x-ray and raman spectra studies on thermal energy storage - icdd
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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
104Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002 Advances in X-ray Analysis, Volume 53
ICDD Website - www.icdd.com
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 1097-0002 Advances in X-ray Analysis, Volume 53
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 1097-0002 Advances in X-ray Analysis, Volume 53
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 1097-0002 Advances in X-ray Analysis, Volume 53
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 1097-0002 Advances in X-ray Analysis, Volume 53
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.)
109Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002 Advances in X-ray Analysis, Volume 53
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, D., Chien, W., Gandikotta, V., and Lindle, D. W. (2002a). “Heat capacities of "plastic crystal" solid state thermal energy storage materials,” Zeitschrift Fur Physikalische Chemie (Muenchen, Germany) - International Journal of Research in Physical Chemistry & Chemical Physics, 216(12), 1433-1444. Chandra, D., Mandalia, H., Chien, W., Lindle, D. W., and Rudman, R. (2002b). “Solid-solid phase transition in trimethylolpropane (TRMP),” Zeitschrift Fur Physikalische Chemie (Muenchen, Germany) - International Journal of Research in Physical Chemistry & Chemical Physics, 216(12), 1389-1400.
110Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002 Advances in X-ray Analysis, Volume 53
Chellappa R. and Chandra D. (2003). “Phase diagram calculations of organic "plastic crystal" binaries: (NH2)(CH3)C(CH2OH)2-(CH3)2C(CH2OH)2 system,” CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry, 27(2), 133-140. Divi, S., Chellappa, R., and Chandra D. (2006). “Heat capacity measurement of organic thermal energy storage materials,” Journal of Chemical Thermodynamics, 38(11), 1312-1326. Eilerman, D. and Rudman, R. (1980). “Polymorphism of crystalline poly(hydroxymethyl) compounds. III. The structures of crystalline and plastic tris(hydroxymethyl)aminomethane,” Journal of Chemical Physics, 72(10), 5656-5666. Kanesaka, I. and Mizuguchi, K. (1998). “Vibrational study of hydrogen bonds and structure of tris(hydroxymethyl)aminomethane,” Journal of Raman Spectroscopy, 29(9), 813-817. Granzow, B. (1996). “Hydrogen bonding and phase transitions of a group of alcohols derived from 2,2-dimethylpropane,” Journal of Molecular Structure, 381(1-3), 127-131. Granzow, B., Klaeboe P., and Sablinskas V. (1995). “Molecular spectroscopic studies and ab initio calculations of four alcohols derived from 2,2-dimethylpropane,” Journal of Molecular Structure, 349, 153-156. Marzocchi, M. P. and Castellucci, E. (1971). “Vibrational crystal spectra of pentaerythritol-do and -d4,” Journal of Molecular Structure, 9(1-2), 129-137. McLachlan, R. D. and Carter, V. B. (1971). “Raman spectra of crystalline pentaerythritol and pentaerythritol-d4,” Spectrochimica Acta Part A: Molecular Spectroscopy, 27(6), 853-861.
Schroetter, S., Bougeard, D. and Lascombe., J. (Eds.) (1986). Dynamics of Molecular Crystals (Elsevier, Grenoble, France), p. 213.
111Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002 Advances in X-ray Analysis, Volume 53
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
104Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002 Advances in X-ray Analysis, Volume 53
ICDD Website - www.icdd.com
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 1097-0002 Advances in X-ray Analysis, Volume 53
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 1097-0002 Advances in X-ray Analysis, Volume 53
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 1097-0002 Advances in X-ray Analysis, Volume 53
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 1097-0002 Advances in X-ray Analysis, Volume 53
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.)
109Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002 Advances in X-ray Analysis, Volume 53
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, D., Chien, W., Gandikotta, V., and Lindle, D. W. (2002a). “Heat capacities of "plastic crystal" solid state thermal energy storage materials,” Zeitschrift Fur Physikalische Chemie (Muenchen, Germany) - International Journal of Research in Physical Chemistry & Chemical Physics, 216(12), 1433-1444. Chandra, D., Mandalia, H., Chien, W., Lindle, D. W., and Rudman, R. (2002b). “Solid-solid phase transition in trimethylolpropane (TRMP),” Zeitschrift Fur Physikalische Chemie (Muenchen, Germany) - International Journal of Research in Physical Chemistry & Chemical Physics, 216(12), 1389-1400.
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Chellappa R. and Chandra D. (2003). “Phase diagram calculations of organic "plastic crystal" binaries: (NH2)(CH3)C(CH2OH)2-(CH3)2C(CH2OH)2 system,” CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry, 27(2), 133-140. Divi, S., Chellappa, R., and Chandra D. (2006). “Heat capacity measurement of organic thermal energy storage materials,” Journal of Chemical Thermodynamics, 38(11), 1312-1326. Eilerman, D. and Rudman, R. (1980). “Polymorphism of crystalline poly(hydroxymethyl) compounds. III. The structures of crystalline and plastic tris(hydroxymethyl)aminomethane,” Journal of Chemical Physics, 72(10), 5656-5666. Kanesaka, I. and Mizuguchi, K. (1998). “Vibrational study of hydrogen bonds and structure of tris(hydroxymethyl)aminomethane,” Journal of Raman Spectroscopy, 29(9), 813-817. Granzow, B. (1996). “Hydrogen bonding and phase transitions of a group of alcohols derived from 2,2-dimethylpropane,” Journal of Molecular Structure, 381(1-3), 127-131. Granzow, B., Klaeboe P., and Sablinskas V. (1995). “Molecular spectroscopic studies and ab initio calculations of four alcohols derived from 2,2-dimethylpropane,” Journal of Molecular Structure, 349, 153-156. Marzocchi, M. P. and Castellucci, E. (1971). “Vibrational crystal spectra of pentaerythritol-do and -d4,” Journal of Molecular Structure, 9(1-2), 129-137. McLachlan, R. D. and Carter, V. B. (1971). “Raman spectra of crystalline pentaerythritol and pentaerythritol-d4,” Spectrochimica Acta Part A: Molecular Spectroscopy, 27(6), 853-861.
Schroetter, S., Bougeard, D. and Lascombe., J. (Eds.) (1986). Dynamics of Molecular Crystals (Elsevier, Grenoble, France), p. 213.
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