1070-4272/01/7401-0077$25.00C2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 1, 2001, pp. 77!81. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 1,
2001, pp. 74!78.
Original Russian Text Copyright + 2001 by Mel’nichenko, Koryakova, Nikitin, Krysenko, Speshneva.
PRODUCTION AND USE
OF NEW MATERIALS
Silicon Dioxide Modified with Fluorine
E. I. Mel’nichenko, M. D. Koryakova, V. M. Nikitin,
G. F. Krysenko, and N. V. Speshneva
Institute of Chemistry, Far East Division, Russian Academy of Sciences, Vladivostok, Russia
Received June 3, 1999; in final form, June 2000
Abstract-IR spectroscopy and X-ray phase and chemical analyses were used to study the physicochemical
properties of fluoride-containing amorphous silicon dioxide obtained by hydrolysis of (NH
, and its
previously unknown biocide properties were discovered. Results of biotesting are presented.
Alkaline hydrolysis of (NH
gives an amor-
phous porous mass with hydrated surface, which is an
active silica filler and is known as [white black] .
A distinctive feature of silica gel obtained by hy-
drolysis of the SiF
ion (or SiF
) is the presence of
fluoride ions in it [2, 3]. The surface of the silicon
dioxide prepared by this procedure is hydrophobic
rather than hydrophilic . However, the presence
of residual fluorine in silicon dioxide has not been
related to any specific physicochemical properties of
silica gel and, therefore, such silicon dioxide was not
classed with fluoride materials.
With account of the fact that ammonium hexa-
fluorosilicate occupies a prominent place in develop-
ing practically all flowsheets for processing of mineral
raw materials based on ammonium hydrofluoride and
is involved in reagent circulation, the SiO
is supposed to be produced in large amounts. This
requires closer analysis of the effect exerted by resid-
ual fluoride ions on some properties of silicon dioxide
and a search for new fields of its application.
The aim of this work was to study the chemical
composition and biocide properties of hydrolytic sili-
con dioxide containing fluoride ions.
Fluoride-containing silicon dioxide was isolated by
precipitation with ammonia from saturated solution of
. The precipitate was washed
with double-distilled water and dried at 903105oC.
Analysis for fluoride ions was made by steam distilla-
tion and titration of the distillate with a Th(NO
solution. A sample obtained upon single washing of
the precipitate contained 6.9% fluoride ions, and that
furnished by triple washing, 3.2%. Further increase in
the number of washings (to 6 or 7) lowered the resid-
ual content of fluoride ions to 0.730.8%.
The presence of the NH
ion was judged from the
IR spectra. A conventional spectrum did not contain
the characteristic bands of the ammonium ion. Only a
spectrum taken in a thick layer, at the band intensities
of the main substance of 200%, demonstrated the
presence of ammonium in hydrolytic silicon dioxide.
Chemical analysis for the ammonium ion was done by
the Kjeldahl method involving evaporation with a
20% NaOH solution. The empirical formula of hy-
drolytic silicon dioxide containing fluoride ions and
ammonium ions was established by chemical analysis:
Found, %: NH
Calculated, %: NH
The biocide activity was evaluated by standard
procedures . The Czapek3Dox medium was ino-
culated with an aqueous suspension of mold spores
taken from a building wall infested by fungi. Glass
tubes 1 cm high, filled with a substance under study,
were placed at the center of a Petri dish inoculated
with fungi, and the culture was grown for 2 days in a
thermostat. The fungicide activity was determined as
the radius of the zone uninfected by fungi.
The algicide activity was evaluated from the action
on larvae of Balanus barnacles, the most common
fouling organisms at the Peter the Great Bay (Sea of
Japan). Fluoride ions were leached with seawater (1 l)
from 1 g of hydrolytic SiO
in the course of 1 and
7 days, with subsequent 2-, 10-, and 100-fold dilution
of the leaching solution. Larvae (1003150 specimens)
were introduced into the prepared solutions, and the