Browsing by Author "U.S. Rai"

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Chemistry and Characterization of Binary Organic Eutectics
(Chemical Publishing Co., 1998) U.S. Rai; R.N. Rai
Phase diagrams of benzil with each of naphthalene, β-naphthol and p-chloronitrobenzene show the formation of simple eutectics. The growth velocity (v) data studied at different undercoolings (ΔT) by measuring the rate of movement of interface in a capillary obey the Hillig-Turnbull equation, v = u(ΔT)n, where u and n are constants depending on the nature of materials involved. Using enthalpy of fusion values, obtained by the DSC method, enthalpy of mixing, interfacial energy, entropy of fusion, excess thermodynamic functions and radius of the critical nucleus were calculated. Microstructural investigations give characteristic features of the eutectics.
Chemistry and characterization of binary organic eutectics and molecular complexes. The urea-m-nitrobenzoic acid system
(Elsevier, 1998) U.S. Rai; R.N. Rai
Solid-liquid equilibrium data on a binary organic system involving urea and m-nitrobenzoic acid show the formation of a 1:1 molecular complex surrounded by two eutectics. Growth data studied by measuring the growth velocity (v) at different undercoolings (ΔT) by following the rate of movement of the interface suggest that they obey the Hillig-Turnbull equation, v = u(ΔT)n, where u and n are constants depending on the nature of the materials involved. From the heat of the fusion values, determined by the D.S.C. method, the heat of mixing, entropy of fusion, roughness parameter, interracial energy, radius of the critical nucleus and the excess thermodynamic functions were calculated. While the X-ray diffraction data show that the eutectics are not a mechanical mixture of the components under investigation, the microstructural investigations give their characteristic features. The spectral studies suggest intermolecular hydrogen bonding between the components forming the molecular complex. © 1998 Elsevier Science B.V.
Chemistry of Binary Organic Eutectics and Molecular Complexes: Phenanthrene-m.Nitrobenzoic Acid System
(1992) U.S. Rai; H. Shekhar
Phase diagram, linear velocity of crystallization, thermochemistry, microstructure, electrical conductivity, X-ray diffraction and spectral behaviour of phenanthrene-m.nitrobenzoic acid system have been studied. The results obtained in the present investigation have been discussed in the light of recent advancement in the area of organic eutectics and molecular complexes. © 1992, Taylor & Francis Group, LLC. All rights reserved.
Chemistry of organic eutectics and 1:1 addition compound: p-phenylenediamine-catechol system
(1989) U.S. Rai; K.D. Mandal
The phase diagram of the p-phenylenediamine-catechol system, determined by the thaw-melt method, shows the formation of a 1:1 molecular compound and two eutectics. The linear velocities of crystallization of the pure components, the eutectics and the addition compound, determined by measuring the rate of movement of the growth front in a capillary, suggest that crystallization data obey the Hillig-Turnbull equation v = u(ΔT)n. where u and n are constants and ΔT is the undercooling. Experimental values of the heats of fusion and the entropy of fusion and calculated excess thermodynamic functions were considered and the results were explained on the basis of cluster formation in the eutectic melt. X-ray diffraction data of the pure components, the eutectics and the addition com- pound infer that these eutectics are not simply a mechanical mixture of the two components; preferential ordering of atomic planes occurs during their formation. The IR studies carried out on this system suggest intermolecular hydrogen bonding between the two components which form the molecular compound. © 1989.
Chemistry of organic eutectics: Phenanthrene — benzoic acid and phenanthrene — cinnamic acid systems
(1990) U.S. Rai; H. Shekhar
Solid‐liquid equilibrium data for binary systems of phenanthrene with benzoic acid and cinnamic acid, expressed in the form of temperature‐composition curves, show the formation of a simple eutectic in each case. Linear velocity of crystallisation (v), studied by capillary method at different undercoolings (ΔT), suggests the applicability of Hillig‐Turnbull equation, v = u(ΔT) n, where u and n are constants depending on the nature of solidification. Data on heats of fusion of pure components and eutectics, determined by the DTA method, infer appreciable interaction among the components in the eutectic melts. To highlight the nature of interactions among the components forming the eutectic melt, the excess thermodynamic functions such as hE, sE, and gE were computed. Microscopic studies reveal that the structure of eutectic is different from those of the parent components. Infrared spectra, recorded in the region, 4000 —625 cm−1, indicate weak interactions among the components in the eutectic. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA
Crystallization behaviour of metal-nonmetal monotectic alloys; succinonitrile-pyrene system
(Elsevier Ltd, 2002) U.S. Rai; Pinky Pandey
The phase-diagram of succinonitrile-pyrene system determined by the thaw-melt method shows the formation of a monotectic (melting point, 143.3°C) and a eutectic (melting point, 55.3°C) at 0.025 and 0.744 mole fractions of succinonitrile respectively. The critical solution temperature is 48.7°C above the monotectic horizontal. Growth behaviour of the parent components, eutectic and the monotectic studied by measuring the rate of movement of the growth front in a capillary suggests the applicability of Hillig-Turnbull equation for the system.
Crystallization, thermal, phase diagram and microstructural studies of organic analog of metal-nonmetal monotectic alloy: 4-Bromochlorobenzene-succinonitrile
(2009) R.S.B. Reddi; Shiva Kant; U.S. Rai; R.N. Rai
The phase equilibrium data on an organic analog of a metal-nonmetal system involving 4-bromochlorobenzene-succinonitrile show the formation of a eutectic and a monotectic with a large miscibility gap containing 0.96 and 0.03 mole fractions of succinonitrile, respectively, with the consolute temperature of 180.0 °C. The heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated from the enthalpy of fusion values, determined by the DSC method using TA Instruments DSC-2010. The effects of solid-liquid interfacial energy on morphological change of monotectic have also been discussed. The microstructures of monotectic and eutectic show the lamellar growth characteristic. © 2009 Elsevier B.V. All rights reserved.
Developments and future directions of phase diagram, physicochemical and optical studies of binary organic complexes
(Elsevier Ltd, 2013) R.N. Rai; R.S.B. Reddi; U.S. Rai
The aim of this review is to emphasize solvent free or green synthesis, a most efficient utilization of starting materials to give maximum yield, and an alternative route to producing novel promising materials. In this regard the phase diagram study has shown applications in the determination of the precise composition of binary compounds of a specific nature and in the identification of the parameters that affect the crystal growth. To provide an overview worthy of phase diagram, physicochemical, thermal and structure investigations; studies of eleven systems, namely, urea–m-nitrobenzoic acid, urea–p-nitrophenol, urea–resorcinol, benzoin–o-phenylenediamine, pyrene–m-dinitrobenzene, vanillin–p-anisidine, resorcinol–p-dimethylaminobenzaldehyde, benzophenone–diphenylamine, anthracene–picric acid, 8-hydroxyquinoline–salicylic acid and 8-hydroxyqunoline–1,2,3-trihydroxybenzene forming organic complexes, have been reported. In addition, the original data of a newly synthesized complex of m-hydroxybenzaldehyde (HB) and p-chloroaniline (CA) is being reported for the first time. The phase diagram of HB–CA system also shows the formation of a complex in 1:1 M ratio, and two eutectics on either side of the complex. The complex's formation was studied using FTIR, NMR, DSC and powder X-ray diffraction techniques. The thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated using the heat of fusion values. The single crystal growth and the atomic packing studies of some of the complexes have confirmed the formation of complexes. The optical transmittance efficiency and transparency of novel HB–CA complex crystal were found to be 70% and 399 nm, respectively. © 2013 Elsevier Ltd
Dielectric and ac impedance studies of nanostructured CaCu 3Ti3.90Ce0.10O12 electro-ceramic synthesized by citrate-gel route
(2013) K.D. Mandal; Laxman Singh; Sunita Sharma; U.S. Rai; M.M. Singh
Effect of doping at Ti4+ site by Ce3+ has been examined in CaCu3Ti3.90Ce0.10O12 synthesized by citrate-gel route. DTA/TG analysis of dry powder gives pre-information about formation of final product around 850 C. X ray diffraction analysis confirmed the formation of CaCu3Ti3.90Ce 0.10O12 phase of the ceramic sintered at 950 C for 12 h. Microstructure has been studied using scanning electron microscopy and confirmed the average grain size found in nano range 200-400 nm in system CaCu 3Ti3.90Ce0.10O12.The nature of relaxation behavior of ceramic was also rationalized by using the impedance and modulus spectroscopy. The bulk conductivity indicates an Arrhenius-type thermally activated process. The ac conductivity spectrum obeyed the Jonscher power law. The complex impedance diagrams of the ceramic exhibited a significant contribution from the grains, grain boundaries and electrode. The activation energies calculated from the grain-boundary relaxation time constant was found to be 0.49 eV which confirmed the Maxwell-Wagner type of relaxation present in the ceramic. © 2013 Springer Science+Business Media New York.
Dielectric behavior of CaCu3Ti4O12 electro-ceramic doped with La, Mn and Ni synthesized by modified citrate-gel route
(Tsinghua University, 2013) Laxman Singh; U.S. Rai; Alok Kumar Rai; K.D. Mandal
The effect of La3+, Mn2+ and Ni2+ doped calcium copper titanate, CaCu3Ti4O12 (CCTO), at higher concentrations (CR1 and CR2 with 5 mol% and 10 mol%, respectively), has been examined by semi-wet route at relatively lower temperature. This semi-wet route employs citrate-nitrate gel chemical method using TiO2 solid powders. X-ray diffraction (XRD) analysis confirms the formation of single phase in the doped samples sintered at 900 °C for 8 h. Scanning electron micrographs (SEM) show that the average grain size for CR2 is larger than that of CR1 composition. The energy dispersive X-ray spectroscopy (EDX) is used to study the percentage compositions of different ions present in both ceramics. Dielectric constant (ɛr) and dielectric loss (tanδ) values of CR1 are comparatively higher than those of CR2 ceramic at all measured frequencies and temperatures. The nature of temperature-dependent relaxation behavior of the ceramics is also studied by impedance, modulus spectroscopic analysis and confirms Maxwell-Wagner relaxation. © 2013, The Author(s).
Dielectric properties of CaCu3-xMgxTi4O12 (x=0.20 and 0.50) material synthesized by the semi-wet route for energy storage capacitor
(SPIE, 2019) Laxman Singh; U.S. Rai; N.B. Singh; Y. Lee; D.K. Mahato; Divyanshu Bhardwaj; K.D. Mandal
Dielectric properties of high percentage Mg doped CaCu3Ti4O12, CaCu3-xMgxTi4O12 (x=0.20 and 0.50) ceramics carried out. They were synthesized by the semi-wet route using a solution based citrate-nitrate method along with inexpensive solid TiO2 powder. X-ray diffraction analysis reveals that the ceramics form single phase when sintered at 950 °C for 12h. SEM analyses show the smooth surfaces of grains with a spherical appearance. The grains of CCMTO2 and CCMTO5 ceramics were found to be in the size range of 1-5 μm and 1-3 μm, respectively. Dielectric studies show that the CCMTO2 ceramic has higher value of dielectric constant and lower dielectric loss in comparison to that of CCMTO5. © 2019 SPIE. Downloading of the abstract is permitted for personal use only.
Dielectric properties of zinc doped nanocrystalline calcium copper titanate synthesized by different approach
(2013) Laxman Singh; U.S. Rai; K.D. Mandal
Zinc doped calcium copper titanate, CaCu2.90Zn 0.10Ti4O12 (CCZTO), nanocrystalline electro-ceramics synthesized by solution-wet route (SR) as well as semi-wet route using citric acid (SWR1) and glycine (SWR2) separately, were characterized by TGA/DTA, XRD, TEM, SEM and EDX techniques. The crystallite sizes of the ceramics obtained by XRD were found to be in the range of 45-90 nm is in good agreement with those observed by TEM analysis. The grain sizes for the ceramics SWR1, SWR2 and SR observed by SEM were found in the range of 10-15 μm, 1-4 μm, and 2-4 μm, respectively. Thermal studies show that the single phase CCZTO ceramic was formed in single step combustion reaction in SWR2 while in the case of SWR1 and SR were obtained in multistep reactions. SWR2 route shows more effective solid state reaction for the formation of nanocrystalline CCZTO single phase at much lower sintering temperature. SWR1 ceramic exhibits higher dielectric constant (εr ∼ 4317) than SWR2 and SR ceramics at room temperature. © 2013 Elsevier Ltd.
Dielectric, modulus and impedance spectroscopic studies of nanostructured CaCu2.70Mg0.30Ti4O12 electro-ceramic synthesized by modified sol-gel route
(2013) L. Singh; U.S. Rai; K.D. Mandal
Effect of doping of Mg2+ at Cu2+ site has been examined in CaCu3Ti4O12. CaCu 2.70Mg.30Ti4O12 was synthesized by semi- wet chemical method, for the first time, using solid TiO2 and metal nitrate solutions. XRD analysis confirmed the formation of single-phase material, and the structure does not change on doping of Mg and it remains cubic similar to CaCu3Ti4O12 (CCTO). The average particle size in sintered powder of the ceramic obtained from XRD and Transmission electron microscopy (TEM) was found 59 ± 05 and 90 ± 25 nm, respectively. SEM image shows the presence of bimodal grains while EDX analysis confirmed copper oxide rich phase a grain boundary. We found exceptionally very high dielectric constant 86,084 at 500 K on partially substituted Mg2+ at Cu-site in CCTO ceramic at 1 kHz. The nature of relaxation behavior of the ceramic was also rationalized by impedance and modulus spectroscopic analysis. Modulus spectroscopic studies confirmed the Maxwell-Wagner relaxation arising due to the interfaces between grain and grain boundary. © 2012 Elsevier B.V. All rights reserved.
Direct observation on solidification of binary organic eutectic alloys
(1993) U.S. Rai; H. Shekhar
With a view to elucidate the chemistry of transparent binary organic systems of phenanthrene with acenaphthene, o-toluic acid and acetanilide, their phase diagram was determined by the thaw-melt method. The data on linear velocity of crystallization (v) of pure components and eutectics, determined by the rate of movement of the interface in a capillary at different undercoolings (ΔT), obey the Hillig-Turnbull equation. The values of heat of fusion, determined by the DTA method, were used to compute enthalpy of mixing and excess thermodynamic functions. These thermodynamic parameters are needed to throw light on the structure, stability and ordering in the eutectic melts. Microstructural studies showed that freshly precipitated eutectics have different characteristics microstructures from their parent components.
Effect of polyacrylamide on the different properties of cement and mortar
(Elsevier BV, 2005) U.S. Rai; R.K. Singh
The effect of polyacrylamide (PAA) addition in the ordinary cement and mortar, on the properties, such as setting time, heat of hydration, compressive and tensile strength has been studied by adding 0.5-5.0% additive by weight of cement. While hardness was determined using the Vickers indentation method, the fracture toughness of cementitious bond and flexural strength have been determined using three point bending system. Corrosion resistance of resulting products was tested against each of 0.1 and 1.0N of HCl and H2SO4 and seawater. FT-IR and X-ray diffraction techniques have been employed to determine the phase compositions of the material. Polymeric phase is interspersed in cement causing decrease in water absorption and also its interaction with hydrating cement resulting additional bond formation leading to the increase in strength. © 2004 Published by Elsevier B.V.
Effect of processing routes on microstructure, electrical and dielectric behavior of Mg-doped CaCu3Ti4O12 electro-ceramic
(2013) Laxman Singh; U.S. Rai; K.D. Mandal; Alok Kumar Rai
In the present communication, data on magnesium-doped calcium copper titanate CaCu2.90Mg0.10Ti4O12 (CCMTO) electro-ceramic, synthesized by the semi-wet route (SWR), ball-milled route (BMR) and solid-state route (SSR), is characterized by TG-DTA, XRD, SEM, EDX and TEM techniques. XRD confirmed the formation of single phase in CCMTO ceramic. The CuO phase present at grain boundaries in SWR ceramic was shown by the SEM micrograph, which was verified by EDX. The TEM image of SWR ceramic shows nanocrystalline particles in the range 80±20 nm. The value of the dielectric constant of SWR (ε r ∼20091) ceramic is higher than those of BMR and SSR (ε r ∼1247) ceramics at 1 kHz at 450 K. A dielectric relaxation has been observed in the frequency range 100 Hz-100 kHz. The high-temperature dielectric dispersion shows one large low-frequency response and two Debye-type relaxations. The impedance and modulus studies show the highest grain-boundary resistance for BMR ceramic. © 2012 Springer-Verlag Berlin Heidelberg.
Effect of site selection on dielectric properties of Fe doped CaCu 3Ti4O12 electro-ceramic synthesized by citrate nitrate gel route
(Scientific Publishers, 2014) L. Singh; K.D. Mandal; U.S. Rai; A.K. Rai
The effect of doping of Fe at Cu2+ and Ti4+ sites in calcium copper titanate, CaCu3Ti4O12, has been examined. The compositions CaCu3-xFexTi4O 12 (CCFTO) and CaCu3Ti4-xFexO 12 (CCTFO), (x = 0.10) have been synthesized by citrate nitrate gel route. XRD analysis confirms the formation of single- phase ceramics on sintering at 900°C for 8 h. Structure of CaCu3Ti 4O12 does not change on doping with iron on Cu-site or Ti-site and it remains cubic. Surface morphology indicates that the average grain size is in range of 30-90 μm and 5-7 μm for systems CCFTO and CCTFO, respectively. EDX studies confirm the presence of Ca2+, Cu 2+, Ti4+ and Fe3+ ions as per stoichiometry of ceramics. The grain resistance of CCTFO is higher than that of CCFTO. Values of dielectric constant (εr) and dielectric loss (tanδ) of CCTFO are higher than those of CCFTO ceramic at all measured frequencies and temperatures. © 2014 Indian Association for the Cultivation of Science.
Erratum: Electron addition to triethylphosphine induced by ionizing radiation: An ESR study (Indian Journal of Chemistry (1995) 34A (692))
(2001) U.S. Rai
[No abstract available]
Green synthesis, characterization and optical properties of eutectics and 1:1 intermolecular compounds: N,N-dimethylaminobenzaldehyde-anthranilic acid and 2-(4-(dimethylamino)benzylideneamino)benzoic acid- p-nitroaniline systems
(Springer, 2019) U.S. Rai; Manjeet Singh; R.N. Rai
Phase diagrams of N,N-dimethylaminobenzaldehyde (DMAB)-anthranilic acid (AA) and 2-(4- (dimethylamino)benzylideneamino)benzoic acid (DMABAB)-p-nitroaniline (PNA) systems, determined by the thaw-melt method, give two eutectics and a 1:1 intermolecular compound (IMC) in each case. Appropriate amounts (10 g) of each of the eutectics and the IMCs were prepared by a green synthetic method involving a solid state reaction without any solvent. These materials were characterized by X-ray diffraction, thermal and spectral methods and the optical properties of the pure components and the IMCs were studied.While negative values of heat of mixing in the case of a DMAB-AA system suggest clustering of molecules in both eutectic melts, those of positive value in E1 and negative value in E2 of the DMABAB-PNA system indicate the formation of a quasi-eutectic structure in E1 melt and clustering of molecules in E2 melt. The IMC of DMAB-AA system shows strong dual emission with two λmax one at 380 nm and the second at 450 nm with a total quantum efficiency of 0.49. The IMC of DMABAB-PNA system also shows a similar observation with two λmax one at 390 nm and second at 435 nm with a total quantum efficiency of 0.31. © Indian Academy of Sciences.
Green synthesis, characterization and some physico-chemical studies on a novel intermolecular compound; 4-nitro-o-phenylenediamine−N, N-dimethylaminobenzaldehyde system
(Elsevier B.V., 2017) U.S. Rai; Manjeet Singh; R.N. Rai
An inter-molecular compound (IMC) L1 was synthesized by taking 1:1 molar ratio of p-nitro-o-phenylenediamine (NOPDA) and N, N-dimethylaminobenzaldehyde (DMAB) via thermally initiated solid state reaction. It was characterized by X-ray diffraction, spectral and optical studies. The single crystal of the (L1) was grown from saturated solution of ethanol using slow evaporation technique at 29 °C. From the single crystal X-ray diffraction analysis, it can be inferred that it crystallizes in triclinic unit cell with P-1 space group (CCDC No 1422765). Absorption spectrum of IMC (L1) shows a band at 318 nm attributed to the intra-molecular charge-transfer (ICT) excited state absorption and the other band at 376 nm is due to n→π* transition. The IMC (L1) shows a strong fluorescence at 418 nm with a Stokes shift (≈100 nm) and quantum efficiency (0.22) upon excitation in methyl alcohol at 318 nm. © 2017 Elsevier B.V.