Compact metallurgy Thermomix for metal production saves up to 40 percent energy

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Max Planck scientists combine the extraction, manufacturing, mixing, and processing of metals and alloys in a single, environmentally friendly step. The compact metallurgy saves up to 40 percent energy and is CO₂-free.

The production of approximately two billion tons of metals annually is responsible for 10 percent of global CO₂ emissions. To produce just one ton of iron, two tons of CO₂ are emitted. In the case of nickel, producing one ton results in 14 tons or more of CO₂. Yet iron and nickel are crucial for aerospace, the transport of liquid hydrogen, and the energy transition. They form so-called invar alloys, which are ideal for these applications due to their low thermal expansion.

How can such alloys be produced CO₂-free and with low energy consumption? Scientists at the Max Planck Institute for Sustainable Materials (MPI-SusMat) have developed a radically new strategy for this purpose. In a single process step and reactor, metal extraction, alloying, i.e., mixing, and thermomechanical processing are integrated, resulting in the finished material. This method enables the direct conversion of ores into applicable products. The Max Planck team has published their results in the scientific journal Nature.

Compact metallurgy saves up to 40 percent energy and is CO₂-free

"We asked ourselves: Can we produce an alloy with optimal properties directly from ores and without CO₂ emissions?" says Dr. Shaolou Wei, Humboldt Research Fellow at MPI-SusMat and first author of the publication. Conventional alloy production has for more than 6000 years typically been a three-step process: First, oxygen is removed from the ores to obtain the pure metal. This step is called reduction: iron or nickel ore is thus reduced to metal. Then, several metals or other elements are heated and liquefied to mix them, known as alloying. Finally, the alloy is thermomechanically processed, i.e., forged, rolled, heated, to achieve the desired properties. Each of these steps is energy-intensive, especially since the ores and metals are repeatedly heated, liquefied, and cooled down. Moreover, carbon is still used as an energy source and reducing agent, leading to significant CO₂ emissions.

The key idea is to understand the thermodynamics and kinetics of each involved element and use elements with similar reduction and mixing behavior at around 700 degrees Celsius.

Dr. Shaolou Wei, Humboldt-Research-Fellow at the MPI-SusMat and first author of the publication

"At 700 degrees Celsius, we can remove the oxygen from the ores and alloy the resulting metals in a single step, without having to liquefy the material. This saves enormous amounts of energy." Unlike conventional methods, where ores are reduced with carbon, the Max Planck scientists use hydrogen as a reducing agent.

The use of hydrogen instead of carbon offers four crucial advantages. First, the hydrogen-based reduction results in only water as a byproduct, and no CO2. Second, it directly produces pure metals or even their finished alloys.

Dierk Raabe, Managing Director at the MPI-SusMat and corresponding author of the study

"You don't have to remove any remaining carbon from the final product. This saves time and energy. Third, we conduct the process at relatively low temperatures and in the solid phase, not in liquid melts, thus saving energy again. Fourth, we avoid the frequent cooling and reheating characteristic of conventional metallurgical processes, allowing us to save significant energy there as well," explains Professor Dierk Raabe, managing director at MPI-SusMat and corresponding author of the study. Overall, the energy consumption is reduced by up to 40 percent compared to conventional metallurgy.

The Invar alloys produced using this method have the same low thermal expansion as conventionally produced Invar alloys and even offer better mechanical strength due to the refined microstructure resulting from this process.

From the laboratory to the industry

The Max Planck scientists have demonstrated that manufacturing Invar alloys through a rapid, CO₂-free, and energy-efficient process is promising. To bring this method from the current laboratory scale to industrial application, the scientists must overcome three key challenges:

Firstly, in the current research work, the scientists used pure oxides. However, in the industry, cheaper, contaminated oxides are used. This means that the Max Planck team must adjust their process to maintain the same quality of alloys. Secondly, the use of pure hydrogen in the reduction process is effective but costly for industrial applications. The team is now conducting experiments with lower hydrogen concentrations at higher temperatures to find an optimal balance between hydrogen consumption and energy costs, making the process more economical for the industry. Thirdly, for industrial purposes, very finely porous metals are needed, which with the new method from the Max Planck scientists would not be produced directly but would require an additional step, sintering.

The new process is not only interesting for invar alloys but also for all alloys based on iron, nickel, copper, or cobalt. The Düsseldorf Max Planck team is now also focusing on complex alloys consisting of more than five different elements, known as high-entropy alloys. These are used, for example, in aircraft turbines and electric motors. Another promising direction could be the use of metallurgical waste instead of pure oxides.

As high temperatures and fossil fuels are no longer required, this one-step, hydrogen-based process could drastically reduce the ecological footprint of alloy production and pave the way for a greener, more sustainable future in metallurgy.

The research was funded by an Alexander von Humboldt Foundation fellowship for Shaolou Wei and a European Advanced Research Grant for Dierk Raabe.