Innovating alloy production: A single step from ores to sustainable metals

Metal production is answerable for 10% of worldwide CO₂ emissions, with iron production emitting two tons of CO₂ for each ton of metal produced, and nickel production emitting 14 tons of CO₂ per ton and much more, depending on the ore used. These metals form the inspiration of alloys which have a low thermal expansion, called Invar. They’re critical for the aerospace, cryogenic transport, energy and precision instrument sectors. Recognizing the environmental toll, scientists on the Max Planck Institute for Sustainable Materials (MPI-SusMat) have now developed a brand new method to supply Invar alloys without emitting CO₂ while saving an enormous amount of energy — achieving this in a single-step process that integrates metal extraction, alloying, and thermomechanical processing right into a single reactor and process step.

Their approach dissolves among the classical boundaries between extractive and physical metallurgy, inspiring direct conversion from oxides to application-worthy products in a single single solid-state operation. Their findings were published within the journal Nature.

One-step-metallurgy saves energy and CO₂

“We asked ourselves: can we produce an alloy with near-optimized microstructure-property combination directly from ores or oxides with zero CO₂emission?” says Dr. Shaolou Wei, Humboldt research fellow at MPI-SusMat and first writer of the publication. Conventional alloy production is usually a three-step process: first, reducing ores to their metallic form, then mixing liquified elements to create the alloy, and eventually applying thermomechanical treatments to realize the specified properties. Each of those steps is energy-intensive and relies on carbon as each an energy carrier and a reducing agent, leading to significant CO₂ emissions. “The important thing idea is to know the thermodynamics and kinetics of every element and use oxides with similar reducibility and mixability at around 700°C,” Shaolou continues, “This temperature is much below the majority melting point, which still allows us to extract metals from their oxide states and blend into alloys via one single solid-state process step without reheating.” Unlike conventional methods where ores are reduced using carbon, which leads to carbon-contaminated metals, the team’s latest method uses hydrogen because the reducing agent. “Using hydrogen as an alternative of carbon brings 4 key benefits,” explains Professor Dierk Raabe, managing director at MPI-SusMat and corresponding writer of the study. “First, the hydrogen-based reduction only produces water as a byproduct, meaning zero CO₂ emissions. Second, it yields pure metals directly, eliminating the necessity to remove carbon from the ultimate product, thus saving time and energy. Third, we do the method at comparably low temperatures, within the solid state. Fourth, we avoid the frequent cooling and reheating characteristic of conventional metallurgical processes.”

The resulting Invar alloys produced using this method not only match the low thermal expansion properties of conventionally produced Invar alloys, but in addition offer superior mechanical strength because of the refined grain size naturally inherited from the method.

Upscaling to industrial dimensions

The Max Planck scientists have demonstrated that producing Invar alloys through a quick, carbon-free, and energy-efficient process will not be only possible but highly promising. Nevertheless, scaling this method to satisfy industrial demands presents three key challenges:

First, while the researchers used pure oxides for a proof-of-concept study, industrial applications would likely involve conventional, impurity-laden oxides. This introduces the necessity to adapt the method to handle less refined materials while maintaining alloy quality. Second, using pure hydrogen within the reduction process, though effective, is expensive for large-scale operations. The team is now conducting experiments with lower hydrogen concentrations at elevated temperatures to search out an optimal balance between hydrogen use and energy costs, making the method more economically viable for industry. Third, while the present method uses pressure-free sintering, producing finely coarsened bulk materials on an industrial scale would likely require the addition of pressing steps. Incorporating mechanical deformation into the identical process could further enhance the fabric’s structural integrity while keeping the production streamlined.

Looking ahead, the flexibility of this one-step process opens up latest possibilities. Since iron, nickel, copper, and cobalt can all be processed this fashion, high-entropy alloys may very well be the subsequent focus. These alloys, known for his or her ability to take care of unique properties across a broad range of compositions, hold potential for developing latest materials, corresponding to soft magnetic alloys, ideal for high-tech applications. One other promising direction may very well be using metallurgical waste as an alternative of pure oxides. By removing impurities from waste materials, this approach could transform industrial byproducts into useful feedstock, further enhancing the sustainability of metal production.

By eliminating the necessity for top temperatures and fossil fuels, this one-step hydrogen-based process could drastically reduce the environmental footprint of alloy production, paving the best way for a greener, more sustainable future in metallurgy.

The research was funded with a fellowship to Shaolou Wei by the Alexander von Humboldt Foundation and a European Advanced Research Grant of Dierk Raabe.