Zirconium oxide, also known as zirconia, is mainly derived from zircon ZrSiO4. It is more often prepared from zirconium silicate using high-temperature heat treatments supplemented with chemical treatments to eliminate the siliceous fraction of zirconia.
As it has phase transitions which may include dimensional variations at high temperatures (>1,000°C), "pure" zirconia cannot be used in powder form. For large parts, the use of oxides known as "stabilising agents" (essentially CaO, MgO or Y2O3) is required in proportions of 5 to 10% producing two major groups: partially stabilised zirconia (Y-TZP, 4YSZ and MgO-PSZ) and fully stabilised zirconia (FSZ, CSZ, 8YSZ, 8DSZ).
The zirconias are formed using traditional pressing or CIM procedures, or newer procedures such as the use of additives, then sintered between 1,400°C and 1,700°C.
Zirconias are mainly used for their thermal properties:
- Good resistance to thermal shocks and extreme temperatures
- Low thermal conductivity and also for their expansion coefficient, which is close to that of metals
They are also used for their chemical inertia/resistance to corrosion, their excellent mechanical properties and in particular their very good tenacity (can reach 10 MPa√m) and relative elasticity compared to other ceramics. For electrical insulation at room temperature, the material becomes ion conducting at higher temperatures (30 W.m-1 at 300°C).
Zirconias are widely used in the following applications, where their thermomechanical properties are particularly appreciated:
- Solid electrolytes
- Fuel cells
- Oxygen sensors
- Coatings for heat barriers in the thermal sector
- Dental implants, orthopaedic implants, insulators/wear parts for surgical instruments in the biomedical field
- Cutting tools, seals, bearings, thread guides in the mechanical engineering industry
- Watch and jewellery components in the watch and jewellery-making industries