Molten Salt Reduction Research Articles

Efficient preparation of metallic titanium from lower valence titanium chloride slurry by electrochemical reduction in molten salts

Short extraction of metallic titanium by the electrochemical reduction process in molten salt has attracted increasing interest due to its many advantages. The electrolysis of high-purity titanium to produce lower valence titanium chlorides has so far been industrialized as balancing agents but large-scale production is still challenging due to the high cost of raw materials and easy deterioration. Herein, metallic titanium was extracted from lower valence titanium chlorides (LTCs) slurries by electrochemical reduction in molten salts. The results of LTC slurries at 260 ºC for 48 h revealed the formation of red-violet α- and γ- TiCl3 with an Al content below 0.09 wt%, which gradually reduced to form metallic titanium in molten salt electrolytes. Porous metallic Ti powders were obtained from TiCl3 by electrochemical reduction in KCl-LiCl-MgCl2 molten salt at 400 °C. The reaction at the anode area was accompanied by TiCl4 gas overflow, and continuous electrolysis of metallic titanium was achieved by supplementing the consumed TiCl3. Overall, the proposed electrolysis process looks promising for large-scale applications due to its simple electrolysis equipment, relatively stable electrolyte components, and good product quality, thereby worth further future investigation.

Nanoparticulate ZrNi: In Situ Disproportionation Effectively Enhances Hydrogen Cycling of MgH2.

High thermal stability and sluggish absorption/desorption kinetics are still important limitations for using magnesium hydride (MgH2) as a solid-state hydrogen storage medium. One of the most effective solutions in improving hydrogen storage properties of MgH2 is to introduce a suitable catalyst. Herein, a novel nanoparticulate ZrNi with 10-60 nm in size was successfully prepared by co-precipitation followed by a molten-salt reduction process. The 7 wt % nano-ZrNi-catalyzed MgH2 composite desorbs 6.1 wt % hydrogen starting from ∼178 °C after activation, lowered by 99 °C relative to the pristine MgH2 (∼277 °C). The dehydrided sample rapidly absorbs ∼5.5 wt % H2 when operating at 150 °C for 8 min. The remarkably improved hydrogen storage properties are reasonably ascribed to the in situ formation of ZrH2, ZrNi2, and Mg2NiH4 caused by the disproportionation reaction of nano-ZrNi during the first de-/hydrogenation cycle. These catalytic active species are uniformly dispersed in the MgH2 matrix, thus creating a multielement, multiphase, and multivalent environment, which not only largely favors the breaking and rebonding of H-H bonds and the transfer of electrons between H- and Mg2+ but also provides multiple hydrogen diffusion channels. These findings are of particularly scientific importance for the design and preparation of highly active catalysts for hydrogen storage in light-metal hydrides.

Mechanochemical enhanced lithium selective extraction from spent cathode material via two-step molten salt treatments

The rapid development and widespread use of lithium-ion batteries (LIBs) in electric vehicles and stationary energy storage systems has been stimulated by the global push toward carbon neutrality. Thus, recycling spent LIBs as an efficient way to cope with the resulting resource scarcity and environmental damage has attracted much attention. Herein, based on previous studies, a process for selective Li extraction from a recovered spent LiMn2O4 (LMO) cathode with two-step molten salt treatments is proposed in this paper. The selective extraction of Li from the spent LMO cathode by (NH4)2SO4 molten salt is significantly promoted by mechanochemical treatment. Approximately 100% of the Li in the spent LMO is selectively extracted after step two of the molten salt treatment, and the Mn-containing phases in the spent LMO cathode are converted to Mn2O3. A Li2SO4·H2O product satisfying the requirements of Standard YS/T 1241–2018 is obtained from the purified Li2SO4 water-leachate after crystallization and calcination. In addition, 93.65% Mn in the water-leaching residue of Mn2O3 achieved sulfate conversion with (NH4)2SO4 molten salt reduction, and a first-grade product of MnSO4·H2O satisfying the requirements of Standard HG/T 4823–2015 was obtained after water-leaching and crystallization.

Molten salt-mediated carbon capture and conversion

The post-combustion capture is a promising technology to reduce industrial CO2 emission. This review articles concluded the recent advances in molten salt strategies for CO2 capture and conversion. In terms of CO2 capture, MgO-based sorbents can efficiently capture CO2 through a reversible carbonation/calcination reaction at intermediate temperatures (300–500 °C). The addition of alkali metal molten salt to MgO-based sorbents can greatly promote the CO2 uptake, which are promising candidates applied in the post combustion CO2 capture technology. Besides, molten salts such as ZnCl2/NaCl can be served as both activating agents and templates for synthesis of porous carbons from biomass and plastics. Particularly, N-doped porous carbons with highly microporous structures are more suitable for CO2 capture under ambient conditions. In terms of CO2 conversion, the electrochemical reduction in molten salts has been widely developed for producing carbon materials and fuels. Additionally, molten salts (normally single and mixed alkali metal carbonates) acting as both catalysts and heat transfer mediums can enhance the CO2 gasification of carbon feedstocks to produce CO-rich syngas. A significant challenge in the CO2 gasification of biomass/coal and their chars in molten alkali metal carbonates is the potential agglomeration between alkali metal species and minerals in the ash under high temperatures. To achieve sorbents regeneration and CO2 utilization, it is strongly recommended that more further researches should be performed on the integrated CO2 capture and in-situ electro-/thermo-chemical conversion processes for selectively production of high-value chemicals and fuels, which can alleviate the crisis of fossil fuels shortage and reduce the greenhouse gas emission.

Wear resistance performance of high entropy alloy–ceramic coating composites synthesized via a novel combined process

Titanium nitride (TiN), characterized by its high hardness and strength, was widely used as ceramic coating to improve the wear resistance of matrix materials. In this work, AlCrFeNiTix high-entropy alloy (HEA) powders were synthesized by direct electrochemical reduction in molten salt from the mixed metal oxides. Then, TiN ceramic coating on the AlCrFeNiTix bulk HEA containing the topologically close-packed (TCP) phase (σ phase, Laves phase, and Ti3Al phase) was prepared by vacuum hot pressing sintering, where nitride element come from boron nitride parting agent sprayed on the graphite mold. The effect of titanium content on the crystal structure, microstructure, hardness, and wear resistance of the products were investigated by X-ray diffraction, field emission scanning electron microscope, field emission electron-probe microanalysis, Vickers hardness tester, and friction–abrasion testing machine. The bulk HEAs exhibit excellent hardness and its hardness increases significantly with the increase of titanium content. The wear mechanism changes from both of predominantly delamination and accompanied oxidative wear to single delamination wear, which is due to ultra-high melting point and high hot hardness of TiN, that can effectively prevent the oxidation and deformation of the worn surface. Formation of the ceramic coatings containing the TiN second phase and TCP phase are the key factor to AlCrFeNiTix alloy with the excellent hardness and wear properties.

Pd-modified LaNi5 nanoparticles for efficient hydrogen storage in a carbazole type liquid organic hydrogen carrier

In this work, we report the synthesis and catalytical property of a palladium catalyst loaded on a hydrogen storage support-Pd/LaNi5 in reversible hydrogen storage of N-ethylcarbazole (NEC). We prepare LaNi5 nanoparticles by the molten salt reduction method and use galvanic replacement to deposit a thin Pd layer on the surface. Catalyzed by 1 wt%Pd/LaNi5, NEC absorbs 5.5 wt% H2 in 0.7 h at 453 K and 7 MPa H2, and perhydro-NEC desorbs 5.5 wt% in 2.1 h at 473 K and 0.1 MPa H2, which significantly outperforms Pd/Al2O3 catalyst with the same Pd loading. The significantly promoted catalytic performance is attributed to the ample lattice hydrogen bonding sites and fast bulk hydrogen diffusion kinetics of LaNi5, which breaks the limitation of active hydrogen bonding sites due to the competitive adsorption of hydrogen and the organic molecule in surface catalysis. The active role of the lattice hydrogen bonding sites makes hydrogen storage materials highly attractive for hydrogen-related catalysis

Single Fe2B Phase Particle Production by Calciothermic Reduction in Molten Salt

In this study, calciothermic single phase iron boride(Fe2B) production was investigated in a scalable molten salt system, starting from inexpensive, easily accessible oxide materials. First, the formation of Fe2B was examined in detail in the light of thermodynamic data and literature. After, effects of CaO amount (0-10 wt.%) and time (30-60 min) on particle synthesis were investigated under at constant 3.0 V cell voltage and 1273 K temperature. It was determined that the average current increased continuously with the increase in the amount of CaO, and the current efficiency increased up to 7% by weight of CaO. After the CaO ratio was determined, the effect of the electrolysis duration was examined. In durations experiments, it has been observed that, in 30 minutes’ duration, the particles are composed of Fe, Fe2B and FeB, and by increasing the experiment time to 60 min, single-phase Fe2B particles are obtained. The magnetic properties of the single-phase Fe2B particles obtained at the end of the experiment period of 60 minutes were investigated by VSM. The saturation magnetization, permanent magnetization and coercivity values of the Fe2B particles were determined as 90.718 emu/g, 33.311 Oe, 1.684 emu/g, respectively.

Preparation of Mg–Nd Alloys by Magnesiothermic Reduction in Molten Salt

Preparation of Mg–Nd Alloys by Magnesiothermic Reduction in Molten Salt

Effect of molten salt reduction on exothermic characteristics of titanium/reduced-silica nanoparticles

This paper describes the effect of molten salt reduction on exothermic characteristics of Ti/reduced-SiO2 nanoparticles. Sputtered Ti/Si multilayer film is known to show exothermic reaction by electrical shock or mechanical impact during intermetallic compound formation. So far, we demonstrated that SiO2/Ti nanoparticles, which are produced by combining atomized heating for porous SiO2 nanoparticle and sputtering for Ti deposition, show exothermic reaction. if an amount of oxygen in SiO2 nanoparticles can be changed, it is expected that exothermic characteristics can be controlled more accurately. In this paper, the effect of reduction on exothermic reaction is investigated, and the mechanism of the reduced effect is discussed based on the result of differential scanning calorimetry analysis.

A Sustainable Approach for Producing Ti and TiS2 from TiC

TiC was examined as a starting material for Ti metal production by sulfidation and electrochemical reduction in molten salt. The sulfur evaporation temperature, sulfidation temperature, and time were optimized in a dual-zone furnace for the efficient and sustainable formation of TiS2 as well as carbon removal from TiC by S2 gas sulfidation. A mixture of TiS2 and Ti2.45S4 powders was synthesized from TiC at 1200 °C, and a perfect carbon removal was achieved to a very clean level as low as 0.025 mass pct C. The sulfides derived from TiC were then electrochemically reduced in molten CaCl2-0.5 mol pct CaS salt. The spherical shape Ti powder consisting of high-purity Ti sheets was obtained from TiS2 without the carbon contamination. This method might be applied for sustainable recycling of waste carbides and for production of low-cost Ti powders via TiC or TiOxCyNz from the titanium ore.

LaNi5.5 particles for reversible hydrogen storage in N-ethylcarbazole

In this work, we demonstrate that the classic hydrogen storage alloy LaNi5 can catalyze the reversible hydrogen storage in N-ethylcarbazole (NEC), one of the most promising liquid organic hydrogen carriers (LOHCs), with high efficiency and cyclic stability. Using CaH2 reduction in molten salt, uniform LaNi5+x particles around 100 nm are obtained from hydroxide precursors. The sub-μm LaNi5.5 particles exhibit excellent catalytic ability for reversible hydrogen storage in NEC, which is originated from the synergism of surface excessive Ni and the LaNi5 core with reversible hydrogen storage property. Hydrogen storage capacity above 5.5 wt% H2 (based on 12 H-NEC) can be achieved for 9 cycles using 10 wt% LaNi5.5. The time required to reach 5.5 wt% hydrogen storage capacity is about 4.5 h for NEC hydrogenation at 453 K and 4.0 h for 12 H-NEC dehydrogenation at 473 K. The results are very promising in developing high-efficiency LOHC-based hydrogen storage systems and provide new insights into hydride-based catalysts.

Exothermically reactive titanium–silica nanoparticles

This paper focuses on developing Ti–SiOx nanoparticles and evaluating their self-propagating exothermic function. In combination with an atomized heating method, molten salt reduction, and sputtering, we established a fabrication technique for Ti–SiOx nanoparticles in which their exothermic characteristics can be designed. In the atomized heating method, porous SiOx nanoparticles with various spherical shapes, sizes, and porosities were fabricated. Porous SiOx nanoparticles with uniformly arranged pores were produced at a polystyrene latex (PSL) concentration of approximately 3.0 wt%. Reduction of the oxygen content of the porous SiOx nanoparticles was conducted using molten salt. Ti was deposited onto the entire surface by stirring and sputtering. The completed 1.0 mg of Ti–SiOx nanoparticle powder exhibited a self-propagating exothermic reaction by applying an electric spark. The relationship between PSL concentration and heat generation characteristics, such as the maximum temperature, time to reach maximum temperature, and duration of the exothermic reaction, was investigated.

A carbon network strategy to synthesize silicon–carbon anodes toward regulated morphologies during molten salt reduction

In this work, a carbon network strategy was proposed to prepare Si/SiOx/C anodes with regulated morphologies during molten salt reduction.

Three-dimensionally interconnected Si frameworks derived from natural halloysite clay: a high-capacity anode material for lithium-ion batteries.

On account of its high theoretical capacity, silicon (Si) has been regarded as a promising anode material for Li-ion batteries. Extracting Si content from earth-abundant and low-cost aluminosilicate minerals, rather than from artificial silica (SiO2) precursors, is a more favorable and practical method for the large-scale application of Si anodes. In this work, three-dimensionally interconnected (3D-interconnected) Si frameworks with a branch diameter of ∼15 nm are prepared by the reduction of amorphous SiO2 nanotubes derived from natural halloysite clay. Benefiting from their nanostructure, the as-prepared 3D-interconnected Si frameworks yield high reversible capacities of 2.54 A h g-1 at 0.1 A g-1 after 50 cycles, 1.87 A h g-1 at 0.5 A g-1 after 200 cycles, and 0.97 A h g-1 at 2 A g-1 after a long-term charge-discharge process of 500 cycles, remarkably outperforming the commercial Si material. Further, when the as-prepared Si frameworks and commercial LiCoO2 cathodes are paired in full cells, a high anode capacity of 0.98 A h g-1 is achieved after 100 cycles of rapid charge/discharge at 2 A g-1. This work provides a new strategy for the synthesis of high-capacity Si anodes derived from natural aluminosilicate clay.

Development of the Fray-Farthing-Chen Cambridge Process: Towards the Sustainable Production of Titanium and Its Alloys

The Kroll process has been employed for titanium extraction since the 1950s. It is a labour and energy intensive multi-step semi-batch process. The post-extraction processes for making the raw titanium into alloys and products are also excessive, including multiple remelting steps. Invented in the late 1990s, the Fray-Farthing-Chen (FFC) Cambridge process extracts titanium from solid oxides at lower energy consumption via electrochemical reduction in molten salts. Its ability to produce alloys and powders, while retaining the cathode shape also promises energy and material efficient manufacturing. Focusing on titanium and its alloys, this article reviews the recent development of the FFC-Cambridge process in two aspects, (1) resource and process sustainability and (2) advanced post-extraction processing.

Raspberry-like Nanostructured Silicon Composite Anode for High-Performance Lithium-Ion Batteries.

Adjusting the particle size and nanostructure or applying carbon materials as the coating layers is a promising method to hold the volume expansion of Si for its practical application in lithium-ion batteries (LIBs). Herein, the mild carbon coating combined with a molten salt reduction is precisely designed to synthesize raspberry-like hollow silicon spheres coated with carbon shells (HSi@C) as the anode materials for LIBs. The HSi@C exhibits a remarkable electrochemical performance; a high reversible specific capacity of 886.2 mAh g-1 at a current density of 0.5 A g-1 after 200 cycles is achieved. Moreover, even after 500 cycles at a current density of 2.0 A g-1, a stable capacity of 516.7 mAh g-1 still can be obtained.

Synthesis of nanostructured graphite via molten salt reduction of CO2 and SO2 at a relatively low temperature

A low temperature graphitization process integrates SO2 and CO2 capture and reduction, promising a novel method to prepare graphite.

Preparation of niobium carbide powder by electrochemical reduction in molten salt

The niobium carbide powder was prepared via electrochemical reduction of the mixture of Nb2O5 and carbon in molten CaCl2–NaCl. The reaction pathway from the sintered precursor to the final product has been investigated. The effect of the working temperature on the reduction of the Nb2O5/C composite precursor was considered. The role of carbon during the electrochemical reduction of the composite pellet was discussed. The samples were analysed by XRD and SEM. The results indicated that the NbC powder was approximately 200 nm after the reduction. Nb2O5 was gradually reduced to Nb, and NbC was subsequently obtained by the reaction of carbon with Nb metal. In addition, Nb2O5 could spontaneously react with CaO in the melt to form a serious of calcium niobates. The participation of carbon was available for the efficiency of electro-reduction of Nb2O5.

High yield fabrication of hollow vesica-like silicon based on the Kirkendall effect and its application to energy storage

Recently, a unique process based on the Kirkendall effect was employed to generate hollow nanostructures with a wide variety of materials. However, a similar hollow structure of silicon based on the fabrication mechanism of the Kirkendall effect is still not proposed. Here, we provide an extensible synthesis method for the high yield fabrication of a uniform vesica-like hollow Si material from SiO2 based on the Kirkendall effect in a molten salt reduction process. Significantly, without further modification, the as-prepared hollow vesica-like Si exhibits a high electrochemical storage capacity and long cycling properties (∼712 mA h g(-1) at 0.36 A g(-1) over 200 cycles).

Low‐Temperature Synthesis of Nanocrystalline NbB2 Powders by Borothermal Reduction in Molten Salt

Nanocrystalline NbB2 powders were successfully prepared by borothermal reduction in molten salt at 800°C–1000°C. Due to the more homogeneous mixing and more rapid diffusion of species in the liquid state than in the solid state, the synthesis temperature of pure NbB2 phase was greatly decreased by the presence of molten NaCl/KCl salt. The NbB2 powders synthesized at 1000°C had the largest specific surface area of 27.09 m2/g and the lowest equivalent average particle size of 32 nm, respectively.