Zirconium oxide is the coating you spec when heat itself is the enemy. Pure ZrO2 has the lowest thermal conductivity in our ceramic lineup — 1.0 to 2.5 W/mK depending on chemistry, roughly 1/15th that of steel — and a 4900°F melting point no realistic combustion or molten-metal service will ever touch. That's the value proposition.

We spray it partially stabilized with CaO (~5%) or MgO (~24%) over a NiCrAlY or NiAl bond coat, typically 8-20 mils thick with 5-10% engineered porosity. Hardness runs 300-340 HV on partially-stabilized APS — this is not a wear coating. It's a thermal-insulation and molten-material-resistance coating, with a service ceiling around 900°C (1650°F) for CaO/MgO chemistries.

Honest positioning: pure ZrO2 is a legacy material for most modern thermal-barrier work. Gas-turbine hot sections and new TBC programs belong to yttria-stabilized zirconia (YSZ) — YSZ handles phase stability, CMAS attack, and long-term drift better than CaO or MgO grades. Where pure ZrO2 still earns its keep: glass-mold cavities where molten glass must not wet the tool, foundry tundishes and ladle surfaces, industrial furnace linings, and overhaul work on older diesel piston crowns or legacy TBC drawings.

Ask us about a modern hot-section turbine, we'll point you to YSZ. Glass plunger or foundry component — this is the right answer.

Technical data

Hardness: 297 HV0.05 for 5 wt% CaO-stabilized (CSZ); 339 HV0.05 for 24 wt% MgO-stabilized (MSZ); 800-1000 HV typical on well-consolidated APS partially-stabilized ZrO2
Hardness (HRC): Not the primary spec — zirconia is specified for thermal insulation, not Rc hardness; Vickers is the standard reference
Bond strength: 2,500-4,000 psi typical APS on steel with NiCrAlY or NiAl bond coat; segmented/vertical-crack coatings run lower but survive thermal cycling better
Max service temp: ~1650°F (900°C) for most CaO/MgO partially-stabilized APS formulations; ZrO2 itself melts at ~4900°F but phase transformation, not melt, is the service limit on pure/unstabilized ZrO2
Max service temp: 900°C standard service; melting point 2715°C; destructive tetragonal-to-monoclinic phase transformation window sits at 950-1170°C on unstabilized ZrO2
As-sprayed porosity: 5-10% on CaO-stabilized APS; 5-8% on MgO-stabilized APS; engineered porosity is desirable — it's what gives zirconia its low thermal conductivity
Typical thickness: 8-20 (200-500 µm) standard; 300 µm (~12 mils) is the most-referenced TBC thickness; segmented architectures can build thicker

Where it earns its keep

Lowest thermal conductivity in the common oxide-ceramic thermal-spray family — 1.0-1.5 W/mK for MgO-stabilized, roughly 1/15th that of steel — which is the entire reason thermal-barrier coatings exist
Melting point of 2715°C (~4900°F) means the ceramic itself never approaches its thermal limit in any practical combustion or melting application
Chemical inertness against molten glass — ZrO2 does not wet, dissolve in, or react with soda-lime or borosilicate melts, which is why it dominates glass-mold coating programs
Resists wetting and dissolution by most molten metals (iron, copper, aluminum), extending mold and tundish life between refurbishments
Tolerates thermal cycling when stabilizer chemistry is right — controlled porosity (5-10%) and segmented microstructure absorb strain that would crack a denser ceramic
Lower cost than yttria-stabilized zirconia (YSZ) when the application is steady-state thermal insulation and not hot-section gas turbine duty

Where it doesn't

Legacy material for modern TBC work — for gas-turbine hot sections, jet engines, and most new thermal-barrier programs, yttria-stabilized zirconia (YSZ) is the right pick and has been for decades. Pure ZrO2 is niche.
Stabilizer chemistry matters more than any other variable. Unstabilized ZrO2 undergoes a tetragonal-to-monoclinic phase transformation at 950-1170°C with a 3-5% volume change that cracks coatings on first thermal cycle. Never spec pure ZrO2 for anything that sees 900°C+ without CaO, MgO, or Y2O3 stabilization.
CaO and MgO stabilization is cost-effective and works for glass molds, foundry tooling, and furnace linings up to ~900°C — but CMAS attack, sintering, and long-term phase drift make these chemistries inferior to YSZ for hot-section turbine work
Relatively low hardness (300-340 HV on partially-stabilized APS) means zirconia is not a wear coating — do not spec it where abrasion or sliding dominates. It's a thermal and chemical coating.
Bond coat is non-negotiable. NiCrAlY or NiAl must sit under any zirconia top coat on metallic substrates; the CTE mismatch between ZrO2 and steel without an interlayer guarantees spallation
Porosity is a feature, not a defect — 5-10% is the sweet spot for thermal insulation and strain tolerance. Specifying 'dense zirconia' usually indicates a spec written for a different material

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

HTS Coatings — Ceramic Coatings (Zirconia)
“Zirconia (ZrO2) offers superior thermal barrier properties due to the presence of thermally stable oxide. Drastically improves the fatigue and creep life of the part resulting in extended service life.”
Scientific Reports — Plasma-sprayed CaO/MgO-stabilized zirconia wear and phase stability
“CSZ coating (5 wt% CaO) hardness 297 HV0.05; MSZ coating (24 wt% MgO) hardness 339 HV0.05. Porosity 5-10% for CSZ and 5-8% for MSZ under APS with NiAl bonding. Reversible transformation of monoclinic to tetragonal phase in the 950-1170°C range causes microcracks in unstabilized zirconia coatings.”
Zhenzhong Fused New Material — Zirconia Thermal Spray Powders (ZrO2/CaO and ZrO2/MgO)
“PCD-AP (CaO 4.5-5.5%, ZrO2+HfO2 ≥91.5%) for coatings on turbine hot components within 900°C, diesel engine pistons, valves and cylinder heads, casting molds and troughs. DMZ (MgO 22-26%, ZrO2+HfO2 ≥74%) for turbine hot components with drastic temperature changes within 900°C, effective against corrosion and wetting from high-temperature molten metals like copper and aluminum.”
Oerlikon Metco — Oxide Ceramic Powders (Zirconia Line)
“Metco 201NS is an unstabilized/partially stabilized zirconia APS powder; Metco 210 is a magnesium-zirconate APS powder. Oerlikon Metco offers oxide ceramic powders with particle size distributions optimized for plasma spray processes, including yttria-, calcia-, magnesia-, and gadolinia-stabilized zirconia chemistries.”
Amp Hard Chrome — Zirconia Thermal Barrier Coatings
“Pure zirconia experiences destructive phase transformations, so stabilisers such as magnesia, ceria, calcia and yttria are alloyed with the zirconia. Most formulations service to approximately 900°C (1650°F); Metco 202NS recommended for erosion resistance above 845°C.”
Reade — Calcia Stabilized Zirconium Oxide (ZrO2 + CaO)
“Calcia-stabilized zirconia (98-99.8% purity, CAS 11129-15-0) is used in refractory ceramic applications, thermal barrier coatings, wear-resistant coatings, and applications requiring high temperature, wear resistance, and frequent thermal cycling.”
Höganäs — Oxide Atmospheric Plasma Spraying Powders (AMPERIT)
“AMPERIT oxide thermal spray powders for APS include Y- and REO-stabilized ZrO2 grades; the production portfolio covers agglomerated and sintered, fused and crushed, and plasma spheroidised (HOSP) morphologies for thermal-barrier coating applications.”
Saint-Gobain Zirconia — Glass Furnace Refractories
“Zirconia is essential in AZS (Alumina-Zirconia-Silica) refractories for glass melting furnaces operating above 1,500°C, contributing exceptional corrosion resistance and chemical stability in the melting, refining, and working ends of industrial glass furnaces.”
Western AM Spec — Metco 210 Magnesium Zirconate Powder
“Metco 210 is a low-silica ZrO2 magnesium zirconate APS powder supplied for thermal-barrier coating applications; historically specified for diesel piston crown and combustion-chamber TBC work.”

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

Zirconium Oxide

Technical data

Where it earns its keep

Where it doesn't

Typical applications

Wear modes addressed

Industries

Substrates

Sources

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