Browsing by Author "Susanta K. Sengupta"

Now showing 1 - 12 of 12

A new amphi-indicator based on cationic colorant methyl violet
(1984) Susanta K. Sengupta
[No abstract available]
A study on acrylamide polymerization by anodic contact glow-discharge electrolysis: A novel tool
(2001) Susanta K. Sengupta; Urvashi Sandhir; Nira Misra
Contact glow-discharge electrolysis (CGDE) is an unconventional electrolytic phenomenon in which a plasma is sustained by a direct current (dc) glow-discharge between an electrode and the liquid electrolyte around it. A remarkable feature of CGDE is highly nonfaradaic chemical effects at the glow-discharge electrode. During anodic CGDE of an aqueous electrolyte, non-Faradaic yields originate mainly from reactions triggered by H and OH radicals generated in high local concentrations near the anodic plasma/liquid electrolyte interface during the process. The radical-generating potentiality of anodic CGDE was explored for the polymerization of acrylamide in aqueous media. The percentage of monomer conversion, rate of polymerization, charge efficiency, and viscometric average molar mass of the polymers produced were measured as functions of the quantities of electricity passed. The charge efficiency of the polymerization of acrylamide by anodic CGDE was at least 1 order of magnitude higher than that of ordinary electrochemically initiated polymerization. © 2001 John Wiley & Sons, Inc.
A study on non-faradaic yields of anodic contact glow discharge electrolysis using cerous ion as the OH• scavenger: An estimate of the primary yield of OH• radicals
(1998) Susanta K. Sengupta; Rajeshwar Singh; Ashok K. Srivastava
Chemical yields of contact glow discharge electrolysis (CODE) show strong deviations from faradaic behaviour. The products are novel for normal electrolysis and yields significantly exceed the Faraday law value. Anodic CODE gives rise to Ce4+ and H2O2 in the anolyte in yields significantly exceeding the faradaic value besides the faradaic yield of O2. The relative yield of Ce4+ and H2O2 depends on the concentration of Ce3+ and the quantity of electricity passed. A kinetic analysis of the variation of the initial differential yield of Ce4+, G0 (Ce4+) with the concentration of Ce3+ after applying certain approximations leads to an estimate of the generation of 12 moles of OH• radicals in the liquid phase reaction zone of anodic CGDE for the passage of each mol electron of electricity.
A study on the origin of nonfaradaic behavior of anodic contact glow discharge electrolysis: The relationship between power dissipated in glow discharges and nonfaradaic yields
(Electrochemical Society Inc., 1998) Susanta K. Sengupta; Rajeshwar Singh; Ashok K. Srivastava
Chemical effects of contact glow discharge electrolysis (CGDE) at an electrode where a plasma is sustained by dc glow discharges between the electrode and the surrounding electrolyte, are remarkably nonfaradaic. A critical analysis of the chemical results of anodic CGDE at varying voltages, currents, power supplies, and pHs clearly shows that nonfaradaic yields originate in two separate reaction zones: the plasma around the anode and the liquid anolyte near the plasma-anolyte interface. The yields from the former zone appear from 250 V onward (the beginning of the onset of partial glow discharge) and vary linearly with the power dissipated in the glow discharge. The yields from the latter zone appear from 410 V onward (the beginning of the full glow discharge) and are independent of the power dissipated in the glow discharge. The relative contribution of the two zones to the total nonfaradaic yields is dependent on the voltage applied: the plasma zone having a share of 100% up to 400 V, followed by 20% up to 450 V, and thereafter rising steadily to 57% at 500 V.
Contact glow discharge electrolysis: a study of its chemical yields in aqueous inert-type electrolytes
(1994) Susanta K. Sengupta; Om Prakash Singh
A study of the chemical yields of contact glow discharge electrolysis (CGDE) at the anode in aqueous inert electrolytes at various quantities of electricity, applied voltages and electrolyte compositions shows that, for the passage of each mole of electrons, 0.25 mol of O2 and more than 1.0 mol of both H2 and H2O2 plus O2 are produced at the anode when the glow discharges there are fully grown. Non-faradaic yields may originate in two reaction zones: the anolyte near the plasma where liquid water molecules are broken up into H2O2, O2 and H2, and the plasma around the anode where gas phase dissociation of water molecules into H2 and O2 occurs. The former is important for anodic CGDE. Hickling's radiolytic mechanism has been applied to interpret the chemical results of the liquid phase reaction zone. A comparative study of the chemical yields of anodic and cathodic CGDE indicates that the breakup of water molecules occurs entirely in the plasma during cathodic CGDE, but primarily in the liquid anolyte and partly in the plasma during the anodic phenomenon. © 1994.
Contact glow discharge electrolysis: a study of its onset and location
(1991) Susanta K. Sengupta; Om Prakash Singh
At sufficiently high voltages a normal electrolysis switches over to a phenomenon called contact glow discharge electrolysis (CGDE) in which glow discharges take place across a gaseous envelope over either the anode or the cathode. A critical investigation on the influence of the relative anode-cathode dimensions, the relative anolyte-catholyte surface tension, the nature of the electrolyte constituents, and the polarity of the electrode on the onset and location of CGDE in aqueous media has been carried out. The mechanism of the growth of a stable vapour envelope on an electrode underneath an electrolyte during normal electrolysis has been examined in the light of the theory of hydrodynamic instabilities. Overall analysis of the results has led to the following conclusions: (a) vaporization, and not gas evolution at an electrode, is the prime requisite for the growth of CGDE in the aqueous phase; (b) an electrode-electrolyte area where the conditions help both easier vaporization and easier onset of hydrodynamic instabilities would be the location of CGDE; and (c) the nature of the glow discharges at an anode is quite different from that at a cathode. © 1991.
Contact glow discharge electrolysis: A study on its origin in the light of the theory of hydrodynamic instabilities in local solvent vaporisation by Joule heating during electrolysis
(Elsevier, 1997) Susanta K. Sengupta; Ashok K. Srivastava; Rajeshwar Singh
Normal electrolysis at high voltages switches over spontaneously to contact glow discharge electrolysis. The transition is profoundly facilitated by raising the temperature and/or lowering the surface tension of the electrolyte. Results of a systematic study on the influence of these two factors on the breakdown voltage for normal electrolysis have been critically analysed. It has been concluded that solvent vaporisation near an electrode by Joule heating during electrolysis and the onset of hydrodynamic instabilities in local solvent vaporisation are the prime causes for the breakdown of normal electrolysis. © 1997 Elsevier Science S.A.
Influence of apolar aprotic solvents on proton transfer equilibrium between m-/o-chlorobenzoic acids and the carbinol base of crystal violet: A chemometric analysis
(2007) Ruchi Shrivastava; Sangeeta Mishra; Susanta K. Sengupta
A chemometric analysis of equilibrium results for apolar aprotic solvent effects on proton transfer between m-/o-chlorobenzoic acids and crystal violet carbinol base using Koppel-Palm's approach shows that the total solvent effect is contributed mainly by dispersion and dipolar/electrostatic interactions in approximately 7:4 ratio. A parallel study with m-and o-fluorobenzoic acids but under conditions favouring acidacid anion homoconjugation reflects the role of homoconjugated complexed acids in substantially modifying the detailed pattern of solvent effects.
Physico-chemical properties and catalytic activities of the spinel series MnxFe3-xO4 towards peroxide decomposition
(1995) Preeti Lahiri; Susanta K. Sengupta
Samples of the spinel series, MnxFe3-xO4 (O ≤ x ≤ 3), have been synthesized by the hydroxide coprecipitation technique and characterised by chemical analysis; XRD and SEM techniques, and measurements of their BET specific surface areas, saturation magnetisations and electrical resistivities. The specimens with values of x ≤ 1.5 are single-phase cubic spinels and those with x > 1.5 are two-phase cubic and tetragonal spinels. The relative catalytic activities of the specimens towards the decomposition of H2O2 in both alkaline and neutral media, measured on the basis of the energies of activation, a microstructure-independent parameter, and the rate constants normalised to unit BET surface area, a microstructure normalised parameter, follow the order, (given as values of x) 1.45 > 2.5 ≈ 2.0 > 1.0 > 1.2 > 0.8 > 0.5. All the MnxFe3-xO4 prepared specimens are potential substitutes for CoFe2O4, the high-performance catalyst for the decomposition of H2O2; the specimen with x = 1.45 is the most powerful and is significantly more active than CoFe2O4. The activity appears to depend on the availability and efficacy of redox conversion of redox conversion of MnII centres in the sublattices of the MnxFe3-xO4 catalysts.
Proton transfer equilibria between m-substituted benzoic acids and the carbinol base of crystal violet in apolar aprotic solvents: A comparison between toluene-phase and aqueous-phase strengths of the acids
(1998) Susanta K. Sengupta; V. Radha Rani
A detailed study on proton transfer equilibria between twelve m-substituted benzoic acids and the carbinol base of crystal violet, the reference base, in toluene at 20°C and 28°C shows that toluene-phase strengths of the acids as compared to their aqueous-phase acidities are more than 4.5 times sensitive to the substituent's structure effects.
Proton transfer equilibria between o-substituted benzoic acids and the carbinol base of crystal violet in apolar aprotic solvents: Chemometric analysis of ortho effect
(2008) Susanta K. Sengupta; Sangeeta Mishra
Toluene-phase reaction equilibria between a set of o-substituted benzoic acids and crystal violet carbinol base producing a coloured ion-pair have been studied spectrophotometrically at 28±1°C. Chemometric analysis on the basis of both Charton's and Fujita-Nishioka's multiparameter approaches for o-substituent effects on the equilibrium constants show that proximity electronic effect of an o-substituent is the main intrinsic contribution to the anomalous ortho effect with its steric factor contributing merely a minor effect. However, in the aqueous phase the steric contribution becomes significant due to hydration induced substantial enhancement in the bulk of the -COOH group and the o-substituent.
The effect of electrolyte constituents on the onset and location of glow-discharge electrolysis
(1981) Susanta K. Sengupta
[No abstract available]