Synthesis and Microstructure Evolution of Nano-Titania Doped Silicon Coatings

The anatase phase of titania (TiO₂), particularly in nanocrystalline form is a well known photocatalyst.  Photocatalysts are commercially used to accelerate photoreactions and increase photovoltaic efficiency such as in solar cells.  This study investigates the in-flight synthesis of titania and its doping into a silicon matrix resulting in a catalyst dispersed coating. A liquid precursor of titanium isopropoxide and ethanol was coaxially fed into the plasma gun via special hardware to form nano-titania particles, while silicon powder was externally injected downstream. Coatings of 75-150 microns thick were deposited onto flat coupons. Further, silicon powder was alloyed with aluminum to promote crystallization and reduce the amorphous phase in the silicon matrix.  Dense coatings containing nano-titania particles were observed under electron microscope.  X-ray diffraction showed that both the rutile and anatase phases of the titania exist. The influence of process parameters and aluminum alloying on the microstructure evolution of the doped coatings is analyzed and presented.