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Synthetic sapphire, renowned for its exceptional optical properties, is fast becoming a staple in the field of optics. With its outstanding transparency spanning from 150 to 5500 nm, synthetic sapphire is increasingly being used in advanced optical devices, including cameras, microscopes, and lasers. The growth in synthetic sapphire production over the past decade has significantly improved its availability and affordability, further broadening its range of applications.

Its mechanical strength is notable, showcasing a hardness rating of 9 on the Mohs scale. This exceptional scratch resistance surpasses that of many other materials. In fact, with a Modulus of rupture of 65000 psi at room temperature, synthetic sapphire is more than 50 times stronger than fused silica.

Chemically inert in nature, synthetic sapphire displays exceptional resistance to various chemical substances. This attribute renders it highly suitable for a broad range of applications, particularly in scientific research.

It is commonly manufactured in boules using the Kyropoulos method, facilitating the production of large single crystals. Its optical transparency can be attributed to the high purity of aluminum oxide from which it is derived. In contrast, natural sapphire used in jewelry derives its color from the presence of metallic ions substituting for Al3+
within its crystalline structure.

While synthetic sapphire boasts a high melting point of 2030 °C, making it attractive for optical applications in high-temperature environments, it experiences a substantial decline in mechanical strength up to 600 °C. Research conducted by Wachtman and Maxwell (J. Am. Chem. Soc., 1959) reveals that within this temperature range, the modulus of rupture of sapphire drops to less than one-third of its room-temperature value. Beyond 600 °C, however, the mechanical strength of sapphire gradually recovers, reaffirming its resilience.

Consequently, the design of sapphire windows for high-pressure or high-temperature applications necessitates careful consideration of this behaviour to ensure optimal performance.