Herein, TiO 2 , La-added, and Fe-added TiO 2 coatings are synthesized by sol-gel spin coating using acid catalyst-free titania precursors, and their microstructural and optical characteristics are studied. The possible reaction mechanism for synthesizing TiO 2 -based coatings using catalyst-free precursor is presented and correlated to their microstructural characteristic. TiO 2 coatings are developed and found to be anatase in phases having submicron morphological features. The anatase composition of TiO 2 coating decreases with increasing La or Fe ion concentrations. This manifests the inhibitory effect of increasing La and Fe ions to the formation of anatase TiO 2 . Moreover, the addition of La ions caused no significant changes in the reflectance spectra and bandgap energy of TiO 2 . In contrast, a remarkable red shift was observed with increasing Fe ion concentration. The calculated bandgap decreases from 3.261 to 2.096 eV with the addition of 7.5 mol% Fe ions, attributed to the formation of new energy states below the conduction band of TiO 2 induced by the Fe ion. These results suggested that a low-cost Fe added-TiO 2 material can be synthesized using an acid catalyst-free precursor that could extend the photocatalytic efficiency of TiO 2 to the visible light region.
The microstructural characteristics and phase composition of solution precursor plasma-sprayed (SPPS) titania-based coatings using a catalyst-free precursor are reported in this work. An ethanol-based solution containing titanium isopropoxide was used to deposit TiO2 coatings. The thermal behavior of the solution precursor changed as its phase transformation temperature increased when the molar concentration was increased from 0.3 M to 0.6 M. Scanning electron micrographs showed that the surface of the coatings was composed of nano- and submicron-sized spherical particles (<1 μm) with sintered and melted particles. The cross-sections showed a porous structure using lower concentrations and dense coating formation with micropores using higher concentrations, with thicknesses of about 5 µm–8 µm. Moreover, the coatings when the number of spray passes was increased were 16 µm–20 µm thick, giving an average layer thickness of 0.6 µm deposited per spray pass in all cases. Phase analysis revealed the presence of both the anatase and rutile phases of TiO2 in coatings sprayed with various concentrations at various stand-off distances. More detailed discussion is presented with respect to the effects of the solution concentration, stand-off distance, and number of spray passes on the coating’s phase composition and microstructure.
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