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

Nanosized needles of ScO(OH) and lozenge shaped platelets of gamma -ScO(OH) were prepared by hydrothermal syntheses (200 degreesC, 10 h) using ScCl3. 6H(2)O as starting material. The influence of hydrothermal conditions on th e nature of the phase, the morphology and the particle size was investigate d. Characterization was achieved by XRD, TEM, FT-IR and TGA. Increasing the acidity of the reaction medium increased the particle size whereas increas ing the concentration of the ScCl3 solutions favored the formation of the p latelet type ScO(OH). The NaCl and NH4Cl mineralizers increased agglomerati on between particles as well as the temperatures of transformation into oxi des (480 to 530 degreesC). The point of zero charge was determined and foun d to be 6.7 for scandium oxide and 5.7 for the scandium oxohydroxide as pre pared. Stabilization of the colloidal suspensions of ScO(OH) was achieved i n aqueous-alcoholic media at pH = 3 by using [3-(2-aminoethyl)aminopropyl]t rimethoxysilane (DAMO). The stabilization is discussed in terms of surface coordination chemistry. These hybrid sols were used to obtain coatings of c rystalline scandia on glass substrates by spin-coating. Thermal decompositi on of scandium formate deposited by dip-coating via aqueous alcoholic media with PVP as an additive was an alternative for producing coatings of amorp hous scandia with good optical properties.