Corrosion

Corrosion is a ubiquitous phenomenon, which is of great importance for the economy, since every year values of about 5% of GDP are destroyed by corrosion. Especially with safety critical structures like bridges a precise understanding of how to prevent corrosion is important. Corrosion research therefore has a high relevance for the economy and society.

 

Corrosion of metallic materials preferably occurs under conditions where a conductive substance is brought into contact with a corrosive medium. Under such conditions, electrochemical reactions can take place on the surface which lead to the steel being attacked. In the worst case the function of the component is no longer given and the total failure of the component can occur.

 

Since its foundation in 2000, CEST has intensively dealt with these questions, in particular with the elucidation of corrosion mechanisms as well as with the development of new coatings of both organic and inorganic nature (e.g. ZnCr alloy layers on galvanized steel, plasma electrolytically produced layers on aluminum or titanium). The development of efficient and environmentally friendly processes for corrosion protection helps to save costs and is of utmost importance for safety, health and environmental protection. In particular, the replacement of heavy metal or environmentally harmful and toxic surface treatments of metals, for example the search for alternatives to chromium (VI) conversion coatings, is a major challenge.

 

For the investigation of corrosion processes, CEST uses proven techniques such as electrochemical impedance spectroscopy (EIS) or salt spray tests as well as novel methods (such as corrosion detection by artificial intelligence).

 

We not only carry out research, but are also partners for companies in the field of corrosion. We carry out corrosion tests in accordance with the necessary standards, investigate cases of damage and are happy to assist our customers when it comes to necessary measures for the prevention and detection of corrosion.

 

In recent years, we have built up special expertise on a number of topics:
a) Corrosion of stainless steels

Stainless steels are materials on which many technologies of today’s world are based. A material that can possess outstanding mechanical properties, as can be seen impressively from a number of buildings in the world’s capitals. However, it is also one that, like any other, is exposed to the natural decay of time.

But not all steels are the same.  Their resistance to corrosive attack depends very much on the alloy composition, which is also reflected in the price of the steels.

Electrochemical experiments largely simulate the natural environmental conditions and identify the type of corrosive failure. This makes it possible, for example, to initiate targeted countermeasures to protect the component from further corrosive attack.

b) Hydrogen embrittlement

The role of atomic hydrogen in material damage (hydrogen embrittlement) is an important phenomenon, which occurs particularly in AHSS (Advanced High Strength Steels). The hydrogen is introduced into the steel samples either electrochemically or by (atmospheric) corrosion processes. In addition, diffusion paths of hydrogen in the microstructure of the steel can be visualized by means of Kelvin probe scanning force microscopy (SKPFM). Since even a very low concentration of only one ppm can cause hydrogen embrittlement, highly sensitive measurement techniques are required to detect the hydrogen in metals. Current technologies such as Kelvin probes, Devanathan-Stachurski cells as well as Thermal Desorption Mass Spectrometry (TDMS) for quantitative hydrogen analysis and various surface analysis methods are available.

c) In situ methods

Corrosion products which are caused by atmospheric corrosion processes under the influence of various environmental factors, e.g. SO2 or CO2, on metallic samples can be investigated by polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS). By coupling the method to a quartz microbalance, even the smallest mass changes can be observed.

In addition to the use of existing methods, the development of new pH/O2/H2/…-microsensors for use in scanning electrochemical microscopy (SECM), which can offer deep, spatially resolved insights into the course of corrosion processes, is the focus of current research.

d) High-temperature corrosion:

Electrochemical investigation methods to determine the oxidation and corrosion behaviour of metals and alloys are only sparsely used at elevated or high temperatures. A reliable method at CEST (together with the TU Vienna) is high temperature cyclovoltammetry (HT-CV), which provides both a simple and well-established cell structure for such investigations. Oxidation and corrosion rates could thus be precisely determined and the materials ranked on the basis of these results as well as the best among them further studies conducted.

Confocal Raman spectroscopy is a valuable and complementary method for characterizing oxide layers on these materials. Raman large area scans of oxidized surfaces have made a successful identification of different oxides including their structural order possible. Thus, the relationship between the oxide layer structure of a material and the HT-CV results can be discussed in detail.