The mechanisms of formation and structure of precipitates hydrolyzed from aqueous solutions of titanium tetrachloride and titanium sulfate were studied by small-angle X-ray scattering (SAXS). SAXS was found a powerful method for that purpose. The small colloidal primary particles that were present in the solutions at room temperature started to aggregate when thermal precipitation started. The aggregated particles coalesced until their radius was approximately 1 nm depending of the precipitation conditions to some extent. After that, the aggregation continued producing either mass fractal or surface fractal structures. The structure was mass fractal when primary particle concentration was high enough and surface fractal when concentrations were closer to the equilibrium state. With a delay ionic titanium started to precipitate. Because of its rather slow precipitation rate in the conditions of this study, only surface fractal aggregates were formed. The mass fractal structure was found X-ray amorphous and the surface fractal aggregates nano crystalline. The mass and surface fractal dimensions of these aggregates were 2.2 (1 s ( 0.1) and 2.7 (1 s ( 0.2), respectively. The "titanic acids" were found to be aggregates of small titanium dioxide particles that have mass fractal structure in ortotitanic acid and surface fractal structure in metatitanic acid. The loose structure of the mass fractal aggregates causes the relatively easy solubility and the X-ray amorphous state found in ortotitanic acid. On the contrary, the more compact structure of metatitanic acid explains its nano crystallinity and insolubility. The changing of ortotitanic acid to metatitanic acid upon aging is obviously a consequence of the restructuring of the primary titanium dioxide particles toward the close-packed porous structure.
The structure of TiO2 hydrates is studied by X-ray
diffraction, atomic force microscopy (AFM),
and transmission electron microscopy (TEM). The samples prepared
by NH4OH precipitation
from an aqueous TiCl4 solution are amorphous or partially
crystalline. They consist of a mixture
of distorted anatase and brookite crystallites, each having a diameter
of 20 nm. The sample
prepared by thermal hydrolysis from a titanium oxide sulfate solution
was totally crystalline,
composed only of distorted anatase crystallites with a diameter of 15
nm. Primary particles
can be oriented in chainlike structures. The crystallinity and the
crystal shape reveal the sample
history. The applicability of the AFM and TEM measurements for
structural investigations of
the powder specimens concerned is briefly discussed.
Fe-P metallic glass samples (14.7-22.9 at. % P) prepared by electrodeposition and melt-spinning technique were studied by using the angle dispersive X-ray diffraction and the Mössbauer spectroscopy. The differences between the samples prepared by different methods are very small: The electrodeposited samples have somewhat broader nearest neighbour peaks in the radial distribution functions, broader hyperfine field distributions and smaller structural disorder parameters. The average nearest neighbour coordinatination numbers are also a little bit larger for electrodeposited than for melt-quenched alloys. The results suggest that the electrodeposited samples are more inhomogeneous than the melt-quenched ones. Some estimations are made concerning the nature and characteristic size of the inhomogeneities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.