All that we need to know about Stabilized Zirconia

Often called as ceramic steel, Zirconia is a tough technical ceramic that has been used in variety of applications. It offers great wear and tear resistance; it is super hard and has good thermal stability. However, Zirconia is often stabilized to retard its changing behaviors with respect to heat loads.

What is Zirconia?

Zirconium dioxide (ZrO2) often termed as Zirconia, in its purest form is found in the natural ore of baddeleyite.  Synthetically, Zirconium dioxide can also be manufactured from Zircon. Zircon (ZrSiO4) is often found in mineral or sand deposits.  Synthetic Zirconia (ZrO2) is prepared by melting the Zircon stand at very high temperature. Given is a figure representing the wide range of properties of ceramics.

The properties of ZrO2: a quick glance

Knowing about the properties of ZrO2 ceramic is very important. Let us have a look at the major properties.

What is Zirconia used for?

Listing out some of the prominent applications of ZrO2:

• For the manufacture of High-Pressure equipment valves such as ball valves and the associated seats

• Thermal barrier coating in Diesel engines and refractory material

• Oxygen sensors

• Crown and bridges and other dental restorations and prosthetics in body

• To prepare toughened ceramic Knifes, threads and wires

• Used as a photocatalyst

• Cubic Zirconia is used as synthetic diamond which is cost effective in comparison with actual diamonds.

• Used to manufacture membrane in Fuel cells due to the ion exchange ability.

Cubic Zirconia: A diamond substitute

Zirconium dioxide in its crystalline form is known to be Cubic Zirconia. Cubic Zirconia is known to be a man-made mineral. Sometimes it is also known as Zirconium silicate as people disguises it with Zircon. Cubic Zirconia is a metal preferred for people who likes diamond and cannot afford to have one. In the global market cubic zirconia is often used as synthetic gemstone.

They are isometric in its crystalline nature and are good diamond material. The density of Cubic Zirconia is in between 5.5 to 6 g/cm3.They are relatively hard. The Mohs value of hardness is in between 8 – 8.5 scale. The refractory index of cubic Zirconia ranges from 2 to 2.18.

Other than being used as diamond, cubic zirconia are also as dental implants, structural components in industries and prosthetics

The effect of temperature on Zirconium dioxide (ZrO2) and the need for stabilization

Let’s discuss about the behavior of Zirconium dioxide at different temperature of operation. ZrO2 undergoes phase transition under subjected temperature. During the temperature change from 1173 degC to 2370 degC, ZrO2 transforms from monoclinic to tetrahedral structure. Further when the temperature reaches 2690 degC, ZrO2 becomes cubic and then further rise in temperature causes ZrO2 to melt.

Since the phase transition also indicates a volume change, the ceramic is prone to cracking and other deformation.  Hence stabilization of ZrO2 is very essential to make the metal work at different temperature of application.

Yttria Stabilized Zirconia (Y2O3.ZrO2)

YSZ is prepared by stabilizing at room temperature with the help of Yttrium Oxide (Y2O3).  Stabilization involves the substitution of Zr4+ with larger ions of Yttrium such as Y3+ in the crystal lattice. The ionic radius of Zr4+ and Y3+ are 0.82 A and 0.96A respectively.

The common stabilizers other than Yttrium are Magnesia (MgO), Ceria (CeO2), Calcia (CaO), Hafnia (HfO2) and Alumina (Al2O3). The stabilized Yttrium Zirconia (YSZ) has cubic structure.

Advantages of Yttria (Y2O3) stabilized (ZrO2) Zirconia

The advantages of Yttrium Zirconia are listed below:

• They offer extreme strength

• The ceramic YZS has high temperature resistance, often used as refractory  and thermal barrier coating

• They are corrosion resistant

• YSZ doesn’t undergo rusting and can be used where there are oxidation chances.

Applications of Yttria Stabilized Zirconia (YSZ)

Dentistry

Yttria stabilized Zirconia (YSZ) is used in dentistry due to their hardness, biocompatibility and chemically inert nature. They are used in dental crowns, Bridges and certain dental restorations. The corrosion resistance in the presence of moisture makes Yttrium Zirconia the best dental constituent.

Refractory

The extreme hardness of Yttrium ceramic makes it an ideal component for refractory and thermal barrier coating in engines. Yttrium Zirconia is also used to provide thermal insulation and handling of hot objects.

Fuels cells

Yttria stabilized Zirconia (YSZ) is used in the production of solid-state fuel cells. The conductivity pertaining to oxygen ion and the retardance of electron are the prominent properties looked at. The temperature of operation is around 800 – 1000 degC.

Other usages

The other uses of Yttrium ceramic are, they are best to make cement of extreme durability. YSZ are used in coatings. They are also used in precision grinding.

Magnesia Stabilized Zirconia (MSZ)

MSZ in comparison with Yttria stabilized Zirconia (YSZ) has less thermal conductivity and more stability in moist conditions. They are wearing resistant, extremely tough and are chemically inert. In structure, MSZ has tetragonal precipitates with cubic grains. The precipitates help the ceramic to attain stability in its monoclinic phase.

Properties of Magnesium Zirconia

• The temperature of operation is above 220 degC

• The prime features are high thermal stability, Wear and tear resistance

• Less thermal conductivity

• The thermal expansion helps to form conjunction of metal with ceramics

• Resistance to acids and base

The major applications of MSZ

• Used as Structural / technical ceramics

• Precision valve components and accessories

• Pump sleeves and pistons

• Solid oxide fuel components

• Used in Tube forming

Calcia Stabilized Zirconia (CSZ)

CSZ is formed when calcium oxide is added to Zirconium dioxide to stabilize it. The melting point of such ceramic is at 2700 degC. The density of the material is around 5.6 g/cm3. They are used in situations where high thermal stability is required. They offer extreme shock and thermal resistance.

Other applications include Coating for ensuring wear resistance and refractory, thermal barrier coatings.

Ceria Stabilized Zirconia (CSZ)

This specific type of ceramic as the name says uses Ceria to stabilize the Zirconia in its crystal lattice. They are chemically resistant and are basically used in application that requites high temperatures. The addition of ceria in it enhances the conductivity of Oxygen. They are used in fuel cells and Oxygen sensors.

The density of the ceramic is in the range of 6.6 g/cm3 and the purity of Ceria stabilized Zirconia is around 99 %. The applications of CSZ includes high stability grinding materials in paints and related industry.  They are also used as catalysts in exhaust systems in automobile industry.

Alumina Stabilized Zirconia (ASZ)

ASZ is made from combining high quality alumina in ZrO2 crystal lattice. This has an alumina percent range from 10 % to 50% depending upon the grade required. They offer high fracture toughness and great strength. ASZ are used in automotive applications, aerospace and components used in medical industry.

ASZ is also used as cutting tool manufacture. They are deployed in applications which require high performing ceramic counterparts. The stabilization helps it working perfect under harsh conditions.  The alumina density used in ASZ is around 3.7 – 3.8 g/cc.

Partially Stabilized Zirconia

Partially stabilized Zirconia (PSZ) has approximately 10 % MgO. This ceramic, offer extreme toughness and works at higher temperature. PSZ holds tetragonal structure which at higher temperature would turn to monoclinic. This type of ceramic holds about 4% - 10 % of YSZ.

The advantages of PSZ include Low thermal conductivity, better structural stability, extreme toughness and cost effectiveness. They are often used in thermocouples. If extreme toughness is a priority, engineers often use PSZ over fully stabilized.

The fracture toughness of PSZ is 12 MPam1/2 and is blended with 10% MgO. They are good shock absorbers. This ceramic is used as weld area pins and often benefit oil and gas industry.

Comparison chart of Prominent ceramics

Bottom Line

The advancement in material technology ensured the best material for every field. Functionality is the key when it comes to choosing new gen ceramic for desired application. Stabilization ensures that it performs best at the desired temperature. When it comes to adaptability, of no doubt stabilized Zirconia Ceramic is superior.