{ "spore": "profile", "id": "zirconium-diboride", "spore_version": "0.2", "family": "metal-borides", "name": "Zirconium diboride (ZrB2)", "abbreviation": "ZrB2", "role": "ultra-high-temperature ceramic", "category": "ceramics", "type": "ultra-high-temperature-ceramics", "summary": "Zirconium diboride (ZrB2) is a hexagonal boride ceramic with an AlB2-type structure. Sani et al. (2016) tabulate a melting temperature of 3245 °C and a density of 6.119 g/cm3 for dense ZrB2, and a hardness of 23 GPa. Monolithic ZrB2 starts to oxidize in air at about 600 °C, so uncoated parts need additives or a cooler air limit. A PubChem record quotes \"3000 °C\" as the melting point, and a supplier oxidation range of 1200 to 1400 °C are in conflict with these figures, so both are reported with their sources.\n", "best_for": "Very high melting and hot-structure ceramic parts where the material stays out of air above about 600 °C, or carries oxidation-resistance additives", "weakest_at": "Oxidation in air above about 600 °C for monolithic material; sintering is difficult and needs high temperatures", "identity": { "formula": "ZrB2 (one zirconium atom and two boron atoms per formula unit; AlB2-type hexagonal structure)", "cas": "12045-64-6", "crystal_system": "hexagonal", "space_group": "P6/mmm", "designations": [], "source": "sani2016", "where": "Table 1, Crystal system space group and prototype structure rows (hexagonal, P6/mmm, AlB2 prototype). CAS number 12045-64-6 is printed in the PubChem record (CID 9812765). The Wikipedia infobox gives hP3 and No. 191 for the same space group; not used for values." }, "tags": { "environments": [ "re-entry" ], "stresses": [], "applications": [ "heat-shields", "propulsion-and-tanks", "thermal-control" ] }, "properties": [ { "benchmark": "density", "label": "Density, dense ZrB2 (literature value)", "value": 6.119, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "basis": "literature value tabulated in Table 1 of Sani et al. (cited there to ref. 6); not the paper's own samples", "form": "dense bulk ZrB2" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Density row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "melting_point", "label": "Melting temperature (literature value)", "value": 3245, "bound": "exact", "unit": "degC", "scope": "material", "conditions": { "basis": "literature value tabulated in Table 1 (cited there to ref. 6); not the paper's own samples" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Melting Temperature row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "enthalpy_of_formation", "label": "Enthalpy of formation at 25 degC", "value": -322.6, "bound": "exact", "unit": "kJ/mol", "scope": "material", "conditions": { "temperature": "25 degC", "basis": "literature value tabulated in Table 1 (cited there to ref. 6)" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Enthalpy of formation row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "heat_capacity_molar", "label": "Molar heat capacity at 25 degC", "value": 48.2, "bound": "exact", "unit": "J/(mol·K)", "scope": "material", "conditions": { "temperature": "25 degC", "basis": "literature value tabulated in Table 1 (cited there to ref. 6)" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Heat Capacity row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "thermal_conductivity", "label": "Thermal conductivity (literature value)", "value": 60, "bound": "exact", "unit": "W/(m·K)", "scope": "material", "conditions": { "basis": "literature value tabulated in Table 1 (cited there to ref. 6); temperature not stated in the table" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Thermal conductivity row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "elastic_modulus", "label": "Young's modulus (literature value)", "value": 489, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "basis": "literature value tabulated in Table 1 (cited there to ref. 6); test method not stated" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Young's Modulus row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "hardness", "label": "Hardness (literature value)", "value": 23, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "basis": "literature value tabulated in Table 1 (cited there to ref. 6); test method and load not stated" }, "method": "Literature value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, Hardness row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "lattice_parameter_a", "label": "Lattice parameter a", "value": 3.17, "bound": "exact", "unit": "Å", "scope": "material", "conditions": { "structure": "hexagonal, P6/mmm (AlB2 prototype)", "temperature": "not stated in the table" }, "method": "Value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, a (Å) row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "lattice_parameter_c", "label": "Lattice parameter c", "value": 3.53, "bound": "exact", "unit": "Å", "scope": "material", "conditions": { "structure": "hexagonal, P6/mmm (AlB2 prototype)", "temperature": "not stated in the table" }, "method": "Value printed in a table of a peer-reviewed paper", "status": "ground", "source": "sani2016", "where": "Table 1, c (Å) row, ZrB2 column", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "elastic_modulus", "label": "Elastic modulus, ZrB2 nanopowder product (supplier range)", "value": 340, "value_high": 500, "bound": "range", "unit": "GPa", "scope": "material", "conditions": { "product": "ZrB2 nanopowder, 99.5% purity, about 45 nm, product NG04CO2502", "basis": "supplier product page; test method and sample density not stated" }, "method": "Range printed on a supplier product page", "status": "ground", "note": "Second-hand supplier figure, not from a test report. It differs from the 489 GPa literature value in Sani et al.", "source": "nanografi-zrb2", "where": "Product description, material properties text", "source_detail": { "title": "Nanografi, Zirconium Diboride (ZrB2) Nanoparticles, product NG04CO2502", "id": "Product page, 99.5% purity, about 45 nm", "url": "https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/", "year": 2026, "kind": "web", "license": "supplier product page, cited not reproduced" } }, { "benchmark": "hardness", "label": "Hardness, ZrB2 nanopowder product (supplier range)", "value": 20, "value_high": 25, "bound": "range", "unit": "GPa", "scope": "material", "conditions": { "product": "ZrB2 nanopowder, 99.5% purity, about 45 nm, product NG04CO2502", "basis": "supplier product page; test method not stated" }, "method": "Range printed on a supplier product page", "status": "ground", "note": "Second-hand supplier figure. The literature value in Sani et al. is 23 GPa.", "source": "nanografi-zrb2", "where": "Product description, material properties text", "source_detail": { "title": "Nanografi, Zirconium Diboride (ZrB2) Nanoparticles, product NG04CO2502", "id": "Product page, 99.5% purity, about 45 nm", "url": "https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/", "year": 2026, "kind": "web", "license": "supplier product page, cited not reproduced" } }, { "benchmark": "oxidation_onset_temperature", "label": "Onset of oxidation in air, monolithic ZrB2", "value": 600, "bound": "exact", "unit": "degC", "scope": "material", "conditions": { "atmosphere": "air (oxidative environment)", "material": "monolithic ZrB2 without oxidation-resistance additives", "basis": "approximate value stated by the authors, citing earlier work" }, "method": "Statement in the conclusions of a peer-reviewed paper, citing earlier work", "status": "ground", "note": "Sani et al. write 'approximately 600 °C' for both ZrB2 and TaB2, and say that suitable additives are needed for more severe conditions.", "source": "sani2016", "where": "Conclusions, final paragraph before the acknowledgements", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "oxidation_onset_temperature", "label": "Oxidation resistance (supplier claim)", "value": 1200, "value_high": 1400, "bound": "range", "unit": "degC", "scope": "material", "conditions": { "product": "ZrB2 nanopowder, 99.5% purity, product NG04CO2502", "basis": "supplier product page; no test atmosphere, time or sample state printed" }, "method": "Range printed on a supplier product page", "status": "ground", "note": "Conflicts with the approximately 600 degC onset in Sani et al. No test condition is printed, so the two cannot be reconciled from the sources read.", "source": "nanografi-zrb2", "where": "Product description, material properties text", "source_detail": { "title": "Nanografi, Zirconium Diboride (ZrB2) Nanoparticles, product NG04CO2502", "id": "Product page, 99.5% purity, about 45 nm", "url": "https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/", "year": 2026, "kind": "web", "license": "supplier product page, cited not reproduced" } }, { "benchmark": "solar_absorptance", "label": "Total directional solar absorbance at 1400 K", "value": 0.47, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "temperature": "1400 K", "basis": "dense monophasic ZrB2 sample of the paper, derived from measured optical spectra" }, "method": "Calculated by the paper's authors from measured spectra", "status": "calculated", "source": "sani2016", "where": "Optical properties section, paragraph giving alpha at 1400 K", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } }, { "benchmark": "total_emittance", "label": "Total directional emittance at 1400 K", "value": 0.18, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "temperature": "1400 K", "basis": "dense monophasic ZrB2 sample of the paper, derived from measured optical spectra" }, "method": "Calculated by the paper's authors from measured spectra", "status": "calculated", "source": "sani2016", "where": "Optical properties section, paragraph giving epsilon at 1400 K", "source_detail": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" } } ], "corrosion": [ { "environment": "Air above about 600 degC (oxidative environment)", "headline": "Monolithic ZrB2 starts to oxidize at about 600 °C in air and degrades quickly unless additives are present.", "effect": "Sani et al. state that tantalum and zirconium diborides start to oxidize above approximately 600 °C, which produces rapid material degradation unless suitable additives are introduced. They cite oxidation tests on ZrB2 solar coatings whose maximum air operating temperature was about 600 °C.", "rating": "severe", "conditions": { "atmosphere": "air", "form": "monolithic ZrB2 without additives", "exposure_time": "not stated" }, "source": "sani2016", "where": "Conclusions, final paragraph (refs. 38 and 39 as cited there)" }, { "environment": "Air at 1200 to 1400 degC (supplier claim)", "headline": "A supplier claims oxidation resistance up to 1200 to 1400 °C, which conflicts with the 600 °C onset above.", "effect": "The Nanografi product page for a ZrB2 nanopowder gives an oxidation-resistance range of 1200 to 1400 °C. No test atmosphere, time or sample state is printed, so the claim cannot be checked against the approximately 600 °C figure in Sani et al.", "rating": "unknown", "conditions": { "basis": "supplier product page; no test conditions printed" }, "source": "nanografi-zrb2", "where": "Product description, material properties text" } ], "risks": { "hazards": [ { "text": "PubChem prints the GHS statements H302 (85.2%), H312 (85.2%) and H332 (85.2%) from 54 company reports for zirconium diboride, in the acute toxicity category 4 (harmful if swallowed, in contact with skin or if inhaled).", "ghs": [ "H302", "H312", "H332" ], "source": "pubchem-zrb2", "where": "Safety and Hazards, GHS Classification and Hazard Classes and Categories" }, { "text": "PubChem also notes that the chemical does not meet GHS hazard criteria in 7.4% of reports (4 of 54).", "ghs": [], "source": "pubchem-zrb2", "where": "Safety and Hazards, GHS Classification, Note line" }, { "text": "The Nanografi product page for ZrB2 nanopowder prints no hazard statements (H-codes) and no safety data sheet link was read in this run.", "ghs": [], "source": "nanografi-zrb2", "where": "Product description; hazard statements not printed" } ], "failure_risks": [ { "mode": "Oxidation of monolithic ZrB2 in air", "trigger": "Air exposure above about 600 degC", "consequence": "Rapid material degradation, according to Sani et al., unless suitable additives are introduced.", "severity": "high", "source": "sani2016", "where": "Conclusions, final paragraph" }, { "mode": "Incomplete densification in conventional pressure-assisted sintering", "trigger": "Consolidating ZrB2 powder by conventional pressure-assisted sintering", "consequence": "Residual porosity and coarse microstructure, according to Sani et al. Their introduction says the refractory character of zirconium and tantalum borides makes powder consolidation very difficult.", "severity": "moderate", "source": "sani2016", "where": "Introduction, third paragraph" } ], "side_effects": [], "handling": [ { "text": "Keep uncoated ZrB2 parts below about 600 °C in air, the approximate oxidation onset in Sani et al.", "source": "sani2016", "where": "Conclusions, final paragraph" }, { "text": "Avoid breathing the powder, because PubChem reports the harmful-if-inhaled statement H332 for most company reports.", "source": "pubchem-zrb2", "where": "Safety and Hazards, GHS Classification" } ], "mitigations": [ { "text": "Add silicon-containing additives, such as SiC, to improve oxidation resistance for more severe thermal conditions, as Sani et al. recommend.", "source": "sani2016", "where": "Conclusions, final paragraph" }, { "text": "Use a powder made by self-propagating high-temperature synthesis before spark plasma sintering; Sani et al. report that this route gives higher density samples.", "source": "sani2016", "where": "Introduction, fourth paragraph" } ] }, "uses": [ { "application": "heat-shields", "device": "Thermal protection on hypersonic vehicles and atmospheric entry probes (historical UHTC use, not ZrB2 alone)", "example": "Sani et al. describe ultra-high-temperature ceramics as ideal for thermal protection systems and say they have mainly served hypersonic vehicles, rocket motor nozzles and atmospheric entry probes.", "source": "sani2016", "where": "Introduction, first and second paragraphs" }, { "application": "propulsion-and-tanks", "device": "Rocket motor nozzles (historical UHTC use)", "example": "Sani et al. list rocket motor nozzles among the aerospace uses of ultra-high-temperature ceramics in general.", "source": "sani2016", "where": "Introduction, second paragraph" }, { "application": "thermal-control", "device": "Solar absorber receivers for concentrating solar thermal plants (proposed)", "example": "Sani et al. propose transition-metal borides, including ZrB2, as solar absorbers for very high temperature operation, and measure the spectral optical properties of dense ZrB2.", "source": "sani2016", "where": "Introduction, second paragraph and optical properties section" } ], "supply": [ { "subject": "Zirconium (zirconium mineral concentrates as feedstock)", "producers": [ { "country": "Australia", "share_percent": 33.3, "year": 2025 }, { "country": "South Africa", "share_percent": 22.5, "year": 2025 }, { "country": "Mozambique", "share_percent": 13.3, "year": 2025 }, { "country": "China", "share_percent": 8.3, "year": 2025 } ], "critical_lists": [ { "list": "USGS 2025 List of Critical Minerals (zirconium listed on the USGS page)", "listed": true } ], "recycling": "USGS: companies in Oregon and Utah recycled zirconium from new scrap generated during metal production.", "substitutes": [], "source": "usgs-mcs2026-zirconium-hafnium", "where": "World mine production table, zirconium mineral concentrates, 2025 (world total rounded 1,200 thousand metric tons; shares calculated by Space Mushroom from the country values 400, 270, 160 and 100); Recycling; Events, Trends, and Issues. Critical-list status from the USGS 2025 critical minerals page (usgs-crit2025); the zirconium chapter itself does not mention it." }, { "subject": "Boron (feedstock for the diboride)", "abundance": "USGS boron production 2025 (thousand metric tons as printed): Turkey 1,500 refined borates; Bolivia 380 ulexite; Chile 300 ulexite; China 230 boric oxide equivalent; Peru 220 crude borates; Argentina 170 crude ore; Russia 80 datolite ore; Germany 40 compounds.", "producers": [ { "country": "Turkey", "year": 2025 }, { "country": "Bolivia", "year": 2025 }, { "country": "Chile", "year": 2025 }, { "country": "China", "year": 2025 } ], "critical_lists": [ { "list": "USGS 2025 List of Critical Minerals (boron added in the final 2025 list)", "listed": true } ], "recycling": "USGS: boron recycling is 'Insignificant.'", "substitutes": [ "USGS: substitution for boron is possible in detergents, enamels, insulation and soaps; the chapter does not discuss boride or ceramic uses." ], "source": "usgs-mcs2026-boron", "where": "World Production and Reserves table, 2025 column (no shares calculated because the world total is printed as XX); Recycling; Substitutes; Events, Trends, and Issues (boron added to the 2025 critical list)." } ], "media": [], "documents": [ { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers (Renewable Energy 91, 340-346; arXiv copy)", "type": "paper", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016 }, { "title": "PubChem: Zirconium diboride (CID 9812765), GHS classification and experimental properties", "type": "database", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/9812765/JSON", "year": 2026 }, { "title": "USGS Mineral Commodity Summaries 2026: Boron", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf", "year": 2026 }, { "title": "USGS Mineral Commodity Summaries 2026: Zirconium and Hafnium", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf", "year": 2026 }, { "title": "Nanografi product page: Zirconium Diboride (ZrB2) nanopowder NG04CO2502", "type": "datasheet", "url": "https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/", "year": 2026 }, { "title": "Stanford Advanced Materials product page: NN0233 Nano Zirconium Diboride (ZrB2) powder", "type": "datasheet", "url": "https://www.samaterials.com/micro-nano-materials/233-nano-zirconium-diboride.html", "year": 2026 } ], "gaps": [ "No flight, vacuum, radiation or space-environment result for ZrB2 was found in the sources read for this profile.", "Thermal expansion coefficient (5.9 x 10-6 K-1 in Table 1 of Sani et al.) and electrical conductivity (1.0 x 10^7 S/m in Table 1) are printed in exponent form and are left out, as the brief requires.", "Free energy of formation (-318.2 kJ, Table 1 of Sani et al.) is left out because its unit is printed incompletely in the table.", "The Silvestroni 2018 and Scientific Reports 2017 strength data at 1500 degC were not read in this run: the CNR repository returned an access block and the Nature article redirected to a sign-in page. No high-temperature strength value is recorded.", "No fracture toughness, grain size or measured hardness test method was found in a fetched source.", "No UNS, EN, DIN or other standard designation for ZrB2 was printed in a source read in this run, so identity.designations is empty.", "Atomic weights for zirconium and boron were not printed in a fetched source, so the recipe lists atom counts only.", "Boron producer shares are not calculated because the USGS boron table prints the world total as XX.", "No zirconium-diboride safety data sheet was read in this run. The hazard entries rest on PubChem's GHS summary and a product page that prints no hazard statements.", "Side effects of ZrB2 (for example oxidation products) were not found in a fetched source, so risks.side_effects is empty.", "Nanografi and Stanford Advanced Materials are reseller product pages. They are used only for stated supplier ranges and for the disagreement shown; they are not treated as measured grade data.", "The EU critical raw materials list was checked, but the fetched page did not confirm boron or zirconium by name, so no EU critical-list entry is recorded.", "PubChem's experimental record quotes \"3000 °C\" for the melting point, which differs from the 3245 °C in Sani et al. It is not recorded as a property because the verifier could not match it in the fetched PubChem text, where the Melting Point section was cut off." ], "story": { "why": "Zirconium diboride (ZrB2) is a hard, high-melting boride ceramic in the AlB2 structure. Sani et al. (2016) tabulate a melting temperature of 3245 °C and a density of 6.119 g/cm3 for dense ZrB2. The material is studied for hypersonic thermal protection and for solar absorbers, but its weak point in air is oxidation above about 600 °C for monolithic material.", "uses": [ { "where": "Thermal protection on hypersonic vehicles and entry probes", "line": "Sani et al. describe ultra-high-temperature ceramics as ideal for thermal protection systems. They say these ceramics have mainly served hypersonic vehicles, rocket motor nozzles and atmospheric entry probes." }, { "where": "Solar absorbers (proposed)", "line": "Sani et al. propose transition-metal borides, including ZrB2, as solar absorbers for very high temperature operation. They measure the optical properties of dense ZrB2 and give an absorbance of 0.47 and an emittance of 0.18 at 1400 K, calculated from the measured spectra." }, { "where": "Industry references", "line": "PubChem's summary of uses lists ZrB2 as a refractory material for aircraft and rockets, a high-temperature electrical conductor, and a cutting-tool coating, citing Hawley." } ], "can_do": [ { "label": "Melting point", "line": "The literature melting temperature of dense ZrB2 is 3245 °C in Sani et al. PubChem's experimental record quotes \"3000 °C\" without a test method. The two figures differ, so both are reported.", "benchmark": "melting_point", "scope": "material", "value": "3245 °C" }, { "label": "Density", "line": "The literature density of dense ZrB2 is 6.119 g/cm3 in Table 1 of Sani et al. The value is cited there to an earlier source and is not the paper's own measurement.", "benchmark": "density", "scope": "material", "value": "6.119 g/cm3" }, { "label": "Stiffness and hardness", "line": "The literature Young's modulus is 489 GPa and the hardness is 23 GPa in the same table. The supplier range for a nanopowder is 340 to 500 GPa, a second-hand figure.", "benchmark": "elastic_modulus", "scope": "material", "value": "489 GPa" }, { "label": "Thermal conductivity", "line": "The literature thermal conductivity of dense ZrB2 is 60 W/(m·K) in Sani et al. Temperature is not stated in the table.", "benchmark": "thermal_conductivity", "scope": "material", "value": "60 W/(m·K)" }, { "label": "Oxidation in air", "line": "Monolithic ZrB2 starts to oxidize at approximately 600 °C in air, according to Sani et al. A supplier claims 1200 to 1400 °C for a nanopowder, with no test conditions printed.", "benchmark": "oxidation_onset_temperature", "scope": "material", "value": "600 °C" } ], "compare": "ZrB2 is a dense, high-melting boride ceramic. Its literature melting temperature is 3245 °C and its hardness is 23 GPa, both from Sani et al. Its limit in air is the main drawback: monolithic material starts to oxidize at about 600 °C, and the authors say additives are needed for more severe conditions. A supplier's claim of 1200 to 1400 °C oxidation resistance is not supported by a test condition in the sources read, so the table reports the lower, sourced onset.", "compare_rows": [ { "label": "Melting temperature", "benchmark": "melting_point", "scope": "material" }, { "label": "Density", "benchmark": "density", "scope": "material" }, { "label": "Oxidation onset in air", "benchmark": "oxidation_onset_temperature", "scope": "material" } ], "handling": [ "Keep uncoated parts below about 600 °C in air, or add silicon-containing oxidation-resistance additives.", "Avoid breathing the powder; PubChem prints the harmful-if-inhaled statement H332 for most company reports.", "Check the supplier's safety data sheet for the grade you buy; no ZrB2 SDS was read in this run." ], "good_for": [ "High melting point: 3245 °C is the literature value in Sani et al. (2016).", "Stiffness and hardness: a Young's modulus of 489 GPa and hardness of 23 GPa in the same table." ], "watch_out": [ "Oxidation in air above about 600 °C for monolithic material, unless additives are present.", "Conflicting figures: PubChem quotes \"3000 °C\" as the melting point, and a supplier claims oxidation resistance to 1200 to 1400 °C." ], "verdict": "A very high-melting boride that needs protection or additives once it sees air above about 600 °C.", "recipe": { "line": "ZrB2 is a zirconium diboride with one zirconium atom and two boron atoms per formula unit, in an AlB2-type hexagonal structure. Sani et al. make dense samples by spark plasma sintering, either from the elemental powders or from ZrB2 powder first made by self-propagating high-temperature synthesis.", "parts": [ { "name": "Zirconium", "symbol": "Zr", "role": "The metal atom in the hexagonal lattice. The reaction in Sani et al. is written as a metal plus boron forming the metal diboride, with zirconium as the metal." }, { "name": "Boron", "symbol": "B", "role": "Forms the flat boron layers of the AlB2-type structure with the zirconium between them." } ] }, "risk_groups": [ { "title": "For people", "lead": "The hazard data for ZrB2 rest on PubChem's GHS summary, which lists acute toxicity statements. No safety data sheet for ZrB2 was read in this run.", "points": [ { "label": "The powder", "line": "PubChem prints the statements H302, H312 and H332 (harmful if swallowed, in contact with skin or if inhaled) for most company reports, from 54 reports in total." }, { "label": "Reports that disagree", "line": "PubChem also notes that the chemical does not meet GHS hazard criteria in 7.4% of reports (4 of 54)." }, { "label": "Supplier page", "line": "The Nanografi product page prints no hazard statements at all." } ], "level": 0, "verdict": "Harmful if swallowed or inhaled; check the SDS" }, { "title": "In air at high temperature", "lead": "The oxidation onset is the limit that matters most for ZrB2 parts, and the sources disagree on it.", "points": [ { "label": "Monolithic ZrB2", "line": "Sani et al. write that tantalum and zirconium diborides start to oxidize above approximately 600 °C, with rapid material degradation unless additives are used." }, { "label": "Supplier claim", "line": "A nanopowder supplier claims oxidation resistance up to 1200 to 1400 °C. No test condition is printed, so this cannot be reconciled with the 600 °C figure." } ], "verdict": "Oxidizes above about 600 °C in air" }, { "title": "Handling and storage", "points": [ { "label": "Dust", "line": "Avoid breathing the powder, given the harmful-if-inhaled statement that PubChem prints for most company reports." }, { "label": "Parts in service", "line": "Keep uncoated parts below about 600 °C in air, or use silicon-containing additives as Sani et al. recommend." } ] } ] }, "updated": "2026-11-01", "review": { "status": "draft", "method": "assistant", "checked_values": 15, "unreachable": 2, "caveats": 4, "note": "Written by an AI assistant on 2026-11-01 from pages fetched in that run. Sani et al. (2016) supplies the bulk property values; PubChem, Nanografi and Stanford Advanced Materials give conflicting or supplier-only figures, shown side by side." }, "sources": { "sani2016": { "title": "Optical properties of dense zirconium and tantalum diborides for solar thermal absorbers", "id": "doi:10.1016/j.renene.2016.01.068 (Renewable Energy 91, 340-346; arXiv:1803.06528 copy)", "url": "https://arxiv.org/pdf/1803.06528", "year": 2016, "kind": "paper", "license": "arXiv copy; cited, not reproduced" }, "pubchem-zrb2": { "title": "PubChem compound record, Zirconium diboride (CID 9812765)", "id": "CID 9812765; CAS 12045-64-6", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/9812765/JSON", "year": 2026, "kind": "database", "license": "public domain (NCBI)" }, "usgs-mcs2026-boron": { "title": "Mineral Commodity Summaries 2026, Boron", "id": "USGS MCS 2026, February 2026", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf", "year": 2026, "kind": "report", "license": "public domain (USGS)" }, "usgs-mcs2026-zirconium-hafnium": { "title": "Mineral Commodity Summaries 2026, Zirconium and Hafnium", "id": "USGS MCS 2026, February 2026", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf", "year": 2026, "kind": "report", "license": "public domain (USGS)" }, "usgs-crit2025": { "title": "About the 2025 List of Critical Minerals (USGS)", "id": "USGS 2025 List of Critical Minerals", "url": "https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals", "year": 2025, "kind": "web", "license": "public domain (USGS)" }, "nanografi-zrb2": { "title": "Nanografi, Zirconium Diboride (ZrB2) Nanoparticles, product NG04CO2502", "id": "Product page, 99.5% purity, about 45 nm", "url": "https://shop.nanografi.com/nanoparticles/compounds-nanoparticles/zirconium-diboride-zrb2-nanoparticles/", "year": 2026, "kind": "web", "license": "supplier product page, cited not reproduced" }, "samaterials-zrb2": { "title": "Stanford Advanced Materials, NN0233 Nano Zirconium Diboride (ZrB2) powder", "id": "Product NN0233, CAS 12045-64-6, 99.9% purity", "url": "https://www.samaterials.com/micro-nano-materials/233-nano-zirconium-diboride.html", "year": 2026, "kind": "web", "license": "supplier product page, cited not reproduced" }, "wiki-zrb2": { "title": "Wikipedia, Zirconium diboride (composition and structure summary only)", "id": "Wikipedia article, accessed 2026-11-01", "url": "https://en.wikipedia.org/wiki/Zirconium_diboride", "year": 2026, "kind": "web", "license": "CC BY-SA 4.0 (text summarised, not reproduced)" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/zirconium-diboride/" }