Communications Materials· 2026Q1
Real-time imaging of cobalt mobility in graphite at elevated temperatures for advanced nuclear applications
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- 2026year
Short summary
Real-time in situ SEM imaging shows cobalt nanoparticles nucleate near 400°C, fragment via spiral motion at ~520°C during a phase transition, and re-grow above 800°C, with minimal migration (<1 µm in 4h) at ~750°C.
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Key points
- Cobalt nanoparticles nucleate near 400°C in graphite.
- Spiral fragmentation of cobalt occurs at ~520°C, coinciding with its hcp–fcc phase transition.
- Cobalt re-grows above 800°C with minimal surface diffusion (<1 µm over 4h) at ~750°C.
- Substantial cobalt release is observed only near 1100°C, above normal operating conditions.
AI-generated from the title and abstract; the full text is not read.
Abstract
Abstract Radionuclide retention within the core at elevated temperatures is essential for the safe operation of Generation IV graphite-moderated reactors. Here, we report real-time in situ Scanning Electron Microscopy (SEM) imaging of cobalt migration in graphite at high temperatures. Cobalt nanoparticles nucleate near 400 °C and undergo a distinctive spiral fragmentation at ~520 °C, coinciding with the cobalt hexagonal close-packed (hcp)–face-centred cubic (fcc) phase transition temperature, before re-growing above 800 °C. Minimal surface diffusion was observed at ~750 °C with movement confined within 1 µm over four hours. Transmission Electron Microscopy (TEM) confirms subsurface clustering and demonstrates the role of graphite microstructure and defect density in retaining cobalt. Mass spectrometry after heating between 550 and 1100 °C validates these observations, indicating that substantial cobalt release occurs only near 1100 °C, above normal operating conditions. These findings demonstrate the low mobility of cobalt at reactor-relevant temperatures and establish a framework for probing high-temperature ion dynamics in advanced materials.
The authors' abstract, as published at the source. Communications Materials, 2026 · DOI ↗
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Field: Materials Chemistry
Materials ChemistryMaterials Science