Reactive Vapor-Phase Dealloying-Alloying Combines Several Metallurgical Processes to Chemically Derive Nano-Structured Porous Alloys from Oxides: Modern Day Alchemy

     Researchers at Max Planck Institute for Sustainable Materials (MPI-SusMat) have discovered a very interesting way to make durable metal alloy materials that involves, rather counterintuitively, the process of dealloying, which is akin to the process of corrosion. The resultant materials are lightweight, have high tensile strength, and the chemical process does not emit greenhouse gases.  

     Tech Xplore explains the breakthrough:

“By combining dealloying with alloying in a single step, the team developed nano-porous martensitic alloys using reactive gases like ammonia, which simultaneously remove oxygen and introduce nitrogen into the material's structure.”

     Strong lightweight materials are desirable especially for reducing energy transport. These materials also have potential for functionality, for example, as new alternatives to rare-earth magnets potentially with better performance.

     The dealloying removes oxygen from the atomic lattice structure. The medium of the reaction is a reactive gas, in this case ammonia. The hydrogen in ammonia acts as a reducing agent to take the oxygen out of the lattice in the chemical process which is known as ‘reactive vapor-phase dealloying.’ The process first increases spaces, or porosity in the lattice. Then the ammonia donates interstitial nitrogen into those spaces, enhancing the material’s properties.

"This dual role of ammonia—removing oxygen and adding nitrogen—is a key innovation in our approach, since it assigns all atoms from both reaction partners specific roles" says Professor Dierk Raabe, managing director of MPI-SusMat and corresponding author of the study.

     Tech Xplore explains that the process involves four metallurgical processes in one step. This seems like a very interesting breakthrough for alloy materials to me.

 

Four crucial metallurgical processes in one step

The team's breakthrough lies in integrating four crucial metallurgical processes into a single reactor step:

1)        Oxide dealloying: Removing oxygen from the lattice to create excessive porosity while simultaneously reducing the metal ores with hydrogen.

2)        Substitutional alloying: Encouraging solid-state interdiffusion between metallic elements upon or after complete oxygen removal.

3)        Interstitial alloying: Introducing nitrogen from the vapor phase into the host lattice of the gained metals.

4)        Phase transformation: Activating thermally-induced martensitic transformation, the most viable pathway for nano structuring.

 

     The process may be applicable for alloys containing iron, nickel, cobalt, and copper. Since hydrogen is used as the energy carrier rather than carbon, there is no CO2 produced. Water is the only byproduct. Waste emissions from Industrial waste could be a future source of reactive gases. Before this breakthrough, the porosity-increasing step of the path to these porous nano-structured alloys required both considerable time and considerable energy.

“Future applications could range from lightweight structural components to functional devices such as iron-nitride-based hard magnetic alloys, which could surpass rare-earth magnets in performance. Looking ahead, the researchers envision expanding their approach to use impure industrial oxides and alternative reactive gases. This could revolutionize alloy production by reducing reliance on rare-earth materials and high-purity feedstocks thus aligning with global sustainability goals.”

 

     The abstract of the paper in Science Advances explains the process and its implications:

“For millennia, alloying has been the greatest gift from metallurgy to humankind: a process of mixing elements, propelling our society from the Bronze Age to the Space Age. Dealloying, by contrast, acts like a penalty: a corrosive counteracting process of selectively removing elements from alloys or compounds, degrading their structural integrity over time. We show that when these two opposite metallurgical processes meet in a reactive vapor environment, profound sustainable alloy design opportunities become accessible, enabling bulk nanostructured porous alloys directly from oxides, with zero carbon footprint. We introduce thermodynamically well-grounded treasure maps that turn the intuitive opposition between alloying and dealloying into harmony, facilitating a quantitative approach to navigate synthesis in such an immense design space. We demonstrate this alloy design paradigm by synthesizing nanostructured Fe-Ni-N porous martensitic alloys fully from oxides in a single solid-state process step and substantiating the critical kinetic processes responsible for the desired microstructure.”

   In order to verify nitrogen interstitial alloying the experiment, first carried out with ammonia (NH3) as the reducing agent, was also performed with hydrogen gas (H2), which produced consistent results. See below.

 

References:

 

Harnessing corrosion: Scientists transform dealloying into sustainable lightweight alloy design. Yasmin Ahmed Salem. Tech Xplore. December 18, 2024. Harnessing corrosion: Scientists transform dealloying into sustainable lightweight alloy design

Reactive vapor-phase dealloying-alloying turns oxides into sustainable bulk nano-structured porous alloys. Shaolou Wei, and Dierk Raabe. Science Advances. 18 Dec 2024. Vol 10, Issue 51. Reactive vapor-phase dealloying-alloying turns oxides into sustainable bulk nano-structured porous alloys | Science Advances