{ "id": "epvfc00m0a", "slug": "flame-synthesis", "title": "Flame synthesis", "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.manufacturing.processes", "label": "Manufacturing processes and fabrication", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.engineering.manufacturing.processes" }, { "id": "technology.engineering.manufacturing.processes.forming-heat-treatment-and-finishing", "label": "Forming, heat treatment, and finishing", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.engineering.manufacturing.processes.forming-heat-treatment-and-finishing" }, { "id": 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"Non-geographic · 1946 to 2000: Forming, heat treatment, and finishing", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology.engineering.manufacturing.processes.forming-heat-treatment-and-finishing", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology" }, { "id": "geo.nongeo.t1946.technology.engineering", "label": "Engineering and manufacturing", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology.engineering" }, { "id": "geo.nongeo.t1946.technology.engineering.manufacturing.processes", "label": "Manufacturing processes and fabrication", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology.engineering.manufacturing.processes" }, { "id": "geo.nongeo.t1946.technology.engineering.manufacturing.processes.forming-heat-treatment-and-finishing", "label": "Forming, heat treatment, and finishing", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology.engineering.manufacturing.processes.forming-heat-treatment-and-finishing" } ] } ], "excerpt": "Flame synthesis is a fabrication method using combustion flames to convert vaporized or liquid precursors into nanoparticles, coatings, and other inorganic solids, including carbon black and fumed silica.", "snippet": "Flame synthesis is a fabrication method using combustion flames to convert vaporized or liquid precursors into nanoparticles, coatings, and other inorganic solids, including carbon black and fumed silica.", "node": "technology.engineering.manufacturing.processes.forming-heat-treatment-and-finishing.powder-metallurgy-and-sintering", "markdown": "# Flame synthesis\n\nFlame synthesis is a materials fabrication method that uses combustion flames to convert vaporized or liquid precursor feedstocks into nanoparticles, coatings, and other inorganic solids. Flame reactors produce 80–90% by value and volume of commercially available aerosol-made products today[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC3591782/), and commodity flame-made products such as carbon black, fumed silica, pigmentary titania, and optical fibers are manufactured at millions of tons per year, valued at over $15 billion annually.[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393)\n\n| Key fact | Value |\n|---|---|\n| Share of aerosol-made products from flame reactors | 80–90% by value and volume[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC3591782/) |\n| Typical primary particle size | 5–80 nm[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) |\n| Spray-flame temperature | Typically above 2000 °C[4](https://www.jstage.jst.go.jp/article/kona/29/0/29_2011025/_pdf/-char/en); up to 3000 °C in FSP of liquid raw materials[5](https://parteq.net/downloads/product%20datasheets/Product%20datasheet_FSP.pdf) |\n| Industrial production rate | Several tons per hour per reactor for carbon black, fumed silica, pigmentary titania[4](https://www.jstage.jst.go.jp/article/kona/29/0/29_2011025/_pdf/-char/en) |\n| FSP pilot production | A few kg/h; below 100 EUR/kg for simple oxides[4](https://www.jstage.jst.go.jp/article/kona/29/0/29_2011025/_pdf/-char/en) |\n| Homogeneous-particle enthalpy criterion | Combustion specific enthalpy above 4.7 kJ/g gas[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393) |\n| Fumed silica world market | Approximately 300,000 tons in 2010[4](https://www.jstage.jst.go.jp/article/kona/29/0/29_2011025/_pdf/-char/en) |\n\n## How it works\n\nA flame converts precursors into particles by two routes. In gas-to-particle conversion, the precursor evaporates, reacts, and forms gaseous monomers that nucleate in the gas phase; in droplet-to-particle conversion, crystal seeds form within liquid droplets at lower temperature.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) Vapor-fed flame processes lead to particles solely by gas-to-particle conversion, while liquid-fed ones may involve both routes.[6](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d) A 2024 laser-induced incandescence study of iron oxide formation distinguished the two pathways directly, with rapid droplet evaporation producing precursor vapor from which gaseous monomers form.[7](https://link.springer.com/article/10.1007/s00340-024-08334-6)\n\nProduct morphology is governed by the competition between the characteristic Brownian coagulation time \\( \\tau_{\\mathrm{coll}} \\) and sintering time \\( \\tau_{\\mathrm{sint}} \\). When \\( \\tau_{\\mathrm{coll}} > \\tau_{\\mathrm{sint}} \\), particles coalesce before the next collision, giving monodisperse nanospheres; when \\( \\tau_{\\mathrm{coll}} < \\tau_{\\mathrm{sint}} \\), chained aggregates form.[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393)\n\nTwo design criteria determine whether the product is homogeneous: the ratio of solvent boiling point to precursor decomposition temperature (threshold 1.05), and the combustion specific enthalpy. Above 4.7 kJ/g gas, sufficient heat evaporates the precursor and homogeneous fine particles form even when the boiling-point ratio is below 1.[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393)\n\n## How it is done\n\nIn flame spray pyrolysis, the precursor solution is fed at the reactor center, for example with a syringe pump, and dispersed by high-velocity gas such as O\\(_2\\) into a fine spray that is ignited and stabilized by a premixed flame; more than 50% of the combustion energy is contributed by the liquid precursor solution.[6](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d) The liquid is atomized through a central nozzle surrounded by a coflowing oxidizer, and because the liquid precursor is highly exothermic the flame is self-sustaining.[8](https://www.mdpi.com/1996-1944/16/3/1192)\n\nProduct powder is collected with baghouse filters or electrostatic precipitators, with HEPA filters or wet scrubbers downstream, and the system is held at slightly negative pressure by a [centrifugal fan](https://www.edgepedia.org/centrifugal-fan).[4](https://www.jstage.jst.go.jp/article/kona/29/0/29_2011025/_pdf/-char/en) Process gases such as Cl\\(_2\\) from titania production are recycled.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC3591782/)\n\nControl strategies include strong swirl stabilization (\\( S > 0.6 \\)) or weak swirl (\\( S \\leq 0.6 \\)), pilot flames, sheath gas, cooling meshes, quenching rings, water addition to the precursor liquid, droplet microexplosion, ultrafine atomization, and plasma discharge; physicochemical properties are tuned by crystal-structure control, element doping, core-shell design, and post-heat treatment.[9](https://www.sciopen.com/article/10.16511/j.cnki.qhdxxb.2023.25.016) Dopants steer the TiO\\(_2\\) phase: Al promotes rutile whereas Si promotes anatase.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC3591782/)\n\n## Origin\n\nSynthesis of fumed silica by combustion of SiCl\\(_4\\) in an oxyhydrogen flame yields a replacement for carbon black as a rubber reinforcing agent.[10](https://www.rti.org/sites/default/files/resources/bk-0003-1109-chapter18.pdf) Since 1943, the commercial Aerosil process has produced fumed SiO\\(_2\\) by hydrolysis of SiCl\\(_4\\) in an oxy-hydrogen flame with a multi-annulus co-flow diffusion burner, and analogous chloride precursors, such as an aluminum chloride for Al\\(_2\\)O\\(_3\\) and TiCl\\(_4\\) for TiO\\(_2\\), are used for other fumed oxides.[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393)\n\nPublished reviews disagree on when liquid-fed flame synthesis originated: one credits a 1977 study of Al\\(_2\\)O\\(_3\\) from aluminum acetylacetonate droplets.[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393) The modern systematic basis is due to L. Mädler and colleagues, who reported controlled synthesis of nanostructured particles by flame spray pyrolysis with an external-mixing gas-assisted atomizer in the Journal of Aerosol Science in 2002[11](https://doi.org/10.1016/s0021-8502%2801%2900159-8), and to Roger Mueller and colleagues, who scaled FSP to high production rates in Chemical Engineering Science in 2003.[12](https://doi.org/10.1016/s0009-2509%2803%2900022-8) The droplet microexplosion mechanism in flame-spray synthesis was reported by Christopher D. Rosebrock and colleagues in the AIChE Journal in 2013.[13](https://doi.org/10.1002/aic.14234)\n\n## Variants\n\n**Vapor-fed flame aerosol synthesis (VAFS)** feeds a volatile precursor and makes particles solely by gas-to-particle conversion[6](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d); the Aerosil process is its industrial archetype.[2](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393) **Flame spray pyrolysis (FSP)** directly introduces liquid, non-volatile precursors into a premix flame, producing highly dispersed, ultrafine, single-crystalline powders of binary, mixed binary, ternary, and mixed ternary metal oxides in a single step[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/); the liquid contributes more than 50% of the combustion energy, making the flame self-sustaining.[8](https://www.mdpi.com/1996-1944/16/3/1192) **Liquid Flame Spray (LFS)** uses a coflow hydrogen-oxygen flame with pneumatically sprayed liquid precursor; at typical flows of 20/10 l/min H\\(_2\\)/O\\(_2\\), the maximum flame temperature exceeds 2600 K.[14](https://www.jstage.jst.go.jp/article/kona/34/0/34_2017020/_html/-char/en) FSP is characterized by short residence time, steep temperature gradients, and rapid cooling of several hundred K·cm\\(^{-1}\\), yielding highly homogeneous and crystalline nanomaterials.[8](https://www.mdpi.com/1996-1944/16/3/1192)\n\n## Applications\n\nBeyond the commodities carbon black, fumed silica, and pigmentary and photocatalytic TiO\\(_2\\)[6](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d), flame-made particles serve in sensors, catalysis, and energy storage.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) FSP has produced more than 500 different materials, is used by more than 30 academic groups, and has been adopted by industry, with [Johnson Matthey](https://www.edgepedia.org/johnson-matthey) announcing an FSP facility.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) A pilot-scale V\\(_2\\)O\\(_5\\)/TiO\\(_2\\) catalyst made in a vapor-fed diffusion flame reactor at 200 g/h showed better NO removal activity at 160–280 °C than a wet-chemistry catalyst of similar composition and specific surface area.[6](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d) Roll-to-roll LFS coating of paperboard runs at line speeds of 50–500 m/min with the paper surface below 300 °C, depositing roughly 20 nm TiO\\(_2\\) particles into porous coatings mainly by thermophoresis.[14](https://www.jstage.jst.go.jp/article/kona/34/0/34_2017020/_html/-char/en) FSP is increasingly explored for miniaturized chemical, chemiresistive, plasmonic, biosensing, and light-sensing device architectures.[15](https://pubs.rsc.org/en/content/articlelanding/2024/nr/d4nr00321g) A 2025 Nature Chemistry paper demonstrated flame synthesis of high-entropy metallic single atoms and/or nanoparticles on soot-like carbon by blending organometallic precursors into paraffin wax fuel; the roughly 1800 K flame temperature enabled homogeneous bonding between up to 25 metals regardless of thermodynamic compatibility, demonstrated with high-performance [electrosynthesis of hydrogen peroxide](https://www.edgepedia.org/electrosynthesis-of-hydrogen-peroxide).[16](https://www.nature.com/articles/s41557-025-01894-w)\n\n## Limitations and alternatives\n\nLow combustion enthalpy density (below 4.7 kJ/g gas) combined with a precursor melting or decomposition temperature above the solvent boiling point yields inhomogeneous or hollow particles.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) Flame-made particles can carry uncombusted carbon impurity when the dispersed O\\(_2\\) flow is low.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) Precursor cost is a key limitation: ideal precursors such as alkoxides and organometallics are expensive, while cheaper nitrates usually give inhomogeneous particles.[6](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d) NO\\(_x\\) in LFS exhaust can exceed 1.5 ppm in open atmosphere but was reduced below 500 ppb by an argon sheath flow[14](https://www.jstage.jst.go.jp/article/kona/34/0/34_2017020/_html/-char/en); the process generates no byproducts requiring costly disposal and yields high chemical purity nanoparticles.[17](https://www.mdpi.com/2305-6304/14/4/330)\n\nCompared with sol-gel, hydrothermal, and precipitation routes, which give 3 nm to 1 µm particles depending on concentration and reaction temperature, flame methods give 5–80 nm.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/) FSP particles are nonporous or microporous (\\( d_{\\mathrm{pore}} < 2 \\) nm) spherical solids, whereas sol-gel and hydrothermal routes yield mesoporous materials; FSP also allows doping beyond the solubility limit of the solid solution and enables heterojunction formation.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/)\n\n## References\n\n1. [Design of Nanomaterial Synthesis by Aerosol Processes](https://pmc.ncbi.nlm.nih.gov/articles/PMC3591782/)\n2. [Flame aerosol synthesis of nanostructured materials and functional devices: Processing, modeling, and diagnostics](https://www.sciencedirect.com/science/article/abs/pii/S0360128515300393)\n3. [Flame-made Particles for Sensors, Catalysis, and Energy Storage Applications](https://pmc.ncbi.nlm.nih.gov/articles/PMC7743895/)\n4. [Pilot Plants for Industrial Nanoparticle Production by Flame Spray Pyrolysis](https://www.jstage.jst.go.jp/article/kona/29/0/29_2011025/_pdf/-char/en)\n5. [Nanoparticle Production by FSP (Parteq technical datasheet)](https://parteq.net/downloads/product%20datasheets/Product%20datasheet_FSP.pdf)\n6. [Synthesis of catalytic materials in flames: opportunities and challenges](https://pubs.rsc.org/en/content/articlehtml/2016/cs/c5cs00011d)\n7. [Investigation of iron oxide nanoparticle formation in a spray-flame synthesis process using laser-induced incandescence](https://link.springer.com/article/10.1007/s00340-024-08334-6)\n8. [Flame Synthesis of Carbon and Metal-Oxide Nanoparticles: Flame Types, Effects of Combustion Parameters on Properties and Measurement Methods](https://www.mdpi.com/1996-1944/16/3/1192)\n9. [Research progress on control technologies for flame synthesis of condensed-phase nanomaterials](https://www.sciopen.com/article/10.16511/j.cnki.qhdxxb.2023.25.016)\n10. [Chapter 18. History of Manufacture of Fine Particles in High-Temperature Aerosol Reactors](https://www.rti.org/sites/default/files/resources/bk-0003-1109-chapter18.pdf)\n11. [Controlled synthesis of nanostructured particles by flame spray pyrolysis (Journal of Aerosol Science, 2002)](https://doi.org/10.1016/s0021-8502%2801%2900159-8)\n12. [Nanoparticle synthesis at high production rates by flame spray pyrolysis (Chemical Engineering Science, 2003)](https://doi.org/10.1016/s0009-2509%2803%2900022-8)\n13. [Christopher D. Rosebrock and colleagues (2013). Disruptive burning of precursor/solvent droplets in flame‐spray synthesis of nanoparticles. AIChE Journal.](https://doi.org/10.1002/aic.14234)\n14. [Liquid Flame Spray, A Hydrogen-Oxygen Flame Based Method for Nanoparticle Synthesis and Functional Nanocoatings](https://www.jstage.jst.go.jp/article/kona/34/0/34_2017020/_html/-char/en)\n15. [Advances in flame synthesis of nano-scale architectures for chemical, biomolecular, plasmonic, and light sensing](https://pubs.rsc.org/en/content/articlelanding/2024/nr/d4nr00321g)\n16. [Flame synthesis achieves compositionally tailorable high-entropy metal-containing nanomaterials](https://www.nature.com/articles/s41557-025-01894-w)\n17. [Synthesis of Metal and Metal Oxide Nanoparticles by Flame Spray Pyrolysis and Safety Assessment](https://www.mdpi.com/2305-6304/14/4/330)\n\n---\n*Topic: Encyclopedia › Technology and the built world › Engineering and manufacturing › Manufacturing processes and fabrication › Forming, heat treatment, and finishing › Powder metallurgy and sintering*\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/flame-synthesis", "markdown_url": "https://www.edgepedia.org/flame-synthesis.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": "\"Flame synthesis\", Edgepedia (EdgeChat), https://www.edgepedia.org/flame-synthesis. Edgepedia Community License 1.0.", "credit_md": "\"[Flame synthesis](https://www.edgepedia.org/flame-synthesis)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/flame-synthesis](https://www.edgepedia.org/flame-synthesis). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Flame synthesis\", Edgepedia (EdgeChat), https://www.edgepedia.org/flame-synthesis. Edgepedia Community License 1.0.", "speakable": "Flame synthesis is a fabrication method using combustion flames to convert vaporized or liquid precursors into nanoparticles, coatings, and other inorganic solids, including carbon black and fumed silica." }