{ "spore": "profile", "id": "anodized-aluminium", "spore_version": "0.2", "family": "coatings", "name": "Anodized aluminium", "abbreviation": "Al2O3 (anodic film)", "role": "hard, electrically insulating oxide skin on aluminium housings and structures", "category": "coatings", "type": "anodize", "summary": "Anodizing grows a porous aluminium oxide film on an aluminium part by electrolysis. Sulphuric acid (Type II) gives a thin decorative or protective film, and hard-coat (Type III) gives a thicker, harder one. The MPO summary of MIL-A-8625F gives Type II thickness as 0.0001 to 0.001 in and Type III as 0.0005 to 0.004 in. Hard-coat films are described as very hard, with one Q&A answer citing 350 to 360 HV on 7075-T6 alloy and another citing 520 to 700 HV (Rockwell C 50 to 60) under suitable process and alloy. NASA RP-1121 gives solar absorptance and thermal emittance for several dyed and undyed anodized aluminium samples, from 0.26 to 0.86 absorptance and 0.56 to 0.87 emittance for the anodized rows.\n", "best_for": "Hard, wear-resistant insulating skin on aluminium housings, with the film thickness set by the drawing", "weakest_at": "The NASA thermal values are 1983 sample data, and the report says coating thickness changes them significantly, so they are indicative only. The hard film is also brittle compared with bare aluminium, and the film's hardness is not a wear rating", "identity": { "formula": "Anodic aluminium oxide (Al2O3 film, porous and hydrated) grown from the aluminium substrate in a sulphuric acid electrolyte", "designations": [], "source": "mpo-milspec", "where": "Type and class descriptions of the MIL-A-8625F summary, which name the film by its anodising process and its Type II, Type III and Class designations" }, "tags": { "environments": [ "low-earth-orbit" ], "stresses": [ "atomic-oxygen", "vacuum-and-outgassing" ], "applications": [ "structures", "thermal-control", "electronics-and-chips" ] }, "properties": [ { "benchmark": "coating_thickness", "label": "Coating thickness, Type II sulphuric acid anodize", "value": 0.0001, "value_high": 0.001, "bound": "range", "unit": "in", "scope": "material", "conditions": { "process": "sulphuric acid anodize, Type II", "standard": "MIL-A-8625F as summarised" }, "method": "Range printed in a finisher's summary of MIL-A-8625F", "status": "ground", "note": "The source gives the thickness only in inches. The same page says the purchase documents or drawing should set the thickness, so the range is a guide.", "source": "mpo-milspec", "where": "Type II entry in the MIL-A-8625F summary, thickness line", "source_detail": { "title": "Key takeaways: MIL-A-8625F anodic coatings, MPO Cincinnati (finishing blog)", "url": "https://www.mpofcinci.com/blog/mil-a-8625f/", "kind": "web", "license": "Finisher web page (cited, not reproduced)" } }, { "benchmark": "coating_thickness", "label": "Coating thickness, Type III hard-coat anodize", "value": 0.0005, "value_high": 0.004, "bound": "range", "unit": "in", "scope": "material", "conditions": { "process": "hard-coat anodize, Type III", "standard": "MIL-A-8625F as summarised" }, "method": "Range printed in a finisher's summary of MIL-A-8625F", "status": "ground", "source": "mpo-milspec", "where": "Type III entry in the MIL-A-8625F summary, thickness line", "source_detail": { "title": "Key takeaways: MIL-A-8625F anodic coatings, MPO Cincinnati (finishing blog)", "url": "https://www.mpofcinci.com/blog/mil-a-8625f/", "kind": "web", "license": "Finisher web page (cited, not reproduced)" } }, { "benchmark": "coating_thickness", "label": "Coating thickness, Class 1 undyed anodize", "value": 10, "value_high": 25, "bound": "range", "unit": "um", "scope": "material", "conditions": { "class": "Class 1 (undyed)", "standard": "MIL-A-8625F as summarised" }, "method": "Range printed in a finisher's summary of MIL-A-8625F", "status": "ground", "note": "The same page's FAQ says the classes relate to sealing processes, which conflicts with its body text. Check the standard before relying on the class wording.", "source": "mpo-milspec", "where": "Class 1 paragraph of the MIL-A-8625F summary", "source_detail": { "title": "Key takeaways: MIL-A-8625F anodic coatings, MPO Cincinnati (finishing blog)", "url": "https://www.mpofcinci.com/blog/mil-a-8625f/", "kind": "web", "license": "Finisher web page (cited, not reproduced)" } }, { "benchmark": "coating_thickness", "label": "Coating thickness, Class 2 dyed anodize", "value": 13, "value_high": 25, "bound": "range", "unit": "um", "scope": "material", "conditions": { "class": "Class 2 (dyed, can be coloured)", "standard": "MIL-A-8625F as summarised" }, "method": "Range printed in a finisher's summary of MIL-A-8625F", "status": "ground", "note": "Black anodize is a dyed film, so this range is the relevant one for black finishes. The page does not give a black-specific thickness.", "source": "mpo-milspec", "where": "Class 2 paragraph of the MIL-A-8625F summary", "source_detail": { "title": "Key takeaways: MIL-A-8625F anodic coatings, MPO Cincinnati (finishing blog)", "url": "https://www.mpofcinci.com/blog/mil-a-8625f/", "kind": "web", "license": "Finisher web page (cited, not reproduced)" } }, { "benchmark": "hardness", "label": "Hardness, Type III hard-coat anodize on 7075-T6", "value": 350, "value_high": 360, "bound": "range", "unit": "HV", "scope": "material", "conditions": { "alloy": "7075-T6", "process": "hard-coat anodize, Type III", "test": "Vickers, value as reported by a reader" }, "method": "Reader-reported value in a Q&A answer on a finishing trade site", "status": "ground", "note": "This is a single reader's measurement on one alloy, not a specification limit. The same article warns that Rockwell testing does not work on thin hard films.", "source": "pfonline-hardness", "where": "Reader question in the Q&A on typical hardness of Type III hard-coat anodized coatings", "source_detail": { "title": "Anodizing Q&A: Typical hardness of Type III hardcoat anodized coatings, Products Finishing", "url": "https://www.pfonline.com/articles/anodizing-qa-typical-hardness-of-type-iii-hardcoat-anodized-coatings", "kind": "web", "license": "Trade magazine web page (cited, not reproduced)" } }, { "benchmark": "hardness", "label": "Hardness, Type III hard-coat anodize, process-dependent", "value": 520, "value_high": 700, "bound": "range", "unit": "HV", "scope": "material", "conditions": { "test": "Rockwell C 50 to 60 converted by the source to HV", "process": "hard-coat anodize, Type III, under certain process and alloy conditions", "alloy": "not named" }, "method": "Value given in an expert answer on a finishing trade site, with the conversion stated in the source", "status": "ground", "note": "The source says this is reached only under certain process and alloy conditions and names no alloy. It is an upper-end figure, not a typical value.", "source": "pfonline-hardness", "where": "Expert answer in the same Q&A, Rockwell C range line", "source_detail": { "title": "Anodizing Q&A: Typical hardness of Type III hardcoat anodized coatings, Products Finishing", "url": "https://www.pfonline.com/articles/anodizing-qa-typical-hardness-of-type-iii-hardcoat-anodized-coatings", "kind": "web", "license": "Trade magazine web page (cited, not reproduced)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, plain (bare) aluminium reference", "value": 0.26, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "surface": "plain aluminium, reference row", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Value in the anodized aluminium samples table of NASA RP-1121, the column order inferred from the report's convention (absorptance then emittance)", "status": "ground", "note": "The text layer of the PDF has no column headers, so the column order is inferred. The same row pairs 0.26 with 0.04, which matches a bare-metal reference. Coating thickness is critical per the table footnote.", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, Plain row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, plain (bare) aluminium reference", "value": 0.04, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "surface": "plain aluminium, reference row", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Value in the anodized aluminium samples table of NASA RP-1121, emittance column (inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, Plain row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, black anodize (sample A)", "value": 0.86, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "black, dyed", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, first Black row (column order inferred)", "status": "ground", "note": "The table lists two black anodized rows with different values. Which sample each row came from is not stated in the text layer.", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, first Black row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, black anodize (sample A)", "value": 0.86, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "black, dyed", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, same first Black row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, first Black row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, black anodize (sample B)", "value": 0.65, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "black, dyed", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, second Black row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, second Black row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, black anodize (sample B)", "value": 0.82, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "black, dyed", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, same second Black row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, second Black row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, clear anodize (sample A)", "value": 0.27, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "clear, undyed", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, first Clear row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, first Clear row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, clear anodize (sample A)", "value": 0.76, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "clear, undyed", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, same first Clear row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, first Clear row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, clear anodize (sample B)", "value": 0.35, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "clear, undyed", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, second Clear row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, second Clear row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, clear anodize (sample B)", "value": 0.84, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "colour": "clear, undyed", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, same second Clear row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, second Clear row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, sulphuric anodize", "value": 0.42, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "process": "sulphuric anodize, undyed as named in the table", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, Sulphuric row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, Sulphuric row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, sulphuric anodize", "value": 0.87, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "process": "sulphuric anodize, undyed as named in the table", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, Sulphuric row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, Sulphuric row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "solar_absorptance", "label": "Solar absorptance, chromic anodize", "value": 0.44, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "process": "chromic acid anodize", "test": "NASA GSFC spectrophotometer, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, Chromic row (column order inferred)", "status": "ground", "note": "The chromic acid anodize (Type I) is the low-emittance option in this table, at 0.56 emittance, against 0.76 to 0.87 for the sulphuric and clear films.", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, Chromic row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } }, { "benchmark": "thermal_emittance", "label": "Thermal emittance, chromic anodize", "value": 0.56, "bound": "exact", "unit": "dimensionless", "scope": "material", "conditions": { "process": "chromic acid anodize", "test": "NASA GSFC emissometer or calorimetric method, room temperature" }, "method": "Anodized aluminium samples table of NASA RP-1121, Chromic row (column order inferred)", "status": "ground", "source": "nasa-rp1121", "where": "Anodized Aluminum Samples table, Chromic row", "source_detail": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" } } ], "corrosion": [ { "environment": "Neutral salt spray, cyclic chamber, up to 80 days, 2A12 and 6061 sulphuric anodize", "headline": "Thin films of 3 to 5 µm pitted and the pits deepened with exposure", "effect": "Pit depth grew steadily in the thin films over the test. The 6061 thin film pitted less than the 2A12 thin film, and the paper says sealing gave effective protection to 6061.", "rating": "moderate", "conditions": { "standard": "neutral salt spray, cyclic chamber", "film": "3 to 5 µm thin sulphuric anodize", "exposure": "up to 80 days" }, "source": "pmc-anodic-corrosion", "where": "Abstract; Conclusions; pitting depth results, Figures 4 and 5" }, { "environment": "Neutral salt spray, cyclic chamber, up to 80 days, thick sulphuric anodize", "headline": "Thick films of 15 to 20 µm were not penetrated by corrosion", "effect": "The paper reports that corrosion did not penetrate the thick 15 to 20 µm films to the substrate, and pitting was more gradual than in the thin films. The 2A12 thick film had cracks and voids, which made it more prone to corrosion.", "rating": "low", "conditions": { "standard": "neutral salt spray, cyclic chamber", "film": "15 to 20 µm thick sulphuric anodize", "exposure": "up to 80 days" }, "source": "pmc-anodic-corrosion", "where": "Conclusions; Figures 6 and 8" } ], "risks": { "hazards": [ { "text": "PubChem's GHS aggregate for aluminium oxide (corundum, CID 14769) shows H319 (causes serious eye irritation) from some company reports, with other reports Not Classified. The record also has a signal word line that does not match the statement list, so check the supplier's SDS for the powder.", "ghs": [ "H319: Causes serious eye irritation" ], "source": "pubchem-corundum", "where": "Safety and Hazards, GHS Classification (CID 14769)" }, { "text": "Precautionary codes listed with the GHS entry include P280 (wear protective gloves, eye protection), P305+P351+P338 (rinse eyes with water), and P337+P317 (get medical help if eye irritation persists).", "ghs": [], "source": "pubchem-corundum", "where": "Safety and Hazards, GHS Classification precautionary statements" } ], "failure_risks": [ { "mode": "Microscopic fissures in the film", "consequence": "Microscopic fissures can lead to corrosion. The film is also dissolved in high or low pH, which strips it and corrodes the substrate.", "source": "wikipedia-anodizing", "where": "Anodizing article, corrosion and sealing sections" } ], "side_effects": [], "handling": [ { "text": "Sealing is required for Type I and II films and optional for Type III, per MIL-A-8625 as summarised by Wikipedia. Hot water or nickel acetate sealing reduces porosity.", "source": "wikipedia-anodizing", "where": "Anodizing article, sealing section" } ], "mitigations": [ { "text": "Sealing sulphuric films reduces porosity and the interstitial pathways that allow corrosive ion exchange.", "source": "wikipedia-anodizing", "where": "Anodizing article, corrosion section" } ] }, "uses": [ { "application": "thermal-control", "device": "Spacecraft thermal-control radiator surfaces", "example": "A 1989 McDonnell Douglas comparison says only sulfuric acid anodizing has a sufficiently low solar absorptance to be a candidate for spacecraft radiators, and it was run under simulated low-Earth-orbit conditions for the planned 30-year Space Station mission.", "source": "le1989-ntrs", "where": "Introduction, paragraph on the three anodizing types; Abstract" }, { "application": "thermal-control", "device": "Clear anodized aluminium thermal-control coatings", "example": "Clear oxalic and sulfuric acid anodized films of 0.012 to 0.0203 cm showed no cracking or spalling, and their emissivity was unchanged, after 4000 thermal cycles from -73 to 38 degC in nitrogen.", "source": "le1989-ntrs", "where": "Thermal cycling section" } ], "supply": [ { "subject": "Primary aluminium smelter production (the metal the film is grown from)", "abundance": "Bauxite resources are estimated at 55 to 75 billion t globally (USGS 2026), enough for world demand well into the future. Bauxite chapter not read in this run.", "producers": [ { "country": "China", "share_percent": 60.8, "year": 2025 }, { "country": "India", "share_percent": 5.7, "year": 2025 }, { "country": "Russia", "share_percent": 5.3, "year": 2025 }, { "country": "Canada", "share_percent": 4.5, "year": 2025 }, { "country": "United Arab Emirates", "share_percent": 3.6, "year": 2025 } ], "critical_lists": [], "substitutes": [], "source": "usgs-al-2026", "where": "Salient Statistics; Import Sources; World Smelter Production and Capacity table" } ], "media": [], "documents": [ { "title": "Comparison of Sulfuric and Oxalic Acid Anodizing for Preparation of Thermal Control Coatings for Spacecraft (Le, Watcher, Smith, McDonnell Douglas, NASA NTRS 19890003246, 1989)", "type": "report", "url": "https://ntrs.nasa.gov/api/citations/19890003246/downloads/19890003246.pdf", "year": 1989 }, { "title": "Anodic coating summary of MIL-A-8625F, MPO Cincinnati", "type": "standard", "url": "https://www.mpofcinci.com/blog/mil-a-8625f/" }, { "title": "Hard-coat anodizing: typical hardness of Type III hard-coat anodized coatings, Products Finishing Q&A", "type": "report", "url": "https://www.pfonline.com/articles/anodizing-qa-typical-hardness-of-type-iii-hardcoat-anodized-coatings" }, { "title": "NASA RP-1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (Hemmer, NASA GSFC, 1983)", "type": "report", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf" }, { "title": "USGS Mineral Commodity Summaries 2026: Aluminum", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-aluminum.pdf", "year": 2026 }, { "title": "PubChem: Aluminium oxide (corundum, CID 14769), GHS classification summary", "type": "database", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14769" }, { "title": "Effect of Film Thickness and Defects on the Corrosion Behavior of Anodic Oxide Films on Aluminum Alloys (MDPI Materials, 2026)", "type": "paper", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12897759", "year": 2026 } ], "gaps": [ "MIL-A-8625F itself was not reached: the anodizing.org page returned HTTP 403, so the Type I, II and III thickness numbers come from a finisher's summary.", "NASA RP-1121 (John H. Hemmer, GSFC, 1983, NTRS 19840015630) is not image-only: its text layer was read. Its table column headers are missing from the text layer, so the absorptance and emittance column order is inferred from the report's convention. Confirm against the printed page.", "The anodized table in RP-1121 has no thickness or process metadata beyond the colour or process name, so the values cannot be tied to a specific anodize type or class. Two black and two clear rows are not labelled by sample.", "The AAC hard-coat guideline PDF (anodizing.org) is image or compressed-stream only, so no thickness or hardness table from it is recorded.", "Salt spray hours (ASTM B117) for Type II and Type III anodize were not read. The 2026 corrosion paper gives neutral salt spray in days (up to 80 days), so no hour figure is recorded.", "No finisher's data sheet with Taber wear values was read. Salt spray results come from one 2026 paper in days, not hours.", "The Type II hardness value and any Type II or Type III Taber wear value were not found in an openly readable source.", "Thermal cycling (-73 to 38 degC, 4000 cycles) was read from the 1989 NTRS paper. Outgassing and atomic-oxygen erosion of anodic films in orbit were not looked up.", "Chromic acid (Type I) process hazards were not sourced, so no hazard entry is recorded for that bath.", "Bauxite and alumina chapter of USGS MCS 2026 was not read; the supply entry uses the aluminium chapter's smelter table.", "solar_absorptance and thermal_emittance are not in spores/property-canon.yaml, so these are snake_case names not yet canonical." ], "story": { "why": "Aluminium is light and conducts heat well, but its bare surface wears and scratches easily and it is a conductor. Anodizing grows a hard oxide film from the aluminium itself, so the skin is electrically insulating and tougher than the metal underneath. For spacecraft and device housings, the film thickness is the main lever, and the MIL-A-8625F summary gives a Type II range of 0.0001 to 0.001 in and a Type III range of 0.0005 to 0.004 in. The Class 2 dyed film, which black anodize uses, is 13 to 25 µm thick in the same summary.", "uses": [ { "where": "Spacecraft thermal control", "line": "NASA's GSFC table lists black and clear anodized aluminium samples as thermal-control coatings, with solar absorptance and thermal emittance printed for each colour (NASA RP-1121)." }, { "where": "Housings and electrical isolation", "line": "Wikipedia notes that anodizing increases wear resistance, corrosion resistance, and electrical and thermal insulation of the part (Wikipedia, anodizing)." } ], "can_do": [ { "label": "Thin protective film", "line": "A Type II sulphuric film runs from 0.0001 to 0.001 in thick according to the MIL-A-8625F summary, enough for corrosion protection and a decorative finish on housings.", "scope": "material", "value": "0.0001 to 0.001 in" }, { "label": "Thick hard film", "line": "One reader's Type III film on 7075-T6 aluminium measured 350 to 360 HV. An expert answer on the same site says a hard-coat film can reach 520 to 700 HV under good process and alloy conditions.", "scope": "material", "value": "350 to 360 HV" }, { "label": "Dyed finish", "line": "The Class 2 dyed film, the family black anodize belongs to, is 13 to 25 µm thick in the MIL-A-8625F summary.", "scope": "material", "value": "13 to 25 µm" }, { "label": "Thermal control", "line": "Clear and sulphuric anodize absorb only 0.27 to 0.42 of solar energy in NASA's table, which is low for a thermal-control skin, and their emittance is 0.76 to 0.87. Black dyed films absorb 0.65 to 0.86.", "scope": "material", "value": "0.27 to 0.35 absorptance" } ], "compare": "The thermal numbers are for the anodic film on aluminium, from one NASA table of 1983 samples. The table warns that coating thickness can change values significantly, so the values are indicative only. The Chromic acid film has the lowest emittance of the anodized rows, at 0.56.", "compare_rows": [ { "label": "Solar absorptance", "benchmark": "solar_absorptance", "scope": "material" }, { "label": "Thermal emittance", "benchmark": "thermal_emittance", "scope": "material" }, { "label": "Hardness", "benchmark": "hardness", "scope": "material" } ], "handling": [ "Sealing: Type II and Type III films are normally sealed. MIL-A-8625 requires sealing for thin coatings, and hot water or nickel acetate sealing reduces porosity (Wikipedia, anodizing).", "Type III sealing improves corrosion resistance but reduces abrasion resistance, so the seal choice depends on the wear requirement (Wikipedia, anodizing)." ], "good_for": [ "Housings and structures that need a hard, insulating skin, where the film thickness can be set on the drawing", "Black or dyed finishes, which use the thicker Class 2 film" ], "watch_out": [ "The hardness figures come from one reader's measurement and one expert answer. They are not specification limits.", "The MIL-A-8625F summary gives thickness in inches for Type II and Type III and in micrometres for the classes, so a unit check is needed before using both together.", "The class wording conflicts within the same summary page, so the standard itself should be checked before buying to a class.", "Wikipedia's Type II and Type III thickness boundaries do not match the MPO inch ranges exactly. Check the drawing before quoting one." ], "verdict": "Anodized aluminium gives a thickness-controlled, hard, insulating film on aluminium, and the film hardness is far above bare metal. The NASA table shows the film can be tuned for thermal control, with black dyed films absorbing most solar energy and the chromic film having the lowest emittance. The thermal values are 1983 samples, and no salt spray or orbital data were read, so the coating still needs test data for a flight choice.", "recipe": { "line": "Anodic aluminium oxide is grown on the part itself. The aluminium is made the anode in a sulphuric acid bath and a direct current releases oxygen at its surface, building an oxide layer. Acid dissolves the oxide while the current forms it, leaving nanopores that let the electrolyte keep growing the film (Wikipedia, anodizing). Type II is the thinner film, and Type III is the thicker hard coat, made in a refrigerated tank at higher voltage. Pores are then sealed, by hot water or a cold nickel acetate bath, to reduce corrosion.", "parts": [ { "name": "Aluminium", "symbol": "Al", "role": "The substrate. The film is grown from the aluminium surface itself, so it is not a coating applied on top.", "atoms": 2, "atomic_weight": 26.982 }, { "name": "Oxygen", "symbol": "O", "role": "Supplied from the electrolyte and the anode surface, which together form the Al2O3 film. The film is porous and hydrated, which is why sealing matters.", "atoms": 3, "atomic_weight": 15.999 } ] }, "risk_groups": [ { "title": "For people", "lead": "The sources read here describe no health hazard for the finished film.", "points": [ { "label": "Finished parts", "line": "No hazard statement for the finished film was read. Handle the anodizing chemicals as the finisher's own safety sheet directs." }, { "label": "Alumina powder", "line": "PubChem's GHS entry for aluminium oxide (corundum, CID 14769) lists H319, causes serious eye irritation, from some company reports. Other reports are Not Classified." } ] }, { "title": "If it fails", "lead": "These are failure routes the sources mention; none of them is measured in this run.", "points": [ { "label": "Brittle hard film", "line": "A hard-coat film is harder and more brittle than the bare alloy, so a heavy impact can crack it. The cracks are not quantified here." }, { "label": "Thickness drift", "line": "Film thickness is set by the drawing. A part anodized to the wrong thickness will not meet its specified protection." }, { "label": "Fissures and dissolution", "line": "Wikipedia says microscopic fissures can lead to corrosion, and the film dissolves in high or low pH, which strips it and corrodes the substrate." } ] }, { "title": "Handling and storage", "points": [ { "label": "Specify on the drawing", "line": "Call out the anodize type, class and thickness on the drawing, since the standard summary says the drawing or purchase document sets them." }, { "label": "Seal the film", "line": "Sealing reduces porosity and corrosion pathways, per Wikipedia. Type III sealing trades some abrasion resistance for corrosion resistance." } ] } ] }, "updated": "2026-10-19", "review": { "status": "draft", "method": "assistant", "checked_values": 20, "unreachable": 4, "caveats": 6, "note": "Values read by an AI assistant on 2026-10-19. Original 6 values from two web pages, plus 14 from NASA RP-1121 (column order inferred from the text layer, no headers) and 5 smelter shares computed from USGS 2026. Unreachable: MIL-A-8625F (403), anodizing.org reference guide (403), AAC hard-coat guideline (image-only PDF), USGS bauxite chapter (not read). Caveats: thickness ranges come from a finisher's summary; hardness values are a reader's measurement and an expert answer; the NASA table is 1983 data without thickness metadata; class wording conflicts within one source; no salt spray hours." }, "sources": { "le1989-ntrs": { "title": "Comparison of Sulfuric and Oxalic Acid Anodizing for Preparation of Thermal Control Coatings for Spacecraft (Le, Watcher, Smith, McDonnell Douglas, 1989)", "url": "https://ntrs.nasa.gov/api/citations/19890003246/downloads/19890003246.pdf", "year": 1989, "kind": "report", "license": "US government work (NASA NTRS)" }, "mpo-milspec": { "title": "Key takeaways: MIL-A-8625F anodic coatings, MPO Cincinnati (finishing blog)", "url": "https://www.mpofcinci.com/blog/mil-a-8625f/", "kind": "web", "license": "Finisher web page (cited, not reproduced)" }, "pfonline-hardness": { "title": "Anodizing Q&A: Typical hardness of Type III hardcoat anodized coatings, Products Finishing", "url": "https://www.pfonline.com/articles/anodizing-qa-typical-hardness-of-type-iii-hardcoat-anodized-coatings", "kind": "web", "license": "Trade magazine web page (cited, not reproduced)" }, "nasa-rp1121": { "title": "NASA Reference Publication 1121, Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings (John H. Hemmer, NASA GSFC, December 1983)", "url": "https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf", "kind": "report", "license": "US government work (NASA NTRS)" }, "usgs-al-2026": { "title": "USGS Mineral Commodity Summaries 2026: Aluminum (Merrill)", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-aluminum.pdf", "kind": "report", "license": "US government work (USGS)" }, "pubchem-corundum": { "title": "PubChem: Corundum / aluminium oxide (CID 14769), GHS classification", "url": "https://pubchem.ncbi.nlm.nih.gov/compound/14769", "kind": "database", "license": "PubChem public data (cited, not reproduced)" }, "wikipedia-anodizing": { "title": "Anodizing, Wikipedia", "url": "https://en.wikipedia.org/wiki/Anodizing", "kind": "web", "license": "CC-BY-SA (cited, not reproduced)" }, "pmc-anodic-corrosion": { "title": "Effect of Film Thickness and Defects on the Corrosion Behavior of Anodic Oxide Films on Aluminum Alloys (Materials, MDPI, 2026)", "id": "PMC12897759", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12897759", "year": 2026, "kind": "paper", "license": "Open access, as listed by PMC" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/anodized-aluminium/" }