Prakash K. Singh

Petrographic characterization and evolution of the Permian coal deposits of the Rajmahal basin, Bihar, India

Abstract Lower Gondwana rocks are exposed as narrow bands and discontinuous patches along the western edges of the Rajmahal Hills covering a large area of the Bengal Basin, North Bengal and Pumea. Two coalfields — Hura and Chuperbhita — have productive coal mines. Pillar coal samples from the working coal seams of Hura and Chuperbhita coalfields were collected and subjected to a detailed petrographic and geochemical study using refined procedures on a large number of samples. The results of the micropetrographic study reveal that the Rajmahal coals are rich in liptinite and inertinite contents. The fluorescence microscopy indicates that a major part, identified as argillaceous mineral matter under white incident light, is composed of liptinite macerals such as bituminite fluorinite and exsudatinite. The volatile matter and reflectance suggest these coals are subbituminous to high volatile bituminous B/C in rank. The quantitative relationships among maceral and microlithotype suggest that these coals were deposited in limnic to limno-telmatic conditions under very wet conditions that resulted from undisturbed peat that developed in situ along with subaquatic (limnic) sedimentation in swampy lakes. Further, the GI and TPI values indicate that the Hura coals were formed under oxic moor conditions with sudden episodes of flooding, while the Chuperbhita coals have originated in wet moors with intermittent moderate to high flooding. In addition, G.I. values suggest the formation of these coals in an upper delta/alluvial valley with braided plains.

Electronic Structure, Electrical and Dielectric Properties of BaSnO3 below 300 K

The electronic structure, electrical and dielectric properties of barium stannate, a semiconducting perovskite oxide prepared by solid state ceramic route were studied by employing X-ray photoelectron spectroscopy (XPS), Mossbauer and impedance spectroscopic techniques in the temperature range 77–300 K. X-ray diffraction (XRD) pattern of BaSnO3 confirms the cubic structure. Scanning electron microscopy (SEM) images show high porosity in the sample and the average grain size was found to be about 1.85 µm which corroborates with the particle size obtained through XRD line broadening analysis. Mossbauer spectra, at 298 and 78 K reveal that tin exists mainly in tetravalent, Sn4+ state. XPS study also shows the same results but it indicates the existence of a trace amount of Sn2+. Electrical conductivity and dielectric constant of this system have been measured in the temperature range 298 to 148 K and in the frequency range 10-2 to 106 Hz. Frequency and temperature dependent electrical conductivity/dielectric properties have been used to separate the contributions of grains and grain boundaries to the total observed conductivity and dielectric constant. Orientational polarisation and space charge polarisation contributes to the observed dielectric properties of the system.

Petrological and Geochemical Investigations of Rajpardi Lignite Deposit, Gujarat, India

The present paper entails the petrographic and chemical characteristics of the lignite samples drawn from the Rajpardi lignite deposit of Bharuch district, Gujarat. This lignite contains a high concentration of huminite which is dominated by telohuminite, followed by detrohuminite. Liptinite and inertinite macerals are very low in concentration. The dominant microlithotype is humite. Its elevated volatile matter and high hydrogen content depicts its perhydrous nature. The study reveals that this lignite originated in a limno-telmatic to telmatic condition. The paleomire is further characterized as a wet moor having moderate to high flooding with good tissue preservation and increasing bacterial activity.

Electrical behaviour of zirconium doped calcium copper titanium oxide

In this investigation, the effect of Zr substitution at the Ti site of the CaCu3Ti4O12 on the electrical properties has been studied. Samples with composition x = 0.00, 0.10 and 0.30 have been synthesized by the solid state ceramic route in the system CaCu3Ti4−xZrxO12. Powder x-ray diffraction data showed the formation of a single phase solid solution. The structure remains cubic similar to an undoped sample. The Seebeck coefficient, α, is measured on a thick pellet in the temperature range 500–800 K and is found to be negative in this temperature range, indicating n-type conduction in the temperature range of measurement. Dc resistivity, ρdc, and ac conductivity, σac, were measured to understand the mechanism of conduction. Immittance analysis is used to separate the contributions of the grains and grain boundaries to the total observed resistance. From the temperature and frequency dependence of ac conductivity, it is concluded that at and around room temperature conduction occurs due to thermally activated rotation of dipoles while at high temperature it occurs due to excitation of charge carriers at the conduction band edge and hopping at energies close to it. From the immittance analysis it is observed that activation energies of conduction for grains and grain boundaries are almost equal indicating the same mechanism of conduction.

Petrological and geochemical considerations to predict oil potential of Rajpardi and Vastan lignite deposits of Gujarat, western India

This paper entails the results of the investigations undertaken to assess the oil potential of two lignite deposits, Rajpardi and Vastan, from Gujarat, western India. They are ‘Low rank B’ type lignite. Petrographically, they are enriched in huminite and are low in liptinite and inertinite. Their elevated hydrogen content, in relation to carbon, has probably made them perhydrous in nature and oil prone. The reactivity of these coals during liquefaction has also been discussed in the light of petrofactor. Good correlation has been noticed between oil yield and conversion (r2 = 0.999) in both the lignite deposits. The VRr (0.24–0.35% in both lignites), H/C atomic ratio (0.11–1.39 in Rajpardi and 1.09–1.88 in Vastan), reactive maceral content (91.6–99.8 vol % mmf in Rajpardi lignite and 75.5–99.7 vol % in Vastan lignite) and VMdaf (64.8–67.9 wt % in Rajpardi lignite and 42.1–80.0 wt % in Vastan lignite) of these lignites have a favourable range required for a coal to generate oil. Huminite is seen to play a vital role in conversion and maintains a good correlation with it. The calculations show that these lignites have a high conversion (> 95%) and oil yield (> 65%).

Petrographic and geochemical characterization of coals from Tiru valley, Nagaland, NE India

In Tiru valley region of Mon district coals occur in Barail Formation and are of Oligocene age. This study is the first investigation on the petrographic and geochemical characterization of these coals. These thinly bedded seams (<2 m) need systematic exploration for proper evaluation of the resource. The coals are bright to moderately bright in appearance and at places look moderately dull. The study reveals that Tiru valley coals are sub-bituminous to bituminous-D in rank. The chemical study reveals that these coals are perhydrous in nature with moderately high volatile matter content. The sulphur content was probably increased with pyrite inclusion as the most abundant mineral. Vitrinite is the most dominant maceral group constituting nearly 98% of all the macerals while liptinite and inertinite occur in very low concentration. Facies-critical models used to decipher the paleodepositional environment suggest that these coals evolved under wet moor with moderately high flooding in the paleomire which allowed the sulphate reducing bacteria to thrive.

Petrological investigations of oligocene coals from foreland basin of northeast India

The results of the petrological investigations carried out on coal samples from the Oligocene deposits of Northeastern India (Assam, Arunachal Pradesh and Nagaland) have been discussed. These deposits occur in the Tikak Parbat Formation (Barail Group) and were probably deposited in the foreland basin. Petrographically, these coals are enriched in vitrinite macerals (65.8–96.6 vol %, mean 87.2 vol %) with variable concentrations of liptinite macerals (2.7–35.4 vol %, mean 11.9 vol %). They contain low concentration of inertinite (nil-3.3 vol %, mean 0.9 vol %) macerals. The microlithotype is dominated by vitrite (61.5–100 vol %, mean 90.8 vol %). An elevated volatile matter (44.15 – 60.20 wt %, mean 52.90 wt %, d.a.f. basis) and reflectance values (VRr 0.39–0.61%) put their rank as sub-bituminous type ‘C’ to high volatile bituminous type ‘C’. The GI and TPI values favour telmatic conditions of origin with high tree density and prolonged wet conditions. This is in agreement with the paleoenvironment interpreted from the vitrinite and liptinite-rich microlithotypes, which suggested a forest and reed facies. However, the presence of inertinite in some coal seams indicates tectonic upheavals / regression of the sea resulting to periodic and short span dryness of the basin.

Studies on thermal maturity and hydrocarbon potential of lignites of Bikaner–Nagaur basin, Rajasthan

In the present investigation, an attempt has been made to study lignite samples from the working mines of Bikaner–Nagaur basin of Rajasthan with reference to their maturity and their hydrocarbon potential. The study has been made on the basis of petrological and geochemical characteristics. The assessments made through the empirically derived equations have been cross-checked and correlated with the rock-eval data. The study reveals that the low rank coals of Bikaner–Nagaur basin contain mainly kerogen type-III organic matter and are dominantly composed of huminite (77–87%) with small concentrations of liptinite (4–11%) and inertinite (2–14%), which are worth liquefying to obtain liquid oil and gas. Further, the high conversion factor (93–95%) and high oil yield (63–65%) make them industrially significant, considering the vast lignite resource of the region.

Experimental study on demineralization of coal with Pseudomonas mendocina strain B6-1 bacteria to obtain clean fuel

We present the results of the investigations carried out on the demineralization of coal of the Rajmahal Gondwana basin of India using Pseudomonas mendocina strain B6–1. Petrographically these coals are characterized by high concentration of inertinite macerals with subordinate amount of vitrinite and liptinite macerals. The mineral matter content occurs in high concentration which gives a high ash yield. This coal contains relatively high content of major, minor and trace elements when compared with the Clarke values in coal. After the bacterial treatment a considerable reduction in the elemental content of oxygen, hydrogen and sulphur was seen. Reduction in the ash content (>5%) was achieved and variable degrees of removal of the various major, minor and trace element concentration was also noticed. Nearly 59% removal of Mn, 53% of Na, 13% of Fe was achieved among the major/minor elements while nearly 54% of As, 41% of Cd, 39% of Cu, 34% of Ni, 32% of Zn, 13% of Cr, 43% of Co and 66% of Pb could be removed. Arsenic, Fe and Ca have a strong positive correlation with the ash removal percentage indicating that the samples having increased concentration of these elements are prone to demineralization with Pseudomonas mendocina strain B6–1. Whereas the elements like Ni, Zn, Cr and Cu maintain a strong negative correlation with the ash removal percentage indicating that their enrichment could have hampered the process of demineralization.

Synthesis, crystallisation and microstructural study of perovskite (Ba,Sr)TiO3 borosilicate glass ceramic doped with La2O3

Abstract Various glass samples, of glass system [(Ba1−xSrx)TiO3]–[2SiO2–B2O3]–K2O with addition of La2O3, were prepared by melt quenched method. Differential thermal analysis of glass samples was carried out in the temperature range of 100–1200°C in order to study the kinetics of crystallisation behaviour. Glass samples were subjected to appropriate heat treatment schedules for their suitable crystallisation from glass to glass ceramics. X-ray diffraction analysis of glass ceramic samples indicated the presence of major crystalline phase of BaTiO3 along with some secondary phases of Ba2TiSi2O8 and Ba2Ti2B2O9. Scanning electron microscopy measurements were also performed to see the morphology of crystallites of the major/secondary phase formation in the glass ceramic samples. We found that La2O3 played an important role to increase nucleation and growth of the crystallites in the glassy matrix.