X-RAY AND RAMAN SPECTRA STUDIES ON THERMAL ENERGY STORAGE MATERIALS
- TRIS(HYDROXYMETHYL)AMINOMETHANEX-RAY AND RAMAN SPECTRA STUDIES ON
THERMAL ENERGY STORAGE MATERIALS -
TRIS(HYDROXYMETHYL)AMINOMETHANE
Wen-Ming Chien1, Vamsi Krishna Kamisetty1, Juan C. Fallas1 ,
Dhanesh Chandra1, Erik D.
Emmons2, Aarron M. Covington3, Raja S. Chellappa4, Russell J.
Hemley4, Stephen A. Gramsch4, and Simon Clark5
1 Metallurgical and Materials Engineering /MS388, University of
Nevada, Reno, Reno, NV 89557
2 U.S. Army Edgewood Chemical Biological Center,
AMSRD-ECB-RT-DL/BLDG E5560, 5183 Blackhawk Road, Aberdeen Proving
Ground, MD 21010-5424
3 Department of Physics /MS220, University of Nevada, Reno, Reno,
NV 89557 4 Carnegie/DOE Alliance Center, Geophysical Laboratory,
Carnegie Institution of Washington,
Washington, DC 20015 5 Advanced Light Source, Lawrence Berkeley
National Laboratory, Berkeley, CA 94720
ABSTRACT
Organic thermal energy storage materials are useful for thermal
energy storage due to the presence of a solid-state phase
transition where the latent heat can store energy. The effects of
temperature and pressure on the X-ray diffraction patterns and
Raman spectra of tris(hydroxymethyl)aminomethane (TRIS,
C(CH2OH)3NH, C5H10NO3) were measured. X-ray diffraction and DSC
results show that the solid state phase transition (-orthorhombic
to -BCC) of TRIS occurs at 133.7oC at ambient pressure (1 atm). The
volume thermal expansion equations of and phases were calculated
as: Vol = 0.01789T + 146.73 (298 K - 403 K) and Vol = 0.07901T +
128.62 (403 K - 418 K). At room temperature, the high pressure
synchrotron X-ray diffraction patterns and Raman spectra by using a
Diamond Anvil Cell (DAC) show that TRIS undergoes a phase
transition () starting at ~1 GPa. A new high pressure -phase was
observed at a pressure range from ~1 GPa to 9.3 GPa. The effects of
hydrogen bonding on the broad OH and sharp NH stretching modes will
be discussed. Detail results of temperature dependent effects on
high pressure Raman spectra are presented.
INTRODUCTION
Thermal energy storage materials, such as amine and alcohol
derivatives of neopentane, can store large amount of heat due to
the presence of thermal transitions from the orientationally
ordered to disordered phases occurring before melting. These
molecules can reorient as a whole about the central carbon atom to
form orientationally disordered crystals (ODIC) and their spherical
shape makes them reorient relatively easier. These molecules are
also known as “Plastic” crystals as they can be plastically
deformed after the transition temperature. These molecules undergo
large changes in enthalpies at solid-solid transitions and one such
compound is tris(hydroxymethyl)aminomethane (TRIS, C(CH2OH)3NH2).
Due to the presence of these enthalpy changes compounds like TRIS
are identified potentially as thermal energy materials (Divi et
al., 2006; Chandra et al., 2002a; Chandra et al., 2002b) and some
of its applications are solar cell systems. Binary mixtures have
been found as a way to adjust the transition properties
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in addition to pure compounds (Chellappa and Chandra, 2003). The
main effect of the transition on the vibrational spectra is
significant broadening and loss of resolution of the internal
modes, and changes and disruptions of hydrogen bonding (Schroetter
et al., 1986; Granzow, 1996; Granzow et al., 1995). Temperature
plays a major role of the disorder in plastic crystal materials,
like TRIS. Schroetter et al. (1986), as well as Kanesaka and
Mizuguchi (1998) studied the vibrational spectra of TRIS as a
function of temperature. For the effect of high pressure on the
disorder in plastic crystal materials, McLachlan et al. (1971) and
Marzocchi et al. (1971) performed the vibrational spectroscopy
studies of other closely related polyalcohols, such as
Pentaerythritol, which are providing the helpful information for
identifying the analogous spectral modes in TRIS. Under ambient
conditions, the crystal structure of TRIS adopts the orthorhombic
Pn21a space group with four molecules per unit cell (Eilerman and
Rudman, 1980). TRIS forms layered structures perpendicular to the
c-axis with strong interlayer hydrogen bonds and relatively weak
interlayer hydrogen bonds. In the case of TRIS, the amino groups
are oriented along the c-axis (Kanesaka and Mizuguchi, 1998), and
are involved only weakly in hydrogen bonding. Kanesaka and
Mizuguchi (1998) found that the structure of TRIS may be more
accurately modeled as a chain structure, where the hydrogen bonds
are stronger along the b-axis than the a-axis
(Kanesaka and Mizuguchi, 1998). In this study, the high-pressure
and high-temperature Raman studies will be performed on TRIS sample
using a Diamond anvil cell (DAC) to determine the phase transition
pressures/temperatures. In-situ X-ray diffraction (XRD) and
Differential scanning calorimetric (DSC) studies will also be
performed to determine the phase transformations at ambient
pressure (1 atm). EXPERIMENTAL A Renishaw In Via Raman microscope
system was used for Raman spectroscopy experiments at the
University of Nevada, Reno (UNR). A low power argon ion laser was
used to generate light at 514.5 nm. The laser emitted a total
output power of around 20-25 mW of which typically 5-7 mW was
incident upon the Diamond anvil cell (DAC). The laser light was
filtered with a laser line filter to remove unwanted light at
wavelengths other than 514.5 nm emitted from the laser tube. The
laser beam was then expanded using a beam expander and directed
with a notch filter to a microobjective. There it was focused by
the microobjective onto the sample. The Raman scattered light
collected in the backscattering geometry through the same
microobjective was dispersed with a 1800 grooves/mm diffraction
grating and detected by a thermoelectrically cooled CCD camera. The
spectrometer entrance slit was set at a width of 50 m leading to a
spectral resolution of ~4-5 cm-1. A 20X long working distance
objective with a numerical aperture of 0.40 was used to obtain the
spectra for samples inside the DAC. The Diamond anvil cell (DAC)
used in this study had 600 m diameter culet size, and is a four-
post-cells design from High-Pressure Diamond Optics, Tucson, AZ.
The gaskets were made by the inconel which were initially 250 m
thick. These gaskets were preindented before drilling a hole of
150-250 m in order to form a sample chamber. The ruby fluorescence
technique was used to calibrate the pressure and no pressure medium
was used (pure sample). The circular heater was used to heat the
DAC, and the samples were resistively heated by cartridge
heaters.
105Copyright ©-International Centre for Diffraction Data 2010 ISSN
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The DAC sits in the block and the entire assembly is heated. An
Omega temperature controller (model number CN76000) was used to
maintain a constant temperature during the measurement. The samples
of tris(hydroxymethyl)aminomethane (TRIS) were purchased from Alfa
Aesar and the purity was 99.8%. TRIS samples were ground to fine
powder with a mortar and pestle before loading them into the DAC
for Raman study. In-situ high temperature X-ray diffraction study
was used to determine the phase transformation of TRIS under
ambient pressure (1 atm) by using PANalytical X’Pert PRO at UNR.
The TRIS sample was heated at a heating rate of 5oC/min inside the
chamber filled with Argon gas. XRD patterns were taken at various
temperatures, and data were analyzed using X’Pert HighScore and MDI
Jade computer programs to determine the phase transformation,
crystal structures and lattice parameters. Differential scanning
calorimetric (DSC) study was used to determine the phase
transformation temperatures and enthalpies by using TA Instruments
DSC Q100 at UNR. RESULTS AND DISCUSSIONS In-situ high temperature
X-ray diffraction (XRD) and DSC studies were used to determine the
phase transformations of TRIS at ambient pressure (1 atm). The
solid-state (S-S) phase transition of TRIS occurs at 133.70 oC, and
the solid to liquid phase transition (S-L) temperature is 171.91 oC
which were determined by DSC. The enthalpies of phase
transformation are determined as HS-S = 267.0 J/g and HS-L = 25.7
J/g. X-ray diffraction patterns of TRIS from 25oC to 145oC were
shown in Figure 1. The low temperature XRD patterns of -TRIS phase
were determined as orthorhombic structure up to 130oC. The high
temperature -phase (BCC) occurs between 135oC to 145oC. There are
only two Bragg’s peaks shown in the XRD patterns of -phase, which
indicated the disordered phase (“Plastic” crystal) (BCC) at high
temperature range. These two Bragg’s peaks were assigned as (110)
and (200). The determination of the lattice parameters and volumes
of the -phase will be calculated based on these two peaks. Lattice
parameters and volumes of both - and -phases were calculated based
on the XRD patterns and the results were listed in Table 1. The
volumes of -TRIS phase were expanded from 608.19 to 616.44 cubic
angstrom from 25oC to 130oC, and from 321.76 to 323.34 cubic
angstrom at the temperature range of 135-145oC for the -TRIS phase.
Since there are four molecules (Z=4) in -TRIS orthorhombic unit
cell and two molecules (Z=2) in -phase BCC unit cell, we define a
new value of “formula volumes” as: volumes of unit cell / Z for
comparing the volume change between two different phases which
contain different Z values. The values of formula volumes can be
used to indicate the phase transformation. It was found there was a
rapid change of the formula volumes between 130oC and 135oC which
the formula volumes of TRIS were increased from 154.11 to 160.73
cubic angstrom.
106Copyright ©-International Centre for Diffraction Data 2010 ISSN
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Table 1. Lattice parameters and volumes of unit cell of - and -TRIS
phase at various temperatures.
Temperature (oC) Lattice Parameters (angstrom) Volume of Unit Cell
(cubic angstrom)
(Orthorhombic) Phase T a b c Vol 25 8.80137 8.85058 7.80759 608.19
50 8.82065 8.85613 7.81741 610.67 75 8.82601 8.85325 7.81986 611.03
100 8.84869 8.85977 7.82840 613.73 120 8.85360 8.86087 7.83207
614.43 130 8.86059 8.86576 7.84717 616.44
(BCC) Phase 135 6.8524 321.76 140 6.8573 322.45 145 6.8636
323.34
Figure 1. X-ray diffraction patterns of TRIS show low () and high
() temperature phase. Si was
used as an internal standard.
107Copyright ©-International Centre for Diffraction Data 2010 ISSN
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The Raman spectroscopy studies are used to determine high-pressure
and high-temperature phase transformation of TRIS. C-H stretching
modes can be found between 2800 cm-1 and 2950 cm-1, and N-H
stretching modes between 3300cm-1 and 3400cm-1. The changes in C-H,
N-H stretching modes (or peaks) and other low frequency regions can
be used to indicate the phase transitions of TRIS in this study. In
Figure 2, the temperature-dependent Raman spectra show that TRIS is
undergoing a phase transition to orientational disorder phase
(-orth.-BCC) between 131°C and 135°C at constant atmospheric
pressure (TRIS sample as-loaded pressure). This result confirmed
the X-ray diffraction results mentioned at above section. In the
left side of Figure 2, the evidence for this phase transition is
that a new peak (at 626 cm-1) emerges above 131° C. It also can be
found there are the two peaks at lower temperature phase at 888
cm-1 and 912 cm-1 converge to a single peak. In the right side of
the Figure 2, there are four peaks in C-H stretching modes region
at low temperature phase region converge into two peaks above 131°
C. The two N-H stretching peaks (3300cm-1 and 3400cm-1) which
significantly broaden above 131° C. It can is noticed that this
transition is from -TRIS (orthorhombic) to -TRIS (BCC) phase. The
pressure-dependent Raman spectra of TRIS at constant room
temperature are shown in Figure 3. In Figure 3, a phase transition
occurs between 0.35 GPa to 3.30 GPa at room temperature. This phase
transition is from (orth.) phase to a new high pressure TRIS phase.
The high pressure phase is denoted here as -TRIS, and it is stable
up to 6.04 GPa. The Raman spectra of 1.97 GPa indicated that the
-TRIS phase is continually transformed to the -TRIS phase at this
pressure range. There are 2 peaks (906 cm-1 and 924 cm-1) found in
(orth.) phase to converge slowly to a single peak in -TRIS phase,
and also can be found at 1037 cm-1and 1069 cm-1 above 0.35 GPa. In
the right side of the Figure 3, the four peaks which are seen in
the C-H stretching modes at low temperature converge into two peaks
above 0.35 GPa. Two N-H stretching peaks which significantly
broaden above 0.35 GPa and also shift towards right.
Figure 2. Temperature-dependent Raman spectra of TRIS at constant
atmospheric pressure. The
orientational order/disorder transition (-orth.-BCC) can be
observed above 131° C.
0 200 400 600 800 1000 1200 1400 1600
152 °C
135 °C
131 °C
126 °C
110 °C
71°C
31 °C
In te
n si
ar b
. u n
it s)
Raman Shift(cm-1)
2 8 0 0 2 9 0 0 3 0 0 0 3 1 0 0 3 2 0 0 3 3 0 0 3 4 0 0 3 5 0
0
( N H )
- T R I S ( o r t h . )
108Copyright ©-International Centre for Diffraction Data 2010 ISSN
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Figure 3. Pressure-dependent Raman spectra of TRIS at constant room
temperature. A new high
pressure -TRIS phase have been found. The phase transition can be
observed between 0.35 GPa to 3.30 GPa.
Figure 4. Pressure-dependent Raman spectra of TRIS at 50oC. The
phase transition can be
observed above 0.34 GPa.
0 200 400 600 800 1000 1200 1400 1600 60000
75000
90000
105000
120000
135000
150000
-TRIS (orth.)
TRIS (Cubic)
0 200 400 600 800 1000 1200 1400 1600 0
20000
40000
60000
80000
TRIS (Cubic)
-TRIS (orth.)
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Other sets of the pressure-dependent Raman spectra of TRIS were
plotted in Figure 4 to determine the phase transitions at 50oC. In
Figure 4, the Raman spectra of TRIS almost behave the same as the
results obtained at room temperature. There is a pressure induced
frequency shift of the peaks at 421 cm-1 and 520 cm-1 which also
slowly disappear at higher pressures. The peak at 470 cm-1 which
appears at lower pressures completely disappears above 0.34 GPa and
also the two peaks at 892 cm-1 and 916 cm-1 slowly converge into a
single peak above 0.34 GPa. Similarly, the C-H and N-H stretching
modes regions show peaks converging or broadening above 0.34 GPa.
Other sets of Raman spectra under various pressures and
temperatures show that the -TRIS phase was stable from room
temperature to 130oC up to 6.04 GPa. No evidence shows if the -TRIS
phase transforms to the -TRIS phase above 130oC due to the
limitation of the instruments which the DAC can not hold the
pressure if the temperature is increased above 130oC.
CONCLUSIONS
The formula volumes of unit cell for the - and -TRIS have been
calculated to indicate the phase transformation at ambient pressure
(1 atm). High-pressures and high-temperatures Raman spectroscopy
studies have been investigated on tris(hydroxymethyl)aminomethane
(TRIS) inside a diamond anvil cell. A phase transition was observed
above 0.35 GPa from -TRIS phase to form the new high pressure -TRIS
phase up to 6.04 GPa and 130oC. The -TRIS phase were also found to
transform to -TRIS (BCC) phase at ~133oC under both as-loaded
sample pressure and ambient pressure.
ACKNOWLEDGEMENTS This research was supported by the U.S. DOE
through the Carnegie-DOE Alliance Center (CDAC) grant
DE-FC-03-03NA00144. The authors also thanks the Optical Properties
of Materials Laboratory at UNR gratefully acknowledge support from
the US DOE under grant No. DEFC5Z-06NA27616. REFERENCES Chandra,
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