{ "id": "ep2rnwgjn7", "slug": "aluminothermic-reduction", "title": "Aluminothermic reduction", "updated": "2026-10-15", "topic_path": [ { "id": "technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/topics/technology" }, { "id": "technology.engineering", "label": "Engineering and manufacturing", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.engineering" }, { "id": "technology.engineering.engineering.materials.metallurgy", "label": "Materials science and metallurgy", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.engineering.engineering.materials.metallurgy" } ], "geo": [ { "id": "geo.nongeo.t1800.technology.engineering.engineering.materials.metallurgy", "label": "Non-geographic · 1800 to 1945: Materials science and metallurgy", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800.technology.engineering.engineering.materials.metallurgy", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1800", "label": "Non-geographic · 1800 to 1945", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800" }, { "id": "geo.nongeo.t1800.technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800.technology" }, { "id": "geo.nongeo.t1800.technology.engineering", "label": "Engineering and manufacturing", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800.technology.engineering" }, { "id": "geo.nongeo.t1800.technology.engineering.engineering.materials.metallurgy", "label": "Materials science and metallurgy", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800.technology.engineering.engineering.materials.metallurgy" } ] } ], "excerpt": "Aluminothermic reduction is a metallurgical method in which aluminum reduces metal oxides to metals or alloys in a strongly exothermic reaction, used to produce ferroalloys and to weld rails.", "snippet": "Aluminothermic reduction is a metallurgical method in which aluminum reduces metal oxides to metals or alloys in a strongly exothermic reaction, used to produce ferroalloys and to weld rails.", "node": "technology.engineering.engineering.materials.metallurgy", "markdown": "# Aluminothermic reduction\n\nAluminothermic reduction is a metallurgical method in which metallic aluminum reduces metal oxides to metals or alloys in a strongly exothermic reaction, used industrially to produce ferroalloys and to weld rails.[1](https://doi.org/10.1007/bf00353167) • [2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf) The heat released is often sufficient to melt both the metal product and the aluminum oxide slag.[1](https://doi.org/10.1007/bf00353167) The method produces ferroalloys such as ferrotungsten, ferromolybdenum, and ferrovanadium that improve the properties of cast iron and steel,[3](https://www.mdpi.com/2075-4701/10/11/1493) and, more recently, it separates cobalt and lithium from spent battery cathodes and reprocesses metallurgical slags.[4](https://www.ausimm.com/globalassets/conferences-and-events/molten/delete-july-2024/poster-20.pdf)\n\n| Key fact | Value |\n|---|---|\n| Reaction enthalpy, Fe₂O₃ + 2Al | −849 kJ per mole of Fe₂O₃ reduced; reaction temperature about 2500 °C[2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf) |\n| Reducibility order by Al (0–2000 °C) | Cu₂O > NiO > CoO > Fe₂O₃ > Cr₂O₃ > MnO > TiO₂[4](https://www.ausimm.com/globalassets/conferences-and-events/molten/delete-july-2024/poster-20.pdf) |\n| Self-propagation criterion | Adiabatic reaction temperature above 2000 K, or at least one product at its melt temperature[5](https://apps.dtic.mil/sti/pdfs/ADA419762.pdf) |\n| Iron thermit mass balance | 214 g of charge yields 112 g iron and 102 g Al₂O₃ slag[2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf) |\n| Chromium recovery, chromite concentrate | 71.8% (laboratory, with CrO₃ and NaClO₃ additions) to 79% (pilot scale)[6](https://www.pyrometallurgy.co.za/InfaconX/031.pdf) • [7](https://www.pyrometallurgy.co.za/InfaconXII/431-Eissa.pdf) |\n| Battery recycling output | Pure metallic Co at 11–20 wt% Al addition; CoAl alloy (86.1 wt% Co) at 28 wt%[8](https://link.springer.com/article/10.1007/s11663-024-03003-7) |\n\n## How it works\n\nThe driving force is the [Gibbs free energy](https://www.edgepedia.org/gibbs-free-energy) of oxide formation. Aluminum oxide is more stable than the oxides of copper, nickel, cobalt, iron, chromium, manganese, and titanium, so aluminum reduces them spontaneously; thermodynamic analysis over 0–2000 °C ranks Cu₂O as the most readily reduced, followed by NiO, CoO, Fe₂O₃, Cr₂O₃, MnO, and TiO₂.[4](https://www.ausimm.com/globalassets/conferences-and-events/molten/delete-july-2024/poster-20.pdf) Differential scanning calorimetry of the Al–V₂O₅ system shows an endothermic peak near 660 °C from aluminum melting followed by an exothermic peak at 670–700 °C, so the reduction starts only after aluminum melts; at 660 °C all such reactions show negative ΔG and ΔH.[9](https://www.mdpi.com/2075-4701/15/7/704)\n\nOnce initiated, the reaction sustains itself if the adiabatic reaction temperature exceeds 2000 K or at least one product reaches its melting point.[5](https://apps.dtic.mil/sti/pdfs/ADA419762.pdf) For 2Al + Fe₂O₃ the adiabatic temperature is 3135 K when solid–solid, solid–liquid, and liquid–gas heats of transition are included.[5](https://apps.dtic.mil/sti/pdfs/ADA419762.pdf) The iron thermit reaction releases −849 kJ per mole of Fe₂O₃ (from −1675 kJ/mol for Al₂O₃ formation minus −826 kJ/mol for Fe₂O₃) and reaches about 2500 °C.[2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf) Aluminum is preferred over calcium or magnesium because Al₂O₃ melts near 2051–2054 °C, well below CaO (2580 °C) and MgO (2800 °C), which eases slag–metal separation, and it is cheaper and needs no pressure-tight vessels.[1](https://doi.org/10.1007/bf00353167)\n\n## How it is done\n\nThe charge contains the oxide (or ore concentrate), aluminum powder as reductant, a slag-forming flux such as CaO, and, where the base reaction is not energetic enough, thermal boosters such as NaClO₄ or KNO₃ plus diluent coolants.[1](https://doi.org/10.1007/bf00353167) In ferrotitanium production from ilmenite, the amounts of the exothermal agent NaClO₃, the slag-forming CaO, and the aluminum are the variables adjusted, and calculations show the exothermal agent plays a crucial role.[3](https://www.mdpi.com/2075-4701/10/11/1493)\n\n[Activation energy](https://www.edgepedia.org/activation-energy) is applied at a single point, for example with an ignition mix, and the exothermic reaction then propagates through the charge self-sustainingly.[2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf) The melt is contained in a lined crucible or reaction vessel; in rail welding, the thermit steel is heated to about 2500 °C in a reaction crucible and poured into preheated casting molds around the rail ends, which it melts and joins, with the mold removed after about 4–5 minutes.[2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf) Output is tuned through the charge: pilot heats on low-grade chromite ore reached 79% chromium recovery and 76% metallic yield by adjusting total input energy, flux composition and amount, and the reductant-to-ore ratio.[7](https://www.pyrometallurgy.co.za/InfaconXII/431-Eissa.pdf)\n\n## Origin\n\nCourt records establish the precursors: the oxide-reduction reaction using aluminum. Goldschmidt, working for the Krupp Steel Works to make carbon-free chromium and manganese, learned of Vautin's discovery, met him in London, and in December 1894 entered an agreement to exploit it. The thermite reaction is a method to obtain pure metals from ores without the use of carbon.[10](https://publica-rest.fraunhofer.de/server/api/core/bitstreams/fa6230b1-4cec-4b7f-8700-6712efdc67df/content) The contribution was not discovering the aluminum reaction but a method of initiating it internally by heating a small portion of the mixture. Chromium, manganese, iron, vanadium, niobium, and ferroalloys were prepared with aluminum as reductant.[1](https://doi.org/10.1007/bf00353167) Thermit welding on tram rails was carried out in [Wuppertal](https://www.edgepedia.org/wuppertal).[2](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf)\n\n## Variants\n\n**Thermit welding** is the most common method for welding rails in the field (maintenance and repair), but [flash butt welding](https://www.edgepedia.org/flash-butt-welding) is now the standard of choice for high-volume, plant-based, or performance-critical rail welding, and copper thermite is used to create electrical joints.[10](https://publica-rest.fraunhofer.de/server/api/core/bitstreams/fa6230b1-4cec-4b7f-8700-6712efdc67df/content) **Aluminothermic ferroalloy smelting** covers low-carbon ferrochromium from chromite concentrate, achievable in the laboratory without external electrical energy,[6](https://www.pyrometallurgy.co.za/InfaconX/031.pdf) ferrotitanium from ilmenite,[3](https://www.mdpi.com/2075-4701/10/11/1493) ferrovanadium from vanadium oxides with scrap steel and burnt lime flux,[11](https://sage.cnpereading.com/doi/10.1179/1743285515Y.0000000019) and ferroboron, where B₂O₃ reduction releases only 3268 kJ/kg against the 5363 kJ/kg needed, so thermite additives are required.[12](http://metalurgija.org.rs/mjom/vol20/No3/6_Manojlovic_MME-2003.pdf) **Self-propagating aluminothermic reduction**, related to self-propagating high-temperature synthesis (SHS), uses the reaction front itself to synthesize alloys: reduction of high-titanium slag with Al powder, KClO₃, and CaO produced titanium-based alloys,[13](https://rmme.ijournals.cn/rmme/article/pdf/20250638) and SHS of Ti6Al4V via Al-driven co-reduction was reported by K. Nazaretyan, H. Kirakosyan, and S. Aydinyan in 2025 in the International Journal of Self-Propagating High-Temperature Synthesis.[14](https://doi.org/10.3103/s1061386225700232) The field was surveyed for synthesis and processing applications in the 1993 review by L. L. Wang, Z. A. Munir, and Y. M. Maximov in the Journal of Materials Science.[1](https://doi.org/10.1007/bf00353167)\n\n## Applications\n\nBeyond ferroalloys and rail welding,[3](https://www.mdpi.com/2075-4701/10/11/1493) • [10](https://publica-rest.fraunhofer.de/server/api/core/bitstreams/fa6230b1-4cec-4b7f-8700-6712efdc67df/content) recent work extends the method to recycling. Aluminothermic reduction of LiCoO₂ cathode material at 750–1020 °C with 11, 20, and 28 wt% Al separates lithium and cobalt from end-of-life batteries; 11–20 wt% Al gave pure metallic cobalt, 28 wt% gave CoAl alloy (86.1 wt% Co, 13.9 wt% Al), and lithium reported to gas as Li(g) and to slag as LiAlO₂.[8](https://link.springer.com/article/10.1007/s11663-024-03003-7) Processing of nickel-bearing slags and concentrates with metallic aluminum or aluminum-containing wastes achieves metallic-phase reduction degrees of 90–95% with lower product carbon content.[15](https://www.nature.com/articles/s41598-026-45605-y)\n\n## Limitations and alternatives\n\nExcessive exothermicity is the main hazard: in the V–Al–Mo–CaO system, temperatures of 2427 °C and violent reaction dynamics under low aluminum conditions caused crucible rupture before reaction completion.[9](https://www.mdpi.com/2075-4701/15/7/704) Violent slag turbulence and splashing trap metallic particles in the slag, and flux must be balanced: moderate CaO additions of 6–8 wt% promote low-melting CaO·Al₂O₃ slag, while more than 12 wt% forms refractory CaO·6Al₂O₃ that impairs slag fluidity.[9](https://www.mdpi.com/2075-4701/15/7/704) Some aluminum dissolves into the liquid alloy, forming undesired intermetallic phases that require further purification,[4](https://www.ausimm.com/globalassets/conferences-and-events/molten/delete-july-2024/poster-20.pdf) and in ferrovanadium the alloy aluminum content rises rapidly with vanadium recovery, limited by commercial specifications.[11](https://sage.cnpereading.com/doi/10.1179/1743285515Y.0000000019) Incomplete reduction occurs without boosters: some chromite charges could not be reduced by aluminum alone,[6](https://www.pyrometallurgy.co.za/InfaconX/031.pdf) and boron utilization in ferroboron was only 45–60%.[12](http://metalurgija.org.rs/mjom/vol20/No3/6_Manojlovic_MME-2003.pdf) Alkali and alkaline-earth oxides, including MgO, are mostly reduced endothermically, requiring elevated temperature and vacuum, and Li₂O reduction by Al is not spontaneous below 1240 °C.[1](https://doi.org/10.1007/bf00353167) Against carbothermic and silicothermic routes, aluminum gives purer metals because silicon and carbon form stable silicides and carbides with product metals,[1](https://doi.org/10.1007/bf00353167) but the high thermal effect demands heat-balance control of charge composition and temperature regime.[15](https://www.nature.com/articles/s41598-026-45605-y)\n\n## References\n\n1. [L. L. Wang, Z. A. Munir, Y. M. Maximov (1993). Thermite reactions: their utilization in the synthesis and processing of materials. Journal of Materials Science.](https://doi.org/10.1007/bf00353167)\n2. [Chemistry lesson: the Thermit process (Elektro-Thermit GmbH technical note)](https://www.elektro-thermit.de/fileadmin/et/user_upload/PDF/Bedienungsanleitungen/Chemistry_lesson.pdf)\n3. [Investigating the Aluminothermic Process for Producing Ferrotitanium Alloy from Ilmenite Concentrate (Metals 10(11):1493)](https://www.mdpi.com/2075-4701/10/11/1493)\n4. [The application of aluminothermic reduction to metal/alloy production from oxides – a review (Nababan, Pownceby, Rhamdhani, CSIRO/Swinburne, Molten16, 2024)](https://www.ausimm.com/globalassets/conferences-and-events/molten/delete-july-2024/poster-20.pdf)\n5. [Thermite, intermetallic, and metal-fuel energetic compositions (DTIC report ADA419762)](https://apps.dtic.mil/sti/pdfs/ADA419762.pdf)\n6. [Effects of Charge Components on Reduction of Chromite Concentrates by Aluminothermic Process (INFACON X)](https://www.pyrometallurgy.co.za/InfaconX/031.pdf)\n7. [The Aluminothermic Production of Extra Low Carbon Ferrochromium from Low Grade Chromite Ore (INFACON XII)](https://www.pyrometallurgy.co.za/InfaconXII/431-Eissa.pdf)\n8. [Separation of Li and Co From LiCoO2 Cathode Material Through Aluminothermic Reduction: Investigation of the Thermite Reaction (Metallurgical and Materials Transactions B, 2024)](https://link.springer.com/article/10.1007/s11663-024-03003-7)\n9. [Exothermic and Slag Formation Behavior of Aluminothermic Reduction of Mo and V Oxides (Metals 15(7):704, 2025)](https://www.mdpi.com/2075-4701/15/7/704)\n10. [Thermite-type reactions: Ellingham analysis and experimental characterization (Fraunhofer, Weiser et al.)](https://publica-rest.fraunhofer.de/server/api/core/bitstreams/fa6230b1-4cec-4b7f-8700-6712efdc67df/content)\n11. [Understanding ferrovanadium smelting through computational thermodynamics modelling (Mineral Processing and Extractive Metallurgy)](https://sage.cnpereading.com/doi/10.1179/1743285515Y.0000000019)\n12. [Semi-empirical software for the aluminothermic and carbothermic reactions (Gavrilovski, Manojlović)](http://metalurgija.org.rs/mjom/vol20/No3/6_Manojlovic_MME-2003.pdf)\n13. [Preparation of Titanium-Based Alloys by Self-Propagating Aluminothermic Reduction of High-Titanium Slag (Rare Metal Materials and Engineering)](https://rmme.ijournals.cn/rmme/article/pdf/20250638)\n14. [K. Nazaretyan, H. Kirakosyan, S. Aydinyan (2025). Self-Propagating High-Temperature Synthesis of Ti6Al4V Alloy via Al-Driven Co-Reduction. International Journal of Self-Propagating High-Temperature Synthesis.](https://doi.org/10.3103/s1061386225700232)\n15. [Application of a complex Si–Al–Fe reducing agent for the production of a nickel-containing alloy (Scientific Reports)](https://www.nature.com/articles/s41598-026-45605-y)\n\n---\n*Topic: Encyclopedia › Technology and the built world › Engineering and manufacturing › Materials science and metallurgy*\n\n*Initially written Sep 29, 2026 · Edited: Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/aluminothermic-reduction", "markdown_url": "https://www.edgepedia.org/aluminothermic-reduction.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Aluminothermic reduction\", Edgepedia (EdgeChat), https://www.edgepedia.org/aluminothermic-reduction. Edgepedia Community License 1.0.", "credit_md": "\"[Aluminothermic reduction](https://www.edgepedia.org/aluminothermic-reduction)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/aluminothermic-reduction](https://www.edgepedia.org/aluminothermic-reduction). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Aluminothermic reduction\", Edgepedia (EdgeChat), https://www.edgepedia.org/aluminothermic-reduction. Edgepedia Community License 1.0.", "speakable": "Aluminothermic reduction is a metallurgical method in which aluminum reduces metal oxides to metals or alloys in a strongly exothermic reaction, used to produce ferroalloys and to weld rails." }