follows from the fact that when thermal (700-1200°C) changes near the surface and at
the surface are terminated, no changes are observed in NMR scandium spectrum as
well.
Thus, the addition of scandium ions to ZrO
2
structure, after pore water and OH
groups are removed, gives rise to forming of a strongly defective nanocrystal surface
structure saturated with additive ions but not as a separate phase of Sс
2
О
3
of similar
composition. Sc NMR spectrum in Sc
2
O
3
(Fig. 5) differs significantly from the spectra
noted above. Formation of such a defective surface is a major obstacle in formation of
large crystals and phase transformations in zirconium dioxide. This can be concluded
from
1
Н and
45
Sс NMR data.
It is rather well established that when preparing ZrO
2
from coprecipitated
zirconium hydroxides - Sc, through their thermal dehydration two types of water
molecules and two types of OH groups are formed in intermediate compounds. Low-
temperature water (up to 150°C) is at the crystal surface and high-temperature water is
(up to 400°C) in pores. Low-temperature (up to 600°C) OH groups are at the surface
and high-temperature (up to 800°C) OH groups are in the crystal structure.
It is also established that the number of high-temperature OH groups in ZrO
2
with
Sc(III) additive correlates with the number of additive ions which are localized near
additive ions and form bridge OH groups Sc-OH-Zr.
45
Sс NMR showed that in
zirconium hydroxides structure with addition of 8% of Sc
2
O
3
the removal of pore water
and structural OH groups is followed by formation of two structurally nonequivalent
positions of Sc ions with a quantitative ratio of 1:2 - purely oxygen polyhedra and
polyhedra with OH groups and anionic vacancies and strongly defective nanocrystal
surface is a major obstacle for formation of large crystals and phase transformations.
Structural and Chemical Pattern of Zirconia Particles Formation on a
Micro-Level When Preparing Them from Solutions. On the basis of the present-day
ideas about chemistry of zirconium, domestic and foreign authors researches it can be
stated that tetrameric hydroxo zirconium complex, which is the basis for formation of
all intermediate heterophase nanostructures, is the main structural unit in formation of
stabilized zirconia powder solid phase throughout the entire formation sequence:
"aqueous solution of zirconium salts and stabilizing element→ hydroxo polymer Zr
1-
х
Ме
х
О
у
(OH)
x
nH
2
O → xerogel Zr
1-х
Ме
х
О
у
(OH)
x
→ amorphous Zr
1-х
Ме
х
О
у
(OH)
x
→
crystalline Zr
1-х
Ме
х
О
у
." [8].
The pattern of the main physicochemical processes which lie at the basis of
nanosized zirconia powders formation at different stages of their preparation from
solutions on the basis of carried out research and analysis of works by K. Matsui [9-
12] is shown in Fig. 6.
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