Figure 6. A generalized scheme of structural and chemical transformations
of initial zirconium (IV) + Me(III) solutions while preparing nano-sized
stabilized zirconia powders.
Let us now take a closer look at the process of stabilized zirconia powder micro
structure formation while preparing it from aqueous zirconium oxychloride solution by
co-precipitation method. In this case polymerization processes which occur in aqueous
medium could be interpreted as "tetramer-tetrameric interaction" and as interactions
between complexes which are going on as polymerization process is progressing.
It is known that tetrameric structure of aqueous zirconium oxychloride is stable
in solution at high HС1 concentrations (<5 М). Under these conditions crystallization
of zirconium dioxychloride salt occurs with formation of the same tetrameric structure
which can be observed in aqueous solution of zirconium oxychloride. At mid-level
HС1 concentrations (1–5 М) tetramers do not structurally interact. At low HCl
concentrations (<1 М) an effect of automatic polymerization has been observed.
Whatever the reasons may be behind tetramer structural interaction whether it is
("outer") alkaline protolysis by adding OH groups to a salt solution or "kinetic"
protolysis with chipping off the boundary ion pair and two tetramers of K
2
complex
from the tetramer. As they approach each other a new polymer complex is formed from
two tetramers.
Complexes K
8-8
are primary particles when precipitating zirconium hydroxides
with regular structure. These complexes are supramolecular structures with
characteristic linear dimensions which are equivalent to dimensions of a polymer
formed from four – ten tetramers.
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