Calciothermic Reduction Research Articles

Study on the extraction of neodymium metal by calciothermic reduction process

The study on the technology of producing neodymium metal using the calciothermic reduction process is reported in this article. The process primarily involves the conversion of neodymium oxide (Nd2O3) into neodymium fluoride (NdF3) followed by the reduction of neodymium fluoride to neodymium metal using calcium as reductant. Fluorinating conditions were standardised to obtain the desired product (NdF3) free of any unwanted impurities. The calciothermic reduction of the resulting neodymium fluoride was studied in detail to establish the reduction conditions to achieve maximum yield and purity of the neodymium metal. This process obtained the neodymium metal with a purity of 99.6% before refining step.

Calciothermic Reduction Reaction Behavior and Samarium Ion Valence Evolution of SmF3

Calciothermic Reduction Reaction Behavior and Samarium Ion Valence Evolution of SmF3

Porous Si/Ca-Si-O nanocomposite lithium storage materials by calciothermic reduction of Si with CaH2

Silicon monoxide (SiO)-based anode materials are one of the most intensively investigated class of materials for use as high-capacity anodes in lithium-ion batteries. However, their low initial Coulombic efficiency (ICE), resulting from the irreversible electrochemical reaction of the amorphous SiO2 (a-SiO2) phase in the SiO, restricts the wide-spread adoption of SiO-based anode materials in lithium-ion batteries. Pre-emptive formation of an irreversible phase that converts a-SiO2 to a non-reactive state with lithium prior to cell assembly has received much attention for enhancing ICE. However, this process has the drawback of not ensuring long-term cycle performance. Herein, the pre-emptive formation of irreversible phase combined with the high-energy mechanical milling (HEMM) process is proposed to simultaneously improve both the ICE and long-term cycle performance. The resulting porous Si/Ca-Si-O nanocomposite electrode exhibits an impressive ICE of 86.4 % and maintains 55 % of its capacity over 200 cycles. The key factor in the significant ICE improvement is the irreversible Ca-Si-O phase, which is formed by the calciothermic reduction of Si with CaH2. In addition, the microstructural changes induced by the HEMM process effectively mitigate the volume expansion of Si during cycling, resulting in improved long-term cycle stability.

Concentrating CaO from Lunar Simulant by Calciothermic Reduction Process

Concentrating CaO from Lunar Simulant by Calciothermic Reduction Process

Investigation of the Calciothermic Reduction of TiO<sub>2</sub> for the Green Production of Ti and TiH<sub>2</sub> Powders

To develop an eco-friendly titanium (Ti) production process, the calciothermic reduction of titanium dioxide (TiO<sub>2</sub>) was investigated. The mechanism involved in the reduction of TiO<sub>2</sub> using calcium (Ca) was examined. The influence of a molten salt, calcium chloride (CaCl<sub>2</sub>), on the calciothermic reduction was investigated by conducting experiments at 1123 – 1223 K in an argon (Ar) atmosphere for the duration of 0.5 – 9 h. When CaCl<sub>2</sub> was used as a molten salt, the oxygen (O) concentration in Ti decreased to 0.162 mass% owing to the removal of calcium oxide (CaO) from the surface of the Ti particles. In addition, the use of a CaCl<sub>2</sub> – lithium chloride (LiCl) molten salt decreased the reaction temperature to 1073 K and the O concentration in the obtained Ti reached 0.333 mass%. Furthermore, after the calciothermic reduction of TiO<sub>2</sub> at 1173 K using a perforated crucible, the residual Ca-containing salt was sufficiently separated in-situ from the crucible, and a mixture of Ti and TiH<sub>1.924</sub> was produced via hydrogenation at 1023 K by changing the atmosphere gas from Ar to hydrogen gas (H<sub>2</sub>). The results of this study demonstrate the feasibility of the calciothermic reduction of TiO<sub>2</sub> for the eco-friendly production of Ti and TiH<sub>2</sub> powders.

A Novel Process for the Recovery of Rare Earth and Fluoride Compounds from Calciothermic Reduction Slag

A Novel Process for the Recovery of Rare Earth and Fluoride Compounds from Calciothermic Reduction Slag

High-performance rare-earth hard magnetic nanoparticles via the calciothermic reduction and chemoselective dissolution

Magnetic Nd2Fe14B nanoparticles are synthesized by a bottom-up process via calciothermic reduction, which complements the negative reduction potential of rare-earth elements, thus affording nanoscale products. However, to obtain high-purity, high-performance magnetic nanoparticles, residual calcium by-products that persist after calcium thermal reduction-diffusion must be selectively removed. In previously reported rinsing methods, H2O or H+ diffuse into the magnetic nanoparticles, thereby leading to hydridation. Herein, we propose a novel rinsing solution, NH4NO3/methanol, that does not deteriorate the magnetic properties. The magnetic properties are enhanced by selectively removing calcium by-products (i.e., CaO) from the magnetic nanoparticles with NH4NO3/methanol solution and by preventing hydridation and oxidation using zeolite and Schlenk line. The intrinsic coercivity (Hci) is maintained at 75.1 % (from 8.5 kOe to 6.3 kOe), and the saturation magnetization (Ms) increases two-fold (110.08 emu/g) after rinsing with NH4NO3 solution, compared with prior to rinsing treatment (47.363 emu/g). Rinsing the magnetic nanoparticles with NH4NO3/methanol solutions does not cause deterioration of the obtained Nd2Fe14B nanostructures, where Ms = 112.0 emu/g and Hci = 8.4 kOe after rinsing with NH4NO3/methanol using the zeolite and Schlenk line. Using rinsing methods in previous studies. 3.5 % of the initial coercivity is maintained, whereas with the new rinsing method, 95.2 % of the coercivity is maintained, thus indicating that rinsing does not induce deterioration of the magnetic properties.

Transformation of YF3 into Y(OH)3 by a Mechanochemical Process: Extracting Yttrium from Rare Earth Smelting Slag under Mild Conditions

The yttrium (Y) element in the calciothermic reduction YF3 smelting slag (YSS) has a recovery value, and the conventional direct alkali transformation-acid leaching method of recovering rare earth elements (REEs) from solid waste, which contains rare earth fluoride, has encountered problems of high energy and alkali consumption and low leaching rate. In this study, a green process for the transformation of YF3 to Y(OH)3 at room temperature was achieved by employing a mechanochemical method. The process is environment-friendly, with zero emission, less acid/alkali consumption, and water recyclability. It was found that YF3 will be “passivated” by a newly formed Y(OH)3 product layer under the alkaline condition, resulting in the unsustainable transformation of YF3 to Y(OH)3. However, the mechanical force could destroy the coating of Y(OH)3 and promoted the transformation of YF3 to Y(OH)3 completely; as such, the transformation efficiency of YF3 reached 98.2%. On this basis, the process of extracting Y from YSS was further studied, and the results showed that YF3 in YSS was successfully transformed into Y(OH)3 and the leaching rate of Y reached 96.2%. Therefore, it is expected to be a new technology to recover REEs from waste slag or minerals that contain rare earth fluoride and has good industrial application prospect.

Synthesis of Cobalt Boride Particles by Molten Salt Assisted Calciothermic Reduction

Synthesis of Cobalt Boride Particles by Molten Salt Assisted Calciothermic Reduction

Tailoring of TiAl6V4 Surface Nanostructure for Enhanced In Vitro Osteoblast Response via Gas/Solid (Non-Line-of-Sight) Oxidation/Reduction Reactions.

An aging global population is accelerating the need for better, longer-lasting orthopaedic and dental implants. Additive manufacturing can provide patient-specific, titanium-alloy-based implants with tailored, three-dimensional, bone-like architecture. Studies using two-dimensional substrates have demonstrated that osteoblastic differentiation of bone marrow stromal cells (MSCs) is enhanced on surfaces possessing hierarchical macro/micro/nano-scale roughness that mimics the topography of osteoclast resorption pits on the bone surface. Conventional machined implants with these surfaces exhibit successful osseointegration, but the complex architectures produced by 3D printing make consistent nanoscale surface texturing difficult to achieve, and current line-of-sight methods used to roughen titanium alloy surfaces cannot reach all internal surfaces. Here, we demonstrate a new, non-line-of-sight, gas/solid-reaction-based process capable of generating well-controlled nanotopographies on all open (gas-exposed) surfaces of titanium alloy implants. Dense 3D-printed titanium-aluminum-vanadium (TiAl6V4) substrates were used to evaluate the evolution of surface nanostructure for development of this process. Substrates were either polished to be smooth (for easier evaluation of surface nanostructure evolution) or grit-blasted and acid-etched to present a microrough biomimetic topography. An ultrathin (90 ± 16 nm) conformal, titania-based surface layer was first formed by thermal oxidation (600 °C, 6 h, air). A calciothermic reduction (CaR) reaction (700 °C, 1 h) was then used to convert the surface titania (TiO2) into thin layers of calcia (CaO, 77 ± 16 nm) and titanium (Ti, 51 ± 20 nm). Selective dissolution of the CaO layer (3 M acetic acid, 40 min) then yielded a thin nanoporous/nanorough Ti-based surface layer. The changes in surface nanostructure/chemistry after each step were confirmed by scanning and transmission electron microscopies with energy-dispersive X-ray analysis, X-ray diffraction, selected area electron diffraction, atomic force microscopy, and mass change analyses. In vitro studies indicated that human MSCs on CaR-modified microrough surfaces exhibited increased protein expression associated with osteoblast differentiation and promoted osteogenesis compared to unmodified microrough surfaces (increases of 387% in osteopontin, 210% in osteocalcin, 282% in bone morphogenic protein 2, 150% in bone morphogenic protein 4, 265% in osteoprotegerin, and 191% in vascular endothelial growth factor). This work suggests that this CaR-based technique can provide biomimetic topography on all biologically facing surfaces of complex, porous, additively manufactured TiAl6V4 implants.

Thermodynamic Simulation and Experimental Investigation of the Calciothermic Reduction of Metals from Manganese and Iron Niobates

Thermodynamic Simulation and Experimental Investigation of the Calciothermic Reduction of Metals from Manganese and Iron Niobates

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.

Calciothermic Reduction of Iron and Manganese Tantalates

Calciothermic Reduction of Iron and Manganese Tantalates

Four-step eco-friendly energy efficient recycling of contaminated Nd2Fe14B sludge and coercivity enhancement by reducing oxygen content

Complete recycling of Nd2Fe14B sludge by chemical methods has gained significance in recent years, however, it is not easy to recycle highly contaminant sludge and obtain product with good magnetic properties. Herein we report a simple four-step process to recycle the Nd2Fe14B sludge containing ~ 10% of contaminants. Sludge was leached in H2SO4 and selectively co-precipitated in two steps. In the first co-precipitation, Al3+ and Cu2+ were removed at pH 6. Thereafter, in the second co-precipitation Fe2+ and RE3+ sulfates were converted to the Fe and RE hydroxides. By annealing at 800 °C RE and Fe hydroxides precipitates were converted to the oxides and residual carbon was oxidized to CO2. After the addition of boric acid, Fe and RE oxides were reduced and diffused to the (Nd-RE)2Fe14B by calciothermic reduction diffusion. Removal of CaO by washing with D.I. water in glove box reduced the oxygen content (~ 0.7%), improved crystallinity and enhanced the magnetic properties significantly. Coercivity increased more than three times (from 242.71 to 800.55 kA/m) and Mr value was also enhanced up to more than 20% (from 0.481 to 0.605 T). In this green process Na2SO4 and Ca(OH)2 were produced as by-product those are non-hazardous and were removed conveniently.

Preparation and Magnetic Properties of 2:17-Type SmCo Alloy by Transition Metal-Induced Calciothermic Reduction

Preparation and Magnetic Properties of 2:17-Type SmCo Alloy by Transition Metal-Induced Calciothermic Reduction

Preparation of Sm2Fe17 alloy and induced mechanism by calciothermic reduction

SmF3 cannot be directly reduced to metallic samarium by calcium. In this work, we presented the thermodynamic calculation and preperation of Sm2Fe17 alloy by calciothermic reduction. The composition, crystal structure, elements distribution, chemical valence and induced mechanism of Sm2Fe17 alloy were analyzed and characterized by ICP, XRD, SEM, EDS and XPS. The results show that the feasibility of preparing Sm2Fe17 alloy by iron-induced SmF3 calciothermic reduction. The Sm and Fe component of SmFe alloy approximates the nominal composition of Sm2Fe17 alloy with 10% excess of SmF3 over the stoichiometry. The micrograph of the SmFe ingot exhibits fish-bone-like morphology and is composed of α-Fe, Sm2Fe17 and SmFe3 phases. The Sm and Fe elements of the samples demonstrate zero valency. Electrons from metallic Sm are drawn toward to the orbits of Fe and an Sm-Fe bond with ionic bond property is formed and being reduced by calcium to obtain Sm2Fe17 alloy.

Calciothermic Reduction of Titanium Oxide Compounds

The reduction of TiO2 and CaTiO3 in a mixture with calcium has been studied in an argon atmosphere and vacuum at temperatures in the range 1023–1123 K. The adiabatic temperature of the reduction reactions involved has been calculated as a function of the excess of calcium in the starting mixture and its initial temperature. The presence of a thin CaCl2 film on calcium particles and the use of calcium titanate as a precursor have been shown to increase the reduction rate. The use of a CaTiO3 precursor and CaCl2-activated calcium has made it possible to obtain titanium powders containing 0.5 wt % oxygen and having a specific surface area of 1.2 m2/g via reduction at a temperature of 1073 K for 6 h.

Effect of oxygen containing compounds in uranium tetrafluoride on its non-adiabatic calciothermic reduction characteristics

Uranium ingot is produced by metallothermic reduction of uranium tetrafluoride using magnesium or calcium as reductant. Presence of oxygen containing compounds viz. uranyl fluoride and uranium oxide in the starting uranium fluoride has a significant effect on the firing time, final temperature of the charge, slag-metal separation and hence the metal recovery. As reported in the literature, the maximum tolerable limit for uranyl fluoride in the UF4 is 2.5 wt% and limit for uranium oxide content is in the range 2–3 wt%. No theoretical or experimental basis is available till date for these limits. Analyses have been carried out in this study to understand the effect of UO2F2 concentration in the starting fluoride on the final temperature of the products and thus the reduction characteristics. UF4 having uranyl fluoride concentration, less than as well as more than 2.5 wt%, have been investigated. Thermodynamic calculations have been carried out to arrive at a general expression for the final temperature attained by the products during calciothermic reduction of UF4. Finally, an upper limit for the oxygen containing impurities has been estimated using the CaO–CaF2 phase diagram.

Calciothermic powders of rare metals and intermetallic compounds

This paper presents a profound review of scientific and technical literature on the issues of calciothermic production of powders of rare metals, intermetallic compounds, composite materials and refractory oxygen-free compounds (carbides, nitrides). Calciothermic reduction is a metallothermic synthesis method for those substances where calcium or its derivatives, such as calcium hydride or calcium carbide, are used as a reducing agent. Thermodynamics aspects of a reduction process are covered in the paper broadly, with particular emphasis on assessing the reduction depth of original oxide raw materials, as TiO2. The mechanism and kinetics of calciothermic synthesis of single-component and multi-component alloys are described. Presented are both technological means of obtaining materials and hardware resources of many varieties of calciothermic method. The key features of the work are generalization and systematization of properties (chemical, physical, technological) of materials synthesized by calciothermic method. The data are accumulated in the appropriate tables and divided by substance classes (powders of metals and alloys, powders of intermetallic compounds, powders of carbides, powders of nitrides, and powders of composite materials). Methods of calciothermic powder making in case of the singlecomponent and complex multi-component systems are briefly described. This work will be interesting to the students of metallurgical profile and specialists whose scientific interests are in the field of material synthesis by methods of powder metallurgy.

Investigation on preparation porous titanium through calciothermic reduction of porous TiO precursors

A route is present for preparing porous titanium scaffolds with open and interconnected pore morphology through calcium thermal in-situ reduction of TiO precursor. Titanium and dioxide titanium powders, with ammonium carbonate as the space holder, were used to prepare porous precursor whose main phase is TiO by a sintering process. Then calcium vapor was conduced to reduce the precursor and CaO was removed by leaching to obtain porous titanium structures. The morphology, pore structure, phase analysis of porous titanium precursor and porous titanium scaffolds were investigated by means of XRD, SEM and EDS. The porosity was observed by Archimedes method. By this route, the porous titanium with multi-gradient pore sizes ranging from a few microns to several hundred microns was formed. The porous titanium is of multi-gradient pore size distribution of 100 μm bigger, 10 μm∼100 μm and 10 μm smaller. The micro-pores on the pore walls increases connectivity between the macro-pores throughout the porous titanium interior. The porous titanium obtained by this method has a porosity of 50–65% and a titanium content more than 99%.