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Role of Y2O3 and Al2O3 Additive during Fabrication of Si3N4-Mo, Si3N4-Mo-Si and Si3N4 Mo-Al Cermets by Powder Metallurgy
No full textCeramics are well known for their high hardness, strength, refractoriness and good chemical resistance but have poor fracture toughness and are brittle in nature. The addition of some metallic phases improves the ductility in the ceramics and hence enhances the toughness. Cermets have the combined characteristic properties of both metals and ceramics and thus, have superior properties to the constituents. Due to this, the cermets are a promising material for use as turbopumps, heat exchangers, high-temperature parts of combustion engines, wear-resistant components as blast nozzles, aero-engine components, fusion reactors, cutting tools, valve components, bearings, refractory lining and coating to protect materials from corrosive environments. Silicon nitride is a refractory ceramic known for its structural applications. As a cutting tool, Si3N4 is more durable than coated carbide tools and has a better surface finish. The performance and machinability of Si3N4 are so good that it can machine difficult to cut materials like hardened steel and nickel-based super alloys. But the only drawback of Si3N4 is its low fracture toughness compared to other engineering materials like steel. Properties of Si3N4 can be improved by reducing the particle size and incorporating some metallic elements into the matrix. Moreover, Si3N4 has poor sinterability due to its covalent nature. The sinterability can be improved by adding suitable additives. In the present study, Si3N4-Mo, Si3N4-Mo-Si and Si3N4-Mo-Al cermet powders have been prepared by mechanical milling of constituents for 2 hours with the help of a high-speed dual-drive planetary mill. Average particle size of 1-2 μm has been achieved after milling. The reduction in particle size has been confirmed by particle size distribution analysis, XRD, SEM and TEM. All the prepared compositions of milled powders have been consolidated by conventional pressure-less sintering in argon (Ar) gas and hydrogen (H) gas atmosphere with Y2O3 and Al2O3 as sintering additives. The individual and combined effects of Y2O3 and Al2O3 additives have been studied, and the amount of additive has been optimized. The sintering temperature was maintained at 1500 °C with a holding time of 1 hour. The optimal compositions of cermets have been chosen for spark plasma sintering (SPS) at 1350 °C with 15 min holding. The relative density, Vickers micro-hardness, indentation fracture toughness (IFT), and wear resistance have been enhanced in the cermets consolidated by SPS and with a combined additive content of 5 wt. % Y2O3 and 10 wt. % Al2O3. Maximum relative density, hardness and IFT of 96.66 %, 15.72 ± 1.23 GPa and 11.12 ± 1.34 MPa.m1/2, respectively, have been obtained in SMS5Y10A-SPS. The addition of Si has enhanced the densification and hardness of the material by forming the phases like Mo3Si, Mo5Si3, MoSi2, YSi2, Y2Si2O7 etc. The reaction between the oxide additives and Si3N4 has resulted in formation of Y3Al5O12 phase which has resided in the molybdenum silicide grain boundaries and hence, have improved the densification and hardness. Presence of Y3Al5O12 phase has resulted in crack deflection through the grain boundaries. Hence the uniform distribution of the molybdenum silicide phase throughout the matrix has enhanced the physical and mechanical properties of the fabricated cermets. The un-lubricated sliding wear resistance of the cermets against a diamond indenter has been examined with the normal applied loads of 20 N and 40 N. It has been observed that the wear rate, weight loss, and wear depth has been increased with the increase in load. The dominant wear mechanisms are observed to be delamination, abrasion and formation of microcracks. Infiltration of the molten Si/Al metals into the cermet preforms has been performed to investigate the extent of infiltration and the effect on the properties of the cermets and to correlate with the properties of the cermet powders prepared by milling followed by conventional sintering at 1500 °C. Aluminium and Silicon have chosen to see the effect of low melting ductile metal (Al) and high melting brittle metal (Si) on the properties of the infiltrated surface. Due to its low melting point, Aluminium has been formed the melt at low temperature and have the maximum time for the reaction by capillary action and, hence, shown better properties than Si infiltrated cermets. After the detailed investigation of all the above factors, it has been concluded that (Si3N4)75-(Mo)15-(Si)10 is the best composition among the discussed cermets due to the presence of Si and SPS is the best method to achieve high density, hardness, fracture toughness and wear-resistance among the discussed cermets. An amount of 5 wt. % Y2O3 and 10 wt. % Al2O3 is the best combination of additives to achieve the optimal mechanical and tribological properties for practical applications
Evolution of Phase and Nanostructure in Early Transition Metal Doped Polymer Derived Silicon Carbonitride Ceramics
No full textSilicon-based polymer derived ceramics like SiC, SiCN, SiBCN poses excellent resistance towards creep and oxidation are future materials for bond coat applications in high temperature resistant environmental barrier coating systems for the protection of C or SiCbased CMC components. SiCN-based amorphous ceramics developed from the pyrolysis of polysilazane precursor, are believed to be ideal for these applications. Additionally, doping of such precursor with metal oxides provides a special advantage of tailoring the phase assemblage, thermal expansion coefficient, thermal conductivity and oxidation resistance. The current work is based on understanding the evolution of phase and nanostructure with the introduction of early transition metals as molecular source in the preceramic polymer. Further, the oxidation behavior of such metal modified SiCN ceramics were studied and compared with undoped SiCN ceramics. In typical experiments, a commercially available polyvinylsilazane polymer was doped with molecular source of metals (M=Ti /Hf /Zr), crosslinked at 300 oC, and pyrolyzed in N2 atmosphere over a temperature range of 900 oC to 1400 oC to synthesize SiTiCNO, SiHfCNO, and SiZrCNO ceramic hybrids, respectively. Also, a parallel synthesis of undoped SiCN samples using polyvinylsilazane with similar crosslinking and pyrolysis conditions was done for benchmarking the different properties of metal doped SiCN ceramic systems. A detail crosslinking mechanism of pure polyvinylsilazane and metal modified precursors was studied using FTIR spectroscopy. Further, the thermogravimetric study of all crosslinked precursors was performed to estimate ceramic yields and ceramization temperatures in N2 atmosphere. The pure SiCN ceramics predominantly remained single phase amorphous ceramic up to 1400 oC. Two different nanostructured SiTiCNO ceramics were prepared from isopropoxide or n-butoxide sources of Ti-doping in polyvinylsilazane, which appeared predominantly single phase amorphous up to 1100 oC, but anatase-TiO2 precipitated within the SiCN matrix at 1200 oC. Ti-isopropoxide based SiTiCNO remained thermally stable up to 1300 oC, whereas the Ti-butoxide based SiTiCNO system remained stable up to 1400 oC. An exceptionally homogeneous distribution of predominantly TiO2 nanocrystals, in the size range of 2-14 nm was observed throughout the SiCN matrix. Further, the SiHfCNO ceramic hybrids prepared by pyrolysis of Hf-modified polyvinylsilazane precursor appeared predominantly single phase amorphous ceramic up to 900 oC. However, Hf within the SiCN matrix evolved as nanostructured tetragonal phase of HfO2 in the SiCN ceramic matrix at 1000 °C. Interestingly the t-HfO2 nanocrystals were homogeneously distributed with extremely fine crystallite size (2.3 to 5.3 nm up to 1400 °C) throughout SiCN matrix. Similarly, the SiZrCNO ceramic hybrids appeared predominantly single phase amorphous ceramic up to 1100 oC. However, the Zr within SiCN ceramics, above 1100 oC pyrolysis temperatures, nucleated and later precipitates as nanocrystals of t-ZrO2 within 2-9 nm size range, throughout the ceramic microstructure with exceptional homogeneity. The tetragonal phase of ZrO2 and HfO2 remained stable in the SiCN ceramic matrix, even after pyrolysis at 1400 °C. Additionally, coarsening kinetics of ZrO2 in the SiZrCNO system was studied at 1400 oC using the Lifshitz-Slyozov-Wagner model, which exhibited cubic kinetics indicating diffusion controlled growth. Finally, the oxidation behaviour of the SiCN, SiTiCNO, SiHfCNO, and SiZrCNO ceramic nanocomposites was investigated by constant rate heating method using thermogravimetry analyzer in flowing oxygen. SiCN ceramics pyrolyzed at higher temperature showed less mass loss during oxidation. SiTiCNO prepared through Tiisopropoxide modification of polyvinylsilazane improved oxidation properties of SiCN up to 1400 oC. However, SiTiCNO prepared through Ti-n-butoxide improved oxidation properties of SiCN up to 1500 oC and showed less material recession than pure SiCN and SiTiCNO synthesized through polyvinylsilazane and Ti-isopropoxide precursor source. Hf and Zr incorporation in SiCN further enhanced oxidation resistance of the nanohybrid ceramics. Moreover, the effect of Ti, or Hf, or Zr doping on the free nanocarbon phase evolution within the SiCN matrix before and after oxidation was studied through micro- Raman analysis. It was interesting to note that the Cfree existed even after oxidation in all the systems, which shows robustness of the ceramic systems against oxidation. The work exhibits some unique ceramic hybrid materials with exceptional homogeneity of nanocrystals of an oxide phases distributed within an amorphous matrix. The improved oxidation resistance, and their polymorphic stability could provide significant advantages for achieving thermostructurally stable, tough and chemically robust nanocomposite materials for various high temperature uses including bond coat of TBC/EBC system
Design of Fluidic-Level Synthesis and Error Recovery Algorithms for Digital Microfluidic Biochips
No full textDigital microfluidic biochips (DMFBs) are a class of lab-on-a-chip (LOC) devices and micro-electro-mechanical systems (MEMS). DMFBs use the electrowetting-on dielectric (EWOD) property to manipulate discrete droplets on a two-dimensional grid of electrodes. The analog microfluidic devices deal with continuous-flow fluids under the influence of micro-pumps and micro-valves. Analog microfluidic devices are cumbersome and complicated. DMFBs offer miniaturization, automation (reduces human effort), portability, efficiency, and software programmability. A few applications of DMFBs are point-of-care diagnostics, DNA analysis, enzymatic analysis, proteomic analysis, and environmental toxicity monitoring. DMFBs face similar challenges faced by any micro-electronic equipment. Several synthesis techniques have been proposed to cope with increasing design complexity for correct, efficient, and fault tolerant assay execution. The existing synthesis techniques have several drawbacks. Being application-specific, they cannot schedule all kinds of assays and are not scalable. A few algorithms are fault-tolerant and can resynthesize based on error feedback. The need for concurrent execution of multiple assays with accuracy has increased the design complexity of DMFBs. Thus there is a requirement for efficient and fault-tolerant synthesis algorithms. The research work documented in this thesis presents several online and offline fluidic-level synthesis and error recovery algorithms for DMFBs. A heterogeneous earliest finish time based online scheduling algorithm called DMHEFT is proposed. A novel upward ranking mechanism is used to prioritize the operations. The earliest finish time (EFT) and least recently used (LRU) policy are used for module allocation. Two meta-heuristic approaches– artificial bee colony hybridized with generalized N-point crossover (ABC-GNX) and invasive weed optimization (IWO) based perturbation techniques are further used to improve the quality of solutions for offline scheduling. Proposed algorithms DMHEFT, ABC-GNX, and IWO are tested on 26 notable benchmarks. Both ABC-GNX and IWO achieve better assay completion times and shorter execution times compared to state-of-the-art algorithms. A unified approach is proposed to solve resource binding, scheduling, and placement problems in a coordinated manner. It attempts to minimize assay completion times and the maximum area used simultaneously. A linear time complexity algorithm known as the flow scan (FS) method is employed for free space management and determining the initial placement of modules. A fast simulated annealing (FSA) algorithm is used to improve the placement quality. Defective cells are treated as blockages for placement. Reconfiguration is used to relocate modules if cells become faulty during assay execution. Reconfiguration uses free space information provided by the FS algorithm. The proposed algorithm is evaluated on different variants of protein and in-vitro benchmarks. Experimental results show that the proposed algorithm is able to produce reduced assay completion times and maximum areas used than existing methods. Reinforcement learning (RL) based droplet routing algorithms are proposed. Q-learning and double deep Q-network (DDQN) based route discovery between a pair of source and target is presented. Stalling and detours are used for route compaction after route discovery. RL-based schemes find shorter routes despite increased blockages (active modules) and guarantee a path if one exists. An ϵgreedy policy is employed to obtain a trade-off between exploration and exploitation for better routes. Compared to existing algorithms, proposed RL-based routing achieves better cell utilization and arrival times. A quasi-static scheduling based error-recovery (QSSER) method is proposed to reduce assay completion time with tolerance for a maximum number of possible transient faults. Online error-recovery algorithms have high response times, and offline error-recovery algorithms are infeasible. Considering this, a quasi-static approach is introduced, combining the benefits of online and offline strategies. The proposed QSSER can work with sensor-based and CCD camera-based error detection methods. Mixed time-space redundancy based recovery schedules are used to reduce assay completion times. QSSER determines a quasi-static tree of schedules and a set of switching points between corresponding schedules depending on the error scenario. Then the schedules are fed to the microcontroller. The tree size is limited using a tree reduction technique so that it can fit in the available memory of the micro-controller. The proposed algorithm is evaluated on three real-life assays: PDNA, Exponential dilution of protein assay, and interpolation dilution of protein assay. Experimental results shows that proposed method is able to schedule assays with varied number of injected errors under deadlines efficiently over compared methods
Synthesis and Characterizations of Ferroelectric, Non-ferroelectric High Dielectric Constant Ceramics Modified BaTiO3 Systems for Multifunctional Applications
No full textHigh dielectric constant materials have become increasingly important due to their wide applications in the electronic industry as capacitors, sensors, actuators, power transmission devices, memory devices, high energy storage devices, etc. High dielectric constant is found both in the ferroelectric as well as in non-ferroelectric class of materials. For the present work, BaTiO3 is selected as the ferroelectric material. But, for dielectric applications, BaTiO3 has following disadvantages: (i) the maximum value of dielectric constant exist near Curie temperature; (ii) Curie temperature (~130 °C) is far away from the room temperature, (iii) temperature sensitive dielectric properties with sharp phase transition. These disadvantages hinder use of this material for various device applications at room temperature. Temperature stability of the dielectric properties of the BaTiO3 system can be enhanced by preparing its solid solutions with other compounds having temperature independent dielectric properties. High dielectric response has also been observed in relaxor ferroelectric like Pb(Mg1/3Nb2/3)O3. PbO based complex perovskite relaxor ferroelectric materials have some advantages over BaTiO3-based system like broad dielectric maxima and high dielectric constant (~30,000). Also, Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O are some of the non-ferroelectric systems with giant dielectric constant (~104-105) at RT and independent of frequency and temperature over a wide range. The selected series of BaTiO3 based materials synthesized by solid state reaction method are: 1. (1-x) BaTiO3-x Ba(Fe1/2Nb1/2)O3 (x=0, 0.02, 0.04, 0.06 and 0.08) 2. (1-x) BaTiO3-x CaCu3Ti4O12 (x=0, 0.02, 0.04, 0.06 and 0.08) 3. (1-x) BaTiO3-x Li0.30Cr0.02Ni0.68O (x=0, 0.02, 0.04, 0.06 and 0.08) 4. (1-x) BaTiO3-x Pb(Mg1/3Nb2/3)O3 (x=0, 0.02, 0.04, 0.06 and 0.08) Based on the highest dielectric properties along with parents system, the following best composition are synthesized by sol-gel route: 1. BaTiO3 2. Ba(Fe1/2Nb1/2)O3 3. 0.94 BaTiO3-0.06 Ba(Fe1/2Nb1/2)O3 Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O modified BaTiO3 ceramics were synthesized by solid state reaction route. XRD study confirmed single phase without any secondary phase peaks in Ba(Fe1/2Nb1/2)O3 and Li0.30Cr0.02Ni0.68O modified BaTiO3 ceramics. However, minor secondary CuO peaks along with major BaTiO3 peaks were observed for CaCu3Ti4O12 modified BaTiO3 ceramics. Experimental density increased for Ba(Fe1/2Nb1/2)O3 modified BaTiO3 ceramics compared to parent BaTiO3 ceramics with highest density obtained for x=0.06 composition of Ba(Fe1/2Nb1/2)O3 modified BaTiO3 ceramics. However experimental density decreased for CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O modified BaTiO3 ceramics. Average grain size was found to decrease for all the modified ceramics. RT highest dielectric constant (at 10 kHz frequency) ~4124, 1404 and 1844 were obtained in x=0.06, x=0.04 and x=0.06 composition of Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O ceramics. However, highest value of dielectric constant at Tc (at 10 kHz frequency) ~11353, 4113 and 7543 was obtained in x=0.04, x=0.02 and x=0.06 composition of Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O ceramics. The transition temperature was found to decrease for Ba(Fe1/2Nb1/2)O3 and Li0.30Cr0.02Ni0.68O modified ceramics however increased for CaCu3Ti4O12 modified ceramics. Diffusivity increased with modification in all the modified BaTiO3 ceramics. Saturated P-E loop was only obtained in x=0.02 composition of Ba(Fe1/2Nb1/2)O3 modified ceramics which turned into lossy loops with high leakage current density with further increase in Ba(Fe1/2Nb1/2)O3 content. Saturated P-E loops were obtained in x=0.02 to x=0.06 compositions and lossy loop in x=0.08 composition for CaCu3Ti4O12 modified ceramics. However, lowest value of remnant polarization and coercive field were obtained in x=0.04 composition with lowest value of leakage current density. Pinched hysteresis loops with low leakage current density were obtained in all the Li0.30Cr0.02Ni0.68O modified ceramics. However, lowest value of remnant polarization and coercive field were obtained in x=0.06 composition with lowest value of leakage current density. Pb(Mg1/3Nb2/3)O3 modified BaTiO3 ceramics were synthesized by solid state reaction route, by mixing calcination powder of BaTiO3 and Pb(Mg1/3Nb2/3)O3 system and sintered at optimized sintering temperature of BaTiO3 ceramics. Single phase peaks were obtained in XRD study without any secondary phase peaks. Experimental density increased for Pb(Mg1/3Nb2/3)O3 modified BaTiO3 ceramics compared to parent BaTiO3 ceramics with highest density obtained in x=0.06 composition. Microstructure confirmed bimodal distribution of grains, larger grains corresponding to BaTiO3 and smaller grains corresponding to Pb(Mg1/3Nb2/3)O3 phase. Highest value of dielectric constant at room temperature (at 10 kHz frequency) ~3447 was obtained in x=0.06 composition. From temperature dependent dielectric study, two transition peaks were observed. Ferroelectric phase transition was found to increase in x=0.02 composition and then decreased for x=0.04 to x=0.08 compositions. Diffusivity was found to increase with Pb(Mg1/3Nb2/3)O3 modification. Saturated P-E loops were obtained in Pb(Mg1/3Nb2/3)O3 modified ceramics. Remnant polarization and coercive field values along with leakage current density were found to decrease for x=0.02 to x=0.06 compositions and increased for x=0.08 composition. Selected composition 0.94BaTiO3-0.06Ba(Fe1/2Nb1/2)O3 along with the parent BaTiO3 and Ba(Fe1/2Nb1/2)O3 systems were synthesized by sol-gel route. 0.94BaTiO3-0.06Ba(Fe1/2Nb1/2)O3 was prepared by two different methods. In one method, all the precursors are taken from the starting itself, and the product obtained is abbreviated as BFN-A. In the second method, calcined powders of BaTiO3 and Ba(Fe1/2Nb1/2)O3 were mixed and then sintered; the product obtained is abbreviated as BFN-B. For modified ceramics, single BaTiO3 phase peaks were obtained in BFN-B system in comparison to BFN-A system where minor secondary phase peaks were also obtained as confirmed from XRD study. Experimental density was found to be higher in BFN-B system in comparison to BFN-A system. Finer grains with homogeneous distribution were obtained in BFN-B system, whereas inhomogeneous distributions of grains were observed in BFN-A system. High value of dielectric constant at room temperature and at 10 kHz frequency was obtained in BFN-B (~1618) system in comparison to BFN-A (~234) system. Dielectric loss was found to be high in both the ceramics, however comparatively lower in BFN-B system. The transition temperature was found to decrease with the BFN modifications along with diffused phase transition. Remnant polarization and coercive field were found to be high for modified system
Internet of Things Based Real-Time Monitoring System for Early Age Properties of Concrete
No full textAutomation in the construction industry is indispensable to significantly improve productivity, quality, economy, safety, flexibility, and accuracy. The possibilities of recently introduced Internet of Things (IoT) based systems are promising to attain a higher level of automation in the construction industry. Real-time monitoring of various parameters of concrete using IoT technology can leverage the process of automation in the construction industry. The research presented in this thesis poposes a novel, cost-effective,and easily deployable IoT-enabled automation system for the real-time monitoring of early-age concrete properties. Some of the most important properties include early age concrete compressive strength and plastic shrinkage. The estimation of the early-age compressive strength of concrete is crucial for quality control in the construction industry. The first part of the thesis proposes an innovative and cost-effective IoT-enabled system for the real time monitoring of early-age concrete strength using the well-established maturity method. The proposed system consists of temperature sensors and Wi-Fi micro-controllers which are connected to a cloud-based platform. Five selected concrete mixes are used to demonstrate the proposed system. The maturity relationships for the selected mixes are developed in the laboratory as per the relevant standards. The early-age compressive strengths of the selected concrete mixes predicted by the proposed system are found to match well with the actual compressive strengths obtained from the break test. The propo ed system is found to be effective in the automation of the maturity method that can trigger the implementation of user-friendly internet/mobile applications. Timely removal of formwork is one of the crucial aspects of construction management that directly influences the safety and quality of the structure as well as the economy of the project. Code recommendations in this regard are not widely practiced because of the difficulties in their implementations. Also, such code recommendations are not robust for all the possible construction conditions. The next part of this thesis demonstrates the application of an IoT-enabled system that notifies the minimum striking time of vertical formwork based on a specified target compressive strength.The implementation of the proposed system is demonstrated on three concrete columns. The proposed system is found to be suitable for any construction condition and can be easily implemented a tthe site.The hot and dry condition often induces plastic shrinkage cracks on concrete slabs and pavements. Such cracks are a concern for the concrete construction industry,as it affects the quality and long-term performance of the concrete structure. Existing approaches to monitoring plastic shrinkage at the site are time-consuming, labour-intensive, and expensive. As a result, these approaches are not attractive to the construction industry and are not generally practiced at the site. The next part of this thesis proposes a novel, costeffective, and easily deployable IoT-enabled system to monitor plastic shrinkage in realtime. Two alternative systems are proposed, one of which monitors the evaporation rate following the recommendation of the codes and standards. However, existing approac es have not considered the status of surface bleed water despite its essential role in monitorin plastic shrinkage. Therefore, the other alternative system is proposed based on the availability of the surface bleed water sheen. The effectiveness of the proposed system is validated by laboratory experiments on three sets of concrete specimens. The last part of the thesis attempts to incorpo ate Long Range (LoRa) technology into the IoT applications for the construction industry in order to take advantage of its large transmission range. This emerging technology is being used in many civil engineering applications such as water quality control, equipment tracking, etc., and the use of this technology is likely to multiply in the coming years. However, the energy efficiency and environmental impact assessment of such LoRa-based systems have not been addressed in the published literature so far. This thesis, therefore, explore the effect of transmission parameters on power consumption and proposes a scheme for controlling transmission parameters to improve the energy efficiency of LoRa end nodes. The effectiveness of the proposed scheme is demonstrated through a case study on a real-time monitoring system which is crucial for quality control and construction management
Assessment of Ocean-Atmosphere Interactions for the Indian Summer Monsoon Intraseasonal Oscillations in CMIP5 and CMIP6 Models
No full textThe Asian monsoon system (AMS) is a largescale phenomenon resulting in the strong coupling of ocean and atmosphere and is highly associated with the remote forcings (e.g., El-Niño southern oscillations, Indian Ocean dipole, Pacific decadal oscillation). The present dissertation focuses on the Indian summer monsoon (ISM) system. ISM covers a large area and about 80% of the annual rainfall occurs over the Indian mainland during this season. Earlier studies reported that the ISM rainfall (ISMR) is highly variable from intraseasonal through interannual to decadal timescales. On intraseasonal timescales, convection anomalies develop in the equatorial Indian Ocean (EIO) and propagate towards north (foot of the Himalayan Mountains in northern India) and eastward to the west Pacific Ocean (WNP). The northward propagation of intraseasonal oscillations is also known as the Boreal Summer Intraseasonal Oscillations (BSISO) and are the prominent South Asian summer monsoon features, mainly governed by the atmospheric internal dynamics and air-sea interactions. However, air-sea interactions role in modulation of the BSISO in the coupled climate models was not well understood. The present study utilizes the extended empirical orthogonal function-based bimodal ISO index to assess the phase-relationship of air-sea fluxes in the North Indian Ocean (NIO) using observations and reanalysis products. These phase-relationships are also evaluated in the historical outputs of Coupled Model Intercomparison Project (CMIP) phase-5 and phase-6. On intraseasonal timescales, enhanced deep convection leads by a phase of 850 hPa westerly winds and negative sea surface temperature (SST) anomalies; and deep convection (clear sky conditions) leads (~ 5-10 days) enhanced westerly (easterly) winds and cool (warm) SST over the NIO. Most CMIP5 models represents the northward propagation of precipitation and zonal winds at 850 hPa. However, models bias of BSISO variance shows significant spatial heterogeneity over the regions of the Arabian Sea (AS), Sub-Continent of India (SCI), and Bay of Bengal (BoB). The CMIP5 models, which shows significant biases in the mean state, causes the failure of models in representing the BSISO propagation. However, the majority of the models show large uncertainty to represent this prominent feature over AS and SCI. Further, improper representation of the lead-lag relationship of SST and precipitation on intraseasonal timescales over the NIO in the CMIP5 models contributes to significant bias variances. The new release of CMIP6 models provides an opportunity to examine models' ability to simulate the characteristic features of BSISO and its associated air-sea interactions. Most CMIP6 models underestimate the precipitation over central India and overestimate the precipitation over the eastern equatorial region. In the observations, the precipitation anomalies propagate northward from the equatorial latitudes to the northern latitudes over the ISM region. However, the initiation of northward propagating convection shows a significant variation with time in the CMIP6 models, and a prominent representation of BSISO propagation is evident over the BoB and the SCI. The phase speed of BSISO over the AS is underestimated by many models, which led to the failure of models in representing the northwest-southeast tilt of convection. Surface turbulent fluxes and zonal winds lag the deep convection over the NIO on intraseasonal timescales. However, misrepresentation of air-sea fluxes in the CMIP6 models leads to the significant biases of intraseasonal variances. Earlier studies suggest that ISOs can modulate the rainfall over India. The role of BSISO during excess/deficit ISM years is analysed in the observations and the CMIP6 models. Models overestimated the moisture transport from the west Indian Ocean to the mainland of India during deficit monsoons, which plays a crucial role in modulating the precipitation and ISOs. During deficit monsoon years, the faster moving 20-100 day oscillations are stronger than the excess monsoon years, which affects the duration of convection activity and causes dry conditions over the regions. Further, a stronger response from underlying SST increases the phase speed of BSISO activity. During excess monsoon years, BoB (AS) responds more strongly (weakly) and quickly (slowly) to the atmosphere than deficit monsoon years. However, models are failed to represent the ocean's response to the atmosphere over BoB. The improvement of freshwater forcing in the models may simulate the ocean's atmosphere response over the Indian region. This study examines the simulation characteristic features of BSISO by CMIP5 and CMIP6 models and mainly attributes them to the atmospheric internal dynamics and air-sea interactions. Compared to the CMIP5 group of models CMIP6 group of models well simulated the BSISO characteristic features over the SCI. The present study further suggests that the better representation of the ISM variability by the coupled general circulation models is possible by improving the ocean and atmosphere feedback mechanisms, sensitivities of the models among internal variables, and orographic features
Household Waste Disposal Leading to Economic Appliance
No full textWaste volume is alarmingly rising in the world. India is the second largest producer of fruits and vegetables in the world (next to China) with 221.431 million metric tons. Urban India is reported to generate 68.8 million tons of Municipal solid waste (MSW) per year with a per capita waste generation rate of 500 g/person/day. Municipal solid waste (MSW) needs to be segregated to collect separately organic biodegradable at its source (before disposal). Many types of compost bins like polyethylene portable twin drum, rotary drum, plastic basket bin, etc. are available in the market for converting all kinds of kitchen waste into fertilizer. Each bin has its own advantages and disadvantages. The cost of the bin available in the market varies from Rs. 1,000 to Rs.17, 000. Moreover, the available bins do not maintain proper process condition for the degradation of bio-waste. Hence, those bins are not the best for household purpose in terms of the degradation time and extent of degradation of the kitchen waste. A bioprocess-based household waste disposal devise has been proposed. The proposed device has the potential to treat our biodegradable daily- household-wastes/kitchen waste very quickly instead of throwing them to the municipal garbage bin/Green bins. The decomposed wastes are viscous liquids / solids can be used as a soil conditioner in our urban kitchen gardens. An organic decomposer has been also prepared using various natural ingredients. The optimum temperature was in the range 40oC±3 to achieve the satisfactory NPK value. The measured pH and moisture content of the bio-mass at the optimum temperature were nearly neutral and 45-50 (%), respectively. The NPK value of the decomposed waste was found satisfactory. The power requirement was found to be minimal. The proposed temperature controlled decomposer (e decomposer) is found to be a promising concept to convert kitchen waste in to soil conditioner
Development of Granular Porous Alumina Adsorbents Using Kaolin for the Mitigation of Excess Fluoride Ions from Aqueous System
No full textAlumina adsorbent has wide acceptance for mitigation of excess fluoride ions from water. The challenging part is preparing this adsorbent in the granule shape with high porosity and PZC value, ensuring its applicability under normal pH of water, i.e., 6.5 to 7.5, and easy separation after use. This research has attempted to prepare highly porous alumina adsorbents in granule form using low-cost ceramic raw material kaolin. The study aims to find a suitable, environment-friendly, and highly effective alumina adsorbent for defluoridation. The adsorbents are prepared both in bead shape and granule shape through oil drop method using aluminium rich leachate extracted from kaolin. Al3+ leachate is obtained by thermal treatment followed by acid leaching of kaolin. Incorporating pore former in the bead-shaped adsorbent (prepared directly using concentrated acid leachate) is challenging, so two sols, namely sol-1 and sol-2, are prepared from Al3+ leachate with and without impurity removal. The sols are mixed with different pore-formers like PEG, PVP, spent tea leave waste (STLW), starch, sucrose individually, and PVA binder to convert into a semi-gel state. This semi gel is then injected into a column containing paraffin oil as an upper layer and ammonia as a bottom layer with the help of a syringe pump to form porous alumina adsorbents. All the prepared adsorbents, both bead-shaped and granule, are washed, dried, and calcined at different temperatures to get the desired alumina phase. Different characterization techniques like XRD, FTIR, FESEM, and BET surface area analysis are employed to get preliminary information about the applicability of the prepared adsorbent for the fluoride adsorption study. A batch adsorption study is then carried out systematically using each type of prepared alumina adsorbents. The adsorbent dose and kinetics parameters are thoroughly studied to achieve the maximum fluoride removal in the fluoride contaminated aqueous system. Bead-shaped adsorbents show lower surface area and porosity than their granular counterparts, resulting in low removal efficiency. The microstructural analysis is carried out before and after the adsorption process using FESEM with EDX to compare the alumina adsorbents' surface morphology and confirm fluoride ions' adsorption on the adsorbent surface. The batch adsorption study shows the mechanism and adsorption capacity of the alumina adsorbents using various kinetic models (i.e., Pseudo-first-order kinetic, Pseudo-second-order kinetic, Intraparticle diffusion and Elovich kinetic) and equilibrium isotherm models (i.e., Langmuir, Freundlich, Redlich-Peterson, and Sips isotherm models). The regeneration of the spent adsorbent and the effect of other co-existing ions on the adsorption process are also estimated. It is observed that at an initial fluoride concentration of 10 mg/L (adsorbent dose = 3 g/L; pH 6.7 ± 0.3; time = 12 h), the defluoridation efficiency is estimated as in the range of 26 to 96 %, in which Sol 1- PEG and Sol 2- Sucrose are the best adsorbent showing ~96 % of fluoride removal efficiency. Groundwater with the presence of fluoride ions always contains some other anions like nitrate (NO3-), chloride (Cl-), phosphate (PO4-3), and bicarbonate (HCO3-2) which competing for the adsorption sites during the defluoridation process. Hence, it's become necessary to investigate the effect of these co-existing ions. Further, a regeneration study of all the spent adsorbents are carried out.Alumina adsorbent has wide acceptance for mitigation of excess fluoride ions from water. The challenging part is preparing this adsorbent in the granule shape with high porosity and PZC value, ensuring its applicability under normal pH of water, i.e., 6.5 to 7.5, and easy separation after use. This research has attempted to prepare highly porous alumina adsorbents in granule form using low-cost ceramic raw material kaolin. The study aims to find a suitable, environment-friendly, and highly effective alumina adsorbent for defluoridation. The adsorbents are prepared both in bead shape and granule shape through oil drop method using aluminium rich leachate extracted from kaolin. Al3+ leachate is obtained by thermal treatment followed by acid leaching of kaolin. Incorporating pore former in the bead-shaped adsorbent (prepared directly using concentrated acid leachate) is challenging, so two sols, namely sol-1 and sol-2, are prepared from Al3+ leachate with and without impurity removal. The sols are mixed with different pore-formers like PEG, PVP, spent tea leave waste (STLW), starch, sucrose individually, and PVA binder to convert into a semi-gel state. This semi gel is then injected into a column containing paraffin oil as an upper layer and ammonia as a bottom layer with the help of a syringe pump to form porous alumina adsorbents. All the prepared adsorbents, both bead-shaped and granule, are washed, dried, and calcined at different temperatures to get the desired alumina phase. Different characterization techniques like XRD, FTIR, FESEM, and BET surface area analysis are employed to get preliminary information about the applicability of the prepared adsorbent for the fluoride adsorption study. A batch adsorption study is then carried out systematically using each type of prepared alumina adsorbents. The adsorbent dose and kinetics parameters are thoroughly studied to achieve the maximum fluoride removal in the fluoride contaminated aqueous system. Bead-shaped adsorbents show lower surface area and porosity than their granular counterparts, resulting in low removal efficiency. The microstructural analysis is carried out before and after the adsorption process using FESEM with EDX to compare the alumina adsorbents' surface morphology and confirm fluoride ions' adsorption on the adsorbent surface. The batch adsorption study shows the mechanism and adsorption capacity of the alumina adsorbents using various kinetic models (i.e., Pseudo-first-order kinetic, Pseudo-second-order kinetic, Intraparticle diffusion and Elovich kinetic) and equilibrium isotherm models (i.e., Langmuir, Freundlich, Redlich-Peterson, and Sips isotherm models). The regeneration of the spent adsorbent and the effect of other co-existing ions on the adsorption process are also estimated. It is observed that at an initial fluoride concentration of 10 mg/L (adsorbent dose = 3 g/L; pH 6.7 ± 0.3; time = 12 h), the defluoridation efficiency is estimated as in the range of 26 to 96 %, in which Sol 1- PEG and Sol 2- Sucrose are the best adsorbent showing ~96 % of fluoride removal efficiency. Groundwater with the presence of fluoride ions always contains some other anions like nitrate (NO3-), chloride (Cl-), phosphate (PO4-3), and bicarbonate (HCO3-2) which competing for the adsorption sites during the defluoridation process. Hence, it's become necessary to investigate the effect of these co-existing ions. Further, a regeneration study of all the spent adsorbents are carried out
Investigations of Crystal Structure, Dielectric, Ferroelectric and Piezoelectric Properties of (1-x) Ba(Zr0.2Ti0.8)O3–x (Ba0.7Ca0.3)TiO3 Ferroelectric Ceramics and its Composites with Ferroelectric Polymer
No full textPerovskite-based ferroelectric oxides have strong potentials to be utilized in piezoelectric sensors, actuators, transducers, non-volatile memory, energy harvesting, and energy storage devices. The development of lead-free ferroelectric materials have drawn a significant attention due to the regulations enacted by different countries on the use of hazardous substance such as Pb in electronic devices. Among the different lead-free ferroelectrics, BaTiO3 (BT) is one of the mostly studied lead-free ferroelectric materials. However, the poor piezoelectric coefficient limits its practical applications for various devices. Fabrication of solid solutions on BT based materials that lies near the morphotropic phase boundary (MPB) region is one of the suitable approaches to enhance the piezoelectric coefficients, dielectric and ferroelectric properties. The BT based ferroelectric solid solutions i.e., (1-x) Ba(Zr0.2Ti0.8)O3 – x (Ba0.7Ca0.3)TiO3 (BZT-xBCT) exhibits a giant piezoelectric property around the MPB composition for x = 0.5. Despite of extensive research on BZT-xBCT system, a clear picture has not been established that explains the coexistence of the crystal structures and enhanced piezoelectricity around the MPB region. In order to understand the structure-property relationship, a wide compositional range must be required. In the present investigations, BZT-xBCT ferroelectric solid solutions for a wide range of compositions (0.3 ≤ x ≤ 1.0) were prepared and characterized using wide variety of experimental techniques. The compositional driven structural phase transition, dielectric, ferroelectric and piezoelectric properties were studied in detailed. The MPB composition i.e., 0.5BZT-0.5BCT (BZT-BCT) shows an enhanced dielectric, ferroelectric and piezoelectric properties which is further well correlated with the crystal structure. The highest piezoelectric response observed for the critical MPB composition at x = 0.5 can be attributed to the combined and cooperative contribution from easy polarization rotation, maximum domain wall motion due to the structural heterogeneity and emergence of polar nano region due to relaxor behaviour. Recently the developments of miniaturization of electronic devices require a flexible ferroelectric ceramic polymer composite with optimum physical properties. Mixing of a ferroelectric ceramic having high dielectric permittivity with flexible polymer matrix having high breakdown strength results into a ferroelectric ceramic polymer composite with high energy storage performance. Solution casting technique is employed to prepare flexible ferroelectric ceramic polymer composite having general formula PVDF-HFP (Poly(Vinylidene fluoride-cohexafluoropropylene)) + ϕ wt.% 0.5BZT-0.5BCT (BZT-BCT) with 0 ≤ ϕ ≤ 40. This BZT-BCT (MPB composition with x = 0.5) has been chosen as the filler for the preparation of composite films as it exhibits highest dielectric, ferroelectric and piezoelectric properties among the entire compositions of BZT-xBCT system. The electroactive β phase fraction increases with the increase of filler concentration up to 20 wt.% and above that it decreases. The change in β phase fraction is well correlated with the enhancement of physical properties such as dielectric, ferroelectric and energy storage density in the composite films. Due to the difference in polarity and surface energy between filler and polymer matrix, it causes certain interfacial defects (pore or void) and agglomeration of fillers which leads to the degradation of physical properties of composite films. Hence, to overcome such problems, surface modification of filler particles using an organic modifier is one of the efficient strategies. In the present study, the surface of BZT-BCT has been modified/hydroxylated using H2O2, (denoted as h-(BZT-BCT)) and prepared PVDF-HFP + ϕ wt.% h-(BZT-BCT) (0 ≤ ϕ ≤ 40) composite films. The effect of hydroxylated filler content on structural, microstructural, vibrational, dielectric and ferroelectric properties of composite films are studied. The dielectric and ferroelectric properties of the composite increases with the increase in filler concentration up to 15 wt.% of h-(BZT-BCT) and after that it decreases. The variation of electroactive β phase fraction shows a similar trend as that observed in dielectric and ferroelectric properties for these polymer composites. The highest dielectric, ferroelectric properties with a low loss and high energy storage density (728 mJ/cm3) is observed for the composite loaded with 15 wt.% h-(BZT-BCT) among all the prepared composite film
Synthesis and Physico-chemical Study of Few Mn-based Ternary Chalcogenides of General Formula MII2AIVQ4
No full textChalcogen (Group 16 of Periodic Table) and chalcogenide compounds are known to humankind from the early days of history. These compounds possess diversified structural features along with several potential applications in various fields like energy, data storage, medicine etc. Oxygen containing compounds (oxides) are the more attractive choice in the chalcogen group as these are relatively easy to synthesize and tuning of the physical properties can be achieved without much problem. On the other hand, compounds with other elements in the chalcogen family (S, Se and Te) are troublesome as their synthesis is not easy and their intentional tuning of the properties is also difficult to do. Further, the metal sulfides, selenides and tellurides are comparatively less studied and understood as compared to the oxides.
Magnetic chalcogenide compounds have a great potential in the field of spintronic and related applications. The 3d-transition metal based ternary chalcogenides, specifically Mn, Fe and Cr based chalcogenides are of significant interest from the view point of magnetism as these transition metals contain more number of unpaired electrons. Particularly, compounds with the general formula MII2AIVQ4 (M = Transition metal; A = Si, Ge, and Sn; Q = S, Se, and Te) are found to exhibit rejuvenated research interest because of their distinct structural and complex magnetic properties. These compounds largely crystallize in olivine structure type. However, Mn2SnS4 is the only compound in the MII2AIVQ4 (M = 3d transition metal; A = Si, Ge, and Sn; Q = S, Se and Te) series known so far with ordered defect rock salt-type structure. Very few reports are available so far in literature on its crystal structure and magnetic properties. In this thesis, the compound, Mn2SnS4 as well as its doped variants are synthesized via sealed tube solid state high temperature reaction method and detailed study of the structure and properties (mainly magnetic) have been done.
Pure phase of Mn2SnS4 was successfully synthesized after several trials and optimized reaction temperature profile from high purity elements. DFT based theoretical calculations on this compound revealed that the valence d-electrons of the magnetic Mn atoms are completely spin-polarized and total Mn–S bond energy contribution (though with low bond energy per Mn–S) is considerably higher than Sn–S bond energy contribution per unit cell. XPS study proved that the oxidation states of the elements in the compound, Mn2SnS4, are +2, +4 and −2 for Mn, Sn and S respectively. Magnetic measurements which were performed in a broad temperature range (3 K to 300 K) revealed the existence of two transitions: i) An ordered antiferromagnetic transition around 152 K (which is previously known) and ii) A weak ferromagnetic transition around 53 K (previously unknown). A high value of magnetization at low temperature and bifurcation of ZFC and FC measurement results were also obtained in the magnetic study. AC susceptibility measurement on Mn2SnS4 also confirms two magnetic transitions and none of the transitions possess any spin glass dynamics. The magnetic material is showing a very high value of frustration parameter, f (around 4), indicating the presence of a frustration in the system. Temperature variable neutron diffraction study was conducted at 3 K, 50 K, 100 K, 200 K and 300 K to understand the microscopic magnetic structure of Mn2SnS4. The magnetic structure determined at 3 K and 100 K revealed that there is a “canted” antiferromagnetic arrangement of spins at low temperature that diminishes at higher temperature (which also explains the higher value of magnetization at low temperature). The specific heat study was only successful to capture the second magnetic transition (i.e., around 152 K).
In order to observe the effect of substitution on the structure and magnetic properties, an aliovalent p-block element was partially substituted at the Sn-site to induce a mixed valence state at the Mn-site. Several trial reactions with different p-block elements were attempted, out of which antimony (Sb) doping was successful. The room temperature neutron diffraction measurement revealed that the dopant Sb occupies the Mn-site instead of Sn-site and expels equivalent amount of Mn to Sn-site resulting disorder at both the sites. However, the oxidation state investigation by XPS, revealed that neither Mn nor Sn changed their oxidation state due to aliovalent substitution, rather the dopant, antimony, exists in mixed valent state with equal amount Sb3+ and Sb5+. The magnetic measurements showed that upon doping Sb in Mn2SnS4, the second transition around 152 K (in parent compound) remained unaffected while the first transition temperature increases with successive substitution. The substituted compounds retained their antiferromagnetic character as that of the parent compound, Mn2SnS4, however, the substitution with a non magnetic ion eased the frustration within the system resulting in the decrease in the frustration parameter value. More interesting information was being found after the thermoremanent magnetization study i.e., substitution induced a low temperature stable spin dynamic state which was not present in the parent compound. This change in magnetic property may be the result of antimony induced Mn- and Sn-site mixing that creats more disorder at the Mn-site.
Substitution of d-block element, such as Cr, Fe at Mn-site in Mn2SnS4 were carried out to understand the effect of different d-electrons containing species on the magnetic properties. Site occupancy of the elements were obtained from the room temperature neutron diffraction study of one typical composition from each substitution series. It was found that chromium is fully occupied at the Mn-site while iron distributes itself to both Mn- (mostly) and Sn-site (partly) generating different degree of disorder upon substitution. The XPS analysis point out to the fact that both the dopants (Cr and Fe) exist in trivalent state (Fe3+ and Cr3+) while some amount of tin reduces from +4 to +2 state (Sn4+ and Sn2+) to maintain the charge neutrality. The evaluation of magnetic properties of Fe- and Cr- doped compounds exhibited contrasting results with respect to the effect on the transition temperatures as well as type of magnetic properties. In case of Cr-doping, both the transition temperatures were observed (as that of the parent compound) with small change in 1st transition temperature (53 K in undoped compound to 37 K in the doped compounds) and no change in the 2nd transition temperature (around 152 K). However, in Fe-doped compounds, a striking phenomenon was observed, as the first transition temperature (around 53 K for pure compound) completely disappeared while the second transition temperature (152 K in the pure compound) increased with higher amount of Fe substitution (around 174 K for 9% of Fe). The frustration parameter value is showing a lower value (than pure compound) in both chromium and iron doping, indicating a release of frustration. AC susceptibility measurements also support the change in the magnetic transition temperatures in both the doping series. M-H isotherm study show that Fe-substituted compounds retained antiferromagnetism while Cr-susbstituted compounds show ferrimagnetism due to incomplete cancellation of spin moment.
Further to understand the effect of substitution of f-block element on the magnetic properties, Ho-doped (Mn-site) Mn2SnS4 compounds were synthesized. The PXRD analysis and refinement proved a pure phase formation in Mn2−xHoxSnS4 till x = 0.2. The XPS analysis revealed that holmium exists in trivalent state i.e., Ho3+ and to maintain the charge neutrality, part of Sn4+ get reduced to Sn2+. The magnetic measurement in these compounds exhibited similar results as that of iron doping. The 1st transition at 53 K for undoped compound vanished upon doping while the 2nd transition temperature (at 152 K for pure Mn2SnS4) increased to a slightly higher temperature i.e., around 160 K for 10% of Ho substitution. In this case also, the frustration parameter shows a lower value than that of the parent Mn2SnS4 indicating a lowering of the frustration present in the system. However, all the doped compounds remained antiferromagnetic in nature (as found from the analysis of inverse susceptibility data, negative value of Weiss constant, θW), similar to the parent compound Mn2SnS4. These magnetic results indicate that the magnetic d-f exchange interaction is complicated in nature