Surface Review and Letters, Vol. 11, No. 1 (2004) 1–4
c World Scientific Publishing Company
CHARACTERIZATION OF KHCO3 SINGLE CRYSTAL
S. ABOUELHASSAN, F. SALMAN, M. ELMANSY and E. SHEHA
Physics Department, Faculty of Science, Banha, Egypt
Received 6 October 2003
Single crystals of KHCO3 were grown by the slow evaporation technique of an aqueous solution.
Characterization of the sample was done using different techniques such as X-ray diffraction,
infrared spectra (IR) and the differential scanning calorimeter (DSC) technique. The analysis
of the X-ray diffraction pattern indicated that the sample was a single crystal. The results
obtained by IR and DSC indicated the presence of phase transition. From the analysis of DSC,
the activation energy of transition was carried out by two methods (Kissinger and Ozawa).
Keywords: Characterization; single crystal; potassium hydrogen carbonate.
1. Introduction
tals are monoclinic, space group P21 /a with cell dimensions a = 1.51725, b = 0.56283, c = 0.37110 nm
and β = 104.631◦. The O–H· · ·O of the dimer is
0.2587 nm.
Different investigators have been reported on
some physical properties of KHCO3 single crystals.
The mechanism of the proton transfer in the dimer
was studied by 17 O quadruple double resonance.6
The anomalous elastic behavior, using ultrasonic
methods between 250 and 350 K, was investigated
by Hassuhl.7 A structural phase transition was observed at ”≈318 K.8 Incoherent neutron scattering
has been used for the determination of the effective
double minimum potential (DMP), which governs
the two-proton jump.
Among theories which have been used to
study the characterization and kinetic properties of
KHCO3 materials. Nevertheless, this point concerning KHCO3 single crystals has drawn less attention
among the contributions in the literature, and therefore we will give more attention to the kinetic and
characterization properties of this type of crystals.
Potassium hydrogen carbonate is a member of the
hydrogen carbonate series of general molecular formula MHCO3 , where M is a monovalent element
or group (M+ = Na+ , K+ , Cs+ , . . . and/or NH+
4 ).
These bicarbonate salts are a rather interesting series of compounds, which illustrate the effect of crystal packing on the internal structure of a covalently
bonded molecule.1
The crystal structures of some members of these
salts were determined.1 – 5 The most interesting
group in the crystal structure of this series is HCO3 .
This group is the source of the hydrogen bonding
system characteristic of the structure of these salts.
From the available structures, it seems likely that although, as we mentioned above, HCO3 is the main
source of hydrogen bonding, the members of this
series utilize different hydrogen bonding schemes.
1 –4
For example, KHCO3 contains (HCO3 )−2
2 dimers,
while the hydrogen bonding in the case of NaHCO13
and NH4 HCO53 is arranged in the form of chains.
Potassium hydrogen carbonate (KHCO3 ) is an
interesting member in this series. Its hydrogen bonding system is arranged in the form of dimers like that
of carboxylic acids. The general feature of the structure that was given earlier by Nitta et al.2 has been
refined by three-dimensional X-ray diffraction3 and
also by neutron diffraction.4 Accordingly, the crys-
2. Experimental
Single crystals of KHCO3 were grown by the slow
evaporation technique7 of an aqueous solution at
temperature 300 K. The procedure enabled us to
obtain colorless and transparent crystals.
1
S. Abouelhassan et al.
X-ray diffractograms have been carried out by using a Philips PW 1840 diffractometer provided with
a CUk∝ source in the 2θ range of 4◦ –80◦ .
IR spectra of KHCO3 single crystals were obtained by mixing the fine ground sample (1–100 mg)
with potassium bromide powder. The mixture was
pressed in an evacuable die at sufficient pressure
to produce a disk. IR spectra were performed with
an IR 1650 (PERKIN ELMER) spectrophotometer in the wave number range of 400–4000 Cm−1 .
The sharp, defined transmission peaks corresponding
to various modes of vibration chemical bonds were
recorded, which gave detailed information about the
primary crystal structure.
A calibrated setearam DSC 131 differential scanning calorimeter was used to record the thermograms of the present material. The DSC curves were
recorded in the temperature range of 300–400 K
and at heating rates of 2, 6, 8 and 10◦ K/min. At
each heating rate the temperature of the reference
specimen was raised uniformly, while the temperature additive to the tested sample depend on the
change, leading to endothermic or exothermic reactions which might occur during heating.
100%
80%
Intensity
2
60%
40%
20%
80
Fig. 1. X-ray powder diffractogram (CuKα) of KHCO3
single crystals at room temperature.
Table 1. X-ray diffraction results for the investigated
sample of KHCO3 crystals
(the present
Fig. (1): X-ray powder diffractogram
(CuKα) of the KHCO3 single crystal at
study).
room temperature.
Figure 2 illustrates the infrared transmittance spectra of KHCO3 single crystals from 4000 to 400 cm−1 .
Table 3 summarizes the characteristic absorption
peaks and the corresponding position;9,10 furthermore, the expected phonon modes energy are given.
2θ
I/Io%
24
30
31
31.5
33.6
37.6
38.6
23
100
78
51
44
40
17
hkl
2θ
I/Io%
40
44
45.6
499
51.6
60.4
68.4
27
24
14
38
22
25
17
hkl
Table 2. X-ray diffraction data for KHCO3 crystals (according to JCPDS).
3.1. X-ray diffraction analysis
2θ
I/Io%
24.2
30.07
31.2
31.3
34.09
38.8
38.9
78
100
91
96
53
35
1
hkl
4
4
3
1
4
5
6
0
0
1
1
1
1
0
0
1
1
1
1
1
1
2θ
I/Io%
40.6
44.4
46
49.3
50.8
60.6
69.3
36
27
10
29
10
8
3
hkl
0
2
7
6
0
5
9
2
2
1
2
0
3
1
1
1
0
0
2
1
2
100.0
0
TRANSMISSION %
3.2. IR measurements
4
20
40
2θ
3. Results and Discussion
Figure 1 shows the X-ray diffractogram of KHCO3
single crystals in the 2θ range of 4◦ –80◦, at
room temperature. Table 1 summarizes the characteristic peaks and their corresponding angles. Table 2 shows the indices of the expected planes of the present crystal that have
been estimated by comparing them with the
databases for KHCO3 crystal [Joint Committee of Powder Diffraction Standards, International
Center for Diffraction (JCPDS-ICDD)].The results
indicate that the sample is a monoclinic crystal with
space group P21 /a at room temperature and the unit
cell dimensions3,4 a = 15.18 Å, b = 5.63 Å and
c = 3.72 Å.
60
0.00
4000
4000
Fig.
3000
3000
2000
2000
1000
1000
-1
WAVE
WaveNUMBER
number(CM
(cm)−1 )
FIG (2) INFRARED SPECTRA OF KHCO3
SINGLE CRYSTAL
2. Infrared spectra
of KHCO3 single
CM-1 -1
CM
crystals.
Characterization of KHCO3 Single Crystals
3
Table 3. The obtained wave number of the characteristic peaks of absorption, and
the expected phonon mode energy.
2949
2627
1633.2
1409.3
1367.8
1006.9
978.9
831.9
702.6
662.2
Expected bond
Peak position cm−1
reference[8,18]
Energy of phonon
mode ~ω (eV)
O–H· · ·O+C...
–O
O–H
C=O
O–H· · ·O
C· · ·O
C–O+C· · ·O
O–H· · ·O
CO3
C=O+O· · ·H
O1 CO2
2920
2620
1650
1405
1367
1001
988
830
698
655
0.0041
0.0044
0.0047
0.0049
0.0050
0.0052
0.0053
0.0054
0.0057
0.0059
The absorption peaks can be explained as follows. Two peaks have been observed at 2949 and
2627 cm−1 . The former has been assigned to O–
H· · ·O bending plus C...
–O stretching, and the latter
to the O–H stretching band. The peak appearing at
1633.2 cm−1 was attributed to the C=O stretching
mode. In addition the two peaks observed at 1409.3
and 1367.8 cm−1 have been assigned to the coupled
vibrations between the O–H· · ·O in-plane bending
and the C...
–O stretching modes. The two peaks appearing at 1006.9 and 978.9 cm−1 were attributed to
the C–O stretching coupling with the C...
–O stretching mode and the O–H· · ·O out-of-plane bending
mode, respectively. On the other hand, the peak at
831.9 cm−1 is definitely due to the out-of-plane bending mode of the CO3 skeleton. The peaks at 702.6
and 662.2 cm−1 are assigned to the C=O in-plane
bending coupled with the O· · ·H stretching and the
O1 CO2 bending modes, respectively. These results
are in agreement with those obtained by others.9,10
3.3. Phase transition kinetic studies
Figure 3 shows the DSC thermograms of KHCO3
single crystals, recorded at the heating rates of 2, 6,
8 and 10◦ C/min. The graphs are characterized by
endothermic peaks, which correspond to ferroelastic
transition temperature (TF ).8 The results indicate
that the values of TF are shifted to higher temperatures by increasing the heating rate. Investigation of
the effect of the heating rate on the observed transi-
-6
2OC/min.
6OC/min
-7
8OC/min
-8
↑ Exo
Heat Flow/ µv
Peak position cm−1
(present study)
-9
-10
-11
-12
10OC/min
-13
-14
-15
-16
-17
293
313
323
343
363
403
383
o
Temperature/ C
Fig.of
(3) the
The effect
of heating
the DSC
Fig. 3. Effect
heating
raterate
ononthe
DSCthermograms
thermoof thecrystals.
KHCO3 Single Crystal System
grams of KHCO3 single
tion temperature TF of the studied material enables
us to calculate the values of the activation energy
of the transition process. The rate process of dimer
order–disorder ferroelastic phase11transition of the investigated samples has been discussed in terms of two
methods of analysis based on the heating rates11,12
4
S. Abouelhassan et al.
-8.4
where R is a universal gas constant and EF is the
activation energy of the ferroelastic transition. The
relation between ln(φ/TF2 ) and 1/TF was found to
be linear, as shown in Fig. 4(a). The obtained value
of the activation energy of the ferrolelastic transition
process EF has been estimated by means of the least
squares method. It was found to be 62 kcal/mol.
-8.4
-9.1
2
Ln(Φ /TF )
2
Ln(Φ /TF )
-9.1
-9.8
-9.8
3.3.2. Calculation using Ozaw’s equation
The variation of the heating rate of the investigated
sample with the transition temperature was found to
obey another linear relation, given by
-10.5
-10.5
-11.2
0.00303
-11.2
0.00303
ln(φ) =
0.00306
0.00309
-1
1/TF (K)0.00309
0.00306
(a)
1/T
F (K)
0.00312
0.00312
-1
2.88
2.88
2.16
Ln( )
Ln( )
2.16
1.44
E TF
+ const.
RTF
(2)
This equation is based on the shifting of the transition temperature with changing heating rate φ. A
plot of ln(φ) versus 1/TF gives a straight line, as
shown in Fig. 4(b), where its slope gives the value of
EF equal to 61.8 kcal/mol.
From the above two methods of calculation it has
been found that the activation energy of ferroelastic
transition equals about 62 kcal/mol, which indicates
that the transition process of the kinetics obeys and
is controlled by one type of mechanism.
1.44
References
0.72
0.72
0
0.00304
0.00307
0
0.00304
0.00307
0.0031
-1
1/TF(k)0.0031
0.00313
0.00313
-1
1/TF(k)
Figure(4(a,b))
12
(b)
Figure(4(a,b))
Fig. 4.
2
(a) ln(φ/T
12 F ) against 1/TF for KHCO3 single
crystals (Kissinger’s formula); (b) ln(φ) versus 1/TF for
KHCO3 single crystals (Ozawa’s formula).
3.3.1. Calculation using Kissinger’s
formula
The variation of the heating rate with transition temperature has been found to obey the linear relation
E TF
φ
+ const. =
,
(1)
ln
2
TF
RTF
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