Corrosion is studied potentiostatically in the corroding environment of distilled water with an instrument that measures the potential of the corroding specimen immediately after interruption of the polarizing current. No current is flowing. The process permits compensation for IR drops when potentiostatic control is used in high resistance systems

Loess, R. E.

Youngdahl, C. A.

English

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September 1969
	 Brief 69-10413 
•	 AEC-NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Instrumentation for Potentiostatic Corrosion Studies With Distilled Water 
The problem: 
To measure the potential of a corroding specimen 
in high-resistance media such as distilled water. It is 
advantageous to measure the potential of the sample 
metal when no current is flowing.
polarizing current. The process is essentially contin-
uous, with interruption of the current for 6 msec of 
every 100-msec period. A method is described for 
control of the polarizing current at a preset level 
J). The process permits compensation for ir drops 
The solution:	 when potentiostatic control is used in high-resistance 
Corrosion may be studied potentiostatically in the 	 systems. 
corroding environment of distilled water with an	 How it's done: 
instrument that measures the potential of the corrod- 	 A simple potentiostat circuit is connected to the 
ing specimen immediately after interruption of the	 pulse voltmeter through an adjustable-bias voltage 
(continued ovcrlcaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000406 2020-03-16T18:16:08+00:00Z
supply. Incorporated in the potentiostat are auto-
matic means for adjustment of the polarization cur-
rent for maintenance of the selected polarization 
potential between the sample and the reference 
electrode. Unidirectional polarizing current is em-
ployed for simplification of the system; current re-
versal, during a test, necessitates manual adjustment. 
The pulse voltmeter circuitry is modified for con-
nection into a potentiostat loop and for the benefits 
deriving from semiconductor components. The be-
havior of the control-loop system during corrosion 
studies of aluminum samples in 70°C distilled water 
is described (I). 
Generally the geometry and materials of the sample-
cell system determine its electrical behavior. The 
temperature of the cell is kept constant by a 70°C 
water bath. The corrosion medium is degassed dis-
tilled water. A hollow platinum cylinder, fitting 
closely inside the closed cell, serves as a current-
carrying electrode. The sample is a solid cylinder of 
aluminum having its ends blanked with TFE fluoro-
carbon insulators for maintenance of equal current 
density at all exposed areas. 
Normally between 75 and 90 V are supplied to the 
20-kohm potentiometer. The current interrupter is a 
vacuum-tube circuit that interrupts the polarizing 
current for 6 msec once every 100 msec. The pulsat-
ing polarization current, flowing through the cell, 
produces a pulsating voltage pattern at the measure-
ment terminals (the sample and reference-electrode 
contacts). 
The pulse voltmeter receives a fluctuating voltage; 
its function is to determine the value of the vOltage 
of interest, regardless of the value of the solution ir
drop, and to provide a nonpulsating output voltage. 
A vacuum-tube cathode-follower input stage is 
employed to provide a high input resistance and 
minimum input capacitance, thus minimizing the 
amount of cell loading through the reference electrode. 
The potentiostat uses thyratron voltage-discrim-
inators that monitor the output voltage of the volt-
meter; these tubes switch motor-control circuits to 
adjust a potentiometer in the current supply. 
Reference: 
1. C. A. Youngdahl and R. E: Loess, J. Elecirochem. 
Soc. 114(5), 489 (May 1967). 
Note: 
Inquiries may be directed to: 
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10413 
Source: C. A. Youngdahl and R. E. Loess 
Metallurgy Division 
(ARG- 10409) 
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief B69-10413	 Category 03


Instrumentation for potentiostatic corrosion studies with distilled water

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