Browsing by Author "V.B. Singh"

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A review of fundamental aspects, characterization and applications of electrodeposited nanocrystalline iron group metals, Ni-Fe alloy and oxide ceramics reinforced nanocomposite coatings
(Elsevier Ltd, 2018) Alok Kumar Chaudhari; V.B. Singh
Electrochemical co-deposition of materials offers some unique advantages over competing technologies and therefore occupies special place in science and technology. Ni-Fe alloys are of great commercial interest owing to their interesting mechanical, electrical, magnetic and corrosion resistant properties. In this communication the present state of art on the electrodeposition of iron group metals and specially Ni-Fe alloy and oxide ceramic reinforced nanocomposites is reported along with a brief overview of fundamental principles, techniques and engineering applications of these metal matrix composites (MMCs) which include their ductility, hardness, electrical resistivity, thermal stability, corrosion resistance, soft magnetic and superparamagnetic properties. These properties of the deposits are mainly dependent on their composition, plating parameters and nature, size, content and distribution of the incorporated ceramic particles in the matrix. Potential commercial applications of these coatings have been discussed and attempts have been made to define accurate and predictive correlations with plating parameters. © 2018 Elsevier B.V.
Active, passive and transpassive dissolution of a nickel base super alloy in concentrated acid mixture solution
(1995) V.B. Singh; U. Arvind
The electrochemical and corrosion behaviour of a nickel base super alloy (C‐263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35°C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H3PO4 + 40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing. Copyright © 1995 Verlag GmbH & Co. KGaA, Weinheim
Active, passive and transpassive dissolution of In-718 alloy in acidic solutions
(2004) V.B. Singh; Archana Gupta
The electrochemical behaviour of In-718 alloy in different compositions of binary and ternary solution mixtures of concentrated phosphoric, sulphuric, acetic acids and in different concentrations of aqueous and methanolic solutions of sulphuric acid has been studied by potentiostatic polarisation technique at 30°C. The cathodic polarisation curves are almost linear and similar in all the solution mixtures and cathodic reaction is hydrogen evolution. The anodic polarisation curves reveal active, passive and transpassive behaviour in all the solution mixtures. In the transpassive region, a current plateau was observed in most of the cases in binary and ternary solution mixtures but electropolishing was not observed in any case. The results show that the existence of a current plateau is not the only sufficient condition for achieving electropolishing of the alloy. © 2003 Published by Elsevier B.V.
Active-passive behaviour of titanium and titanium alloy (VT-9) in sulphuric acid solution
(1993) S.M.A. Hosseini; V.B. Singh
Corrosion behaviour of titanium and VT-9 has been studied in sulphuric acid solution in the whole range of concentration at 30 °C. Effect of temperature on the corrosion behaviour has also been investigated. Titanium and its alloy (VT-9) showed active-passive behaviour. A large range of potential for passivity was observed in all the concentrations at different temperatures. Critical current density for passivation (icr) increased with increasing temperature while it increased with concentration up to 11 M; thereafter it decreased. In general, Ti and VT-9 exhibited similar corrosion behaviour, however passivation current density (ip) and critical current density (icr) differed to some extent. The passivation current density is higher in case of VT-9 than Ti while icr is lower under similar conditions. The stability of the film formed on the surface of the titanium and VT-9, examined under different experimental conditions, reveals the formation of protective uniform passive film on the metal and alloy. © 1993.
Aktive, passive und transpassive Aufloesung einer Nickelbasissuperlegierung in konzentrierten Saeureloesungen; [Active, passive and transpassive dissolution of a nickel base super alloy in concentrated acid mixture solution]
(VCH Verlagsgesellschaf mbH, 1995) V.B. Singh; U. Arvind
The electrochemical and corrosion behaviour of a nickel base super alloy (C-263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35 °C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H3PO4+40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy. The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing.
An investigation on dissolution and passivation behaviour of Ti-6Al-4V in sulphuric acid
(1998) V.B. Singh; S.M.A. Hosseini
Potentiostatic technique has been employed to investigate the polarization behaviour of a titanium alloy (Ti-6Al-4V) in a wide concentration range (1-17 M) of sulphuric acid, at 30°C and 40°C. Effect of temperature variation of the experimental solution has been studied in selected concentrations (5M and 9M) of the acid. The cathodic current density increased in accordance with increasing acid concentration, temperature and applied potential. Anodic polarization studies showed active-passive transition and broad passivity range of potential available for the stability of alloy. The critical current density and passivity current density (ic and ip) increased with an increase in the concentration and temperature of the solution. However, these values decreased in solution above 11M sulphuric acid. The passivated specimen revealed formation of uniform and stable anodic film during longer exposure time. Apparent activation energy, obtained from Arrhenius plots, corresponding to critical current densities is of order for the chemical reaction. Impedance measurements indicate that the passive film has the characteristics of valve metal in respect of capacitance and formation potential, and consists of two types of grains on the surface.
Characteristics of electrodeposited nickel from mixed organic solvents
(Cambey and West, 1998) R. Sadeghi Sarabi; V.B. Singh
[No abstract available]
Characteristics of electrodeposited nickel from mixed organic solvents
(Elsevier Science Inc, 1998) R.Sadeghi Sarabi; V.B. Singh
The effect of current density and bath and annealing temperature on the hardness of nickel deposited from a nickel sulfamate-ethylene glycol-diethylene glycol mixed solvent solution is studied. It is shown that the hardness of nickel deposits decreases with increasing current density but show a declining trend with elevated annealing temperature. SEM micrographs show fine-grained deposits under optimum conditions, recrystallization of grains, and grain growth at high annealing temperatures. TEM studies indicate that the deposits are free from twinning and dislocations.
Corrosion and inhibition studies of copper in aqueous solutions of formic acid and acetic acid
(1995) V.B. Singh; R.N. Singh
Corrosion behaviour of copper has been investigated in different compositions of formic acid and acetic acid at 30 °C by a potentiostatic method. The maximum corrosion rate was found in 20-40 mol/o formic acid and in 20 mol/o acetic acid in aqueous solution mixtures. The corrosion rate depended on the concentration of either acid. Formic acid is observed to be more corrosive than acetic acid. The metal exhibited active-passive behaviour in the concentration range of 30-70 mol/o of HCOOH acid in the solution mixture. A short passivity range of potential with a high passivity current density was observed for the metal in the solution mixtures of HCOOH acid while in solution mixtures of acetic acid the metal exhibited only active dissolution. Some organometallic compounds, viz. Bu2SnCl2, PhSnCl3, Ph2SnCl2, Ph3SnCl have been subjected to inhibition studies in the aqueous solution mixture (20 mol/o) of either acid. Among the inhibitors used Ph3SnCl functions as a better inhibitor in both acids. A strong interaction between the inhibitor and corroding surface of copper is speculated due to adsorption of the inhibitor. © 1995.
Corrosion and pitting behaviour of AISI 302 stainless steel in methanol + H2SO4 mixtures
(1988) V.K. Singh; V.B. Singh
Electrochemical and corrosion behaviour of austenitic stainless steel (AISI 302) has been investigated in deaerated methanolic solution containing different concentrations of H2SO4 (0.001 M-1M) using potentiostatic and potentiodynamic techniques. Cathodic polarization studies show that the cathodic process is initially activation controlled and at more negative potentials it tends to be diffusion controlled, particularly in low acid concentrations. Frequent active-passive transitions are observed and the critical current density for the passivity is dependent on the sulphuric acid content in methanol. In anodic polarization studies in 1 M and 0.1 MH2SO4-methanol solutions cathodic loops appear. SEM examination of the electrode surface after the polarization studies showed severe pitting in each concentration of acid-methanol mixtures. Different corrosion parameters and pitting potentials have been evaluated. Repassivation has also been observed. Current vs time transients have been recorded at constant potential. Protection potential is always less nobler than the pitting potential.
Corrosion behavior and inhibitive effects of organotin compounds on nickel in formic acid
(1993) R.N. Singh; V.B. Singh
Corrosion behavior of nickel (Ni) in different compositions of formic acid (HCOOH) at 30°C was studied using the potentiostatic polarization method. The shape of the polarization curve was evaluated, and the corrosion current density, critical current density, and passive current density were determined. HCOOH solutions of different composition were aggressive for the anodic dissolution of Ni, except for 20 and 30 mol/O HCOOH, in which feeble passivity was observed. The organometallic compounds dibutyltin dichloride, phenyltin trichloride, diphenyltin dichloride, and triphenyltin chloride ([C6H5]3SnCl), reduced the corrosion rate of Ni in 20 mol/O and 40 mol/O HCOOH. (C6H5)3SnCl was the most efficient. Inhibitive action was explained on the basis of adsorption following the Langmuir adsorption isotherm, with the highest surface coverage given by (C6H5)3SnCl. The inhibitive action of organometallic compounds toward Ni in HCOOH was caused by the group and delocalized Π electrons.
Corrosion behaviour of stainless steel (AISI 321) in alcoholic-H2SO4 mixtures
(1991) V.B. Singh; V.K. Singh
The electrochemical and corrosion behaviour of austenitic stainless steel (AISI 321) in alcoholic environment containing different contents of H2SO4 has been investigated. The electrochemical polarization curves of the stainless steel in ethanol, iso-propanol and t-butanol containing 0.001-1 kmol/m3 H2SO4 show active, passive and transpassive behaviour. The critical current density for passivation, current density in the passive state and the potential range of passivity has been found to depend on the concentration of acid and the type of alcohol in alcohol-H2SO4 mixtures. The stainless steel suffered localized attack due to pitting in ethanol containing higher concentrations of H2SO4. The results have been discussed in light of physicochemical properties of the alcohols.
Corrosion behaviour of Ti-6Al-4V in phosphoric acid
(Kluwer Academic Publishers, 1994) V.B. Singh; S.M.A. Hosseini
Ti-6A1-4V shows distinct active-passive behaviour in phosphoric acid over a wide concentration range. The cathodic polarization curves are similar over a wide range of acid concentration and temperatures. The alloy undergoes active dissolution and turns passive in the negative potential region followed by a wide range of passivity at all acid concentrations at different temperatures. Increasing acid concentration up to 11 M results in an increase in critical current density (icr). The passive current density (ip) increases up to an acid concentration of 9 M while at 13 M icr and ip decrease appreciably. A significant increase in both icr and ip occurs with increase in solution temperature. The passive specimen remained stable for a long time when exposed to phosphoric acid under open circuit conditions. © 1994 Chapman & Hall.
Corrosion of Plated Nickel in Formamide-Water Mixtures
(1981) Lai Bahadur; V.B. Singh; P.K. Tikoo
Corrosion behavior of plated nickel in formamide-water mixtures has been studied at 25 °C galvanostatically covering the whole range of solvent composition. It has been observed that solvent composition has a pronounced effect on the corrosion behavior of nickel and it has been found that nickel is anodically active in water-rich solvent composition region while it becomes passive in formamide-rich region. © 1981, The Electrochemical Society, Inc. All rights reserved.
Corrosion resistance of austenitic stainless steels in non-aqueous neutral chloride solution
(National Institute of Science Communication and Information Resources (NISCAIR), 2015) Monali Ray; V.B. Singh
The corrosion resistance of two standard austenitic stainless steels (AISI 304 and 321 SS) has been investigated in non-aqueous methanolic solution containing lithium chloride. The effect of chloride concentration on the general corrosion behaviour of the steels has been investigated using open circuit potential (OCP), potentiostatic polarization and scanning electron microscopic (SEM) techniques. Both the steels have undergone active corrosion. The rate of corrosion is found to depend directly on the concentration of chloride ion in methanol similar to the aqueous solutions. The polarization measurements reveal that the corrosion resistance of the Ti-alloyed 321 SS is superior as compared to the 304 SS due to the presence of titanium in it. AISI 321 SS suffer from pitting corrosion whereas grain boundary attack is apparent in 304 SS. © 2015, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
CORROSION STUDIES IN AQUEOUS-ORGANIC BINARY SOLUTIONS I COPPER IN WATER - DMF MIXTURES.
(1984) N.Nageswara Rao; V.B. Singh
Corrosion behavior of copper in N,N-dimethylformamide-water mixtures has been studied at 30 plus or minus 1 degree C galvanostatically covering the whole range of solvent composition. The solvent composition has been found to have marked influence on the observed active, passive behavior of copper. Copper exhibited passivity in solvent mixtures containing above 40m///o DMF on impressing a small constant current, while larger currents are needed to observe passivity in solvent compositions below 40m///o DMF. The corrosion behavior has been explained in terms of various physicochemical properties of solvent mixtures and a semiempirical view has been speculated for the dissolution of copper.
CORROSION STUDIES IN AQUEOUS-ORGANIC BINARY SOLUTIONS. COPPER IN ADMIXTURES OF WATER AND N-METHYLFORMAMIDE.
(Natl Research Council of Canada, 1984) N.Nageswara Rao; V.B. Singh
This paper presents the results of corrosion studies of copper metal in various binary mixtures of N-methylformamide(NMF) and water by potentiostatic method. N-methylformamide is characterized by a high dielectric constant and is a powerful dissociating solvent. These binary mixtures are found to be corrosive to copper. Addition of small amount of NMF (0. 5 moles) to water increased the critical anode current density by a factor of 10**1-10**2. Scanning Electron Micrographs of the test-specimens after anodic polarization revealed pitting. The anodic behaviour of copper in above binary mixtures has been explained by complex forming ability of NMF. Spectral studies also confirm the complex formation.
Corrosion studies of Ni-free austenitic stainless steel in methanol containing H2SO4, HCl and LiCl
(2007) V.B. Singh; Monali Ray
The corrosion behaviour of an austenitic stainless steel containing nitrogen with negligible amount of nickel has been investigated in methanol-H2SO4, methanol-HCl, and methanol-LiCl solutions using potentiostatic polarization technique. The cathodic reaction was the hydrogen evolution reaction. Active, passive and transpassive behaviours were observed only at high concentrations of H2SO4 (0.01-1.0 M) in methanol, and passivity was due to the high inherent water content in sulphuric acid. Pitting was also observed on the steel surface. The pitting potential became nobler as the concentration of H2SO4 increased. In 0.1 and 1.0 M H2SO4, a cathodic loop, characterized by measured negative current in the anodic region, was also observed. In methanol-HCl and methanol-LiCl solutions, the steel dissolved actively and no active-passive transition was observed. The corrosion rate was significantly higher in methanol-HCl solution as compared to methanol-LiCl due to the synergistic effects of acid and chloride ion.
Dissolution and passivation of nickel-free austenitic stainless steel in concentrated acids and their mixtures
(National Assoc. of Corrosion Engineers International, 2001) V.B. Singh
Electrochemical polarization behavior of nickel-free austenitic stainless steel in concentrated phosphoric (H3PO4), sulfuric (H2SO4), acetic (CH3COOH), and formic (HCOOH) acids and binary and ternary solution mixtures was investigated by a potentiostatic polarization technique at 30 ± 1°C. The cathodic polarization curves were almost linear and similar in all binary and ternary solution mixtures and resembled that of the hydrogen evolution reaction. However, in ternary solution mixtures of H3PO4, H2SO4, and HCOOH, the shape of the curves indicated composite reactions of hydrogen and oxygen reduction. Anodic polarization curves showed active, passive, and transpassive behaviors in all the solution mixtures. When H2SO4, CH3COOH, or HCOOH was added to H3PO4, the aggressive nature of the binary solution mixtures toward the alloy was intensified in the same order. Thus, maximum corrosion was observed in the case of binary solutions of H3PO4 with HCOOH. However, in the ternary solution mixtures, the corrosion of the alloy decreased. In the transpassive region, a secondary current peak and current plateau were observed in most cases. However, electropolishing was not achieved in these solution mixtures. The mass-transfer-controlled condition is probably not achieved in such cases even when a current plateau is observed. Resulting surface morphologies were characterized with scanning electron microscopy (SEM) and atomic force microscopy (AFM). A smoothing action was observed in the transpassive region. © 2001, NACE International.
Effect of H2SO4 addition on the corrosion behaviour of AISI 304 austenitic stainless steel in methanol-HCL solution
(2007) V.B. Singh; Monali Ray
Effect of sulphuric acid addition on the corrosion behaviour of AISI 304 austenitic stainless steel was investigated in different concentrations of HCl (0.001 - 1.0 M) in methanol using potentiostatic polarization, cyclic anodic polarization and open-circuit potential (OCP) measurements. In methanol-HCl solution, only active anodic dissolution occurred and the rate of corrosion increased with concentration of HCl. Scanning electron microscopic studies revealed grain boundary attack of the specimen. The addition of H2SO4 into methanol-HCl solutions with H2SO4 to HCl concentration ratio ≥ 10:1 stimulated the dissolution rate in the active region, but at higher potentials, facilitated passivation with occurrence of pitting on the steel surface. Increase in H2SO4 concentration enhanced passivity by broadening the range of passivity and making the pitting potential (Epit) and the protection potentials (Eprot) nobler due to higher inherent water content of H2SO4. Simultaneously, the passivation current density (ip) also increased indicating the formation of a more defective passive film probably due to higher acidity of the solution. © 2007 by ESG.