Premium
Isothermal Structural Evolution of SnO 2 Monolithic Porous Xerogels
Author(s) -
Brito G. G. S.,
Pulcinelli S. H.,
Santilli C. V.,
Craievich A. F.
Publication year - 1997
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889897002434
Subject(s) - small angle x ray scattering , materials science , scattering , isothermal process , nanoporous , porosity , intensity (physics) , phase (matter) , scaling , small angle scattering , maxima , chemical physics , crystallography , thermodynamics , chemistry , nanotechnology , optics , composite material , physics , art , geometry , mathematics , organic chemistry , performance art , art history
Monolithic samples of SnO 2 xerogel were produced by careful control of the gelation and drying steps of material preparation. In these samples, small and nanoporous aggregates stick together, yielding a monolithic (nonpowdered) material. The material was analyzed by in situ small‐angle X‐ray scattering (SAXS) during isothermal treatment at temperatures ranging from 473 to 773 K. At 473 K, the SAXS intensity does not change significantly with time. All experimental scattering intensity functions for T > 473 K are composed of two wide peaks, which evolve with increasing time. Each of them was associated with one of the modes of a bimodal distribution of pore sizes corresponding to a fine (intra‐aggregate) and a coarse (inter‐aggregate) porosity. The SAXS intensities of the maxima of both peaks increase with increasing treatment time, while the position of their maxima, associated with an average correlation distance, decreases. The time dependences of the SAXS intensity corresponding to both families of pores qualitatively agree with those expected for a two‐phase separating system exhibiting dynamic scaling properties. The time evolutions of the several moments of the structure function of samples heat treated at 773 K exhibit a good quantitative agreement with the theory of dynamic scaling for systems evolving by a coagulation mechanism. The kinetic parameters are the same for both peaks, indicating that the same mechanism is responsible for the structural evolution of both families of pores.