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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Understanding Trigger Linkage Dynamics in Energetic Materials Using Mixed Picramide Nitrate Ester Explosives

The ability to predict the handling sensitivity of new organic energetic materials has been a longstanding goal. We report the synthesis and characterization of six new nitropicramide energetic materials with mixed functional groups that mimic known explosives such as nitroglycerin, erythritol tetranitrate (ETN), and pentaerythritol tetranitrate (PETN). The molecules have been studied theoretically using quantum molecular dynamics (QMD) simulations and density functional theory (DFT) calculations to identify the weakest bond in the reactants - the trigger-linkages - which control handling sensitivity, and to quantify their specific enthalpies of explosion. In good accord with the drop weight impact sensitivity data, our calculations predict that the sensitivities of the molecules are very similar owing to the small variations of the energy output and rates of trigger linkage rupture. In addition, both the QMD and DFT calculations point to the nitropicramide N–NO 2 bonds as the trigger linkages rather than the more typical O–NO 2 bonds. We propose that the switch of the trigger linkage from the nitrate esters to the nitramine groups arises from the strongly electron withdrawing character of the adjacent trinitrobenzene groups.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Direct Observations of Ion Densities at Functionalized Interfaces to Test Hypotheses Regarding the Origin of Specific Ion Effects

Interactions of anions with protonatable groups were investigated using X-ray fluorescence near total reflection (XFNTR) on floating monolayers at the surface of water. The number of ions attracted to the interfacial region, which XFNTR measures directly, is ion-specific as well as monolayer-specific. Our observation of the distinctly different behaviors of ClO 4 – and ReO 4 – , two ions with the same tetrahedral structure and almost the same sizes and hydration enthalpies, challenges current theories of ion specificity. Our observations are inconsistent with not only the Gouy–Chapman model (as expected) but also size-modified Poisson–Boltzmann theory and the “law of matching water affinity”. Furthermore, we suggest that factors other than ion size and ion–water interactions, including possibly ion–ion interactions and lateral ordering at the interface, must be considered to account for specific ion effects.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Physicochemical Gas–Solid Sorption Properties of Geologic Materials Using Inverse Gas Chromatography

The goal of this study was to determine the physicochemical properties of a variety of geologic materials using inverse gas chromatography (IGC) by varying probe gas selection, temperature, carrier gas flow rate, and humidity. This is accomplished by measuring the level of interaction between the materials of interest and known probe gases. Identifying a material’s physicochemical characteristics can help provide a better understanding of the transport of gaseous compounds in different geologic materials or between different geological layers under various conditions. Our research in this study focused on measuring the enthalpy (heat) of adsorption, Henry’s constant, and diffusion coefficients of a suite of geologic materials, including two soil types (sandy clay-loam and loam), quartz sand, salt, and bentonite clay, with various particle sizes. The reproducibility of IGC measurements for geologic materials, which are inherently heterogeneous, was also assessed in comparison to the reproducibility for more homogeneous synthetic materials. This involved determining the variability of physicochemical measurements obtained from different IGC approaches, instruments, and researchers. For the investigated IGC-determined parameters, the need for standardization became apparent, including the need for application-relevant reference materials. The inherent physical and chemical heterogeneities of soil and many geologic materials can make the prediction of sorption properties difficult. Characterizing the properties of individual organic and inorganic components can help elucidate the primary factors influencing sorption interactions in more complex mixtures. This research examined the capabilities and potential challenges of characterizing the gas sorption properties of geologic materials using IGC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Model for the Solid–Liquid Interfacial Free Energy at High Pressures

The free energy involved in the formation of an interface between two phases (e.g., a solid–liquid interface) is referred to as the interfacial free energy. For the case of solidification, the interfacial free energy dictates the height of the energy barrier required to nucleate stable clusters of the newly forming solid phase and is essential for producing an accurate solidification kinetics model using classical nucleation theory (CNT)-based methods. While various methods have been proposed for modeling the interfacial free energy for solid–liquid interfaces in prior literature, many of these formulations involve making restrictive assumptions or approximations, such as the system being at or near equilibrium (i.e., the system temperature is approximately equal to the melt temperature) or that the system is at pressures close to atmospheric. However, these approximations and assumptions may break down in highly non-equilibrium situations, such as in dynamic-compression experiments where metastable liquids that are undercooled by hundreds of kelvin or over-pressurized by several gigapascals or more are formed before eventually solidifying. We derive a solid–liquid interfacial free-energy model for such high-pressure conditions by considering the enthalpies of interactions between pairs of atoms or molecules. We also consider the contribution of interface roughness (disordering) by incorporating a multilayer interface model known as the Temkin n-layer model. Our formulation is applicable to a diverse variety of materials, and we demonstrate it by developing models specifically for two different materials: water and gallium. We apply our interfacial free-energy formulation to CNT-based kinetics simulations of several suites of dynamic-compression experiments that cause liquid water to solidify to the high-pressure solid polymorph ice VII and have found good agreement to the observed kinetics with only minor empirical fitting.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Adsorption Thermodynamics for Process Simulation

Adsorption has rapidly evolved in recent decades and is an established separation technology extensively practiced in gas separation industries and others. However, rigorous thermodynamic modeling of multicomponent adsorption equilibrium remains elusive, and industrial practitioners rely heavily on expensive and time-consuming trial-and-error pilot studies to develop adsorption units. Here, this article highlights the need for rigorous adsorption thermodynamic models and the limitations and deficiencies of existing models such as the extended Langmuir isotherm, dual-process Langmuir isotherm, and adsorbed solution theory. It further presents a series of recent advances in the generalization of the classical Langmuir isotherm of single-component adsorption by deriving an activity coefficient model to account for the adsorbed phase adsorbate–adsorbent interactions, substituting adsorbed phase adsorbate and vacant site concentrations with activities, and extending to multicomponent competitive adsorption equilibrium, both monolayer and multilayer. Requiring a minimum set of physically meaningful model parameters, the generalized Langmuir isotherm for monolayer adsorption and the generalized Brunauer–Emmett–Teller isotherm for multilayer adsorption address various thermodynamic modeling challenges including adsorbent surface heterogeneity, isosteric enthalpies of adsorption, BET surface areas, adsorbed phase nonideality, adsorption azeotrope formation, and multilayer adsorption. Also discussed is the importance of quality adsorption data that cover sufficient temperature, pressure, and composition ranges for reliable determination of the model parameters to support adsorption process simulation, design, and optimization.

09 BIOMASS FUELS↗
DOE OSTI2023

Polymer Tacticity Effects in Polymer–Lanthanide Chelation Thermodynamics

Metal-chelating polymers are critical components in numerous applications. However, despite the known influence of polymer tacticity on both bulk and solution properties, most materials used in metal-chelation applications are atactic. Here, we investigate the relationship between polymer tacticity and polymer–lanthanide interactions in aqueous solution. We synthesized a series of five poly(methacrylic acid)s with systematic variations in tacticity (20–99% m diads) and used isothermal titration calorimetry to measure the thermodynamics of lanthanide binding to each material (ΔH, ΔG, ΔS, K a , and stoichiometry). We observed enthalpy–entropy compensation across this tacticity series, finding that both |ΔH| and |ΔS| decreased with decreasing m diad content while ΔG remained similar. Molecular dynamics simulations of the polymer–metal interactions revealed that the observed differences in binding thermodynamics may be largely ascribed to differences in polymer flexibility. Furthermore, these combined experimental and computational results demonstrate that metal binding can be influenced by altering the polymer stereochemistry, ultimately influencing the design of more efficient metal-chelating materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Reversible Ligand Protonation in Noninnocent Constrained-Geometry-Like Group 4 Complexes

The proligands C 5 H 5 CMe 2 CHPhOx R (R = Me 2 , CHMe 2 , and CMe 3 ) react with M(NMe 2 ) 4 (M = Ti, Zr, and Hf) to give monodeprotonated (Ox R CHPhCMe 2 C 5 H 4 )M(NMe 2 ) 3 , doubly deprotonated (C 5 H 4 CMe 2 CPhOx R )M(NMe 2 ) 2 , or a mixture of both. The observed products depend on reaction conditions, the oxazoline substituent, and the metal center, with 4-t-butyl-oxazoline or Ti giving only the monodeprotonated (Ox R CHPhCMe 2 C 5 H 4 )M(NMe 2 ) 3 . Amine elimination from (Ox R CHPhCMe 2 C 5 H 4 )M(NMe 2 ) 3 to give (C 5 H 4 CMe 2 CPhOx R )M(NMe 2 ) 2 is reversible for 4,4-dimethyl- and 4-isopropyl-oxazoline-based ligands in Zr or Hf complexes. Temperature-dependent kinetic studies of the equilibration of (C 5 H 4 CMe 2 CPhOx Me2 )Zr(NMe 2 ) 2 , HNMe 2 and (Ox Me2 CHPhCMe 2 C 5 H 4 )Zr(NMe 2 ) 3 provide the experimental thermodynamic parameters ΔS° = -17.4 ± 2.6 cal·mol –1 K –1 and ΔH° = -6.8 ± 0.8 kcal·mol –1 . An Eyring plot of the rate constants, determined from the system as it approaches equilibrium, gives the activation entropy and activation enthalpy for the addition of (C 5 H 4 CMe 2 CPhOx Me2 )Zr(NMe 2 ) 2 and HNMe 2 as -36 ± 4 cal·mol –1 K –1 and 8.9 ± 1.3 kcal·mol –1 , respectively; the elimination of HNMe 2 from (Ox Me2 CHPhCMe 2 C 5 H 4 )Zr(NMe 2 ) 3 is characterized by ΔS ‡ = -19 ± 5 cal·mol –1 K –1 and ΔH ‡ = 15.7 ± 1.5 kcal·mol –1 . DFT computational models indicate a single-step, nonlinear transfer of the H between the benzylic position of the noninnocent, oxazoline-coordinated ligand and NMe 2 . Computations also confirm the negative activation entropy and the trends in the barriers support the experimental results. Together, these studies indicate the importance of steric effects from the oxazoline ligand, metal center, ancillary ligands, and leaving group on the shuttling of the proton between HNMe 2 and the noninnocent ligand. Finally, these effects suggest that coordination of oxazoline to the metal center is a key part of the benzylic deprotonation and noninnocent behavior of the cyclopentadienyl-oxazoline ligand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Carbon Dioxide Insertion into Rhenium Hydrides as a Probe for the Impact of Solvent on Linear Free Energy Relationships between Thermodynamic and Kinetic Hydricity

The kinetics of CO 2 insertion into electronically different Re( R bpy)(CO) 3 H ( R bpy = 4,4'-R-2,2'- bipyridine; R = OMe, t Bu, Me, H, Br, COOMe, CF 3 ) complexes to form Re( R bpy)(CO) 3 {OC(H)O} compounds were determined in acetone, dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), and 3-methoxypropionitrile (3-MPN) and compared with previous data in acetonitrile (MeCN). The rates of CO 2 insertion for any one complex of the type Re(Rbpy)(CO) 3 H in different solvents correlates with the Dimroth-Reichardt (E T (30)) solvent parameter. Hammett plots in each solvent indicate that insertion reactions are faster for bpy ligands with electron-donating groups. There is, however, no correlation between the slope of the Hammett plot in different solvents and any common solvent parameter. Similarly, the enthalpies and entropies of activation and kinetic isotope effects associated with CO 2 insertion into Re(bpy)(CO) 3 H in different solvents do not correlate with any common solvent parameters. Theoretical calculations were used to determine the relative thermodynamic hydricities of Re( R bpy)(CO) 3 H type complexes in MeCN, acetone, DMF, and DMSO and in each solvent complexes with more electron-donating substituents on the bpy ligand are stronger hydride donors. Linear Free Energy Relationships (LFERs) between calculated thermodynamic and experimental kinetic hydricity, as measured through CO 2 insertion reactions, were observed in MeCN, acetone, DMF, and DMSO. Furthermore, the slopes of the LFERs correlate with the dielectric constant of the solvent. Overall, this work provides fundamental information about the thermodynamics and kinetics of hydride transfer reactions in different solvents, which is valuable for catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Re-examination of the Claimed Isolation of Stable Noncyclic 1,2-Disulfoxides

Re-examination of the claimed isolation and X-ray characterization of di-p-tolyl and dimesityl 1,2-disulfoxides from thermolysis of the corresponding aryl sulfinimines and thiosulfinates showed that the isolated disulfide dioxides are instead the wellknown isomeric thiosulfonates, as confirmed by XAS, DART-MS, X-ray, IR and NMR methods. Concerns with the original X-ray structures are addressed. Our results agree with the DFT prediction of very weak diaryl 1,2-disulfoxide S–S bond dissociation enthalpies. For now, room-temperature-stable noncyclic 1,2-disulfoxides remain unknown.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Defect-Limited Mobility and Defect Thermochemistry in Mixed A-Cation Tin Perovskites: (CH3NH3)1-xCsxSnBr3

Hybrid organic-inorganic semiconductors crystallizing in the perovskite structure present a significant opportunity for realizing defect-tolerant semiconductors. In this work, we examine the solid solution, (CH3NH3)1-xCsxSnBr3, and identify the thermochemistry dictating the intrinsic carrier concentrations and how local structural distortions influences this electronic behavior. This family of compounds exhibits the expected systematic trend in decreasing optical gap with the cesium to methylammonium A-site mixing ratio, x, in the visible region. However, the carrier mobility, as determined from time-resolved microwave conductivity measurements, trends opposite to that expected from first-principles calculations combined with Boltzmann scattering theory calculations of the carrier mobility. We propose that this is a result of increasing carrier scattering with x in (CH3NH3)1-xCsxSnBr3 due to a significant increase in the carrier density with x. By examining the dependence of the carrier density as a function of x, we infer the compositional-dependence of the average enthalpy and nonconfigurational entropy per defect. While diffraction reveals a cubic aristotypic perovskite structure as a function of x at room temperature, the pair distribution functions obtained from synchrotron X-ray total scattering from these materials are better described by symmetry-adapted displacement modes of the Pm3m crystal structure, which we attribute to a large degree of anharmonic dynamics of the atom positions. This analysis shows that CH3NH3+-rich compositions retain mostly linear Sn-Br-Sn bonding environments through the displacements, while Cs+-rich compositions lead to more significantly bent Sn-Br-Sn environments. We propose that these bent bonding arrangements in Cs-rich compositions yield a higher propensity for defect formation. This also provides a rationale for carrier trapping that gives rise to anomalous microwave transients. Together, these results provide insight into the structure-dynamics-properties relationships in this highly anharmonic system with high amplitude atomic motions and low defect formation energies.

defect thermochemistry↗
DOE OSTI2025

LASSO for CALPHAD Model Selection Enables Data-Efficient Thermodynamic Modeling: An Application in Thermochemical Hydrogen Production Materials

Phenomenological CALPHAD (CALculation of PHAse Diagrams) models, widely used for multicomponent materials, often contain a considerable number of parameters and require fitting using data from a relatively small number of experimental measurements or theoretical calculations. Sometimes these parameters are introduced for the purpose of improving model fits but without clear physical justification, which leads to overparametrized models with poor generalization performance. Automated approaches for optimal model selection based on the available data therefore become critical. Here, in this work, a least absolute shrinkage and selection operator (LASSO)-based approach is developed for model selection by leveraging the linearity of the CALPHAD model with respect to its parameters to convert the model selection and fitting to a LASSO minimization problem. We demonstrate its utility for thermodynamic modeling of thermochemical hydrogen (TCH) production materials using lanthanum strontium manganite (LSM) as an example. Various TCH-relevant properties, including oxygen stoichiometry as a function of oxygen partial pressure, enthalpy of reduction, and entropy of reduction, are successfully predicted with reasonable accuracy using a minimal set of model parameters. Importantly, the model selection and fitting involve minimal human decision; it can therefore be applied to high-throughput DFT defect calculations and yield efficient workflows for TCH material modeling and optimization.

CALPHAD↗
DOE OSTI2020

Computationally Predicted High-Throughput Free-Energy Phase Diagrams for the Discovery of Solid-State Hydrogen Storage Reactions

The design of multinary solid-state material systems that undergo reversible phase changes via changes in temperature and pressure provides a potential means of safely storing hydrogen. However, fully mapping the stabilities of known or newly targeted compounds relative to competing phases at reaction conditions has previously required many stringent experiments or computationally demanding calculations of each compound’s change in Gibbs energy with respect to temperature, G(T). Here, we have extended the approach of constructing chemical potential phase diagrams based on ΔG f (T) to enable the analysis of phase stability at non-zero temperatures. We first performed density functional theory calculations to compute the formation enthalpies of binary, ternary, and quaternary compounds within several compositional spaces of current interest for solid-state hydrogen storage. Temperature effects on solid compound stability were then accounted for using our recently introduced machine learned descriptor for the temperature-dependent contribution G δ (T) to the Gibbs energy G(T). From these Gibbs energies, we evaluated each compound’s stability relative to competing compounds over a wide range of conditions and show using chemical potential and composition phase diagrams that the predicted stable phases and H2 release reactions are consistent with experimental observations. This demonstrates that our approach rapidly computes the thermochemistry of hydrogen release reactions for compounds at sufficiently high accuracy relative to experiment to provide a powerful framework for analyzing hydrogen storage materials. This framework based on G(T) enables the accelerated discovery of active materials for a variety of technologies that rely on solid-state reactions involving these materials.

08 HYDROGEN↗
DOE OSTI2021

Process Engineering to Increase the Layered Phase Concentration in the Immediate Products of Flame Spray Pyrolysis

Flame-spray-pyrolysis (FSP) is a robust and scalable process to synthesize particles at the commodity-scale. FSP has been used to produce the precursor powders which were converted to the layered structure $(R\bar{3m} \text { phase})$ by a postannealing step in making nickel-rich cathode materials (NCMs). Theoretically, the high flame temperature (normally >1500 K) in FSP can provide adequate energy for the phase conversion from rock-salt to layered structures and potentially enables one-step synthesis. However, the high flame temperature is a critical issue to cause lithium loss and structural degradation, preventing the formation of the layered phase. Here, guided by the gaseous nucleation theory, we implemented several FSP processes with different solution recipes. The layered phase concentration in the as-burned products can be increased with the solution enthalpies. By adding a rapid quench step to suppress the lithium loss and phase degradation, the layered phase can be further increased. This work contributes new ideas to innovating process regarding the process efficiency and throughput of manufacturing cathode materials at a large scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Stability Criteria for Self-Propagating Reaction Waves in Co/Al Multilayers

The propagation of self-sustained formation reactions in sputter-deposited Co/Al multilayers is known to exhibit a design-dependent instability. Multilayers having thin bilayers (<55 nm period) exhibit stable propagating waves, whereas those with a larger period react unstably. The specific two-dimensional (2D) instability observed involves the transverse propagation of a band in front of a stalled front commonly referred to as a “spin band.” Previous finite-element studies have shown that these instabilities are thermodynamically driven by the forward conduction of heat away from the flame front. However, the magnitude of that loss is inherently tied to the bilayer design in traditional bimetallic multilayers, which couples any proposed stability criteria to a varying critical diffusion distance. Here, this work utilizes a recently developed class of materials known as “inert-mediated reactive multilayers” to decouple the thermodynamic and kinetic contributions to propagating wave stability by reducing the stored chemical energy density in normally stable bilayer designs. By depositing an inert product phase (B2-CoAl) within the mid-plane of Co and Al reactant layers, spin instabilities arise as a function of both diluted volume and critical diffusion distance. From there, a stability criterion is determined for Co/Al multilayers based on enthalpy loss from the reaction zone, and its physical significance is explored.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O 2−δ Nanoparticles

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. Here, in this work, Pr 0.2 Ce 0.8 O 2−δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strain and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO 2 (1 to 10 –4 atm O 2 ). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO 2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO 2 . STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.

ceria↗
DOE OSTI2026

Designing the Platinum Catalyst Layer for Improved Performance and Durability in Anion Exchange Membrane Water Electrolysis

To lower the cost of hydrogen produced by anion exchange membrane water electrolysis (AEMWE), it is critical to reduce the use of platinum group metal (PGM) catalysts within the device. While iridium has been successfully replaced with PGM-free catalysts at the anode, platinum-based (Pt) cathode catalysts are still required to meet the activity and durability targets. This study investigates the impact of commercial Pt/C catalyst loading, ionomer type and content, and electrode fabrication method on the cathode catalyst layer properties and AEMWE performance with the aim of determining the feasibility of reduced Pt loadings. While increased Pt loading is found to improve beginning-of-life performance, the effects are minimal above 0.6 mg/cm 2 . Ink characterization shows that ionomer type and content affect the ink stability, particle size, and percent of unbound ionomer, which further impact the homogeneity of the sprayed catalyst layers. The 5% PiperION cathode exhibited the highest performance, which may be attributed to a balance between the small particle size and the low proportion of unbound ionomer, minimizing kinetic and transport losses. Theoretical calculations show that the ionomers interact differently with the Pt surface, causing different surface charges and water adsorption strength and activating different mechanisms for hydrogen evolution. Pt-PiperION lowered the enthalpy of water-splitting by 0.1 eV compared to Pt alone and allowed for equal site access between adsorbed H* and OH* (both adsorbed at circa −2.2 eV). Although catalyst-coated membrane (CCM) fabrication techniques are desirable for scale-up, no performance enhancement is observed compared with the catalyst-coated substrate approach. Durability, as measured by degradation rates, Pt loss, and catalyst layer restructuring, was found to improve with increased Pt loadings, higher ionomer content, and CCM architectures. These findings provide important insight into the significant role of the cathode in AEMWE and strategies for maintaining the performance with low Pt loading or PGM-free catalysts.

08 HYDROGEN↗
DOE OSTI2020

Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores

Ce-bastnäsite is the single largest mineral source for light rare-earth elements. In view of the growing industrial importance of rare-earth minerals, it is critical to develop more efficient methods for separating the valuable rare-earth-containing minerals from the surrounding gangue. In this work, we employ a combination of periodic density functional theory (DFT) and molecular mechanics (MM) calculations together with the de novo molecular design program HostDesigner to identify bis-phosphinate ligands that preferentially bind to the (100) Ce-bastnäsite surface rather than the (104) calcite surface. DFT calculations for a simple phosphinate ligand were employed to qualitatively understand key behaviors involved in ligand–metal, ligand–solvent, and solvent–metal interactions. These insights were then used to guide the search for flexible, rigid, and semirigid hydrocarbon linkers to identify candidate bis-phosphinate ligands with the potential to bind preferentially to Ce-bastnäsite. Among the five most promising bis-phosphinate ligands suggested by theoretical studies, three ligands were synthesized and their adsorption characteristics to bastnäsite (100) interfaces were characterized using vibrational sum-frequency (vSFG) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and isothermal titration calorimetry (ITC). The efficacy of the selective interfacial molecular binding was demonstrated by identifying a bis-phosphinate ligand capable of providing an overall higher surface coverage of alkyl groups relative to a monophosphinate ligand. The results highlight the interplay between adsorption binding strength and maximum surface coverage in determining ligand efficiency to render the mineral surface hydrophobic. DFT calculations further indicate that all tested ligands have higher affinity for Ce-bastnäsite than for calcite. Finally, this is consistent with the ITC data showing stronger adsorption enthalpy to bastnäsite than to calcite, making these ligands promising candidates for selective flotation of Ce-bastnäsite.

58 GEOSCIENCES↗
DOE OSTI2022

Alginate–Sodium Sulfate Decahydrate Phase Change Composite with Extended Stability

Here, this study reports on the use of sodium alginate to effectively stabilize sodium sulfate decahydrate (Na 2 SO 4 ∙10H 2 O, SSD) based phase change material (PCM) for application as a thermal energy storage material. Alginate/SSD composite PCMs were prepared by blending SSD with different concentrations of alginate polymer. The resulting composite PCMs demonstrate high phase change enthalpy ~160 J/g and extended cycling stability compared to existing PCM composites. The analysis carried out by optical microscopy, X-ray scattering, and periodic density functional theory (DFT) calculations demonstrated that the stabilization effect was caused by the interplay between ionic and hydrogen bond interactions between the alginate and SSD. Additionally, the variation in mechanical properties of PCM composites with polymer concentrations made it possible to formulate a composite that maintains stable performance after 3D printing. The advanced properties make this composite a promising candidate for application as a thermal energy storage material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗