{ "spore": "profile", "id": "zirconium-carbide", "spore_version": "0.2", "family": "carbide-nitride-boride-ceramics", "name": "Zirconium carbide", "abbreviation": "ZrC", "role": "very high melting point ultra-high-temperature ceramic (carbide), a candidate for hypersonic leading edges and nuclear thermal propulsion coatings", "category": "ceramics", "type": "carbides", "summary": "Zirconium carbide is a hard, stiff ceramic with a rock-salt (FCC) structure. A 2023 open-access review in Materials gives a density of 6.73 g/cm3, a melting point of 3532 degC (Table 1) and an elastic modulus of 435 GPa at room temperature. Thermal conductivity is 17.5 to 31.5 W/m·K at room temperature and rises to 27.5 to 37.5 W/m·K at 1500 degC (review text). Flexural strength is 460 MPa at room temperature in the same table, though the review's Table 4 gives that value for a different alloy, so it is kept with a note. The review and a NASA patent both describe oxidation and hot-hydrogen attack as the main chemical limits. Zirconium, one of its two elements, is produced mostly in Australia and South Africa (USGS 2026).\n", "best_for": "Hard, stiff, high melting point ceramic parts and coatings where oxidation is handled by a protective layer, such as hypersonic leading edges and nozzle liners", "weakest_at": "Oxidation in air above about 600 degC (the review) and brittleness, with little plastic deformation before fracture", "identity": { "formula": "ZrC", "cas": "12070-14-3", "crystal_system": "cubic", "designations": [], "source": "zrc-review-2023", "where": "Section 1.2 (ZrC Crystal Structure), text that gives an FCC rock-salt structure. CAS from the PubChem record CID 11159298, Other Identifiers, CAS." }, "tags": { "environments": [ "re-entry" ], "stresses": [ "extreme-heat" ], "applications": [ "heat-shields", "propulsion-and-tanks", "structures" ] }, "properties": [ { "benchmark": "density", "label": "Density, ZrC (review Table 1)", "value": 6.73, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "temperature": "room temperature", "basis": "ZrC column of Table 1" }, "method": "Table 1, Density row, as printed in g cm-3", "status": "ground", "source": "zrc-review-2023", "where": "Table 1, Density row, ZrC column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "density", "label": "Density, ZrC (PubChem experimental)", "value": 6.73, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "temperature": "25 degC" }, "method": "Experimental Properties, Density section, printed as 6.73 @25 degC", "status": "ground", "source": "pubchem-zrc", "where": "Experimental Properties, Density section", "source_detail": { "title": "PubChem compound CID 11159298, Zirconium carbide (GHS classification, uses, experimental density, CAS 12070-14-3)", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/11159298/JSON", "kind": "database", "license": "PubChem public database" } }, { "benchmark": "melting_point", "label": "Melting point, ZrC (review Table 1)", "value": 3532, "bound": "exact", "unit": "degC", "scope": "material", "conditions": { "basis": "ZrC column of Table 1" }, "method": "Table 1, Melting Point row. The review text gives 3427 degC in Sections 1 and 2.2.1, and the abstract gives 3825 K. Both are listed in the note.", "status": "ground", "note": "The review gives three melting points. The table value is kept; the text value (3427 degC) and the abstract value (3825 K) differ from it.", "source": "zrc-review-2023", "where": "Table 1, Melting Point row, ZrC column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "elastic_modulus", "label": "Elastic modulus, ZrC (review Table 1)", "value": 435, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "temperature": "room temperature", "basis": "ZrC column of Table 1" }, "method": "Table 1, Elastic Modulus row. Table 4 also gives 435 for the ZrC row.", "status": "ground", "source": "zrc-review-2023", "where": "Table 1, Elastic Modulus row, ZrC column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "elastic_modulus", "label": "Elastic modulus, pure ZrC (spark plasma sintered)", "value": 464, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "grade": "pure ZrC, no sintering aid", "method_detail": "spark plasma sintering at 2100 degC, 3 min, 65 MPa, mean grain size 13 micrometre", "uncertainty": "plus or minus 22 GPa, as printed" }, "method": "Table 5, pure ZrC row (Elastic Modulus column). Other rows in the table add MoSi2 and are not used.", "status": "ground", "source": "zrc-review-2023", "where": "Table 5, ZrC row (2100/3/65), Elastic Modulus column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "poissons_ratio", "label": "Poisson ratio, ZrC (review Table 3)", "value": 0.18, "bound": "exact", "unit": "unitless", "scope": "material", "conditions": { "temperature": "room temperature" }, "method": "Table 3, Poisson Ratio column, both DFT and experimental rows", "status": "ground", "source": "zrc-review-2023", "where": "Table 3, Poisson Ratio column, DFT and Experimental rows", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "hardness", "label": "Hardness, monolithic ZrC (Castle et al., as quoted in the review)", "value": 31.3, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "basis": "monolithic ZrC, quoted as 31.3 plus or minus 1.4 GPa in the review text", "load": "not stated in the review" }, "method": "Review text, high-entropy ceramics paragraph (Section 3.1.1), which cites Castle et al. The test method and load are not printed, and no primary paper was read.", "status": "ground", "source": "zrc-review-2023", "where": "Section 3.1.1 (High-Entropy Ceramics), paragraph on Castle et al.", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "hardness", "label": "Nanoindentation hardness, pure ZrC (spark plasma sintered)", "value": 25.2, "bound": "exact", "unit": "GPa", "scope": "material", "conditions": { "grade": "pure ZrC, no sintering aid", "method_detail": "spark plasma sintering at 2100 degC, 3 min, 65 MPa", "uncertainty": "plus or minus 1.4 GPa, as printed" }, "method": "Table 5, pure ZrC row, Nanoindentation Hardness column", "status": "ground", "note": "Table 5 also prints a Vickers HV1.0 value (17.9 plus or minus 0.6) with no unit in the header, so it is left out.", "source": "zrc-review-2023", "where": "Table 5, ZrC row, Nanoindentation Hardness column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "thermal_conductivity", "label": "Thermal conductivity, ZrC (review Table 1)", "value": 17.5, "value_high": 31.5, "bound": "range", "unit": "W/m·K", "scope": "material", "conditions": { "temperature": "room temperature", "basis": "ZrC column of Table 1" }, "method": "Table 1, Thermal Conductivity row, printed as 17.5-31.5", "status": "ground", "note": "The review text gives about 20 W/m·K at room temperature (Section 2.2.4). That falls inside this range.", "source": "zrc-review-2023", "where": "Table 1, Thermal Conductivity row, ZrC column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "thermal_conductivity", "label": "Thermal conductivity, ZrC at 1500 degC (review text)", "value": 27.5, "value_high": 37.5, "bound": "range", "unit": "W/m·K", "scope": "material", "conditions": { "temperature": "1500 degC" }, "method": "Section 1.1 text, which says the conductivity increases from 17.5 to 31 at room temperature to 27.5 to 37.5 W m-1 K-1 at 1500 degC. The review attributes this to its reference 21 and says the range covers different experiments.", "status": "ground", "source": "zrc-review-2023", "where": "Section 1.1 (ZrC Physical Properties), thermal conductivity paragraph", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "thermal_conductivity", "label": "Thermal conductivity, ZrC room temperature literature range", "value": 20, "value_high": 40, "bound": "range", "unit": "W/m·K", "scope": "material", "conditions": { "temperature": "room temperature", "basis": "range of published measurements, not one material" }, "method": "Introduction, paragraph on experimental scatter, which says the values vary from as low as 20 to as high as 40 W m-1 K-1 at room temperature", "status": "ground", "note": "A range across published experiments, not a single material value. Shown to mark the scatter in the literature.", "source": "arxiv-tc-zrc", "where": "Introduction, paragraph beginning \"the thermal conductivity data of ZrC\"", "source_detail": { "title": "Tiwari J, Feng T, Intrinsic thermal conductivity of ZrC from low to ultra-high temperatures: A critical revisit, arXiv:2304.06805 (2023)", "url": "https://arxiv.org/pdf/2304.06805", "kind": "paper", "license": "arXiv preprint" } }, { "benchmark": "cte", "label": "Coefficient of thermal expansion, ZrC (NASA patent Table 1)", "value": 4, "value_high": 10.2, "bound": "range", "unit": "10-6/K", "scope": "material", "conditions": { "temperature": "293 to 3000 K, as printed in the patent" }, "method": "Table 1 of US 10,068,675, ZrC row, printed as 4.0-10.2 (x 10-6 K-1). The review's Table 1 prints the CTE as 4 with no exponent, so that entry is not used.", "status": "ground", "source": "nasa-patent-zrc", "where": "Table 1 (Coefficients of thermal expansion), ZrC row", "source_detail": { "title": "Raj et al., US Patent 10,068,675 B1, Advanced Protective Coatings for Graphite-Based Nuclear Propulsion Fuel Elements (NASA, 2018), NTRS 20180006260", "url": "https://ntrs.nasa.gov/api/citations/20180006260/downloads/20180006260.pdf", "kind": "report", "license": "US government patent, public domain" } }, { "benchmark": "cte", "label": "Coefficient of thermal expansion, ZrC at 1500 degC (review text)", "value": 9, "bound": "exact", "unit": "10-6/K", "scope": "material", "conditions": { "temperature": "1500 degC" }, "method": "Section 1.1 text, which gives 9.0 x 10-6 K-1 at 1500 degC and 10.2 x 10-6 K-1 at 2500 degC", "status": "ground", "source": "zrc-review-2023", "where": "Section 1.1 (ZrC Physical Properties), CTE paragraph", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "cte", "label": "Coefficient of thermal expansion, ZrC at 2500 degC (review text)", "value": 10.2, "bound": "exact", "unit": "10-6/K", "scope": "material", "conditions": { "temperature": "2500 degC" }, "method": "Section 1.1 text, same sentence as the 1500 degC value", "status": "ground", "source": "zrc-review-2023", "where": "Section 1.1 (ZrC Physical Properties), CTE paragraph", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "flexural_strength", "label": "Flexural strength, ZrC (review Table 1)", "value": 460, "bound": "exact", "unit": "MPa", "scope": "material", "conditions": { "temperature": "room temperature", "uncertainty": "plus or minus 24 MPa, as printed", "basis": "ZrC column of Table 1" }, "method": "Table 1, Flexure Strength row. The review text repeats 460 plus or minus 24 MPa for ZrC (Section 1.1), but Table 4 gives the same number for TZN-3, another alloy. Treat the attribution as unresolved.", "status": "ground", "note": "The review puts 460 plus or minus 24 MPa against ZrC in Table 1 and text, and against TZN-3 in Table 4.", "source": "zrc-review-2023", "where": "Table 1, Flexure Strength row, ZrC column; Section 1.1 text", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "flexural_strength", "label": "Flexural strength, pure ZrC (spark plasma sintered, 3-point)", "value": 407, "bound": "exact", "unit": "MPa", "scope": "material", "conditions": { "grade": "pure ZrC, no sintering aid", "method_detail": "three-point flexure, spark plasma sintering at 2100 degC, 3 min, 65 MPa", "uncertainty": "plus or minus 38 MPa, as printed" }, "method": "Table 5, pure ZrC row, 3-pt Flexure Test column", "status": "ground", "source": "zrc-review-2023", "where": "Table 5, ZrC row (2100/3/65), 3-pt Flexure Test column", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "flexural_strength", "label": "Flexural strength, ZrC at 1600 degC (review text)", "value": 494, "bound": "exact", "unit": "MPa", "scope": "material", "conditions": { "temperature": "1600 degC", "uncertainty": "plus or minus 44 MPa, as printed" }, "method": "Section 1.1 text, attributed to ZrC. It rises from room temperature values before falling at higher temperature.", "status": "ground", "source": "zrc-review-2023", "where": "Section 1.1 (ZrC Physical Properties), flexure paragraph", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "flexural_strength", "label": "Flexural strength, ZrC at 1800 degC (review text)", "value": 366, "bound": "exact", "unit": "MPa", "scope": "material", "conditions": { "temperature": "1800 degC", "uncertainty": "plus or minus 46 MPa, as printed" }, "method": "Section 1.1 text, same sentence as the 1600 degC value", "status": "ground", "source": "zrc-review-2023", "where": "Section 1.1 (ZrC Physical Properties), flexure paragraph", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "oxidation_resistance_temp", "label": "Temperature to which ZrC is chemically stable in air (review text)", "value": 600, "bound": "exact", "unit": "degC", "scope": "material", "conditions": { "atmosphere": "air", "basis": "stated as the temperature up to which ZrC remains chemically stable, compared with C/C" }, "method": "Section 2.3.2 text. It is a statement of stability, not a rate or a test result.", "status": "ground", "note": "Custom property name; no oxidation-limit name in the canon file. The review gives it as the limit of stability, not as a rate.", "source": "zrc-review-2023", "where": "Section 2.3.2 (Reaction Kinetics), paragraph comparing ZrC with C/C composites", "source_detail": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" } }, { "benchmark": "particle_size_d50", "label": "Particle size D50, ZrC powder grade A", "value": 5, "value_high": 13, "bound": "range", "unit": "micrometre", "scope": "material", "conditions": { "grade": "Grade A", "method_detail": "laser diffraction, ASTM C 1070 (Microtrac)" }, "method": "Particle Size Distribution table, D50 row, Grade A column (datasheet issue 6, 2017)", "status": "ground", "note": "Custom property name. Powder property, not a bulk property.", "source": "hoganas-pd4004", "where": "Physical Characteristics, Particle Size Distribution table, D50 row, Grade A", "source_detail": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" } }, { "benchmark": "particle_size_d50", "label": "Particle size D50, ZrC powder grade B", "value": 3, "value_high": 5, "bound": "range", "unit": "micrometre", "scope": "material", "conditions": { "grade": "Grade B", "method_detail": "laser diffraction, ASTM C 1070 (Microtrac)" }, "method": "Particle Size Distribution table, D50 row, Grade B column", "status": "ground", "note": "Custom property name. Powder property, not a bulk property.", "source": "hoganas-pd4004", "where": "Physical Characteristics, Particle Size Distribution table, D50 row, Grade B", "source_detail": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" } }, { "benchmark": "particle_size_d50", "label": "Particle size D50, ZrC powder grade AX", "value": 7, "value_high": 12, "bound": "range", "unit": "micrometre", "scope": "material", "conditions": { "grade": "Grade AX", "method_detail": "laser diffraction, ASTM C 1070 (Microtrac)" }, "method": "Particle Size Distribution table, D50 row, Grade AX column", "status": "ground", "note": "Custom property name. Powder property, not a bulk property.", "source": "hoganas-pd4004", "where": "Physical Characteristics, Particle Size Distribution table, D50 row, Grade AX", "source_detail": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" } }, { "benchmark": "zr_hf_content", "label": "Zr plus Hf content, ZrC powder grade A (minimum)", "value": 87.8, "bound": "exact", "unit": "mass percent", "scope": "material", "conditions": { "grade": "Grade A", "basis": "minimum mass fraction as printed" }, "method": "Chemical Characteristics table, Zr + Hf row, Grade A column (min. 87.8)", "status": "ground", "note": "Custom property name. Bulk powder chemistry, a minimum. Grade B is 87.4 and grade AX is 87.9.", "source": "hoganas-pd4004", "where": "Chemical Characteristics table, Zr + Hf row, Grade A column", "source_detail": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" } }, { "benchmark": "total_carbon_content", "label": "Total carbon content, ZrC powder grade A (minimum)", "value": 11.4, "bound": "exact", "unit": "mass percent", "scope": "material", "conditions": { "grade": "Grade A", "basis": "minimum mass fraction as printed" }, "method": "Chemical Characteristics table, Ctotal row, Grade A column (min. 11.4)", "status": "ground", "note": "Custom property name. Bulk powder chemistry, a minimum. Grade B is 10.8 and grade AX is 11.2.", "source": "hoganas-pd4004", "where": "Chemical Characteristics table, Ctotal row, Grade A column", "source_detail": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" } }, { "benchmark": "oxygen_content", "label": "Oxygen content, ZrC powder (maximum, all grades)", "value": 0.6, "bound": "exact", "unit": "mass percent", "scope": "material", "conditions": { "grade": "Grades A, B and AX", "basis": "maximum mass fraction as printed" }, "method": "Chemical Characteristics table, O row, max 0.6 for all three grades", "status": "ground", "note": "Custom property name. Bulk powder chemistry, a maximum, not a typical value.", "source": "hoganas-pd4004", "where": "Chemical Characteristics table, O row", "source_detail": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" } } ], "corrosion": [ { "environment": "Oxidizing air up to about 600 degC, compared with carbon-carbon composites", "headline": "ZrC stays chemically stable up to about 600 degC, where C/C composites oxidize above 500 degC.", "effect": "The review says ZrC resists oxidation better than C/C up to 600 degC, and that C/C composites readily oxidize above 500 degC. Oxidation of C/C is measured as weight loss and oxidation of ZrC as oxide thickness, so the two are not directly comparable.", "rating": "moderate", "conditions": { "temperature": "up to 600 degC", "atmosphere": "air" }, "source": "zrc-review-2023", "where": "Section 2.3.2 (Reaction Kinetics), paragraph comparing ZrC with C/C composites" }, { "environment": "Air at 1000 degC for 30 minutes (Gasparrini et al., as cited in the review)", "headline": "An oxide layer about 0.25 cm thick formed in 30 minutes, and oxidation was linear in time.", "effect": "The review says Gasparrini et al. heated ZrC to 1000 degC for 30 min in air and got an oxide layer approximately 0.25 cm thick. It also says ZrC shows linear oxidation kinetics, so the surface chemical reaction is the rate-limiting step, and that a coating that keeps air off the surface can be effective.", "rating": "severe", "conditions": { "temperature": "1000 degC", "time": "30 min", "atmosphere": "air" }, "source": "zrc-review-2023", "where": "Section 2.3.2 (Reaction Kinetics), paragraphs on Gasparrini et al. and Figures 11 and 12" }, { "environment": "Flow-tube furnace, hot-pressed ZrC, 1000 to 1600 degC (gas with nitrogen)", "headline": "Above about 1400 degC, nitridation and reduction may matter as well as oxidation.", "effect": "The abstract says that above 1400 degC, oxidation mechanisms remain dominant, but nitridation and reduction mechanisms may be large enough to need consideration. The abstract gives no rate constants, and only the abstract was read.", "rating": "moderate", "conditions": { "temperature": "1000 to 1600 degC", "form": "hot-pressed ZrC" }, "source": "arxiv-ox-zrc", "where": "Abstract" }, { "environment": "Hot hydrogen in nuclear thermal propulsion, on graphite fuel elements with ZrC coatings", "headline": "Graphite is attacked by hot hydrogen, and a ZrC coating can debond from graphite because of thermal expansion mismatch.", "effect": "The NASA patent says graphite substrates are susceptible to hot hydrogen attack and that an NbC or ZrC coating tends to debond from the substrate. Its Table 1 gives ZrC a CTE of 4.0 to 10.2 x 10-6 K-1 against 4.7 to 6.9 for graphite. The patent's answer is a multilayer coating with compliant layers, which the patent describes but which was not tested in this source.", "rating": "severe", "conditions": { "temperature": "operating temperatures of nuclear thermal propulsion fuel elements, not stated in the patent", "atmosphere": "hot hydrogen" }, "source": "nasa-patent-zrc", "where": "Background text on debonding of NbC or ZrC coatings; Table 1 (Coefficients of thermal expansion)" } ], "risks": { "hazards": [ { "text": "PubChem aggregated GHS for zirconium carbide (CID 11159298, signal word Danger): H228 flammable solid in 99.1 percent of the 217 company reports that gave hazard codes. H302, H312 and H332 (harmful if swallowed, in skin contact or if inhaled) appear in 18 percent of the reports. 0.9 percent (2 of 217) say the substance does not meet GHS hazard criteria.", "ghs": [ "H228", "H302", "H312", "H332" ], "source": "pubchem-zrc", "where": "Safety and Hazards, GHS Classification" }, { "text": "Supplier data (Hoganas PD-4004, 2017): the datasheet states under hazard identification (Regulation EC 1272/2008) that there are none. This conflicts with the PubChem entry above.", "ghs": [], "source": "hoganas-pd4004", "where": "Hazards identification row, Storage and Handling" } ], "failure_risks": [ { "mode": "Brittle fracture of dense ceramic", "trigger": "Tensile or bending load on a flaw or pore", "consequence": "The review says ZrC is a ceramic that fractures in a brittle way with little plastic deformation, so its defect density sets its strength.", "severity": "moderate", "source": "zrc-review-2023", "where": "Section 1.2 (ZrC Crystal Structure), paragraph on defects and vacancies" }, { "mode": "Oxide scale growth at high temperature", "trigger": "Exposure to oxidizing air above about 600 degC", "consequence": "An oxide layer about 0.25 cm thick formed in 30 minutes at 1000 degC in air (Gasparrini et al., via the review). The review concludes that ZrC needs a protective coating for high temperature use.", "severity": "high", "source": "zrc-review-2023", "where": "Section 2.3.2 (Reaction Kinetics), paragraph on Gasparrini et al." }, { "mode": "Coating cracking and delamination from thermal expansion mismatch", "trigger": "Thermal cycling with a coating or substrate that has a different CTE", "consequence": "The review says cracks and delamination let oxygen diffuse to the ZrC and speed oxidation. The NASA patent reports the same debonding for ZrC coatings on graphite.", "severity": "moderate", "source": "zrc-review-2023", "where": "Section 2.2.2 (Coefficient of Thermal Expansion), CTE mismatch paragraph" }, { "mode": "Property change with carbon-to-zirconium ratio", "trigger": "Carbon vacancies from non-stoichiometry, or sintering with carbon deficiency", "consequence": "The review says carbon vacancies lower thermal conductivity and change the lattice parameter, so reported property values vary between studies.", "severity": "low", "source": "zrc-review-2023", "where": "Section 1.2 (ZrC Crystal Structure) and Section 3.2.1 (Melting Point Increase by Lattice Parameter Reduction)" } ], "side_effects": [], "handling": [ { "text": "Powder: PubChem lists H228 (flammable solid) and H302, H312 and H332. The PubChem hazards summary, citing Hawley, says the powder or dust may spontaneously ignite. Keep it away from heat and ignition sources, and control dust.", "source": "pubchem-zrc", "where": "Safety and Hazards, Hazards Identification" }, { "text": "Storage: the Hoganas datasheet says to store in a closed container, and that the product is under export control.", "source": "hoganas-pd4004", "where": "Storage and Handling row; footnote e" }, { "text": "Oxidation: above about 600 degC in air, ZrC needs a protective coating (review, Section 2.3.1 and Section 3.3.2).", "source": "zrc-review-2023", "where": "Section 2.3.1 (Thermodynamic Stability of ZrC) and Section 3.3.2 (Oxidation Resistant Coatings)" } ], "mitigations": [ { "text": "The review says ZrC needs protective coatings, alloying or doping to resist oxidation, and that an SiC overcoat is inadequate because of its melting point, strength and propensity to crack.", "source": "zrc-review-2023", "where": "Section 2.3.1 (Thermodynamic Stability of ZrC), Section 3.3.2 (Oxidation Resistant Coatings)" } ] }, "uses": [ { "application": "heat-shields", "device": "Hypersonic wing leading edges (proposed)", "example": "The review argues that ZrC is promising as a replacement for C/C composites as a wing leading edge material, and that its melting point exceeds design requirements for hypersonic leading edges. This is a proposal in the review, not a flight record.", "source": "zrc-review-2023", "where": "Section 1 (Introduction), first paragraphs; Section 2.2.1 (ZrC Melting Point)" }, { "application": "propulsion-and-tanks", "device": "Coatings on graphite fuel elements for nuclear thermal propulsion", "example": "US 10,068,675 describes a multilayer protective coating for graphite fuel elements whose first layer includes ZrC, with niobium, molybdenum and molybdenum carbide layers below it. The coating is meant to stop hot hydrogen attack. The patent describes the design; it does not report test results.", "source": "nasa-patent-zrc", "where": "Abstract and claims text (layer list); background text on hot hydrogen attack" }, { "application": "propulsion-and-tanks", "device": "Ceramic liner on carbon-carbon nozzle extension components", "example": "NASA Tech Briefs (February 2011) describes an Ultramet carbon-carbon structure with a ZrC or Zr-Si-C ceramic matrix liner, rated to 4,200 F (about 2,315 C). Nozzle extension components were fabricated and hot-fire tested.", "source": "ntrs-ultramet-2011", "where": "Tech Briefs article text, column 1, paragraphs on ZrC CMC liner and nozzle extensions (LEW-18618-1)" }, { "application": "structures", "device": "Refractories, cutting-tool coatings, abrasives and cermets", "example": "PubChem lists uses as incandescent filaments, abrasives, cermets, high-temperature electrical conductors, refractories and coatings for cutting tools (Hawley, via PubChem).", "source": "pubchem-zrc", "where": "Use and Manufacturing, Uses" } ], "supply": [ { "subject": "Zirconium (the zirconium half of ZrC, from zirconium mineral concentrates)", "abundance": "USGS: world zirconium reserves (ZrO2 content) are more than 70,000 thousand metric tons, of which Australia has 55,000 thousand. World mine production in 2025 was 1,200 thousand tons gross weight (rounded). The text says about 1 million tons, which differs from the table.", "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 }, { "country": "Senegal", "share_percent": 5.8, "year": 2025 } ], "critical_lists": [], "recycling": "USGS: companies in Oregon and Utah recycled zirconium from new scrap generated during metal production. Refractories are often recycled but could not be quantified.", "substitutes": [], "source": "usgs-mcs2026-zirconium-hafnium", "where": "World Mine Production and Reserves table, 2025 column (shares calculated by Space Mushroom against the printed rounded world total of 1,200 thousand tons; the printed country values do not sum to that total); Import Sources (2021 to 2024); Recycling" }, { "subject": "Zirconium chemical intermediates (compounds, used to make ZrC powder)", "abundance": "USGS: U.S. imports of zirconium compounds 2021 to 2024 came from China (41 percent), South Africa (31 percent), France (12 percent), Australia (10 percent) and other (6 percent). These are import shares, not production shares.", "producers": [], "critical_lists": [], "recycling": "USGS: recycling is not quantified for compounds.", "substitutes": [], "source": "usgs-mcs2026-zirconium-hafnium", "where": "Import Sources (2021 to 2024), Zirconium, compounds" } ], "media": [], "documents": [ { "title": "Peterson, Carr, Marinero and Mortalo, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023)", "type": "paper", "url": "https://doi.org/10.3390/ma16186158", "year": 2023 }, { "title": "Hoganas datasheet PD-4004, Zirconium Carbide Grade A, Grade B, Grade AX (issue 6, 2017)", "type": "datasheet", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "year": 2017 }, { "title": "PubChem compound record CID 11159298, Zirconium carbide (GHS classification, uses, experimental density)", "type": "database", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/11159298", "year": 2026 }, { "title": "Raj et al., US Patent 10,068,675 B1, Advanced Protective Coatings for Graphite-Based Nuclear Propulsion Fuel Elements (NASA, 2018)", "type": "report", "url": "https://ntrs.nasa.gov/api/citations/20180006260/downloads/20180006260.pdf", "year": 2018 }, { "title": "NASA Tech Briefs, February 2011, Ultramet carbon-carbon structure with ZrC or Zr-Si-C CMC liner (LEW-18618-1)", "type": "report", "url": "https://ntrs.nasa.gov/citations/20110012228", "year": 2011 }, { "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": "Tiwari and Feng, Intrinsic thermal conductivity of ZrC from low to ultra-high temperatures, arXiv:2304.06805 (2023)", "type": "paper", "url": "https://arxiv.org/pdf/2304.06805", "year": 2023 }, { "title": "arXiv:2402.04337, influence of nitrogen on the oxidation of hot-pressed zirconium carbide, 1000 to 1600 C (abstract read)", "type": "paper", "url": "https://arxiv.org/pdf/2402.04337", "year": 2024 } ], "gaps": [ "No fracture toughness value for pure ZrC was found. Table 5 prints a dash for pure ZrC, and the review's Section 2.1.3 refers only to a modelled curve.", "Electrical resistivity of ZrC: the review gives none. Wikipedia gives an electrical conductivity of about 2.3 MS/m with no citation, so it is not used.", "Melting point conflict: Table 1 gives 3532 degC, the review text gives 3427 degC, and the abstract gives 3825 K. Wikipedia gives 3,532 to 3,540 degC with no primary source, so it is not used.", "Table 1 CTE value of 4 for ZrC has no exponent in the printed table, so it is not used. The CTE values used come from the NASA patent Table 1 and the review text.", "Flexural strength of 460 plus or minus 24 MPa is printed against ZrC in Table 1 and text, and against TZN-3 in Table 4. Not resolved.", "Table 5 prints a density of 10.1 for pure ZrC, above the theoretical 6.73 in Table 1. That value is not used.", "Hardness of 31.3 GPa comes from the review's text citing Castle et al. Load and method are not printed, and no primary Castle paper was read.", "Oxidation rate constants and activation energy: not read. The arXiv oxidation paper was read as an abstract only.", "Space use: no NASA, ESA or flight record for ZrC was read. The nuclear thermal propulsion irradiation test (Oak Ridge, 2025) appeared in search results only; the ORNL page could not be read, and no published results were found.", "Crystal space group (Fm3m) and lattice constant (4.6976 Angstrom) are on Wikipedia and cite a 1960 crystallographic paper. Wikipedia is used for composition only, so they are not used here.", "Designations: no UNS, EN, DIN, JIS, AISI or ASTM code for ZrC was printed in a source read in this run. PubChem lists EC number 235-125-1, which is not one of the designation systems used here, so it is not listed.", "Critical mineral status: the USGS zirconium chapter read in this run does not print a critical-list status. The EU critical raw materials list was not read.", "Supply: zirconium substitutes were not discussed for ZrC specifically in the USGS chapter, so substitutes are empty.", "Custom property names used because they are not in spores/property-canon.yaml: hardness, oxidation_resistance_temp, particle_size_d50, oxygen_content.", "Hoganas datasheet hazard statement (none, under Regulation EC 1272/2008) conflicts with PubChem (H228, H302, H312, H332). Both are kept, with sources named." ], "story": { "why": "ZrC is a hard, stiff ceramic with a very high melting point. The review gives a density of 6.73 g/cm3, a melting point of 3532 degC (Table 1) and an elastic modulus of 435 GPa at room temperature. Those properties are why the review proposes it as a wing leading edge material for hypersonic flight, in place of carbon-carbon composites. Oxidation above about 600 degC is the main limit, and the review says it needs a protective coating.", "uses": [ { "where": "Hypersonic wing leading edges (proposed)", "line": "The review argues ZrC could replace C/C composites as a wing leading edge material. This is a proposal, not a flight record." }, { "where": "Nuclear thermal propulsion fuel elements", "line": "NASA patent US 10,068,675 describes a multilayer coating for graphite fuel elements with a ZrC layer, meant to stop hot hydrogen attack. It is a patent with no test results." }, { "where": "Nozzle extension liners", "line": "NASA Tech Briefs (2011) describes a ZrC ceramic liner on carbon-carbon nozzle extensions, rated to 4,200 F (about 2,315 C). Components were fabricated and hot-fire tested." } ], "can_do": [ { "label": "Stiffness", "line": "The elastic modulus is 435 GPa at room temperature (review Table 1), and 464 GPa for pure sintered ZrC (review Table 5).", "benchmark": "elastic_modulus", "scope": "material" }, { "label": "Hardness", "line": "The review quotes 31.3 GPa for monolithic ZrC (Castle et al.) and gives 25.2 GPa by nanoindentation for pure sintered ZrC (Table 5).", "benchmark": "hardness", "scope": "material" }, { "label": "Melting", "line": "Table 1 gives 3532 degC. The review text gives 3427 degC for the same melting point.", "benchmark": "melting_point", "scope": "material", "value": "3532 degC" }, { "label": "Heat conduction", "line": "Room temperature conductivity is 17.5 to 31.5 W/m·K (Table 1). It rises to 27.5 to 37.5 W/m·K at 1500 degC (review text).", "benchmark": "thermal_conductivity", "scope": "material", "value": "17.5 to 31.5 W/m·K" } ], "compare": "Against carbon-carbon composites, Table 1 of the review puts the melting point of ZrC (3532 degC) close to that of C/C composites, with a density of 6.73 g/cm3 against 1.3 to 2.5, and a room temperature elastic modulus of 435 GPa against 43 to 240. Its room temperature flexure strength is 460 MPa against 140 MPa for C/C. ZrC is much denser than C/C, and it stays chemically stable to about 600 degC, where C/C composites oxidize above 500 degC.", "compare_rows": [ { "label": "Density", "benchmark": "density", "scope": "material" }, { "label": "Hardness", "benchmark": "hardness", "scope": "material" }, { "label": "Thermal conductivity", "benchmark": "thermal_conductivity", "scope": "material" } ], "handling": [ "Powder: PubChem lists H228 (flammable solid) and H302, H312 and H332. Keep it away from heat and ignition sources, and control dust.", "Storage: the Hoganas datasheet says to store in a closed container, and that the product is under export control.", "Oxidation: above about 600 degC in air, ZrC needs a protective coating (review, Sections 2.3.1 and 3.3.2)." ], "good_for": [ "Hard, stiff parts. The review gives 435 GPa elastic modulus at room temperature (Table 1).", "Hot parts where a very high melting point matters, with a protective coating (review, Section 3.3.2).", "Ceramic liners on carbon-carbon nozzle structures (NASA Tech Briefs, 2011)." ], "watch_out": [ "Oxidation: ZrC is stable in air only to about 600 degC. An oxide layer about 0.25 cm thick formed in 30 minutes at 1000 degC (review).", "Sources disagree: melting point 3532 degC in Table 1 against 3427 degC in the text, and thermal conductivity 17.5 to 31.5 W/m·K in Table 1 against about 20 in the text and 20 to 40 across published measurements (arXiv).", "Brittleness: the review says ZrC fractures with little plastic deformation, and no fracture toughness value for pure ZrC was found.", "Properties depend on the carbon-to-zirconium ratio and porosity, so reported values vary between studies." ], "verdict": "Zirconium carbide is a hard, stiff ceramic with a very high melting point, and it has a sourced role as a candidate for hypersonic leading edges and for coatings in nuclear thermal propulsion. Its limits are oxidation above about 600 degC in air, brittleness and difficult sintering. The space-related uses are proposals or ground tests, and no flight record was found.", "recipe": { "line": "ZrC has one zirconium atom and one carbon atom per formula unit in a rock-salt (FCC) structure. The review gives a stable carbon range of 36 to 50 at percent carbon. Hoganas sells the powder as grades A, B and AX, and grade A has at least 87.8 percent Zr plus Hf and at least 11.4 percent total carbon. The review says ZrC is hard to sinter: it has low self-diffusion and grows grains quickly, so dense parts need spark plasma sintering at 2100 degC and 65 MPa unless a sintering aid is used.", "parts": [ { "name": "Zirconium", "symbol": "Zr", "role": "Metal atom in the rock-salt lattice. Its metallic and covalent bonds with carbon give ZrC its high melting point and hardness." }, { "name": "Carbon", "symbol": "C", "role": "Non-metal atom in the lattice. Carbon vacancies from non-stoichiometry change the thermal and mechanical properties." } ] }, "risk_groups": [ { "title": "For people", "lead": "PubChem's aggregated company reports give H228 (flammable solid) for 99.1 percent of reports, and the harmful-category codes H302, H312 and H332 for 18 percent.", "points": [ { "label": "Dust", "line": "The PubChem hazards summary, citing Hawley, says the powder or dust may spontaneously ignite. The Hoganas datasheet lists no hazard." }, { "label": "Ingestion and skin", "line": "H302 (harmful if swallowed) and H312 (harmful in contact with skin) appear in 18 percent of the reports that gave hazard codes." } ], "level": 0, "verdict": "Flammable solid, and harmful by three routes (PubChem)" }, { "title": "If a part fails", "lead": "These numbers come from the review, which uses a mix of room temperature and high temperature tests.", "points": [ { "label": "Brittleness", "line": "The review says ZrC fractures in a brittle way with little plastic deformation, so defects set the strength." }, { "label": "Oxidation", "line": "An oxide layer about 0.25 cm thick formed in 30 minutes at 1000 degC in air, according to the review (Gasparrini et al.)." } ] } ] }, "updated": "2026-10-26", "review": { "status": "draft", "method": "assistant", "checked_values": 25, "unreachable": 2, "caveats": 4, "note": "Written in this run from the 2023 Materials review (Europe PMC full text), the Hoganas PD-4004 datasheet, PubChem (GHS, uses, density), the NASA patent (Table 1 CTE), the NASA Tech Briefs 2011 article, USGS MCS 2026 zirconium chapter, and two arXiv papers. The MDPI and RSC pages and the ORNL 2025 news page were not readable." }, "sources": { "zrc-review-2023": { "title": "Peterson GR, Carr RE, Marinero EE, Mortalo C, Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges, Materials 16(18), 6158 (2023), doi 10.3390/ma16186158", "url": "https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10532790/fullTextXML", "kind": "paper", "license": "CC BY (per the PMC licence reference)" }, "pubchem-zrc": { "title": "PubChem compound CID 11159298, Zirconium carbide (GHS classification, uses, experimental density, CAS 12070-14-3)", "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/11159298/JSON", "kind": "database", "license": "PubChem public database" }, "hoganas-pd4004": { "title": "Hoganas, Zirconium Carbide Grade A, Grade B, Grade AX, datasheet PD-4004 (issue 6, 07.04.2017)", "url": "https://www.hoganas.com/globalassets/downloads/stc/PD-4004.pdf", "kind": "datasheet", "license": "vendor datasheet, cited not reproduced" }, "nasa-patent-zrc": { "title": "Raj et al., US Patent 10,068,675 B1, Advanced Protective Coatings for Graphite-Based Nuclear Propulsion Fuel Elements (NASA, 2018), NTRS 20180006260", "url": "https://ntrs.nasa.gov/api/citations/20180006260/downloads/20180006260.pdf", "kind": "report", "license": "US government patent, public domain" }, "ntrs-ultramet-2011": { "title": "NASA Tech Briefs, February 2011, Ultramet carbon-carbon structure with ZrC or Zr-Si-C CMC liner (LEW-18618-1), NTRS 20110012228", "url": "https://ntrs.nasa.gov/citations/20110012228", "kind": "report", "license": "US government work, public domain" }, "usgs-mcs2026-zirconium-hafnium": { "title": "USGS Mineral Commodity Summaries 2026, Zirconium and Hafnium", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zirconium-hafnium.pdf", "kind": "report", "license": "US government work, public domain" }, "arxiv-tc-zrc": { "title": "Tiwari J, Feng T, Intrinsic thermal conductivity of ZrC from low to ultra-high temperatures: A critical revisit, arXiv:2304.06805 (2023)", "url": "https://arxiv.org/pdf/2304.06805", "kind": "paper", "license": "arXiv preprint" }, "arxiv-ox-zrc": { "title": "arXiv:2402.04337, influence of nitrogen on the oxidation of hot-pressed zirconium carbide in a flow-tube furnace, 1000 to 1600 C", "url": "https://arxiv.org/pdf/2402.04337", "kind": "paper", "license": "arXiv preprint" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/zirconium-carbide/" }