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Large volumes of steel slag are produced annually, leading to significant environmental protection and sustainable development issues. An online technology to monitor the solidification process of steel slag can assist in obtaining the right mineralogy to valorize these slags or render them harmless. For this purpose, we investigated the electrical properties and microstructural relationships of a CaO-Al2O3-SiO2-MgO (CASM) slag during cooling using an innovative setup. The electrical impedance was determined over the frequency range of 20 Hz to 300 kHz at two cooling rates, and the solidification behaviour was observed simultaneously by confocal scanning laser microscopy (CSLM). Four zones can be distinguished in the conductivity-temperature curves for the slag cooled at 10 °C/min, whereas only two distinct zones are visible at 100 °C/min. The liquid fraction of the slag has a significant impact on the slag conductivity during cooling. The electrical conductivity is, therefore, an accurate indicator of the solidification degree. Different theoretical and empirical models were evaluated on their ability to relate the bulk conductivity of the slag to the liquid fraction. The empirical Archie's model proved to be the most suitable model for relating the bulk conductivity of the slag to the liquid fraction. In-situ electrical conductivity measurements during cooling can provide an online assessment of the slag solidification process, including indicating the appearance of solid precipitates, monitoring the growth of crystals, indicating complete solidification when no liquid phase remains, and indicating the cooling rate.

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The dissolution of rare earth oxides in molten fluorides is a critical step in the preparation of the corresponding rare earth metals by oxide-fluoride electrolysis. However, quantitatively understanding the nature of dissolution, especially in the case of molten salts, is usually difficult to be achieved by postmortem characterization. In this paper, the dissolution behavior of Nd2O3 particles in molten fluorides was studied via in situ observation with confocal scanning laser microscopy. Combining direct observation with thermodynamic analyses on the oxide dissolution, the rate-limiting step(s) and the effects of parameters like temperature, salt type, and composition on the dissolution rate are identified. This study provides a methodology to estimate the dissolution kinetics of rare earth oxides in molten fluorides during their primary and secondary processing.

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Guided by predictive theory, a new compound with chemical composition (Cr2/3Zr1/3)2AlC was synthesized by hot pressing of Cr, ZrH2, Al, and C mixtures at 1300 °C. The crystal structure is monoclinic of space group C2/ c and displays in-plane chemical order in the metal layers, a so-called i-MAX phase. Quantitative chemical composition analyses confirmed that the primary phase had a (Cr2/3Zr1/3)2AlC stoichiometry, with secondary Cr2AlC, AlZrC2, and ZrC phases and a small amount of Al-Cr intermetallics. A theoretical evaluation of the (Cr2/3Zr1/3)2AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (Cr2/3Hf1/3)2AlC, of the same structure, was predicted to be stable.

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Electromagnetic interference (EMI) shielding receives attention due to the increasing abundance of electronics. The Cement based material can obtain EMI shielding properties through the use of appropriate "fillers" such as carbon, metal, and ferrite. As the most important by-product of stainless steelmaking operations, through the metal droplets and ferrite that it contains, stainless-steel dust can be considered as a potential filler for EMI shielding applications. We have therefore utilized stainless-steel dust as an admixture for the synthesis of cement-based EMI shielding composites and show that it raises the EMI shielding effectiveness. In particular, a 45 mass pct of stainless-steel dust mixture of 5 mm thickness results in the enhancement of EMI shielding effectiveness to 6-9 dB as tested in the frequency range of 500 MHz-1.5 GHz.

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The title compound, Ca2+x Nd8-x (SiO4)6O2-0.5x (x = 0.49), was synthesized at 1873 K and rapidly quenched to room temperature. Its structure has been determined using single-crystal X-ray diffraction and compared with results reported using neutron and X-ray powder diffraction from samples prepared by slow cooling. The single-crystal structure from room temperature data was found to belong to the space group P63/m and has the composition Ca2.49Nd7.51(SiO4)6O1.75 [dicalcium octa-neodymium hexa-kis-(ortho-silicate) dioxide], being isotypic with natural apatite and the previously reported Ca2Nd8(SiO4)6O2 and Ca2.2Nd7.8(SiO4)6O1.9. The solubility limit of calcium in the equilibrium state at 1873 K was found to occur at a composition of Ca2+x Nd8-x (SiO4)6O2-0.5x , where x = 0.49.

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The reaction kinetics of Zn vapor with Fe3O4 (magnetite) were studied from 907 to 1100 °C using a new experimental setup that only allows contact between the reactants through a gas-solid reaction. Hematite was used to create the reaction pellets. Because of the reducing atmosphere in the setup, a magnetite layer is formed on the outside of the pellet, which in turn reacts with the Zn vapor. After reaction, Zn concentration profiles were measured in the reacted magnetite layer using field-emission gun electron probe microanalysis. The reaction was confirmed to be diffusion-controlled. The effect of both volume and grain-boundary diffusion was observed in each experiment. The temperature dependence of both the volume and grain-boundary diffusion coefficients was obtained along with the activation energies of the diffusion coefficients. This study provides crucial information for the development of technologies that are dependent on the reaction. One example is the in-process separation technology for the separation of Zn vapor from electric arc furnace off-gas.

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With an aim of producing high value cementitious binder, stainless steel refining slag containing a high amount of CaO in γ-dicalcium silicate form was activated with NaOH and Na-silicate as well as KOH and K-silicate solutions, followed by steam curing at 80 °C. Higher levels of alkali-silicate in the activating solution resulted in higher cumulative heat suggesting accelerated reaction kinetics. With respect to compressive strength, higher levels of alkali silicate resulted in higher strength and the mortars with Na activator were found to have higher early strength than the ones with K activator. The long term strength was found to be similar, regardless of the alkali metal. Thermogravimetric, QXRD and FTIR analyses showed an increase in the amount of reaction products (C-S-H type) over time, further confirming the reactivity of the crystalline slag. Batch leaching results showed lower leaching of heavy metals and metalloids with K activator compared to the Na activator. These results demonstrate that the alkali type and the ratio of hydroxide to silicates have a significant impact on the hydration and mechanical strength development of the stainless steel slag. The above findings can aid in the recycling and valorization of these type of slags which otherwise end up landfilled.

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Phase-field modeling has proven to be a versatile tool for simulating microstructural evolution phenomena, such as grain growth in polycrystalline materials. However, the computing time and computing memory requirements of a phase-field model pose severe limitations on the number of phase-field variables that can be taken into account in a practical implementation. In this paper, a sparse bounding box algorithm is proposed that allows the use of a large number of phase-field variables without excessive memory usage or computational requirements. The algorithm is applied to a three-dimensional model for grain growth in the presence of second-phase particles.