Molten salts are important in a number of energy applications, but the fundamental mechanisms operating in ionic liquids are poorly understood, particularly at higher temperatures. This is despite their candidacy for deployment in solar cells, next-generation nuclear reactors, and nuclear pyroprocessing. We perform extensive molecular dynamics simulations over a variety of molten chloride salt compositions at varying temperature and pressures to calculate the thermodynamic and transport properties of these liquids. Using recent developments in the theory of liquid thermophysical properties, we interpret our results on the basis of collective atomistic dynamics (phonons). We find that the properties of ionic liquids well explained by their collective dynamics, as in simple liquids. In particular, we relate the decrease of heat capacity, viscosity, and thermal conductivity to the loss of transverse phonons from the liquid spectrum. We observe the singular dependence of the isochoric heat capacity on the mean free path of phonons, and the obeyance of the Stokes-Einstein equation relating the viscosity to the mass diffusion. The transport properties of mixtures are more complicated compared to simple liquids, however viscosity and thermal conductivity are well guided by fundamental bounds proposed recently. The kinematic viscosity and thermal diffusivity lie very close to one another and obey the theoretical fundamental bounds determined solely by fundamental physical constants. Our results show that recent advances in the theoretical physics of liquids are applicable to molten salts mixtures, and therefore that the evolution and interplay of properties common to all liquids may act as a guide to a deeper understanding of these mixtures.
We use extensive molecular dynamics simulations to calculate the thermal conductivity and thermal diffusivity in three common molten salts, LiF, LiCl, and KCl. Our analysis includes the total thermal conductivity and intrinsic conductivity, excluding mass currents, measured experimentally. The latter shows good qualitative agreement with the experimental data. We also calculate their key thermodynamic properties, such as constant-pressure and constant-volume specific heats. We subsequently compare the results to the lower bound for thermal diffusivity expressed in terms of fundamental physical constants. Using this comparison and recent theoretical insights into thermodynamic and transport properties in liquids, we interpret thermal properties on the basis of atomistic dynamics and phonon excitations. We finally find that the thermal diffusivity of molten salts is close to their kinematic viscosity.
This paper addresses the problem of science and exploration systems to survive the lunar night. We have proposed that a thermal mass can be manufactured from lunar regolith by electrical resistance heating. The thermal mass can then store heat during the lunar day and release it slowly throughout the night, providing protection to science and exploration systems from the detrimental effects of cold. When engineering a thermal mass, accurate characterization of how the mass conducts and emits heat is vital. Two regolith stimulants, JSC-1AF and NU-LHT-2M, and Columbia River Basalt BCR-2 were used to study the effect of experimental conditions (T, t, and atmosphere) on sintering and densification and to identify the optimal conditions for manufacturing the thermal mass material. The sintering and densification of small samples was performed in the electrical furnaces at different final temperatures, different cooling rates, under air or vacuum, or in an argon atmosphere. To determine the impact of sample microstructure (size, shape, and concentration of open and closed pores) and crystallinity on the range of thermal diffusivities for sintered/densified materials and to obtain emissivities of densified materials as a function of temperature, the manufactured samples were analyzed with high magnification, X-ray diffraction (XRD), a laser-flash thermal diffusivity (LFTD) system, and the millimeter-wave (MMW) system. The sintered/densified samples were analyzed for thermal diffusivity by the laser flash method in air and under vacuum in the temperature range 27 to 390°C. Thermal diffusivities of densified low-porosity JSC-1AF and BCR-2 samples were about the same in air or under vacuum and ranged from 0.46 to 0.76 mm 2 /s at 27°C. On contrary, thermal diffusivities of high open-porosity and fully crystalline NU-LHT-2M samples were approximately 2 to 3 times smaller under vacuum because of the longer conductive path through the pores boundary layer. The thermal diffusivities of tested samples decreased with temperature and were ≈ 20 to 25% lower at 390°C than at 27°C. The effect of temperature on radiative emissivity was monitored with a millimeter wave radiometer/interferometer during the temperature rise from 25 to 325°C. The emissivities for all the tested materials increased with temperature in the same way and ranged from 0.67 at 25°C to 0.96 at 325°C.
The component concentration limits that most influence the predicted Hanford life-cycle HLW glass volume by HTWOS were re-evaluated. It was assumed that additional research and development work in glass formulation and melter testing would be performed to improve the understanding of component effects on the processability and product quality of these HLW glasses. Recommendations were made to better estimate the potential component concentration limits that could be applied today while technology development is underway to best estimate the volume of HLW glass that will eventually be produced at Hanford. The limits for concentrations of P2O5, Bi2O3, and SO3 were evaluated along with the constraint used to avoid nepheline formation in glass. Recommended concentration limits were made based on the current HLW glass property models being used by HTWOS (Vienna et al. 2009). These revised limits are: 1) The current ND should be augmented by the OB limit of OB ≤ 0.575 so that either the normalized silica (NSi) is less that the 62% limit or the OB is below the 0.575 limit. 2) The mass fraction of P2O5 limit should be revised to allow for up to 4.5 wt%, depending on CaO concentrations. 3) A Bi2O3 concentration limit of 7 wt% should be used. 4) The salt accumulation limit of 0.5 wt% SO3 may be increased to 0.6 wt%. Again, these revised limits do not obviate the need for further testing, but make it possible to more accurately predict the impact of that testing on ultimate HLW glass volumes.
The structure of homogeneous bulk As x S100− x (25 ≤ x ≤ 42) glasses, prepared by the conventional rocking–melting–quenching method, was investigated using high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It is shown that the main building blocks of their glass networks are regular AsS3/2 pyramids and sulfur chains. In the S-rich domain, the existence of quasi-tetrahedral (QT) S = As(S1/2)3 units is deduced from XPS data, but with a concentration not exceeding ∼3–5% of total atomic sites. Therefore, QT units do not appear as primary building blocks of the glass backbone in these materials, and an optimally-constrained network may not be an appropriate description for glasses when x < 40. It is shown that, in contrast to Se-based glasses, the ‘chain-crossing’ model is only partially applicable to sulfide glasses.
Bismuth vanadate (BiVO4) is a promising photoelectrode material for the oxidation of water, but fundamental studies of this material are lacking. To address this, we report electrical and photoelectrochemical (PEC) properties of BiVO4 single crystals (undoped, 0.6% Mo, and 0.3% W:BiVO4) grown using the floating zone technique. We demonstrate that a small polaron hopping conduction mechanism dominates from 250 to 400 K, undergoing a transition to a variable-range hopping mechanism at lower temperatures. An anisotropy ratio of ~3 was observed along the c axis, attributed to the layered structure of BiVO4. Measurements of the ac field Hall effect yielded an electron mobility of ~0.2 cm(2) V(-1) s(-1) for Mo and W:BiVO4 at 300 K. By application of the Gärtner model, a hole diffusion length of ~100 nm was estimated. As a result of low carrier mobility, attempts to measure the dc Hall effect were unsuccessful. Analyses of the Raman spectra showed that Mo and W substituted for V and acted as donor impurities. Mott-Schottky analysis of electrodes with the (001) face exposed yielded a flat band potential of 0.03-0.08 V versus the reversible H2 electrode, while incident photon conversion efficiency tests showed that the dark coloration of the doped single crystals did not result in additional photocurrent. Comparison of these intrinsic properties to those of other metal oxides for PEC applications gives valuable insight into this material as a photoanode.
The success of hydrocarbon exploration, field development and reservoir surveillance depends significantly on effective reservoir imaging, characterization and detection of seismic signal. It is therefore imperative to acquire high quality seismic data to eliminate noise, attenuate unwanted water-bottom (or other type) multiples and increase the signal-to-noise ratio. With the development of seafloor sensor (4-components Ocean Bottom Node), acquiring high-quality seismic data has now become reality. Compared to conventional streamer surveys, the OBN acquisition technology is particularly useful for reservoir surveillance in congested oil field to monitor oil production, identify by-passed hydrocarbons, minimize unnecessary wells, and help mitigate risk of premature field decline. The cable-less node allows full-azimuth seismic surveys with continuous coverage and recording of P-and converted PS-waves even in highly obstructed areas. The high accuracy node deployment system allows nodes to be placed within 5 meters from wells and seafloor structures. The combination of new acquisition and processing technologies (e.g. shot record migration, mirror imaging and Reverse Time Migration) provides step changes in seismic imaging quality in complex subsurface and challenging deepwater areas.
A series of microwave resonant oscillator sensors were designed and characterized using bandpass planar and volumetric electrical resonators having loaded quality factor (Q) values in the range of 2 to 20. The use of these resonators in positive feedback circuits yielded sensor Q-factors of up to 2 × 107, demonstrating Q-factor amplifications on the order of 106. It is shown that the Q-factor amplification can be increased in a positive feedback system through the selection of feedback loop group delay, allowing use of resonators with lower static, loaded Q-factor values. A low-frequency electromagnetic interference sensing application is demonstrated for two resonant oscillator configurations, showing considerable frequency sensitivity to 45 kHz emitters.
