Oxide Ceramics
Oxide ceramics are the sintered oxides of aluminum, zirconium and magnesium: alumina from 96 to 99.8 % Al₂O₃, yttria-stabilized zirconia (Y-TZP) and the alumina–zirconia blends between them. Alumina gives a hardness around 1,500 HV, dielectric strength above 10 kV/mm and service to about 1,600 °C at the lowest cost of any technical ceramic; zirconia trades some hardness for a flexural strength near 1,000 MPa and the highest fracture toughness of any monolithic ceramic. Together they account for most technical-ceramic parts made: insulators, substrates, seals, wear parts, knives and implants.
Popular oxide ceramic grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Alumina 96 | 350 | 190 | 3.72 | Not recommended | Not recommended | Default insulator and wear part at lowest cost |
| Alumina 99.5 | 380 | 260 | 3.9 | Not recommended | Not recommended | High purity: RF, high voltage, vacuum, 1,600 °C |
| Zirconia Y-TZP | 1,000 | 450 | 6.05 | Not recommended | Not recommended | Toughest ceramic; knives, seats, implants |
| ZTA | — | 260 | 4.15 | Not recommended | — | Alumina hardness with added zirconia toughness |
| Mg-PSZ | — | 350 | 5.75 | Not recommended | — | Thermal-shock-tolerant zirconia for pumps |
| 8Y-FSZ | — | 150 | 5.95 | Not recommended | — | Oxygen-ion conductor for sensors and fuel cells |
| Synthetic Sapphire | — | 400 | 3.98 | Not recommended | — | Transparent single-crystal alumina windows |
Choose oxide ceramics for
Electrical insulators and substrates that see heat, plasma or high voltage; wear liners, guides, seal faces and nozzles in abrasive flow; furnace tubes, thermocouple sheaths and crucibles; valve components, knives and implants that need the toughness of zirconia; and any ceramic part where price matters and the temperature stays below about 1,600 °C.
Look elsewhere when
The part is quenched or heated fast (Silicon Nitride or Cordierite — alumina cracks at a 200 °C step across a thick section), it must conduct heat while insulating (Aluminum Nitride), it sits in steam or hot water above about 200 °C for years (Y-TZP degrades — use Mg-PSZ, ATZ or alumina), the abrasive is harder than alumina or the part runs above 1,500 °C under load (Silicon Carbide), or one prototype must be machined to size without a firing run (Macor or Boron Nitride).
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Oxide ceramic by application
- High-voltage and RF insulation
- Alumina 99.5 for feedthroughs, standoffs and RF windows where dielectric loss must stay low; Alumina 96 for terminal blocks, sensor bodies and spark-plug insulators made in volume.
- Wear liners and seal faces
- Alumina 96 or ZTA for guides, liners, thread guides and seal rings; Zirconia Y-TZP where an edge takes impact — pump plungers, valve seats and balls.
- Implants and dental restorations
- Zirconia Y-TZP for crowns, abutments and femoral heads; ATZ where hydrothermal ageing is a concern; Alumina 99.5 for bearing couples.
- Furnace and molten-metal contact
- Alumina 99.5 tubes and crucibles to about 1,700 °C in air; MgO Ceramic and Spinel (MgAl2O4) crucibles for basic slags and reactive melts; Y2O3 where even alumina is attacked.
Working with oxide ceramic
- Forming & sintering
- Alumina and zirconia are dry-pressed, isostatically pressed, extruded or injection-molded from spray-dried powder, then sintered at 1,500–1,700 °C with 15–20 % linear shrinkage. As-fired tolerance is about ±1 % of the dimension; features that need better are green-machined before firing or ground afterwards.
- Grinding & lapping
- Dense oxides are finished only with diamond: surface and cylindrical grinding to ±0.01 mm, lapping and polishing to Ra 0.05 µm for seal faces. Zirconia grinds slower than alumina and can transform at the surface if it overheats — flood coolant and light passes. Chamfer every edge; a sharp ground edge is a starter crack.
- Joining & sealing
- Alumina is metallized (Mo-Mn or thin-film Ti-W) and brazed to Kovar or copper for hermetic packages; active-metal brazes (Ag-Cu-Ti) join it directly. Both oxides take epoxy below 150 °C, shrink fits and clamped joints with compliant gaskets. Zirconia is harder to metallize; design a mechanical joint where possible.
- Tolerances & design rules
- Keep the ceramic in compression; radius internal corners (≥ 0.5 mm) and avoid sharp threads. Wall thickness 1 mm minimum for pressed alumina, thinner in zirconia. Specify ground surfaces only where function needs them — every finished face adds cost.
Other ceramic series
Oxide Ceramics — frequently asked
What is oxide ceramic?
Oxide ceramics are the sintered oxides of aluminum, zirconium and magnesium: alumina from 96 to 99.8 % Al₂O₃, yttria-stabilized zirconia (Y-TZP) and the alumina–zirconia blends between them. Alumina gives a hardness around 1,500 HV, dielectric strength above 10 kV/mm and service to about 1,600 °C at the lowest cost of any technical ceramic; zirconia trades some hardness for a flexural strength near 1,000 MPa and the highest fracture toughness of any monolithic ceramic. Together they account for most technical-ceramic parts made: insulators, substrates, seals, wear parts, knives and implants.
Which grade of oxide ceramic should I use?
Alumina 96 for most insulators, wear liners, guides and seals — it is pressed in volume, metallizes well and costs the least. Alumina 99.5 when purity, dielectric loss or high-temperature strength matter: RF and high-voltage insulators, vacuum feedthroughs, semiconductor parts, anything above 1,500 °C. Zirconia Y-TZP when the part must survive a knock or a bending load — knives, valve seats, implant components, thin pins — with about three times the toughness of alumina. ZTA (alumina toughened with 10–20 % zirconia) sits between them for cutting tools and wear parts that need more than alumina without the cost of zirconia; Mg-PSZ is the coarser, thermal-shock-tolerant zirconia for pump and wire-drawing parts. 8Y-FSZ is chosen for its oxygen-ion conductivity (sensors, fuel-cell electrolytes), not its strength, and Synthetic Sapphire is single-crystal alumina for windows and wear surfaces that must be transparent.
Which grade of oxide ceramic is the strongest?
Zirconia Y-TZP has the highest yield strength in the series at 1,000 MPa; Alumina 99.5 follows at 380 MPa. Values are for each grade's default condition.
Which grade of oxide ceramic is easiest to machine?
C-820 Porous Magnesia (machinability fair, 45/100), then MgO Ceramic (22/100).
Y-TZP, Mg-PSZ, ZTA or ATZ?
Zirconia Y-TZP (3 mol % yttria, tetragonal) is the standard: 900–1,200 MPa flexural strength, toughness around 6–10 MPa·√m, fine grain for polished edges and implants. Mg-PSZ is coarser and lower in strength but tolerates thermal shock and hot water far better, which is why it is used for pump seals and extrusion dies. ZTA is alumina with 10–20 % zirconia — harder and cheaper than Y-TZP, tougher than alumina; ATZ is the reverse, a zirconia matrix with about 20 % alumina that resists low-temperature degradation. Pick by the failure mode you fear most: impact (Y-TZP), steam (Mg-PSZ or ATZ), abrasion (ZTA).
Is 96 % alumina good enough, or do I need 99.5 %?
For insulators, wear parts and structural pieces below 1,500 °C, 96 % is the engineering default — the 4 % glassy phase helps it sinter and metallize and costs less. Go to 99.5 % when the glass phase is the problem: RF loss at GHz frequencies, resistivity above 1,000 °C, attack by hot alkalis or plasma, semiconductor purity, or service above 1,500 °C where the grain-boundary glass softens. Strength is similar (300–400 MPa); thermal conductivity is higher in 99.5 % (about 30 versus 24 W/m·K).