Coefficient of thermal expansion of advanced ceramics

What is the coefficient of thermal expansion of advanced ceramics?

The coefficient of thermal expansion (CTE) is one of the most critical parameters in the design and application of advanced ceramics. It determines how much a material expands or contracts with temperature and plays a decisive role in multi-material components, high temperature environments and precision systems. Known for their excellent dimensional stability and low CTE values, advanced ceramics are used in a wide range of industries to meet demanding thermal performance requirements.

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Why the coefficient of thermal expansion is important

Thermal expansion mismatches between different materials can lead to thermal stress, cracking or delamination of composite structures. By selecting ceramics with the right coefficient of thermal expansion, engineers can minimize such risks and improve product reliability and service life.

Benefits of using low thermal expansion advanced ceramics:

Dimensional stability under thermal cycling

Low coefficient of thermal expansion (CTE) ceramics, such as silicon nitride (Si₃N₄), silicon carbide (SiC), and aluminum nitride (AlN), virtually do not expand or contract during temperature changes. This ensures that:

Consistent dimensional accuracy in high-precision applications (e.g., optics, semiconductors).
Prevents warping, distortion or misalignment during heating and cooling cycles.

Improved thermal shock resistance

The lower coefficient of expansion reduces internal stresses during rapid temperature fluctuations, thereby minimizing the risk of thermal cracking. This makes materials such as Si₃N₄ and SiC ideal for the following applications:

heat exchanger
Burner nozzles
Aerospace components
Automobile engine parts

Enhanced compatibility of multi-material components

When bonding ceramics to metals or other substrates, thermal mismatch is the primary cause of joint failure. Low coefficient of thermal expansion ceramics:

Reduction of interfacial stress in metal-ceramic brazing.
Improve the long-term hermeticity and reliability of electronic packages and feedthroughs.
Allows better CTE matching with semiconductors in electronics (e.g. GaN, Si).

Optical system excellence

In telescopes, laser systems, and metrology equipment, even micron-scale expansion can cause distortions in the optical path. Low coefficient of thermal expansion ceramics:

Optical alignment is maintained throughout the temperature range.
Widely used for mirrors, lens mounts and support structures in space and defense optics (e.g., SiC in space telescopes).

Extended component life

By reducing thermal fatigue and microcrack propagation, low CTE ceramics extend the life of the following components:

High Power Electronic Modules
High speed bearings
high temperature reactor

High reliability in vacuum or inert environments

In ultra-high vacuum or chemically inert systems where thermal stresses cannot be relieved by diffusion or relaxation, low CTE ceramics help:

Prevent structural failure.
Maintain tight tolerances on vacuum chambers, X-ray tubes and ion beam systems.

Coefficient of thermal expansion data for major advanced ceramics

Ceramic materials	(×10-⁶/K) at 20-300°C	hallmark
Silicon Carbide (SiC)	2.3	Extremely hard, excellent corrosion and wear resistance, high thermal conductivity
Silicon Nitride (Si₃N₄)	~3.7	High fracture toughness, thermal shock resistance, low density
Aluminum Nitride (AlN)	4.2~5.6	High thermal conductivity, electrical insulation, low dielectric loss
Beryllium oxide (BeO)	~6	Very high thermal conductivity, electrically insulating, toxic in powder form
Boron nitride (h-BN)	~7.2	Lubricating, thermally stable, electrically insulating
Aluminum oxide (Al₂O₃)	7.2~7.5	High hardness, good abrasion resistance, excellent electrical insulation properties
Machinable Glass Ceramics (MGC)	9.3	Easy processing, good dielectric strength, low thermal conductivity
Zirconium oxide (ZrO₂)	~10	High toughness, low thermal conductivity, phase change toughening

*Data is for reference only.

Need help choosing the right ceramic?

Choosing the right high-strength ceramic material is critical to ensuring long-term reliability and optimal performance. Whether you need zirconia, silicon nitride, or alumina-based ceramics, our materials provide industry-leading strength, durability, and precision.

Our technical team is here to help - contact us today for expert customized advice on your specific needs.

Comparison: Ceramics vs. metals and plastics

The bar chart below shows the coefficients of thermal expansion of various engineering materials - from super-hard ceramics to common industrial plastics, in descending order.

Ceramic

Metal

Plastic

*Data is for reference only.

Applications based on the coefficient of thermal expansion of ceramics

Semiconductor Equipment - Aluminum Nitride and Silicon Nitride Fixtures

Challenge:

During lithography and wafer processing, even micron-scale thermal expansion can lead to misalignment or equipment failure. Metal parts tend to expand significantly when exposed to heat.
Solution:
- Silicon nitride (Si₃N₄) and aluminum nitride (AlN) are used as structural or mounting components due to their low CTE (3.2-4.5 × 10-⁶/°C), ensuring dimensional stability during rapid thermal cycling.
- These materials also offer excellent thermal shock resistance and electrical insulation, further enhancing their suitability for use in semiconductor environments.

Metal-Ceramic Components - Alumina and Zirconia in Brazed Structures

Challenge:

Brazing ceramics to metals (e.g., deletable alloys, molybdenum) requires materials with matching or compatible CTEs to avoid cracking of the joint during temperature changes.
Solution:
- Aluminum oxide (Al₂O₃) has a coefficient of thermal expansion (CTE) of about 7.1, which is very close to that of a logging alloy (CTE) of about 6.5, making it a standard material for hermetically sealed feedthroughs, sensor housings, and electronic packages.
- For higher strength or toughness, zirconium oxide (ZrO₂) can be used, but with specialized brazing alloys or interlayers to accommodate its higher expansion (~10.5).

High Power LED Substrate-Aluminum Nitride

Challenge:

High-brightness LEDs generate a lot of heat, and the substrate must conduct it efficiently while maintaining mechanical integrity.
Solution:
- Aluminum nitride (AlN) has a high thermal conductivity (~170 W/m-K) and medium CTE (~4.5), making it an ideal substrate material.
- Its thermal expansion is compatible with GaN and other semiconductors, minimizing failures caused by thermal mismatch.

Aerospace and Defense - Silicon Carbide Optics

- Challenge:
  
  In satellites and space telescopes, optics experience extreme thermal gradients, which can lead to distortion and defocusing.
Solution:
- Silicon Carbide (SiC) was selected for the mirror structure due to its low CTE (~4.0), high stiffness and light weight.
- The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) use silicon carbide mirrors in missions such as the Gaia and Herschel space observatories.

Machinable glass-ceramics in precision fixtures

Challenge:

In prototype tools and metrology devices, thermal expansion affects dimensional accuracy.
Solution:
- MGC (machinable glass-ceramics) e.g. composites based on fluoro-gold mica have a moderate CTE (~9.0), close to some metal and glass types.
- These materials are used where custom molding, fast delivery and moderate thermal performance are required.