Search results for:
Pages: 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36
by V.M.M. Lobo
569-570
DOI:
by V.M.M. Lobo
571-576
DOI:
Study of ‘Transition State’ with Applied Potential [Mn – Sulfonamides – Cephalothin] System
Read Abstract
by M. S. Parihar, F. Khan
377-384
DOI:
Kinetic parameters and stability constants of [Mn – sulfonamides – cephalothin] system were reported at pH = 7.30 ± 0.01 in 1.0 M NaClO4 at 25 ºC. The sulfonamides were sulfadiazine, sulfisoxazole, sulfamethaxyzole, sulfamethazine, sulfathiazole, sulfacetamide and sulfanilamide as primary ligands, and cephalothin as secondary ligand. Values of transfer coefficient (α) varied from (0.41 to 0.59), showing that transition state behaves between oxidant and reductant response to applied potential and it adjusts itself in such a way that the transition state is located midway between dropping mercury electrode and solution interface. The rate constants (k) varied from 3.61 x 10-3 cm.sec.-1 to 9.93 x 10-3 cm.sec.-1, confirming that the electrode processes were quasi reversible. Small changes in potential not only affect the rate of the electrochemical reaction, but also strongly affect the rate constant. Values of stability constants (log β) varied from 1.75 to 9.13, showing that these drugs or their complexes could be used against Mn toxicity.
Structural Aspects Related to Lithium Intercalation and Ionic Dynamics: Frequency Response Analysis of (Snx,Ti1-x)O2 Based Systems
Read Abstract
by P. R. Buenoa, L. O. S. Bulhões
385-405
DOI:
Diffusion models capable of describing the ionic diffusion inside host materials, e.g. oxides, during intercalation processes, have been reported in the literature. However, the majority of the models do not succeed in establishing a good correlation between diffusion and structural environment. What is frequently described is the influence of an addition solid state reaction. In this paper we discuss about such additional reaction and its influence on the diffusion. The responses were evaluated by means of impedance patterns analyzed in (Snx,Ti1-x)O2 binary systems whose structural disorder control provides a way to evaluate how such structural disorder influences the global diffusion.
Studies on the Evaluation of the Performance of two Types of Polyurethane Coatings on Steel Rebars for the Prevention of Corrosion in Concrete Structures
Read Abstract
by R. Selvaraj, M. Selvaraj, S. V. K. Iyer
407-416
DOI:
The performance of two resin combinations, such as acrylic polyol – aromatic isocyanate and polyester polyol – aromatic isocyanate as durable and effective rebar coatings for steel in concrete has been examined by studying their mechanical properties and by using accelerated tests such as salt spray test and electrochemical impedance spectroscopy. It is found that polyester polyol-aromatic isocyanate combination performs better than acrylic polyol-aromatic isocyanate combination. Incorporation of fly ash in the coating is found to influence the performance of the coating.
Evaluation of Cementitious Repair Mortars for Corrosion Resistance
Read Abstract
by V. Saraswathya, H.-W. Song
417-432
DOI:
Repair and rehabilitation of deteriorated concrete structures are essential not only to utilize them for their intended service life, but also to assure the safety and serviceability of the associated components. A good repair improves the function and performance of the structure, thus prevents ingress of aggressive species to the steel/concrete interface and improves its durability. It is important to evaluate the performance of repair materials available for repairing the deteriorated concrete structures. This investigation was carried out to evaluate the durability characteristics of five types of modified cement based repair mortars. The corrosion resistance of the repair materials was evaluated by conducting various tests such as water absorption, rapid chloride ion penetration test, impressed voltage, 90 days ponding test, macro cell corrosion test, weight loss measurement, etc. Details of the test and their results were discussed. It is concluded that the modified cement based repair mortars formulated with different mineral admixtures (fly ash and/or silica fume) showed improved corrosion resistance.
Study of Acid Catalyzed Reactions of Proton Pump Inhibitors at D.M.E.
Read Abstract
by H. P. Gupta, K. Saini, P. Dhingra, R. Pandey
433-448
DOI:
Acid catalyzed reactions of three proton pump inhibitors (PPIs), namely omeprazole, lansoprazole and pantoprazole, have been investigated and monitored by direct current polarography at dropping mercury electrode (D.M.E) in phosphate buffer (0.1 M) of pH 3-7.5. This gives well defined current-time profiles of individual electroactive degradation products along with their starting materials. The investigation shows that the order of stability of three PPIs can be written as: pantoprazole omeprazole lansoprazole. The rate of degradation of PPIs decreases with decreasing the basicity of the corresponding benzimidazole nitrogen of PPIs, as predicted by the effect of individual substituents on each of the benzimidazole rings. At pH 7.5 all three PPIs are almost stable and the observed half wave potentials (E1/2 ) are –1.07 V for omeprazole, –1.25 V for lansoprazole and –1.32 V for pantoprazole. On decreasing the pH from 7.5 to 3.0 the anodic shift in E1/2 values were observed along with degradation of the PPIs and simultaneous appearance of degradation products. The present study may provide an insight for designing more potent new proton pump inhibitors.
Electrochemical Studies on the Corrosion Behavior of Carbon Steel in Presence of Cu and Ni
Read Abstract
The work presented in this paper deals with the investigations on the effect of Cu and Ni on the corrosion behavior of carbon steel under different experimental conditions. Electrochemical techniques like potentiodynamic polarization, linear polarization resistance and AC impedance have been used to investigate the effect of Cu and Ni on the corrosion behavior of carbon steel. The important experimental conditions which include the nature of aqueous medium, metal ion concentration and pH have been taken into account.
The instantaneous corrosion parameters as computed by potentiodynamic polarization, linear polarization resistance and AC impedance show an increase in corrosion rates of carbon steel with increasing Cu and Ni concentrations. However, the corrosion parameter as computed by AC impedance for an extended period of one month follows an interesting trend. The presence of Cu and Ni in the aqueous medium produces almost identical effect on the corrosion behavior of carbon steel. The microscopic examination of the test samples, under controlled laboratory conditions, did not show the evidence of localized attack on carbon steel in presence of different concentrations of Cu and Ni.
Cathodic Stripping Voltammetric Determination of Losartan in Bulk and Pharmaceutical Products
Read Abstract
by I. H. I. Habib, S. A. Weshahy, S. S. Toubar, M. M. A. El-Alamin
459-459
DOI:
Erratum to
Port. Electrochim. Acta 2008, 26(4), 315-324
Cathodic Stripping Voltammetric Determination of Losartan in Bulk and Pharmaceutical Products
Read Abstract
by I. H. I. Habib, S. A. Weshahy, S. Toubar, M. M. A. El-Alamin
315-324
DOI:
Cathodic stripping voltammetric determination of losartan using hanging mercury drop electrode HMDE was described. The method was based on adsorptive accumulation of the species at HMDE and at pH 7, followed by alternating current AC sweep. The behavior of adsorptive stripping response was studied under various experimental conditions, e.g. type of supporting electrolyte, pH, accumulation time, scan rate and mode of sweep (direct current DC, differential pulse DP, square wave SW and AC). In Britton-Robinson buffer solution, pH 7, a quasi-reversible reaction took place. The reduction response was more sensitive than the oxidation one and it was linear over the concentration range of 0.16-1.2 microg/mL. The determination of the cited compound in oral dosages was achieved using the standard addition method. The average of determinations obtained by square wave adsorptive voltammetric method with its standard deviation was 100.1±3%.
Glyphosate Determination in Soil, Water and Vegetables Using DPV Optimized by Response Surface Methodology
Read Abstract
by R. F. Teófilo, E. L. Reis, C. Reis, G. A. da Silva, J. F. Paiva, L. T. Kubota
325-337
DOI:
A voltammetric procedure optimized by experimental design for glyphosate determination in soil, water and vegetable samples is described. The voltammetry experiments were performed using a hanging mercury drop electrode (HMDE). The DPV variables involved in the optimization process were: voltage step, pulse amplitude, pulse interval, voltage step time and concentration of the supporting electrolyte. A full 25 factorial design was chosen to evaluate these effects. From the results obtained by the factorial design the three most important factors were determined. These variables were evaluated with a central composite design. Under the optimized conditions, the operational range was from 0.050 to 100.0 mg dm-3 and the detection and quantification limits were 14 and 48 µg dm-3, respectively. The optimized method was successfully applied to glyphosate determination in soil, water and vegetables after purifying with an ion exchange resin and derivation.
Phosphate of Aluminum as Corrosion Inhibitor for Steel in H3PO4
Read Abstract
by L. M. Alaoui, S. Kertit, A. Bellaouchou, A. Guenbour, A. Benbachir, B. Hammouti
339-347
DOI:
The influence of phosphate of aluminum (PA) on the corrosion inhibition of mild steel in phosphoric acid solution was studied using the weight-loss method. The electrochemical performance of the inhibitors was also investigated through potentiodynamic polarisation and EIS measurements. The inhibition efficiency of inhibitor increases with concentration to attain 84 % at 10-2M of PA in 0.33 M H3PO4. Polarization studies show that PA is a mixed-type inhibitor and acts both on the cathodic and anodic reactions without changing the mechanism of the hydrogen evolution reaction. The inhibition efficiency of PA is temperature-dependent in the range 298 - 363 K, the associated activation energy has been determined. PA adsorbs on the steel surface according to a Langmuir isotherm adsorption model.
Computational Simulation of Bray-Liebhafsky (BL) Oscillating Chemical Reaction
Read Abstract
by J. Ren, J. Z. Gao, W. Yang
349-360
DOI:
The computational simulation of the Bray-Liebhafsky (BL) oscillating chemical reaction by differential kinetic methodology is carried out in this work. According to the mechanism of Treindl and Noyes involving 10 reaction steps, the changes of the concentrations of I2 and O2 in solution are simulated. When the control parameters are alpha = 0.55, beta = 0.2882 and delta < 0.6, the differential equations present periodic solution, and the oscillations can be observed in 150 min. If , alpha and beta are taken as the control parameters, respectively, the bifurcation points would be observed in the processes of control parameters, changing successively with the critical values of alpha = 0.55,beta = 0.2882,and delta = 0.6. The acidity of solution on the nonlinear phenomena is also investigated in detail.
Comparison of Regression Model and Artificial Neural Network Model for the Prediction of Volume Percent of Diamond Deposition in Ni-Diamond Composite Coating
Read Abstract
by K. Ramanathan, V. M. Periasamy, U. Natarajan
361-368
DOI:
Nickel-diamond composite coatings are produced by electro deposition using sedimentation techniques on mild steel substrate at various cathode current density, pH and temperature. Electro deposition was carried out from a conventional Watts bath. Natural diamond powder of 6-12 m size was used in the study. The volume percent incorporation of diamond on the coated specimens was measured gravimetrically. Artificial Neural Network (ANN) and regression models (a mathematical model) were used to predict the volume percent incorporation of diamond in the Ni-diamond metal matrix. In this work, Volume fraction of diamond deposition (Vfd) was taken as response variable (output variable) and current density, pH and temperature were taken as input variables. The prediction of response variable was obtained with the help of empirical relation between the response variable and input variables using ANN and also through DOE. The predicted values of the responses by ANN and regression models were compared with the experimental values and their closeness with the experimental values was determined.
Calculation of the Streaming Potential Near a Rotating Disk with Rotational Elliptic Coordinates
Read Abstract
by F. S. Lameiras, E. H. M. Nunes
369-375
DOI:
The calculation with rotational elliptic coordinates of the streaming potential in the vicinity of a disk-shaped sample rotating in an electrolytic solution is presented. The measurement of this streaming potential is used to determine the zeta potential of planar surfaces. Rotational elliptic coordinates are favored in relation to integral transform methods because only simple mathematical methods are employed to explain the theory of this technique.
Hydrochloric Acid Corrosion Inhibition of Zn-Al-Cu Alloy by Methyl-Substituted Piperidines
Read Abstract
by S. S. Mahmoud
245-256
DOI:
The corrosion behavior of Zn-Al-Cu alloy was investigated in HCl solution in absence and in presence of different concentrations of inhibitors. The techniques of measurements were: weight loss, linear polarization and galvanic static polarization. It was found that the corrosion rate of this alloy was higher than that of zinc or aluminum. The inhibitors used were: heterocyclic piperidine (PP), 2- methyl piperidine (2mp), 3-methyl piperidine (3mp) and 4- methyl piperidine (4mp). These inhibitors are mixed type and their inhibition efficiency, I%, increases according to the order: 2mp < 3mp < pp < 4mp. The values of activation energy of corrosion were determined in absence and in presence of inhibitors. It was found that the presence of these inhibitors increases the values of activation energy. The adsorption of these inhibitors on the surface of the alloy follows Frumkin’s isotherm.
Natural Products as a Source of Environmentally Friendly Corrosion Inhibitors: The Case of Gum Exudate from Acacia seyal var. seyal
Read Abstract
by J. Buchweishaija, G. S. Mhinzi
257-265
DOI:
The inhibitive effect of the gum exudate from Acacia seyal var. seyal on the corrosion of mild steel in drinking water was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results obtained show that gum exudates could serve as effective inhibitors for the corrosion of steel in drinking water network. The percentage inhibition increases with increasing the concentration of the gum at 30 oC. The percentage inhibitor efficiency above 95 % was attained at gum concentration 400 ppm. The corrosion rates of steel and inhibition efficiencies of the gum exudates obtained from impedance and polarization measurements were in good agreement. Potentiodynamic polarization studies clearly reveal that the gum behaves predominantly as an anodic inhibitor. The study also shows that the inhibition efficiency was insignificantly affected by the temperature rise of the medium.
Eco-friendly Inhibitors from Naturally Occurring Exudate Gums for Aluminium Corrosion Inhibition in Acidic Medium
Read Abstract
by S. A. Umoren, I. B. Obot, E. E. Ebenso, P. C. Okafor
267-282
DOI:
Exudates gums from Pachylobus edulis (PE) and Raphia hookeri (RH) were evaluated as corrosion inhibitors for aluminium in HCl using weight loss and thermometric measurements at 30 – 60 oC. The exudates were found to retard corrosion rate of aluminium. The inhibition efficiency (%1) increased with increase in concentration of the exudates. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PE and RH exudate gums were found to obey Temkin adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady et al. at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. Exudate gum from RH was found to be a better inhibitor than PE.
2.5-Difuryl-N-Methylpyrrole as Corrosion Inhibitor for Steel in 1 M HCl
Read Abstract
by O. Krim, M. Bouachrine, B. Hammouti, A. Elidrissi, M. Hamidi
283-289
DOI:
This work is a study of 2.5-difuryl-N-methylpyrrole (B1) compound on the corrosion of steel in HCl medium. The investigation was carried out using gravimetric and electrochemical polarisation measurements. The corrosion rate decreases continuously with concentration of the compound (B1) and the efficiency increases to reach 90 % at 10-3 M. Polarisation results indicate that B1 is a cathodic inhibitor. B1 is adsorbed on metal surface according to the Langmuir isotherm. Value of free enthalpy of adsorption obtained involves chemisorption between inhibitor molecules and metal surface.
Comparative Study of Corrosion Behavior of AA2014/15 Vol%Al2O3p and AA2009/20 Vol% SiCw
Read Abstract
by S. B. Jamaludin, Z. Yusoff, K. R. Ahmad
291-301
DOI:
The influence of heat treatment on the corrosion behavior of two aluminium matrix composites (AA2014/15 vol% Al2O3p - composite A and AA2009/20 vol% SiCw -composite B) was analyzed in 3.5% sodium chloride solution. The kinetic of the corrosion process was studied based on the gravimetric measurements. The corrosion damage and pit shape were analyzed by Image Analyzer. The corrosion damage in both composites was caused by the pitting attack on the surface. Pit shape of the composite A is different to the composite B. The corrosion rate of composite A is higher than composite B because the voids or gap between reinforcement particles and matrix are larger than in the composite B. The main attack of nucleation sites was at the interface region of the matrix and the reinforcement.