Why is sapphire significantly better than ceramics in harsch process conditions?
Crytur sapphire products are single crystals. Thus, the entire probe consists of one single corundum crystal grown into the shape of a protective sheath. In contrast, ceramics consist of vast quantities of sintered corundum grains. The boundaries between these grains present weak points where corrosion begins. Furthermore, sapphire is an extremely pure form of aluminium oxide (5N purity). No sintering additives which compromise material properties are used during its production as is the case with ceramics. The melting point of sapphire is 2057 °C and essentially, no shape change is possible below this temperature. The material’s hardness of Mohs 9 guarantees minimum abrasion. For a comparison, the hardness of diamond is 10 and quartz is Mohs 6. dfadfa
Sapphire (left) is perfectly homogeneous single crystal, while SEM pictures of C799 ceramics shows clear inhomogeneities in between crystal grains.
Order of magnitude longer life-time than any tested ceramics in some applications:
Identical time (20 months) and position (1250 oC) in the glass furnace during glass melting.