Influence of simultaneous doping of Sb & Pb on phase formation, superconducting and microstructural characteristics of HgBa2Ca2Cu3O8+\delta

We report systematic studies of structural, microstructural and transport properties of (Hg_0.80 Sb_0.2-x Pb_x)Ba_2 Ca_2 Cu_3O_8+\delta (where x = 0.0, 0.05, 0.1, 0.15, 0.2) compounds. Bulk polycrystalline samples have been prepared by two-step solid-state reaction route at ambient pressure. It has been observed that simultaneous substitution of Sb and Pb at Hg site in oxygen deficient HgO_\delta layer of HgBa2Ca2Cu3O8+\delta cuprate high-Tc superconductor leads to the formation of Hg-1223 as the dominant phase. Microstructural investigations of the as grown samples employing scanning electron microscopy reveal single crystal like large grains embodying spiral like features. Superconducting properties particularly transport current density (Jct) have been found to be sensitive to these microstructural features. As for example (Hg0.80Sb0.05Pb0.15)Ba2Ca2Cu3O8+\delta compound which exhibits single crystal like large grains (~ 50 micrometer) and appears to result through spiral growth mechanism, shows highest Jct (~ 1.85 x 103 A/cm2) at 77K. A possible mechanism for the generation of spiral like features and correlation between microstructural features and superconducting properties have been put forward.Comment: 16 pages, 6 figures. Accepted in Physica

ADDITIVES FOR CRACKED FUEL OIL TO ENHANCE STORAGE AND THERMOXIDATIVE STABILITIES

The cracked fuel oil comprises mainly of unconverted bottoms from residue conversion in H-oil unit, whichhas undergone significant thermal cracking.The sediment content of this oil is of the order 700-1500 mg/ 100ml as against the required value of 250 mg/100ml this fuel oil caused frequent plugging of the fuel lines and burners. High asphaltene and thermoxiditively unstable constituents cause large-scale deposits during storage, transportation and uses. Several synthesized addtives/compounds were evaluated tor stabilzation of these fuel oils. The fuel oil was doped with these dispersants/stabilizers in 5000 PPM dosage.It was observed that these additives cause considerable reduction in total sediments and unfilterable residue after aging at elevated temperatures and storageovera longperiod of time atmoderate temperatures.A synergeticcombination of several disprsants and stabilizers developed which are able to reduce the sediments almost 10 times and reduction of unfilterable residue by 2.5 times. it is thus possible to improve quality of cracked fuel oil to an acceptable performance level by blending it with a synergistic combination of additives

Studies on sulphonates for enhanced oil recovery

The hydrocarbon/surfactant solution IFT characteristics for several commercial and synthesized sulphonates were studied with various alkanes and the crude oils. It was found that only sulphonates of specific structures and their combination in specific proportions produced ultra low interfacial tension (ULIFT) (<10-2 dynes/cm) with specific hydrocarbons and crude oils. The mixtures of sulphonates of specific structures in specific proportion, which produced ultra low tension with one or more crude oil also, gave higher tertiary recovery under laboratory conditions as compared to commercial sulphonates. The solubilization of hydrocarbons by sulphonates studied also show that very high solubilization (20 moles/g) of sulphonates is highly specific and depends upon the structure of sulphonates and their specific combinations in specific proportions. None of the commercial sulphonates solubilized crude oil in large quantities and only a few combinations of sulphonate solutions solubilized large quantities of different crude oils. These sulphonates produced much higher oil recovery of Ankleswar crude under laboratory conditions in low-tension floods. It is recommended that pilot studies be taken for synthesis of these sulphonates in large quantities for undertaking field trials to study the tertiary oil recovery from Indian oil fields and the economics of recovery and conditions of substantial recovery of crude oil established in view of high crude oil prices prevalent from time to time. Keywords: Enhanced oil recovery, Sulphonates, Interfacial tension, Crude oil, Reservoi

Urea, thiourea and guanidine derivatives as multifunctional fuel stabilisers

Different N-substituted derivatives of urea, thiourea and guanidine have been synthesised and characterised for structural information by FT-IR and 13C NMR spectroscopy. Accelerated stability tests have been done to evaluate their sediment inhibition and dispersant characteristics on distillate fuels containing high proportions of unstable components and results discussed. It is inferred that urea and guanidine derivatives not only inhibit the reactions responsible for sedimentation in the test fuel but also effectively disperse the gum and sediment formed. It is concluded that the nature of substituents on the central carbon atom and on the amino groups determines the performance behaviour of these compounds. q 2002 Elsevier Science Ltd. All rights reserved

BEHAVIOR OF ALKYL ARYL SULFONATE IN HEPTANE

The interfacial tension, surface tension, intrinsic viscosity and solubilization of a series of Hexadecyl long chain, alkyl cycloalkyl and alkyl aryl sulfonates have been studied in Heptane as the hydrocarbon medium. It was observed from a distinct and significant change in the properties of sulfonate in Heptane media, within a narrow range of concentration, upon micellization (1,2). A decrease in magnitude of hydrocarbon/water interfacial tension continues even after micellization, indicating that surfactant continues to contribute to surface concentration at hydrocarbon/air & hydrocarbon/water interface even beyond cmc. The surface tension starts increasing after certain concentration beyond cmc, which indicates that number of surfactant molecules at air/hydrocarbon interface, decrease and instead, contribute to micellization. The axial ratio and micellar weights show that medium size micelles of un-spherical shape and narrow size distribution are formed in hydrocarbon medium (3,4). The solubilization of alkanes in aqueous sulfonates does not depend upon the hydrocarbon/ water interfacial tension but is directly related to the structure of the hydrocarbon portion of the sulfonate. While saturates hardly increases the solubilization (5.6). The mono and di- rings aromatic derivatives, Hexadecyl Naphthalene sulfonate in particular, greatly enhances the solubilization. The structure of hydrocarbon solubilized as well as that of sulfonate influences the amount of solubilization. The studies are important from the point of view of application of sulfonates as surfactants and additives. KEYWORDS : Sulfonates, Heptane, Interfacial Tension, Surface Tension, Intrinsic viscosity, Micelle, Solubilization, Thermodynamic, Shape & Size

BEHAVIOUR OF POLYNUCLEAR ARYL SULFONATES

A Series of Hexadecyl poly-nuclear aromatic, Decalin and Tetralin sulfonates have been synthesized. The detergency increases with the increase in size of aromatic moiety in these sulfonates. The structure thus has profound influence on the surface and micellar properties of the sulfonates. The studies are important from the point of view of application of synthetic sulfonates as additives / surfactants in place of petroleum sulfonates. KEY WORDS Hexadecyl poly-nuclear sulfonates, aqueous & non-aqueous medium, surface tension and energy, CMC, micelle, shape and size of micelle, thermodynamic parameter, solubilization, detergency, viscosity

Studies on Acid Sludge - Part V: Hydrocarbon/ Water Solubilizing Characteristics of Sulphonates

The hydrocarbon/water micro-emulsions prepared from sodium petroleum sulphonates obtained from various acid sludges have been evaluated as additives for solubilized metal working and fire resistant hydraulic fluids. The type and the quantities of hydrocarbon solubilized per gram of the sulphonates depend upon the structure of the hydrocarbon portion of the sulphonate and the proportion of disulphonates. Sulphonates with a higher proportion of carbon in paraffinic side chains solubilise larger quantities of hydrocarbons. The solubilisation of hydrocarbon decreases with increasing content of disulphonates and increases in the presence of long chain alcohols. The tolerance towards the presence of electrolytes, especially bivalent cations, how,ever, increases due to the presence of disulphonates. These sulphonates are particularly useful in preparing hydrocarbon micro-emulsions in water containing relatively large proportion of electrolytes particularly the bivalent cations

Studies on Acid Sludge: Part IV-Separation and Characterization of Mono & Disulphonic Acids

Mono and disulphonic acids have been separated from the acid sludges in the form of their barium salts by solvent extraction based on their solubility characteristics in chloroform and water. The suIphonic acids and their barium salts have been converted into their corresponding hydrocarbons by a modified desulphonation procedure. The probable structures of the hydrocarbons portions have been deduced by n-d-M , IR and UV techniques