Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 12, pp. 2060−2064.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.I. Kichigin, I.V. Petukhov, S.S. Mushinskii, V.I. Karmanov, D.I. Shevtsov, 2011, published in Zhurnal Prikladnoi Khimii, 2011,
Vol. 84, No. 12, pp. 1976−1980.
AND CORROSION PROTECTION OF METALS
Electrical Conductivity and IR Spectra
of Molten Benzoic Acid
V. I. Kichigin
, I. V. Petukhov
, S. S. Mushinskii
, V. I. Karmanov
, and D. I. Shevtsov
Perm State University, Perm, Russia
Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, Perm, Russia
Received May 13, 2011
Abstract—Impedance method was used to measure the electrical conductivity of benzoic acid melts, and the
concentration of free protons in these melts was estimated. IR spectroscopic data are presented and the existence
of benzoic acid in melts in the form of molecules is suggested.
One of ways to form waveguides in single crystals
of lithium niobate for a broad spectrum of integrated
optical circuits is the proton exchange . The proton
exchange is used in industrial manufacture of integrated
optical circuits based on lithium niobate for optical-ﬁ ber
gyroscopes with navigational precision, electric and
magnetic ﬁ eld sensors, and light intensity modulators
for telecommunication purposes .
The method of proton exchange (PE) employs the
reaction between LiNbO
and a source of protons
where x is the degree of proton exchange (x < 1).
The refractive index of phases of composition
, formed as a result of PE, exceeds that
of the lithium niobate substrate, which is a prerequisite
for appearance of waveguide properties in proton-
exchange layers. Various proton sources can be used
for PE in lithium niobate, but benzoic acid (BA) is the
most frequently used. The choice is due to the fact that
BA is in the liquid state at temperatures that are the best
suitable for PE (170–200°C), but are still far from the
boiling point. Use of BA provides an acceptable PE
intensity and formation of waveguides with required
Despite the wide use of the PE process in BA, some
questions related to the behavior of BA in the bulk of the
melt and at the interface between lithium niobate and
the melt remain unresolved. A BA melt is strongly acidic
[3–5]; however, it has been noted  that there are no
quantitative data on the proton concentration in the
melts, and values of dissociation constants, measured in
aqueous solutions at room temperature, cannot be used
for estimations. In some cases, the proton exchange is
performed using a melt composed of benzoic acid mixed
with lithium benzoate additive taken in an amount of
up to 5% . The additive substantially diminishes the
intensity of proton exchange. There is an opinion that
addition of lithium benzoate makes lower the acidity of
the melt , although it is better to use the term “mild
proton exchange” for characterizing the PE in a benzoic
acid + lithium benzoate mixture .
The goal of our study was to examine BA melts
by measuring the electrical conductivity in order to
estimate the free proton concentration in the melt and by
IR spectroscopy to obtain information about existence
forms of BA molecules in the melt.
We carried out experiments with benzoic acid of
analytically pure grade. The electrical conductivity
of BA melts was measured in a specially fabricated