Zirconia ceramic is an extremely hard, resilient material with excellent thermal and fracture toughness properties that is resistant to oxidation. Additionally, it boasts high heat tolerance as well as having high heat tolerance - all qualities which have led to its widespread application across metal casting to grinding wheels - even known by some as ZrO2.
Producing zirconia ceramics involves several processes. These include calcination, cold sintering, hot sintering and the creation of yttrium-stabilized zirconia (YTZ). Of these methods, calcination is usually employed as it creates thermal decomposition by heating materials at extreme temperatures while restricting oxygen - thus leading to decomposition and eliminating impurities from their material composition.
Yttrium-stabilized zirconia ceramic is an ultrahard ceramic that contains yttrium oxide for increased durability and hardness, making it more resilient than alumina ceramics and capable of withstanding temperatures of up to 1900o C without chemical reaction, while having a higher melting point than other ceramics. Crucibles and melting pots commonly use this type of ceramic.
Zirconia has long been used in dentistry as a material for restorations such as crowns and bridges, due to its excellent survival rate when cemented with resin cements. Furthermore, monolithic zirconia restorations with translucent properties are also possible; however complications with such restorations such as bond failure and ceramic veneer damage should still be taken into consideration when making decisions regarding them.
One or more factors could contribute to zirconia veneering failure, including differences in thermal coefficients, liner material and core wetting, cooling compressive stresses, phase transformation stresses, loading stresses, flaw formation, color pigments and surface properties. Some factors are easier to manage than others, yet understanding and preventing zirconia veneering failure cannot be understated.
This issue can be alleviated by opting for pre-sintered zirconia blocks and avoiding overpressing. This will ensure the zirconia densifies to its full theoretical density for superior mechanical properties.
An alternative solution would be to switch over to using an electric field for sintering instead of conventional furnaces, as this will help avoid issues related to overpressing and the formation of microvoids.
Sintering zirconia ceramic involves mixing powdered mix and liquid carrier together and placing this in an electric furnace at very low temperatures, where it is then sintered at high pressures and temperatures. The liquid carrier acts to aid rearrangement and interdiffusion between particles while also increasing strength while decreasing porosity of ceramic structures.
Pre-sintered zirconia provides many advantages over alumina in terms of uniformity and density, resistance to abrasion and corrosion, as well as increased longevity.
