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Microstructural Correlation of Creep, Tensile and Corrosion Behaviour of AZ91 Magnesium Alloy with Bi, Ca and Sr Additions
No full textIn the present investigation, five new alloys AZ91+1.0Ca (AZX911), AZ91+0.5Bi (AZB910), AZ91+1.0Ca+0.5Bi (AZXB9110), AZ91+1.0Ca+1.0Bi (AZXB9111), AZ91+2.0Ca+0.5Bi (AZXB9120) (wt.%) have been fabricated by squeeze-cast. The first part of the thesis investigates the influence of combined additions of Ca and Bi on the microstructure, creep, tensile, and corrosion behaviour of the squeeze-cast AZ91 alloy. The same is also studied on the AZ91 alloy with and without single additions of Ca and Bi for comparison. Another three new alloys AZ91+0.5Bi+0.25Sr, AZ91+0.5Bi+0.5Sr, AZ91+1.0Bi+0.5Sr (wt.%) have also been fabricated by squeeze-cast. The second part of the thesis investigates the influence of combined additions of Bi and Sr on the microstructure and creep behaviour of the AZ91 alloy. The creep behaviour of all the alloys is evaluated using impression creep tests in the temperature and stress ranges of 423 to 523 K and 300 to 480 MPa, respectively. The tensile tests of the Ca and Bi added AZ91 alloys are performed at 298, 423, and 473 K with a strain rate of 8.33×10-5 s-1. The corrosion behaviour of the Ca and Bi added AZ91 alloys is studied by immersion, hydrogen evolution, and electrochemical corrosion tests at 0.5 wt.% NaCl solution (pH 7) at room temperature. Both the single and mixed contents of Ca and Bi in the AZ91 alloy refine the grain size of α-Mg and reduce the volume fraction of the β-Mg17Al12 phase considerably. The effect is more noticeable in combined additions than in individual additions. The reticular-shaped Al2Ca and needle-shaped Mg3Bi2 phases additionally form with the α-Mg and β-Mg17Al12 phases because of the sole Ca and Bi additions in the AZ91 alloy. The Al2Ca and Bi3Ca5 phases are formed when Ca and Bi are added together, suppressing the Mg3Bi2 phase formation. The modified AZ91-based alloys containing Ca and/or Bi exhibit improved creep behaviour than the AZ91 alloy at all the stress and temperature levels tested. The individual additions of the elements in the AZ91 alloy show a higher creep rate than the combined additions. The individual Ca addition is better than Bi addition for resisting creep deformation in the AZ91 alloy as the Al2Ca phase in the AZX911 alloy has superior thermal stability compared to that of the Mg3Bi2 phase in the AZB910 alloy. The AZXB9120 exhibits the best creep performance owing to the lower volume fraction of the β-Mg17Al12 phase and the existence of a larger quantity of thermally stable Al2Ca and Bi3Ca5 phases. The values of stress exponents and activation energies conclude that the dominant creep mechanism for all the alloys is dislocation climb aided by pipe diffusion. The microstructural investigation following creep indicates that the β-Mg17Al12 phase is broken into small pieces. In contrast, the thermally stable Al2Ca, Mg3Bi2, and Bi3Ca5 phases preserve their continuity, which results in piled-up dislocations and tangling of dislocations in the interior of the α-Mg grains that leads to the improved resistance to creep deformation of the modified AZ91 alloys. The values of yield strength (YS) are higher, and ductility is lower of all the modified alloys. The ultimate tensile strength (UTS) of the modified AZ91 alloys is lower except at 473 K. The UTS values decrease with an increase in test temperature for all the alloys. The improved YS of the modified alloys is owing to reduced grain size. The brittle Mg3Bi2, Al2Ca, and Bi3Ca5 phases in the modified alloys reduce their UTS and ductility. The transgranular cleavage fracture at 298 K changes to quasi-cleavage fracture at 473 K. Several dislocations piled up around the β-Mg17Al12 and Al2Ca phases are seen. All the modified alloys exhibit better corrosion resistance than the base AZ91 alloy. The AZX911 alloy unveils better corrosion resistance than the AZB910 alloy owing to the Al2Ca phase formation. The combined Ca and Bi added AZ91 alloys acquire better corrosion resistance than the individual Ca or Bi added AZ91 alloys. The AZXB9120 and AZXB9111 alloys exhibit the lowest and the highest corrosion rates among the combined additions. The combined Bi and Sr additions form the Al4Sr and Sr2Bi phases besides the α-Mg and β-Mg17Al12 phases and improve the creep resistance of the AZ91 alloy. The AZ91+1.0Bi+0.5Sr alloy reveals the best creep resistance among the alloys. The stress exponent and activation energy values of all the alloys confirm the pipe diffusion-controlled dislocation creep as the governing creep mechanism. The post creep microstructural study reveals several dislocations pile-ups around the Al4Sr and Sr2Bi phases resulting in improved creep resistance of the modified AZ91 alloys. To conclude, the additions of Ca and/or Bi improve the creep, tensile, and corrosion behaviour of the squeeze-cast AZ91 alloy. The effect is more significant with combined additions. The combined Bi and Sr additions also improve the creep behaviour of the AZ91 alloy. Therefore, the additions of Ca, Bi, and Sr to the AZ91 alloy are beneficial
Development of Process Technology for Valorization of Pomegranate Peel and its Application in Powdered Infant Formula
No full textInfants have a low developed immune system, which raises the possibility of microbial infections when exposed to contaminated foods. Infant foods, especially powdered infant formula (PIF), have been epidemiologically linked with various food-borne infections. Staphylococcus aureus is one of the major pathogens that could be related to these infant food outbreaks. Though traditional thermal processing and the use of synthetic antibiotics effectively kill food-borne pathogens, they have been found to degrade quality attributes that are objectionable to consumers. To resolve this issue, notable efforts have been taken, among which the use of natural antimicrobials is the foremost approach. Pomegranate peels are known to exhibit various groups of phytochemical compounds consisting of polyphenols, anthocyanins, flavonoids, phenolic acids, and hydrolysable tannins at significant levels compared to fruit arils. The hydrolysable tannins present within pomegranate peel have been known for their noteworthy antimicrobial properties. However, owing to the lack of proper value addition methods, the antimicrobial property of pomegranate peels is not still utilized to their full potential. This urges the need to develop a process technology that could utilize pomegranate peels as a robust natural antimicrobial compound. In the present work, a process protocol is being developed that aids to determine the antimicrobial activity of encapsulated pomegranate peel extract against strains of S. aureus isolated from PIF. Unit operations namely drying, grinding, extraction and encapsulation are vital for the appropriate use and value-addition of the pomegranate peels as a natural antimicrobial. For the maximum recovery of phytochemical compounds, the fresh pomegranate peels were dried using the microwave vacuum drying method. The drying experimental runs were performed on varied ranges of microwave power (175, 330, 485 W) and vacuum pressure (10, 15, 20 kPa) using a face‐centered composite design. Optimized condition for microwave- vacuum drying of pomegranate peel (within the chosen range) was observed as 276 W microwave power and 10 kPa vacuum. At the optimized condition, the phytochemical compounds targeted were considerably preserved. Amino acid analysis of dried peels at optimized conditions exhibited the retention of 11 amino acids at significant levels with glycine possessing the highest concentration 5.93 mg/g. The dried pomegranate peel was ground using conventional and cryogenic grinding techniques. From the numerous powder properties studied, say bulk density, true density, porosity, product temperature, moisture content, water activity, phytochemical compounds, and surface morphology analysis, it was concluded that the properties of the cryogenically ground peel powders were superior to that of the conventionally produced peel powders. The extract from cryogenically ground pomegranate peel powder, containing maximum phytochemical compounds (with the highest recovery of hydrolysable tannins) was extracted using pulsed system ultrasound. The process variables in total hydrolysable tannin extraction were modeled and optimized by an artificial neural network and genetic algorithm respectively. The optimal extraction conditions attained for process variables were; solvent concentration of 56%, solvent-feed ratio of 26.5 mL/g, extraction time of 15 min, and ultrasound amplitude of 50% respectively. Pulsed system ultra-sonication significantly augmented total hydrolysable tannins of pomegranate peel extract to 98.12 mg TAE/g compared to 50.14 mg TAE/g with conventional extraction. The Fourier transform infrared spectroscopy (FTIR) and high performance liquid chromatography (HPLC) analyses established that pomegranate peel extract produced at above optimal conditions contained a significant amount of hydrolysable tannin compounds (gallic acid and tannic acid derivative) than conventional extraction methods. The pomegranate peel extract was encapsulated using external gelation technique. The process variables in encapsulation were modeled and optimized by Box-Behnken design. The encapsulation efficiency and properties of encapsulate were found to be optimum at 4% sodium alginate concentration, 2.5% CaCl2 concentration, and 30% PPE concentration. The encapsulation efficiency at the optimized condition was 83.65%. A comparative study was performed to evaluate the properties of encapsulates produced by external gelation (at its optimum conditions) and spray drying. The encapsulates were analyzed for various physical properties, phytochemical parameters, release profile, storage stability, and thermal stability. The performed analyses revealed the superiority of the encapsulates produced by external gelation over spray drying. Further the thermal stability and antibacterial activity of developed pomegranate peel extract encapsulates was carried out. The outcomes revealed that the zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) of encapsulated pomegranate peel extract against S. aureus (ATCC 25923) identified in PIF were 32 ± 0.01 mm, and 300 μg/mL respectively. The outcomes are promising and recommend the possibility of utilizing encapsulated pomegranate peel extract as natural antimicrobials or as a systemic natural antibiotic replacing the synthetic antibiotics for inactivation of S. aureus strains isolated from powdered infant formula at an industrial level
Analysis of Pedestrian Level of Service and Capacity at Various Transportation Facilities
Get PDFOver the years, pedestrian mode is the most accessible mode of transportation, in which a person has freedom to move from one place to another easily and flexibly between different regions. Hence, sustainability of community development largely depends upon the establishment of efficient transportation facilities to serve pedestrian mode effectively in a transportation network. The review of literature suggests that the service quality of transportation facilities has been evaluated since nineties. However, the developments of transportation facilities in developing countries like India is still far away from satisfactory than the developed countries, because of the fact that application of pedestrian level of service criteria developed for homogeneous traffic conditions will fail to quantify the service provision criteria and heterogeneity of transportation facilities in developing countries. At the same time, handling the pedestrian traffic becomes extremely challenging due to limited space and resources. In accordance with this, pedestrian level of service, which is a complex expression represents the operating condition of transportation facilities and satisfaction levels of pedestrian experience while using these facilities. In this regard, this study aims at defining Pedestrian level of service categories for three transportation facilities such as railway foot over bridge, signalized intersection crosswalk and un-signalized midblock crosswalk by using qualitative data sets under non-uniform pedestrian flow condition. On the other part of this study, while going through the literature, various researchers developed several methods for capacity estimation. Also, Highway Capacity Manual (2010) provides procedures in detail for determining capacity of facilities, but due to the heterogeneous conditions of traffic flow in India, these models doesn’t fit well in Indian condition. Therefore, in the present study, Artificial Intelligence based Genetic Programming models, which are empirical in nature, are developed for railway foot over-bridges three facilities such as staircase, deck and junction by considering capacity as the dependent variable and geometric variables as independent variables, under non-uniform pedestrian flow condition in India. To achieve the objectives of this research, a broad spectrum of pedestrian perception data sets are collected from three transportation facilities: Railway foot over-bridges, signalized intersection crosswalks and un-signalized midblock crosswalks. Around, 12 railway stations’ foot over-bridges, 9 cities’ signalized intersection crosswalks and un-signalized midblock crosswalks were investigated in this perception study. From each investigated station or city, 600 pedestrian’s real time sense of satisfaction data are collected with the help of prepared inventory questionnaire. For capacity estimation of these railway stations’ foot over-bridges three facilities, namely staircase, deck and junction, pedestrian flow and inventory data were collected. With the help of videography survey, pedestrian flow data are collected. Consequently, by eye observations and field measurements of various geometrical variables, inventory data were collected. The method of sensitivity analysis is employed to determine the impact of an independent variable with a particular dependent variable under a given set of assumption. Factors sensitivity analysis for three transportation facilities were carried out in this study. Significant factors are identified to have influence on pedestrians’ satisfaction level at railway stations’ foot over bridges, such as: width, length, rise, trade, railing and surface under staircase, frequency and size are under landing, railing, surface, position with respect to halting of train and position with respect to entry/exit of station are under foot over bridge, display, announcement at proper time and at all the platforms are under information provided, and requirement of foot over bridge, escalator, travellator, more platforms and directional separator are under requirement of facilities. Similarly, location of signalized intersection, visibility of zebra crossing line, width of zebra crossing line, observation of signal color, pedestrian traffic signal color, time allocation for pedestrian crossing, location of zebra crossing, following of traffic signal, waiting time, vehicle occupy the zebra line, lighting of zebra lines at night, grade separation and requirement of subway and foot over bridge are the factors, which have significant influence on pedestrians’ service quality at signalized intersection crosswalks. For un-signalized midblock crosswalks, pedestrian crossing of median, median space, road surface and lighting system at night, safety in front of vehicles, time taken to cross the road, safety while waiting across the road, vehicle speed variance, nature of traffic volume, median opening, zebra crossing, choice between foot over bridge or subway facilities, requirement of zebra crossing, foot over bridge and subway, and lighting of zebra crossing at night are found to have significant influence on pedestrian’s comfort level under non-uniform pedestrian flow condition. Consequently, sensitivity of each railway stations’ foot over-bridges, cities’ signalized intersection crosswalks, and cities’ un-signalized midblock crosswalks are obtained. Defining the pedestrian level of service criteria for urban pedestrian facilities is basically classification problem and cluster analysis is found to be more suitable technique for solving this problem. In this study, k-means clustering technique is used to determine the Pedestrian level of service of three transportation facilities. In accordance with the HCM (2010), to define pedestrian level of service for these facilities, sensitivity is employed as service measure. An associative Pedestrian level of service category is assigned to six classes (A-F) for corresponding facilities. For railway stations’ foot over-bridges, pedestrian level of service categories were defined. Consequently, with respect to service levels, the railway stations are classified in decreasing order. More than 70% of the studied railway stations’ foot over-bridges are examined to offer pedestrian level of service ‘C’ or above. Similarly, pedestrian level of service classification for various cities’ signalized intersection crosswalks and un-signalized midblock crosswalks are determined. Accordingly, the cities’ facilities are categorized in decreasing order corresponding to levels of service. More than 65% of the cities’ signalized intersection crosswalks and un-signalized midblock crosswalks were found to be offering pedestrian level of service ‘C’ or above. Based on the obtaining offered service quality of these transportation facilities, which will help the transport authorities to identify operational issues of existing facilities, and to design a pedestrians’ friendly transport system with better pedestrian movement. Also, this will help in defining service levels for transportation facilities in other developing countries having non-uniform pedestrian flow condition like India. As defined by highway capacity manual (2010), capacity is the maximum flow that could be carried in the approach stream under prevailing geometric and traffic conditions. Various researchers over the years, developed several methods for capacity estimation. The traffic condition in India is very heterogeneous in nature, whereas, the traffic condition of developed countries is homogeneous in nature. Therefore, the methods recommended by highway capacity manual (2010), for estimation of capacity in terms of models under homogeneous traffic flow condition, which doesn’t fit well in Indian condition. Hence, Genetic programming modelling based on Artificial Intelligence is used for model development in the present study, as it’s the latest technique. In this regard, for railway foot over bridges’ three facilities, namely staircase, deck and junction, Genetic programming models were developed under non-uniform pedestrian flow condition in India. Models are developed for these facilities by taking geometric variables as independent variables and capacity as dependent variable. For development of three models, from total data sets, 70% and 30% of the data sets were used for training and testing of the models, respectively. Also, these models are obtained for a maximum of 50 generations with mutation probability of 15% and population size of 1000. For model development of staircase, in both training and testing stage, the statistical factors such as coefficient of determination of the model, Average absolute error, Mean absolute error, Root mean squared error were measured to be (0.92, 0.09, 0.12, 0.10) and (0.91, 0.11, 0.15, 0.13), respectively, which indicates that the model’s prediction capability is significant under non-uniform pedestrian flow. The method of data splitting was employed for the model validation and found that observed capacity varying 8% corresponding to predicted capacity with the measured R square value of 0.92. This shows that the capacity model for staircase found to best fit at 92% confidence level. In deck model development, the statistical parameters like R square of the model, Average absolute error, Mean absolute error, Root mean square error are measured to be (0.91, 0.10, 0.16, 0.12) and (0.88, 0.13, 0.18, 0.15), in both training and testing stage of the model development, respectively, which shows that under non-uniform pedestrian flow, the prediction capability of model is significant. Data splitting method was used for validation of model and found that the capacity model for deck is well fit at 91% confidence level. Also, the variation between observed capacity and predicted capacity is 9%, with the value of R Square is measured to be 0.91. Model development for junction, the prediction capability of the model is significant under non-uniform pedestrian flow as the statistical parameters such as R square of the model, Average absolute error, mean absolute error, root mean square error are measured to be (0.87, 0.12, 0.16, 0.14) and (0.84, 0.15, 0.19, 0.17) in both training and testing stage of the model development, respectively. For the model validation, method of data splitting was employed and found that observed capacity varying 13% corresponding to predicted capacity with the measured R square value of 0.87. Further, this signifies that at 87% confidence level, the capacity model for junction is best fit. The proposed models are suggested for application in the field by practitioners because the models provides unique equations for prediction. The models can be widely acceptable for their simplicity and manageability. Therefore, these models are quite useful for planning and design of respective facilities. Also, these findings will be useful for the researchers, planners and designers for making key policy decisions
Structural, Spectroscopic and Photophysical Features of Rare earth Activated Phosphate Phosphors
No full textThe solid state lighting technology and its progressive fundamental scientific research supplements one of goals in the Sustainable Development Goal (SDG), to ensure the access to affordable, reliable, sustainable and modern energy for all; in terms of energy efficient light that enhances quality of human life and productivity of workforce. In this endeavor, this thesis work aspires to study a new set of phosphate based phosphors, and evaluation of their structural, spectroscopic as well as the photophysical properties. The phosphors are prepared by solid state-reaction methods and are designed by the sensitizer-activator approaches by incorporating rare-earth ions as light emitting centers. The material science description of the synthesis techniques used to synthesize different series of inorganic phosphate based phosphors are outlined here. The experimental exploration and characterization of the phosphors along with the results based on the structural, morphological, vibrational and optical band gaps are discussed in a systematic manner. The x-ray photoelectron spectroscopy characterization and photophysical properties of synthesized phosphors are examined in this work and are systematically documented. ABPO4 (A and B are mono- and divalent cations, respectively) have excellent thermal stabilities for potential efficient host materials as well as advantages of diverse structural frame works depending on the relative size of A and B cations. In this class, a series of maricite structured NaCd1-xPO4: xEu3+ are synthesized and various structural as well as optical properties are studied extensively. With Eu3+, increased broadening of band gap is explained by Burstein–Moss (BM) effect. This phosphor exhibits emissions rich in red at 617 nm due to hypersensitive transition line 5D0 → 7F2 due to the induced electric dipole (ED) under suitable excitations at 393 nm and the colour co-ordinate of the emission spectrum is concentrated to a very confined spot in the colour space indicates a high colour purity. In this phosphors, a wide bandgap and rigid structure along with sharp red emission are found suitable for design considering of LED phosphors which may find applications in pcLEDs. In an attempt to synthesize and characterize in details of a broad spectrum emitting phosphors that covers the span of visible light, another series of phosphors NaCd1-xPO4: xDy3+ (x = 0.02 – 0.1) are prepared by adopting conventional solid-state reaction routes. The photoluminescence characteristics are recorded at room temperature, in which the excitation maxima are observed at 347 nm, indicating a near-ultraviolet (UV) excitation which can be iuseful for light-emitting diodes with a UV chip. The emission spectra show three major emission lines at 480 nm (4F9/2 → 6H15/2) a blue emission, a yellow emission around 570 nm (4F9/2 → 6H13/2) and a red emission around 662 nm (4F9/2 → 6H11/2). Therefore, the resulting spectrum is nearly white under UV excitation, which enables them to be tuned suitably with co-activator ions or by means of sensitizations and can be useful as solid-state lighting sources. A wide bandgap of 5.72 eV and a small variation is observed with increasing concentrations while studying the optical reflectance properties of a series of Sm3+ doped phosphors constituted with the CsMgPO4 host. A systematic study of photoluminescence properties of Sm3+ doped CsMgPO4 phosphors is carried out and along with investigations of the structural as well as morphological, vibrational and photoelectron emission characteristics. The room temperature excitation and emission spectra, reveals that the phosphor emits the orange rich red light under the suitable excitation of 402 nm in the UV region. The emission peaks confirm the characteristic Sm3+ 4f-4f transitions. The temperature-dependent photoluminescence (TD-PL) is also explored for the selective composition with x = 0.02 (optimum doping), which has been recorded from 30 °C to 210 °C and is showing good thermal stability even at 150 °C. The thermal quenching mechanisms are discussed based on the configuration coordinate model of excitation and emission. The prepared phosphors are found to exhibit near thermal stability compared to the commercially available red phosphors. = The PLQY for this optimum composition is estimated to be 42.1 %. The color coordinates are found to lie in the orangish-red region of the color space. Thus the prepared phosphors CSMP: x Sm3+ can be useful as a red component in designing UV excitable chip-based phosphorconverted white LED applications. In a similar context, a series of phosphate phosphors KZnPO4: xEu3+, yBi3+ (x = 0 – 0.06, y = 0.005-0.05) are prepared and a systematic study of photoluminescence properties along with structural as well as morphological and vibrational characteristics are carried out. The concentration quenching of Eu3+ occurs at x = 0.04 and considering this as the optimum level of Eu3+ doping concentration, Bi3+ is added to act as the sensitizer for further enhancing the PL emission and mediate the efficient energy absorption processes. This chapter is aimed to explore the co–doping approach of activators and sensitizers in phosphor
Detection and Delineation of Coal Mine Fire and Estimation of Greenhouse Gas Emissions Using Satellite Data
No full textCoal is a fossil fuel that tends to catch fire in in-situ conditions primarily due to spontaneous combustion. Many other coal-producing nations across the world, including China, India, the United States of America (USA), Australia, Indonesia, face significant risks due to subsurface and surface coal fires. In-situ coal fires lead to substantial loss of coal and pollute the environment through the emission of toxic gases due to coal burning. Thus, monitoring coal fire propagation is needed to minimize the environmental risk and extreme loss of energy resources. However, monitoring coal fires using the traditional survey method is challenging and incurs a higher cost and workforce. The present study aims to develop a methodology to detect and delineate the surface and subsurface coal fires using a remote sensing-based approach. The study also analyzed the dynamics of coal fires using time-series analysis of satellite data. The study also extended to estimate the role of coal burning on greenhouse gas emission using remote sensing-based approaches. The study region selected for conducting the study is Jharia coalfield (JCF). JCF is one of India's largest and oldest coalfields, affected by fire for the last few decades. The coal fire detection using remote sensing data was done using multiple approaches and validated using field data. The study used different techniques to detect the surface and sub-surface coal fires. The sub-surface fire detection was done using two different methods (radiative transfer method (RTM) and single-channel algorithms (SCA)), and surface fire detection was done using one method (index method). In the current study, the fire-affected regions from 1989 to 2019 at an interval of 5 years were analyzed to understand coal fire dynamics. The remote sensing data used to determine the surface and sub-surface fire are thermal infrared, near-infrared, and red band data of Landsat-5 and Landsat-8 sensors. In both the methods of sub-surface fire detection, the land surface temperature (LST) was estimated using Landsat data, and fire zones were detected based on the estimated threshold LST values. The threshold LSTs were determined using a statistical method. The study results indicated the land surface temperature (LST), derived from satellite data, was saturated within 55 °C in both the methods (RTM and SCA). Therefore, the surface fire locations with a much higher temperature than 55 °C cannot be distinguished using these methods. Thus, the surface fire estimation was done using the index-based method without estimating the LST. The study results indicated that the locations are situated within the subsurface fire zones in most of the cases and have smaller coverage areas. The LST estimated using Landsat data was validated with field LSTs, measured at 20 different locations using a thermal camera during the same day of satellite data acquisition. The locations of each station were tracked using a GPS device (GARMIN 72S). It was found that the predicted LSTs from satellite data using RTM and SCA method are highly correlated with the field data with a correlation coefficient of 0.91 and 0.94, respectively. The RMSE values between the predicted LST and observed LSTs were 1.29 and 1.63, respectively, for SCA and RTM. The predicted LSTs using two approaches exhibit nearly similar patterns, but the SCA approach offers relatively better accuracy. The results reveal that the coal fire zones estimated using both techniques have good agreement with the field LSTs, and thus either of the methods can be used for fire detection with greater preference to SCA. Thus, SCA was used to analyze the time-series satellite data from 1989 to 2019 at an interval of five years for understanding the coal-fire dynamics in JCF. The study used thermal band data of Landsat-5 and Landsat-8 along with the radiosonde data for estimating the land surface temperature (LST). The results of time-series analysis can be used to determine the extinguished fire zones, new fire zones, and active fire zones. All the maps were stacked in ArcGIS 10.8 software, and an overlay analysis was performed to estimate the propagation characteristics with time. The Landsat data for seven different years (1989, 1994, 1999, 2004, 2009, 2014, and 2019) were downloaded from USGS online portal. The spatial resolutions of the thermal band in Landsat-5 and Landsat-8 data are 120 m and 100 m, respectively but resampled to 30 m spatial resolution. The coal fire maps were generated for seven different years from 1989 to 2019 at five-year intervals. The new fire zones established at every five-year interval from 1989 to 2019 were mapped for understating the fire dynamics. The fire area coverages were found to be 2.026 km2, 3.009 km2, 3.159 km2, 3.991 km2, 4.664 km2, 8.656 km2 and 9.957 km2 respectively for the year 1989, 1994, 1999, 2004, 2009, 2014 and 2019. The study results revealed that the coverage area of coal fire had been continuously increased from 1989 to 2019. Moreover, the results of the temporal analysis of coal fire indicated that the fire propagation was not in any specific direction. That is, new fire zones have been developed pocket-wise due to multiple factors and not due to the continuous burning of in-situ coals. It has been observed that the production level in the mines during this period (1989 to 2019) has also been continuously increased, possibly due to the higher number of working mines. Thus, a higher number of coal blocks are exposed to the atmosphere, which leads to catches of fire due to spontaneous heating. Also, few coal fire pockets have been extinguished with time. The coal fire in a typical zone may be extinguished either due to entire coals being burned or extracted out. The change in fire area coverage of extinguished fire zones and the new fire zones indicate that the formations of new fire zones were always higher than the extinguished fire zones. Thus, the fire area coverage has been continuously increased. The current study also analyzed the spatio-temporal profiles of columnar density of three major greenhouse gases (carbon monoxide (CO), sulphur dioxide (SO2), and nitrogen dioxide (NO2)) over the coal-mining region (JCF, India) using hyperspectral TROPOspheric Monitoring Instrument (TROPOMI) sensor data for the year 2019. The columnar density of the gaseous pollutants in the mining region was also compared with the columnar density of the same over the rural, urban, and forest regions for identifications of the major emission inventories. The results indicated that coal fire is the major source of CO emission over the study region, as the columnar density of CO was high over the fire regions compared to that of the non-fire regions. But the primary source of NO2 is the traffic, as the columnar density of NO2 was high in the city area compared to other areas. The spatial distribution of columnar density of SO2 did not reveal any specific emission sources. However, the results indicated that approximately 7575.6 tonnes of CO and 40.641 tonnes of SO2 had been emitted only from six collieries (Kenuadih, Godhar, Kusunda, Alkusha Ena, and Dhansar) of JCF during 2009 – 2019 based on the assumptions that the entire coal is burned with complete combustion. Thus, the present study demonstrated the potential of satellite remote sensing approaches for monitoring and mapping coal fire dynamics. The TROPOMI onboard Sentinel-5P sensor gridded datasets also aided to analyzed the spatio-temporal pattern of greenhouse gaseous over the coal fire regions. The outcome of the study shall be decisive and key inputs for policy-making, planning, and implementing sustainable development programs over the mining region. The study further assists in identifying the coal fire emission inventories. Moreover, satellite-based earth observation offers information to understand and manage greenhouse gas emissions over a large area
Recognition, Characterization, Categorization, and Forecasting of Counter-Current Gas-Liquid and Liquid-Liquid Two-Phase Flow-Structures: Experimental, Computational, And Numerical Attempts
No full textThe simultaneous flow of several phases or states is known as multiphase flow. Flow-regime or flow-structure is the morphological arrangement (interfacial structure) of the component phases. Transport phenomena like momentum transfer, mass transfer, or heat transfer in the multiphase flow strongly depend on the interfacial distribution (flow-structure). The time variation of pressure drop in the conduit of any multiphase flow system is oscillating in nature. This pressure oscillation may generate some unwanted vibrations in the flow systems. The frequency and amplitude of the said pressure oscillations strongly depend on its flow-structure. Therefore, proper analysis, understanding, and diagnosis of the flow-structures are essential to tackle any multiphase flow system and its safety issues. It is compulsory to monitor and track the flow-structures to optimize the performance of any steady or transient operations in the multiphase flow system. It is necessary to know the flow-structure to have smooth and safe operations in multiphase flow systems. It is not unexpected that copious attempts have so far been made to analyze the two-phase flow-structure or flow-regime. However, most of such attempts have been made for co-current gas-liquid and liquid-liquid two-phase flow only. Literature review reveals that sufficient research attempts have not been made on the diagnosis of flow-structures of counter-current two-phase flow (CCTPF). Characterization of CCTPF-regime has not received adequate attention to date. A few attempts have been found on the CCTPF-structure. Again, most of these few attempts have been made by considering the air-water fluid pair only. Attention is not paid to the CCTPF-regimes of other working fluid pairs. The flow-structure analysis of liquid-liquid CCTPF has rarely been attempted. The effect of flow-orientation on the CCTPF-structures has been explored up to a very small extent. Research attempts in CCTPF-patterns in smaller diameter tube is rarely found. Automatic online recognition, characterization, categorization, and forecasting of the CCTPF-structures based on objective signatures of the flow (using various sensors) are hardly found in the literature. Identification, characterization, parameterization, categorization, and forecasting of flow-structures are the prime issues in multiphase flow systems. Recognition of CCTPF is very challenging due to its inherent complexity and nonlinearity. The characterization of different flow structures poses huge difficulties, as the underlying process is filled with uncertainty, complexity, high nonlinearity, lack of knowledge, and fuzziness. The existence of these issues in CCTPF-structure is much more compared to that in co-current flow-structure as the CCTPF contains more significant variations in the relative velocity (between the phases) than the co-current two-phase flow. Situations of no solution or multiple solutions may frequently arise in CCTPF-hydrodynamics. Flooding may occur in CCTPF, which is generally undesirable in the flow system. However, gas-liquid and liquid-liquid CCTPF are very common and witnessed in several industrial applications. Thus, though it is challenging, the study of the CCTPF-structures under different flow situations is essentially required to design any CCTPF system and its safety issues. Thus, in the present thesis, at first, rigorous investigation (experimentations, characterization, parameterization, categorization, and forecasting) are made on gas-liquid CCTPF-structures in a 11 mm ID tube by varying the fluid pair and flow-orientations. Investigations are done for three different fluid pairs, namely: air-water, air-aqueous glycerine, and air-aqueous butanol. For each fluid pair, studies are conducted for three different flow-orientations: 0°, 45°, 90°. For each of the orientations, analyses are made for various combinations of the superficial velocities of the constituent phases covering a wide range. Secondly, extensive investigations on the gas-liquid CCTPF-structures in a conduit of 15 mm ID are made exactly in the same way as explained above (in the previous paragraph) to grasp the effect of the conduit ID on the developed gas-liquid CCTPF-structures. Here also the studies are made by considering the same three fluid pairs. Here also, a total of 3 flow-orientations (0°, 45.0°, 90.0°) are considered for each fluid pair, and various combinations of the superficial phase velocities are considered at each flow-orientation during investigations. Next, exhaustive investigations (experimentations, characterization, parameterization, and categorization) are made on the liquid-liquid CCTPF-structures in a conduit of 11 mm ID by varying the duct-orientations and combinations of the individual liquids’ superficial velocities. The kerosene-water fluid pair is considered for the present liquid-liquid CCTPF experimentations. A total of 7 tube-orientations (5°, 10°, 22.5°, 45°, 67.5°, 80°, 85°) are considered during investigations. During investigations, various combinations of the superficial velocities of the constituent phases covering a wide range are considered at each of the orientations. Then, exhaustive investigations on the liquid-liquid CCTPF-structures in a 15 mm ID tube are made exactly in the same way as explained in the previous paragraph to grasp the effect of the tube ID on the developed flow-structures. Here also, the studies are made by considering the kerosene-water fluid pair. A total of 5 tube orientations (0°, 22.5°, 45.0°, 67.5°, 90.0°) are considered during investigations. Analyses are made for various combinations of the superficial velocities of the constituent phases covering a wide range at each of the orientations, For each of the above four investigations, exhaustive experimental investigations are performed, and the CCTPF-structures are explored. High-resolution photographs of the flow-structures are captured and stored using a high-resolution DSLR camera to grasp the highly complex interfacial distributions in the flow-structures. High-speed videos of the flow-structures are recorded using a high-speed video camera (and then analyzed) to capture the rapidly time-varying nonlinear flow attributes. Sensors-based flow-regime identifiers are developed. Different sensors like differential pressure transmitters (DPT) and in-house fabricated conductivity probes are simultaneously employed to collect the flow-structures’ objective signatures in the form of time-series current and voltage signals, respectively. It is done to avoid possible confusion arising from subjective descriptions, which vary from subject to subject. The current signals of DPT are converted to corresponding ΔP signals. Statistical analysis of the normalized time-series voltage and ΔP signals is made using MATLAB coding to extract the non-parametric probability distribution (NPPD) functions and statistical parameters from those signals. Thus, the objective time-series data are converted into some statistical objective countable properties or parameters. The high-resolution photographs, high-speed videos (and the split snaps), time-series ΔP and voltage signals, and their NPPD function plots with statistical parameters are used together to recognize and distinguish the individual CCTPF-structures. Flow-structures are characterized and parameterized using those countable statistical parameters extracted from the objective time-series data. Computational intelligence (CI) based categorizer inspired by the EM algorithm is developed using MATLAB coding to categorize the developed gas-liquid and liquid-liquid CCTPF-structures automatically, considering various sets of those statistical parameters as inputs. CI-based forecaster employing a multilayer perception neural network is also developed by MATLAB coding to forecast different gas-liquid CCTPF-structures considering various sets of those statistical parameters as inputs. Some novel gas-liquid and liquid-liquid CCTPF-structures, which have not yet been reported in the literature, are found through the present investigation. The CCTPF-structures are successfully parameterized and characterized in terms of the NPPD plots and those statistical parameters of the objective signatures. These extracted NPPD plots and statistical parameters are found to be very useful for recognizing and distinguishing the individual flow-structures. The developed categorizer categorizes the generated gas-liquid and liquid-liquid flow-structures (under different working situations) automatically and successfully with high accuracy. The proposed forecaster forecasts the generated gas-liquid CCTPF-structures automatically and successfully with high accuracy in different working situations. Thus, the proposed categorizer and forecaster are robust enough and can be used for online automatic CCTPF-regime categorization and forecasting, respectively. Lastly, the concept of diagnosing the flow-structures using objective signatures is applied to a practical problem. The dynamics of CCTPF characteristics and CCFL mechanisms in the hot-leg of a PWR during the loss of coolant accident (LOCA) have not yet been revealed completely. Again, no such attempt is found in the literature regarding characterization, categorization, or prediction of flow-condition (flow-structure) in the hot-leg during LOCA. Numerical and computational attempts are made here to investigate and characterize the flow-condition in the hot-leg of a Pressurized Water Reactor (PWR) during the LOCA. 1/3rd model of German Konvoi PWR (Deendarlianto et al., 2008) is considered for the present numerical investigation. The finite Volume-based Volume of Fluid (VOF) model (with single momentum equation) is employed for transient numerical simulations of the two-phase hydrodynamics in hot-leg during LOCA. The turbulence effect is captured using ‘k-w’ model. Effect of individual fluid-flowrates and stored water (initial water-level), on the developed CCTPF-structures in hot-leg are extensively studied. Variations of the spatial distribution of phases with time are evaluated. Flow-structures in the hot-leg are characterized and parameterized in terms of statistical parameters extracted from the time variation of pressure drop (PD) and volume fraction (VF) across the flow domain. CI-based hybrid methodology employing neuro-biological schemes with the evolutionary-based algorithm (GA tuned MLFFNN with BPA) is developed using ‘C’ programming language to predict the flow-situation (occurrence or absence of plugging/blocking) in the hot-leg using the extracted statistical parameters as input. A computational approach is also developed to relate the flow-situation (occurrence or absence of plugging) in the hot-leg with the working conditions of PWR. Plugging is found to be most responsive to the gas-flowrate. Plugging/blocking easily occurs at a high gas-flowrate. It may occur even at moderate gas-flowrate when the initial stored water-level in hot-leg crosses the threshold limit. It is found that the developed methodology is able to perfectly capture the relationship between the flow-condition in hot-leg and the said statistical parameters and predict the flow-situation with a high success rate. The complex nonlinear relation between the flow-situation in the hot-leg and the working conditions is also perfectly captured by the developed computational approach
Tectono-metamorphic Evolution of the Madurai and Trivandrum Blocks of Southern Granulite Terrane, South India: Relevance to Gondwanaland Assembly
No full textThe southern part of Southern Granulite Terrane is separated into Trivandrum Block (TB) in the south from Madurai Block (MB) to the north by the Pan-African Achankovil shear zone system (AKSZ). A combined structural, metamorphic, geochemical and geochronological data is presented here from the common lithologies of the MB and TB to understand the tectono metamorphic evolutionary history of this terrane. Detailed field-based analysis of contrasting mesoscale structures and deformation kinematics in the granulite facies rocks across the AKSZ show distinct differences in the geometry of superposed fold structures between the MB and TB prior to their accretion along the AKSZ. Deformation microstructures and garnet-bearing melt-hosted syn-D3 extensional shears attest to the persistence of high temperature during D2 D3 deformations. The metamorphic temperatures and pressures estimated from different lithologies of the MB and TB using various thermobarometers are of the same range i.e. 600–880 °C and 5–8 kbar. The similar clockwise P-T path retrieved by phase equilibrium modelling from the MB and TB represents the last deformation metamorphism shared between the MB and TB during their accretion along the AKSZ. The distinct evolutionary history of the MB and TB is supported by the chronological contrasts between them e.g. the prominent Mid Neoproterozoic (~ 750 Ma) dates in the MB are rare in the TB, and the Paleoproterozoic (~2200 Ma) dates in the TB is rare in the MB. The strong imprints of 500–600 Ma monazite ages shared between the TB, MB and AKSZ attest to the deformation-metamorphism occurred during their Late-Neoproterozoic to Cambrian accretion along the AKSZ. The geochemical data from various lithounits suggest post-Archean granitoid affinity and subduction settings in both the blocks. The structural discordances along with the differences in metamorphic P-T conditions, geochemistry and chronological contrasts suggest that both the blocks have distinct crustal evolutionary histories prior to their accretion along the AKSZ. From the new data, a southward subduction model is proposed which provides insight into the subduction–accretion–collision tectonics associated with the Late-Neoproterozoic to Cambrian evolutionary history of this region. Integration of structural-metamorphic and chronological data from Madurai and Trivandrum Blocks (India) and south-central Madagascar suggests that the TB is equivalent to Androyan and Anosyan domains in southern Madagascar; by contrast, the MB is tectonically equivalent to central Madagascar which includes the Antananarivo and Itremo-Ikalamavony Blocks. Thus, it is concluded that the block north of the Pan-African Achankovil Shear Zone Ranotsara Shear Zone comprising the Madurai Block (India) and central Madagascar share a common history, but this is different from the southern block comprising the Trivandrum Block (India) and the high-grade gneisses and felsic intrusives of southern Madagascar. The present study propose that the sinistral steep-dipping Ranotsara Shear Zone separating the southern and central Madagascar continues into India as the AKSZ – the accretion boundary between the Trivandrum and the Madurai Blocks
Mechanical and Tribological Behaviour of Natural Fiber (Eulaliopsis Binata) Reinforced Polymer Composite
Get PDFEnvironmental awareness today motivates the researchers, worldwide on the studies of natural fiber reinforced polymer composite and cost effective option to synthetic fiber reinforced composites. The availability of natural fibers and ease of manufacturing have tempted researchers to try locally available inexpensive fibers and to study their feasibility of reinforcement purposes and to what extent they satisfy the required specifications of good reinforced polymer composite for different applications. With low cost and high specific mechanical properties, natural fiber represents a good renewable and biodegradable alternative to the most common synthetic reinforcement, i.e. glass fiber. Despite the interest and environmental appeal of natural fibers, there use is limited to non-bearing applications, due to their lower strength compared with synthetic fiber reinforced polymer composite. The stiffness and strength shortcomings of bio composites can be overcomed by structural configurations and better arrangement in a sense of placing the fibers in specific locations for highest strength performance. Accordingly, extensive studies on preparation and properties of polymer matrix composite (PMC) replacing the synthetic fiber with natural fiber like Jute, Sisal, Pineapple, Bamboo, Kenaf and Bagasse were carried out. These plant fibers have many advantages over glass fiber or carbon fiber like renewable, environmental friendly, low cost, lightweight and high specific mechanical performance. There are many potential natural resources, which India has in abundance. Most of it comes from agriculture or forest. Eulaliopsis Binata (EB) fiber (locally known as “sabai fiber”) is one of such fiber whose potential as a reinforcement material in the PMCs has not been studied to an extent that comparable to jute, banana, bamboo, sugarcane etc. This fiber plant belongs to “poacceae” family of plant kingdom, which is known for its good fiber quality. These plants are grown in the eastern part of India along with some Asian countries such as China, Nepal, Pakistan, Myanmar, Thailand, Philippines, and Malaysia etc. The eulaliopsis binata (EB) fiber plant is generally grown on waste lands and also contributes to the soil conservation of the inclined and waste lands. The fiber quality of this plant could be recognized by its existing applications of the fibers as rope, mats, carpets, sofa sets, wall hangings and other sophisticated, fashionable articles, which have proved its worth as a structural material with reasonably good mechanical properties. A fiber to be used as reinforcement material must possess cellulose, hemicellulose and lignin along with other constituents like carbon, which makes it lighter. This fiber structure consists of 52% cellulose, 27% hemicellulose and 17% lignin along with other constituents such as ash and moisture etc. The constituents of the fiber material conform the requirements to be used as a reinforcement material in polymer based composites for structural and other applications. In India, the EB plants are cultivated in various parts of India such as Odisha, Uttar Pradesh, Bihar, West Bengal, Punjab, Haryana and Himachal Pradesh. The availability of EB fiber in India is about 3, 50,000 tons out of which only 82,000 tons are used in paper industry. The EB fiber is provides 25% of total fiber raw material requirement of India for various applications. These plants once grown, provide yield for 10-15 years and the cost of cultivation per acre decreases with progressing years from 47.89 dollar from the 1st year to 5.44 dollar in the 12th year due to lower maintenance requirements. From the economic point of view, EB plantation is very economical with an average net return 323 dollars per annum from the degraded lands whose opportunity cost is almost zero. The cost of EB long fibers per kilogram varies between 5-8 Indian rupees. The EB plants are considered to be the “money plants” due to cheap and profitable cultivation throughout the year. Against this background, the present research work has been undertaken with an objective to explore the use of natural fiber Eulaliopsis Binata as a reinforcement material in epoxy base. The work presented in this dissertation involves investigation of three distinct problems of natural fiber composites: i. A study of favorable mechanical properties of Eulaliopsis Binata fiber in thermosetting matrix composite. ii. Investigation of weathering behavior of Eulaliopsis Binata fiber composites and its influence on the mechanical performance iii. An experimental investigation of tribological properties (abrasive and erosive) of Eulaliopsis Binata reinforced epoxy composite. To study the mechanical properties of the composite, different weight fractions of fiber have been taken. Usual hand-lay-up technique has been adopted for manufacturing the composite. To have a good compatibility between the fiber and matrix, chemical modification of fibers such as acetone,
alkali, and benzoyl-chloride and treatments has been carried out. It was found that benzoyl-chloride treated fiber composite exhibits favorable strength and stiffness in comparison to other treatments. Moisture absorption behavior of both treated and untreated fiber composite was also carried out. The moisture absorption kinetics of the composite has also been studied. The study confirms that the Fickian’s diffusion can be used to adequately describe the moisture absorption in the composite. The EB fiber epoxy composites exhibited better abrasive wear resistance properties as compared to neat epoxy. However, it is limited to twenty weight percent in comparison to thirty weight percent for strength and modulus under all tested conditions. The formation of fibrils and debonding between fiber and matrix material due to low load transfer is the main cause of reduction in fiber content for wear analysis. To study the tribo-potential of Eulaliopsis Binata fiber, solid particle erosion behavior by air jet erosion test rig have been carried out. All these tests have been carried out as per ASTM standard. The solid particle erosion test clearly indicates that the composite behavior is semi-ductile in nature. There are other fabrication techniques available like injection moulding, compression moulding and extrusion, where the volume fraction of reinforcement can be increased. In addition, there are other chemical methods by which the fiber surface modification could be carried out. This work can be further extended to those techniques. However, the results reported here can act as a starting point for both industrial designer and researchers to design and develop polymer matrix composite components using Eulaliopsis Binata fiber as reinforcement. The whole dissertation has been divided in to seven chapters to put the analysis independent of each other as far as possible. Major works on mechanical characterization, moisture absorption characteristics, abrasive and erosive wear characteristics of EB-epoxy composite is given in chapter 3, 4, 5, and 6 respectively
Phase and Photoluminescence Behaviour of Rare-Earth Doped Zirconia Nanopowders for Luminescent Applications
No full textThe concept of this Ph.D. research work is to explore the potential use of zirconium oxide as an inorganic oxide-based luminescent material due to its excellent optical properties such as wide bandgap, better transparency, high refractive index and low phonon energy. A large transparency window from short ultraviolet to near-infrared frequencies and the presence of low phonon energy in the zirconia host can avail low to high activator concentrations to widen its luminescent applications. Among three polymorphs of zirconia, the tetragonal and/or cubic phase of zirconia are considered stabilized phases and has been explored for different luminescent applications. Most of the literatures stated that the stabilized phases can be accomplished by either decreasing the particle size or incorporating the trivalent rare-earth ions such as Ce3+, Eu3+ and Tb3+ in the zirconia matrix to illuminate blue, red and green emissions, respectively. Also, it revealed higher concentration of rare-earth ions for stabilizing zirconia phases up to moderate temperatures. In addition, the stabilization of zirconia phases relies on the size of the initial or as-synthesized particles. It has been found that the wet chemical synthesis with the use of sodium borohydride as a precipitant supports to form ultrafine nanoparticles in the as-synthesized condition and minimizes the particle’s growth during calcination process. Also, the calcination atmospheric conditions depict the stabilization along with modification in the photoluminescence behaviour due to the alteration of particle size, lattice parameter, and strain. However, the influence of inert calcination atmosphere on the structural and luminescence behavior of Ce3+ / Eu3+ / Tb3+-ions based zirconia luminescent materials is found limited. So, the main objective of this work aims to explore the phase and photoluminescence characteristics of blue / red / green based zirconia luminescent materials, by considering lower (i.e., 0.1, 0.5 and 1 mol %) and moderate (i.e., 3 and 6 mol %) concentration of dopant (i.e., Ce3+/ Eu3+/ Tb3+) via adopting precipitation route using sodium borohydride as a precipitant and calcined under air and argon atmosphere to demonstrate these materials in latent fingerprint, anti-counterfeiting and near white light emission applications. This research work explores the influence of dopant concentration and calcination atmosphere (air and argon) on the phase stabilization and photoluminescence behaviour of zirconia. It also discloses the correlation of phase and photoluminescence behaviour of rare-earth-based zirconia luminescent materials. The nanosized ultrafine particles with tetragonal and monoclinic phases of zirconia were observed at lower dopant concentrations, and better crystalline behaviour of tetragonal zirconia was found at moderate dopant concentrations up to moderate calcination temperature. Phase analysis of zirconia has been investigated based on particle size, lattice parameter and strain by considering XRD, FESEM and Raman spectroscopy. Valence state of Ce, Eu and Tb in zirconia sample calcined under air and argon atmosphere has been analysed through XPS analysis. Further, the luminescence behaviour of Ce3+/ Eu3+/ Tb3+-based zirconia luminescent materials has been examined based on the crystallinity, particle size and distortion/strain. Moreover, the photoluminescence characteristics such as excitation/emission behaviour, asymmetric ratio and CIE coordinates of Ce3+/Eu3+/Tb3+ based zirconia nanopowders have been studied by dopant concentration, calcination atmosphere at different excitation wavelengths. The Ce3+-doped zirconia samples indicate violet-bluish colour, and this blue emissive Ce3+- doped zirconia nanopowders were applied for latent fingerprint visualization at porous and non-porous substrates under UV-illumination of 254 nm. The photoluminescence characteristics feature of Eu3+- doped zirconia nanopowders suggested shades of dual emissions at different excitation wavelengths for the samples. The tuning of emission of Eu3+-doped zirconia was utilized in the advanced security feature of anti-counterfeiting at the UV illumination of 254 nm and 365 nm. The asymmetric ratio i.e., G/B ratio and CIE chromaticity coordinates indicate green emission for Tb3+-doped zirconia nanopowders. Further, an appropriate amount of green Tb3+-doped zirconia powders have been mixed with the blue (Ce3+) and red (Eu3+) emissive zirconia powders to illuminate near white emission
Silanized and Chitosan Conjugated Graphene Oxide: Synthesis, Characterization and Evaluation of Its Potential as Biomaterial and Drug Delivery Vehicles
No full textIn recent years, graphene oxide (GO) has been explored for various application in biomedical engineering that include biosensing, tissue engineering and drug delivery. However, the biomedical application of GO is often being strongly scrutinized because of its potential toxicity. A strategy to surmount this problem is to functionalize GO with bioactive molecules. For this purpose, we have decided to explore three kinds of functionalized GO, namely silanized graphene oxide (SiGO), reduced silanized graphene oxide (rSiGO) and chitosan conjugated graphene oxide (CSGO). Recently, SiGO has shown good performance as reinforcing material. However, its biological properties, especially the cytocompatibility and in vivo compatibility have not been investigated in details. rSiGO, a derivative of SiGO, has not been explored as a biomaterial yet; so we include it in our study. In the case of CSGO, chitosan was chosen considering the promising performances of chitosan-GO composites as biomaterial. All the materials were subjected for comprehensive characterization. The goals of the thesis are: (i) to study the in vitro cytocompatibility and in vivo compatibility of SiGO, rSiGO, and CSGO, and (ii) to evaluate its performance as osteogenic material and drug delivery vehicles. The purpose of setting such aims is to find out the suitability of the aforesaid functionalized GO for its application in tissue engineering and drug delivery. The whole study is divided into three main parts. In the first part, we have reported the synthesis and physico-chemical characterization of five materials namely GO, reduced GO (rGO), SiGO, rSiGO and CSGO. GO was synthesized by modified Hummer’s method. SiGO was synthesized by treating GO with (3-aminopropyl) triethoxysilane (APTES). Both GO and SiGO were reduced through hydrazine treatment to obtain rGO and rSiGO. CSGO was prepared by crosslinking GO with chitosan using EDC-NHS. Physico-chemical characterization of the functionalized GO was done by XRD, FT-IR, Raman spectroscopy, XPS, elemental mapping, SEM and TEM. Silanization led to an increase in the interlayer distance and disorder in the lattice which became more prominent in the case of rSiGO. Chitosan functionalization showed minimal effect on basic architecture of GO. In the second part of the study, in vitro cytocompatibility of the materials was tested in details along with the acute toxicity study in vivo in murine model. Study of the in vitro toxicity of functionalized materials on three different cell lines namely primary human dermal fibroblast (HADF), murine embryonic fibroblast (NIH 3T3) and human osteosarcoma cell lines (MG63) revealed that toxicity of functionalized GO was significantly less than GO. Among all the functionalized derivatives, CSGO was found to be the most cytocompatible. The effect of functionalization was found concentration dependent which was more prominent at higher concentration of the materials. We further showed that in vitro activation of macrophage was less in the case of functionalized GO in comparison to GO. Study of the acute toxicity in the murine model indicated that GO was mildly hepatotoxic at experimental concentration whereas functionalized GO were not.In the last part, we evaluated the performances of these functionalized materials as (i) osteogenic biomaterials, and (ii) as a delivery system for hydrophilic anticancer drug. Analysis of the expression of different osteogenic differentiation markers such as runx2, collagen type I, alkaline phosphatase, osteocalcin, in human mesenchymal stem cell (hMSCs) revealed that CSGO possess the highest osteogenic potential among all the samples. Osteogenic differentiation induced by all other materials was almost same to that of GO. The loading of doxorubicin hydrochloride was almost same in the case of GO and SiGO but the release was higher in the case of SiGO. Further, among all samples, SiGO was found as the best drug delivery system in terms of efficacy when tested in vitro in 2D human hepatocarcinoma model. In the appendix of the thesis, we also reported the reinforcing effect of functionalized GO in polymeric film in the context of tissue engineering application. The study altogether implied that both SiGO and CSGO are more cytocompatible than GO and could be better alternatives of GO for tissue engineering and drug delivery application