Properties of sapphire windows

Sapphire occurs both naturally and could be synthesized in factories. Although, both of these kinds of sapphire are quite different. A sapphire window is made from synthetic growth processes. Natural sapphire is a gemstone that is a form of aluminum oxide. Aluminum oxide is nature’s one of most abundant compounds. It is a white powdery substance that is commonly used as an abrasive in industries. Aluminum oxide is melted by heating at a very high temperature to form a single sapphire crystal.

To successfully make a sapphire crystal, industry-standard growth methods must be followed. Synthetic sapphire has the same crystal structure as the natural sapphire gem but it is much purer than natural sapphire and therefore appears crystal clear. 

What are sapphire windows?

Made from aluminum oxide, sapphire windows are thin pieces of sapphire crystals that are used in a wide range of applications that require the strength and durability of sapphire. Sapphire windows are used in both large and small-sized devices and equipment. The large ones include vacuum chambers and submarines. While some of the not-so-large devices include smartphones, cameras, lasers, and sensors. Both of these kinds of devices need sapphire’s excellent durability and transmittance.  

Sapphire windows are made from synthetically grown sapphire. They are grown in large cylindrical boules. Rods are cut out from these cylindrical boules that are further sliced and polished to make a thin sapphire window. The product is way more scratch-resistant than Gorilla Glass.

Properties of sapphire windows

Heedlessly, you might be having one of the toughest substances in the world in your pocket right now. Some Apple watches and the latest Apple smartphones use sapphire lenses on their cameras. Also, a very high-end watch has a good chance of being made of sapphire. Synthetically made sapphire has unmatched properties because of which it is used in such high-end gadgets. Sapphire delivers excellent optical properties, high hardness, chemical resistance, high modulus of rupture, high thermal conductivity, and high dielectric constant. The properties of sapphire windows are discussed below:


There are two common ways to measure the hardness of materials like sapphire. They are Mohs scale and compressive/tensile stress. The scratch resistance of a material is measured by the Mohs scale. Silicon carbide ranks second while sapphire is third. Sapphire has a Mohs rating of 9 while diamond has a rating of 10.

Sapphire can withstand immense pressure before breaking. The compressive strength of sapphire is about 2GPa. This is equivalent to about 40 elephants stacked on top of each other. Surprisingly, steel has a compressive strength of 250 MPa while Gorilla Glass’s value stands at 900MPa.

Chemical resistance

Sapphire is chemically inert to almost all chemicals, making it an excellent choice to withstand corrosive materials. It has an extremely low thermal expansion coefficient of 5.8×10^6 °C and thermal conductivity of 25 W m^(-1) K^(-1).


Sapphire can cover a wide range of spectrums in terms of transmittance. Light from the ultraviolet to mid-infrared spectrum can pass through sapphire windows. The transmittance range of sapphire is from 150nm to 5500nm. The range is more effective if no anti-reflective coatings are used. The optical properties of a sapphire depend on the crystalline orientation because it is birefringent material. Because of the wide range of wavelength transmission, sapphire windows are used in infrared lens designs.

Mechanical strength

The melting point of the glass is 1400 degrees. While sapphire can withstand a temperature of about 1900 degrees. This makes sapphire windows an excellent choice where the devices are likely to be exposed to such high temperatures. Sapphire is also resistant to different chemicals and corrosive agents. It does not react with acid or alkalis, hence it is chemically inert. 

A satellite lens system that is exposed to extreme temperatures, a refractive index optical sensor that is exposed to caustic acids, or monitoring the conditions inside a pressure chamber – all of these needs the exquisite properties of sapphire.

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