ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2009, Vol. 83, No. 11, pp. 1879–1882. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © T.P. Rebrova, V.L. Cherginets, T.V. Ponomarenko, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 11, pp. 2068–2071.
PHYSICAL CHEMISTRY
OF SOLUTIONS
A Study of Lux–Flood AcidꢀBase Reactions in KBr Melts at 800°C
T. P. Rebrovaa, V. L. Cherginetsb, and T. V. Ponomarenkoa
a Institute of Scintillation Materials, National Academy of Sciences of Ukraine, Kharkov, Ukraine
b National Technical University “Kharkov Polytechnical Institute,” Kharkov, Ukraine
eꢀmail: inorg@isc.kharkov.com
Received July 1, 2008
Abstract—The dissociation of CO23– (p
KBr melt at 800°C were studied potentiometrically with the use of a Pt(O2)
electrode. The direct calibration of the electrochemical circuit allowed only the equilibrium concentration of
2– (of strong bases) to be determined in the melt. The total concentration of oxygenꢀcontaining impurities,
K
= 2.4 0.2) and precipitation of MgO (pLMgO = 10.66 0.1) in a
|
ZrO2 (Y2O3) membrane oxygen
|
O
including CO32– and SO24– weak bases, can be found by the potentiometric titration of a sample of KBr by
adding MgCl2 (Mg2+), a strong Lux–Flood acid, which causes the decomposition of these oxygenꢀcontainꢀ
ing anions. This reaction can also be used to remove oxo anions from alkali metal halide melts.
DOI: 10.1134/S0036024409110120
Potassium bromide is the initial compound for the right. We must therefore estimate the content of oxyꢀ
preparation of optical materials extensively used in
modern science and technology. These are largely KBr
single crystals used to manufacture windows for infraꢀ
genꢀcontaining impurities in KBr to introduce correcꢀ
tions into the composition of charge mixtures taking
into account the precipitation of rareꢀearth metal
oxides. The content of oxo anions in initial KBr is as a
rule lower than in melt because of the presence of
organic impurities, which decompose to release water
and СО2 when the initial salt is heated. This results in
red instruments. K2LaBr5 single crystals activated by
и
Ce3+ ions (K2La1 – xCexBr5) are a promising scintillaꢀ
tor, whose technical characteristics excel those of
broadly used NaI : Tl [1].
Fairly stringent requirements are imposed on the the pyrohydrolysis of KBr according to the scheme
purity of halide materials for optics, because the presꢀ
2KBr + H2O
↑
+ CO2
↑
K2CO3 + 2HBr
↑
(5)
ence of impurities negatively influences the functional
characteristics of end products. For instance, the presꢀ
, )
ence of oxygenꢀcontaining impurities (CO23– SO42–
causes the appearance of absorption bands in the IR
range. As far as the K2La1 – xCexBr5 compound is conꢀ
cerned, it is prepared from a melt with the composiꢀ
and the appearance of some additional amount of oxyꢀ
genꢀcontaining impurities in melts compared with
unmolten potassium bromide.
The purpose of this work was to study the behavior
tion 2KBr + (1 – x)LaBr3 + xCeBr3, and the presence of anionic oxygenꢀcontaining impurities in a KBr melt
potentiometrically with the use of a Pt(O2) YSZ oxygen
|
of oxygenꢀcontaining impurities in KBr results in the
precipitation of La2O3 and CeO2 when the salt mixture
melts,
electrode (YSZ is a membrane on the basis of ZrO2 staꢀ
bilized with 10 mol% Y2O3) and develop a method for
estimating the total concentration of oxo anions in this
melt.
2La3+ + 3O2–
La2O3
↓
,
(1)
(2)
Ce3+ + 2O2– –
e
CeO2
↓
.
The behavior of oxygenꢀcontaining impurities is
described in terms of the Lux–Flood definition,
according to which an acceptor of oxide ions is an
acid, and a donor of O2– is a base [2]; that is,
This causes composition deviations from stoichiomeꢀ
try. О2– ions appear in melts because of the dissociaꢀ
tion of oxygenꢀcontaining impurities,
CO23–
SO24–
O2– + CO2
O2– + SO3
↑
,
(3)
(4)
Acid O2–
Base.
(6)
By this definition, metal cations (Eqs. (1) and (2)),
CO2 (Eq. (3)), and SO3 (Eq. (4)) are acids, and metal
oxides, CO23– , and SO24– are bases.
↑
.
The precipitation of oxides according to reacꢀ
tions (1) and (2) shifts equilibria (3) and (4) to the
1879