in2science #6

The whole magazine in2science

Corrosion and Surface Technology

The WZK department develops fault-tolerant anti-corrosion coatings which remain effective even when subjected to mechanical damage as well as coatings for magnesium-based medical implants that dissolve in the body according to a set timetable. More about the Department Corrosion and Surface Technology

Magnesium Innovation Centre

The main focus of the research in MagIC, headed by Prof. Karl Ulrich Kainer, is the development of magnesium-based materials for diverse applications, for example in the transport and medical sectors. More about the Magnesium Innovation Centre

Clean Sky

Be it greenhouse gas emissions or noise pollution, the aviation industry’s environmental reputation isn’t always positive. The overarching Clean Sky 2 aviation project is therefore researching new technologies for cleaner and quieter aircraft. A joint, broad spectrum initiative between the European Commission and the aviation industry to improve all realms of technology and service, ranging from aircraft concept development to new propulsion methods and environmentally friendly operations. One inconspicuous but vital aspect is developing new, chromate-free coatings for magnesium components used in aerospace engineering to provide corrosion protection.

What moves us

Sleepless at the microscope: The exhaustive search for chromate replacements

For Dr Sviatlana Lamaka, a scientist at the Magnesium Innovation Centre at HZG, coatings are her passion. As a corrosion expert, she researches new coating additives as part of the ALMAGIC project (“Aluminium and Magnesium Alloys Green Innovative Coatings”). The Clean Sky initiative is funding her work with 280 thousand Euros until 2019.

Dr. Sviatlana Lamaka und Bahram Vaghefinazari in the laboratory

"It is very satisfying for me that countless sleepless nights in front of an electron microscope contribute to solving the pressing problem of replacing carcinogenic, highly toxic chromates with environmentally friendly materials"- Lamaka. Photo: HZG/ Christian Schmid


Photo: HZG/ Christian Schmid

“We are working closely with our partners at the Complutense University of Madrid, Delft University of Technology, with the project coordinator at the Spanish company CIDAUT, with AkzoNobel, Henkel and MTU Aero Engines,” explains Dr Lamaka, leader of the HZG team. “Our task in Geesthacht is to find non-toxic coating additives that effectively prevent magnesium and mag-nesium alloys from corroding.”

magnesium on the carriage

Photo: HZG/ Christian Schmid

It is precisely this aspect, that often restricts the use of magnesium in automotive and aerospace engineering. If untreated, the light metal easily reacts in salty and humid atmospheres, i.e., it corrodes. Chromates are the corrosion inhibitors currently widely used as additives for protective coatings.

Bahram Vaghefinazari measures here in different liquids at them the hydrogen production with and without inhibitor.

The small magnesium chips were produced from the six alloys and three pure magnesium varieties. Due to their shape, they have a particularly large surface area. Bahram Vaghefinazari measures hydrogen production due to magnesium dissolution in saline solution with or without the inhibitors. Photo: HZG/ Christian Schmid

The problem is that chromates are extremely toxic, highly carcinogenic and harmful for aquatic life, flora and fauna. New European Union legislation has therefore banned the use of chromates beginning in January 2019. Only in exceptional cases will an authorized extension be granted.

Chromate replacement would therefore be enormously important in many realms of industry. It is, however, a Herculean task: Sviatlana Lamaka, with HZG doctoral candidates Bahram Vaghefinazari and Di Mei have tested more than 150 chemical compounds as preparatory work for the ALMAGIC project. The inhibiting effect was tested against six different alloys and three types of pure magnesium.

Dr. Sviatlana Lamaka and Bahram Vaghefinazari at work

Samples of coated magnesium plates
are exposed to salty moist air for
several days or weeks. Photo: HZG/ Christian Schmid

The most promising candidates, after several thousand tests, proved to be compounds binding trivalent and divalent iron (Fe3+/Fe2+). Iron, always present as a minor impurity in magnesium, tends to initiate an expanding cathodic reaction. Blocking its dissolved species results in magnesium corrosion inhibition. This concept has been previously introduced by the HZG team at the Department of Corrosion and Surface Technology.

Dr. Sviatlana Lamaka and Bahram Vaghefinazari at work

Sviatlana Lamaka and Bahram
Vaghefinazari check the samples. Photo: HZG/ Christian Schmid

The search for these magnesium corrosion inhibitors took approximately two years. This work resulted in several scientific publications, but also, as Lamaka points out, “It is very satisfying for me that countless sleepless nights in front of an electron microscope contribute to solving the pressing problem of replacing carcinogenic, highly toxic chromates with environmentally friendly materials. The quest for replacement of carcinogenic chromates continues because it is one thing to find an effective inhibitor, but it is much more difficult to ensure that the inhibitor keeps performing once it is incorporated into the protective coating”.

Author: Heidrun Hillen (HZG)
Published in in2science #6 (June 2018)