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Studies on Pr1-xLnxBa0.5Sr0.5Co0.5Fe1.5O5+δ (Ln = Nd, Gd, La; x = 0, 0.25, 0.5, 0.75 and 1) Double Perovskite Oxides for SOFC Application
No full textGood cathode material for solid oxide fuel cell (SOFC) should possess sufficient electronic conductivity (EC), compatible thermal expansion coefficient (TEC), phase stability, large triple phase boundary, able to transmit both ions and electrons, and low polarization resistance. Among perovskite materials possessing mixed ion and electronic conductivity (MIEC) properties, layered perovskites (AAʹB2O5+δ) appeared to be more advantageous due to their layered stacking, easier oxygen ion diffusion, and faster surface oxygen exchange. By introducing A-site cation doping, chemical and physical properties such as TEC, EC, oxygen non-stoichiometry, and ionic conductivity of materials can be altered. Thus, the aim of the present study is to observe the influence of A-site cation doping with Ln = Nd, Gd, La on the properties of Pr1 xLnxBa0.5Sr0.5Co0.5Fe1.5O5+δ (where x = 0, 0.25, 0.5, 0.75 and 1.0). The cathode powders and electrolyte gadolinium doped ceria (GDC) were synthesized by the Glycine-Nitrate method. Optimization of process parameters such as fuel to oxidant ratio and calcination temperature was performed to achieve phase purity of reference cathode material Pr1 xLnxBa0.5Sr0.5Co0.5Fe1.5O5+δ (x = 0). The optimized parameters were used to synthesis other doped compositions. Further, structural refinement was performed to obtain crystallographic information of the phase. Bulk samples were prepared from powders to attain dense ceramic properties. Variation in sintering time and the temperature was also conducted to study their effect on reduction in percentage porosity, grain growth, and on the EC behavior exhibited by the A-site doped Fe rich cathode systems. Thermal and chemical compatibility of cathode systems with GDC were examined from TEC measurements and by carrying out XRD analysis of sintered cathode-GDC mixtures respectively. Cathode inks were prepared and coated on GDC circular pellets for impedance analysis to analyze oxygen reduction kinetics. Finally, the electrochemical performance of the cathode systems was evaluated by fabricating symmetric cells with the configuration of Pr1 xLnxBa0.5Sr0.5Co0.5Fe1.5O5+δ/GDC/ Pr1 xLnxBa0.5Sr0.5Co0.5Fe1.5O5+δ. Electrochemical study exhibited that A-site doping had shown a significant effect on the cathode polarization resistance (Rp) and activation energy (Ea). The Rp and Ea values obtained for Ln = Nd, Gd, La-substituted cathode systems fall in the suitability criterion for cathode applications. Therefore, the above findings and observations led to recommend the cathode systems prepared in the present study as working electrode materials in SOFC stack for a power grid system
Mutagenesis, Structure, Stability and in Silico Studies on Fibroblast Growth Factor Homologous Factor 2
No full textFibroblast growth factor homologous factors (FHFs) belong to a subclass of Fibroblast Growth Factor (FGF) family owing to their high sequence and structural similarities with FGFs. However, despite these similarities, there are properties which set them apart from FGFs. FHFs lack the secretion signal sequence unlike other FGF members, except FGF1 and 2. It may be possible that FGF1 partially unfolds and secretes outside the cell, suggesting that lower stability of protein may be trade-off for secretion. Unlike FGFs, FHFs are not able to bind to FGF receptors (FGFRs) and trigger a cascade of cellular events. FHFs have been implicated in development of mammalian nervous system by binding to intracellular domains of voltage-gated sodium channels (VGSCs), neuronal MAP kinase scaffold protein and islet-brain-2 (IB2). The two amino acids Arg52 and Val95 are conserved in all FHFs and mutation of these residues lead to its inability to bind with VGSC/IB2. However, it is not clear whether the loss of binding is due to destabilization of the protein on mutation leading to partial denaturation or due to involvement of Arg52 and Val95 in conferring functionality to FHFs. The aim of the study is to mutate the two conserved residues of FHF2 (Arg52 and Val95) with its corresponding FGF counterpart amino acids and to study the effects of the single and double mutations on the overall structure, stability and functionality of FHF2. The single and double mutations were prepared using site directed mutagenesis approach and were confirmed by DNA sequencing. The wild type and recombinant proteins were expressed in E. coli by inducing with IPTG and were purified to high yield using a novel two step method involving nickel affinity followed by heparin affinity column chromatography. Biophysical characterisation studies of the proteins using methods like fluorescence intrinsic and extrinsic spectroscopy, circular dichroism spectroscopy, FTIR analysis, trypsin digestions studies etc. revealed that while V95N mutation remarkably destabilizes FHF2, R52G mutation exhibits slight stabilising effect on FHF2, whereas, the double mutant exhibited no effect on stability of FHF2. Thus, it can be assumed that the contradictory effects of the two different mutations on the protein stability, nullify each other in the double mutant. In silico studies on the wild type and mutant proteins using docking analysis, site directed mutator (SDM) tool, protein interaction calculator (PIC) and molecular dynamic simulation studies seem to corroborate with the findings of the biophysical studies. Docking studies reveal that R52 is directly involved in stable interactions with VGSC whereas, V95 though not directly involved in interaction with VGSC but plays an important role in imparting stability to the protein and hence its mutation leads to significant destabilization of FHF2. Overall these studies shed light towards the role of specific amino acids in determining protein stability and functionality and will provide the rationale for different function of FHFs despite being highly similar to FGFs in terms of sequence and structure
Environment Friendly Development of Modified Oxide-based Nanostructures for Removal of Water Contaminants
No full textOxide-based nanostructures with their unique qualities like simple processability, high surface activity, reproducibility, and superior conductivity with controllable band gaps have become promising materials for wide range of environmental restoration applications. Furthermore, these oxide nanostructures allow structural modifications which offer the ability to alter their activity, surface stability and selectivity during any reaction. From a green synthesis strategy the use of environmentally benign solvents, non toxic chemicals, and renewable resources are some of the major problems that require important consideration. Among all available nanostructured oxides, SiO2 and Al2O3 have been preferred materials for adsorption applications. Similarly, CeO2 and WO3 are known as a special class of oxides with unique light harvesting capacity for photocatalytic applications. Keeping this in mind, this thesis is broadly divided into two major types; (1) environment friendly synthesis and modification of oxide nanostructures such as SiO2 and Al2O3 for adsorptive removal of inorganic pollutants from water and (2) environment friendly synthesis and modification of oxide nanostructures such as CeO2 and WO3 for photocatalytic degradation of organic pollutants from water. All the oxide based nanocomposites [SiO2-Graphene Oxide (GO), Al2O3–Hydroxy Propyl Methyl Cellulose (HPMC)-Chitosan, CeO2-ZnFe2O4-Bioreduced Graphene Oxide (BRGO), WO3-ZnWO4- Polyaniline (PANI), and WO3-CoFe2O4-PANI] depicted in this thesis have been utilized for water remediation applications via adsorption and photocatalysis process. In the initial stage of research, very few literatures reported about the environment friendly synthesis of modified oxide based nanostructures for removal of inorganic contaminants from water. In the first project, the objective was to remove the cationic inorganic contaminants like Pb (II) and As (III) from wastewater. In this direction, a graphene oxide modified SiO2 (SiO2-GO) nanocomposite was designed to enhance the adsorption power of bare SiO2. After successful removal of cationic inorganic contaminants, focus was on the removal of anionic species like F ion from wastewater. Al2O3 is considered to be an excellent adsorbent for fluoride removal from polluted water. To improve its adsorption capacity, the alumina nanostructures were modified with cross-linked chitosan-HPMC biocomposite film (CgHA) for superior fluoride removal capacity from water/wastewater. Another major part of this PhD thesis is to use modified oxide-based nanostructures for organic contaminant removal from water by photodegradation process. CeO2 has been a prominent photoharvesting oxide nanostructure with improved photcatalytic efficiency. Keeping an eye on this, a direct Z-scheme CeO2-ZnFe2O4-BRGO (BRZC) nanocomposite was designed via in situ reflux method with leaf extract as green solvent. Here, the BRZC photocatalyst showed excellent photodegradation efficiency towards chloropyrifos pesticide. In the fourth project, visible light active WO3 nanostructures were modified with a conducting polymer PANI and ZnWO4 nanostructures and synthesized a WO3-ZnWO4-PANI (PZW) ternary nanocomposite following an ionic liquid (IL) assisted in situ oxidative polymerization method. The ternary nanocomposite was utilized for enhanced photocatalytic degradation of glyphosate herbicide. Motivated by the potential results of WO3 in photocatalysis, the final project involved the modification of WO3 nanostructures with PANI and magnetic spinel nanostructures CoFe2O4. The WO3-CoFe2O4-PANI (PCFW) nanocomposite, synthesized by microwave assisted ionic liquid method was found to be an excellent photocatalyst for visible light mediated degradation of tetracycline anti-biotic. All the oxide based nanocomposites demonstrated in this PhD thesis are stable, efficient, and recyclable for adsorptive and photocatalytic water purification applications
Study of Tailored La2NiMnO6 and its Derivatives for Magnetoelectric Applications
No full textWith the ever increasing demand for up-gradation in technology, there has been a sudden gush for the materials exhibiting magnetoelectric coupling. In this regard, La2NiMnO6 and its derivatives are synthesized and studied for magnetoelectric applications in this thesis.
Crystal symmetry phase diagram of La2NiMnO6 prepared via sol-gel route and sintered under ambient conditions at various high temperatures and times are studied via powder X-ray diffraction (laboratory source and synchrotron source), powder neutron diffraction and X-ray Photoelectron Spectroscopy (XPS). The XPS results suggest emergence of 2+ oxidation state of Mn with increase in sintering temperature. The diffraction studies establish rhombohedral (R-3c) symmetry for the samples sintered below 800°C, whereas above this temperature, the monoclinic (P21/n) phase gradually increases. Also, a thermodynamic phase diagram of symmetry evolution as a function of sintering temperature and time is drawn. However, crystallographic phase transition from mixed (P21/n + R-3c) to R-3 is seen at high temperature (at ~650 K). Since this transition does not follow the group-subgroup relationship, it is suspected to be of displacive type and chances of it being of first order phase transition is not ruled out. Interestingly this structural transition is also accompanied by slight magnetic ordering. An explicit dependence of relative crystallographic phases on the measured magnetoelectricity is observed. The maximum value of magnetoelectricity is observed when the two phases are in nearly equal proportion i.e., the sample sintered at 1000°C for 6 hours. The results obtained, suggests interfacial magnetoelectricity in these samples.
The prepared ceramic sample 4H is found to be highly porous and it is difficult to study the true magnetoelectric coupling associated with it because of the leakage current. So poly(vinylidene fluoride) (PVDF) impregnated 4H samples are synthesized and a comparative study with its parent sample (4H) and 24H sample (which is relatively more compact) were done. DC magnetization study reveals the single magnetic transition in 4H sample whereas double magnetic transition in 24H sample. In impregnated sample, beta phase crystallization of PVDF is observed in FTIR spectra. The magnetoelectric voltage is measured as a function of temperature, and it is found that the room temperature region is dominated by the magnetoconductivity / magnetoloss which results in low ME voltage. At low temperatures (T < 200 K) the coefficient of magnetoelectric voltage improves, the loss component becomes negligible so that the true magnetoelectricity is observed. Comparative study on all the three samples (4H, 24H and 4H+PVDF) shows significant enhancement in the magnetoelectricity in the 4H+PVDF sample. The highlight of this work is the unique way to arrest the porosity by PVDF impregnation into the pores of La2NiMnO6, so that leakage is minimized.
Thereafter, various forms of multiferroic polymer composites of La2NiMnO6 and PVDF were synthesized in the form of discs and thick films, via a two-step method and solution casting method respectively. And all the prepared composite samples are studied via powder X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Field Emission Scanning Electron Microscope (FESEM). The XRD result suggests the biphasic (P21/n + R-3c) nature of La2NiMnO6 nanoparticles for disc samples and single phase (R-3c) for film sample. The FTIR analysis indicates strong interactions of La2NiMnO6 nanoparticles with polymer molecules in terms of electro-active beta-phase formation. Maximum fraction of beta-phase PVDF (~37 wt. %) with zero porosity was found in polymer composite film through FTIR and FESEM analysis. Interestingly, significant ME voltage is observed in all the polymer composites up to 400K (reported as the upper end of short-range magnetic ordering of the LNM sample). The maximum magnetoelectric voltage (10mV/cm-Oe) at room temperature is found in film composite samples. The results indicate that this synthesis technique integrates the formation of electro-active beta-phase PVDF with reduced porosity and hence large magnetoelectric voltage were obtained as an outcome.
Thin film of La2NiMnO6 is deposited successfully on Pt/TiOx/SiO2/Si substrates using pulsed laser deposition technique. The X-ray diffraction, Raman spectra, and X-ray photoelectron spectroscopy hints toward the formation of ordered double perovskites. Interestingly, significant magnetoelectric voltage up to 400 K is measured. Metallic behavior of the thin film is observed in the resistivity vs. temperature measurement
Wire Electro-discharge Machining of Sub-cooled AISI P20 Tool Steel
No full textAISI P20, also known as “General Mold Steel Grade” steel is a chrome-moly (added nickel) tool steel created explicitly for zinc die casting and plastic molding applications like hydroforming tools, frames for plastic pressure dies and plastic molds to fill the requirements for its strength and machined cavities. Sub-cooling of metals is an effective method that is acknowledged for many years for the enhancement of wear life and reduction of residual stress for tool steel. The major problem in the whole process of heat-treatment of tool steel is the retained austenite. It should be noted that retained austenite is unstable and soft and freshly formed martensite is brittle. Hence, the tool steel can only be suitable for use after tempering, which also relieves its residual stresses. The extent of sub-cooling decides the capability of austenite to transform into martensite. Thus, to increase the wear properties of the tool steel, it is heat-treated with sub cooling and tempering. In this research work, the P20 samples are heat-treated with six distinct steps, stated as groups (FS50, FS100, FS150, Q, WSN and F600WSN). The physical and mechanical properties of all the groups are studied. The physical characterization is done revealing the microstructure and phases present in the metal. The mechanical characterization includes hardness test, impact resistance test, compressive strength test, wear test. It is then concluded that the sub cooled groups (FS50, FS100 and FS150) gives better properties than others, and are considered for further studies. Extensive wear test and sub-surface micro-hardness measurement of three sub-cooled groups are studied to find out the influence of sub-zero temperature on the wear characteristics of the metal. The tool steel sub-cooled at -150 ◦C (FS150 group) has maximum wear resistance and micro-hardness as compared to other sub-cooling temperatures. This group has the most suitable properties for die material and is taken for further studies involving non-conventional machining. Wire electro-discharge machine (WEDM) is considered to study the non-conventional machining of metal. The machining characteristics of the sub-cooled group (FS150 group) are compared with that of the parent metal and the results are discussed. The machining of sub-cooled tool steel is faster than untreated tool steel (parent metal) showing more suitable surface characteristics. The machining and surface characteristics of the sub-cooled group (FS150 group) is elaborately studied further. Grey Relational Analysis (GRA) is used to optimize the machining of sub-cooled metal (FS150). This optimum parametric setting to obtain better cutting speed, kerf width, surface roughness, not only increases productivity, but also improves the quality of the finished surface. To know more about the machining characteristics, the WEDMed surfaces machined with optimum and initial parametric settings are compared with the un-machined surface. Sub-surface micro-hardness and wear tests are also done to study the effect of the optimum and initial parametric WEDM setting on the sub-cooled metal for achieving better surface characteristics. Wear test done also reveals that due to the formation of recast layer while machining, the wear resistance of the machined surface increases. The micro-hardness of the surface machined with the optimized setting gives a higher hardness value than the surfaces of that machined with initial parametric machining conditions and un-machined metal. Thus, the tool steel sub-cooled at -150 ◦C (FS150 group) has much higher wear resistance and micro-hardness with a significant enhancement in its compressive strength and energy absorption capacity. By decreasing the sub-cooling temperature involved in different heat treatment processes, the wear resistance of tool steel increases. The WEDMing of sub-cooled tool steel is more efficient than un treated tool steel showing more suitable surface characteristics. The GRA optimized parametric setting to obtain better MRR, KW and SR improves the productivity and quality of the component and also produces a thicker recast layer. Wear test revealed that the surface machined with an optimized parametric setting gives higher wear resistance. The recast layer produced by WEDMing helps to improve the wear resistance of tool steel. The micro-hardness of the surface machined with the optimized setting gives a higher hardness value than both the surfaces of that machined with initial parametric machining conditions and un-machined metal
Enhancement of Spray Cooling in Transition and Nucleate Boiling Regimes by Using Novel Techniques
No full textMetals used in the manufacturing of submarine, multi-storey building, automotive industries and oil transporting pipelines require high tensile strength with moderate hardenability and these are directly related to the microstructure of the steel. The implementation of fast quenching technology in Run-Out Table (ROT) of a hot strip mill mitigates the above stated requirement. However, the development of fast quenching process is still a challenging task for the current generation researchers due to the early onset of Leidenfrost effect. Furthermore, the literature also does not disclose any fast quenching methodology which is able to mitigate the requirements. Therefore, in the current research, an attempt has been made to develop fast quenching techniques for the mitigation of the requirement of metal processing industries. In the current research, initially the role of surface, chemical and mechanical modification methodologies in heat extraction process have been separately investigated. In case of surface modification, PEG is added to modify the surface during cooling in the favourable direction of heat transfer. For this type of modification, initially, theoretical calculations have been performed to obtain the exact conditions. For the chemical modification, various additives such as Al2O3, dextrose, soapnut added water have been used for the attainment of fast quenching technology. In addition to the above, the third implemented technique for the achievement in enhancement is mechanical modification. For this, by altering the inertia of the plate, augmentation is focused. In case of mechanical modification, inertia is altered by conduction cooling on a moving plate. Then, the process depicting the combined modification has been investigated. For the combined modification, water with various additives are used to cool the plate which is in moving condition. For the experimentation, two experimental set-ups were fabricated i.e. one for static plate and another is for moving plate. In addition to the above, for the determination of heat transfer mechanism, dropwise experiments were carried out and for this purpose another separate experimental set-up was used. For the prediction of surface heat flux and temperatures, INTEMP software has been used. Among Al2O3 nanofluid, Dextrose and Soapnut added water, the heat extraction capacity is found to be maximum (CHF = 1.72MW/m2) in case of spray quenching conducted by nanofluid (0.15 % Al2O3). This is due to the alteration of thermo-physical properties in the favourable direction of heat transfer which enhances the heat transfer co-efficient, latent heat extraction period and the vapour film instability. The above stated value becomes 2.2MW/m2, when along with the chemical modification, mechanical modification is also performed. In case of Polyethylene glycol (PEG) added water spray, the surface morphology analysis clearly ensures the surface modification by PEG. According to the droplet dynamics, the exact condition (VF/CF ˃ 30×10-4) describing the hydrophilic behaviour which is essential for high heat removal rate are determined. The experimental result illustrates that the conditions indicated by the modelling lead to the enhancement and as a consequence, an average heat flux of 1.82 MW/m2 is obtained. However, in this case, the achieved critical heat flux is lower than the maximum value obtained in case of chemical modification. In case of mechanical modification, augmentation is noticed. However, the intensity of enhancement is not significant. Furthermore, the maximum enhancement (CHF = 2.23 MW/m2) is obtained in the presence of chemical, mechanical and surface modifications. Finally, a comparative study is performed to identify the appropriate coolant for various cases
Development of Ear Biometric Systems with Forensic Validation
No full textGenerally, it is observed that face is the most feature dense region in human body. The natural way of identifying a human being is through looking at his or her face. But automated authentication of a user through face biometric bears some demerits like inconsistent variability due to facial expression, orientation of face, effect of aging, etc. These challenges can be overcome using ear biometric. Ear detection is easier due to its location on two sides of the head, making it orthogonal to frontal face. A person can willingly change the shape of his or her face through alteration in expression, but one cannot change his ear shape by own will. This makes ear a suitable candidate for being tested for its performance as a biometric trait. The thesis aims to extract ear feature which is rotation and scale invariant in nature, so that the feature can be used for matching two images captured in unconstrained condition. The thesis mainly concentrate on two application areas in ear biometrics: (a) Ear recognition, and (b) Forensic validation of ear biometric system. Handcrafted as well as deep features are extracted from ear images to recognize a person using ear biometric. Then forensic validation of ear recognition system is proposed, and finally forensic validation is perform with reduced feature vector size
Study of Single-Channel EEG Signal Analysis for Drowsiness Detection using Machine Learning
No full textElectroencephalogram (EEG) is an essential tool used to analyze the activities effectively and different states of the brain. Drowsiness is a short period state of the brain that is also called an inattentiveness state. Drowsiness can be observed during the transition from being awake state to a sleepy state. Drowsiness reduces a person’s attention that increases accidental risks when involved in their personal and professional activities like vehicle driving, operating a crane, working with heavy machineries such as mine blasts. Drowsiness Detection (DD) has a significant role in preventing the problems mentioned above. So many traditional algorithms are proposed to detect drowsiness, but among these, the combination of neuroscience with artificial intelligence can effectively diagnose the state of drowsiness. Neuroscience with artificial intelligence algorithms used to detect drowsiness is also popularly known as brain-computer interface (BCI) systems.
Single-channel EEG BCIs are highly preferred for convenient use in real-time applications, even though there are many challenges in the actual experimental process. They are feature extraction, feature selection and choosing the best channel. These challenges have badly affected the performance of the BCI in the detection of drowsiness. In this work, a novel channel selection approach is proposed for a single-channel EEG BCI system by integrating the statistical characteristics of the available channels EEG signal to detect drowsiness state successfully. This thesis addresses some EEG sub-band extraction methods and their limitations. These limitations and practical issues are overcome by proposing a time-domain sub-band based feature extraction procedure using the wavelet packet transformation method. This thesis also addresses the asymmetric feature interference between the subjects. These limitations are overcome by proposing a novel feature selection technique using a nonparametric statistical test. In addition to this, a novel single-channel EEG signal analysis approach and single feature computation are also offered to deploy most quickly on low computing capacity systems. Apart from the machine learning methods, this thesis also discusses a novel deep learning architecture based on a convolutional neural network (CNN) for automated single-channel EEG signal classification to detect drowsiness
Subject wise, cross-subject wise, and combined subject’s wise validations are also employed to improve the generalization capability of the proposed techniques in this thesis. The whole work is carried out over prerecorded EEG databases such as Physionet real-time sleep-analysis-EEG and simulated-virtual-driving-driver-EEG
Designing Lightweight Authentication Schemes for IoT Applications
No full textIn the Internet-driven world, not only computers but things also get connected. It also allows the things such as light, cars, and many more to share information over a publicly accessible channel. Validation of the participating entities with each other is the foremost step to establish secure communication. Authentication refers to verifying the claimed identity by or for a system. The level of security in the validation mechanism depends on the type and number of factors involved. Authentication followed by key exchange protocols allows only the authenticated entities to negotiate upon a secret key without revealing any information to the eavesdropper. Due to the resource-constrained nature of IoT devices and vulnerability to physical attacks by an attacker, designing a lightweight authentication scheme for IoT systems is a challenging research area in recent years.
This thesis contributes to the designing of authentication schemes for the various types of IoT applications. The schemes are formally verified using the cryptographic verification tool Proverif. Security features comparison and informal security analysis of the schemes are done to ensure their security strength compared to existing schemes. The communication and computation cost analysis describe the scheme’s suitability for light-weight devices and IoT applications.
The first contribution presents an Elliptic Curve Cryptography (ECC) based authentication and key agreement scheme for a single gateway IoT system. Here, all the participating entities are verified, and data are transmitted to or from the designated entities. Single Gateway Authentication Scheme (SGAS) supports interoperability allowing sensors and gateway of two different manufacturers to authenticate each other. The formal verification of the SGAS and its informal security analysis proves it to be resilient against attacks. It maintains a low computation cost for IoT devices compared to existing authentication schemes.
The second contribution presents a Multi Gateway Authentication Scheme (MGAS) for IoT systems. It is suitable for application that requires connectivity of a large number of IoT devices. The throughput comparison of the single and multi gateway IoT system with different parameters using NS2 proves the multi gateway system to be efficient for large-scale applications. The scheme is verified using the Proverif tool, and an informal security analysis demonstrates it to resist various attacks. The performance comparison with the existing schemes proves MGAS to be appropriate for resource-constrained IoT devices.
The third contribution contributes to designing an authentication scheme for a multi Vi controller-based IoT architecture for the smart farming system. The existing single gateway architecture resists the connectivity of IoT devices to the gateway capacity. The controller-based architecture introduces a controller layer between the gateway and IoT devices to support connecting more IoT devices. It overcomes the incapability of managing massive peer-to-peer communication, high computation, and set up cost. The throughput comparison using NS2 with different parameters between the multi-controller and the single gateway IoT system shows the multi-controller to be efficient and scalable compared to a single gateway IoT system. Further, the scheme is verified using Proverif. The security features and their performance is compared with the existing schemes. The comparison outcomes conferred the proposed scheme is secure and suitable for resource-constrained IoT systems
Deposition of Fly Ash+Bauxite Coatings on Metals Using Nitrogen and Hydrogen Plasma
No full textThe technological progression in the modern time has been not only a boon for enhancing human life but also a bane to produce a huge amount of (industrial) wastes, which has caused immense concern regarding its utilization and in avoiding environmental threats viz. pollution etc. Coal-fired power plants are the primary source of fly ash generation. In the past few years, fly ash has been utilized for multiple purposes, viz., mines filling, making bricks, cement, etc. The present research aims at the utilization of fly ash as more valuable substance, i.e., as a ceramic coating substance for the improvement of thermal spray coatings for various applications. The plasma spray technology is advantageous to prepare value-added products from low-grade-ore and also to deposit ceramics, metals, and a combination of these producing approximately a homogenous composite coating with the required microstructure and on an array of substrates to provide tailor-made properties. In the present work, bauxite mineral with different proportions (10% and 20%) is added to fly ash for the development of wear resistance ceramic coatings on SS 304 and Ni superalloy substrates. The three coating compositions prepared are, fly ash (hereafter referred to as C 1), fly ash + bauxite 10% (hereafter referred to as C 2), and fly ash + bauxite 20% (hereafter referred to as C 3). Overlay plasma spray coatings are deposited using N2 (hereafter referred to as PSN2) and H2 (hereafter referred to as PSH2) as secondary gases, varying the input power level of the plasma torch. The maximum deposition efficiency of 23.74% is achieved with C 3, 25 kW PSH2 coating, and a minimum deposition efficiency of 9.21% is observed with C 1, 10 kW PSN2 coating. The coating thickness also indicated similar kinds of results, i.e., a maximum of 260 μm with C 3, 25 kW PSH2 coating, and a minimum of 97 μm with C 1, 10 kW PSN2 coating. From the surface and interface morphology, it can be observed that bauxite addition to fly ash does not favour in homogenous melting in PSN2 coating, whereas in PSH2 coating bauxite addition prompts particle melting and coagulation/agglomeration significantly. This results in minimum surface roughness of 9.002 μm with C 3 25 kW PSH2 coating and a maximum 17.4571 μm with C 3 20 kW PSN2 coating. Magnetite, along with cristobalite and quartz phases, are detected with C 2 and C 3 PSN2 and PSH2 coatings. Adhesion strength decreases with bauxite addition in PSN2 coatings, whereas increases for PSH2 coatings. The porosity levels of the coatings decrease with an increase in power level; after an optimum power level, it increases in both cases. The microhardness of the deposited coatings on the SS 304 substrate is higher than that of coatings on Ni superalloy. Maximum hardness of 598 HV is measured with C 3 25 kW PSH2 coating. Further, an erosion wear test is conducted to evaluate the wear behaviour of the coatings. This piece of research work will be beneficial for the use of industrial waste and ore minerals for high-valued applications