Apr 3 2001
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The lack of a fully developed, commercially viable sintering process has limited the use of zirconium carbide (ZrC) in engineering applications.
At 1900 °C–2300 °C, hot pressing powders can achieve densities higher than 93%. Additives such as ZrB2 enhance the sintering process, and create ZrC with low porosity levels (2% to 4%) for 2 hours at approximately 2100 °C.
Zirconium carbide coatings can be deposited using two methods, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD).
Key Properties
Zirconium carbide (ZrC) is a transition metal carbide characterized by:
- High melting point
- Excellent hardness
- High strength
- Electrical conductivity
These properties of zirconium carbide make it a useful engineering ceramic.
Just like other carbides, the oxidation to carbon dioxide and zirconium oxide restricts the use of zirconium carbide in oxidizing environments.
Table 1. Typical Physical and Mechanical Properties of Zirconium Carbide
| Property |
Value |
| Density (g.cm-3) |
6.73 |
| Fracture Toughness K1c (MPa.m0.5) |
2.8 |
| Bend Strength (MPa) |
990 |
| Hardness (GPa) |
24.4 |
| Electrical Conductivity (Ohm.cm) |
78 x 10-6 |
| Melting Point (°C) |
3250 |
Applications
So far, the material has not been widely used in commercial applications, and it is usually found in development prototypes.
The following are applications mentioned in the literature:
Field Emitters
Field emission arrays are employed in flat video displays but they can also be used in spacecraft charge dissipation devices and microwave devices. When compared to display applications, many promising applications require high current per tip and the potential to operate in a vacuum. Moreover, transition metal carbides fulfill the property needs, and have been produced through vapor deposition.
Coating for UO2 Particle Fuel
The most promising fuel for high-temperature gas-cooled reactors is ZrC coated UO2 particle fuel. For metal fission products such as Cs, the layer serves as a diffusion barrier. SiC, which is used more often, can be replaced by ZrC. The CVD process is used to deposit the ZrC layer, which is compatible with fission products and UO2. The ZrC layer can also sustain a large strain at high temperatures.
Ultrahigh Temperature Applications
ZrC has good thermal shock resistance, high melting point, and does not exhibit phase changes in the solid-state. These aspects make it suitable for ultrahigh temperature applications. Components that operate at 2200 °C to 3000 °C would lead to a cleaner-burning rocket engine.
The applications of ZrC are limited by the lack of coating to protect it against oxidation, and the absence of a low-cost manufacturing process for near-net shaped components.