ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 7, pp. 995–1001. © Pleiades Publishing, Inc., 2009.
Original Russian Text © Yu.A. Karavanova, I.A. Stenina, A.B. Yaroslavtsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 7, pp. 1059–1065.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Kinetics of Solid-Phase H+/M+ Ion Exchange on Hafnium
Hydrogen Phosphate
Yu. A. Karavanova, I. A. Stenina, and A. B. Yaroslavtsev
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
Received April 1, 2008
Abstract—The kinetics of solid-phase reactions between hafnium hydrogen phosphate and alkali metal chlo-
rides were studied by thermogravimetry with subsequent analysis of leaving gases. For sodium and potassium
chlorides, the reaction occurs in two stages; the first stages produces MHHf(PO4)2, and the second yields the
MHf2(PO4)3 NASICON phosphate. For rubidium chloride, the reaction is one stage and produces Rb2Hf(PO4)2.
For cesium chloride, the reaction is an analogue of the reaction for rubidium chloride, but has two stages.
Kinetic data were used to determine interdiffusion coefficients for hydrogen and alkali-metal ions at various
temperatures and the activation energies of interdiffusion.
DOI: 10.1134/S0036023609070018
Studies of cationic mobility and diffusion processes the solution was slowly evaporated for 5 h until precip-
are an important field of solid-state chemistry. Ion and itation occurred [8]. The precipitate was separated by
atom mobility in inorganic materials holds a significant centrifugation. The product composition was formu-
place in contemporary materials science on account of lated as Hf(HPO4)2 · 2H2O using thermogravimetry.
both fundamental interest and the importance of this
The kinetics of the solid-phase reaction were stud-
problem for particular practical tasks. These tasks
ied on stirred mixtures of hafnium hydrogen phosphate
include search for new synthetic routes for a number of
inorganic and organic materials and description of
preannealed at 175°ë for 0.5 h with sodium, potassium,
rubidium, and cesium chlorides in the proportion 1 : 1
practically important properties of solids, such as elec-
and 1 : 2. The reaction with lithium chloride was not
trical and ionic conduction [1]. Ion-exchange kinetic
studied because of its high tendency to hydration.
studies in solids are an important and interesting source
X-ray powder diffraction was measured on a Rigaku
of data on diffusion processes [2].
D/MAX-2000 diffractometer equipped with a high-
Reactions of hydrogen phosphates of polyvalent
metals HxÄ(PO4)2, where A = Ta, Sn, Zr, and Ti, with
alkali metal halides were gravimetrically studied earlier
[3–7]. These studies showed two possible mechanisms
of proton exchange for an alkali metal ion. One scheme
involves the displacement of the interface between the
substituted phase and the unsubstituted one [3, 5]. The
other involves the formation of a continuous solid solu-
tion [4, 5, 7]. The first kinetic scheme (for example, for
Sn(HPO4)2 and Zr(HPO4)2) is well described by the Jan-
der model. In cases of tantalum and zirconium hydro-
gen phosphates, an insignificant part of the reagents
reacts even during mechanochemical treatment [4, 5].
temperature unit and an RTS-30 temperature controller
using CuKα radiation.
Thermal analysis was carried out on a Netzsch TG
209 F1 thermobalance in platinum crucibles and was
followed by analysis of leaving gases on a Netzsch
QMS 403 C mass spectrometer. Heating rate were
5 and 10 K/min; sample sizes were 40–60 mg; and the
temperature range was 25–950°C. In isothermal experi-
ments, a test sample was heated to a set temperature at
10 or 20 K/min and then weight loss was monitored for
1 h at a constant temperature.
Particle sizes were ascertained by digitizing micro-
graphs obtained using an MFN-11 LOMO microscope.
The average particle size of hafnium hydrogen phos-
phate was 2 µm.
This work studies the reaction between hafnium
hydrogen phosphate Hf(HPO4)2 and alkali metal chlo-
rides using thermogravimetry followed by analysis of
leaving gases.
RESULTS AND DISCUSSION
Heat-induced degradation of hafnium hydrogen
phosphate occurs in two stages (Fig. 1). In the range
EXPERIMENTAL
Hafnium hydrogen phosphate was prepared as fol- 100–400°ë, water of crystallization is eliminated. Then,
lows. Hafnium oxide was dissolved in hydrofluoric within 540–700°ë, anhydrous hafnium hydrogen phos-
acid; then, 50% orthophosphoric acid was added, and phate degrades to hafnium pyrophosphate:
995