Acid Solution Calorimetry Research Articles

Thermodynamics of hybrid manganese formate perovskites.

Hybrid organic-inorganic materials, both dense and porous, have gained significant attention in recent years due to their extreme tunability in terms of compositions and functional properties. A deep understanding of their intrinsic stability is crucial to accelerate the discovery of new compositions that are not only functional but also thermodynamically stable. Here, we report the first systematic experimental study of the effect of A-site cations on the thermodynamic stability of a series of hybrid manganese formate perovskites [AH]Mn[HCOO]3 with AH+ = CH3NH3 +, (CH3)2NH2 +, (CH2)3NH2 +, CH(NH2)2 +, and C(NH2)3 + using acid solution calorimetry. Our studies show that the thermodynamic stability among these does not directly correlate with their tolerance factors, in contrast to trends seen among inorganic perovskites. On the other hand the enthalpy of formation correlates linearly with the enthalpy of dissolution in aqueous hydrochloric acid of the corresponding A-site cation salt, suggesting that the interactions between the A-site cation and the framework, rather than geometric factors, dominate the energetics of these perovskites.

Enthalpy of mixing of solid solution rhomboclase – Indium-substituted rhomboclase (H3O) Fe1−xInx(SO4)2·nH2O

Solid solution of rhomboclase [nominally (H3O) Fe(SO4)2·3H2O] with Fe-In substitution was synthesized by coprecipitation and hydrothermal treatment and investigated by chemical, X-ray diffraction, and thermodynamic analysis in this study. The solid solution is continuous over the whole stoichiometric range despite significant differences in ionic radii between Fe3+ and In3+. Enthalpy of formation of rhomboclase and enthalpies of mixing of solid solution rhomboclase – indium-substituted rhomboclase were determined by acid-solution calorimetry in 5 mol·dm−1 HCl at T = 298.15 K and p = 1 bar. The actual compositions of the studied synthetic end members are (H3O)0.798Fe(SO4)1.899·3.078H2O (rhomboclase with molecular mass of 308.8719 g·mol−1) and (H3O)1.067In(SO4)2.034·3.017H2O (indium-substituted rhomboclase with molecular mass of 384.8377 g·mol−1). The enthalpies of mixing were obtained for a series of four indium-incorporating rhomboclase synthetic samples with molar In/(In + Fe) ratios of 0.115, 0.226, 0.537, and 0.733. The enthalpy of formation from elements in their standard state at T = 298.15 K and p = 1 bar obtained in this study by thermochemical cycle for (H3O)0.798Fe(SO4)1.899·3.078H2O is: ΔfH298.15°=-2815.2±2.8 kJ·mol−1. Mean measured enthalpies of dissolution for (H3O)0.798Fe(SO4)1.899·3.078H2O and (H3O)1.067In(SO4)2.034·3.017H2O are: ΔdissH°=14.47±0.42 kJ·mol−1 and -6.68±0.27 kJ · mol−1, respectively. Enthalpies of mixingΔmixH° have small positive values and can be fitted by a regular solid solution model with a mixing parameter W=4.26±0.32 kJ·mol−1.

Experimental Investigation of Thermodynamic Stabilization in Boron Imidazolate Frameworks (BIFs) Synthesized by Mechanochemistry.

This study experimentally explores the energetics for the formation of boron-imidazolate frameworks (BIFs), which are synthesized by mechanochemistry. The topologically similar frameworks employ the same tetratopic linker based on tetrakis(imidazolyl)boric acid but differ in the monovalent cation metal nodes. This permits assessment of the stabilizing effect of metal nodes in frameworks with sodalite (SOD) and diamondoid (dia) topologies. The enthalpy of formation from endmembers (metal oxide and linker), which define thermodynamic stability of the structures, has been determined by use of acid solution calorimetry. The results show that heavier metal atoms in the node promote greater energetic stabilization of denser structures. Overall, in BIFs the relation between cation descriptors (ionic radius and electronegativity) and thermodynamic stability depends on framework topology. Thermodynamic stability increases with the metallic character of the cation employed as the metal node, independent of the framework topology. The results suggest unifying aspects for thermodynamic stabilization across MOF systems.

Thermodynamic and structural variations along the olivenite–libethenite solid solution

Abstract. Many natural secondary arsenates contain a small fraction of phosphate. In this work, we investigated the olivenite–libethenite (Cu2(AsO4)(OH)–Cu2(PO4)(OH)) solid solution as a model system for the P–As substitution in secondary minerals. The synthetic samples spanned the entire range from pure olivenite (Xlib=0) to libethenite (Xlib=1). Acid-solution calorimetry determined that the excess enthalpies are non-ideal, with a maximum at Xlib=0.6 of +1.6 kJ mol−1. This asymmetry can be described by the Redlich–Kister equation of Hex= Xoli⋅Xlib [A+B(Xoli−Xlib)], with A=6.27 ± 0.16 and B=2.9 ± 0.5 kJ mol−1. Three-dimensional electron diffraction analysis on the intermediate member with Xlib=0.5 showed that there is no P–As ordering, meaning that the configurational entropy (Sconf) can be calculated as -R(Xoliln⁡Xoli+Xlibln⁡Xlib). The excess vibrational entropies (Svibex), determined by relaxation calorimetry, are small and negative. The entropies of mixing (Sconf+Svibex) also show asymmetry, with a maximum near Xlib=0.6. Autocorrelation analysis of infrared spectra suggests local heterogeneity that arises from strain relaxation around cations with different sizes (As5+ / P5+) in the intermediate members and explains the positive enthalpies of mixing. The length scale of this strain is around 5 Å, limited to the vicinity of the tetrahedra in the structure. At longer length scales (≈15 Å), the strain is partially compensated by the monoclinic–orthorhombic transformation. The volume of mixing shows complex behavior, determined by P–As substitution and symmetry change. A small (0.9 kJ mol−1) drop in enthalpies of mixing in the region of Xlib=0.7–0.8 confirms the change from monoclinic to orthorhombic symmetry.

Role of Anions in Stabilizing the [Zn–Al] Layered Double Hydroxides: A Thermodynamic Study

Room-temperature acid solution calorimetry, high-temperature oxide melt solution calorimetry, and low-temperature heat capacity measurements were employed to calculate the thermodynamic stabilities of the [Zn–Al–X] layered double hydroxides (LDH) containing different anions (X = Cl–, CO32–, and SO42–). Cryogenic heat capacity measurements demonstrated a Schottky-type anomaly in the heat capacity of all three LDHs below 11 K. This anomaly is attributed to the tunneling of protons between adjacent oxygen atoms in the LDH interlayer as this creates an energy system similar to a two-level system modeled with a Schottky term. These heat capacity measurements were also used to determine vibrational entropies which, when combined with configurational entropies, provide standard entropies of these LDHs. Enthalpies of formation of LDHs from binary components were determined and combined with the entropies of formation to calculate Gibbs free energies. Based on these values, the order of stability is [Zn–Al–SO4] > [Zn–Al–CO3] > [Zn–Al–Cl]. This trend results from a combination of the interlayer spacing, amount of water in the interlayer, interactions among the interlayer species, and interactions between the metal hydroxide layer and the interlayer.

Thermodynamic and magnetic properties for Dy2Fe14B determined by heat capacity measurement from very low to high temperatures and solution calorimetry

The thermodynamic and magnetic properties for Dy2Fe14B, a principal constituent of rare-earth magnets, were investigated as a function of temperature via calorimetric measurements. Its standard entropy, Δ0TSm∘, was obtained from the molar heat capacity, Cp,m∘, at 2 − 850 K using Debye-Einstein spin-wave functions. The standard enthalpy of formation, ΔfHm∘, was determined by acid solution calorimetry to provide the standard Gibbs energy of formation ΔfGm∘(T) as a function of temperature. ΔfGm∘(T) is useful for Calphad phase diagram calculations. The magnetic moment was calculated by separating the spin and lattice vibration terms for Cp,m∘ via the Curie temperature of 594.1 K. The results agree with direct magnetization measurements and indicate that the Fe 3d magnetic moments magnetize Dy2Fe14B by aligning by an exchange interaction between the Dy 4f and Dy 5d and Fe 3d moments in a second-order phase transition. These findings will contribute to the design of magnetic materials.

Stability and solubility of members of tin perovskites in the schoenfliesite subgroup, [formula omitted](BSn[formula omitted])(OH,O)[formula omitted] (B = Ca, Fe[formula omitted], Mg, Mn[formula omitted], Zn, Cu)

In this work, we determined thermodynamic properties of a suite of tin perovskites □2(BSn4+)(OH,O)6 that correspond to the minerals burtite (B = Ca), jeanbandyite (Fe3+), schoenfliesite (Mg), wickmanite (Mn), vismirnovite (Zn), and mushistonite (Cu). Purity of the samples was verified by powder X-ray diffraction, chemical analysis (ICP-OES), solid state 119Sn magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, 57Fe Mössbauer spectroscopy, thermogravimetry (TG), and Karl-Fischer titration. Enthalpies of formation (ΔfHo) were determined by acid-solution calorimetry (in 5 N HCl at T = 298 K, with SnCl4 as the reference phase), that for jeanbandyite also in high-temperature oxide-melt calorimetry (in sodium molybdate at T = 973 K, with SnO2 as the reference phase). For the two methods, the difference for the ΔfHo values is 10.7 kJ·mol−1, a fair agreement. Because of the high H2O content of the studied phases, acid-solution calorimetry was given preference as it is less sensitive to errors in H2O determination. Entropy was estimated, including configurational or magnetic contribution. The resulting ΔfGo (kJ·mol−1) and logKsp values are: CaSn(OH)6−1885.8±7.6, 7.7; FeSn(OH)5O −1425.4±7.6, −5.8; MgSn(OH)6−1812.4±7.5, 3.3; ZnSn(OH)6−1519.6±7.6, 0.7; MnSn(OH)6−1598.7±7.7, 1.0; CuSn(OH)6−1311.2±7.9, 0.0. The logKsp value relate to reaction MSn(OH)6 + 6H+→ M2+ + Sn4+ + 6H2O or FeSn(OH)5O + 7H+→ Fe3+ + Sn4+ + 6H2O. The solid solution between vismirnovite and mushistonite was found to be thermodynamically non-ideal, with a mixing parameters W=−15.38 kJ·mol−1. Calculations of Gibbs free energies of selected reactions show that the tin perovskites are stabilized at basic pH. For example, burtite becomes stable with respect to cassiterite (SnO2) in systems buffered by calcite, gypsum or the C-S-H phase from cement at pH > 9–10.5. Similarly, jeanbandyite is stabilized in systems buffered by ferrihydrite [Fe(OH)3] but not in those buffered by goethite (FeOOH). Saturation indices calculated from polluted water in field settings show the same trend; the tin perovskites are stable under alkaline conditions and the solutions become supersaturated with respect to the tin perovskites. Hence, under alkaline conditions, such phases could take up and retain tin in the environment.

Drop Solution Calorimetric Studies of Interface Enthalpy of Cubic Silver (I) Oxide (Ag<sub>2</sub>O) Nanocrystals

The nanoscale, cubic silver (I) oxide (Ag2O.nH2O) with different particles sizes and surface areas were synthesized by a wet chemical technique. The prepared crystallite size ranges were from (33.3±0.3 to 39.4±0.4 nm). Interface areas were estimated by comparing the surface areas measured by N2adsorption to the crystallite sizes refined from X-ray diffraction data. The interface enthalpy of Ag2O.nH2O nanocrystal was measured using isothermal acid solution calorimetry in 25%HNO3at 26°C. The interface enthalpy was verified by utilizing thermodynamic cycle. The enthalpies of drop solution (ΔHds) for Ag2O.nH2O are exothermic and range from (-62.228±0.197) to (-64.025±0.434 kJ/mol), while its interface enthalpy is (0.842±0.508 J/m2). This work provides the first calorimetric measurement of the interface enthalpy of nanocrystalline silver (I) oxide (Ag2O.nH2O).

Thermodynamic properties, crystal structure and phase relations of pushcharovskite [Cu(AsO<sub>3</sub>OH)(H<sub>2</sub>O) ⋅ 0.5H<sub>2</sub>O], geminite [Cu(AsO<sub>3</sub>OH)(H<sub>2</sub>O)] and liroconite [Cu<sub>2</sub>Al(AsO<sub>4</sub>)(OH)<sub>4</sub> ⋅ 4H<sub>2</sub>O

Abstract. The phases pushcharovskite, geminite and liroconite were synthesized or acquired and characterized by powder X-ray diffraction, infrared spectroscopy, electron microprobe analysis, thermogravimetric analysis and optical emission spectrometry, as needed. Their thermodynamic properties were determined by a combination of acid-solution calorimetry and relaxation calorimetry, resulting in Gibbs free energies of formation (ΔfGo, all values in kilojoules per mole) of -1036.4±3.8 (pushcharovskite, Cu(AsO3OH)(H2O)⋅0.5H2O) and -926.7±3.2 (geminite, Cu(AsO3OH)(H2O)). For the natural liroconite (Cu2Al[(AsO4)0.83(PO4)0.17](OH)4⋅4H2O), ΔfGo=-2996.3±9.2 kJ mol−1. The estimated ΔfGo for the endmember Cu2Al(AsO4)(OH)4⋅4H2O is −2931.6 kJ mol−1. The crystal structure of liroconite was refined (R1=1.96 % for 962 reflections with I>3σ(I)) by single-crystal X-ray diffraction and the positions of H atoms, not known previously, were determined. Liroconite is a rare mineral, except for several localities, notably Wheal Gorland in England. Thermodynamic modelling showed that liroconite will be preferred over olivenite if the Al(III) concentration in the fluid reaches levels needed for saturation with X-ray amorphous Al(OH)3. We assume that such fluids are responsible for the liroconite formation during contemporaneous oxidation of primary Cu–As ores and pervasive kaolinization of the host peraluminous granites. pH had to be kept in mildly acidic (5–6), and the activities of dissolved silica were too low to form dioptase. The main stage with abundant liroconite formation was preceded by an acidic episode with scorodite and pharmacosiderite and followed by a late neutral to mildly basic episode with copper carbonates. Geminite and pushcharovskite, on the other hand, are minerals typical for very acidic solutions. At the studied site in Jáchymov (Czech Republic), extremely acidic water precipitates arsenolite; sulfate is removed by formation of gypsum. Geminite associates with other acidic minerals, such as slavkovite, yvonite and minerals of the lindackerite group. Pushcharovskite is metastable with respect to geminite and probably converts quickly to geminite under field conditions.

Energetic Cost for Being "Redox-Site-Rich" in Pseudocapacitive Energy Storage with Nickel-Aluminum Layered Double Hydroxide Materials.

Defining the energetic landscape of pseudocapacitive materials such as transition metal layered double hydroxides (LDHs) upon redox-site enrichment is essential to harnessing their power for effective energy storage. Here, coupling acid solution calorimetry, in situ XRD, and in situ DRIFTS, we demonstrate that as the Ni/Al ratio increases, both as-made (hydrated) and dehydrated NiAl-LDH samples are less stable as evidenced by their enthalpies of formation. Moreover, the higher specific capacity at an intermediate Ni/Al ratio of 3 is enabled by effective water-LDH interactions, which energetically stabilize the excessive near-surface Ni redox sites, solvate intercalated carbonate ions, and fill the expanded vdW gap, paying for the "energetic cost" of being "redox-site-rich". Thus, from a thermodynamic perspective, engineering molecule/solid-LDH interactions on the nanoscale with confined guest species other than water, which energetically impose stronger stabilization, may help us to achieve their specific capacitance potential.

Thermodynamic properties of mixed-layer illite-smectite by calorimetric methods: Acquisition of the enthalpies of mixing of illite and smectite layers

The stability of illite-smectite interstratified with respect to discrete illite and smectite minerals was investigated by measuring their thermodynamic properties. The standard thermodynamic properties of the illite-smectite ISCz-1 mineral (G, H, S, Cp, and V) were determined between 298.15 K and 375 K by using calorimetric methods. Moreover, the enthalpies of mixing between the illite and smectite layers were measured at 298.15 K by acid solution calorimetry from a complete series of illite-smectite interstratified minerals (Shinzan area, Japan). The measured values were slightly negative, with a minimum value of −3.7 kJ.mol−1. This contributed to the stability of the mixed-layer with respect to a mechanical mixture of illite and smectite. In addition, the model from Blanc et al. (2015) was implemented to estimate the thermodynamic properties of the interstratified illite-smectite ISCz-1 mineral. The predicted values were consistent with the experimental results. However, the estimates were slightly improved by considering the thermodynamic properties of the mixture of the illite and smectite components and then adding the terms of energies of mixing. This could be confirmed by establishing the stability domains of ISCz-1 and those of the corresponding illite and smectite end-members according to Meunier and Velde’s determination of the smectite to illite reaction pathways (Meunier and Velde, 1989).

Calorimetric method for determining the thermochemical energy storage capacities of redox metal oxides

Transition metal oxide compounds have been demonstrated to be promising candidates for thermochemical processes, particularly energy storage. A calorimetric method for measuring enthalpy of these materials is developed in this work. A combination of drop calorimetry and acid-solution calorimetry is used to measure the total enthalpy and standard enthalpy of formation of these materials for compounds that form at high temperatures (≥ 1000 °C) after undergoing thermal reduction. These measurements are used to compute the energy storage potential of these materials for a specified set of redox cycle operating temperatures. The construction and calibration of appropriate calorimeter devices are described. A novel approach to performing acid-solution calorimetry is introduced by including tin (II) chloride as a reducing agent for enhancing the dissolution rate of these compounds sufficiently so that acid-solution calorimetry can be implemented accurately. The general procedure is presented and applied to three variations of magnesium-manganese oxide materials for a redox cycle operating under an oxygen partial pressure of 0.2 atm between 1000 and 1500 °C. Using this method, the total energies stored by magnesium-manganese oxides of molar ratios Mn/Mg of 2/1, 1/1, and 2/3 were found to be 924 ± 56.7, 1029 ± 57.0, and 1070 ± 64.2 kJ kg−1, respectively.

Magnesium-manganese oxides for high temperature thermochemical energy storage

Abstract The reactive stability and energy density of magnesium-manganese oxides for high-temperature thermochemical energy storage have been investigated. Three variations of material with molar ratios of manganese to magnesium of 2/3, 1/1, and 2/1 were prepared using solid-state reaction synthesis and were tested for thermochemical reactive stability and energy storage capability. Results show that oxygen released and absorbed (standard cm3 g−1) by the materials remains unchanged over 20 cycles when cycled between 1200 and 1500 °C under an oxygen partial pressure (PO2) of 0.2 atm, indicating excellent reactive stability at high temperatures. Additional confirmation of reactive stability was obtained through testing over 10 energy storage cycles between 1000 and 1500 °C. The energy density of the material between 1000 and 1500 °C was determined through a combination of acid-solution calorimetry and drop calorimetry. The total volumetric energy densities (chemical, phase change, and sensible) obtained for samples of Mn/Mg of 2/3, 1/1, and 2/1 cycled between 1000 and 1500 °C are 1596, 1626 and 1654 MJ m-3, respectively.

Analysis of thermodynamic data of calcium aluminate monocarbonate hydrate

Some thermodynamic properties of calcium aluminate monocarbonate hydrate (3CaO⋅Al2O3⋅CaCO3⋅10.7H2O), a typical hydration product of cement were determined in this study. This includes enthalpy ΔfH° = −8166.4 ± 7.7 kJ/mol, standard entropy S° = 652.4 ± 2.2 J/(mol⋅K) and heat capacity Cp° = 716.8 ± 3.6 J/(mol⋅K) at 298.15 K. The Gibbs free energy calculated from these values is in good agreement with solubility measurements. This demonstrates that the enthalpy and entropy of phases related to cement chemistry can be correctly determined using acid solution calorimetry and low temperature relaxation calorimetry in combination with heat of dissolution reference data for CaO, calcite and AlCl3⋅6H2O reported in this study.

Lithium aluminum‐layered double hydroxide chlorides (LDH): Formation enthalpies and energetics for lithium ion capture

AbstractLayered aluminum double hydroxide chloride sorbents, LiCl∙Al2(OH)6.nH2O, Li‐LDH, have shown promising application in selective Li extraction from geothermal brines. Maintaining LiCl uptake capacity and retaining a long cycle life are critical to widespread application of sorbent materials. To elucidate the energetics of Li capture, enthalpies of LDH with different Li content have been measured by acid solution calorimetry. The formation enthalpies generally become less exothermic as the Li content increases, which indicates that Li intercalation destabilizes the structure, and the enthalpies seem to approach a limit after the Li content x = 2Li/Al exceeds 1. To improve stability, metal doping of the aluminum LDH structure with iron was performed. Introduction of a metal with greater electron density but a similar ionic radius was postulated to improve the stability of the LDH crystal structure. The calorimetric results from Fe‐doped LDH samples corroborate this as they are more exothermic than LDH‐lacking Fe. This suggests that Fe doping is an effective way to stabilize the LDH phase.

Determination of the standard molar enthalpies of formation and heat capacities of Bi25FeO39 (s) and Bi2Fe4O9 (s) by calorimetry

Abstract The standard enthalpies of formation of Bi25FeO39 (s) and Bi2Fe4O9 (s), at 298.15 K were determined by acid solution calorimetry and are found to be (−7.55 ± 0.32) × 103 kJ mol−1 and (−2.17 ± 0.07) × 103 kJ mol−1, respectively. Heat capacities of Bi25FeO39 (s) and Bi2Fe4O9 (s) were measured using differential scanning calorimetry (DSC). The measured heat capacities as a function of temperature are expressed as: Cp (J K−1 mol−1) ± 49.9 = 1529.9 + 200.6 × 10−3 T − 21.6 × 106 T−2 (T/K: 308–818), Cp (J K−1 mol−1) ± 11.0 = 395.5 − 23.0 × 10−3 T − 7.6 × 106 T−2 (T/K: 313–773). Deviation of measured Cp values from the estimates by the Neumann-Kopp rule (NKR) has also been discussed.

Thermochemistry of the simplest metal organic frameworks: Formates [M(HCOO)2]·xH2O (M = Li, Mg, Mn, Co, Ni, and Zn)

Abstract The simplest organic-inorganic hybrid material, with the smallest organic moiety, is a metal formate with divalent cations connected by formate anions. These metal formates have shown enormous potential for applications, particularly in gas storage and recently as anodes in lithium ion battery materials. Since formic acid is produced industrially on a large scale, metal formates could become very significant from an economic point of view. We report the enthalpies of formation of this important class of materials, measured using acid solution calorimetry. The formation enthalpies calculated from the respective metal chlorides/oxides and formic acid are negative for all the samples, with the energetic stability decreasing in the order Mg > Zn > Mn > Co > Ni > Li. Thus these materials show thermodynamic stability with respect to their oxides and should persist for long times when used in applications/devices.

Thermodynamic Investigation of Selected Compositions in the LiNiO2-LiMnO2-LiCoO2 System As Lithium Ion Battery Cathode Materials

The choice of cathode material is critical for determining the performance and safety of lithium ion batteries. Therefore, the development and optimization of new chemistries for cathodes of lithium ion cells is of major importance. Layered structured lithium mixed transition metal oxides with the general formula of LiNixMnyCozO2 (x + y + z = 1) and an α-NaFeO2-type layered structure (space group ) are attractive intercalation type cathode materials which overcome the limitations of LiCoO2, the most commonly used cathode for lithium ion batteries in portable applications. These NMC materials not only are isostructural to LiCoO2, but also offer comparatively higher reversible capacity, lower cost, and improved thermal stability, which are important characteristics for large scale applications. Although the structural characteristics and electrochemical behavior of many promising compositions in the NMC system have been investigated to some extent, there are very few studies devoted to the thermodynamic properties of this class of materials. The enthalpies of formation of LiNi1−xCoxO2 compounds were determined by Wang and Navrotsky [1] using high temperature oxide solution calorimetry and the enthalpy of formation of LiNi1/3Mn1/3Co1/3O2 and its chemically delithiated phases were measured by Idemoto and Matsui [2] using acid solution calorimetry. In the present work, with the aim of investigating the effect of cation substitution on thermodynamic stability of NMC materials, the standard enthalpies of formation of two different series of sol-gel made NMC samples, namely LiNixMnxCo1-2xO2 (0 ≤ x ≤ 0.5) and LiNi0.8-yMnyCo0.2O2 (0 ≤ y ≤ 0.4), are determined by high-temperature oxide-melt drop solution calorimetry. The compositions are selected to include the technologically relevant NMC111, NMC442, NMC532 and NMC622 compounds. It is shown that LiNixMnyCozO2 with layered structure is a nearly ideal solid solution of LiCoO2, LiNiO2 and LiNi0.5Mn05O2. Our calorimetry results show that the standard enthalpies of formation of the compounds from the elements vary almost linearly with composition in the respective area. Furthermore, based on our experimental heat of formation data and available low temperature heat capacity data for LiCoO2, LiNiO2 and LiNi0.5Mn05O2, a model for the variation of the Gibb’s free energy of formation and equilibrium potentials of the NMCs with composition at room temperature is presented. In addition, key electrochemical tests were performed to establish a relationship between the thermodynamic properties and electrochemical performance of the cathode materials. This work should help clarify the structure–property relationships in these compounds. M.Wang, & A. Navrotsky, Solid State Ionics 166 (2004), 167-173.Y.Idemoto & T. Matsui, Solid State Ionics 179 (2008), 625-635.

Thermodynamics and crystal chemistry of rhomboclase, (H5O2)Fe(SO4)2·2H2O, and the phase (H3O)Fe(SO4)2and implications for acid mine drainage

The system Fe 2 O 3 -SO 3 -H 2 O contains the most important minerals of acid mine drainage (AMD), iron oxides, and iron sulfates. For geochemical modeling of the AMD systems, reliable thermodynamic data for these phases are needed. In this work, we have determined thermodynamic data for the most acidic sulfates rhomboclase [(H 5 O 2 )Fe(SO 4 ) 2 ·2H 2 O or (H 3 O)Fe(SO 4 ) 2 ·3H 2 O] and the phase (H 3 O)Fe(SO 4 ) 2 . The actual compositions of the studied phases are (H 3 O) 1.34 Fe(SO 4 ) 2.17 (H 2 O) 3.06 (molecular mass of 344.919 g/mol) and (H 3 O) 1.34 Fe(SO 4 ) 2.17 (289.792 g/mol). Structural details for both phases were refined from synchrotron powder X-ray diffraction data. Enthalpies of formation were determined by acid-solution calorimetry. Low-temperature heat capacity was measured for rhomboclase by relaxation calorimetry but a critical analysis of entropies for several oxysalts showed that these data are too high. Entropies for both phases were estimated from a Kopp-rule algorithm. The enthalpies of formation and entropies were combined with previously published temperature-relative humidity brackets to generate an internally consistent thermodynamic data set for rhomboclase: Δ f H ° = –3202.03 kJ/mol, S ° = 378.7 J/(mol∙K); and for (H 3 O) 1.34 Fe(SO 4 ) 2.17 : Δ f H ° = –2276.25 kJ/mol, S ° = 253.2 J/(mol∙K). Solubility experiments at room temperature and at T = 4 °C agree well with previously reported data in the system Fe 2 O 3 -SO 3 -H 2 O. An inspection of the extended Pitzer model for Fe 3+ -SO 4 solutions shows that this model reproduces the general topology of the phase diagram, but the position of the calculated solubility curves deviates substantially from the experimental data. Solid-state 2 H MAS NMR spectra on deuterated rhomboclase show two isotropic chemical shifts δ iso ( 2 H) = of 8 ± 1 and 228 ± 1 ppm, assigned to D 5 O 2 + and Fe-OD 2 groups, respectively. Canonical ensemble (NVT) molecular dynamics simulations for (H 3 O)Fe(SO 4 ) 2 at T = 300 K showed that the H 3 O groups maintain their trigonal pyramidal geometry and perform different types of motion.

Thermodynamic properties of tooeleite, Fe63+(As3+O3)4(SO4)(OH)4·4H2O

Tooeleite, nominally Fe63+(As3+O3)4(SO4)(OH)4·4H2O, is a relatively uncommon mineral of some acid-mine drainage systems. Yet, if it does occur, it does so in large quantities, indicating that some specific conditions favor the formation of this mineral in the system Fe-As-S-O-H. In this contribution, we report the thermodynamic properties of synthetic tooeleite. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, extended X-ray absorption fine-structure spectroscopy, and Mössbauer spectroscopy. These methods confirmed that the sample is pure, devoid of amorphous impurities of iron oxides, and that the oxidation state of arsenic is 3+. Using acid-solution calorimetry, the enthalpy of formation of this mineral from the elements at the standard conditions was determined as −6196.6±8.6kJmol−1. The entropy of tooeleite, calculated from low-temperature heat capacity data measured by relaxation calorimetry, is 899.0±10.8Jmol−1K−1. The calculated standard Gibbs free energy of formation is −5396.3±9.3kJmol−1. The log Ksp value, calculated for the reaction Fe6(AsO3)4(SO4)(OH)4·4H2O+16H+=6Fe3++4H3AsO3+SO42−+8H2O, is −17.25±1.80. Tooeleite has stability field only at very high activities of aqueous sulfate and arsenate. As such, it does not appear to be a good candidate for arsenic immobilization at polluted sites. An inspection of speciation diagrams shows that the predominance field of Fe3+ and As3+ overlap only at strongly basic conditions. The formation of tooeleite, therefore, requires strictly selective oxidation of Fe2+ to Fe3+ and, at the same time, firm conservation of the trivalent oxidation state of arsenic. Such conditions can be realized only by biological systems (microorganisms) which can selectively oxidize one redox-active element but leave the other ones untouched. Hence, tooeleite is the first example of an “obligatory” biomineral under the conditions prevailing at or near the Earth's surface because its formation under these conditions necessitates the action of microorganisms.