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An alternative explanation for the apparent passivation of molybdenum in 1 mol/L hydrochloric acid

DSpace at IIT Bombay

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Title An alternative explanation for the apparent passivation of molybdenum in 1 mol/L hydrochloric acid
 
Creator FALKENBERG, F
RAJA, VS
AHLBERG, E
 
Subject ferritic stainless-steels
cr-mo alloys
anodic-dissolution
fe-cr
corrosion
surface
films
hcl
electrode
passivity
 
Description A key question arising from studies on the corrosion behavior of molybdenum has been whether the passivation of molybdenum originates from a three-dimensional oxide film or from chemisorbed oxygen. In the present paper an alternative explanation for the apparent passivation behavior of molybdenum is given based on XPS measurements in combination with electrochemical techniques. Below the transpassive potential region, anodic current is obtained only if the sample has been cathodically activated and not after activation by ion etching. The experiments also show that the commonly used cathodic activation is insufficient to reduce the air-formed film. Thus, for such samples the anodic current in the apparent passive region could be due to oxidation of low valent oxides on the surface. However, a transient anodic current is observed also for ion-etched samples that have been subjected to cathodic polarization In addition, impedance measurements show an unexpectedly large capacitance in the apparent passive region, indicating some kind of adsorption equilibrium at the metal-solution interface. This leads to the suggestion that hydrogen formed in the reduction process can diffuse into the molybdenum metal and cause a limiting oxidation of hydrogen upon positive polarization. Thus, in the apparent passive region the current is mainly due to oxidation of hydrogen and an extension of the transpassive corrosion yields a very low corrosion current for molybdenum. This is in agreement with the XPS experiments, where no more than a monolayer of oxidized molybdenum can be detected in the apparent passive region. (C) 2001 The Electrochemical Society. .
 
Publisher ELECTROCHEMICAL SOC INC
 
Date 2011-07-21T14:31:59Z
2011-12-26T12:52:02Z
2011-12-27T05:38:58Z
2011-07-21T14:31:59Z
2011-12-26T12:52:02Z
2011-12-27T05:38:58Z
2001
 
Type Article
 
Identifier JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 148(4), B132-B137
0013-4651
http://dx.doi.org/10.1149/1.1354597
http://dspace.library.iitb.ac.in/xmlui/handle/10054/5894
http://hdl.handle.net/10054/5894
 
Language en