A new simultaneous apparatus for X-ray diffractometry and differential scanning calorimetry (XRD-DSC)

Article abstract of DOI:10.1016/S0040-6031(98)00573-5

An instrument was developed for performing simultaneous X-ray diffractometric and differential scanning calorimetric (XRD-DSC) measurement using a power compensation DSC (pc-DSC). The feasibility of the technique is demonstrated by examining the thermal dehydration measurement of zinc formate dihydrate (Zn(HCO₂)₂·2H₂O). The DSC curve shows apparent double endothermic peaks during the dehydration process, while X-ray diffraction analysis indicated that the resulting anhydrous product, Zn(HCO₂)₂, was crystalline. The simultaneous measurement reveals that the DSC curve arises from a combination of the endothermic dehydration peak and the exothermic crystallization peak which resulted from the progression of the anhydrous products.

Full text of DOI:10.1016/S0040-6031(98)00573-5

Thermochimica Acta 325 (1999) 151±156
A new simultaneous apparatus for X-ray diffractometry and
differential scanning calorimetry (XRD-DSC)
Tadashi Ariia,*, Akira Kishia, Yuji Kobayashib
a Thermal Analysis Division, RIGAKU Corporation, 3-9-12 Matubara, Akishima, Tokyo 196-8666, Japan
b X-ray Diffraction Division, RIGAKU Corporation, 3-9-12 Matubara, Akishima, Tokyo 196-8666, Japan
Received 7 July 1998; received in revised form 5 October 1998; accepted 12 October 1998
Abstract
An instrument was developed for performing simultaneous X-ray diffractometric and differential scanning calorimetric
(XRD-DSC) measurement using a power compensation DSC (pc-DSC). The feasibility of the technique is demonstrated by
examining the thermal dehydration measurement of zinc formate dihydrate (Zn(HCO2)2Á2H2O). The DSC curve shows
apparent double endothermic peaks during the dehydration process, while X-ray diffraction analysis indicated that the
resulting anhydrous product, Zn(HCO2)2, was crystalline. The simultaneous measurement reveals that the DSC curve arises
from a combination of the endothermic dehydration peak and the exothermic crystallization peak which resulted from the
progression of the anhydrous products. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Power compensation DSC (pc-DSC); X-ray diffractometer; Simultaneous XRD-DSC apparatus; Thermal
dehydration; Recrystallization
1. Introduction
form infrared spectroscopy (TG-FTIR) [8±11], have
been developed only in the past decade.
Most thermal analysis techniques provide physical
information, therefore ancillary data is required for
chemical interpretation of the observed thermal
events. Recently, simultaneous measuring methods
have rapidly developed and their achievements have
attracted much attention. For example, simultaneous
measurements with evolved gas analysis (EGA),
namely gas chromatography±mass spectrometry
(GC-MS), thermogravimetry±mass spectrometry
(TG-MS) [1±7] and thermogravimetry±Fourier trans-
Differential scanning calorimetry (DSC), however,
gives physical information and is widely accepted as a
useful thermo-analytical tool for the study of phase
transitions. A DSC curve may show several endother-
mic and exothermic peaks, and baseline shifts, since
the chemical and physical reactions generally proceed
through various steps. Unfortunately, this method does
not reveal the identity of the transforming phases.
Identi®cation of each peak is often quite impossible
without the aid of techniques that yield information
regarding structures and reactions.
Phase transitions between the various solid states
have been the focus of much attention for several
decades, and a variety of methods have been used to
*Corresponding Author: Fax: +81-42-544-9650; e-mail:
t-arii@rigaku.co.jp
0040-6031/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 4 0 - 6 0 3 1 ( 9 8 ) 0 0 5 7 3 - 5

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T. Arii et al. / Thermochimica Acta 325 (1999) 151±156
study their thermodynamic, structural, and kinetic
properties. Among them, calorimetry and X-ray dif-
fraction have proven to be two of the most useful
techniques.
DSCs provide almost the same information, but their
measuring principles are fundamentally different.
In previous similar studies of XRD-DSC, various
types of hf-DSC have been used. For example, a
commercially available unit developed for optical
microscopy [14,15], and an original cell unit modi®ed
for this purpose [16,17] have been reported. Such a
cell unit has a small aperture through which the X-ray
beam can pass unhindered, and a sample material
mounted in a standard aluminum DSC crucible with
a cover. In this case, the DSC had been modi®ed to
allow transmission of the X-ray beam which passes
through the specimen and, therefore, the scattering
geometry requires mounting the DSC cell vertically.
In addition, modi®cation of the XRD-DSC stage is
necessary in order to minimize beam attenuation. The
sample holder of the DSC cell has apertures of a few-
millimeter diameter for the transmission of an X-ray
beam. The collimated X-ray beam passes through a
smaller aperture in order to eliminate parasitic scatter-
ing. A large irradiated area in the sample cell is
required to get strong X-ray diffraction patterns. How-
ever, this is especially troublesome when using an hf-
DSC. Keeping of an open window for the X-ray beam
makes it dif®cult to assure the small heat exchange
between the sample and surroundings, and to assure
the adequate measuring sensitivity of the DSC.
On the other hand, a pc-DSC has several advantages
over hf-DSC for the simultaneous XRD-DSC mea-
surement. Pc-DSCs may be roughly classi®ed into two
types by the electrical heater arrangement for heating
the sample. In one type, the electrical microheaters
separately heat the sample and the reference holders
and they control the energy required not only to heat
the sample and the reference, but to make the tem-
perature difference zero between the sample and the
reference. In the other type, an additional electrical
heater located around the sample and reference
holders acts as a source of controlled energy to heat
both, the sample and the reference. The former type of
pc-DSC makes it possible to maintain the path of the
X-ray beam, because the additional heater does not
interfere with the X-ray beam.
In this respect, X-ray diffraction (XRD) is probably
the most reliable technique for phase identi®cation
and structure characterization. Both the methods,
namely DSC and XRD, are considered complemen-
tary to each other, and the development of the simul-
taneous measuring instrument of DSC and XRD has
been anticipated. Parallel measurements of different
specimens using DSC and XRD, and a combination of
both data are one of the popular ways of studying
thermal reactions of solids. Problems arise, however,
because many chemical reactions of solids, for
instance the dehydration of hydrates, depend mark-
edly on the sample preparation and on the experi-
mental conditions such as the nature of the
atmosphere, shape of the crucible, the heating rate,
etc. The differences in measuring conditions compli-
cate the combination and comparison of the obtained
data. Such problems can be overcome by simulta-
neously performing DSC and XRD measurements on
the same sample.
Masuda et al. studied crystallinities of dehydrated
product phases and described the effect of water vapor
pressure on the kinetics of the thermal dehydration of
some formate hydrates by means of a combination of
TG-DTA and XRD [12,13]. These results reveal that
more sophisticated simultaneous measuring systems
under identical measuring conditions are preferred for
the determination of reaction mechanisms based on
structural and thermal data.
We have assembled a simultaneous XRD-DSC
measuring apparatus using a power compensation
DSC (pc-DSC) which was specially designed for
the above-mentioned purposes. Then, we have applied
it to the complicated dehydration behavior of zinc
formate dihydrate measured by this XRD-DSC, as an
example. It is the purpose of this paper to report on this
simultaneous apparatus and demonstrate its perfor-
mance.
1.1. Instrumentation of the simultaneous XRD-DSC
measuring apparatus
We tried to combine a pc-DSC of the former type
with an XRD apparatus to realize simultaneous mea-
surements. Fig. 1 shows a close-up of a pc-DSC
whose geometry is designed to perform XRD mea-
surement. The sample was mounted horizontally to the
Generally, a pc-DSC and a heat-¯ux DSC(hf-DSC)
are widely used for DSC measurements. Both these

T. Arii et al. / Thermochimica Acta 325 (1999) 151±156
153
Fig. 1. Photograph showing simultaneous XRD-DSC apparatus.
incident X-ray beam on an optical bench. Fig. 2 shows
a schematic diagram of the DSC geometry compart-
ment. In order to realize the smallest heat loss to
surroundings and to maintain the highest measuring
precision, twin heat-shield covers, with X-ray trans-
mission windows of thin aluminum ®lm, are placed
around the DSC holders, and both, the incidence and
re¯ection X-ray beam paths are maintained.
plied by Masuda, and it was pulverized with a mortar
and pestle, and sieved to a fraction below 150 mesh
size. The sample of ca. 30 mg in an open aluminum
pan was used for the XRD-DSC measurements in
static air.
2.2. Procedure
For the CuKꢀ radiation, a graphite monochromator
was used for the XRD measurements. A line shape X-
ray source used was a RIGAKU/RINT-Ultima sys-
2. Experimental
‡
2.1. Material
tem, and it was operated at 50 kV and 30 mA. The X-
ray diffraction measurements were carried out in the
5<2ꢁ<358 range at 208 min 1, taken at intervals of
0.028.
Commercially available zinc formate dihydrate
(Zn(OCH2)2Á2H2O) was recrystallized and kindly sup-
Fig. 2. Schematic power-compensation DSC part.

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T. Arii et al. / Thermochimica Acta 325 (1999) 151±156
Fig. 3. Relationship between the DSC curve and XRD patterns in the dehydration of Zn(HCO2)2Á2H2O by simultaneous XRD-DSC.
3. Results and discussion
DSC peak suggests overlapping of peaks brought
about by several concurrent multiple reactions. From
the analytical point of view, the DSC curves can be
interpreted in two ways. The apparent double
endothermic peaks may be attributed to a concurrent
phase change brought about by an overlapping of the
exotherm and the endotherm. The other hypothesis is
that the dehydration may proceed through the forma-
tion of an intermediate, such as a monohydrate. As
discussed below, the XRD data simultaneously
obtained with DSC can give us very important infor-
mation in regard to the choice of the foregoing alter-
native hypotheses.
We shall now look more carefully into the relation-
ship between the XRD and DSC data in Fig. 3. The
DSC curve and the integrated XRD intensity in the
range of the diffraction angles characterizing the
structural changes are compared in Fig. 5 as a function
of temperature. The integrated intensity curve of
XRD patterns of crystalline dihydrate between 178
and 218 shows a broad sigmoidal decay according to
the progress of the dehydration, while the increment of
the integrated peak intensity in the diffraction
angles between 128 and 168 reveals a concurrent
growth of the crystalline anhydrous product. These
trends could well explain the shift of DSC curve
in the exothermic direction between 373 and 383 K.
That is, the DSC double peaks are attributable to a
combinatin of the endothermic dehydration peak and
the exothermic crystallization peak of the anhydrous
product.
Fig. 3 shows the relationship between the DSC
curve and X-ray diffraction patterns during the dehy-
dration of zinc formate dihydrate recorded by means
of the simultaneous XRD-DSC for a heating rate of
1 K min 1. The DSC curve indicates the dehydration
of the sample begins at around 360 K and ends at
around 390 K. This curve also shows apparent, double
endothermic peaks in the dehydration process. On the
other hand, it can be clearly observed that the change
in XRD patterns gradually starts from 373 K of the
®rst endothermic peak, and is completed after the
second endothermic peak at 383 K. Fig. 4 shows
XRD patterns obtained at 354 K with the DSC curve.
It is noteworthy that the resulting anhydrous product
shows crystalline patterns.
This type of behavior has been observed previously
and it was proved that the crystallinity of the dehy-
drated product was affected by the experimental tem-
perature and the water-vapor pressure in XRD, as has
been described recently by Masuda et al. [12,13].
However, the shape of the present DSC curve does
not correspond with that of the DTA of a previous TG-
DTA, in which the smoothness of curve observed
suggested that the dehydration proceeds without an
intermediate [12].
As regards the results of the present experiment, the
apparent double DSC peaks do not provide enough
evidence to decide upon the detailed dehydration
behavior. It seems likely, however, that the shape of

T. Arii et al. / Thermochimica Acta 325 (1999) 151±156
155
Fig. 5. Comparison of the DSC curve and the integrated XRD
curves obtained from the selected diffraction angle range in the
dehydration of Zn(HCO2)2Á2H2O.
cal conditions are problematic. The XRD-DSC has
been applied to the dehydration process followed by
concurrent with recrystallization of the anhydrous
product. The XRD-DSC data are especially useful
to verify the interpretation of thermal transitions (or
overlapping transitions) with thermal reactions. The
structural changes observed by the XRD-DSC give
the strongest proof that explains the actual dehydra-
tion process. These results clearly demonstrate the
potential capability of this new experimental method,
particularly for the examination of the complex
thermal behaviors inherent in many important chemi-
cal systems.
Acknowledgements
The authors would like to acknowledge Professor
Yoshio Masuda of Niigata University, in providing
guidelines for the scope, supplying the material and
making pertinent comments. We also acknowledge
assistance and support by Mr. Nobuo Yakuno and Mr.
Takashi Kanaya as well as other staff members of the
RIGAKU Corporation without whom this work would
not have been possible.
Fig. 4. DSC curve and XRD patterns obtained at 345 and 400 K in
the dehydration of Zn(HCO2)2Á2H2O.
4. Conclusions
We have described a new type of method by which
XRD and pc-DSC measurements can be carried out
simultaneously. XRD-DSC is an especially powerful
method for collecting structural and thermal data on
systems, where separate measurements under identi-
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