Energetics of Nanomaterials

This project, "Energetics of Nanomaterials," represents a three-year collaboration among Alexandra Navrotsky (UC Davis), Brian Woodfield and Juliana Boerio-Goates (BYU), and Frances Hellman (UC Berkeley). It's purpose has been to explore the differences between bulk materials, nanoparticles, and thin films in term of their thermodynamic properties, with an emphasis on heat capaacities and entropies, as well as enthalpies. the three groups have brought very different expertise and capabilities to the project. Navrotsky is a solid-state chemist and geochemist, with a unique Thermochemistry Facility emphasizing enthalpy of formation measurements by high temperature oxide melt and room temperatue acid solution calorimetry. Boerio-Goates and Woodfield are calorimetry. Hellman is a physicist with expertise in magnetism and heat capacity measurements using microscale "detector on a chip" calorimetric technology that she pioneered. The overarching question of our work is "How does the free energy play out in nanoparticles?", or "How do differences in free energy affect overall nanoparticle behavior?" Because the free energy represents the temperature-dependent balance between the enthalpy of a system and its entropy, there are two separate, but related, components to the experimental investigations: Solution calorimetric measurements provide the energetics and two types of heat capacity measurements the entropy. We use materials that are well characterized in other ways (structurally, magnetically, and chemically), and samples are shared across the collaboration

Heat capacity from 5 to 350 K and thermodynamic properties of cesium nitrate to 725 K

The low-temperature heat capacity (5 to 350 K) of CsNO3 was determined by adiabatic calorimetry. No anomalies were observed in this temperature region, the curve of heat capacity against temperature having the normal sigmoid shape. These measurements yielded the thermodynamic properties at 298.15 K: Cp[deg]=(96.47+/-0.19)J K- mol-; S[deg]=(153.95+/-0.31)J K- mol-; {H[deg](T) - H[deg](O)} =(20046+/-40)J mol-; {G[deg](T) - H[deg](O)}/T =(86.71+/-17)J K- mol-.These measurements have been combined with published high-temperature heat capacities to give the thermodynamic properties of CsNO3 to 725 K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24563/1/0000844.pd

Thermodynamics of thallium alkanoates I. Heat capacity and thermodynamic functions of thallium(I) n-hexanoate

The sub-ambient heat capacity of thallium(I) n-hexanoate is characterized by transitions at 203.5 and 208.3 K which show Cp, m/R maxima of about 400 and 2500 and ([Delta]Sm/R)'s of 1.03 and 1.07. Both appear to be essentially first order and show typical under-cooling phenomena. The heat capacities are in excellent accord with the d.s.c. values of Fernandez-Martin, Lopez de la Fuente, and Cheda over the common range of super-ambient values. At T = 298.15 K the values of {Smo(T)-Smo(0)}/R, {Hmo(T)-Hmo(0)}/R, and -{Gmo(T)-Hmo(0)}/RT are 39.06, 5880 K, and 19.33. Smoothed thermodynamic functions are tabulated through melting.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25683/1/0000237.pd

Thermodynamic Studies Of Reorientational Motion In Pi-molecular Compounds.

Ph.D.ChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/178876/2/8007709.pd

Thermophysics of the lanthanide trihydroxides IV. The heat capacity of Ho(OH)3 from 11 to 350 K. Lattice and Schottky contributions

From values of the heat capacity of microcrystalline Ho(OH)3 determined by precise adiabatic calorimetry from 11 to 350 K, the Schottky contribution associated with the Stark splitting of the ground J-manifold (5I8) was resolved by means of an extrapolation of the known lattice heat-capacity variation between La(OH)3 and Gd(OH)3. This calorimetrically deduced Schottky contribution is compared with that calculated from spectroscopically derived energy levels of Ho3+ doped Y(OH)3. Because the lattice parameters of Y(OH)3 and Ho(OH)3 are nearly identical it is assumed that the electronic energy levels of the Ho3+ ions are the same in either host lattice. These results together with independent heat-capacity measurements made at lower temperatures were used to adjust the low-temperature thermophysical functions to evaluate Cp/R, So/R, and -["Go - Ho(0)'/RT], at 298.15 K as 13.80, 15.64, and 7.855.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24580/1/0000863.pd

Low Temperature Heat Capacity Study of Fe₃PO₇ and Fe₄(P₂O₇)₃

The low temperature heat capacities of Fe3PO7 and Fe4(P2O7)3 have been measured using a Quantum Design Physical Property Measurement System (PPMS) over the temperature range from (2 to 300) K. Phase transitions due to Fe3+ magnetic ordering have been determined in the heat capacities at temperatures of (164.5 and 47.6) K for Fe3PO7 and Fe4(P 2O7)3, respectively, which agrees well with the magnetic measurements reported in the literature. Also, another small transition occurring at around 27 K for Fe4(P2O 7)3 has been found for the first time. The thermodynamic functions and magnetic heat capacities have been calculated based on the curving fitting of the experimental heat capacity values. Using the fitted heat capacity results, the standard molar entropies have been calculated to be (219.73 ± 2.42) J · K-1 · mol-1 and (561.03 ± 6.17) J · K-1 · mol-1 for Fe3PO7 and Fe4(P2O7) 3, respectively. The calculated magnetic entropy of Fe 3PO7 using the magnetic heat capacity suggests that the five 3d-electrons in the Fe3+ are in the t2g orbital with a low spin state according to crystal field theory. © 2013 Published by Elsevier Ltd

Low Temperature Heat Capacity Study of Fe(PO₃)₃ and Fe₂P₂O₇

The heat capacities of two iron phosphates, Fe(PO3)3 and Fe2P2O7, have been measured over the temperature range from (2 to 300) K using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). A phase transition related to magnetic ordering has been found in the heat capacity at T = 8.76 K for Fe(PO3)3 and T = 18.96 K for Fe2P 2O7, which are comparable with literature values from magnetic measurements. by fitting the experimental heat capacity values, the thermodynamic functions, magnetic heat capacities, and magnetic entropies have been determined. Additionally, theoretical fits at low temperatures suggest that Fe2P2O7 has an anisotropic antiferromagnetic contribution to the heat capacity and a large linear term likely caused by oxygen vacancies. Further data fitting in a series over widened temperature regions found that this linear term exists only below 15 K and disappears gradually from (15 to 17) K. © 2013 Published by Elsevier B.V. All rights reserved

Low Temperature Heat Capacity Study of FePO₄ and Fe₃(P₂O₇)₂

The heat capacities of FePO4 and Fe3(P 2O7)2 have been measured using a Quantum Design Physical Property Measurement System (PPMS) over the temperature range from (2 to 300) K. The phase transition due to the Fe3+ magnetic ordering in FePO4 has been determined to occur at T = 25.0 K, which agrees well with magnetic measurements reported in the literature. For Fe3(P 2O7)2, a Schottky anomaly and a four-peak phase transition have been found below 50 K. The thermodynamic functions, magnetic heat capacities, and magnetic entropies of these two compounds have been calculated based on curve fitting of the experimental heat capacity values. The standard molar entropy at T = 298.15 K has been obtained to be (122.21 ± 1.34) J · K-1 · mol-1 and (384.12 ± 4.23) J · K-1 · mol-1 for FePO4 and Fe3(P2O7)2, respectively. All rights reserved

Entropy of Pure-Silica Molecular Sieves

The entropies of a series of pure-silica molecular sieves (structural codes ^*BEA, FAU, MFI, and MTT) are obtained by calorimetric measurements of low-temperature heat capacity. The third-law entropies at 298.15 K are (on the basis of 1 mol of SiO_2):  ^*BEA, 44.91 ± 0.11 J·K^(-1)·mol^(-1); FAU, 44.73 ± 0.11 J·K^(-1)·mol^(-1); MFI, 45.05 ± 0.11 J·K^(-1)·mol^(-1); MTT, 45.69 ± 0.11 J·K^(-1)·mol^(-1); while the corresponding entropies of transition from quartz at 298.15 K are ^*BEA, 3.4 J·K^(-1)·mol^(-1); FAU, 3.2 J·K^(-1)·mol^(-1); MFI, 3.6 J·K^(-1)·mol^(-1); MTT, 4.2 J·K^(-1)·mol^(-1). The entropies span a very narrow range at 3.2−4.2 J·K^(-1)·mol^(-1) above quartz, despite a factor of 2 difference in molar volume. This confirms that there are no significant entropy barriers to transformations between SiO_2 polymorphs. Finally, the Gibbs free energy of transformation with respect to quartz is calculated for eight SiO_2 phases and all are found to be within twice the available thermal energy of each other at 298.15 K