In the chemical, semiconductor and petrochemical industries, there is a common issue: how to ensure that optical windows remain transparent, stable and non-leaking when subjected to the repeated erosion of strong acids, strong alkalis and organic solvents. Ordinary glass is often not corrosion-resistant and will fog up, become brittle and even dissolve in a short period of time. Sapphire, renowned for its exceptional chemical stability, provides a dependable solution to these challenges.

1. The root cause of chemical inertness

Sapphire is composed of single-crystal aluminium oxide, a compound known for its remarkably strong interatomic binding forces. At room temperature, most chemical substances are incompatible with sapphire. This includes concentrated sulfuric acid, concentrated nitric acid, aqua regia, sodium hydroxide, ammonia water and various organic solvents. This inertness means that when sapphire comes into contact with corrosive liquids or gases, it neither dissolves nor releases any impurities. This is of vital importance for semiconductor processes or analytical chemistry experiments that require high purity.

2. The performance of corrosion resistance in different scenarios

The corrosion resistance of sapphire is not merely theoretical; it is supported by practical applications. In the field of semiconductor manufacturing, plasma etching processes frequently utilize corrosive gases comprising fluorine or chlorine. These gases rapidly erode ordinary glass windows, while sapphire can withstand a longer period of erosion, significantly reducing the frequency of cavity maintenance. In chemical analysis instruments, the sample cell window made of sapphire can repeatedly come into contact with flowing strong acid or strong alkali solutions. This keeps the surface smooth and prevents interference signals from being generated due to corrosion.

Furthermore, sapphire is characterized by its notable resistance to organic solvents. In the pharmaceutical and biotechnology sectors, sapphire windows are utilized in the manufacture of sensors that necessitate regular cleaning and disinfection. Regardless of whether ethanol, acetone or hydrogen peroxide is used for disinfection, sapphire will not be affected.

3. The unique advantage of combining corrosion resistance with high-temperature resistance

Another key benefit of sapphire is its ability to resist corrosion and high temperatures at the same time. Notably, sapphire retains its resistance to most acids and alkalis, even at temperatures in excess of several hundred degrees Celsius. Sapphire is one of the few materials that can simultaneously meet the three requirements of optical transmission, high-temperature resistance, and corrosion resistance in the observation windows of high-temperature reaction vessels, high-temperature plasma process chambers, and high-temperature chemical gas analysis equipment.

4. Sapphire is not omnipotent

It should be noted that sapphire is not impervious to all chemicals. It is important to note that at extremely high temperatures, molten alkali metal salts may cause slow erosion to the material. Furthermore, prolonged exposure to high pressures and temperatures may result in slight corrosion to the surface of sapphire, particularly when exposed to strong alkaline solutions. However, when used in conventional chemical corrosion environments, sapphire has been shown to have a significantly longer lifespan than other common optical materials.