Browsing by Author "Mamta Sharma"

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Genesis of natural cokes: Some Indian examples
(Elsevier B.V., 2008) Ashok K. Singh; Mamta Sharma; Mahendra P. Singh
In Indian coalfields huge amounts of natural coke have been produced due to magmatic intrusions. Jharia Coalfield in eastern part of India alone contains approximately 2000 Mt of baked coking coal as a consequence of these intrusions in the form of discordant and concordant bodies. This paper is an effort to investigate the effect of carbonization in two intrusion affected coal seams of Ena (seam XIII) and Alkusa (seam XIV) collieries of Jharia Coalfield. Natural coke is derived from coking coal under in-situ conditions due to intense magmatic induced heat and overburden pressure. Natural coke is characterized by the presence of low volatile matter and high ash contents and organic constituents showing isotropy and anisotropy. Through physical, petrographic and chemical properties of natural coke or 'jhama' as determined by various methods it has been established that the reactives in the unaltered coals (vitrinite, liptinite, pseudovitrinite, reactive semifusinite, etc.) are < 25.0 vol.%, moisture < 2.5%, volatile matter < 15.0% and hydrogen < 4.0%. The temperatures attained in the coal seams have been deciphered using some standard models, which indicate that a temperature ~ 1000 °C was attained. This produced huge amount of anisotropic and deposited carbons. An attempt has been made to understand the factors that influence the genesis of natural coke and heat altered maceral products in coals in Indian coalfields. © 2008 Elsevier B.V. All rights reserved.
Microstructures and microtextures of natural cokes: A case study of heat-affected coking coals from the Jharia coalfield, India
(Elsevier B.V., 2007) Ashok K. Singh; Mahendra P. Singh; Mamta Sharma; Sunil K. Srivastava
In Jharia coalfield, nearly 1250 Mt of coking coal has been devolatilized due to igneous intrusives and ∼ 1900 Mt due to mine fires. This paper is an effort to investigate the effect of carbonization in two intrusive affected coal seams of Ena (seam XIII) and Alkusa (seam XIV) collieries of this coalfield. Through petrographic studies by microscopy, characterization of normal and heat-affected coals was carried out. The microstructures and microtextures produced due to extraneous heat have been related to nature and extent of heat, location of heating source, and quality and quantity of natural coke produced. Based on the results of this study and earlier studies, an effort has been made to study the classification scheme for microtextures of natural cokes generated through in-situ carbonization of the coal seams. It has been observed that in case of such heat effects under overburden pressure, the anisotropy is much more pronounced as compared to laboratory-carbonized cokes. In the mildly carbonized coals (pre-plastic phase, < 300 °C) the vitrinite attained higher reflectance than normal vitrinite, liptinite started disappearing, and inertinite remained unaffected. In the moderately affected coals (plastic phase, 300-500 °C), mesophase spheres and fused natural cokes were generated from the reactives (vitrinite and liptinite maceral groups), the liptinites disappeared, and structurally, the inertinites remained almost unchanged with slight increase in the reflectance value. In the severely heat-affected coals (post plastic phase, > 500 °C) the identified microtextures were mesophase spheres, different shapes and sizes of natural cokes, graphitic sphaeroliths, pyrolytic carbons, inerts with morpho-structural changes and slightly higher reflectance values, and altered and unaltered mineral matters. A gradual change in the heat-affected coals with increasing temperature was observed with respect to location of intrusive body. It has been concluded that, barring the effect of pressure, the changes due to heat effect on coking coals, whether in situ or laboratory carbonization, are almost similar. Organic and inorganic constituents undergoing changes at a particular temperature are nearly similar in both conditions. In case of pronounced overburden pressure, flow structures develop in the natural coke groundmass. Higher reflectance and very strong anisotropy, as evidenced in completely baked coking coals with fine to very coarse mosaic structures, may be a good criterion to explore these heat altered coals for the carbon artifact industry and further efforts are required to be made in this line. © 2006 Elsevier B.V. All rights reserved.
SEM and reflected light petrography: A case study on natural cokes from seam XIV, Jharia coalfield, India
(Elsevier Ltd, 2013) Ashok K. Singh; Mamta Sharma; Mahendra P. Singh
This paper is an attempt to characterize the natural coke (local name 'jhama') and associated unaltered coal drawn from seam XIV, Burragarh colliery, Jharia coalfield with help of Scanning Electron Microscopy (SEM) and organic petrography techniques. The organic petrography was carried out using DM4500 advanced polarizing microscope, while scanning electron micrography was performed on a JEOL-840A JSM. The coal and natural coke samples were pulverized and beneficiated, and fractions of different sizes (50-0.50 mm) at varying specific gravities (1.4 to >1.8) were subjected to this study with a view to expose the concentrations of microstructures and microtextures of natural coke in different specific gravity fractions. In addition, an effort was made to compare the variety of textures as seen with the help of optical microscopy with those as revealed under scanning electron microscope. SEM photographs revealed some textural features of natural coke, which remained unexposed in optical microscopy. This may be due to the use of unpolished samples and greater depth of focus achieved by SEM. The features which were studied through these two microscopy methods are characterization of carbonized matrix, mosaics, flow textures, micro, meso and macropores and cracks formed due to escape of volatiles including properties of mineral matter or their altered products (glassy matrix). The different washability fractions of Burragarh natural coke have shown that there is gradual decrease of reactive macerals and increase of anisotropic mosaics, flow textures and deposited carbons up to specific gravity of 1.70. The approach thus enabled a combined maceral-mineral analysis, which bears good implications on academic and industrial use of natural cokes. © 2013 Elsevier Ltd. All rights reserved.
SEM study of some Indian natural cokes (jhama)
(International Pittsburgh Coal Conference, 2010) Ashok K. Singh; Mamta Sharma; Mahendra P. Singh; Nandita Choudhury
Scanning Electron Microscopy (SEM) is an indispensable tool for studying the mineral and organic matrix, particularly in the baked coals or natural cokes, which form due to magmatic intrusion (dykes and sills) in coal seams. In this paper this tool has been used to demonstrate the relationship between morphology and genesis of natural coke or jhama samples derived from Damodar Valley Coalfields of India. The SEM studies were carried out using JEOL-840A JSM under magnifications ranging from 200X to 50000X on selected heat altered coal/natural coke, CPC and graphite samples to decipher the microstructures of these samples and comparative studies. The chips of coal lithotypes, heat altered coal/natural cokes, CPC and graphite, of about 1cm size were isolated from the coal blocks using hammer, chisel and forceps and were washed with alcohol to remove the superficial dust and mounted on brass stubs using silver paste as glue and coated with gold (thickness about 400A°). SEM photographs reveal some textural features of natural coke which would not be detectable using optical microscopy. The similarity between images of natural and artificial coke and also the mineral assemblages present in the natural coke matrix is proof that temperatures over 350°C were experienced during contact metamorphism. Due to its greater depth of focus compared to optical microscopy, SEM provides information on textures in unpolished samples complementary to microscopic data. The main findings include identification of carbonized matrix, mosaics and flow structures of various dimensions, nature and dimensions of the micro, meso, macropores and cracks formed due to escape of volatiles and relationship and association of mineral matter or their altered products (glassy matrix) with the generated pores. The system thus permits a combined maceral-mineral analysis, which can be used to advantage in coal geology studies.
Study of Hydrocarbon Source Potential of Kapurdi Lignites of Barmer Basin, Rajasthan, Western India
(Springer, 2021) P.K. Rajak; V.K. Singh; Aniruddha Kumar; Vishvajeet Singh; Ankita Rai; Shweta Rai; K.N. Singh; Mamta Sharma; A.S. Naik; Neeraj Mathur; Prakash K. Singh
The present investigation is an attempt to study hydrocarbon source potential of early Paleogene lignites of Kapurdi, Barmer Basin. The samples collected from the working mines have been subjected to petrographic and geochemical analyses. The petrographic study includes both maceral as well as microlithotype analyses whereas geochemical study includes proximate and ultimate analyses. Besides, rock eval pyrolysis, FTIR and NMR studies have also been carried out. The analytically generated data were also correlated and checked with empirical equations. The study shows that these lignites of Barmer Basin are rich in kerogen type-III organic matter and contain high concentration of reactive macerals (huminite + liptinite) to the tune of ∼98% (mineral matter free basis) and they have attained low maturity (Rmax is 0.43%). These lignites have a fairly high conversion factor (95–97%) and oil yield (65–67%) which is also supported by the rock-eval data. Further, 1H and C13 shifts of NMR also suggest a high potential of hydrocarbon of Kapurdi lignites. © 2021, GEOL. SOC. INDIA.
Variability in phytophthora drechsleri f. sp. cajani and effect of temperature
(Journal of Pure and Applied Microbiology, 2017) Chandra Kant Singh; Ichini Sudhir; Ramesh Chand; Vineeta Singh; Mamta Sharma
The present experiment was undertaken to study the cultural, morphological and pathological variation in six isolates of Phytophthora cajani. The isolates were collected from pigeonpea growing areas of eastern Uttar Pradesh. Isolates exhibited considerable variations in cultural characters and growth on potato dextrose agar medium. The universal ITS1 and ITS4 primers showed the difference among P. cajani isolates. There was significance influence of temperature on the growth of isolates, however isolates could not be differentiated based on the temperature. The average growth (1.69 cm2) at 30°C temperature was recorded with all the isolates followed by average growth (1.25 cm2) at 35°C temperature. The maximum radial growth (3.6 cm2) was observed at 96 h in isolate PDC015-1. The isolate PDC013-1 and PDC014-3 showed highest 47.0% plant mortality on ICP 7119 genotype. Among the isolates PDC014-3 killed 28.6% plants after 4th day of inoculation.