Publications

Electrochemical impedance spectroscopy (EIS) was used to evaluate the degree of delamination of the epoxy primer Uniprime ED-4 1 electrocoated on phosphate–treated cold–rolled steel in 3.5% NaCl exposed to air. Specimens with coating thicknesses of 20.3 and 20.8 pm and surface areas of 78.5 cm 2 were used. Coating parameters were obtained using a circuit–analog model. The area of delamination was estimated using several EIS parameters, including the pore resistance and the break point frequency. These values were compared to the corroded area determined visually. All methods considered exhibited a strong correlation over some or all of the range of exposure times. © 1991, The Electrochemical Society, Inc. All rights reserved.

Electrochemical dc methods were used to study the reduction of chromium (VI) in the presence of organic additives. It is shown that F - , thiourea, and citric acid are essential to enable deposition of black chrome from concentrated chromic acid solutions. A new formulation of the plating bath is defined. The optimum operating conditions under which spectrally selective surface of black chrome is deposited have been determined.

It is shown that the open circuit potential of a titanium electrode in TiCl3 solutions of molten lithium chloride-potassium chloride melts behaves according to the Ti(III)/Ti(II) redox electrode potential of the reaction: Ti + 2TiCl3 ⇄ 3TiCl2. A dependence of 75 mV per a logarithmic concentration ratio of (CTi(III))2 to (CTi(II))3 was obtained. The initial dissolution rate of titanium in TiCl3 showed a first order process with respect to the TiCl3 concentration with a specific rate constant of 5.05 × 10-3 min-1. The rate determination was extended from 723 to 803 K and the activation energy was calculated to be 88.68 kJ mol-1. The actual titanium dissolution rate in TiCl3 was measured and used to verify the validity of the results obtained by the electrochemical techniques (linear polarization and Tafel methods). A correlation was developed that relates the corrosion current obtained from the Tafel methods, Icorr(Tafel), to that obtained from the actual metal dissolution, Icorr(w.d.). Tafel slopes for Ti dissolution were 90 mV decade-1 which gives an anodic transfer coefficient, $\beta$, of 1.55 while the cathodic Tafel slope is 100 mV decade-1 giving a cathodic transfer coefficient, a, of 0.5. A dissolution mechanism compatible with the experimental facts is proposed. © 1991.

Autocatalytic (electroless) deposition of Ni-P alloy films has been carried out since 1946. Industrial applications of autocatalytic deposition have grown extensively in the last five years and now touch on a wide range of engineering fields. The addition of transition metal elements such as chromium, molybdenum or tungsten to Ni-P alloy films improve their chemical and physical properties (such as corrosion resistance and thermal stability). Chemical characterization of Ni-Mo-P alloy films has been carried out using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS)

Experimental and theoretical cyclic voltammograms for electronically conducting polypyrrole film are obtained from the identical conditions and compared to each other to characterize electrochemical behavior of the polymer. A comparison of the simulated and experimental cyclic voltammograms shows quantitative agreement. The profiles of the dependent variables show that the switching process is governed by the availability of the counterion to the polypyrrole electrode and the amount of electroactive sites. Sensitivity analysis shows that the double layer effects have more influence in the cyclic voltammograms than the electrokinetic effects.