# C–Hf system

> C–Hf system: 42 accepted literature values (invariant reaction 15, formation 13, crystal structure 7, heat capacity / entropy / enthalpy 7) and 0 calculated phase diagram(s) from ORCHID, each value with evidence class, source, page and quote.

HTML: https://data.orchid-project.org/systems/C-HF.html · Markdown: https://data.orchid-project.org/systems/C-HF.md

42 accepted literature values from 2 paper(s) (experimental 23, model 8, unspecified 11); 0 calculated phase diagram(s). 8 further extracted value(s) not accepted by the reader-agreement checks are only in the JSON/CSV.

Data: [JSON](https://data.orchid-project.org/literature/systems/C-HF.json) · [CSV](https://data.orchid-project.org/systems/C-HF.csv) · [interactive explorer](https://orchid-project.org/data-explorer/#C-HF) · [phases (6)](https://data.orchid-project.org/phases/pages/C-HF.html) · [papers (bibliography)](https://data.orchid-project.org/bibliography/pages/systems/C-HF.html) · [Markdown](https://data.orchid-project.org/systems/C-HF.md)

Table: Accepted values by evidence class

| Evidence class | Values |
|---|---:|
| experimental | 23 |
| model | 8 |
| unspecified | 11 |

Table: Accepted values by property group

| Property group | Values |
|---|---:|
| invariant reaction | 15 |
| formation | 13 |
| heat capacity / entropy / enthalpy | 7 |
| crystal structure | 7 |

Convex hulls: [Materials Project DFT hull](https://data.orchid-project.org/hulls/dft-mp/C/C-HF.json) · [OQMD DFT hull](https://data.orchid-project.org/hulls/dft-oqmd/C/C-HF.json) · [CALPHAD hull HfC-97Bit-LB](https://data.orchid-project.org/hulls/calphad-sgte/C/C-HF--HfC-97Bit-LB.json)

## Invariant reactions (literature)

Table: Invariant reactions reported in the literature for the C–Hf system (15)

| T (K) | Reaction / phases | Compositions (mole fraction) | Class | Source | Location | Quote |
|---:|---|---|---|---|---|---|
| 4223 | congruent melting: L \<-> HfC1-x | L: C 0.485; HfC1-x: C 0.485 | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 1, p. 2, row 17; `ORC-WFA4WCTDYL` |  |
| 4215 | congruent melting: L \<-> HfC1-x | L: C 0.484; HfC1-x: C 0.484 | model | [1] Bittermann 1997 | Table 1, p. 2, row 18; `ORC-7LOELXGC3F` |  |
| 4201 | congruent melting: L \<-> HfC1-x | L: C 0.485; HfC1-x: C 0.485 | experimental | [1] Bittermann 1997; _cites Rudy 1965_ | Table 1, p. 2, row 16; `ORC-WR37WUD7KJ` |  |
| 3453 | eutectic: L \<-> HfC1-x + C | L: C 0.65; HfC1-x: C 0.495 | experimental | [1] Bittermann 1997; _cites Rudy 1965_ | Table 1, p. 2, row 13; `ORC-3SLIL2HVAF` |  |
| 3453 | eutectic: L \<-> HfC1-x + C | L: C 0.68; HfC1-x: C 0.495 | unspecified | [1] Bittermann 1997; _cites Rudy 1969_ | Table 1, p. 2, row 14; `ORC-V36OQJYC2R` |  |
| 3446 | eutectic: L \<-> HfC1-x + C | L: C 0.68; HfC1-x: C 0.499; C: C 1 | model | [1] Bittermann 1997 | Table 1, p. 2, row 15; `ORC-6IEGRUCV5I` |  |
| 2649 | peritectic: L + HfC1-x \<-> αHf | L: C 0.0602; HfC1-x: C 0.335; αHf: C 0.14 | model | [1] Bittermann 1997 | Table 1, p. 2, row 12; `ORC-LPFKRR2THG` |  |
| 2633 | peritectic: L + HfC1-x \<-> αHf | L: C 0.05; HfC1-x: C 0.34; αHf: C 0.15 | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 1, p. 2, row 11; `ORC-H2YYEKLZFP` |  |
| 2633 | peritectic: L + HfC1-x \<-> αHf | L: C 0.05; HfC1-x: C 0.34; αHf: C 0.14 | experimental | [1] Bittermann 1997; _cites Rudy 1965_ | Table 1, p. 2, row 10; `ORC-O6RTTTWE3P` |  |
| 2506 | congruent melting: L \<-> βHf | L: C 0; βHf: C 0 | model | [1] Bittermann 1997 | Table 1, p. 2, row 9; `ORC-7HWWUVPQ2F` |  |
| 2504 | congruent melting: L \<-> βHf | L: C 0; βHf: C 0 | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 1, p. 2, row 8; `ORC-ANOJRH4JJ6` |  |
| 2491 | eutectic: L \<-> βHf + αHf | L: C 0.015; βHf: C 0.01; αHf: C 0.02 | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 1, p. 2, row 5; `ORC-ECKTQO5ETT` |  |
| 2491 | congruent melting: L \<-> βHf | L: C 0; βHf: C 0 | experimental | [1] Bittermann 1997; _cites Rudy 1965_ | Table 1, p. 2, row 7; `ORC-QEL7P7ZREN` |  |
| 2480 | eutectic: L \<-> βHf + αHf | L: C 0.0137; βHf: C 0.005; αHf: C 0.0293 | model | [1] Bittermann 1997 | Table 1, p. 2, row 6; `ORC-P5WHHJBWOK` |  |
| 2453 | eutectic: L \<-> βHf + αHf | L: C 0.015; βHf: C 0.01; αHf: C 0.02 | experimental | [1] Bittermann 1997; _cites Rudy 1965_ | Table 1, p. 2, row 4; `ORC-5GVDP4JJOP` |  |

## Formation enthalpies

Literature values in kJ/mol-atom where the per-atom basis is known. DFT columns: the lowest-energy entry at the same composition (Materials Project 2026.04.13, OQMD v1.8; different energy references, never averaged), from [dft_parity.json](https://data.orchid-project.org/literature/dft_parity.json).

Table: Enthalpies of formation, C–Hf system (13)

| Phase | Compound | Value | T (K) | Class | MP DFT (kJ/mol-atom) | OQMD DFT (kJ/mol-atom) | Source | Location | Quote |
|---|---|---:|---:|---|---:|---:|---|---|---|
| HfC |  | -262.7 kJ/mol (basis unstated) | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites Coffman 1963_ | Table 3, p. 3, row 1; `ORC-HKOEZXIF3S` |  |
| HfC |  | -210.5 kJ/mol (basis unstated) ± 20.9 | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites Fesenko 1966_ | Table 3, p. 3, row 5; `ORC-RMCGK62JBP` |  |
| HfC |  | -209.4 kJ/mol (basis unstated) | 298.15 | model |  |  | [1] Bittermann 1997 | Table 3, p. 3, row 9; `ORC-NMJERRALKA` |  |
| HfC |  | -209.4 kJ/mol (basis unstated) | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites ref. 77Kor_ | p. 7; `ORC-RSG35SBR5A` | “Thus, the value Ae/-/(HfC, 298 K) = -209.4 kJ/mol from \[77Kor\] was selected in the present assessment, which was also confirmed by the calculation of the phase relations in the ternary Hf-B-C system \[97Bit\].” |
| HfC0.6 |  | -140.9 kJ/mol (basis unstated) | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites ref. 77Kor_ | Table 3, p. 3, row 6; `ORC-4EMGIZRDJ4.2e7a9d` |  |
| HfC0.621 |  | -133.1 kJ/mol (basis unstated) | 1780 | experimental |  |  | [1] Bittermann 1997; _cites ref. 89Ber_ | Table 3, p. 3, row 8; `ORC-65DNMZFNBQ.68fa12` |  |
| HfC0.67 |  | -220.9 kJ/mol (basis unstated) ± 1.7 | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites Zehlankin 1964_ | Table 3, p. 3, row 4; `ORC-ETLPIOEYDC.fd6ac4` |  |
| HfC0.93 |  | -197.5 kJ/mol (basis unstated) ± 3.8 | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites Maslov 1978_ | Table 3, p. 3, row 7; `ORC-HC6LULJ2MB` |  |
| HfC0.958 |  | -218.4 kJ/mol (basis unstated) ± 1.7 | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites Mah 1964_ | Table 3, p. 3, row 2; `ORC-KVEAKBY2VS` |  |
| HfC0.97 |  | -238.1 kJ/mol (basis unstated) ± 29.3 | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites McClaine 1964_ | Table 3, p. 3, row 3; `ORC-GS5GPR5EZY` |  |
| HfC0.980 |  | -209.7 kJ/mol (basis unstated) ± 13.5 | 1780 | experimental |  |  | [1] Bittermann 1997; _cites ref. 89Ber_ | Table 3, p. 3, row 8; `ORC-65DNMZFNBQ.711faf` |  |
| HfC1.0 |  | -209.4 kJ/mol (basis unstated) | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites ref. 77Kor_ | Table 3, p. 3, row 6; `ORC-4EMGIZRDJ4.f2aab5` |  |
| HfC1.00 |  | -231.1 kJ/mol (basis unstated) ± 2.1 | 298.15 | experimental |  |  | [1] Bittermann 1997; _cites Zehlankin 1964_ | Table 3, p. 3, row 4; `ORC-ETLPIOEYDC.f02cd6` |  |

## Other properties

### Heat capacity / entropy / enthalpy (7)

Table: Heat capacity / entropy / enthalpy, C–Hf system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Entropy; _printed: Derived S298_ | 39.64 unknown | 298.15 | HfC; _alloy: Hf 0.5_ | model | [1] Bittermann 1997 | Table 4a, p. 5, row 5; `ORC-T25OPZJFXR.6ce7d3` |  |
| Entropy; _printed: Derived S298_ | 39.5 unknown ± 0.42 | 298.15 | HfC0.96; _alloy: Hf 0.510204_ | experimental | [1] Bittermann 1997; _cites McClaine 1964_ | Table 4a, p. 5, row 1; `ORC-LSVLPYWRDO.d43bad` |  |
| Entropy; _printed: Derived S298_ | 39.36 unknown | 298.15 | HfC0.968; _alloy: Hf 0.50813_ | experimental | [1] Bittermann 1997; _cites E 1977_ | Table 4a, p. 5, row 4; `ORC-KYB2SMOI66.c9a02c` |  |
| Heat capacity; _printed: Cp (298)_ | 37.56 J/mol (basis unstated)/K | 298.15 | HfC; _alloy: Hf 0.5_ | model | [1] Bittermann 1997 | Table 4a, p. 5, row 5; `ORC-T25OPZJFXR.294538` |  |
| Heat capacity; _printed: Cp (298)_ | 37.49 J/mol (basis unstated)/K | 298.15 | HfC0.96; _alloy: Hf 0.510204_ | experimental | [1] Bittermann 1997; _cites McClaine 1964_ | Table 4a, p. 5, row 1; `ORC-LSVLPYWRDO.2d74de` |  |
| Heat capacity; _printed: Cp (298)_ | 37.37 J/mol (basis unstated)/K | 298.15 | HfC0.968; _alloy: Hf 0.50813_ | experimental | [1] Bittermann 1997; _cites E 1977_ | Table 4a, p. 5, row 4; `ORC-KYB2SMOI66.05b769` |  |
| Heat capacity; _printed: Cp (298)_ | 41.82 J/mol (basis unstated)/K | 298.15 | HfC0.99; _alloy: Hf 0.502513_ | experimental | [1] Bittermann 1997; _cites Buravoi 1974_ | Table 4a, p. 5, row 3; `ORC-HFDFSZVSLJ` |  |

### Crystal structure (7)

Table: Crystal structure, C–Hf system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Lattice a | 2.4612 Å | 298.15 | (C); _alloy: Hf 0_ | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 2, p. 2, row 3; `ORC-RO2ZGX2BFQ.1d583b` |  |
| Lattice a | 3.1946 Å | 298.15 | (αHf); _(αHf): C 0.15, Hf 0.85_ | unspecified | [1] Bittermann 1997 | Table 2, p. 2, row 1; `ORC-2TRBOQCDKH.519ffb` |  |
| Lattice a | 4.62225 Å (range 4.606 to 4.6385) | 298.15 | HfC1−x | experimental | [1] Bittermann 1997; _cites Rudy 1969_ | Table 2, p. 2, row 4; `ORC-TIA5MI3IL7` |  |
| Lattice a | 4.6385 Å | 3942 (\<) | HfC1-x; _HfC1-x: C 0.495_ | unspecified | [2] Bittermann 2002; _cites ref. 1969Rud_ | Table 1, p. 4, row 21; `ORC-JDF4VPRIP4` |  |
| Lattice c | 6.709 Å | 298.15 | (C); _alloy: Hf 0_ | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 2, p. 2, row 3; `ORC-RO2ZGX2BFQ.03b113` |  |
| Lattice c | 5.051 Å | 298.15 | (αHf); _(αHf): C 0.15, Hf 0.85_ | unspecified | [1] Bittermann 1997 | Table 2, p. 2, row 1; `ORC-2TRBOQCDKH.cab331` |  |
| lattice c a | 2.7258 not_printed | 298.15 | (C); _alloy: Hf 0_ | unspecified | [1] Bittermann 1997; _cites ref. 2_ | Table 2, p. 2, row 3; `ORC-RO2ZGX2BFQ.b24e3d` |  |

## Sources

Reporting papers the values were read from (a value cited from another work names that work in its row).

1. H. Bittermann, P. Rogl, Critical assessment and thermodynamic calculation of the binary system hafnium-carbon (Hf-C), JPE 18, 344-356 (1997). [doi:10.1007/s11669-997-0061-3](https://doi.org/10.1007/s11669-997-0061-3)
2. H. Bittermann, P. Rogl, Critical assessment and thermodynamic calculation of the ternary system C-Hf-Zr (Carbon-Zirconium-Hafnium), JPE 23, 218-235 (2002). [doi:10.1361/105497102770331703](https://doi.org/10.1361/105497102770331703)

## Please cite

- R. Arróyave, J. Saal, D. Shin, ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23735569
- R. Arróyave, J. Saal, D. Shin, ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD) (version 2026.10), Zenodo (2026). https://doi.org/10.5281/zenodo.23735891
- R. Arróyave, J. Saal, D. Shin, ORCHID data: umbrella record of the ORCHID datasets (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23736065

Also cite the original source of every value you use (paper_citation / paper_doi, and cited_dois for values the paper cites from earlier work); A. Jain et al., The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002, https://doi.org/10.1063/1.4812323 (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501, https://doi.org/10.1007/s11837-013-0755-4 and S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010, https://doi.org/10.1038/npjcompumats.2015.10 (CC BY 4.0); B. Hallstedt, The SGTE collection of binary datasets, Calphad 89 (2025) 102833, https://doi.org/10.1016/j.calphad.2025.102833 (CC BY 4.0), and the original assessment named in each file.

Version 1, machine-extracted: values were read by language-model readers constrained to quote their source and checked automatically, and the release was then audited on the printed pages by adversarial audits, an independent second review of fit-facing records and a preliminary human review of a frozen sample. Flags such as accepted and ESPEI-ready record screening results, not certification; known issues are listed in the release notes.

```bibtex
@misc{orchid_literature_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735569},
  url       = {https://doi.org/10.5281/zenodo.23735569},
  note      = {Version 1, machine-extracted}
}

@misc{orchid_hulls_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD)}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735891},
  url       = {https://doi.org/10.5281/zenodo.23735891}
}

@misc{orchid_data_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID data: umbrella record of the ORCHID datasets}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23736065},
  url       = {https://doi.org/10.5281/zenodo.23736065},
  note      = {Version 1, machine-extracted}
}
```

---

Derived data CC BY 4.0 ([licence](https://creativecommons.org/licenses/by/4.0/)): cite ORCHID ([CITATION.cff](https://data.orchid-project.org/CITATION.cff)) and the original sources. Quotes are short excerpts kept so that each value can be checked; they remain under the publishers' copyright and are not relicensed. Source papers, page images and full text are not redistributed. Field reference: [SCHEMA.md](https://data.orchid-project.org/literature/SCHEMA.md). Machine-readable guide: [llms.txt](https://data.orchid-project.org/llms.txt). Found an error? The report link of a value (Markdown: its id, ORC-..., in the Location column) opens a pre-filled GitHub issue, https://github.com/orchid-calphad/orchid-data/issues/new?template=report-value-error.yml&record_id=\<id>, carrying only the record id, source and value; [how to contribute](https://orchid-project.org/contribute/).