Stabilization of ScO(OH) dispersions in aqueous-alcoholic media by aminosilanes. Solution routes to scandia coatings

Abstract

Nanosized needles of ScO(OH) and lozenge shaped platelets of γ-ScO(OH) were prepared by hydrothermal syntheses (200 °C, 10 h) using ScCl3·6H2O as starting material. The influence of hydrothermal conditions on the nature of the phase, the morphology and the particle size was investigated. Characterization was achieved by XRD, TEM, FT-IR and TGA. Increasing the acidity of the reaction medium increased the particle size whereas increasing the concentration of the ScCl3 solutions favored the formation of the platelet type ScO(OH). The NaCl and NH4Cl mineralizers increased agglomeration between particles as well as the temperatures of transformation into oxides (480 to 530 °C). The point of zero charge was determined and found to be 6.7 for scandium oxide and 5.7 for the scandium oxohydroxide as prepared. Stabilization of the colloidal suspensions of ScO(OH) was achieved in aqueous-alcoholic media at pH = 3 by using [3-(2-aminoethyl)aminopropyl]trimethoxysilane (DAMO). The stabilization is discussed in terms of surface coordination chemistry. These hybrid sols were used to obtain coatings of crystalline scandia on glass substrates by spin-coating. Thermal decomposition of scandium formate deposited by dip-coating via aqueous alcoholic media with PVP as an additive was an alternative for producing coatings of amorphous scandia with good optical properties.