Zirconium oxide and aluminum oxide put together yield Zirconia Toughened Alumina (ZTA), an exceptional material in many applications. Mechanical properties, strength, fracture toughness, elasticity, hardness and wear resistance are highly appreciated in this composite ceramic material which belongs to the class of AZ composites. ZTA has become the preferred choice for high mechanical strength, thermal resistance and corrosion resistance.
Decoding the Composition and Structure
Among other things, Zirconia Toughened Alumina consists of zirconia grains dispersed uniformly within an alumina matrix. Normally, this includes 10-20% volume of ZrO2 in alumina. Depending on their proportions, constituent mixtures contribute to ceramics with specific features depending on a particular application.
Building Blocks: Alumina and Zirconia
The main components that are mixed to form ZTA are alumina and zirconia. Moreover, orthopedic implants have been utilizing this ceramic material known as Aluminum Oxide (Al2O3) in history due to its good biocompatibility as well as its great mechanical strength and fracture resistance.
Another outstanding property of zirconia is its low rates of corrosion as well as good chemical stability and high mechanical strength. Its Young’s modulus is in the same order of magnitude with stainless steel alloys.
How It Is Made
To produce ZTA means creating tetragonal-phase zirconia grains uniformly distributed throughout an alumina matrix. A crack tip stress concentration can alter a tetragonal crystal structure into a monoclinic one thereby leading to an associated increase in volume of zirconia. Such volume expansion effectively reverses or stops the growth of crack leading to greater toughness and strength.
Mechanical Properties of ZrO2-Al2O3 Ceramics
There is a wide range of mechanical properties exhibited by ZTA including superior hardness than conventional aluminas with similar density values, higher flexural strength than conventional aluminas and lower than conventional zirconias coefficient of linear thermal expansions (CLTE).
Zirconia Toughened Alumina has high mechanical strength and is thermally resistant hence it does not corrode. Below are some of ZTA’s properties:
Property Value
Chemical Formula Zr-Al2O3
Density 4.1-4.38 g/cm^3
Hardness 1750-2100 Knoop
Elasticity 45-49 x 10^6 psi
Flexure Strength 100-145 ksi
Poisson’s Ratio 0.26
Fracture Toughness 5-7 MPa m^1/2
Coefficient of Thermal Expansion 8.0-8.1 x 10^-6 1/C
Thermal Conductivity 20.0-21.0 W/mK
Shock Resistance 325 °C
Maximum Working Temperature 1650 °C
Applications of ZrO2-Al2O3 Ceramics
Zirconia Toughened Alumina is used in various applications such as those which require high strength and wear resistance. These include valve seals, sleeves, pump pistons, spraying nozzles and other industrial parts.
Biocompatibility of ZTA
In various studies, ZTA has been reported to produce no adverse tissue reaction upon implantation thus making it a good candidate for orthopedic load-bearing components. In addition, the hardness, toughness and strength exhibited by zirconia-alumina ceramics make them fit for orthopedic load-bearing components.
ZTA in Hip Arthroplasty
There have been considerable deliberations on ceramics like alumina, zirconia and zirconia toughened alumina (ZTA) as suitable materials in hip arthroplasty . These advantages of ZTA were achieved without having to incorporate the disadvantages associated with yttria-stabilized zirconia that exhibits high mechanical properties or alumina with its high inertness.
ZTA in Knee Arthroplasty
Mostly, ceramic implant designs for total knee arthroplasty (TKA) have been developed in order to handle the issue of allergic reactions that may occur in patients when modern titanium or cobalt-chromium alloy components release wear particles. The Zirconia Toughened Alumina (ZTA) Matrix Composite is a cutting edge biomaterial for such applications.
ZTA: The Promising Future
This involves continuous research as well as development on ways improving ZTA’s attributes and its potential uses. Another batch-processed Zirconia Toughened Alumina has been designed with mechanical properties in terms of flexural strength substantially lesser than those from commercially available Biolox® Delta. Another, such as silicon nitride ceramics composites introduced recently into hip arthroplasty also exhibits higher strength than alumina.The future is bright for ZTA with many applications and superior properties. Therefore, with evolving technology, it is expected that ZTA will be the basis for new concepts on various fronts especially on biomedicine.