Sapphire, which goes by the mineral name corundum, is a crystalline form of Al2O3 with a hexagonal structure. It boasts extreme physical, chemical and thermal durability, earning it an exceptionally broad range of applications in areas where resilience to extreme environments is required. Sapphire’s high electrical resistance and optical transmission properties also lend it to applications in photonics and electronics.
In this article, we outline the properties of sapphire and take a look at how Edge-defined Film-fed Growth is enabling the production of large and complex sapphire pieces that open up a range of previously impossible applications.
Although it is a naturally occurring precious gemstone, the sapphire used in high tech applications is usually synthetic.1,2 Commonly, applications of sapphire involve small quantities – e.g. watch face crystals and small lenses. However, thanks to breakthroughs in Edge-defined Film-fed Growth (EFG), sapphire can actually be manufactured in large, continuous pieces to suit virtually any application.
In EFG, a single-crystal piece of sapphire can be mechanically drawn from a liquid solution, enabling the production of complex shapes and very large single-crystal pieces of sapphire: Saint Gobain use EFG to produce the largest single-crystal sapphire tubes (up to 3” diameter) and windows (1 ft x 3 ft) in the world. Being able to control the shape and size of a sapphire crystal during its formation means that sapphire can now be produced for a much broader range of applications than was previously thought possible.
The increased manufacturability offered by EFG means that today, sapphire is more frequently being specified over commonplace but sub-optimal materials that were traditionally easier to work with; such as quartz, silicon carbide and zinc sulphide.12
Synthetic sapphire manufacturing is environmentally friendly and much less polluting than the production of many alternative materials. What’s more, synthetic sapphire is highly pure, with minimal contamination, no grain boundaries, and minimal defects; giving it a range of desirable properties:1,-3
- It's hard, stiff, and almost impossible to scratch.
Sapphire is one of the hardest materials on earth. Mechanical hardness is typically measured using the Mohs scale: glass generally has a Mohs score between 6 and 7, and hardened steel which comes in at 8 Mohs. Sapphire has a Mohs hardness value of 9, placing it just below diamond which has a hardness of 10 Mohs.
Furthermore, sapphire is very stiff. Its Young’s modulus is 435 GPa, making it 6 times stiffer than quartz, so it can’t be stretched or deformed easily.
These properties make sapphire one of the strongest and most durable materials on the planet.
- It’s chemically inert.
Sapphire’s stable crystal structure means that it won’t react with its surroundings. As a result, it can survive harsh chemical environments without damage.
- It transmits light without interference.
Sapphire has a high refractive index and a broad transmission window spanning the UV, visible, and infrared range. It also transmits X-rays.
- It conducts heat but is an electrical insulator.
Sapphire’s crystal structure makes it a superior thermal conductor (0.1 watts/cm°K at 1000°C) compared with ceramics and glass. It even maintains excellent conductivity at low temperatures (0.4 watts/cm°K at 25°C).
- It is temperature resistant.
Sapphire has a melting point of 2050 °C, so it can withstand extremely high temperatures without damage.
Applications of Sapphire
Sapphire is a truly multifunctional material, so it’s no surprise that it is already used in a wide range of high-tech applications. In fact, it’s difficult to find a branch of science or technology that doesn't use sapphire in some way. Here are some of the most demanding applications where sapphire proves its worth:
Semiconductor manufacturing components
The processes involved in semiconductor production are often extremely aggressive, requiring industrial-strength acids, alkalis, fluorine-based plasmas, and high temperatures. Quartz, alumina, and ceramics are frequently used in semiconductor manufacturing components, but these are quickly eroded by the aggressive chemicals meaning they must be replaced frequently.1,4
Sapphire is highly resistant to the semiconductor manufacturing environment, making it durable and preventing contamination. As a result, sapphire is the ideal choice for production components, including windows, tubes, pins, rods, injector nozzles, and even more complex parts. Sapphire components can be used indefinitely, increasing productivity and throughput by reducing contamination and reducing maintenance stoppages compared with other materials.1,4
Protective Glass Windows
Sapphire is hard, durable, and scratch-resistant, making it a superior option for transparent sapphire protection of high velocity (kinetic energy) projectiles.1,5
Ground vehicles and aircrafts often use glass protection to stop high kinetic energy projectiles from entering the cab and or cockpit. But glass protection can be heavy and thick. On the other hand, Sapphire protection is 50% thinner and lighter than glass alternatives, while providing the same stopping power. What's more, it offers better abrasion and chemical resistance to outside threats.1,5
Sapphire's broad transmission range, thermal conductivity, abrasion resistance, durability and stiffness make it a fantastic material for sensor protection and windows in scientific equipment, autonomous vehicles, helicopters, civilian and military air crafts, and even drones.1,6,7
Sapphire windows can be used to protect with a range of spectral analysis solutions that rely on light transmission without affecting performance, including UV-Vis and IR sensors, vision systems, cameras, night vision cameras, navigation systems, defense systems, and LiDAR.1,3,6,7
Transmission and ionization tubes
Sapphire tubes are strong and provide excellent light transmission. They are used in infrared countermeasure systems designed to protect aircraft pilots and passengers from heat-seeking missiles by firing infrared beams to confuse their tracking systems.8
Sapphire tubes are also used as essential components in excimer lasers, replacing alumina tubes. Excimer lasers are widely used in medical technologies, scientific research and photolithography machines for microchip manufacturing.9,10
Sapphire is a fabulous, multifunctional material that can help solve a vast range of complex engineering challenges. The demand and applications of sapphire are continually increasing. So, if you haven’t considered sapphire for your application yet, you may be falling behind.11
To talk to the sapphire experts and find out how sapphire can improve performance, durability, and productivity in your application, head over to Saint Gobain’s website.
References and further reading
- ‘Sapphire: Material, Manufacturing, Applications’ – Dobrovinskaya ER, Lytvynov LA, Pishchik V, Springer, 2009.
- ‘Sapphire Materials’ - https://www.crystals.saint-gobain.com/products/synthetic-sapphire-materials
- ‘Semiconductor Manufacturing’ - https://www.crystals.saint-gobain.com/markets/industrial-speciality-materials#nav:microwave-applications
- ‘Sapphire Crystal Growth and Applications’ – Tartartchenko VA in ‘Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials’, John Wiley & Sons, 2005.
- ‘Transparent Armor Window Systems’ https://www.crystals.saint-gobain.com/products/sapphire-transparent-window
- ‘Saint-Gobain Crystals Sapphire. The Clear Advantage for EO-IR Window Solutions’ https://www.crystals.saint-gobain.com/sites/imdf.crystals.com/files/documents/sapphire-eo-ir-solutions.pdf
- ‘SAPPHIRE for Enhanced Flight Vision Systems https://www.crystals.saint-gobain.com/markets/aerospace#nav:optical-vision-systems
- ‘SAPPHIRE for Infrared Countermeasures’ https://www.crystals.saint-gobain.com/markets/aerospace#nav:countermeasures
- ‘Sapphire for Excimer Laser Applications and Products’ https://www.crystals.saint-gobain.com/markets/industrial-speciality-materials#excimer-laser
- ‘Excimer Laser Technology’ - Basting D, MarowskyG, Springer, 2005.
- ‘Sapphire crystal screens: why Apple is interested in a gemstone’ https://www.theguardian.com/technology/2014/feb/10/sapphire-crystal-screens-why-apple-is-interested-in-a-gemstone