ORIGINAL RESEARCH article
Front. Chem.
Sec. Astrochemistry
Shock-Induced Nucleation of Nanophase Fe-Ni Alloy and Its Implications for Interstellar Iron Reservoirs
Provisionally accepted
- Vellore Institute of Technology, Vellore, India
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Shock waves are ubiquitous in star-forming regions, protoplanetary disks, and cometary environments, yet their role in processing refractory metals remains poorly understood. Here, we demonstrate that laboratory shock-tube experiments produce Fe–Ni alloy nanoparticles from micron-sized Fe and Ni powders under conditions similar to low-velocity (1-2 km/s) dust-heating shocks in the interstellar medium and cometary comae. Peak temperatures of ~6000 K and reflected-shock pressures around 14.5 bar are sustained for about 2-3 ms. The subsequent cooling rate at ~106 K s⁻¹ drives direct vapor-phase condensation of bcc kamacite (α-Fe-Ni), without forming any intervening taenite phase. X-ray diffraction and Rietveld refinement confirm a homogeneous kamacite solid solution. Meanwhile, FESEM images display octagonal to sub-spherical particles forming loose clusters, indicating condensation from a transient fluid phase (vapor/melt droplets). HRTEM, SAED, and FFT analyses reveal well-ordered bcc lattices, high densities of dislocations and deformation twins suggesting rapid quench crystallisation under extreme nonequilibrium conditions. HAADF–STEM and EDS mapping show atomic-scale compositional uniformity, with Fe:Ni ratios closely matching the initial composition. The microstructures, compositions, and sizes of these shock-synthesised nanophase Fe-Ni alloy particles closely resemble nanophase metals observed in GEMS-bearing IDPs and Wild 2 samples, aligning with Ni-enriched metal vapor inferred from Fe I and Ni I detections in cometary comae. These experiments show that transient, low-velocity shocks (1-2 km/s) can produce nanophase Fe–Ni metal with meteoritic and cometary characteristics, establishing a strong mechanistic link between metal vapor chemistry, dust reprocessing, and the formation of nanoscale kamacite in primitive solar system and interstellar materials.
Keywords: Cometary dust, laboratory astrochemistry, Nanophase Fe-Ni Alloy, Rapid formation, shock-wave
Received: 24 Dec 2025; Accepted: 09 Feb 2026.
Copyright: © 2026 Chandrasekaran and Velampatti Selvaraj. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Vijayanand Chandrasekaran
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