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Martin Bremholm

In-Situ Synchrotron Radiation Study of Formation and Growth of Crystalline CexZr1-xO2 Nanoparticles Synthesized in Supercritical Water

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In situ synchrotron powder X-ray diffraction (PXRD) measurements have been conducted to
follow the nucleation and growth of crystalline CexZr1-xO2 nanoparticles synthesized in supercritical
water with a full substitution variation (x = 0, 0.2, 0.5, 0.8, and 1.0). Direction-dependent growth
curves are determined and described using reaction kinetic models. A distinct change in growth
kinetics is observed with increasing cerium content. For x = 0.8 and 1.0 (high cerium content), the
growth is initially limited by the surface reaction kinetics; however, at a size of ∼6 nm, the growth
changes and becomes limited by the diffusion of monomers toward the surface. For x=0 and 0.2, the
opposite behavior is observed with the growth initially being limited by diffusion (up to∼3.5 nm) and
later by the surface reaction kinetics. Thus, although a continuous solid solution can be obtained for
the ceria-zirconia system, the growth of ceria and zirconia nanoparticles is fundamentally different
under supercritical water conditions. For comparison, ex situ synthesis has also been performed using
an in-house supercritical flow reactor. The resulting samples were analyzed using PXRD, small-angle
X-ray scattering (SAXS), and transmission electron microscopy (TEM). The nanoparticles with x=
0, 0.2, and 0.5 have very low polydispersities. The sizes range from 4 nm to 7 nm, and the particles
exhibit a reversibly pH-dependent agglomeration.
Udgivelsesdato: 2010
Original languageEnglish
JournalChemistry of Materials
Pages (from-to)1814-1820
Number of pages7
Publication statusPublished - 2010

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