Fabrication of sol-gel derived cladding for sapphire fibers and their performance evaluation under harsh environment

Sapphire single crystal fibers have shown great potential in fiber-based high temperature sensing applications. As single crystals are grown without cladding, there have been a lot of different techniques that have been proposed to achieve a core-clad structured fiber. A common approach is to achieve this is by using sol-gel deposition where the cladding layer is grown on a crystal fiber via dip-coating and subsequent thermally treatment. In this work we describe the synthesis of magnesium aluminate spinel via sol-gel methods and application of it as a cladding material for sapphire crystal fibers. The thermal stability of spinel coatings on sapphire substrates is investigated as the formation of non-stoichiometric spinel at high temperature is well-documented. Sapphire fibers with the spinel cladding layers are tested under different gas atmosphere at elevated temperatures, to demonstrate the efficacy of spinel as a cladding layer.