizes lattice (space) and time in discretized form (Chen and Doolen, 1998; He and Luo, 1997a; Mohamad and Kuzmin, 2010). Mc Namara and Zanetti (1988) presented LBM to overwhelm the weaknesses of the lattice gas cellular automata (LGA). Whereas the conventional numerical tool depends on the discretization of continuum partial differential equations (e.g., Navier-Stokes energy equations, etc.), LBM is established on microscopic models and mesoscopic kinetic equations. In LBM, the fluid is replaced by the distribution functions of the discrete particles. The fundamental notion of LBM is to build the discrete models over the domain (based upon the Boltzmann equation). Such models encompass the essential physics of microscopic and mesoscopic processes. Lastly, the recovery of relevant macroscopic equations can be achieved by multi-scale Expansion (viz., Chapman-Enskog analysis). Advantages of LBM include simple algorithm, ease in implantation of boundary conditions, making it suitable for complex domain problems, ease in parallel computing, easy estimation of pressure term, etc., (Mohamad, 2011). The objective of the thesis is to explore the hydrodynamics and thermal characteristics in the enclosed systems (i.e., enclosure or cavity) due to DDC associated with MHD. The influence of the aspect ratio of blockage as well as the location of the blockage has been studied. The effect of flow pertinent parameters, such as Hartmann number, Rayleigh number, Prandtl number, Lewis number, and Buoyancy ratio on the convection characteristics, along with the geometric parameters, have been explored. The study was conducted for the general assumptions of steady-state, incompressible, laminar and two-dimensional flows. The simulations are conducted using an LBM solver. The robustness of the solver has been ascertained by a thorough numerical validation and ensuring proper lattice size. Three differen cases have been considered in this work. The first case study explores the combined influence of aspect ratio and blockage on DDC-MHD characteristics and entropy generation for sodium-Potassium alloy liquid metal in the rectangular cavity. The second case study explores the effect of different non-uniform boundary conditions on the MHD-DDC characteristics for similar pertinent parameters. And finally, the third case study explores the influence of different blockage locations at various separation distances from the bottom wall of the cavity for above mentioned hydrodynamic pertinent parameters. Out of this study, some important conclusion has been drawn. The formation of multi-cell flow within the cavity with the increase in the Ra and Le was seen. Moreover, the formation and elongation of vortex cells along either side of the block with the increase in AR was noticed. Higher crowding of temperature and concentration contour lines along the heated/highly concentrated block was noticed for N = 2 compared to N = 2 for a given Ra. The increase in Ra and AR promoted a higher mixing of thermally differential fluid layers. The increase in the Ha restricted the fluid circulation by convection and was also noticed from the contours. The increase in ar and AR enhanced the rate of heat and mass transfer. The augmentation of Ra enhances different irreversibilities. The intensity of increase was noticed to be higher for Sff . The maximum values of Sff were observed to be increasing with the aspect ratios of cavity and blockage. At the same time, the reverse was true for Sth and Sc. When Ra increased from 104 to 105, the STH and SC showed an increase by about 56% and 47%, respectively. The dominance of thermal and species transport irreversibility (Beavg > 0:5) in the cavity was noticed for AR = 2;N = 2. On the other hand, for AR = 4, the significance of flow friction irreversibility within the cavity was observed (Beavg _ 0:5). NuTotal and ShTotal showed an enhancement of about 22% and 21%, respectively, for the sinusoidal profile as compared to linear for AR = 2 of the enclosure. For AR = 4 with sinusoidal boundary treatment, NuTotal and ShTotal showed the augmentation of about 19% and 17% as compared to linear. The variation plots of Nu and Sh demonstrate that a higher; HMT rate was noticed in the sinusoidal boundary condition profile of the enclosure in comparison to the linear boundary condition profile of the enclosure. As the obstruction between the bottom wall of the blockage and the adiabatic bottom wall of the cavity increases, shear force occurs, and the buoyancy-driven flow decreases, which leads to the diminishment in the local HMT rate. When the rectangular block moves farther away from the bottom wall of the cavity (Sd = H=6 and H=4), the buoyancy-driven increases, which tends to the enhancement in the local HMT characteristics. At separation distance (Sd = H=4) higher HMT is observed. The overall HMT rate enhances within the cavity with the augmentation in N and Sd
Transition Metal-Catalyzed C-C and C-Heteroatom Bond Formation Through Radical Process
No full textDuring the past few decades, radical reactions have been exploited extensively to generate carbon-carbon and carbon-heteroatom bonds in synthesizing valuable natural products and organic compounds. Free-radical reactions have advantages over ionic reactions in terms of wider functional group tolerance, ease in performing group and atom replacement, the potential to build complex structures from simple building blocks, and most notably, the mild reaction condition. Radicals are single electron species and are highly reactive; hence undergoes a variety of chemical reaction such as addition, substitution, cyclization, fragmentation, and hydrogen atom transfer reaction. Since the addition reaction of radicals to multiple bonds is generally a kinetically controlled process, the steric effect and radical stability are less significant in product formation, especially in radical addition and cyclization reactions. In recent years, TM-catalyzed radical cross-coupling reactions have created a revolution in organic chemistry by assembling simpler coupling partners into more complex organic compounds in a sustainable, economical, and efficient manner. The current thesis entitled “Transition Metal-Catalyzed C-C and C-Heteroatom Bond Formation through Radical Process” mainly describe a study on the development of some newer catalytic protocols for C-C and C-heteroatom bond formation reactions with the aid of transition-metal catalyst via a radical pathway. In particular, we have developed new radical cross-coupling protocols for the synthesis of N-sulfonyl ketimines, symmetrical and unsymmetrical biarylsulfones, symmetrical biaryls and vinyl arenes. Iron-catalyzed oxidation of diols to α-hydroxy ketone through a radical process, and subsequent reaction with hydrazones to afford 1,3- and 1,3,5-substituted pyrazoles in the presence of iron-catalyst was also explained. The current thesis contains 5 chapters which are summarised as follows: Chapter 1: A short review on transition metal-catalyzed radical cross-coupling reaction This chapter briefly overviews the TM-catalyzed radical cross-coupling reaction for C-C and C-heteroatom bond formation. Additionally, nitrogen heteroatom containing directing group mediated C-H acylation of different arenes has been described. In addition, a critical overview and objective of the present work are also presented.
Chapter 2: Palladium-catalyzed ortho-benzoylation of sulfonamides through C–H activation: Expedient synthesis of cyclic N-sulfonyl ketimines In this chapter, Pd-catalyzed ortho-carbonylation of sulfonylarene by non-hazardous carbaldehydes as a carbonyl precursor has been discussed. Sulfonamide group served as the directing group for C-H activation under ligand-free conditions. The scope of the strategy has been extended towards the one-pot two-step synthesis of cyclic N-sulfonyl ketimines under mild-reaction conditions. Chapter 3. N-Methoxyarenesulfonamide as a sulfonyl equivalent for palladium-catalyzed sulfonylation of arenes through C-H activation This chapter deals with the synthesis of diaryl sulfones from the unbiased arenes through palladium-catalyzed C−H activation. N-methoxy arenesulfonamide was exploited as a potential sulfonyl donor by the cleavage of the S−N bond through a radical pathway. The present methodology has several advantages: a simple, readily available catalytic system; the use of a stable sulfonyl donor; a relatively moderate excess of arene coupling partner for an undirected C−H activation process, along with the tolerances of aryl bromides and iodides, which in turn permits further cross-coupling reactions to afford cross-coupled sulfones. Chapter 4: Pd-catalyzed desulfitative arylation of olefins by N-methoxysulfonamide This chapter describes a Pd-catalyzed protocol desulfitative Heck-type reaction of N-methoxy aryl sulfonamides with alkenes. Expectedly, the reaction proceeds through the CuCl2- promoted generation of nitrogen radical and subsequent desulfonylation to afford the aryl radical for the Pd-catalyzed coupling reaction. N-methyl sulfonamide was further exploited for the synthesis of symmetrical biaryls under a similar reaction condition. Chapter 5. Facile Synthesis of Pyrazoles by Iron-catalyzed Regioselective Cyclization of Hydrazones and 1,2-diols under Ligand-free Conditions This chapter describes a facile synthesis of pyrazoles by the cyclization of hydrazones and 1,2-diols. In the presence of ferric nitrate, the reaction occurs under neat conditions and makes use of the potassium persulfate to oxidize the diol to α-hydroxy carbaldehyde for the reaction with hydrazones to produce 1,3- and 1,3,5-substituted pyrazoles selectively. The overall regioselective transformation occurs in one pot under ligand-free, mild conditions even in the presence of air. Chapter 5. Conclusion and Future Scope In the last chapter, the overall summary and future scopes of the present work have been described
Application Of Bismuth Titanate And Bismuth Ferrite Based Binary/Ternary Heterostructure Nanomaterials Towards Photocatalytic Degradation Of Agrochemical Contaminants
No full textIn this thesis, the facile synthesis and photocatalytic application of bismuth titanate and bismuth ferrite based binary and ternary heterostructure materials has been presented for visible light assisted degradation of agrochemical contaminants with strong endocrine disrupting properties. Initially, suitable combustion synthesis routes were designed for phase pure synthesis of Bi4Ti3O12, Bi2Fe4O9 and Bi20TiO32/Bi4Ti3O12 composites. The synthesized complex oxides were integrated with metal sulfide nanoparticles to prepare binary/ternary p-n and Z-scheme heterostructure materials with improved optical absorption and enhanced photoelectochemical features. The photocatalytic application of the synthesized heterostructure materials were evaluated for photodegradation of pesticides/herbicides/insecticides and water pathogens under visible light irradiation. The detailed mechanistic study and evaluation of degradation pathway was carried out to understand the mechanism of photocatalytic action. Bi4Ti3O12MCPA degradationDiazinon degradationEndosulfan degradationBi2Fe4O9Sulfamethoxazole degradationPhenyl urea herbicides degradationBacterial Inactivation A series of CuS/Bi4Ti3O12 p-n heterojunction materials were synthesized by a two-step process. Initially, the Aurivillius phase Bi4Ti3O12 (BT) was synthesized by a facile combustion route using urea as a fuel. The Bi4Ti3O12 was subsequently modified by deposition of CuS (5-20 wt%) using a hydrothermal route to prepare the heterojunction materials. The methods of synthesis and calcination temperature were important factors which influenced the morphology, particle size and phase purity of Bi4Ti3O12 material. The heterostructure materials exhibited hierarchical flower like structure consisting of ultrathin CuS nanosheets and BT nanoflakes. HRTEM and microstructural study revealed microscopic close interaction between the two phases. The optical and photoelectrochemical measurement study suggested significant improvement in visible light absorption (400-800 nm) and charge carrier separation due to heterojunction formation. The CuS/Bi4Ti3O12 materials showed excellent photocatalytic activity for aqueous phase degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicide under visible light (> 95 % degradation in 3 h). The rate constant for CuS/Bi4Ti3O12 materials was 4.5 times higher than the pure BT material towards MCPA degradation. The OH and O2– radicals were identified as the reactive species, the formation of which was confirmed by spectrometric method using terephthalic acid and nitroblue tetrazolium as molecular probes. Further, the combustion synthesized Bi4Ti3O12 material was hybridized with SnS2 to prepare Z-scheme SnS2/Bi4Ti3O12 heterostructure photocatalyst materials. The SnS2 nanoparticles (10-20 nm) were decorated over BT surface using a hydrothermal method. Structural and morphological characterization suggested the presence of orthorhombic BT and hexagonal SnS2 crystalline phases with high interfacial contact and strong interaction at microscopic level. Optical and photoelectrochemical (PEC) measurements revealed improved visible light absorption and enhanced charge carrier separation and migration properties. The SnS2/Bi4Ti3O12 materials displayed excellent photocatalytic activity for degradation of diazinon insecticide (> 90% with kapp ~ 0.019 min-1) in aqueous media under visible light illumination. The valence band (VB) h+ and •OH radicals were identified as major transient species responsible for photodegradation of diazinon. A Z-scheme electron transfer pathway has been proposed to explain adequately the generation of these radicals which was deduced from PEC measurements, scavenger and radical trapping experiments. Mechanistic study revealed that diazinon degradation occurred in a series of steps to produce 2-isopropyl-6-methyl-pyrimidin-4-ol as a major intermediate which was further mineralized over the photocatalyst surface. The process potential of the developed photocatalytic method has been tested for different water matrices and interfering anionic species with radical quenching activity. A series of ternary multi-heterojunction CdS/Bi20TiO32/Bi4Ti3O12 (CdSxBTC) photocatalysts were prepared by hydrothermal deposition of CdS nanoparticles (15-25 nm) over one pot combustion synthesized Bi20TiO32/Bi4Ti3O12 (BTC) nanostructures. Comprehensive characterization of the ternary composites revealed enhanced optical absorption, high interfacial contact, fast electron channelization and a prolonged excited state life time in comparison to pure components. The CdSxBTC composite materials displayed enhanced photocatalytic activity for endosulfan degradation (kapp value 6-12 times greater than pure semiconductors). The cell viability assay study disclosed non-cytotoxic nature of the treated endosulfan solution. A synergistic Type-I bridged coupled Z-scheme electron migration process accounted for robust radical generation ability (•O2− and •OH) and photocatalytic activity of the ternary composites. The facile fabrication of In2S3/Bi2Fe4O9 (ISxBFO) binary heterostructure was performed by hydrothermal deposition of In2S3 nanoparticles (20-40 nm) over combustion synthesized Bi2Fe4O9 nanocuboids. In depth characterization of the composite revealed broad spectrum UV-Vis response, large interfacial contact, facile charge carrier separation and mobility and a prolonged life time of excited state photoelectrons. The ISxBFO heterostructure material exhibited enhanced photocatalytic efficiency for aqueous phase degradation of sulfamethoxazole antibiotics (kapp=0.06 min-1) and phenyl urea herbicides (kapp= 0.028 min-1) with reaction rates 5-8 times higher than the pure components. The cell viability study confirmed non-cytotoxic nature of treated sulfamethoxazole and diuron solutions. The composite materials also showed convincing antibacterial behavior towards toxigenic Vibrio cholerae pathogen. Haemagglutination assay study revealed excellent biocompatibility of the binary composite up to a concentration of 200 mg/L. A Z-scheme electron migration mechanism accounted for the robust radical generation ability (•OH and O2–) and multidimensional photocatalytic activity of the ISxBFO heterostructure material
Development of Al and Cu-Based Hybrid Nanocomposites using Graphite Nanoplatelets and Multiwalled Carbon Nanotubes as Nanoreinforcements
No full textNanocomposites are a new class of material that contain a relatively small amount of nano-sized particles having a high specific surface area as reinforcement. Metal matrix nanocomposites (MMnCs) are an emerging class of nanocomposites that have excellent physical and mechanical properties and have potential applications in a wide range of areas. These reinforcements have higher interaction with the metal matrix leading to superior physical, structural, thermal, and mechanical properties of the nanocomposites. MMnCs reinforced with carbonaceous nanofillers like multiwalled carbon nanotube (MWCNT) and graphene are novel materials showing excellent mechanical and wear performance even under adverse environmental conditions with respect to that exhibited by monolithic conventional materials. Hybrid nanocomposites are a recent advancement in the area of nanocomposites that can show far better properties as compared to conventional monolithic materials and monocomposites. Hybrid composites can have a combination of different materials or two or more forms of reinforcements like fibers, particulates, whiskers, and nanotubes. The focus of the present study is mainly on the fabrication of Al and Cu-based MMnCs by reinforcing them with two carbon allotropes, namely, MWCNTs and exfoliated graphite nanoplatelets (xGnPs), a derivative of graphene. Apart from the MWCNT-xGnP hybrid nanofiller, MWCNT and xGnP monofillers were also used to develop Al and Cu-based nanocomposites. The MMnCs were fabricated through the powder metallurgy (PM) route, and sintering was carried out by both conventional sintering and spark plasma sintering (SPS). The microstructure, mechanical properties, and wear performance of the Al and Cu-based nanocomposites were investigated in the present study. The characterization of the various powder mixtures and the sintered MMnCs along with the sintered pure Al and Cu samples has been carried out through various analytical tools like x-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. Density, Vickers microhardness, compressive strength, and strain to failure of the various sintered samples were also determined. Five different MWCNT-xGnP hybrids having MWCNT-xGnP in weight ratios of 1:9, 3:7, 1:1, 7:3, and 9:1 were prepared by ultrasonicating the MWCNT and xGnP in appropriate weight ratios. Along with pure Al and Cu samples, 1, 2, 3, and 5 wt.% of each of the five MWCNT-xGnP hybrids were added to Al and Cu to develop the various Al-MWCNT-xGnP and Cu-MWCNT-xGnP hybrid nanocomposites. MWCNT and xGnP were also added as monofillers to develop Al-MWCNT, Al-xGnP, Cu-MWCNT, and Cu-xGnP nanocomposites. From the characterization and mechanical properties analysis, it has been observed that conventionally sintered and SPSed Al and Cu-based hybrid nanocomposites exhibited superior mechanical properties and wear behaviour as compared to the similarly developed monoreinforced Al and Cu-based nanocomposites and pure Al and Cu samples. Among the various MWCNT-xGnP hybrid MMnCs, the MMnCs reinforced with hybrid having MWCNT:xGnP weight ratio of 1:1 exhibited the best mechanical and wear performance. In the case of monofiller reinforced nanocomposites, the addition of xGnP gave better results as compared to MWCNT. SPSed nanocomposites show a very high relative density of ~98.90% for Al-1 wt.% MWCNT50xGnP50 nanocomposite and ~98.23% for Cu-2 wt.% MWCNT50xGnP50 nanocomposite, which is ~3.35% and ~6.12% higher than that of similarly developed pure Al and Cu samples. A significant improvement in hardness was observed for both the Al and Cu-based hybrid nanocomposites and a hardness of ~654.2 MPa was achieved for Al-5 wt.% MWCNT50xGnP50 nanocomposite and ~1.35 GPa for Cu-2 wt.% MWCNT50xGnP50 nanocomposite developed by SPS which is ~45.57% and ~29.31% higher than that of similarly developed pure Al and Cu samples. Orowan strengthening, grain refinement, and dislocation strengthening are the major reasons for the enhanced mechanical properties. The compressive strength of SPSed Al-1 wt.% MWCNT50xGnP50 nanocomposite was found to be ~700 MPa and SPSed Cu-3 wt.% MWCNT50xGnP50 nanocomposite was found to be ~720 MPa which is higher than that of similarly developed pure Al and Cu samples by ~95.8% and ~73.9% respectively. The wear characteristics of both the Al and Cu-based nanocomposites were also improved significantly, up to a loading level of 2 wt.% MWCNT50xGnP50 hybrid reinforcement. Further addition of the hybrid nanofiller led to a deterioration in the wear properties due to agglomerations of the nanofiller in the metal matrix
Studies on the Synthesis and Utilization of Fine Alumina Powder for the Fabrication of Sintered Mullite Ceramic
No full textThe high demand and various applications of mullite in structural ceramic instigate the ceramic researchers to study in-depth for the development of mullite ceramic with improved quality and performance. Mullite is an excellent material for advanced electrical, optical, and structural ceramics applications. An extensive literature study shows that solid-state reaction and the chemical route can synthesize the dense mullite ceramic. In solid-state, kaolinite is used for mullite synthesis due to its occurrence in nature, lower cost and good availability. It is an excellent natural source of silica and alumina but needs extra alumina from outside to prepare stoichiometric mullite. The sintering of mullite is difficult due to the slow aluminium and silicon ion interdiffusion in the mullite lattice structure. Different sintering additives are tried to solve the issue. In the clay alumina system, most additives are added in a higher amount, and the densification is enhanced by the extensive liquid formation, resulting in poor strength. Incorporating fine alumina powder can also improve densification and mechanical strength by reducing the porosity with inter-particle voids fillings and faster sintering. The reactivity and particle size of the added α-Al2O3 can be modified by applying different synthesis routes. The approach in this research work is first to synthesize fine alumina powder using various chemical routes. Then the use of these synthesized alumina powder and calcined kaolinite for further processing of mullite ceramic. Some oxide additives are also tried here in nominal amounts to get a higher sintered density. The strengthening of bulk mullite ceramic using a rare earth oxide additive is attempted to obtain columnar interlocking mullite grains. Fine α-alumina powder is prepared following two different methods named sol-gel and combustion. The detailed characterization of synthesized α-alumina powder is carried out in each case and is added to kaolinite for further processing of mullite. A batch comprising kaolinite and available commercial boehmite is also prepared for comparison. A detailed study on adding these three different α-Al2O3 in kaolinite showed the effectiveness of the combustion synthesized alumina powder in producing sintered mullite ceramic with a theoretical density of 87%. Three different oxide additives, TiO2, MgO and La2O3, are chosen, and the effects on densification and strength development are studied. The maximum densification achieved for the clay- α-Al2O3 system in the presence of 3% MgO and 2% TiO2 reported earlier are 92% and 80% at 1600°C. However, in the present work, 1% MgO and 1% TiO2 individually is sufficient to improve the densification up to 94% at 1600°C. The use of reactive alumina here helps reduce the dose of additive, which removes the possibility of the formation of secondary phases like aluminium titanate and magnesium aluminate spinel. 3% La2O3 additive further enhances the densification up to 96% with improvement in flexural strength. The elongated mullite grains with interlocked structures are found in the micrographs. Therefore, using a combustion synthesized α-Al2O3 in kaolinite reduces the sintering additive's dose and assists in developing a sintered, low-cost, high-strength mullite ceramic
Study on Membrane Parameters Involved in ZnONP Penetration and Amyloid Beta Interaction in Neurodegeneration
No full textThis thesis attempts to investigate the membrane parameters associated with neurodegeneration caused by zinc oxide nanoparticles (ZnONPs) and Amyloid Beta-40 (Aβ- 40) leading to neuronal cell deformation. Intrinsically disordered peptides (IDPs) like Aβ- 40 are known to cause neurodegeneration, although the exact mechanism through which they elicit this toxicity is still elusive. And lately, the extensive use of nanoparticles, specifically ZnONP, in cosmetics, coating, and pigments has increased tremendously. This leads to the possibility of unintentional exposure of NPs as a hazardous pollutant for humans. Recent studies have shown the implication of ZnONP exposure that induces neuronal damage. But the mechanism of entry of these NPs into the cells is poorly understood. The current understanding of nanoparticle–membrane interaction is drawn mostly from computational studies and lacks sufficient experimental evidence. We firstly explored the ZnONP-membrane interactions. Here, we try to investigate the lipid specificity and the role of the membrane biochemical and physical forces at play in modulating the penetration of ZnONPs. Using confocal fluorescence imaging and potentiometric dye-based fluorimetry, we first investigated the interaction of ZnONP in both multi-component and individual lipid membranes using cell-like giant unilamellar vesicles to dissect the lipid specificity; also, we measured the changes in membrane order, anisotropy and hydrophobicity. Amongst the single lipid membranes, ZnONP interacted strongly with phosphatidylinositol followed by phosphatidylcholine head-group containing lipids. We further compared the interaction of ZnONP with three physiologically relevant membrane conditions varying in composition and dipole potential. We found that ZnONP interaction leads to a photoinduced enhancement of phase separation that ranges from partial to complete depending upon the membrane composition and cholesterol content. Interestingly, while the lipid order of a partially-phase-separated membrane remained unchanged upon ZnONP crowding, a fully-phase-separated membrane showed an increase in the lipid order. Strikingly, ZnONP crowding induced a contrasting effect on the rigidity of the membrane upon binding to the two membrane conditions, which was inferred through fluorescence anisotropy, in line with the measured diffusion coefficient. ZnONP seems to preferentially penetrate through the liquid disordered areas of the membrane and the boundaries of the phase-separated regions driven by the interplay between the electrostatic forces and phase boundary conditions, which are collectively dictated by the composition and ZnONP induced lipid reorganization. The results may lead to a greater understanding of the interplay of membrane parameters and ZnONP interaction in driving passive penetration. Coming to Amyloid-beta (Aβ-40) aggregation mediated neuronal membrane deformation, although poorly understood, is implicated in Alzheimer's Disease (AD). The peptide aggregates, forming amyloid plaques which were long suspected to be toxic to the neurons. But lately, the leitmotif in the field has changed, where now the more soluble forms of the peptide are considered toxic for the neurons. Hence, we set out with a motive to find synthetic molecules, specifically the arylamines that could compete with the aggregating peptide for the binding pockets leading to retardation or complete arrest of the fibrillation of the peptide. Further, we also looked into whether these molecules had the potential to dissolve pre-formed aggregates. The screening of these molecules led to two potential molecules that retarded the Aβ-40 aggregation and one of which could also dissolve the preformed aggregates. Furthermore, We then wanted to emulate the Aβ-40 mediated myelin membrane deformation observed physiologically. For which myelin membrane mimic was incubated with Aβ-40 in vitro and temporally mapped for 24 hours using confocalmicroscopy, initial strong binding and extensive tubulated structures at longer timescales were observed. To dissect the lipid specificity of Aβ-40 in the myelin membrane, we used the single lipid models. ThT assay & fluorescence microscopy were used to check for potential modulation of the Aβ-40 aggregation and binding. Binding was observed in PI, PG, PC/BSM, and DOPC/PIP2. As observed, negatively charged lipids bound strongly, and hence electrostatic forces seem to play a role in binding. Interestingly zwitterionic PC/BSM too showed strong binding leading us to suspect that something else apart from electrostatics is also at play. Using the differences in the shapes of the individual lipids, we formulated three different conditions along with myelin membrane and estimated the packing defect densities through MD simulation and then further experimentally confirming The binding of Aβ-40 depends predominantly on the lipid packing defect densities and electrostatic interactions and results in rigidification of the myelin membrane in the early time scales. Furthermore, elongation of Aβ-40 into higher oligomeric and fibrillar species leads to eventual fluidization of the myelin membrane followed by extensive membrane tubulation observed in the late phase. \ Taken together, our results capture mechanistic insights into snapshots of temporal dynamics of Aβ-40 - myelin membrane interaction and demonstrate how short timescale, localphenomena of binding, and fibril mediated load generation manifests into long timescale, global phenomena of myelin tubulation and demonstrates the ability of Aβ-40 to demyelinate
Microwave Processed NBT and SBT based Ferroelectric Composites for Multifunctional Device Applications
No full textFerroelectric materials are widely employed in electronic devices such as sensors, actuators, and non-volatile random access memory (NVRAM), etc. due to their multifunctional properties. In these device applications, the ferroelectric materials are subjected to different loading cycles. This results in fatigue behaviour, which becomes a serious issue and restricts their commercial applications. This fatigue factor determines the stability and lifetime of ferroelectric devices. Among many ferroelectric materials, perovskite-based PbZr0.52Ti0.48O3 (PZT) and bismuth layered-based SrBi2Ta2O9 have been widely investigated for their use in non-volatile memory applications. Lead-based systems, despite their superior ferroelectric characteristics, are prohibited from being used in device applications owing to health and environmental concerns. Among various lead-free ferroelectrics, Na0.5Bi0.5TiO3 (NBT) system promises to be a potential replacement for lead-based perovskites. However, certain drawbacks of NBT system such as poor fatigue resistance and high coercive field need to be addressed. Though SrBi2Ta2O9 system has better fatigue resistance, the low switchable polarization (2Pr) and high processing temperature to synthesize this system make them incompatible to be used in device applications.
Synthesis of NBT and SrBi2Ta2O9 based materials by conventional solid-state reaction route necessitates high processing temperatures, which may result in the loss of volatile components due to their high volatilities, resulting in deterioration of material properties. Therefore, to lower the processing temperature and time, microwave processing technique is used. XRD study revealed that the optimal calcination and sintering temperatures for microwave synthesized NBT ceramics are 800 oC for 15 minutes and 1000 oC for 30 minutes. Whereas, the optimal calcination and sintering temperatures for conventionally synthesized NBT ceramics are 850 oC for 4 hours and 1150 oC for 4 hours, respectively. Similarly, for microwave synthesized Sr0.8Bi2.15Ta2O9 (SBT) ceramics, optimal calcination and sintering temperatures are 950 oC for 30 minutes and 1100 oC for 30 minutes, respectively, which is significantly lower than the same system synthesized by conventional processing routes. Because the processing temperature and time of microwave processing technique differ noticeably and lower than those of conventional synthesis processes, microwave processing technique offers a potential benefit in terms of time and energy savings. Dense microstructure with smaller and fine grains distribution was observed in microwave processed NBT and SBT based ceramics. Microwave processed NBT and SBT based ceramics showed lower loss and lower leakage current density that can be associated to their increased density.
There have been several attempts to enhance the characteristics of NBT system by different ionic substitution or doping at A or B-sites for wider applications. Donor doping has been shown to improve the ferroelectric characteristics of materials. To investigate the effect of doping, several dopants, based on their ionic radii and valency, to replace A and B-sites were chosen. Microwave-assisted solid-state reaction method was used to synthesize NBT doped systems with varying mol % of dopants, as given below,
1. (Na0.5Bi0.5)(1-x)LaxTi(1-x/4)O3 (where x=0.01,0.02,0.03)
2. (Na0.5Bi0.5)(1-x)SmxTi(1-x/4)O3 (where x=0.01,0.02,0.03)
3. (Na0.5Bi0.5)(1-x/2)Ti(1-x)NbxO3 (where x=0.005, 0.01, 0.015)
4. (Na0.5Bi0.5)(1-x)Ti(1-x)WxO3 (where x=0.005, 0.01, 0.015)
XRD analysis of A-site and B-site doped NBT systems indicated that the solubility limits of B-site dopants (around 1 mol %) were lower than those of A-site dopants (around 3 mol %). XRD patterns of both A-site and B-site doped NBT systems with single perovskite phase were matched with JCPDS file- 36-0340 of NBT having rhombohedral structure. Rietveld refinement indicated no structural change with doping, however, doping induced lattice deformation due to differences in dopant ionic radii and host atom radii. Substitution of La3+ and Sm3+ ions at A-sites tends to shrink the lattice due to their lower ionic radii than Na1+ and Bi3+ of host A-site ions. Whereas occupancy of Nb5+ and W6+ ions at B-site expands the lattice a little due to their comparable but slightly larger ionic radii than Ti4+ of host B-site ions. Density of all the doped systems was found to be lower than the parent system. Thus, higher sintering temperature is required to get densified modified NBT ceramics. Incorporation of donor dopants resulted in reduction in grain size as the cation vacancies accumulates at grain boundary, which inhibited grain growth, thus, all the dopants act as grain growth inhibitors in modified NBT systems. Minimal decrease in leakage current density was observed up to 2 mol% of A-site and 1 mol% of B-site doping and all the modified ceramics displayed Ohmic type conduction behaviour. Overall, 1mol% Sm-doped NBT (abbreviated as NBST1) showed the better ferroelectric characteristics among all the doped ceramics with 2Pr and Ec of ~20.65 μC/cm2and ~20.23 kV/cm, respectively compared to ~13.37 μC/cm2 and ~23.84 kV/cm for NBT. Hence NBST1 system was chosen as the matrix to synthesize composites with SBT system as filler.
Some researchers have put an effort to develop composites of efficient lead-free perovskite material with an appropriate bismuth-layered material to compensate for the required properties. In the present study, composites of perovskite NBST1 system and bismuth layered based SBT system have been prepared by microwave-assisted solid-state reaction route to improve their overall fatigue as well as ferroelectric properties. Two parent systems were prepared individually and were mixed by varying wt.% of each phase to produce the composite systems. The composites synthesized by microwave-assisted solid-state reaction route are;
(1-x) NBST1-xSBT (where x= 0, 4, 8, 12, 16wt.%)
X-ray diffraction patterns of (1-x)NBST1-xSBT composites revealed the coexistence of both perovskite and bismuth layered phases in all the composites. Change in peak intensity was thought to be induced by a change in composition, i.e., when SBT content increases, the peak intensity of the NBST1 perovskite phase decreased while the peak intensity of the bismuth layered SBT phase slowly increased. Density of all the composites was between that of matrix NBST1 (~5.28 g/cm3) system and filler SBT (~8.92 g/cm3) system. It was observed that well-developed grains of various sizes were densely distributed throughout the surface of ceramics. From the room temperature dielectric study, it was found that both dielectric constant and loss decreased with the increase of SBT content in composites. Increase in internal stress in composites owing to adjustment of two separate systems with considerably differing lattice parameters was evidenced by decrease in transition temperatures. Leakage current density and ferroelectric parameters like remnant polarization and coercive field decreased with the incorporation of SBT system in composites. Polarization fatigue study confirmed that fatigue endurance increased with the increase of SBT content. Among the studied (1-x)NBST1-xSBTcomposites, composite with x= 8 wt.% appeared to be the best in terms of dielectric, ferroelectric, and fatigue resistance for multifunctional device applications, especially for ferroelectric memory
Processing, Characterization and Flammability Behavior of Coir Fiber/Sirisha Bark Filler Reinforced Hybrid Polymer Composite
No full textRecently, natural fibers are replaced synthetic fibers to a great extent as reinforcement to the polymer composites. Among the natural fibers, coir fiber has the potential to be used in various applications because of its abundant availability, non-toxicity, low cost, and resilient properties. Coir fiber has high lignin content (46 %) as compared to jute (23 %), hemp (10 %), and kenaf (16 %) fibers making it a preferable reinforcement in the development of polymer composites to enhance the flame-resistant properties. Generally, polymeric materials are susceptible to flame. That is why it is essential to measure the performance of polymer composites before their applications in construction, automotive parts, etc. The neat polypropylene (PP) is extremely sensitive to flame and therefore it is a challenging task for the researchers to reduce the flammability properties of PP-based composites. Though the artificial flame retardant fillers reduce the flame propagation, these are hazardous, costly, not environment friendly and they reduce the mechanical strength of the polymer composites upon higher loading. To overcome these limitations, in this work the novel natural Sirisha bark filler is reinforced as flame retardant filler to the coir fiber reinforced PP composites. The objective of the present investigation is to produce a compatibilized blend of a natural fiber with a thermoplastic to produce coir fiber/Sirisha bark filler-based PP hybrid composites with improved fire performance for applications in the auto industry for indoor application where the load is not a critical issue and to study the mechanical and flammability properties. The dynamic mechanical behavior, thermal stability, and wettability properties of composites are also studied. The PP hybrid composites may also be used in decking and cladding. The hybrid composites provide satisfactory fire performance along with the mechanical properties at lower filler loading without any compatibilizer. The 10 wt. % bark filler reinforced composites attain a V-0 rating with zero flame propagation speed. The time to ignite (TTI) of the hybrid composites increases due to the filler addition in comparison to neat PP. The impact strength also increases with the filler loading. The thermal stability of the hybrid composites increases due to the bark filler loading than the neat PP and the coir fiber/PP composites. The SEM micrographs show the well-defined grain boundaries of the composites that reveal the strong bond of the bark filler with the PP matrix. The char morphology conforms to the formation of carbonaceous char coating over the hybrid composites surface that act as a hindrance to flame
Study of Fracture Properties of Composites and Aluminium Alloys Using Size Effect Method
Get PDFThe size effect is a problem of scaling, which is central to every physical theory. In fluid mechanics research, the problem of scaling continuously played a prominent role for over a hundred years. In solid mechanics research, though, the attention to scaling had many interruptions and became intense only during the last decade. The question of size effect recently became a crucial consideration in the efforts to use advanced fiber composites and sandwiches for large ship hulls, bulkheads, decks, stacks and masts, as well as for large load-bearing fuselage panels. The scaling problems are even greater in geotechnical engineering, arctic engineering, and geomechanics. In analyzing the safety of an excavation wall or a tunnel, the risk of a mountain slide, the risk of slip of a fault in the earth crust or the force exerted on an oil platform in the Arctic by a moving mile-size ice floe, the scale jump from the laboratory spans many orders of magnitude. In the present investigation, tested 186 specimens made of glass fibre composites with three different widths 30 mm, 40 mm and 50 mm, these composite specimens were tested at four different displacement loading rates to know the effect of displacement loading rate on fracture parameters by using size effect method. The fracture parameters of three different alloys 5052 – H32, 6061 – T6 and 8011 at constant strain rate were determined by using size effect method. The fracture properties of composites and aluminium alloys determined by using linear regression analyis, R-curve approach and work of fracture methods. Size-effect method is used in determining mode-I fracture characteristics of woven fiber glass/epoxy composite laminates for varying loading rates. Tensile testing of geometrically similar single edge notch (SEN) specimens with three widths 30 mm, 40 mm, and 50 mm is carried out for four different displacement loading rates, namely 1, 10, 100, and 500 mm/min. For each width (D) and loading rate, the crack-length (a) is varied as 0.125D, 0.25D, 0.375D, and 0.5D. A total of 186 specimens were tested. The peak stresses (_Nu), the initial Young’s modulus (Exx), and the shear modulus (Gxy) were calculated. The fracture toughness (KIC), critical strain energy release rate (Gf ), and material characteristic length (Cf ) were calculated using linear regression analysis of nonlinear fracture mechanics equations. The values of Gf and Cf first decrease and then increase monotonically as the loading rate changes from 1 to 500 mm/min. This behavior was explained using Bažant size effect equation relating nominal strength and specimen size. The study revealed the change in modes of failure characterized by a jump in brittleness number as loading rate increases from 1 mm/min to 10 mm/min, followed by decrease in brittleness number as loading rate increases from 10 mm/min to 500 mm/min. This conclusion was supported by highly magnified images of failed specimens using scanning electron microscope. A numerical algorithm to determine crack growth resistance curves (R-curves) from peak load is also implemented. The R-curves are geometry as well as loading rate-dependent and give Gf , Cf values which agree qualitatively and to some extent quantitatively with the linear regression approach.\ Size-effect method is used to determine the fracture properties of three aluminium alloys. Mode-I tensile testing of thin rectangular sheets of aluminium alloys 5052−H32, 6061−T6, and 8011 is carried out. The test specimens are scaled geometrically in the ratio of 1:2:3:4 for a constant length (L) to width (D) ratio (L/D = 4). The notch depth (a) to width (D) ratio is 0.25. The size-dependency of strength is observed. The fracture toughness values and the crack growth resistance curves (R-curves) for these three alloys are determined using the equivalent elastic crack model. The R-curves predict the peak loads accurately with only 0-7% difference from the experimental values. The pre-peak load-deflection curves calculated from the R-curves closely match the experimental curves. Bažant’s size effect law could be used to fit the peak load data. Scaling laws for strains at peak loads are proposed. The transition length (D0) determined for these strain scaling laws differ from those obtained using the size effect law