Center for Materials Engineering

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Browsing Center for Materials Engineering by Author "Anteneh Marilegn (PhD)"

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    A Study on Optical Quality Enhancement of Alpha-Alumina/Titania Pearlescent Pigment Via Insitu Ph Control
    (Addis Ababa University, 2023-10) Buziye Guye; Anteneh Marilegn (PhD)
    Pigment is a material that changes the color of reflected or transmitted light as the result of wavelength- picky immersion. During high-temperature calcination, there is a problem with the thermal expansion coefficient mismatch between mica and titania and the resulting thermal stress and crack formation. Thermal stress and crack formation is an issue during high-temperature calcination. Formation of cracks in the coating layer results in the scattering of light and the consequent decline of pearl luster. Various researchers have conducted a study on the low temperature rutile phase formation; however, the attempts have resulted in higher rutile phase fraction on the final coating but in most cases with compromised optical quality. In this study, α-Al2O3 platelets of average particle size ⁓ 10μm have been synthesized to be used as a substrate for the pearlescent pigment. Coating of TiO2 on the surface of the synthesized α-Al2O3 was performed via co-precipitation method. Urea was utilized as a hydrolyzing and pH-regulating agent along with TiOSO4 as a precursor to TiO2The sample with lower oxysulfate:urea ratio (i.e. strongly acidic synthesis media) resulted in higher rutile phase fraction (41.5%) while the other two samples, where the oxysulfate:urea ratios are 1:25 (i.e. close to neutral pH) and 1:50 (i.e. strongly basic synthesis media), resulted in extremely lower rutile phase fraction, 2.9% and 1.4% ,respectively. The coated samples' morphology showed that the entire coating was smooth. When compared to samples with lower rutile phase fractions, those with greater rutile phase fractions exhibit higher reflactance in the visible area, according to the optical performance of the samples. The color value measurments have also revealed that, samples with higher rutile fractions exhibit higher lightness values (L*) in comparison to those with lower rutile phase fractions. The study showed that, in general, controlling the rutile phase fraction by adjusting the pH of the synthesis media using in-situ urea decomposition was effective in producing TiO2 coatings with higher rutile phase fractions and better surface smoothness, which in turn results in higher optical quality.