# Ralf Riedel

Ralf Riedel is a German materials scientist who was Professor at the Institute of Materials Science of Technische Universität Darmstadt and is now Professor (Emeritus) there, where he leads work on dispersively structured solids.<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup><sup> • </sup><sup>[18](https://www.mawi.tu-darmstadt.de/mr/mr/employees/team_df/index.en.jsp)</sup> His research covers silicon-based preceramic polymers, the synthesis and properties of novel functional and structural ceramics, polymer-derived ceramics for energy applications, and high-pressure and high-temperature materials synthesis.<sup>[2](https://nfri.web.nitech.ac.jp/en/prof-ralf-riedel/)</sup> His work on the polymer-derived ceramics (PDC) route, in which ceramics are made by pyrolysing molecular precursors rather than sintering (fusing powder particles into a solid using heat) powders, and on a silicoboron carbonitride ceramic reported stable to 2,000 °C, is the subject of reviews surveying decades of Si–B–C–N research.<sup>[3](https://doi.org/10.1038/382796a0)</sup>

| Fact | Detail |
|---|---|
| Position | Professor (Emeritus), Institute of Materials Science, TU Darmstadt<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup><sup> • </sup><sup>[18](https://www.mawi.tu-darmstadt.de/mr/mr/employees/team_df/index.en.jsp)</sup> |
| Field | Polymer-derived ceramics; non-oxide ceramics; high-pressure nitride synthesis<sup>[2](https://nfri.web.nitech.ac.jp/en/prof-ralf-riedel/)</sup> |
| Training | PhD in inorganic chemistry, University of Stuttgart, 1986, under E. Fluck<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup> |
| Signature work | "A silicoboron carbonitride ceramic stable to 2,000°C", *Nature*, 1996<sup>[3](https://doi.org/10.1038/382796a0)</sup> |
| Key result | According to *Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics*, SiBCN ceramics are stable to 2,000–2,200 °C in inert atmosphere, versus about 1,500 °C for boron-free PDCs<sup>[4](https://www.jstage.jst.go.jp/article/jcersj/114/1330/114_1330_425/_article/-char/en)</sup> |
| Major honors | Gustav Tammann Award (2012); Fellow of the American Ceramic Society (2000) and European Ceramic Society (2013); International Ceramics Prize 2020<sup>[5](https://ecers.org/uploads/FELLOWS/2013/R%20Riedel%20Fellow%202013.pdf)</sup><sup> • </sup><sup>[6](https://www.iiss-sci.org/index.php/ralf-riedel)</sup> |
| Editorship | Editor in Chief of the Journal of the American Ceramic Society and of Ceramics International<sup>[6](https://www.iiss-sci.org/index.php/ralf-riedel)</sup> |

## Career record

Riedel studied chemistry at the University of Stuttgart from 1977 to 1984, completing a diploma thesis on the reduction of aldehydes with white phosphorus under E. Fluck, and took his doctorate in inorganic chemistry there in 1984–1986 with a thesis on white phosphorus as a starting material for [organophosphorus compounds](https://www.edgepedia.org/organophosphorus-compounds).<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup> He was a postdoctoral researcher at the Max Planck Institute for Metals Research in [Stuttgart](https://www.edgepedia.org/stuttgart) from 1986 to 1989 and at the University of Stuttgart's Institute of Inorganic Chemistry from 1990 to 1992, completing his habilitation in 1992 on non-oxide ceramics from inorganic precursors under Gerd Becker and Fritz Aldinger.<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup>

**Darmstadt.** He has held the professorship in the Dispersive Solids group at TU Darmstadt since 1993.<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup> According to his European Ceramic Society Fellow profile, he served as Dean of the Department of Materials and Earth Sciences, a role recorded in 2012 and 2013.<sup>[5](https://ecers.org/uploads/FELLOWS/2013/R%20Riedel%20Fellow%202013.pdf)</sup> According to his TU Darmstadt profile, he was a visiting professor at the University of Colorado at Boulder in the winter semester 1997/98 and at the University of Rennes in June and July 2005, and he has been a Guest Professor at the [University of Tokyo](https://www.edgepedia.org/university-of-tokyo).<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup><sup> • </sup><sup>[6](https://www.iiss-sci.org/index.php/ralf-riedel)</sup> 

## Representative work

The 1996 Nature paper reported [a silicoboron carbonitride ceramic stable to 2,000 °C](https://doi.org/10.1038/382796a0), published on 1 August 1996.<sup>[3](https://doi.org/10.1038/382796a0)</sup> It demonstrated that adding boron to a silicon carbonitride derived from a preceramic polymer raises the temperature at which the amorphous ceramic resists crystallization and decomposition far beyond the range of boron-free materials, and it became the reference point for three decades of Si–B–C–N research.<sup>[7](https://onlinelibrary.wiley.com/doi/10.1002/adem.201800360)</sup> His earlier *Nature* paper, "Synthesis of dense silicon-based ceramics at low temperatures", appeared on 1 February 1992.<sup>[8](https://doi.org/10.1038/355714a0)</sup> 

## Research program: polymer-derived ceramics

A polymer-derived ceramic is made by shaping a preceramic polymer and then pyrolysing it. The common precursors are poly(organosilazanes), poly(organosilylcarbodiimides), and poly(organosiloxanes); the 2006 review by Riedel's group notes that no other synthetic approach is known to produce silicon oxycarbide (SiCO) or silicon carbonitride (SiCN) ceramics of this type.<sup>[4](https://www.jstage.jst.go.jp/article/jcersj/114/1330/114_1330_425/_article/-char/en)</sup> Riedel's 1993 monograph, *Nicht-oxidische Keramiken aus anorganischen Vorstufen*, built on earlier work such as Yajima and colleagues' 1975–1976 preparation of silicon carbide fibers from polycarbosilane by pyrolysis, and showed that solid-state pyrolysis (decomposing material by heating it without oxygen) of inorganic polymers yields non-oxide silicon ceramic bodies at 800–1,200 °C without sintering additives.<sup>[9](https://www.schweizerbart.de/publications/detail/isbn/9783443230135/Riedel_Nicht_Oxidische_Keramiken_aus_A)</sup><sup> • </sup><sup>[19](https://pmc.ncbi.nlm.nih.gov/articles/PMC9055389/)</sup> In 1997 his group published the first thermal transformation of poly(organosilylcarbodiimides) into SiCN ceramics.<sup>[10](https://webapps.unitn.it/public/store/ermete/allegato/per0003532/3829c275-73c7-4349-8b8f-9a5422450ac7.pdf)</sup>

**Why the route matters.** [Pyrolysis](https://www.edgepedia.org/pyrolysis) at 1,000–1,300 °C is economically favorable against the 1,700–4,200 °C needed to sinter covalent Si3N4- and SiC-based ceramics by classical powder processing.<sup>[10](https://webapps.unitn.it/public/store/ermete/allegato/per0003532/3829c275-73c7-4349-8b8f-9a5422450ac7.pdf)</sup> The route also produces amorphous microstructures that cannot be obtained by powder sintering or chemical vapor deposition, and it allows shaping as fibers, layers, or bulk composites with plastics-industry techniques.<sup>[11](https://www.mdpi.com/1996-1944/14/3/614)</sup><sup> • </sup><sup>[4](https://www.jstage.jst.go.jp/article/jcersj/114/1330/114_1330_425/_article/-char/en)</sup> A 2018 review of 30 years of Si–B–C–N work, on which Riedel was a co-author, attributes the interest in these multi-component ceramics to the stability of their amorphous inorganic network, which arises from strong covalent bonding.<sup>[7](https://onlinelibrary.wiley.com/doi/10.1002/adem.201800360)</sup>

## Applications and high-temperature limits

Polymer-derived ceramic nanocomposites from polysiloxanes and polysilazanes are candidate materials for high-temperature sensors, micro glow plugs, electrochemical devices, and MEMS and NEMS operating under harsh conditions.<sup>[12](https://pubs.rsc.org/en/content/articlehtml/2012/cs/c2cs90050e)</sup>

**Limits.** According to a 2006 review in the Journal of the Ceramic Society of Japan, silicon-based PDCs in general show temperature stability up to about 1,500 °C; when the preceramic polymer contains boron, stability against decomposition and crystallization extends to about 2,000 °C, and boron-containing SiBCN has been reported stable up to 2,200 °C in inert atmosphere.<sup>[4](https://www.jstage.jst.go.jp/article/jcersj/114/1330/114_1330_425/_article/-char/en)</sup><sup> • </sup><sup>[10](https://webapps.unitn.it/public/store/ermete/allegato/per0003532/3829c275-73c7-4349-8b8f-9a5422450ac7.pdf)</sup> Below that ceiling, amorphous SiCN crystallizes and segregates into SiC, Si3N4, carbon, or silicon above about 1,100 °C, and the conversion, segregation, and decomposition of amorphous nanodomains decreases the reliability of PDC products above 1,400 °C.<sup>[11](https://www.mdpi.com/1996-1944/14/3/614)</sup>

## Honors, editorships and society roles

Riedel received a [Max Planck Society](https://www.edgepedia.org/max-planck-society) doctoral fellowship in 1983, the Dionyz Stur Gold Medal of the [Slovak Academy of Sciences](https://www.edgepedia.org/slovak-academy-of-sciences) in 1999, and an honorary doctorate from that academy in 2006; he became a Fellow of the American Ceramic Society in 2000, joined the World Academy of Ceramics in 2004, and received an honorary professorship from [Tianjin University](https://www.edgepedia.org/tianjin-university) in 2009.<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup> The German Society of Materials Science awarded him the Gustav Tammann Award in 2012 for fundamental achievements in ceramic science, and the European Ceramic Society elected him a Fellow in 2013.<sup>[5](https://ecers.org/uploads/FELLOWS/2013/R%20Riedel%20Fellow%202013.pdf)</sup> The World Academy of Ceramics awarded him the International Ceramics Prize 2020 for Basic Science.<sup>[6](https://www.iiss-sci.org/index.php/ralf-riedel)</sup>

**Editorial and society roles.** He became a member of the Advisory Board of the German Society of Materials Science in 1999 and coordinated the DFG Priority Program SPP 1181, "Nanoscaled Inorganic Materials by Molecular Design", from 2005.<sup>[1](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)</sup>

## Group and funding

His group sits at the Fachgebiet Disperse Feststoffe, Otto-Berndt-Straße 3, [Darmstadt](https://www.edgepedia.org/darmstadt), within the Department of Materials and Geosciences; the DFG project registry marks the Fachgebiet as dissolved.<sup>[13](https://gepris.dfg.de/gepris/person/1234487?contrast=0&displayMode=print&findButton=historyCall&hitsPerPage=5&index=1445&language=en&orderBy=name&predefinedSearch=mathematik)</sup> His DFG-funded projects include high-pressure synthesis of nitrides of the type M3-xAxN4 with M and A drawn from V, Nb, Ta, Ti, Zr, Hf, and Pb; superhard phases in the Si-C-N and B-C-N systems; polymer-derived SiCO/HfO2 and SiCN/HfO2 nanocomposites for ultrahigh-temperature applications; and polymer-derived ceramic coatings on carbon fibers for customizing interfaces in thixoforged aluminum matrix composites.<sup>[13](https://gepris.dfg.de/gepris/person/1234487?contrast=0&displayMode=print&findButton=historyCall&hitsPerPage=5&index=1445&language=en&orderBy=name&predefinedSearch=mathematik)</sup> 

## Recent developments

In February 2023 Riedel was invited to Nagoya Institute of Technology for joint research on polymer-derived functional ceramic-based materials for clean energy, and lectured there on "Si-B-C-N-Based Ceramics, History and Perspectives".<sup>[2](https://nfri.web.nitech.ac.jp/en/prof-ralf-riedel/)</sup> His recent papers continue the ultrahigh-temperature and energy themes of his DFG portfolio.

**Dense Si-Al-C-N ceramics (2025/2026).** According to a study published online on 18 November 2025 in the *International Journal of Applied Ceramic Technology*, aluminum incorporation densified Si-C-N to monoliths with porosity as low as 2 volume percent, thermal conductivity fell to 0.6 W m−1 K−1 while hardness stayed near 14.5 GPa and [Young's modulus](https://www.edgepedia.org/youngs-modulus) near 156 GPa, and its authors state this is the first report of thermal and mechanical properties of dense, mainly amorphous Si-Al-C-N ceramics, pointing to thermal insulation use beyond 1,000 °C.<sup>[14](https://doi.org/10.1111/ijac.70119)</sup><sup> • </sup><sup>[15](https://publikationen.bibliothek.kit.edu/1000187493)</sup> 

**Cold sintering (2026).** A Journal of the American Ceramic Society paper published on 1 June 2026 demonstrated cold sintering of amorphous SiHfBN ceramics at only about 200 °C using aqueous NaOH, producing monoliths of about 70 percent relative density with a Vickers hardness of roughly 2 GPa and compressive strength of about 90 MPa; the parts lost only about 0.2 percent mass at 1,000 °C in air and showed thermal conductivity of roughly 0.6–1 W m−1 K−1.<sup>[16](https://doi.org/10.1111/jace.70944)</sup> Work on ultra-high temperature ceramic nanocomposites in the Si(Hf_xTa_1−x)(C)N system, synthesized via the polymer-derived route, continues this line.<sup>[17](https://publikationen.bibliothek.kit.edu/1000153468/175185222)</sup>

## References

1. [Prof. Dr. Ralf Riedel – TU Darmstadt](https://www.mawi.tu-darmstadt.de/mr/mr/employees/kontakt_details_113152.en.jsp)
2. [Ralf Riedel, Prof. | NITech Frontier Research Institutes](https://nfri.web.nitech.ac.jp/en/prof-ralf-riedel/)
3. [A silicoboron carbonitride ceramic stable to 2,000°C (Nature, 1996)](https://doi.org/10.1038/382796a0)
4. [Silicon-Based Polymer-Derived Ceramics: Synthesis Properties and Applications – A Review (J. Ceramic Society of Japan, 2006)](https://www.jstage.jst.go.jp/article/jcersj/114/1330/114_1330_425/_article/-char/en)
5. [Ralf Riedel – European Ceramic Society Fellow 2013](https://ecers.org/uploads/FELLOWS/2013/R%20Riedel%20Fellow%202013.pdf)
6. [Ralf Riedel – IISS](https://www.iiss-sci.org/index.php/ralf-riedel)
7. [Polymer Derived Si–B–C–N Ceramics: 30 Years of Research (Advanced Engineering Materials, 2018)](https://onlinelibrary.wiley.com/doi/10.1002/adem.201800360)
8. [Synthesis of dense silicon-based ceramics at low temperatures (Nature, 1992)](https://doi.org/10.1038/355714a0)
9. [Nicht-oxidische Keramiken aus anorganischen Vorstufen (Schweizerbart, 1993)](https://www.schweizerbart.de/publications/detail/isbn/9783443230135/Riedel_Nicht_Oxidische_Keramiken_aus_A)
10. [Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics (J. American Ceramic Society, 2010)](https://webapps.unitn.it/public/store/ermete/allegato/per0003532/3829c275-73c7-4349-8b8f-9a5422450ac7.pdf)
11. [High-Temperature Properties and Applications of Si-Based Polymer-Derived Ceramics: A Review (Materials, 2021)](https://www.mdpi.com/1996-1944/14/3/614)
12. [Nanoscaled inorganic materials by molecular design – Chemical Society Reviews (RSC, 2012)](https://pubs.rsc.org/en/content/articlehtml/2012/cs/c2cs90050e)
13. [DFG GEPRIS – Project Details: Professor Ralf Riedel](https://gepris.dfg.de/gepris/person/1234487?contrast=0&displayMode=print&findButton=historyCall&hitsPerPage=5&index=1445&language=en&orderBy=name&predefinedSearch=mathematik)
14. [Synthesis and thermal properties of dense Si─Al─C─N-based polymer-derived ceramics (Int. J. Applied Ceramic Technology)](https://doi.org/10.1111/ijac.70119)
15. [KITopen record: Synthesis and thermal properties of dense Si─Al─C─N-based polymer-derived ceramics](https://publikationen.bibliothek.kit.edu/1000187493)
16. [Cold Sintering Breaks Temperature Barriers: Aqueous-NaOH-Driven Densification of Amorphous SiHfBN Ceramics at 250°C (J. American Ceramic Society, 2026)](https://doi.org/10.1111/jace.70944)
17. [Microstructural evolution of Si(HfₓTa₁₋ₓ)(C)N polymer-derived ceramics upon high-temperature anneal](https://publikationen.bibliothek.kit.edu/1000153468/175185222)
18. [Dispersive Solids – TU Darmstadt](https://www.mawi.tu-darmstadt.de/mr/mr/employees/team_df/index.en.jsp)
19. [pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC9055389/)

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*Topic: Encyclopedia › Technology and the built world › Engineers and computer scientists › Engineers and materials scientists › Researchers in materials science and nanotechnology › Structural and functional ceramics and composites*

*Initially written Sep 21, 2026 · Reviewed: Sep 25, 2026 · Edited: Sep 25, 2026; Oct 11, 2026; Oct 15, 2026 · Last review: Sep 25, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license