Scientists create a sustainable method combining metal extraction, alloying, and processing into one eco-friendly step.
Researchers from the Max Planck Institute have developed a holistic approach that integrates the extraction of metals, the creation of alloys, and processing—all in a single, environmentally friendly operation. Their innovative work has been reported in the journal Nature.
Metal manufacturing is responsible for 10% of the world’s CO2 emissions. Specifically, the production of a ton of metal from iron results in two tons of CO2, while nickel production emits a staggering 14 tons of CO2 per ton, with even higher emissions possible depending on the type of ore used. These metals are essential for creating alloys known as Invar, which possess low thermal expansion and are vital in various sectors, including aerospace, cryogenic transport, energy, and precision instruments. Aiming to mitigate the environmental impact, scientists at the Max Planck Institute for Sustainable Materials (MPI-SusMat) have successfully devised a new method for producing Invar alloys that emits no CO2 and conserves an extensive amount of energy. This is accomplished through a single-step process that combines metal extraction, alloying, and thermomechanical processing within a single reactor.
Their groundbreaking methodology challenges traditional distinctions between extractive and physical metallurgy, enabling the direct transformation from oxides to usable products in one efficient solid-state operation. Their research findings have been published in the journal Nature.
One-step-metal production reduces energy use and CO2
“We challenged ourselves with the question: Is it possible to create an alloy with an optimized combination of microstructure and properties directly from ores or oxides without emitting CO2?” states Dr. Shaolou Wei, a Humboldt research fellow at MPI-SusMat and the leading author of the study. Typical alloy production consists of three stages: first, converting ores into metal; second, mixing melted elements to form the alloy; and finally, applying thermomechanical treatments to obtain the desired characteristics. Each of these stages consumes a significant amount of energy and relies on carbon both as an energy source and a reducing agent, leading to notable CO2 emissions. “Our pivotal idea centers around understanding the thermodynamics and kinetics of each element, utilizing oxides that share similar reducibility and mixability at approximately 700°C,” Dr. Wei adds. “This temperature is significantly lower than the melting point, allowing us to extract metals from their oxide forms and blend them into alloys through a single solid-state process without the need for reheating.” In contrast to traditional methods, where reduction is achieved using carbon, resulting in carbon contamination in the metals, the new process uses hydrogen as the reducing agent. “Switching to hydrogen offers four main benefits,” explains Professor Dierk Raabe, managing director at MPI-SusMat and corresponding author of the paper. “Firstly, the hydrogen reduction process generates only water as a byproduct, thereby producing zero CO2 emissions. Secondly, it produces pure metals straight away, eliminating the need to remove carbon later, which saves both time and energy. Thirdly, this process operates at relatively low temperatures in a solid-state environment. Lastly, we avoid the repeated cycles of cooling and reheating that are common in traditional metallurgical procedures.”
The Invar alloys generated through this innovative technique not only display the low thermal expansion traits typical of conventional Invar alloys but also provide enhanced mechanical strength due to the fine grain size achieved naturally via this process.
Scaling Up for Industrial Use
The researchers at Max Planck have shown that creating Invar alloys with a fast, carbon-free process that is energy-efficient is not just feasible but highly promising. However, there are three major challenges in scaling this method for industrial applications:
Firstly, the researchers utilized pure oxides for their proof-of-concept study, whereas industrial uses would likely involve standard oxides containing impurities. This necessitates modifications to the process to manage lower-grade materials without compromising the quality of the alloys. Secondly, while the use of pure hydrogen for reduction is effective, it can be expensive for large-scale production. Consequently, the team is experimenting with lower hydrogen concentrations at higher temperatures to strike a balance between hydrogen efficiency and energy costs, making the approach more financially viable for industrial usage. Thirdly, although the current method employs pressure-free sintering, creating finely coarsened bulk materials at an industrial scale may require incorporating pressing steps. Adding mechanical deformation into the process could further bolster the structural integrity of the material while keeping production streamlined.
Looking forward, the flexibility of this one-step technique opens numerous new avenues. Since iron, nickel, copper, and cobalt can all be processed in this way, the development of high-entropy alloys might be the next area of focus. These alloys are esteemed for their unique properties across a wide range of compositions and could lead to the creation of new materials, such as soft magnetic alloys suited for advanced technological applications. Another avenue worth exploring is the utilization of metallurgical waste instead of pure oxides. By purging impurities from waste materials, this strategy could convert industrial byproducts into valuable resources, further promoting the sustainability of metal manufacturing.
By eliminating the necessity for high temperatures and fossil fuel reliance, this one-step hydrogen-based process could significantly lessen the environmental impact of alloy production, heralding a greener and more sustainable future for the metallurgy industry.
This research was supported by a fellowship awarded to Shaolou Wei by the Alexander von Humboldt Foundation, along with a European Advanced Research Grant provided to Dierk Raabe.
