Effects of large computational time steps on the computed turbulence were investigated using a fully implicit method. In turbulent channel flow computations the largest computational time step in wall units which led to accurate prediction of turbulence statistics was determined. Turbulence fluctuations could not be sustained if the computational time step was near or larger than the Kolmogorov time scale.

Effects of the computational time step on numerical solutions for turbulent flow

We report on the energetics of intercalation of lithium, sodium and potassium in graphite by density functional theory using recently developed van der Waals (vdW) density functionals. First stage intercalation compounds are well described by conventional functionals like GGA, but van der Waals functionals are crucial for higher stage intercalation compounds and graphite, where van der Waals interactions are important. The vdW-optPBE functional gave the best agreement with reported structure and energetics for graphite and LiC6 and was further applied for intercalation of Na and K. The enthalpy of formation of LiC6 and KC8 were found to be −16.4 and −27.5 kJ mol−1 respectively. NaC6 and NaC8 were unstable with positive enthalpies of formation (+20.8 and +19.9 kJ mol−1). The energetics of stacking of graphene and intercalant layers was investigated from first to fifth stage intercalation compounds. Higher stage compounds of Li and K were stable, but with less negative enthalpy of formation with increasing stage order. The higher stage Na compounds possessed positive enthalpy of formation, but lower in magnitude than the energy difference of 0.6 kJ mol−1 between graphite with AB and AA stacking. The abnormal behaviour of the lower stage Na intercalation compounds was rationalized by the lower energy involved in the formation of the chemical bond between carbon Na relative to the corresponding bond with Li or K. The chemical bond between alkali metal and carbon is characterized by charge transfer from the alkali-metal to carbon resulting in ionized alkali-metals. The intercalation induces only a subtle increase in the in-plane C–C bond lengths, with longer C–C bonds in the vicinity of the alkali metals but without breaking the hexagonal symmetry.

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Van der Waals density functional study of the energetics of alkali metal intercalation in graphite

The first € price and the £ and $ price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for Germany, the €(A) includes 10% for Austria. Prices indicated with ** include VAT for electronic products; 19% for Germany, 20% for Austria. All prices exclusive of carriage charges. Prices and other details are subject to change without notice. All errors and omissions excepted. D. Li (Ed.) Encyclopedia of Microfluidics and Nanofluidics

Encyclopedia of Microfluidics and Nanofluidics

Rare-earth metals, particularly neodymium, dysprosium, and praseodymium are becoming increasingly important in the transition to a green economy due to their essential role in permanent magnet applications such as in electric motors and generators. With the increasingly limited rare-earth supply and complexity of processing Nd, Dy, and Pr from primary ores, recycling of rare-earth based magnets has become a necessary option to manage supply and demand. Depending on the form of the starting material (sludge or scrap), there are different routes that can be used to recover neodymium from secondary sources, ranging from hydrometallurgical (based on its primary production process), electrochemical to pyrometallurgical. Pyrometallurgical routes provide solution in cases where water is scarce and generation of waste is to be limited. This paper presents a systematic review of previous studies on the high-temperature (pyrometallurgical) recovery of rare earths from magnets. The features and conditions at which the recycling processes had been studied are mapped and evaluated technically. The review also highlights the reaction mechanisms, behaviors of the rare-earth elements, and the formation of intermediate compounds in high-temperature recycling processes. Recommendations for further scientific research to enable the development of recovery of the rare-earth and magnet recycling are also presented.

/pdf/review-of-high-temperature-recovery-of-rare-earth-nd-dy-from-46u25vg96j.pdf

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

The traditional electrolyte for aluminum electrolysis is composed of molten cryolite (Na3AlF6) and alumina (Al2O3). One of the objectives of the industry is to lower the operating temperature of the electrolytic process, which is currently around 960 °C. The benefits commonly evoked of a temperature decrease in the aluminum plotlines are multiple: reduction of the energetic consumption and thus of the global environmental footprint, increase of the cell life due to limited corrosion, reduction of production costs, etc. In this work, an overview of some properties of molten fluoride systems (Na−cryolite-based electrolytes (NaF−AlF3) and K−cryolite-based electrolytes (KF−AlF3)) is presented. To a lesser extent, the case of all-chloride and mixed chloro-fluoride salts is also discussed. Many physicochemical properties of salt mixtures are of major importance to evaluate the potential of a given electrolyte. When available, the following properties are reported and compared: the liquidus temperature, the elec...

Properties of Low-Temperature Melting Electrolytes for the Aluminum Electrolysis Process: A Review

Temperatures for primary crystallization of Na3AlF6 in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na3AlF6 was derived:
 
$$\begin{gathered} t/(^\circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - \frac{{3.45[CaF_2 ]}}{{1 + 0.0173[CaF_2 ]}} \hfill \\ + 0.124[CaF_2 ] \cdot [AlF_3 ] - 0.00542([CaF_2 ] \cdot [AlF_3 ])^{1.5} \hfill \\ - \frac{{7.93[Al_2 O_3 ]}}{{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \cdot [Al_2 O_3 ]}} \hfill \\ - \frac{{8.90[LiF]}}{{1 + 0.0047[LiF] + 0.0010[AlF3]^2 }} - 3.95[MgF_2 ] - 3.95 \hfill \\ \end{gathered} $$

 wheret is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na3AlF6-AlF3-CaF2-Al2O3-LiF-MgF2-KF. The composition limitations are [AlF3] ≈ [CaF2] ≈ [LiF] < 20 wt pct, [MgF2] ≈ [KF] < 5 wt pct, and [A12O3] up to saturation.

Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis

The solubility of alumina in molten Na3AlF6 containing various amounts of AlF3, CaF2, and LiF was determined by measuring the weight loss of a rotating sintered corundum disc. The results were fitted to the following empirical expression: 1
 $$
[Al_2 O_3 ]_{sat} = A\left( {\frac{t}
{{1000}}} \right)^B 
$$
 where 2
 $$
\begin{gathered}
 A = 11.9 - 0.062[AlF_3 ] - 0.003[AlF_3 ]^2 - 0.50[LiF] \hfill \\
 - 0.20[CaF_2 ] - 0.30[MgF_2 ] + \frac{{42[LiF] \cdot [AlF_3 ]}}
{{2000 + [LiF] \cdot [AlF_3 ]}} \hfill \\
 B = 4.8 - 0.048[AlF_3 ] + \frac{{2.2[LiF]^{1.5} }}
{{10 + [LiF] + 0.001[AlF_3 ]^3 }} \hfill \\ 
\end{gathered} 
$$
 where the square brackets denote weight percent of components in the system Na3AlF6-Al2O3 (sat)-AlF3-CaF2-MgF2-LiF and t is the temperature in degree Celsius. The standard deviation between the equation and the experimental points in the temperature range from 1050 °C to about 850 °C was found to be 0.29 wt pct Al2O3. A series of revised phase diagram data of interest for aluminum electrolysis was derived based on the present work and recently published data for primary crystallization of Na3AlF6 in the same systems.

Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data

Modifications of CaO-based sorbents with various inorganic salts to overcome the degradation in the reactivity between the active material and CO2 in a carbon capture process have previously been evaluated. The present paper focuses on the performance of a novel CO2 capture technology, where CaCl2 is applied as the solvent for the dissolution/dispersion of CaO and CaCO3. CO2 capture by CaO was carried out with carbonation temperatures in the range of 770–830 °C by bubbling simulated flue gas through the melt, using a fully automated flow-through atmospheric pressure reactor. Subsequently, decomposition of the formed CaCO3 to CaO and CO2 was conducted at 910–950 °C using pure N2. Online gas analysis was performed using a Fourier transform infrared (FTIR) gas detector and gravimetric analysis. The results indicate that the CaO carbonation efficiency decreases at temperatures higher than 800 °C. Increasing the concentration of CaO enhances the carbonation reaction. The amount of CO2 uptake for 15 wt % CaO in...

Investigation of High-Temperature CO2 Capture by CaO in CaCl2 Molten Salt

Rare earth metals (REM) are called "keyenablers of green technologies", as many environmental technologies such as electric and hybrid cars or wind power are dependent on these elements. Currently, these technologies are nearly 100% reliant on Chinese-sourced materials, as China is responsible for nearly 95% of the world’s RE production (both oxides and metals), although it has only around 36% of the world reserves. In addition, China has been limiting the export in the last years (1).

Extraction of Rare Earth Metals from Nd-based Scrap by Electrolysis from Molten Salts

A literature review concerning the heat transfer coefficient between bath and sideledge (h) is given. Normally, the heat transfer is controlled mainly by the circulating bath motion due to gas drainage into the peripheral channel. After the introduction of slotted anodes that direct the gas towards the centre channel, it is likely that h will be determined by natural convection in some cases, and an equation is suggested to take this into account. The coupling between heat and mass transfer during melting and freezing of sideledge was studied in a numerical model involving multicomponent diffusion. During freezing, the concentration of bath components other than cryolite is higher at the ledge surface than in the bulk of the bath. The surface temperature of the ledge varies with the rate of freezing and melting, in such a way that the variation of the ledge thickness becomes slower than thought earlier.

Asbjørn Solheim

Papers

Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis

Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data

Investigation of High-Temperature CO2 Capture by CaO in CaCl2 Molten Salt

Extraction of Rare Earth Metals from Nd-based Scrap by Electrolysis from Molten Salts

Some Aspects of Heat Transfer Between Bath and Sideledge in Aluminium Reduction Cells