Chromium oxide thermal spray coating (Cr2O3, chromia) Cr2O3
Cr2O3 · CAS 1308-38-9 · trigonal, R-3c (No. 167)
Also known as Metco 6156
Chromium(III) oxide (chromia, Cr2O3) is sprayed onto steel by atmospheric plasma spraying to form a hard ceramic layer.
Evidence level
2 of 5
Lab-measured
- 0Predicted only. No one has made it, or no measurement exists.
- 1Calculated. Only calculated or predicted values from sources.
- 2Lab-measured. Measured properties with their conditions stated.
- 3Space-relevant tests. Measured in conditions relevant to space, such as vacuum or atomic oxygen.
- 4Ground-qualified. Qualified for an application on the ground.
- 5Flown or field-proven. Flight or field results exist.
Recipe, share of the weight
- Cr not statedChromium
- O not statedOxygen
Best for
Wear-resistant, sliding and abrasive contact faces on steel, such as printing anilox rolls and mechanical seal faces, where the part does not take impact
Weakest at
Brittleness: chromia chips under point-loaded impact or edge loading, and thick build-up risks spalling (HTS Coatings)
Risk at a glance
- People None found. Classification differs between sources
- If it fails Moderate. Chipping under impact
- Corrosion Moderate. Open porosity is the weak point: standard APS coatings run up to 5% porosity, so sealing is specified for aggressive chemistry.
Quick facts: Cr2O3
| Property | Value | Basis |
|---|---|---|
| Density | 4.5 to 5.22 g/cm³ | 2 sourced values across conditions |
| Melting point | 2,435 °C | 1 sourced value |
| Maximum service temperature | 177 to 540 °C | 2 sourced values across conditions |
What is the density of Chromium oxide thermal spray coating (Cr2O3)?
Chromium oxide thermal spray coating (Cr2O3) has a density of 4.5 to 5.22 g/cm³. The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the melting point of Chromium oxide thermal spray coating (Cr2O3)?
Chromium oxide thermal spray coating (Cr2O3) has a melting point of 2,435 °C. The source and test conditions are listed in the properties table on this page.
What is the maximum service temperature of Chromium oxide thermal spray coating (Cr2O3)?
Chromium oxide thermal spray coating (Cr2O3) has a maximum service temperature of 177 to 540 °C. The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is Chromium oxide thermal spray coating (Cr2O3) used for?
Uses recorded in the sources include Mechanical seal faces, pump sleeves and impellers; Flexographic printing anilox rolls, laser engraved after coating; Wire drawing capstans, draw blocks and sheaves.
Why it exists
Chromium(III) oxide, Cr2O3, is a corundum-structure oxide that is sprayed onto steel to make a hard, wear-resistant layer. The HTS Coatings technical table gives a typical Vickers hardness of 900 to 1200 HV300 for plasma sprayed coatings, and the Odhiambo paper measured 1496 HV300 g and 1762 HV300 g for two coatings sprayed at different currents. The trade-off is brittleness: the same sources say chromia chips under impact and must be sealed for chemical service. The HTS page points to sliding, abrasive and corrosive duty as where it is used.
Where it's used
Printing anilox rolls
The HTS page says chromia is the industry standard surface for flexographic and gravure printing rolls because it takes laser-engraved cells cleanly. It also lists mechanical seal faces and pump sleeves.
Pump and seal parts
The Saint-Gobain Rokide C bulletin lists pump sleeves, pump shafts, impellers, mechanical seal faces and ball valves among the parts it coats. The rod is mostly Cr2O3 with silica and alumina, so it is not pure chromia.
Wire drawing
Wire drawing capstans, draw blocks, sheaves and pulleys are also listed for the Rokide C rod. No space or flight use was found in any source we hold.
Recipe
Cr2O3
Chromia is chromium(III) oxide, Cr2O3. It is made from chromite ore by converting it through sodium dichromate, which is reduced with sulfur at high temperature. The Metco 6156 feedstock used in the Odhiambo paper is a sintered and crushed powder.
| Ingredient | Share of the weight | What it does |
|---|---|---|
| Chromium Cr | not stated | The oxide-forming metal. Chromium sits at the centre of the corundum framework that the oxide forms. |
| Oxygen O | not stated | Fills the close-packed oxide framework with chromium in its octahedral holes, which gives a hard, brittle ceramic. |
Weight shares are as printed in the sources.
What it can do
Wear
Resist sliding and abrasive wear on steel parts. The HTS page calls chromia the hardest common oxide ceramic in thermal spray.
Finish
Take a laser-engraved cell pattern for printing rolls, which is why it is used for anilox rolls.
Chemistry
Hold up in alkaline or mildly acidic media when the coating is sealed, according to the HTS page.
Seal faces
Work as a seal face where the part does not take impact.
How it compares
Chromia is hard and brittle. Its melting point is 2435 °C as bulk crystal, and a typical plasma sprayed coating has a Vickers hardness of 900 to 1200 HV300. The HTS technical table caps wear service at 540 °C. Adding titania to chromia makes the coating less brittle, according to the Oerlikon data sheet for a chromia-titania blend. The Oerlikon sheet does not give hardness values for the blend that can be compared here, so this profile compares only pure chromia figures.
The same measurements for each material, so you can compare them. Each row names the key condition under the value; the full conditions and methods are in the numbered notes under Technical details. Compare every grade in the family.
| Measurement | Cr2O3 |
|---|---|
| Thermal behavior and safety | |
| Melting point of chromium(III) oxide | 2435 °C2 |
| Physical and electrical | |
| Density of crystalline chromium(III) oxide | 5.22 g/cm³1 |
| Typical hardness of atmospheric plasma sprayed chromia | 900 to 1200 HV3003 |
| Hardness of chromia coating in Rockwell C | 62 to 72 HRC4 |
| Microhardness of plasma sprayed Metco 6156, first coating | 1496 HV300 g5 |
| Microhardness of plasma sprayed Metco 6156, second coating | 1762 HV300 g6 |
| Typical thickness of thermal sprayed chromia | 75 to 640 µm17 |
| Bulk density of Rokide C ceramic rod | 4.5 g/cc18 |
| Other measurements | |
| Bond strength of atmospheric plasma sprayed chromia on steel | 4000 to 6000 psi7 |
| Tensile bond strength, first coating (550A) | 12.24 MPa8 |
| Tensile bond strength, second coating (650A) | 23.6 MPa9 |
| Bond strength of Rokide C combustion-sprayed rod coating | 4545 psi10 |
| Porosity of plasma sprayed Metco 6156, first coating (550A) | 8 %11 |
| Porosity of plasma sprayed Metco 6156, second coating (650A) | 4 %12 |
| Porosity of standard atmospheric plasma sprayed chromia | < 5 %13 |
| Total porosity of Rokide C combustion-sprayed rod coating | 8.4 %14 |
| Maximum service temperature for wear service | 540 °C15 |
| Maximum service temperature for sealed corrosive service | 177 to 205 °C16 |
| Feedstock particle size, Metco 6156 powder | -35 to 15 µm19 |
Why choose it, and why not
Good for
- Wear on sliding and abrasive surfaces, such as seal faces and printing rolls. The HTS page says the coating outlasts steel in these duties.
- Corrosion in mild acid and alkali once the coating is sealed. The HTS page quotes 'hold up through 30-day immersion across pH 0-10'.
Watch out for
- Brittleness. Point impact chips the coating, and the HTS page says not to specify it for impact.
- Porosity. Standard plasma sprayed coatings run up to 5% porosity, and the Odhiambo paper ties higher porosity to lower bond strength.
- Temperature. The wear ceiling in the table is 540 °C and the sealed corrosive ceiling is 177 to 205 °C.
Chromia is the hard, brittle choice for sliding wear and seal faces, and it works only if impact is kept out and the coating is sealed for chemistry.
Technical details
For scientists and researchers. Everything above comes from the record below: every number with its method, its conditions and its source.
Other names and standards
The same grade under other systems, as datasheets and standards print them. Each code was checked against the page it comes from.
| System | Codes |
|---|---|
| Trade name | Metco 6156 |
Notes
The method, full conditions and any caveat for the numbered rows above.
| # | Measurement | Method | Conditions | Caveat |
|---|---|---|---|---|
| 1 | Density of crystalline chromium(III) oxide | Value printed in the experimental-properties section of the PubChem record, citing the Merck Index | basis bulk crystalline Cr2O3 at 25 °C as printed in the Merck Index entrynot a sprayed coating density | — |
| 2 | Melting point of chromium(III) oxide | Value printed in the Chembox properties of the Wikipedia article (melting point 2435 °C, printed as 2,435 °C); the PubChem record prints the same figure from the Merck Index | basis bulk crystalline Cr2O3 as printed in the Merck Index entry | — |
| 3 | Typical hardness of atmospheric plasma sprayed chromia | Range printed in the HTS Coatings technical data table, Hardness (Vickers) row | form atmospheric plasma sprayed coating (typical APS)basis range printed for typical APS coatings in the technical data table | — |
| 4 | Hardness of chromia coating in Rockwell C | Range printed in the HTS Coatings technical data table, Hardness (HRC) row | form chromia coating, range depends on formulation as printed | — |
| 5 | Microhardness of plasma sprayed Metco 6156, first coating | Mean Vickers microhardness on polished cross-sections, as stated in the microhardness section | feedstock Metco 6156 chromium oxide powderprocess atmospheric plasma spray, no bond coat, 550 A arc currentload 300 gdwell 15 s | The conclusion section of the same paper prints 1497 HV for this coating, one unit higher. |
| 6 | Microhardness of plasma sprayed Metco 6156, second coating | Mean Vickers microhardness on polished cross-sections, as stated in the microhardness section | feedstock Metco 6156 chromium oxide powderprocess atmospheric plasma spray, no bond coat, 650 A arc currentload 300 gdwell 15 s | The conclusion section of the same paper prints 1763 HV for this coating, one unit higher. |
| 7 | Bond strength of atmospheric plasma sprayed chromia on steel | Range printed in the HTS Coatings technical data table, Bond strength row | form atmospheric plasma spray on steelbasis range printed in the technical data table | — |
| 8 | Tensile bond strength, first coating (550A) | Tensile adhesion test in the paper, which says it followed the ASTM C633 procedure | feedstock Metco 6156process atmospheric plasma spray, no bond coat, 550 Athickness 348 um as printedfailure adhesive | — |
| 9 | Tensile bond strength, second coating (650A) | Tensile adhesion test in the paper, which says it followed the ASTM C633 procedure | feedstock Metco 6156process atmospheric plasma spray, no bond coat, 650 Athickness 391 um as printedfailure adhesive | — |
| 10 | Bond strength of Rokide C combustion-sprayed rod coating | Value printed in the Rokide C technical bulletin, Mechanical section | product Rokide C chrome oxide ceramic rod (mostly Cr2O3 with silica and alumina), combustion rod sprayform combustion-sprayed rod coating | — |
| 11 | Porosity of plasma sprayed Metco 6156, first coating (550A) | Porosity by image analysis of SEM micrographs, as stated in the paper | feedstock Metco 6156process atmospheric plasma spray, 550 A | The results section text is garbled for this value; the correlation section prints 8% in full. |
| 12 | Porosity of plasma sprayed Metco 6156, second coating (650A) | Porosity by image analysis of SEM micrographs, as stated in the paper | feedstock Metco 6156process atmospheric plasma spray, 650 A | The results section text is garbled for this value; the correlation section prints 4% in full. |
| 13 | Porosity of standard atmospheric plasma sprayed chromia | Upper limit printed in the HTS Coatings technical data table | form standard APS coating, not the dense sintered-powder anilox grade | — |
| 14 | Total porosity of Rokide C combustion-sprayed rod coating | Value printed in the Rokide C technical bulletin, Physical section | product Rokide C chrome oxide ceramic rod, combustion rod spray | — |
| 15 | Maximum service temperature for wear service | Value printed in the HTS Coatings technical data table, metric row | service dry abrasive wear service | — |
| 16 | Maximum service temperature for sealed corrosive service | Range printed in the HTS Coatings technical data table, metric row | service sealed coating in corrosive chemical environments | — |
| 17 | Typical thickness of thermal sprayed chromia | Range printed in the HTS Coatings technical data table, Typical thickness row | process typical thermal spray chromia coating | — |
| 18 | Bulk density of Rokide C ceramic rod | Value printed in the Rokide C technical bulletin, Physical section | product Rokide C chrome oxide ceramic rod, mostly Cr2O3note a rod product figure, not the density of pure chromia | — |
| 19 | Feedstock particle size, Metco 6156 powder | Size range printed in the Experimental details section of the paper | product Metco 6156 powder as received, sieve range as printed | — |
Corrosion and compatibility
What happens when it meets other materials and environments.
| Environment | Concern | What happens |
|---|---|---|
| Sealed chromia in acidic and alkaline solutions | low | The HTS page says sealed coatings hold up through 30-day immersion across pH 0-10 with no loss of wear resistance.1 |
| Unsealed plasma sprayed coating with open porosity | moderate | Open porosity is the weak point: standard APS coatings run up to 5% porosity, so sealing is specified for aggressive chemistry.2 |
| High temperature in wear or sealed corrosive service | moderate | The table gives a wear ceiling of 540 °C and a sealed corrosive ceiling of 177 to 205 °C.3 |
| # | Environment | Details | Test conditions |
|---|---|---|---|
| 1 | Sealed chromia in acidic and alkaline solutions | The HTS page attributes this to a Journal of Thermal Spray Technology study of plasma sprayed chromia and alumina sealed with aluminum phosphates. The primary paper could not be opened for this profile, so the result rests on the HTS summary. | sealant aluminum phosphate (per the HTS page)test immersion in acidic and alkaline solutions, as summarized by HTSbasis secondary summary of a primary study |
| 2 | Unsealed plasma sprayed coating with open porosity | The HTS page lists sealing with epoxy, aluminum phosphate or polymer impregnation for aggressive chemical environments. The Odhiambo paper finds that the coating with higher porosity (8%) had the lower tensile bond strength (12.24 MPa against 23.60 MPa at 4%), so porosity also weakens the bond to the steel. This is an adhesion result, not a corrosion test. | basis qualitative corrosion ranking from the HTS page; porosity and bond comparison from the Odhiambo paper |
| 3 | High temperature in wear or sealed corrosive service | The HTS page says the sealed corrosive ceiling is the limit in chemical service and advises stepping over to Cr3C2-NiCr for higher-temperature wear. The page does not say what fails above these ceilings. | basis service ceilings as printed by HTS Coatings |
Risks and side effects
Hazards to people, what happens when a cell overheats, and how the material is handled and stored.
For people
Chromium(III) oxide is classed as hazardous by some sources and not by others. The sources disagree, so handle the powder as a possible sensitizer and reproductive hazard until your own safety data sheet says otherwise.
- The powder
- PubChem's summary says the substance does not meet GHS hazard criteria for 57.8% (1112 of 1924) of all reports. The rest carry hazard statements H302, H317, H319 and H360.
- Stricter registrant entry
- A Johnson Matthey classification for Katalco 71-5, a Grade 2 chromium(III) oxide, lists H314, H340, H350, H361 and H371 with the signal word Danger. That is a different product, but it shows how far classifications can differ.
- Powder dust
- The Oerlikon blend data sheet advises a dry place and an original container. It does not give a dust exposure limit for chromia.
If a coating fails
These points describe the coating's own limits, not people's exposure.
- Impact
- Chromia is brittle. Point impact or edge loading chips the coating, so the HTS page says to specify it for sliding, erosive and corrosive duty, not impact.
- Thickness
- The HTS page says 'Thickness limited to roughly 25-30 mils on cylindrical work before residual stress risks spalling'.
- Temperature
- The table sets the wear ceiling at 540 °C and the sealed corrosive ceiling at 177 to 205 °C.
Handling and storage
- Storage
- Keep Metco 6485 powder in its original container in a dry location, and dry any open container in an oven before use. That data sheet is for a chromia-titania blend, not pure chromia.
- Finishing
- Finishing needs diamond wheels, so the HTS page says to plan the cost and lead time.
Test details
The original wording and numbers from the sources, for readers who want them.
Failure risks
| Failure | Trigger and consequence |
|---|---|
| Chipping under impactmoderate severity | Point-loaded impact or edge loadingChromia is a ceramic, so impact chips the coating. The HTS page says to specify it for sliding, erosive and corrosive duty, not impact. |
| Spalling of thick build-upmoderate severity | Build-up beyond the practical limit on cylindrical workThe HTS page says 'Thickness limited to roughly 25-30 mils on cylindrical work before residual stress risks spalling'. Typical thickness is 75 to 640 µm. |
| Service above the ceiling for the dutymoderate severity | Service above 540 °C for wear, or above 177 to 205 °C in sealed corrosive serviceThe table gives these as ceilings. The HTS page does not describe the failure mode above them. |
Handling and storage
- For the Cr2O3-TiO2 blend Metco 6485 from the same maker (not pure chromia), keep the powder in its original container in a dry location, tumble it gently before use, and store open containers in a drying oven to prevent moisture pickup.
- The HTS page says finishing requires diamond wheels, so plan the cost and lead time.
Mitigations
- Seal the coating with epoxy, aluminum phosphate or polymer impregnation for aggressive chemical service.
- Apply over a corrosion-resistant bond coat for chemical service, as the HTS page describes for its own process.
Supply and geography
How common the raw materials are and where they come from.
Chromium (chromite ore, the feedstock for chromia)
- Top producers (2025)
- South Africa 45.1%, Turkey 17.6%, Kazakhstan 13.7%, India 5.9%, Brazil 3.9%, Zimbabwe 3.9%, Finland 3.7%
- Recycling
- USGS: 'recycled chromium (contained in reported stainless-steel scrap receipts) accounted for 21% of apparent consumption' in the United States in 2025.
Documents
Datasheets, safety data sheets, papers and standards you can open.
Full record
The complete spore, as stored. Free to reuse under CC-BY-4.0. Images keep the licence shown with each one.
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spore: profile
id: chromium-oxide-coating
spore_version: 0.2
family: oxide-ceramics
name: Chromium oxide thermal spray coating (Cr2O3, chromia)
abbreviation: Cr2O3
role: Hard ceramic wear and seal-face coating, sprayed onto steel parts
category: coatings
type: anodize
summary: |
Chromium(III) oxide (chromia, Cr2O3) is sprayed onto steel by atmospheric plasma spraying to form a hard ceramic layer. Vickers microhardness of the plasma-sprayed Metco 6156 coating was 1496 HV300 g in one test and 1762 HV300 g in another, per Odhiambo et al. The coating is brittle, so it chips under point impact and its thickness is limited before it spalls, according to the HTS Coatings technical data table.
best_for: Wear-resistant, sliding and abrasive contact faces on steel, such as printing anilox rolls and mechanical seal faces, where the part does not take impact
weakest_at: 'Brittleness: chromia chips under point-loaded impact or edge loading, and thick build-up risks spalling (HTS Coatings)'
identity:
formula: Cr2O3
cas: 1308-38-9
crystal_system: trigonal (corundum structure)
space_group: R-3c (No. 167)
source: wikipedia-cr2o3
where: 'Chembox: CAS number, crystal structure (corundum) and space group sections'
designations:
- system: Trade name
code: Metco 6156
source: odhiambo2021
where: 'Experimental details, first paragraph: commercially available powder (Metco 6156)'
tags:
environments: []
stresses: []
applications: []
properties:
- benchmark: density
label: Density of crystalline chromium(III) oxide
value: 5.22
unit: g/cm3
scope: material
conditions:
basis: bulk crystalline Cr2O3 at 25 degC as printed in the Merck Index entry
not_a: sprayed coating density
method: Value printed in the experimental-properties section of the PubChem record, citing the Merck Index
status: ground
source: pubchem-cr2o3
where: Chemical and Physical Properties > Experimental Properties > Density, first entry (5.22 g/cm3 at 25 degC)
- benchmark: melting_point
label: Melting point of chromium(III) oxide
value: 2435
unit: °C
scope: material
conditions:
basis: bulk crystalline Cr2O3 as printed in the Merck Index entry
method: Value printed in the Chembox properties of the Wikipedia article (melting point 2435 °C, printed as 2,435 °C); the PubChem record prints the same figure from the Merck Index
status: ground
source: wikipedia-cr2o3
where: 'Chembox Properties, melting point: 2,435 °C (2435 °C in the infobox source)'
- benchmark: vickers_hardness
label: Typical hardness of atmospheric plasma sprayed chromia
value: 900
value_high: 1200
bound: range
unit: HV300
scope: material
conditions:
form: atmospheric plasma sprayed coating (typical APS)
basis: range printed for typical APS coatings in the technical data table
method: Range printed in the HTS Coatings technical data table, Hardness (Vickers) row
status: ground
source: hts-chrome-oxide
where: 'Technical data table, Hardness (Vickers) row: 900-1200 HV300 typical APS'
- benchmark: rockwell_c_hardness
label: Hardness of chromia coating in Rockwell C
value: 62
value_high: 72
bound: range
unit: HRC
scope: material
conditions:
form: chromia coating, range depends on formulation as printed
method: Range printed in the HTS Coatings technical data table, Hardness (HRC) row
status: ground
source: hts-chrome-oxide
where: 'Technical data table, Hardness (HRC) row: 62-72 HRC depending on formulation'
- benchmark: vickers_hardness
label: Microhardness of plasma sprayed Metco 6156, first coating
value: 1496
unit: HV300 g
scope: material
conditions:
feedstock: Metco 6156 chromium oxide powder
process: atmospheric plasma spray, no bond coat, 550 A arc current
load: 300 g
dwell: 15 s
method: Mean Vickers microhardness on polished cross-sections, as stated in the microhardness section
status: ground
note: The conclusion section of the same paper prints 1497 HV for this coating, one unit higher.
source: odhiambo2021
where: Microhardness section (Vickers microhardness values for 550A)
- benchmark: vickers_hardness
label: Microhardness of plasma sprayed Metco 6156, second coating
value: 1762
unit: HV300 g
scope: material
conditions:
feedstock: Metco 6156 chromium oxide powder
process: atmospheric plasma spray, no bond coat, 650 A arc current
load: 300 g
dwell: 15 s
method: Mean Vickers microhardness on polished cross-sections, as stated in the microhardness section
status: ground
note: The conclusion section of the same paper prints 1763 HV for this coating, one unit higher.
source: odhiambo2021
where: Microhardness section (Vickers microhardness values for 650A)
- benchmark: bond_strength
label: Bond strength of atmospheric plasma sprayed chromia on steel
value: 4000
value_high: 6000
bound: range
unit: psi
scope: material
conditions:
form: atmospheric plasma spray on steel
basis: range printed in the technical data table
method: Range printed in the HTS Coatings technical data table, Bond strength row
status: ground
source: hts-chrome-oxide
where: 'Technical data table, Bond strength row: 4,000-6,000 psi on steel (APS)'
- benchmark: bond_strength
label: Tensile bond strength, first coating (550A)
value: 12.24
unit: MPa
scope: material
conditions:
feedstock: Metco 6156
process: atmospheric plasma spray, no bond coat, 550 A
thickness: 348 um as printed
failure: adhesive
method: Tensile adhesion test in the paper, which says it followed the ASTM C633 procedure
status: ground
source: odhiambo2021
where: Table 4, averaged tensile bond strength results (550A, 12.24 MPa, adhesive failure)
- benchmark: bond_strength
label: Tensile bond strength, second coating (650A)
value: 23.6
unit: MPa
scope: material
conditions:
feedstock: Metco 6156
process: atmospheric plasma spray, no bond coat, 650 A
thickness: 391 um as printed
failure: adhesive
method: Tensile adhesion test in the paper, which says it followed the ASTM C633 procedure
status: ground
source: odhiambo2021
where: Table 4, averaged tensile bond strength results (650A, 23.60 MPa, adhesive failure)
- benchmark: bond_strength
label: Bond strength of Rokide C combustion-sprayed rod coating
value: 4545
unit: psi
scope: material
conditions:
product: Rokide C chrome oxide ceramic rod (mostly Cr2O3 with silica and alumina), combustion rod spray
form: combustion-sprayed rod coating
method: Value printed in the Rokide C technical bulletin, Mechanical section
status: ground
source: rokide-c-tds
where: 'Coating features, Mechanical: Bond Strength 4545 psi'
- benchmark: porosity
label: Porosity of plasma sprayed Metco 6156, first coating (550A)
value: 8
unit: '%'
scope: material
conditions:
feedstock: Metco 6156
process: atmospheric plasma spray, 550 A
method: Porosity by image analysis of SEM micrographs, as stated in the paper
status: ground
note: The results section text is garbled for this value; the correlation section prints 8% in full.
source: odhiambo2021
where: 'Correlation of the results and the discussion: porosities 8% and 4% for 550A and 650A'
- benchmark: porosity
label: Porosity of plasma sprayed Metco 6156, second coating (650A)
value: 4
unit: '%'
scope: material
conditions:
feedstock: Metco 6156
process: atmospheric plasma spray, 650 A
method: Porosity by image analysis of SEM micrographs, as stated in the paper
status: ground
note: The results section text is garbled for this value; the correlation section prints 4% in full.
source: odhiambo2021
where: 'Correlation of the results and the discussion: porosities 8% and 4% for 550A and 650A'
- benchmark: porosity
label: Porosity of standard atmospheric plasma sprayed chromia
value: 5
bound: upper
unit: '%'
scope: material
conditions:
form: standard APS coating, not the dense sintered-powder anilox grade
method: Upper limit printed in the HTS Coatings technical data table
status: ground
source: hts-chrome-oxide
where: 'Technical data table, As-sprayed porosity row: up to 5% on standard APS'
- benchmark: porosity
label: Total porosity of Rokide C combustion-sprayed rod coating
value: 8.4
unit: '%'
scope: material
conditions:
product: Rokide C chrome oxide ceramic rod, combustion rod spray
method: Value printed in the Rokide C technical bulletin, Physical section
status: ground
source: rokide-c-tds
where: 'Coating features, Physical: Total porosity 8.4%'
- benchmark: max_service_temp
label: Maximum service temperature for wear service
value: 540
unit: °C
scope: material
conditions:
service: dry abrasive wear service
method: Value printed in the HTS Coatings technical data table, metric row
status: ground
source: hts-chrome-oxide
where: 'Technical data table, Max service temp (metric row): 540 °C wear service'
- benchmark: max_service_temp
label: Maximum service temperature for sealed corrosive service
value: 177
value_high: 205
bound: range
unit: °C
scope: material
conditions:
service: sealed coating in corrosive chemical environments
method: Range printed in the HTS Coatings technical data table, metric row
status: ground
source: hts-chrome-oxide
where: 'Technical data table, Max service temp (metric row): 177-205 °C sealed corrosive service'
- benchmark: coating_thickness
label: Typical thickness of thermal sprayed chromia
value: 75
value_high: 640
bound: range
unit: µm
scope: material
conditions:
process: typical thermal spray chromia coating
method: Range printed in the HTS Coatings technical data table, Typical thickness row
status: ground
source: hts-chrome-oxide
where: 'Technical data table, Typical thickness row: 3-25 (75-640 µm)'
- benchmark: density
label: Bulk density of Rokide C ceramic rod
value: 4.5
unit: g/cc
scope: material
conditions:
product: Rokide C chrome oxide ceramic rod, mostly Cr2O3
note: a rod product figure, not the density of pure chromia
method: Value printed in the Rokide C technical bulletin, Physical section
status: ground
source: rokide-c-tds
where: 'Coating features, Physical: Bulk Density 4.5 g/cc'
- benchmark: particle_size
label: Feedstock particle size, Metco 6156 powder
value: -35
value_high: 15
bound: range
unit: µm
scope: material
conditions:
product: Metco 6156 powder as received, sieve range as printed
method: Size range printed in the Experimental details section of the paper
status: ground
source: odhiambo2021
where: 'Experimental details, first paragraph and Table 1: particle size -35 to +15 um'
corrosion:
- environment: Sealed chromia in acidic and alkaline solutions
headline: The HTS page says sealed coatings hold up through 30-day immersion across pH 0-10 with no loss of wear resistance.
effect: The HTS page attributes this to a Journal of Thermal Spray Technology study of plasma sprayed chromia and alumina sealed with aluminum phosphates. The primary paper could not be opened for this profile, so the result rests on the HTS summary.
rating: low
conditions:
sealant: aluminum phosphate (per the HTS page)
test: immersion in acidic and alkaline solutions, as summarized by HTS
basis: secondary summary of a primary study
source: hts-chrome-oxide
where: Sources section (Journal of Thermal Spray Technology entry) and Where it doesn't section
- environment: Unsealed plasma sprayed coating with open porosity
headline: 'Open porosity is the weak point: standard APS coatings run up to 5% porosity, so sealing is specified for aggressive chemistry.'
effect: The HTS page lists sealing with epoxy, aluminum phosphate or polymer impregnation for aggressive chemical environments. The Odhiambo paper finds that the coating with higher porosity (8%) had the lower tensile bond strength (12.24 MPa against 23.60 MPa at 4%), so porosity also weakens the bond to the steel. This is an adhesion result, not a corrosion test.
rating: moderate
conditions:
basis: qualitative corrosion ranking from the HTS page; porosity and bond comparison from the Odhiambo paper
source: hts-chrome-oxide
where: Porosity bullet in Where it doesn't; Porosity row of the technical data table
- environment: High temperature in wear or sealed corrosive service
headline: The table gives a wear ceiling of 540 °C and a sealed corrosive ceiling of 177 to 205 °C.
effect: The HTS page says the sealed corrosive ceiling is the limit in chemical service and advises stepping over to Cr3C2-NiCr for higher-temperature wear. The page does not say what fails above these ceilings.
rating: moderate
conditions:
basis: service ceilings as printed by HTS Coatings
source: hts-chrome-oxide
where: Technical data table, Max service temp row; Where it doesn't section
risks:
hazards:
- text: PubChem's GHS summary for CID 517277 says the substance 'does not meet GHS hazard criteria for 57.8% (1112 of 1924) of all reports'. Its hazard statements are H302, H317, H319 and H360, with the signal word Danger and pictograms GHS07 and GHS08.
ghs:
- H302
- H317
- H319
- H360
source: pubchem-cr2o3
where: Safety and Hazards, GHS Classification (CID 517277)
- text: A Johnson Matthey safety data sheet for Katalco 71-5, a Grade 2 chromium(III) oxide classified by an EU registrant, is stricter. It lists H314 (causes severe skin burns and eye damage), H340, H350 (may cause cancer), H361 and H371, with the signal word Danger. It is a different product, but it shows that classifications for this oxide disagree between sources.
ghs:
- H302
- H312
- H332
- H314
- H334
- H317
- H340
- H350
- H361
- H335
- H371
- H373
- H411
source: jm-katalco-sds
where: 'Section 1, classification and labelling: hazard statements and classification table'
failure_risks:
- mode: Chipping under impact
trigger: Point-loaded impact or edge loading
consequence: Chromia is a ceramic, so impact chips the coating. The HTS page says to specify it for sliding, erosive and corrosive duty, not impact.
severity: moderate
source: hts-chrome-oxide
where: Limitations list, Brittle bullet
- mode: Spalling of thick build-up
trigger: Build-up beyond the practical limit on cylindrical work
consequence: The HTS page says 'Thickness limited to roughly 25-30 mils on cylindrical work before residual stress risks spalling'. Typical thickness is 75 to 640 µm.
severity: moderate
source: hts-chrome-oxide
where: Limitations list, thickness bullet; Technical data table, Typical thickness row
- mode: Service above the ceiling for the duty
trigger: Service above 540 °C for wear, or above 177 to 205 °C in sealed corrosive service
consequence: The table gives these as ceilings. The HTS page does not describe the failure mode above them.
severity: moderate
source: hts-chrome-oxide
where: Technical data table, Max service temp row
handling:
- text: For the Cr2O3-TiO2 blend Metco 6485 from the same maker (not pure chromia), keep the powder in its original container in a dry location, tumble it gently before use, and store open containers in a drying oven to prevent moisture pickup.
source: metco-6485-ds
where: Section 4.2, Handling Recommendations
- text: The HTS page says finishing requires diamond wheels, so plan the cost and lead time.
source: hts-chrome-oxide
where: Introduction, closing caveats paragraph
mitigations:
- text: Seal the coating with epoxy, aluminum phosphate or polymer impregnation for aggressive chemical service.
source: hts-chrome-oxide
where: Porosity bullet in Where it doesn't
- text: Apply over a corrosion-resistant bond coat for chemical service, as the HTS page describes for its own process.
source: hts-chrome-oxide
where: Introduction paragraph
uses:
- application: mechanisms
device: Mechanical seal faces, pump sleeves and impellers
example: The HTS page lists mechanical seal faces, pump sleeves and impellers in abrasive slurry among the parts it coats with chromia.
source: hts-chrome-oxide
where: Introduction paragraph (We use it for ...) and Applications list
- application: mechanisms
device: Flexographic printing anilox rolls, laser engraved after coating
example: The HTS page says chromia is the industry-standard surface for flexographic and gravure printing rolls because it takes laser engraving cleanly.
source: hts-chrome-oxide
where: Applications list and Where it earns its keep
- application: mechanisms
device: Wire drawing capstans, draw blocks and sheaves
example: The Saint-Gobain Rokide C bulletin lists wire drawing capstans, wire draw blocks and sheaves among the parts for which the rod is used.
source: rokide-c-tds
where: Applications list (right column)
supply:
- subject: Chromium (chromite ore, the feedstock for chromia)
producers:
- country: South Africa
share_percent: 45.1
year: 2025
- country: Turkey
share_percent: 17.6
year: 2025
- country: Kazakhstan
share_percent: 13.7
year: 2025
- country: India
share_percent: 5.9
year: 2025
- country: Brazil
share_percent: 3.9
year: 2025
- country: Zimbabwe
share_percent: 3.9
year: 2025
- country: Finland
share_percent: 3.7
year: 2025
recycling: 'USGS: ''recycled chromium (contained in reported stainless-steel scrap receipts) accounted for 21% of apparent consumption'' in the United States in 2025.'
substitutes: []
source: usgs-mcs2026-chromium
where: World Mine Production and Reserves table, 2025e column (world total printed as 51,000 thousand t; the table header gives chromium content); shares calculated by Space Mushroom from the seven countries listed; Recycling paragraph. Other countries (3,000 thousand t) are excluded from the shares.
documents:
- title: 'HTS Coatings: Chrome oxide technical data table (web product page)'
type: datasheet
url: https://htscoatings.com/coatings/chrome-oxide
year: 2026
- title: Saint-Gobain Rokide C (Chrome Oxide) ceramic rod technical bulletin, copy hosted by Alloy Coating Supply
type: datasheet
url: https://store.alloycoatingsupply.com/wp-content/uploads/2023/11/Rokide-C-Rods-Technical-Data-Sheet.pdf
year: 2023
- title: Influence of plasma spraying current on the microstructural characteristics and tribological behaviour of plasma sprayed Cr2O3 coating (open access)
type: paper
url: https://www.elsevier.es/en-revista-boletin-sociedad-espanola-ceramica-vidrio-26-articulo-influence-plasma-spraying-current-on-S0366317520300340
year: 2021
- title: 'USGS Mineral Commodity Summaries 2026: Chromium'
type: report
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
year: 2026
- title: 'PubChem: Chromium(III) oxide (CID 517277), GHS classification and experimental properties'
type: database
url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/517277/JSON
year: 2026
- title: 'Oerlikon Metco data sheet DSM-0387.1: Chromium Oxide - Titanium Oxide Powders (Metco 6485)'
type: datasheet
url: https://www.oerlikon.com/ecoma/files/DSM-0387_Cr2O3_40TiO2.pdf?download=true
year: 2024
- title: Johnson Matthey (C&L) safety data sheet, Cr - Chromium (III) Oxide, Katalco 71-5 (IUCLID 6 export)
type: sds
url: https://matthey.com/documents/161599/166998/Cr-Chromium-III-Oxide-Katalco-715.pdf/dcfbe5f7-6cc9-a7c9-0d92-7d2339ca4759
year: 2020
gaps:
- No vacuum, radiation, thermal-vacuum or flight data for chromia coatings were found in any source we hold; this profile has no space application.
- 'The Saint-Gobain chromia data sheet, the Saint-Gobain #300 series chromium oxide data sheet, the Cincinnati Thermal Spray CT1302-1 data sheet, the American Elements SDS and the Journal of Thermal Spray Technology paper by Leivo et al. on sealed chromia could not be opened (403, access denied or not found), so their figures are not used.'
- The two MDPI papers on plasma sprayed Cr2O3 (Crystals 2023 and Coatings 2023) returned access denied, so their porosity, hardness and bond figures are not used.
- The Odhiambo paper states the feedstock as Blended in Table 1 but as sintered and crushed in its text, and gives 99.7 in Table 1 but 99% purity in its text; neither composition figure is recorded as a property.
- Odhiambo paper results section porosity values are garbled (8.% and 4.%); the correlation section values of 8% and 4% are used instead.
- Density of a sprayed pure chromia coating was not found; the 5.22 g/cm3 value is for bulk crystalline Cr2O3, and the 4.5 g/cc value is for the Rokide C rod, which is mostly Cr2O3.
- Coefficient of thermal expansion, thermal conductivity and total emittance for Rokide C are printed in exponent or estimate form and are left out (Rokide C bulletin, Thermal section).
- Atomic weights of chromium and oxygen and the crustal abundance of chromium were not read in any source we hold.
- Critical-mineral list status for chromium was not confirmed in the fetched USGS text, so no critical_lists entry is given.
- No UNS, EN, DIN, JIS or AISI designation was found for chromia powder or coating; only the Metco 6156 trade name is printed in a source.
- The sealed-chromia corrosion result rests on the HTS summary of the primary paper; no coating corrosion rate in mm per year or mass loss was found.
- Pure-chromia supplier SDS for hazards was not reachable; hazard data rest on PubChem and on one registrant classification for a different product (Katalco 71-5).
- Non-canonical benchmark names are used for hardness (vickers_hardness, rockwell_c_hardness), bond strength (bond_strength), porosity, coating thickness (coating_thickness) and particle size (particle_size).
sources:
hts-chrome-oxide:
title: 'Chrome oxide thermal spray coating: technical data table, applications and sources (HTS Coatings)'
id: HTS Coatings product page, /coatings/chrome-oxide
url: https://htscoatings.com/coatings/chrome-oxide
year: 2026
kind: web
license: supplier web page, linked not reproduced
wikipedia-cr2o3:
title: Chromium(III) oxide, Wikipedia
id: Wikipedia article Chromium(III) oxide
url: https://en.wikipedia.org/wiki/Chromium(III)_oxide
year: 2026
kind: web
license: CC BY-SA 4.0 (Wikipedia)
rokide-c-tds:
title: Rokide C (Chrome Oxide) ceramic rod for thermal spraying, Saint-Gobain Coating Solutions technical bulletin
id: Saint-Gobain Coating Solutions Rokide C bulletin, copy on Alloy Coating Supply
url: https://store.alloycoatingsupply.com/wp-content/uploads/2023/11/Rokide-C-Rods-Technical-Data-Sheet.pdf
year: 2023
kind: datasheet
license: manufacturer document, linked not reproduced
odhiambo2021:
title: Influence of plasma spraying current on the microstructural characteristics and tribological behaviour of plasma sprayed Cr2O3 coating
id: doi:10.1016/j.bsecv.2020.03.007 (Bol. Soc. Esp. Ceram. Vidr. 60, 338-346, 2021)
url: https://www.elsevier.es/en-revista-boletin-sociedad-espanola-ceramica-vidrio-26-articulo-influence-plasma-spraying-current-on-S0366317520300340
year: 2021
kind: paper
license: open access, as listed on the journal page
usgs-mcs2026-chromium:
title: Mineral Commodity Summaries 2026, Chromium
id: USGS MCS 2026, February 2026
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
year: 2026
kind: report
license: public domain (USGS)
pubchem-cr2o3:
title: 'PubChem compound record, Chromium(III) oxide (CID 517277): GHS classification and experimental properties'
id: CID 517277; CAS 1308-38-9
url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/517277/JSON
year: 2026
kind: database
license: public domain (NCBI)
metco-6485-ds:
title: Chromium Oxide - Titanium Oxide Powders (Metco 6485), Oerlikon Metco data sheet DSM-0387.1
id: DSM-0387.1 (c) 2024 Oerlikon Metco
url: https://www.oerlikon.com/ecoma/files/DSM-0387_Cr2O3_40TiO2.pdf?download=true
year: 2024
kind: datasheet
license: manufacturer document, linked not reproduced
jm-katalco-sds:
title: Cr - Chromium (III) Oxide C&L Katalco 71-5, classification and labelling (IUCLID 6 export)
id: Johnson Matthey C&L record, Grade 2 Chromium (III) Oxide, generated 11/12/2020
url: https://matthey.com/documents/161599/166998/Cr-Chromium-III-Oxide-Katalco-715.pdf/dcfbe5f7-6cc9-a7c9-0d92-7d2339ca4759
year: 2020
kind: datasheet
license: registrant document, linked not reproduced
license: CC-BY-4.0
updated: '2026-11-02'
review:
status: draft
method: assistant
checked_values: 19
unreachable: 7
caveats: 3
note: Written by an AI assistant on 2026-11-02 from fetched pages only; 19 benchmark values carry a source read in this run. Seven further sources were blocked or not found and are listed in gaps.
story:
recipe:
line: Chromia is chromium(III) oxide, Cr2O3. It is made from chromite ore by converting it through sodium dichromate, which is reduced with sulfur at high temperature. The Metco 6156 feedstock used in the Odhiambo paper is a sintered and crushed powder.
parts:
- name: Chromium
symbol: Cr
role: The oxide-forming metal. Chromium sits at the centre of the corundum framework that the oxide forms.
- name: Oxygen
symbol: O
role: Fills the close-packed oxide framework with chromium in its octahedral holes, which gives a hard, brittle ceramic.
risk_groups:
- title: For people
level: 0
verdict: Classification differs between sources
lead: Chromium(III) oxide is classed as hazardous by some sources and not by others. The sources disagree, so handle the powder as a possible sensitizer and reproductive hazard until your own safety data sheet says otherwise.
points:
- label: The powder
line: PubChem's summary says the substance does not meet GHS hazard criteria for 57.8% (1112 of 1924) of all reports. The rest carry hazard statements H302, H317, H319 and H360.
- label: Stricter registrant entry
line: A Johnson Matthey classification for Katalco 71-5, a Grade 2 chromium(III) oxide, lists H314, H340, H350, H361 and H371 with the signal word Danger. That is a different product, but it shows how far classifications can differ.
- label: Powder dust
line: The Oerlikon blend data sheet advises a dry place and an original container. It does not give a dust exposure limit for chromia.
- title: If a coating fails
lead: These points describe the coating's own limits, not people's exposure.
points:
- label: Impact
line: Chromia is brittle. Point impact or edge loading chips the coating, so the HTS page says to specify it for sliding, erosive and corrosive duty, not impact.
- label: Thickness
line: The HTS page says 'Thickness limited to roughly 25-30 mils on cylindrical work before residual stress risks spalling'.
- label: Temperature
line: The table sets the wear ceiling at 540 °C and the sealed corrosive ceiling at 177 to 205 °C.
- title: Handling and storage
points:
- label: Storage
line: Keep Metco 6485 powder in its original container in a dry location, and dry any open container in an oven before use. That data sheet is for a chromia-titania blend, not pure chromia.
- label: Finishing
line: Finishing needs diamond wheels, so the HTS page says to plan the cost and lead time.
why: 'Chromium(III) oxide, Cr2O3, is a corundum-structure oxide that is sprayed onto steel to make a hard, wear-resistant layer. The HTS Coatings technical table gives a typical Vickers hardness of 900 to 1200 HV300 for plasma sprayed coatings, and the Odhiambo paper measured 1496 HV300 g and 1762 HV300 g for two coatings sprayed at different currents. The trade-off is brittleness: the same sources say chromia chips under impact and must be sealed for chemical service. The HTS page points to sliding, abrasive and corrosive duty as where it is used.'
uses:
- where: Printing anilox rolls
line: The HTS page says chromia is the industry standard surface for flexographic and gravure printing rolls because it takes laser-engraved cells cleanly. It also lists mechanical seal faces and pump sleeves.
- where: Pump and seal parts
line: The Saint-Gobain Rokide C bulletin lists pump sleeves, pump shafts, impellers, mechanical seal faces and ball valves among the parts it coats. The rod is mostly Cr2O3 with silica and alumina, so it is not pure chromia.
- where: Wire drawing
line: Wire drawing capstans, draw blocks, sheaves and pulleys are also listed for the Rokide C rod. No space or flight use was found in any source we hold.
can_do:
- label: Wear
line: Resist sliding and abrasive wear on steel parts. The HTS page calls chromia the hardest common oxide ceramic in thermal spray.
- label: Finish
line: Take a laser-engraved cell pattern for printing rolls, which is why it is used for anilox rolls.
- label: Chemistry
line: Hold up in alkaline or mildly acidic media when the coating is sealed, according to the HTS page.
- label: Seal faces
line: Work as a seal face where the part does not take impact.
compare: Chromia is hard and brittle. Its melting point is 2435 °C as bulk crystal, and a typical plasma sprayed coating has a Vickers hardness of 900 to 1200 HV300. The HTS technical table caps wear service at 540 °C. Adding titania to chromia makes the coating less brittle, according to the Oerlikon data sheet for a chromia-titania blend. The Oerlikon sheet does not give hardness values for the blend that can be compared here, so this profile compares only pure chromia figures.
compare_rows:
- label: Melting point
benchmark: melting_point
- label: Vickers hardness (typical APS)
benchmark: vickers_hardness
- label: Maximum service temperature (wear)
benchmark: max_service_temp
handling:
- The coating powder is not classed as hazardous by every source. The sources disagree, so read the supplier's safety data sheet for the exact product.
- Keep the powder dry and in its original container, and dry open containers in an oven before use (Oerlikon blend data sheet).
- Finish with diamond wheels, and plan the cost and lead time.
good_for:
- Wear on sliding and abrasive surfaces, such as seal faces and printing rolls. The HTS page says the coating outlasts steel in these duties.
- Corrosion in mild acid and alkali once the coating is sealed. The HTS page quotes 'hold up through 30-day immersion across pH 0-10'.
watch_out:
- Brittleness. Point impact chips the coating, and the HTS page says not to specify it for impact.
- Porosity. Standard plasma sprayed coatings run up to 5% porosity, and the Odhiambo paper ties higher porosity to lower bond strength.
- Temperature. The wear ceiling in the table is 540 °C and the sealed corrosive ceiling is 177 to 205 °C.
verdict: Chromia is the hard, brittle choice for sliding wear and seal faces, and it works only if impact is kept out and the coating is sealed for chemistry.
References
Every number above carries a reference number. Click one to see the source and where in it the value comes from.
| # | Source | Type | Year | Used for |
|---|---|---|---|---|
| Chrome oxide thermal spray coating: technical data table, applications and sources (HTS Coatings) | web | 2026 | 18 values | |
| Chromium(III) oxide, Wikipedia | web | 2026 | 2 values | |
| Rokide C (Chrome Oxide) ceramic rod for thermal spraying, Saint-Gobain Coating Solutions technical bulletin | datasheet | 2023 | 4 values | |
| Influence of plasma spraying current on the microstructural characteristics and tribological behaviour of plasma sprayed Cr2O3 coating | paper | 2021 | 7 values | |
| Mineral Commodity Summaries 2026, Chromium | report | 2026 | 1 value | |
| PubChem compound record, Chromium(III) oxide (CID 517277): GHS classification and experimental properties | database | 2026 | 2 values | |
| Chromium Oxide - Titanium Oxide Powders (Metco 6485), Oerlikon Metco data sheet DSM-0387.1 | datasheet | 2024 | 1 value | |
| Cr - Chromium (III) Oxide C&L Katalco 71-5, classification and labelling (IUCLID 6 export) | datasheet | 2020 | 1 value |