{ "spore": "profile", "id": "zinc-oxide", "spore_version": "0.2", "family": "oxide-ceramics", "name": "Zinc oxide", "abbreviation": "ZnO", "role": "wide-bandgap oxide for thermal-control coatings, varistors and transparent conductors", "category": "ceramics", "type": "oxides", "summary": "Zinc oxide (ZnO) is a white oxide that crystallizes in the hexagonal wurtzite structure. Its melting point is 1975 °C, and a review of its physical constants gives a density of 5.67 g/cm3 and a band gap of 3.37 eV at 300 K. In space it is used as a pigment in a potassium silicate binder, sold as Z-93. NASA flew that white coating on the ISS and on LDEF, and its solar absorptance stayed near 0.14 to 0.15 after years in orbit, unless silicone contamination was present. Ceramic zinc oxide is also the base of metal-oxide varistors for surge protection, with typical breakdown fields of 2 to 5 kV/cm. Aluminium-doped (AZO) and gallium-doped (GZO) zinc oxide films are transparent conductors: a 2004 sputtered AZO film reached 0.00037 ohm cm with more than 85% visible transmission, and a 2023 sputtered GZO film reached 29 ohm per square at 94% transmission.\n", "best_for": "Low-absorptance white thermal-control coating on spacecraft, where flight data show little change in solar absorptance over years when contamination is kept low", "weakest_at": "Silicone contamination, which raised the solar absorptance of a Z-93P coating from 0.16 to 0.23 in one flight test (POSA-I)", "identity": { "formula": "ZnO", "cas": "1314-13-2", "crystal_system": "hexagonal", "space_group": "P63mc", "designations": [], "source": "arxiv-zno-2011", "where": "Introduction, paragraph on the wurtzite structure (hexagonal cell, space group P63mc); CAS number printed in Section 1.1 of the U.S. Zinc SDS (sds-usz-zno)" }, "tags": { "environments": [ "low-earth-orbit" ], "stresses": [ "atomic-oxygen", "uv" ], "applications": [ "thermal-control", "electronics-and-chips" ] }, "properties": [ { "benchmark": "density", "label": "Density, wurtzite ZnO (review value)", "value": 5.67, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "crystal": "wurtzite", "temperature": "not stated in the review" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "melting_point", "label": "Melting point (review value)", "value": 1975, "bound": "exact", "unit": "°C", "scope": "material", "conditions": { "crystal": "wurtzite" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "melting_point", "label": "Melting point, U.S. Zinc SDS (zinc oxide, all grades)", "value": 1975, "bound": "exact", "unit": "°C", "scope": "material", "conditions": { "grade": "all product grades, as stated in the SDS" }, "method": "Value printed in a supplier safety data sheet", "status": "ground", "source": "sds-usz-zno", "where": "Section 9 (Physical and Chemical Properties), Melting point row", "source_detail": { "title": "U.S. Zinc safety data sheet: Zinc Oxide, all product grades (Rev. 1.2, 2026)", "id": "CAS 1314-13-2; document USZ_ZincOxideSDS_GLOBAL_Rev8", "url": "https://sds.chemicalstore.com/uszincoxide.pdf", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "vapor_pressure", "label": "Vapour pressure of zinc oxide", "value": 12, "bound": "exact", "unit": "mm Hg", "scope": "material", "conditions": { "temperature": "1500 °C" }, "method": "Value printed in a supplier safety data sheet", "status": "ground", "source": "sds-usz-zno", "where": "Section 9 (Physical and Chemical Properties), Vapor Pressure row", "source_detail": { "title": "U.S. Zinc safety data sheet: Zinc Oxide, all product grades (Rev. 1.2, 2026)", "id": "CAS 1314-13-2; document USZ_ZincOxideSDS_GLOBAL_Rev8", "url": "https://sds.chemicalstore.com/uszincoxide.pdf", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, { "benchmark": "thermal_conductivity", "label": "Thermal conductivity, wurtzite ZnO at room temperature", "value": 50, "bound": "exact", "unit": "W/mK", "scope": "material", "conditions": { "crystal": "wurtzite, single crystal (first-principles lattice dynamics)", "temperature": "room temperature" }, "method": "Calculated in the paper by first-principles lattice dynamics; the abstract gives the value and compares it with 400 W/mK for wurtzite GaN", "status": "calculated", "note": "A calculated value, not a measurement. The paper says earlier literature values for ZnO disagree widely.", "source": "srep-zno-2016", "where": "Abstract (comparison with wurtzite GaN); main text, thermal conductivity results", "source_detail": { "title": "Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics: a Comparative Study with Gallium Nitride (Scientific Reports)", "id": "Sci Rep, published 1 March 2016 (srep22504)", "url": "https://www.nature.com/articles/srep22504", "year": 2016, "kind": "paper", "license": "open access (cited, not reproduced)" } }, { "benchmark": "band_gap", "label": "Band gap, ZnO at 300 K", "value": 3.37, "bound": "exact", "unit": "eV", "scope": "material", "conditions": { "temperature": "300 K" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "note": "The same review gives 3.437 eV at 1.6 K.", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "exciton_binding_energy", "label": "Exciton binding energy, ZnO", "value": 60, "bound": "exact", "unit": "meV", "scope": "material", "conditions": { "crystal": "wurtzite" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "dielectric_constant", "label": "Low-frequency dielectric constant, parallel to c axis", "value": 8.75, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "direction": "parallel to the c axis (printed as ||)", "frequency": "low frequency" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "dielectric_constant", "label": "Low-frequency dielectric constant, perpendicular to c axis", "value": 7.8, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "direction": "perpendicular to the c axis (printed as perpendicular sign)", "frequency": "low frequency" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "dielectric_constant", "label": "High-frequency dielectric constant, parallel to c axis", "value": 3.75, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "direction": "parallel to the c axis (printed as ||)", "frequency": "high frequency" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "lattice_constant_a", "label": "Lattice constant a, wurtzite ZnO", "value": 3.25, "bound": "exact", "unit": "Å", "scope": "material", "conditions": { "crystal": "wurtzite, hexagonal cell" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "lattice_constant_c", "label": "Lattice constant c, wurtzite ZnO", "value": 5.207, "bound": "exact", "unit": "Å", "scope": "material", "conditions": { "crystal": "wurtzite, hexagonal cell" }, "method": "Value stated in an optical-properties review of ZnO", "status": "ground", "source": "arxiv-zno-2011", "where": "Introduction, paragraph beginning \"Other characteristics of ZnO\"", "source_detail": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, Z-93 zinc oxide coating, LDEF control and exposed samples", "value": 0.14, "value_high": 0.15, "bound": "range", "unit": "-", "scope": "material", "conditions": { "coating": "Z-93, zinc oxide pigment in potassium silicate binder (a coating, not bare ZnO)", "exposure": "LDEF, about 5.8 years in space, sample S0069 (pre-flight 0.14, post-flight 0.15)", "contamination": "minimal (300 Å or less, per the report)" }, "method": "Value printed in the text of a NASA MISSE thermal-control review", "status": "flight", "note": "The report states that the Z-93 family showed very little change in solar absorptance and no change in infrared emittance after 5.8 years in space.", "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), text on the LDEF samples", "source_detail": { "title": "MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (NASA Marshall Space Flight Center; Boeing Phantom Works)", "id": "NTRS 20080031037", "url": "https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf", "year": 2008, "kind": "report", "license": "public domain (NASA)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, Z-93 on MISSE-2, MISSE-3 and MISSE-4, post-flight", "value": 0.14, "value_high": 0.15, "bound": "range", "unit": "-", "scope": "material", "conditions": { "coating": "Z-93 on aluminium, 5 mil layer (the report says normally applied to aluminium at 5 mils)", "exposure": "ISS MISSE-2, MISSE-3 and MISSE-4, 1 to 4 years, UV 1,200 to 5,660 ESH", "pre_flight": 0.14 }, "method": "Pre- and post-flight solar absorptance printed in Table 1", "status": "flight", "source": "nasa-misse-2008", "where": "Table 1 (Alion Zinc Oxide/Potassium Silicate Coatings), Z-93 rows", "source_detail": { "title": "MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (NASA Marshall Space Flight Center; Boeing Phantom Works)", "id": "NTRS 20080031037", "url": "https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf", "year": 2008, "kind": "report", "license": "public domain (NASA)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, Z-93P after silicone contamination (POSA-I)", "value": 0.23, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "coating": "Z-93P, zinc oxide pigment in potassium silicate binder with the Kasil 2130 binder", "contamination": "about 5,000 Å of silicone on the space-facing side", "uv": "571 ESH", "pre_flight": 0.16 }, "method": "Post-flight solar absorptance printed in the report text for the POSA-I sample", "status": "flight", "note": "The increase is a contamination effect; the same report says that with 300 Å or less of contamination, Z-93 keeps its beginning-of-life absorptance.", "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), text on Z-93P from POSA-I; Figure 3", "source_detail": { "title": "MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (NASA Marshall Space Flight Center; Boeing Phantom Works)", "id": "NTRS 20080031037", "url": "https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf", "year": 2008, "kind": "report", "license": "public domain (NASA)" } }, { "benchmark": "optical_transmittance", "label": "Average visible transmission, Al-doped ZnO film (AZO)", "value": 85, "bound": "lower", "unit": "%", "scope": "material", "conditions": { "range": "visible, 300 to 800 nm", "film": "the same optimized AZO film" }, "method": "Value printed in the abstract of a 2004 sputtering study", "status": "ground", "source": "stdj-azo-2004", "where": "Abstract", "source_detail": { "title": "Studying and making transparent conducting ZnO:Al thin films by magnetron DC sputtering (Le Tran, Nguyen Huu Chi, Tran Tuan, Ho Van Binh; VNUHCM Journal of Science and Technology Development, Vol. 7 No. 6)", "id": "doi:10.32508/stdj.v7i6.3212", "url": "https://stdj.scienceandtechnology.com.vn/index.php/stdj/article/view/3212", "year": 2004, "kind": "paper", "license": "open access (cited, not reproduced)" } }, { "benchmark": "sheet_resistance", "label": "Sheet resistance, Ga-doped ZnO film (GZO), after post-annealing at 450 °C", "value": 29, "bound": "exact", "unit": "Ω/square", "scope": "material", "conditions": { "dopant": "gallium", "film_thickness": "100 nm", "deposition": "RF sputtering, then post-annealing under nitrogen and hydrogen forming gas", "anneal_temperature": "450 °C" }, "method": "Value printed in the abstract of a 2023 study on ZnO:Ga films", "status": "ground", "note": "Sheet resistance, not resistivity. The paper compares it with commercial indium tin oxide.", "source": "mdpi-gzo-2023", "where": "Abstract", "source_detail": { "title": "Effects of Post-Annealing on the Properties of ZnO:Ga Films with High Transparency (94%) and Low Sheet Resistance (29 Ω/square) (Li-Wen Wang et al.; Materials)", "id": "PMID 37834601; PMC10573347", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10573347/", "year": 2023, "kind": "paper", "license": "open access (cited, not reproduced)" } }, { "benchmark": "optical_transmittance", "label": "Transparency, Ga-doped ZnO film (GZO), after post-annealing at 450 °C", "value": 94, "bound": "lower", "unit": "%", "scope": "material", "conditions": { "film_thickness": "100 nm", "anneal_temperature": "450 °C" }, "method": "Value printed in the abstract of a 2023 study on ZnO:Ga films", "status": "ground", "source": "mdpi-gzo-2023", "where": "Abstract", "source_detail": { "title": "Effects of Post-Annealing on the Properties of ZnO:Ga Films with High Transparency (94%) and Low Sheet Resistance (29 Ω/square) (Li-Wen Wang et al.; Materials)", "id": "PMID 37834601; PMC10573347", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10573347/", "year": 2023, "kind": "paper", "license": "open access (cited, not reproduced)" } }, { "benchmark": "breakdown_field", "label": "Typical varistor breakdown field, ZnO-based metal-oxide varistors", "value": 2, "value_high": 5, "bound": "range", "unit": "kV/cm", "scope": "material", "conditions": { "material": "ZnO-based metal-oxide varistor ceramics, breakdown voltage at 1 mA", "basis": "typical range stated in the review" }, "method": "Range stated in an open-access review of ZnO-V2O5 varistors (the review cites earlier work for it)", "status": "ground", "source": "mdpi-varistor-2023", "where": "Section 1.1 (Specific Features of ZnO-Based Varistors), voltage rating paragraph", "source_detail": { "title": "Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review (Materials)", "id": "doi:10.3390/ma16103725; PMC10221863", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10221863/", "year": 2023, "kind": "paper", "license": "open access (cited, not reproduced)" } }, { "benchmark": "nonlinear_coefficient", "label": "Nonlinearity coefficient, doped ZnO varistor example", "value": 50, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "composition": "ZnO with 0.5% Bi2O3, 1% Sb2O3, 0.5% CoO, 0.5% MnO2 and 0.5% Cr2O3 (as printed in the review)", "sintering": "1350 °C", "breakdown_field": "1.35 kV/cm (as printed in the review)" }, "method": "Value quoted in an open-access review, which cites the study it describes", "status": "ground", "note": "One multi-oxide example from the review, not a typical value for all varistors.", "source": "mdpi-varistor-2023", "where": "Section 1.2 (Brief History of ZnO-Based Varistors), example of the best nonlinearity", "source_detail": { "title": "Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review (Materials)", "id": "doi:10.3390/ma16103725; PMC10221863", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10221863/", "year": 2023, "kind": "paper", "license": "open access (cited, not reproduced)" } } ], "corrosion": [ { "environment": "Atomic oxygen and ultraviolet in low Earth orbit (Z-93 coating on LDEF and ISS)", "headline": "Z-93 kept its solar absorptance through years of exposure, because atomic oxygen can reverse the darkening that ultraviolet causes on oxides.", "effect": "On LDEF, Z-93 and related zinc oxide coatings showed very little change in solar absorptance and no change in infrared emittance after 5.8 years. On MISSE-2, -3 and -4, Z-93 went from 0.14 to 0.14 or 0.15. The report says that atomic oxygen may reverse the ultraviolet darkening of oxides, while it erodes polymer binders.", "rating": "low", "conditions": { "exposure": "LDEF about 5.8 years; MISSE-2 to MISSE-4 on the ISS, up to about 5,660 ESH of UV (as printed in Table 1)", "contamination": "minimal, 300 Å or less" }, "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), text and Table 1" }, { "environment": "Silicone contamination with ultraviolet in orbit (Z-93P on POSA-I)", "headline": "Silicone deposits turned the zinc oxide coating yellow or tan and raised its solar absorptance.", "effect": "Z-93P on the space-facing side of POSA-I got about 5,000 Å of silicone contamination and 571 ESH of UV, and its solar absorptance rose from 0.16 to 0.23. The report says the contaminated inorganic white coatings became yellowed or tan, and that ground tests of contaminated zinc oxide gave much higher absorptance with more UV.", "rating": "moderate", "conditions": { "contamination": "about 5,000 Å silicone", "uv": "571 ESH" }, "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), text on POSA-I and Figure 3" }, { "environment": "Acids and bases (chemical attack)", "headline": "The supplier SDS lists acids and bases as suitable solvents for zinc oxide, and gives no rate of attack.", "effect": "The SDS states that zinc oxide is insoluble in water in practice (solubility negligible) and lists acids and bases as suggested solvents. It gives no corrosion rate, so the rate of attack in a given acid or base is not known from this source.", "rating": "unknown", "conditions": { "form": "zinc oxide powder, all grades (as stated in the SDS)" }, "source": "sds-usz-zno", "where": "Section 9 (Physical and Chemical Properties), Solubility in water and Suggested Solvents rows" } ], "risks": { "hazards": [ { "text": "The U.S. Zinc SDS classifies zinc oxide as Aquatic Chronic 1 with H410 (very toxic to aquatic life with long lasting effects) and the signal word Warning, with P273, P391 and P501. PubChem's record for CID 14806 reports it as not classified, based on one company report.", "ghs": [ "H410" ], "source": "sds-usz-zno", "where": "Section 2 (Hazards Identification), GHS Classification and Labeling" }, { "text": "PubChem's GHS summary for CID 14806 reports that zinc oxide does not meet GHS hazard criteria, from 1 of 1 company reports, so the classification differs between sources.", "ghs": [], "source": "pubchem-zno", "where": "Safety and Hazards, GHS Classification" }, { "text": "At high temperatures the SDS lists zinc oxide fumes as a decomposition product in a fire, and it lists heated magnesium and chlorinated rubbers above 215 °C as incompatible.", "ghs": [], "source": "sds-usz-zno", "where": "Section 5.2 (Special hazards) and Section 10 (Conditions to avoid)" } ], "failure_risks": [ { "mode": "Trade-off between breakdown field and nonlinearity in varistors", "trigger": "Raising the breakdown voltage of a ZnO varistor by design or processing", "consequence": "The review says that an increase in breakdown field can decrease nonlinearity and increase the leakage currents, so a higher-voltage varistor clamps less sharply.", "severity": "moderate", "source": "mdpi-varistor-2023", "where": "Section 1.1 (Specific Features of ZnO-Based Varistors), text on E_B and nonlinearity" }, { "mode": "Darkening and absorptance rise from contamination", "trigger": "Silicone or other molecular contamination on a Z-93 type coating, with ultraviolet exposure", "consequence": "Solar absorptance rose from 0.16 to 0.23 on a contaminated Z-93P sample. Heavier contamination turns the coating yellow or tan, which raises the temperature of the spacecraft surface.", "severity": "moderate", "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), text on POSA-I" } ], "side_effects": [], "handling": [ { "text": "Avoid creating airborne dust. Use adequate exhaust ventilation, gloves and eye protection when dust may form. The SDS says to wash hands and forearms after handling.", "source": "sds-usz-zno", "where": "Section 7.1 (Precautions for Safe Handling); Section 8.2 (Exposure Controls)" }, { "text": "Clean up spills without dry sweeping. Vacuum or wet-sweep the powder into a closable, labelled container, and keep waste out of drains and surface water.", "source": "sds-usz-zno", "where": "Section 6.3 (Spill Cleanup Recommendation); Section 6.2 (Environmental Precautions)" }, { "text": "Store in a cool, dry, well-ventilated space, sealed in the original container, and use the product within 1 year.", "source": "sds-usz-zno", "where": "Section 7.2 (Conditions for Safe Storage)" } ], "mitigations": [ { "text": "Keep the exposure to the OSHA permissible exposure limit: 5 mg/m3 for fumes and 15 mg/m3 total dust (5 mg/m3 respirable dust), 8-hour TWA. The NIOSH IDLH is 500 mg/m3.", "source": "sds-usz-zno", "where": "Section 8.1 (Control Parameters)" }, { "text": "Keep contamination of the coating at 300 Å or less, which the report says keeps Z-93 close to its beginning-of-life absorptance. The report says this needs materials selection, venting design and other contamination controls.", "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), text on contamination levels" } ] }, "uses": [ { "application": "thermal-control", "device": "Z-93 white thermal-control coating on spacecraft radiators (ISS)", "example": "NASA's MISSE report says the inorganic zinc oxide white coating was selected for use on the ISS radiators, based on its performance on LDEF.", "source": "nasa-misse-2008", "where": "Section A (Zinc Oxide/Potassium Silicate), first paragraph" }, { "application": "thermal-control", "device": "Z-93 coating on ISS experiments (MISSE-2 to MISSE-4)", "example": "Z-93 flown on MISSE-2, MISSE-3 and MISSE-4 kept its solar absorptance at 0.14 pre-flight and 0.14 to 0.15 post-flight, for UV exposure up to about 5,660 ESH.", "source": "nasa-misse-2008", "where": "Table 1 (Alion Zinc Oxide/Potassium Silicate Coatings)" }, { "application": "electronics-and-chips", "device": "Metal-oxide varistors for surge arresters and surge protection", "example": "A 2023 review of ZnO-V2O5 varistors gives typical breakdown fields of 2 to 5 kV/cm for ZnO varistors, and says that 1000 kV surge arresters need a breakdown field above 4 kV/cm.", "source": "mdpi-varistor-2023", "where": "Section 1.1 (Specific Features of ZnO-Based Varistors), text on ZnO systems for 1000 kV surge arresters" }, { "application": "electronics-and-chips", "device": "Transparent conducting films, Al-doped (AZO) and Ga-doped (GZO) zinc oxide", "example": "A 2004 sputtered AZO film reached 0.00037 ohm cm with more than 85% visible transmission. A 2023 RF-sputtered GZO film, annealed at 450 °C, reached 94% transparency and 29 ohm per square at 100 nm thickness, which the authors compare with commercial indium tin oxide.", "source": "stdj-azo-2004", "where": "Abstract (AZO); mdpi-gzo-2023 Abstract (GZO)" } ], "supply": [ { "subject": "Zinc (feedstock for zinc oxide)", "producers": [ { "country": "China", "share_percent": 31.5, "year": 2025 }, { "country": "Peru", "share_percent": 11.5, "year": 2025 }, { "country": "Australia", "share_percent": 8.5, "year": 2025 }, { "country": "India", "share_percent": 6.7, "year": 2025 }, { "country": "Mexico", "share_percent": 6, "year": 2025 }, { "country": "United States", "share_percent": 5.2, "year": 2025 } ], "critical_lists": [ { "list": "USGS 2025 List of Critical Minerals (zinc is on the final list)", "listed": true } ], "recycling": "USGS zinc chapter: refined zinc is recovered from secondary materials, including galvanizing residues and crude zinc oxide recovered from electric arc furnace dust.", "substitutes": [ "USGS zinc chapter: many elements are substitutes for zinc in chemical, electronic and pigment uses; the chapter does not name a substitute for zinc oxide." ], "source": "usgs-mcs2026-zinc", "where": "World Mine Production and Reserves table, mine production 2025e (world total 13,000 thousand t zinc content, rounded; shares calculated by Space Mushroom against that total, excluding the other countries); Recycling; Substitutes. Zinc is the feedstock, not zinc oxide itself: the USGS does not give a zinc oxide production table. The critical-list entry is confirmed on the USGS 2025 list page (usgs-crit2025)." } ], "media": [], "documents": [ { "title": "U.S. Zinc safety data sheet: Zinc Oxide (CAS 1314-13-2, Rev. 1.2, 2026; effective 16 July 2015)", "type": "sds", "url": "https://sds.chemicalstore.com/uszincoxide.pdf", "year": 2026 }, { "title": "PubChem: Zinc oxide (CID 14806), GHS classification and properties", "type": "database", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14806", "year": 2026 }, { "title": "Optical and Luminescence Properties of Zinc Oxide (Rodnyi and Khodyuk, arXiv 1203.4366; published in Optics and Spectroscopy 2011)", "type": "paper", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011 }, { "title": "Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics (Scientific Reports, 2016)", "type": "paper", "url": "https://www.nature.com/articles/srep22504", "year": 2016 }, { "title": "MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (Finckenor, Pippin, Frey; NASA MSFC; NTRS 20080031037)", "type": "report", "url": "https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf", "year": 2008 }, { "title": "Studying and making transparent conducting ZnO:Al thin films by magnetron DC sputtering (VNUHCM Journal of Science and Technology Development, 2004)", "type": "paper", "url": "https://stdj.scienceandtechnology.com.vn/index.php/stdj/article/view/3212", "year": 2004 }, { "title": "Effects of Post-Annealing on the Properties of ZnO:Ga Films with High Transparency (94%) and Low Sheet Resistance (29 Ω/square) (Materials, 2023; PMC10573347)", "type": "paper", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10573347/", "year": 2023 }, { "title": "Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review (Materials, 2023; PMC10221863)", "type": "paper", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10221863/", "year": 2023 }, { "title": "USGS Mineral Commodity Summaries 2026: Zinc", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf", "year": 2026 } ], "gaps": [ "The AZO resistivity (0.00037 ohm cm, 2004 sputtering study) is printed with a decimal comma and a superscript exponent, so the value check cannot match it. It is kept out of the properties and stated only in the text, until it is checked by hand against the abstract.", "No thermal expansion coefficient for bulk ZnO was found in a source read in this run.", "Atomic weights for zinc and oxygen were not read in a source opened for this profile, so the recipe parts carry no atomic_weight.", "No zinc oxide production table by country was found; the USGS zinc chapter gives zinc metal mine production, and the producer shares above are for zinc, not zinc oxide.", "Crustal abundance of zinc was not read in a source opened for this profile.", "The EU critical raw materials list was not read for zinc, so it is marked not listed here only because it was not checked; this entry should be confirmed.", "No sensor source was read, so the sensing use named in the brief is not included.", "Z-93 is a zinc oxide pigment in a potassium silicate binder. Its absorptance values describe that coating, not pure ZnO, and they are kept with scope material and a coating condition.", "The thermal conductivity of 50 W/mK is a calculated value from the Scientific Reports paper. No measured bulk value from a source read in this run was found.", "Carrier concentration, mobility and the gallium content of the GZO film were not read in a source opened for this profile.", "A vacuum outgassing (TML or CVCM) result for ZnO or Z-93 was not found in a source read in this run.", "Band gap and lattice constants are from one optical-properties review; density-functional theory values were not used.", "Hazard data rest on one supplier SDS and the PubChem summary; other supplier SDSs, including one with a different H-statement list, were not read for this profile.", "The varistor breakdown range and nonlinearity example come from a review that cites earlier work; the original studies were not read." ], "story": { "why": "Zinc oxide is a white, inexpensive oxide with a wide band gap of 3.37 eV at 300 K. Its wurtzite structure and its chemistry give it three uses in this collection: a space-proven white thermal-control coating (Z-93, a zinc oxide pigment in a potassium silicate binder), a ceramic base for surge-protection varistors, and a transparent conductor when it is doped with aluminium or gallium. The flight data are the strongest part of the record: a coating that kept its solar absorptance through years of ultraviolet and atomic oxygen exposure, as long as silicone contamination was kept out.", "uses": [ { "where": "Thermal-control coatings in orbit", "line": "NASA chose the zinc oxide white coating Z-93 for the ISS radiators after its performance on LDEF. On MISSE-2 to MISSE-4 it kept a solar absorptance of 0.14 before flight and 0.14 to 0.15 after exposure." }, { "where": "Surge-protection varistors", "line": "ZnO varistors have a typical breakdown field of 2 to 5 kV/cm, according to a 2023 review, which also says that 1000 kV surge arresters need more than 4 kV/cm." }, { "where": "Transparent conductors", "line": "Al-doped ZnO (AZO) films sputtered in 2004 reached 0.00037 ohm cm with more than 85% visible transmission. Ga-doped ZnO (GZO) films annealed at 450 °C in 2023 reached 94% transparency and 29 ohm per square at 100 nm." } ], "can_do": [ { "label": "Thermal control", "line": "Z-93 kept a solar absorptance of 0.14 to 0.15 in flight on LDEF and MISSE, with little change in infrared emittance after 5.8 years on LDEF.", "scope": "material", "value": "Solar absorptance 0.14 to 0.15" }, { "label": "Surge protection", "line": "A ZnO varistor with a typical breakdown field of 2 to 5 kV/cm clamps overvoltages, and one multi-oxide example in the review reached a nonlinearity coefficient of 50.", "scope": "material", "value": "2 to 5 kV/cm breakdown field" }, { "label": "Transparent conduction", "line": "A 100 nm GZO film annealed at 450 °C reached 29 ohm per square and 94% transparency. The 2004 AZO film reached 0.00037 ohm cm.", "scope": "material", "value": "29 ohm per square at 94%" }, { "label": "Heat conduction", "line": "A first-principles calculation gives about 50 W/mK for wurtzite ZnO at room temperature, against 400 W/mK for wurtzite GaN.", "scope": "material", "value": "50 W/mK (calculated)" } ], "compare": "The thermal-control coating and the transparent-conductor films use zinc oxide in different forms, so their numbers are not directly comparable. Compared with wurtzite gallium nitride, the calculated thermal conductivity of ZnO is about one-eighth. Its melting point of 1975 °C is high, but the coating and varistor data show that its real limits are contamination and the trade-off between breakdown field and nonlinearity. The table gives ZnO's melting point, thermal conductivity and density.", "compare_rows": [ { "label": "Melting point", "benchmark": "melting_point", "scope": "material" }, { "label": "Heat conduction", "benchmark": "thermal_conductivity", "scope": "material" }, { "label": "Density", "benchmark": "density", "scope": "material" } ], "handling": [ "Avoid creating dust. Use exhaust ventilation and gloves, and keep to the OSHA limit of 5 mg/m3 for fumes.", "Clean up spills by vacuum or wet sweeping, and keep the powder out of drains.", "Store cool, dry and sealed, and use within 1 year." ], "good_for": [ "Low-absorptance white coatings in orbit. Z-93 kept a solar absorptance of 0.14 to 0.15 in flight when contamination was kept low.", "Surge protection. Varistors made from ZnO have a typical breakdown field of 2 to 5 kV/cm.", "Low-cost transparent conductors. Doped films reach 29 ohm per square at 94% transparency (GZO) or 0.00037 ohm cm (AZO)." ], "watch_out": [ "Silicone contamination. A contaminated Z-93P sample rose from 0.16 to 0.23 in solar absorptance.", "The H410 aquatic hazard, and the dust and fume limits in the SDS.", "Calculated versus measured data. The thermal conductivity is calculated, and the AZO and GZO values come from single laboratory films." ], "verdict": "Zinc oxide is a proven low-absorptance white coating in orbit, as long as contamination is controlled, and a useful base for varistors and cheap transparent conductors once doped. Its weak points are the contamination and the coating-versus-bulk gap, and the flight record is for a coating, not a bulk part.", "recipe": { "line": "ZnO combines one zinc atom with one oxygen atom. Pure zinc oxide crystallizes in the hexagonal wurtzite structure, in which each zinc atom is surrounded by four oxygen atoms at the corners of a nearly regular tetrahedron. For transparent conductors the oxide is doped with small amounts of aluminium or gallium, which provide extra electrons.", "parts": [ { "name": "Zinc", "symbol": "Zn", "role": "The metal cation. Each zinc ion sits in a tetrahedron of four oxygen anions in the wurtzite structure." }, { "name": "Oxygen", "symbol": "O", "role": "The anion. Each oxygen sits at a corner of the tetrahedron around one zinc ion." }, { "name": "Aluminium (dopant, AZO)", "symbol": "Al", "role": "A dopant added to make the film conductive. The 2004 study used a sputtering powder target of ZnO with 2 wt% Al2O3." }, { "name": "Gallium (dopant, GZO)", "symbol": "Ga", "role": "A dopant in sputtered GZO films. The Ga content of the 2023 film was not read in this run." } ] }, "risk_groups": [ { "title": "For people", "lead": "The supplier SDS classifies zinc oxide as hazardous only to aquatic life, but it gives exposure limits for dust and fume. PubChem's record of one company report says it is not classified.", "points": [ { "label": "The powder", "line": "The U.S. Zinc SDS gives the signal word Warning and the H410 statement for aquatic life. It gives no skin or eye hazard statement." }, { "label": "Dust and fume", "line": "The OSHA permissible exposure limit is 5 mg/m3 for fumes and 15 mg/m3 for total dust. Fumes can form from a hot fire." }, { "label": "Aquatic life", "line": "Keep the powder out of drains and surface water." } ], "level": 1, "verdict": "Dust and fumes; aquatic H410" }, { "title": "If the coating is contaminated", "lead": "These results come from flight and ground tests of the coating, not from incidents on the spacecraft.", "points": [ { "label": "Contamination", "line": "Silicone contamination of about 5,000 Å raised the solar absorptance of a Z-93P sample from 0.16 to 0.23 after 571 ESH of UV on POSA-I." }, { "label": "Clean coatings", "line": "With 300 Å or less of contamination, Z-93 kept its solar absorptance close to its starting value on LDEF and MISSE." }, { "label": "Varistors", "line": "In a varistor, a higher breakdown field can reduce nonlinearity and raise leakage current, according to the review." } ] }, { "title": "Handling and storage", "points": [ { "label": "Dust", "line": "Avoid creating dust. Use exhaust ventilation and gloves, and clean up spills with a vacuum or by wet sweeping." }, { "label": "Storage", "line": "Store in a cool, dry, ventilated space in sealed containers, and use the product within 1 year." }, { "label": "Incompatible", "line": "Keep the powder away from heated magnesium and from chlorinated rubbers above 215 °C." } ] } ] }, "updated": "2026-10-26", "review": { "status": "draft", "method": "assistant", "checked_values": 20, "unreachable": 2, "caveats": 5, "note": "Read by an AI assistant on 2026-10-26 from the pages and PDFs fetched in that run. MDPI's own page returned HTTP 403 and PubChem's experimental-properties page returned a verification screen, so the PubChem melting point and density were not used. The AZO and GZO values come from one paper each, not from a review. The thermal conductivity is a calculated value. The EU critical-list entry was not checked. Caveats: the Z-93 values describe a coating, not bare ZnO; the varistor range and nonlinearity example come from a review; the SDS hazard classification differs from PubChem's." }, "sources": { "arxiv-zno-2011": { "title": "Optical and Luminescence Properties of Zinc Oxide (P. A. Rodnyi and I. V. Khodyuk; published in Optics and Spectroscopy, vol. 111, no. 5, 2011)", "id": "arXiv 1203.4366", "url": "https://arxiv.org/pdf/1203.4366", "year": 2011, "kind": "paper", "license": "arXiv preprint (cited, not reproduced)" }, "srep-zno-2016": { "title": "Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics: a Comparative Study with Gallium Nitride (Scientific Reports)", "id": "Sci Rep, published 1 March 2016 (srep22504)", "url": "https://www.nature.com/articles/srep22504", "year": 2016, "kind": "paper", "license": "open access (cited, not reproduced)" }, "sds-usz-zno": { "title": "U.S. Zinc safety data sheet: Zinc Oxide, all product grades (Rev. 1.2, 2026)", "id": "CAS 1314-13-2; document USZ_ZincOxideSDS_GLOBAL_Rev8", "url": "https://sds.chemicalstore.com/uszincoxide.pdf", "year": 2026, "kind": "datasheet", "license": "supplier document, linked not reproduced" }, "pubchem-zno": { "title": "PubChem compound record, Zinc oxide (CID 14806)", "id": "CID 14806; CAS 1314-13-2; molecular formula OZn", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14806", "year": 2026, "kind": "database", "license": "public domain (NCBI)" }, "usgs-mcs2026-zinc": { "title": "Mineral Commodity Summaries 2026, Zinc", "id": "USGS MCS 2026, February 2026", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf", "year": 2026, "kind": "report", "license": "public domain (USGS)" }, "usgs-crit2025": { "title": "About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)", "id": "Final 2025 List of Critical Minerals, November 2025", "url": "https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals", "year": 2025, "kind": "web", "license": "public domain (USGS)" }, "nasa-misse-2008": { "title": "MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (NASA Marshall Space Flight Center; Boeing Phantom Works)", "id": "NTRS 20080031037", "url": "https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf", "year": 2008, "kind": "report", "license": "public domain (NASA)" }, "stdj-azo-2004": { "title": "Studying and making transparent conducting ZnO:Al thin films by magnetron DC sputtering (Le Tran, Nguyen Huu Chi, Tran Tuan, Ho Van Binh; VNUHCM Journal of Science and Technology Development, Vol. 7 No. 6)", "id": "doi:10.32508/stdj.v7i6.3212", "url": "https://stdj.scienceandtechnology.com.vn/index.php/stdj/article/view/3212", "year": 2004, "kind": "paper", "license": "open access (cited, not reproduced)" }, "mdpi-gzo-2023": { "title": "Effects of Post-Annealing on the Properties of ZnO:Ga Films with High Transparency (94%) and Low Sheet Resistance (29 Ω/square) (Li-Wen Wang et al.; Materials)", "id": "PMID 37834601; PMC10573347", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10573347/", "year": 2023, "kind": "paper", "license": "open access (cited, not reproduced)" }, "mdpi-varistor-2023": { "title": "Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review (Materials)", "id": "doi:10.3390/ma16103725; PMC10221863", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10221863/", "year": 2023, "kind": "paper", "license": "open access (cited, not reproduced)" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/zinc-oxide/" }