Oberflächenpotentialverteilungen durch galvanostatische 3-D-Rastermessungen

Objective of the present work is the measurement of electrochemical potential data on real surfaces in their state under operating conditions. During such a potential measurement a constant distance between the probe and the surface is the main parameter. A literature overview shows that only the Scanning Vibrating Electrode Technique (SVET) is suited for 3D scanning procedures, all others are restricted to plane surface applications. Yet, if a specimen has to be prepared for a 2D measurement, the surface of interest is changed and the recorded potential data are affected. The development of the measurement technique SCAn (Scanning Corrosion Analysis) is described here which allows to establish the potential map at deformed surfaces with a constant measurement distance. The procedure is executed in two steps: First, the topography of the surface of interest is measured by means of an opto-electronic device. Subsequently the scanning probe detects the potential distribution controlled by the stored surface data to attain a con-stant working distance between the probe tip and the specimen. Because of the measurement procedure in two steps, a relocalisation of the topographical data and the potential distribution is required. This is the main restriction for the detection of very small surface irregularities. During pilot tests with plane copper samples the main parameters of galvanostatic potential measurements were figured out. The measurement distance, which depends on the geometry of the probe, mainly affects the surface potential, and also the influence of the polarisation current of the electrochemical cell on the potential profiles is demonstrated. The line scans were additionally disturbed by microgeometric changes of the surface which may occur e.g. at weld seams. 3D potential distributions were taken from weld joints of micro-alloyed steels preferentially used in the shipbuilding industry. A measuring bed was set up for 3D SCAn comprising a controler for electrochemical cell measurements with the related software, a three axis manipulator, an electrochemical cell, a laser device and a computer. The computer controls the scanning procedures and the data handling by an especially developed software package written in LABView. Its modular structure offers the opportunity to expand the measurement software and to apply new or modified scanning techniques with the measuring bed. The 3D potential distributions around weld seams permit to distinguish the effect of changes of microstructure in the heat affected zones and the effect of the chemical composition of the applied filler materials. The strong influence of the measurement distance on the potential values, which was already detected by 2D potential profiles with copper materials, has been confirmed with potential scanning studies of technical surfaces. For future investigations, an improved measurement equipment can lead to a higher stability of the electronic periphery and an accurate reproducibility of the 3D-manipulator. Additionally, a micromechanically manufactured probe is highly appreciated. These measurement components are well known from other mapping techniques and enable a better mechanical and electrochemical resolution at 3D surfaces. One advantage of the measurement principle and the present assembly is the procedure performance in two steps. The topographical data scanning runs completely independent of the electrochemical potential record. Therefore the installation of an established scanning procedure like the Scanning Kelvin Probe (SKP) or the Scanning Reference Electrode Technique (SRET) is feasible. The modular structure of the measurement software can easily be adapted to a modified scanning equipment; a 3D-SKP or 3D-SRET measurement can be performed.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Reckers, Stephan

Contributors dc:contributor

• Beiss, Paul

• info:eu-repo/classification/ddc/530
• Physik
• elektrochemische Zelle
• wässrige Korrosion
• Rastersondenmessung
• Lasertriangulationssensoren
• Topographie
• Potential-Abstand-Kurve
• lokale Auflösung

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-120617%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:58782