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Electrochemical characterization of an aqueous lithium rechargeable battery: The effect of CeO2 additions to the MnO2 cathode
No full textThe effect of CeO2 additions on an aqueous rechargeable lithium battery has been investigated. The CeO2
additions (0, 2, and 5 wt.%)were made to the manganese dioxide (MnO2) cathode of a cell comprising zinc
as an anode and an aqueous saturated lithium hydroxide solution as the electrolyte. The CeO2 enhances
the performance of the cell in terms of capacity and resistance to capacity fade with cycling. This effect is
only evident after the first charge cycle. The mechanism by which this occurs may be due to suppression
of the oxygen evolution reaction during charging. This results in full reversion of the products of discharge
(principally LixMnO2) to MnO2 during charging, and suppresses the formation of non-rechargeable oxyhydroxides.
CeO2 additions of 2 wt.% were found to be most effective, since additions at the 5 wt.% level
caused a decrease in capacity during long-term cycling. This could be due to a synchronizing effect. The
effect of additions of a rare earth oxide (CeO2) and an alkaline earth oxide (CaO) on the electrochemical
behavior of the cell is also compared and discussed
A comparative study of anodic fluorination of N-alkyl and N,N-dialkyl phenylacetamides in Et3N 4HF medium
No full textAnodic fluorination of N-alkyl and N,N-dialkyl phenylacetamides (alkyl = methyl, ethyl, propyl and nbutyl)
was carried out in Et3N 4HF medium. Effects of current density, quantity of electric charge and
alkyl chain length on the overall conversion efficiency and selectivity of fluorinated products are
reported. 1H NMR, 19F NMR and GC/MS were employed for product identification and characterization.
Under galvanostatic condition, N-alkyl phenylacetamides lead to predominantly monofluoro derivative
at ortho position in the aromatic ring. Mono and difluoro active methylene derivatives and p-fluoro
compounds were also formed in smaller quantities. The selectivity was low in the case of N,N-dialkyl
phenylacetamides. On increasing the electricity passed beyond 2 F/mol, the o-fluoro compound produced
1,4 addition compounds followed by further chemical and electrochemical transformations. Cyclic voltammetric
studies indicated significant adsorption of N,N-dialkyl compounds. Potentiostatic electrolysis
lead to predominantly side chain fluorination at the active methylene group. The product distribution
under different experimental conditions is explained on the basis of reactant adsorption and protonation
at the amide group
Evaluation of menthol as vapor phase corrosion inhibitor for mild steel in NaCl
No full textMenthol has been studied as a vapor phase corrosion inhibitor for the temporary protection of mild steel in a
NaCl environment. Its vapor corrosion inhibition property was gravimetrically evaluated in 100% relative humidity
(RH) at 40±1 ºC by a continuous condensation method. Electrochemical properties, such as Tafel polarization and
AC impedance, of menthol impregnated craft paper was studied by a thin layer technique using an atmospheric
corrosion monitor. It has been found from the results that the inhibition efficiency of menthol increases with an
increase in the concentration of menthol from 250 mg/sq.ft to 1,000 mg/sq. ft. The adsorption behavior of menthol
on mild steel surface was found to obey Temkin’s adsorption isotherm
Computation of Current Distributions using FEMLAB
No full textAn efficient method for the computation of current density and surface concentration
distributions in electrochemical processes is analyzed using the commercial
mathematical software FEMLAB. To illustrate the utility of the software, the
procedure is applied to some realistic problems encountered in electrochemical
engineering, such as current distribution in a continuous moving electrode, parallel plate electrode, hull cell, curvilinear hull cell, thin layer galvanic cell,
through-hole plating, and a recessed disc electrode. The model equations of the
above cases are considered and their implementations into the software, FEMLAB,
are analyzed. The technique is attractive because it involves a systematic way
of coupling equations to perform case studies
Application of harmonic analysis in measuring the corrosion rate of rebar in concrete
No full textThe corrosion rate (CR) of rebar embedded in cement mortar, concrete and cement extract is determined
using harmonic analysis technique (HA). Simultaneously using other electrochemical techniques such as
impedance spectroscopy (EIS) and Tafel extrapolation (TET), the CR was determined and compared with
the weight loss method. CR obtained from HA is comparable to that of EIS provided that the Stern–Geary
constant (B value) obtained from HA is used in the calculation. In concrete, comparable corrosion rates
are obtained between TET and HA only under active condition of the rebar whereas under passive state,
the corrosion current (icorr) by TET is 10 times lower than that of HA. A good agreement is obtained
between the HA and weight loss method. The outcome of the result suggests that HA is capable of providing
a higher degree of accuracy than that of EIS and TET in the determination of icorr in the medium like
rebar in concrete having very low rate of corrosion
Determination of diffusion coefficient of chloride in concrete using Warburg diffusion coefficient
No full textAssessment of diffusion coefficient of chloride (D) using chloride profile method based on Fick’s law (DFL)
is either overestimates or underestimates the time to initiation of corrosion (Ti). An alternate method for
predicting ‘D’ using Warburg diffusion coefficient (DWI) which is determined from Electrochemical
Impedance Spectroscopy technique (EIS) is established. The results reveal that EIS being non-destructive
appears a promising technique to arrive at time-dependent characteristics of DWI in situ in concrete structures.
DWI is an intrinsic effective diffusivity measures the diffusion of free chloride through the pore
solution present in the interconnected pores. Pore constriction by pozzolanic reaction and higher chloride
binding capacity reduces the DWI in PPC and PSC concrete by a factor of 1.65 and 4 times that of OPC concrete
in 20 MPa concrete; 1.83 and 2.52 in 30 MPa concrete; 24 and 16 times in 40 MPa concrete
respectively
Optimization of the process parameters for the removal of phosphate from drinking water by electrocoagulation
No full textThe present studies provide the purification of drinking water containing phosphate by electrocoagulation
process using zinc as the anode and stainless steel as the cathode. The experimental
parameters like electrolyte pH, temperature and current density, and so forth, on the removal efficiency
of phosphate were carried out. The adsorption capacity was evaluated using both Langmuir
and Freundlich isotherm models. The kinetic studies show that the adsorption obeys second-order
kinetics. The maximum removal efficiency of 98.8% was achieved at a current density of 0.05 A/dm2,
at a pH of 7.0. Thermodynamic parameters were evaluated. Overall adsorption process was endothermic
and spontaneous. The adsorption of phosphate preferably fitting the Langmuir adsorption
isotherm suggests monolayer coverage of adsorbed molecules
Electrocarboxylation and related radical coupling processes of aryl and benzyl halides in microemulsion
No full textRemediation of phosphate-contaminated water by electrocoagulation with aluminium, aluminium alloy and mild steel anodes
No full textThe present study provides an electrocoagulation process for the remediation of phosphate-contaminated
water using aluminium, aluminium alloy and mild steel as the anodes and stainless steel as the cathode.
The various parameters like effect of anode materials, effect of pH, concentration of phosphate, current
density, temperature and co-existing ions, and so forth, and the adsorption capacity was evaluated using
both Freundlich and Langmuir isotherm models. The adsorption of phosphate preferably fitting the Langmuir
adsorption isotherm suggests monolayer coverage of adsorbed molecules. The results showed that
the maximum removal efficiency of 99% was achieved with aluminium alloy anode at a current density
of 0.2Adm−2, at a pH of 7.0. The adsorption process follows second-order kinetics
Investigation of the quasi-ternary system LaMnO3–LaCoO3– ‘‘LaCuO3’’. II: The series LaMn0.252xCo0.752xCu2xO32d and LaMn0.752xCo0.252xCu2xO32d
No full textThis paper investigates the crystal structure,
thermal expansion, and electrical conductivity of two
series of perovskites (LaMn0.25-xCo0.75-xCu2xO3-d and La
Mn0.75-xCo0.25-xCu2xO3-d with x = 0, 0.025, 0.05, 0.1,
0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO3–
LaCoO3–‘‘LaCuO3’’. The Mn/Co ratio was found to have a
stronger influence on these properties than the Cu content. In
comparison to the Co-rich series (LaMn0.25-xCo0.75-xCu2x
O3-d), the Mn-rich series (LaMn0.75-xCo0.25-xCu2xO3-d)
showed a much higher Cu solubility. All compositions in
this series were single-phase materials after calcination at
1100 �C. The Co-rich series showed higher thermal expansion
coefficients (amax = 19.6 9 10-6 K-1) and electrical
conductivity (rmax = 730 S/cm at 800 �C) than the Mnrich
series (amax = 10.6 9 10-6 K-1, rmax = 94 S/cm at
800 �C). Irregularities in the thermal expansion curves
indicated phase transitions at 150–350 �C for the Mn-rich
series, while partial melting occurred at 980–1000 �C for the
Co-rich series with x[0.15