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State-of-the-art soft magnetic (SM) alloy systems such as electrical steels and permalloys exhibit large eddy current losses at high-frequency (kHz range and above), limiting their application in fast switching devices. Eddy current losses can be reduced for metallic alloys through a decrease in characteristic length scale or embedding them in an insulation layer. This work proposes the development of fine-scale core materials consisting of metallic SM nano/microparticles with magnetic, inorganic insulation layers, and their synthesis using a wet chemistry-based, scalable method for high frequency and high-power applications. More specifically, a magnetic ferrite coating (Ni0.5-xMnxZn0.5Fe2O4, x = 0.0–0.5) was applied via deposition of ferrite powder produced using a "wet chemistry-based" co-precipitation method; the ferrite was distributed through the Fe micropowder via either ball milling or ultrasonic mixing. Powder cores were prepared by compaction of the synthesized composites. Relative magnetic permeability and core loss were measured at excitation frequencies to 200 kHz. A core loss of 127 kW/m3 was measured at excitation frequency of 100 kHz and magnetization of 0.02 T. This value improves on the 199.3 kW/m3 reported in literature at identical excitation conditions for a compact formed from a composite comprising Fe microparticles coated with low-permeability Ni0.5Zn0.5Fe2O4. Ultrasonic mixing resulted in slightly lower core loss than ball milling, possibly because ball milling causes loss-increasing deformation of the Fe micropowder. XRD and SEM were used to observe composite composition and core cross-section microstructure. [ABSTRACT FROM AUTHOR]

Citric acid has been identified as an environmentally sustainable organic acid capable of leaching up to ~30% of easily accessible REEs from underclay material. An analysis of the leaching profiles was performed to discern the reaction rates, extraction efficiencies, and potential leaching mechanisms of REEs and cations of interest from ion-adsorbed underclays. The initial leaching stage follows a slow intraparticle diffusion mechanism followed by a second stage controlled by a mixed diffusion regime. The leaching profiles of Ca and P were similar to those of REEs, suggesting that REEs are most likely derived from mineral surfaces such as hydroxyapatite or crandallite rather than predominately from underclays. Fitting to a modified diffusion control model found diffusion-controlled leaching to be the primary mechanism whereas non-diffusive mechanisms made up about 22% of the extracted REEs. Gangue cations associated with underclays had less non-diffusive leaching than REE species, indicating that their leaching kinetics may be dominated by diffusion from within the material or potentially from product layer formation. Fitting to Boyd plots further indicated that REEs were leached following intraparticle diffusion control. These results have important implications for the development of more efficient and sustainable methods for extracting REEs or critical minerals from alternative feedstocks. [ABSTRACT FROM AUTHOR]

Cubic Equations of State (EoSs) typicallyprovide unreliable predictionsfor phase density and derivative properties at the high-temperature,high-pressure (HTHP) conditions associated with ultradeep petroleumreservoirs (that is, temperatures to 533 K and pressures to 241 MPa).The perturbed-chain statistical associating fluid theory (PC-SAFT)EoS returns improved predictions for density but still can overpredictthe experimental value by up to 5% at HTHP conditions. Not surprisingly,when a modified set of the pure-component PC-SAFT parameters m, σ, and ε/kare fit to HTHPexperimental density data, density predictions throughout the HTHPrange agree with reference data to better than ±1%. However,the lack of such HTHP density data for many hydrocarbons presentsa hurdle to the more widespread use of this PC-SAFT method. This studypresents a group-contribution (G-C) method for calculating PC-SAFTparameters that are designed to yield accurate HTHP density predictions.First- and second-order group contributions are considered. We haveextended the group contribution model of Tihic and co-workers, developedfor polymers, to accurately determine PC-SAFT parameters for alkanes,aromatics, and cycloalkanes at temperatures to 533 K and pressuresto 276 MPa. The parameter values are a function of contributions fromthe various functional groups present and the nature of the variouscarbon atoms (aliphatic, aromatic, and naphthenic) comprising themolecule. Furthermore, when using second-order group contributions,it is possible to distinguish the differences in density among isomers.Density values are usually calculated to within ±1–2%.Isothermal compressibility values are calculated to within ±10%,isobaric heat capacity to within ±5%, and speed of sound to within±4%. [ABSTRACT FROM AUTHOR]

This study presents methods for accurate viscosity modelingusingthe frictional theory (f-theory) and the free volume theory (FV theory)of viscosity at temperatures to 533 K and pressures to 276 MPa, whichare high-temperature, high-pressure (HTHP) conditions associated withultradeep porous sandstone or carbonate layers that retain crude oilor natural gas. The perturbed-chain statistical associating fluidtheory (PC-SAFT) equation of state (EoS), the HTHP-volume-translated(VT) Peng–Robinson EoS, and the HTHP-volume-translated-Soave–Redlich–KwongEoS (HTHP-VT-PR and HTHP-VT-SRK, respectively) are used to provideinput information for both the f-theory and the FV theory. Viscosityvalues returned by these models are compared to available experimentaldata for n-alkanes with carbon numbers 1–18,branched alkanes, single and double ring aromatics, and naphtheniccompounds. As currently constituted, the f-theory model underpredictsviscosity by as much as 20% at pressures near 276 MPa, but this deficiencyis reduced by incorporating an empirical correction term that is afunction of temperature and normal melting point. Viscosity predictionsfrom the modified f-theory are comparable with viscosity values returnedby FV theory for n-alkanes, although FV theory providesbetter viscosity modeling than either the f-theory or the modifiedf-theory for branched and aromatic hydrocarbons. FV theory viscosityvalues are characterized by a mean absolute percent deviation (MAPD)of 3% or less from the experimental data, with the most accurate results(MAPD ∼ 2%) obtained when the PC-SAFT is used to calculatethe density input needed for the FV theory calculations. However,FV theory viscosity values actually become slightly less accuratewhen experimental density data are used, which indicates that FV theoryitself has an inherent inaccuracy at extreme conditions unrelatedto the accurate prediction of the density input. [ABSTRACT FROM AUTHOR]