Феригідрит належить до метастабільних залізокисневих фаз, розповсюджених у природних системах. Він є перспективним матеріалом для практичного застосування в техніці, біології та медицині. До теперішнього часу залишаються дискусійними питання щодо його загальної формули, структуральної та поверхневої моделей, координації та валентності заліза, кількості модифікацій та ін. У роботі зроблено спробу проаналізувати літературні
першоджерела, присвячені вивченню структури та фазових перетворень феригідриту.
Ферригидрит относится к метастабильным железокислородным фазам, распространенным в природных
системах. Он служит перспективным материалом для практического применения в технике, биологии и медицине. До настоящего времени остаются дискуссионными вопросы о его общей формуле, структуральной и поверхностной моделях, координации и
валентности железа, количестве существующих модификаций и др. В работе предпринята попытка проанализировать литературные источники, посвященные исследованию структуры и фазовых превращений ферригидрита.
The search of new materials with nanosized particles leads
to the interest in nature disperse minerals particularly iron
oxides and hydroxides and their synthesized analogs.
Nowadays such structures are widely used for technical
and medico-biological applications. One of the iron-oxygen
structures which has great prospects for practical aims
is ferrihydrite. It was found by academic F.V. Chukrov and
was recognized as a mineral by the International Mineralogical
Association in 1975. But the information about
ferrihydrite is too contradictory, because this mineral belongs
to metastable phases and is a precursor for the
formation of goethite and hematite. Now there is no common
opinion about its general formula, structural mo del
(mono or polyphase), iron coordination (octahedral or
both octahedral and tetrahedral positions) in the lattice
and in the presence of ferric or ferrous iron forms in
lattice, number of modifications (only two- and six-lines
or their intermediate forms), as well as properties and
mechanisms of phase transformation. The purpose of the
present work is the review of the literature sources devoted
to investigations of ferrihydrite. The synthesis of ferrihydrite
in laboratory conditions has been carried out by different
methods, i. e.: hydrolysis and precipitation of ferric salts,
phase transformation Fe(II)—Fe(III) LDH, sol-gel syn thesis,
formation of the particles in organic-inorganic
polymer matrixes, and pyrolysis of sprays. Depending on
the way of synthesis the ferrihydrite particles have different
size and crystallinity. In the first part of the review we
showed the structural peculiarity of two- and six-line ferrihydrite.
The development of the classical structural models
by K.M. Towe and W.F. Bradley; J.D. Russell; R.A.
Eggleton and R.W. Fitzpatrick; V.A. Drits et al. A. Manceau
and modern positions about this question were monitored.
For the structural studying of ferrihydrite X-ray
diffraction, M ssbauer spectroscopy, IR-FT, EXAFS,
XANS, XANES, NEXAFS, TEM and SEM are used as
the main methods. Ferrihydrite can transform not only
into the phases of structural α-row but into iron oxides
and hydroxides of other structural modifications. The
chemical composition and pH values of dispersion medium,
temperature of carrying out the process and red-ox
condition belong to the most important parameters which
influence the mechanisms of the phase tran sfor mation. The examples of the phase transformation of 2-line ferrihydrite to 6-line ferrihydrite, their transfor mation into goe thite, hematite, lepidocrocite and mag netite are shown in numerous literature sources. This opens the way for direct synthesis of pure iron-oxygen nano- and microsized structures from ferrihydrite precur sors. In the second part of the review the sorption and magnetic properties of ferrihydrite, its interaction with species of environment, the specific character of biogenic and corrosion ferrihydrite as well as usage of the ferrihydrite particles for medicobiological
applications will be presented.
