Zirconia Oxide Characteristics and Applications

Zirconia all-ceramic material is a crucial material for the development of modern high-tech industries. With the advent of the 5G era for mobile phones, zirconia all-ceramic has gained significant attention and become a hotspot in the industry due to its jade-like warm texture, scratch and Wear Resistance, minimal signal shielding, and excellent thermal dissipation properties. It is now applied in structural components such as phone cover plates and fingerprint modules.

I. Introduction to Zirconia Oxide

Zirconia all-ceramic, or ZrO₂ ceramic (Zirconia Ceramic), possesses excellent properties including high melting and boiling points, high strength coupled with toughness, excellent wear resistance, high surface smoothness, and insulating behavior at room temperature while exhibiting conductivity at high temperatures. Pure ZrO₂ is white but appears yellow or gray when containing impurities, often including HfO₂, which is difficult to separate. Global proven zirconium resources are approximately 19 million tons. Zirconia is typically purified from zirconium ore. Due to its phase transformation toughening characteristics, most high-end ceramic materials for consumer electronics are zirconia all-ceramic.

Zirconium dioxide (ZrO₂) exists in three crystal forms: low-temperature monoclinic (m-ZrO₂), mid-temperature tetragonal (t-ZrO₂), and high-temperature cubic (c-ZrO₂). These three crystal forms exist within different temperature ranges and can transform into one another.

II. Performance and Characteristics

Zirconia all-ceramic is a new type of high-tech ceramic, often regarded as the nobility among ceramics. Besides meeting conditions such as high strength, hardness, high-temperature resistance, acid and alkali corrosion resistance, and high chemical stability, it also features scratch and wear resistance, no signal shielding, excellent thermal dissipation, strong machinability, good aesthetic appeal, and suitability for mass production.

1. High Melting Point
   Zirconia has a melting point of 2715°C. Its high melting point and chemical inertness make it an excellent refractory material. This property also addresses concerns in dentistry—if a zirconia restoration detaches, the adhesive can be burned off with an alcohol lamp without affecting re-bonding or reuse.

2. High Hardness and Excellent Wear Resistance
   Zirconia exhibits high hardness and excellent wear resistance. In terms of specific data, cubic zirconia (synthetic diamond) has a Mohs hardness of around 8.5, very close to sapphire's rating of 9. In comparison, polycarbonate has a Mohs hardness of only 3.0, tempered glass 5.5, aluminum-magnesium alloy 6.0, and Corning® Gorilla® Glass approximately 7.

3. Relatively High Strength and Toughness
   Zirconia possesses high strength (up to 1500 MPa). Although its toughness lags behind some metals, it is considered outstanding within the "ceramic realm" compared to other ceramic materials (fracture toughness typically ranging 1-35 MPa·m¹/²).

4. Low Thermal Conductivity and Low Coefficient of Thermal Expansion
   Zirconia has the lowest thermal conductivity among common ceramic materials (1.6-2.03 W/(m·K)), and its coefficient of thermal expansion is close to that of metals. Therefore, zirconia ceramic is suitable for structural ceramic components, such as mobile phone exterior structural parts.

5. Excellent Electrical Properties
   Zirconia's dielectric constant is three times that of sapphire, leading to more sensitive signal response, making it more suitable for components like fingerprint recognition patches. From the perspective of shielding effectiveness, zirconia ceramic, as a non-metallic material, does not shield electromagnetic signals at all. It completely avoids interference with internal antenna layout, allows for convenient integrated molding, and is well-suited for the upcoming 5G era.

III. Typical Applications (Fields)

Zirconia finds extensive applications in modern industry and daily life. Below is a brief introduction to its main applications.

1. Mobile Phones and Other 3C Electronic Fields
   Due to its non-signal shielding, drop/wear/bend resistance, jade-like appearance, and comfortable feel, zirconia is widely used in mobile phones and other 3C electronic fields, primarily as mobile phone backplates and other structural components.

2. Optical Communication Field
   Ceramic ferrules and sleeves are now widely used in fiber optic connector plugs. Ferrules made from high-strength and high-toughness ceramics not only meet high-precision requirements but also offer long service life with very low insertion loss and return loss.

3. Automotive Field
   Zirconia ceramic has a small thermal conduction coefficient but a relatively large coefficient of thermal expansion. This combination provides good thermal insulation when used for engine combustion chamber components, while its thermal expansivity remains relatively close to metal materials. Potential applications include cylinder head baseplates, cylinder liners, piston tops, and valve seat rings. However, due to the harsh working conditions of engines and significant changes in the strength of ceramic components at high temperatures, commercial application still requires further development.