Deoxidation Process Research Articles

Study on the deep deoxidation mechanism of titanium powder using Y/YOCl/YCl3 and Y/Y2O3 systems

Low-oxygen high-purity titanium (oxygen concentration ≤ 500 ppm) is a critical material for advanced semiconductor and biomedical applications. Current deoxidation methods limit oxygen concentration in titanium to approximately 1000–2000 ppm, failing to meet the demand for ultra-low oxygen levels in high-performance materials. This study investigated the preparation mechanism and conditions for low-oxygen high-purity titanium utilizing a molten salt thermochemical method, employing Y as the deoxidant with a theoretical deoxidation limit below 10 ppm. We experimentally explored the deoxidation mechanisms of titanium using Y/YOCl/YCl3 and Y/Y2O3 systems, successfully reducing the oxygen concentration in titanium to 200 ppm, and proving that the Y/YOCl/YCl3 system is more efficient than the Y/Y2O3 system. Additionally, the titanium samples were analyzed using SEM-EDS, XRD, XPS, and 3D surface profilometry before and after deoxidation. These analyses examined the impact of the deoxidation process using Y on the crystal structure, oxide film, and surface roughness of titanium specimens, which are useful for understanding the deoxidation mechanism. During the sintering process of titanium powder attached to Y, the deoxidation process will produce YOCl or Y2O3. The formation of these deoxidation products leads to local oxygen diffusion, and the crystals of YOCl or Y2O3 are gathered at grain boundaries, which will resolve during the subsequent acid etching process, thus reducing the oxidation concentration of the titanium. The above results provide further theoretical guidance and technical support for the production of ultra-high-purity titanium powder.

The Inclusion Characteristics and Mechanical Properties of M2 High-Speed Steel Treated with a Vacuum Carbon Deoxidation Process

The oxygen content of M2 high-speed steel has not been intentionally controlled in industrial production through secondary refinement in vacuum furnaces. However, a lower oxygen content has a significant effect on the cleanliness, toughness, and addition of rare-earth elements to M2 high-speed steel. The changes in total oxygen content controlled by vacuum carbon deoxidation (VCD) treatment and inclusion evolution were investigated in M2 high-speed steel to understand the effects of carbon on dissolved oxygen and oxides in the carbon–oxygen (C-O) reaction process. Furthermore, the microstructure and properties of M2 high-speed steel caused by vacuum insulation and the role of reducing oxygen content in rare-earth alloying were briefly demonstrated. The results showed that the [O%] decreased from 30 ppm to 3 ppm in a vacuum at holding times above 25 min through the C-O reaction, leading to an inclusion reduction of approximately 70%. In the case of [O%] = 3 ppm in M2 high-speed steel, the addition of rare-earth elements has a greater effect on the inclusion characteristics. Lowering the oxygen content of M2 high-speed steel improves cleanliness and plays a significant role in rare-earth alloying.

Study on the control of transverse cracks at the corners of large square billets for continuous casting of marine 945 hypo-peritectic micro-alloyed steel

Hypo-peritectic micro-alloyed steel has strong crack sensitivity, and marine 945 steel, as a kind of sub-encapsulated crystalline micro-alloyed steel, has frequent corner cracks during production, which seriously affects the production rhythm and reduces the product quality. Through the study of the morphology and composition of the matrix near the crack, the study and analysis of the high-temperature mechanical properties of the steel itself, and combined with the actual production situation, the causes of the corner cracks were clarified and the process optimisation was carried out accordingly. The results of the study show that the generation of corner cracks is due to the improper deoxidation process, uneven heat transfer inside the crystallizer and inappropriate cooling water parameters in the steelmaking process. By changing the deoxygenation method, crystallizer protective slag performance, crystallizer cooling water volume, water volume in the second cooling zone and other measures, the occurrence of billet corner cracks was effectively reduced, and the frequency of billet corner cracks was reduced from 6.3 to 2/m.

Study on the Migration Patterns of Oxygen Elements during the Refining Process of Ti-48Al Scrap under Electromagnetic Levitation.

This study investigated the migration patterns of oxygen in the deoxidation process of Ti-48Al alloy scrap using electromagnetic levitation (EML) technology. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the oxygen distribution patterns and migration path during EML. The refining process resulted in three types of oxygen migration: (1) escape from the lattice and evaporation in the form of AlO, Al2O; (2) formation of metal oxides and remaining in the alloy melt; (3) attachment to the quartz tube wall in the form of metal oxides such as Al2O3 and Cr2O3. The oxygen content of the scrap was dropped with a deoxidation ratio of 62%. It indicated that EML can greatly promote the migration and removal of oxygen elements in Ti-Al alloy scrap.

An insight into the characteristics of some oxidized low-grade coals of Indian origin

ABSTRACT The conversion of coal to a hydrophilic state presents a significant challenge for process engineers, especially when treating oxidized coals in flotation-based beneficiation plants. Flotation of oxidized coal often requires a substantial consumption of oily collectors, resulting in unacceptably low yields. To address this, several pre-processing methods have emerged for coal deoxidation, including mild grinding, surface activation, and ultrasonic or microwave treatment. However, their effective application depends on a thorough understanding of the degree of oxidation in the coals. Therefore, it is crucial to gain insights into the nature of oxidized coal before initiating the deoxidation process. This present study provides various characterization techniques such as XRD, SEM-EDS, FTIR Spectroscopy, Raman Spectroscopy, TGA, and Zeta Potential Analysis employed on oxidized low-grade coals. The study revealed that the proximate analysis of low-grade coals KC, DC, RC, and PC contains varying ash percentages of 32.65%, 44.47%, 25.44%, and 37.53%, respectively, with SiO2 and Al2O3 comprising over 80% of the total ash. XRD characterizations identified quartz and kaolinite as major mineral phases in all samples, while SEM-EDS confirmed rough coal surfaces with peeling, off-white aggregations, and surface pores. HGI value ranging from 80 to 91 was attributed to partial decomposition and surface cracking due to oxidation. FTIR spectra revealed pronounced oxidation behavior, with strong −OH peaks in the 3600–3700 cm−1 range. Zeta potential analysis affirmed the oxidized nature of the coals with a pH below 3.1 and an extremely negative zeta potential beyond 3.1. The findings mentioned above showcase the distinct characteristics of oxidized low-grade coals, which serve as crucial indicators for exploring coal beneficiation, especially through the flotation process.

A first-principles study on the hydrodeoxygenation mechanism of the lignin-derived phenolic compounds over MoS2 catalysts

Understanding the hydrodeoxygenation (HDO) mechanism of phenolic compounds is crucial for advancing catalytic upgrading techniques of bio-oil. Herein, a comprehensive theoretical study of the HDO of lignin-derived phenolic compounds (phenol, cresols, and guaiacol) on the MoS2 surface was carried out using periodic density functional theory (DFT) calculations. Adsorption of phenolic compounds on different crystal faces was first compared. The MoS2 (100) crystal face is more favorable for the adsorption of phenolic compounds which show the horizontal adsorption configurations. Three kinds of HDO patterns were explored for the phenolic compounds. Phenol tends to transform into benzene via stepwise deoxygenation and hydrogenation under the induction of active hydrogen. For cresol isomers, their HDO mechanisms differ from each other due to the influence of the methyl group on the dehydroxylation process. Specifically, o-cresol follows a synergistic process of deoxidation and hydrogenation, m-cresol undergoes a two-step reaction involving direct dehydroxylation and hydrogenation, and p-cresol involves the identical HDO pathway as phenol. With regard to guaiacol, the preferred HDO route involves successive dehydroxylation and demethoxylation to benzene with the anisole intermediate. In addition, the adsorption of phenolics over transition metal-doped MoS2 catalysts was further explored to examine the potential of metal doping for the HDO of phenolics. The doping of Ta and W increases the adsorption capacity, which shows the potential to enhance the HDO activity of the catalyst theoretically.

Effect of Silicon–Manganese Deoxidation on Oxygen Content and Inclusions in Molten Steel

In order to improve the cleanliness of steel, non-aluminum deoxidation processes have begun to replace aluminum deoxidation processes. Although the aluminum deoxidation process can reduce the oxygen content in steel to <10 × 10−6, this deoxidation method causes fatigue failure resulting from the formation of large-grained spherical (Ds-type) inclusions composed of calcium–aluminate. It also tends to lead to nozzle blockage during casting. Given the above problems, this study conducted an in-depth investigation of silicon–manganese deoxidation. Thermal experiments and thermodynamic calculations were used to assess the impact of different Mn–Si ratios on the oxygen content and inclusion characteristics during the deoxidation process of molten steel with different initial oxygen contents. The experimental samples were analyzed using an oxygen–nitrogen–hydrogen analyzer, a direct reading spectrometer, and an automatic scanning electron microscope. After that, the samples were electrolyzed to observe the 2D morphology and 3D morphology of the inclusions using scanning electron microscopy. Finally, thermodynamic calculations were carried out using FactSage to verify the experimental results. The results indicated that, regardless of the initial oxygen content, silicon–manganese deoxidation maintained the total oxygen content at 35 × 10−6. It effectively managed the plasticization of inclusions in molten steel, predominantly yielding spherical silicates while minimizing Al-containing inclusions. Nevertheless, as the initial content of [O] increased, the size and density of the silicate inclusions in the steel also increased. An optimal point in the number and size of inclusions was observed with an increased Mn–Si ratio. Moreover, the combined utilization of silicon–manganese deoxidation, diffusion deoxidation, and vacuum deoxidation enabled ultra-low oxygen content control of molten steel.

High-Entropy Alloy Al0.2Co1.5CrFeNi1.5Ti0.5 Prepared from High-Entropy Oxide (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a Deoxidation Process via a CaH2-Assisted Molten Salt Method

High-entropy alloys (HEAs) have attracted a great deal of research interest these days because of their attractive properties. Low-temperature chemical synthesis methods are being developed to obtain nanoscale HEAs with low energy consumption. In this study, we prepared HEA Al0.2Co1.5CrFeNi1.5Ti0.5 nanoparticles from high-entropy oxide (HEO) (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a deoxidation process via a CaH2-assisted molten salt method at 600 °C. X-ray diffraction measurements demonstrated that the oxide precursor and the reduced product have single-phases of spinel structure and face-centered cubic structures, indicating the formation of HEO and HEA, respectively. The HEA nanoparticles exhibited superior catalytic performance in the liquid-phase hydrogenation of p-nitrophenol at room temperature with little leaching of the component elements. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX) exhibited a good distribution of constituent elements over the HEA nanoparticles in a micro-sized range. However, transmission electron microscopy (TEM) with EDX revealed a slight deviation of elemental distributions of Al and Ti from those of Co, Cr, Fe, and Ni in a nano-sized range, probably due to the incomplete reduction of aluminum and titanium oxides. The elemental homogeneity in the HEA nanoparticles could be improved by taking advantage of the HEO precursor with homogeneous elemental distributions, but the experimental results suggested the importance of the total reduction of oxide precursors to prepare homogeneous HEAs from HEOs.

Universal Deoxidation of Semiconductor Substrates Assisted by Machine Learning and Real-Time Feedback Control.

Substrate oxidation is inevitable when exposed to ambient atmosphere during semiconductor manufacturing, which is detrimental to the fabrication of state-of-the-art devices. Optimizing the deoxidation process in molecular beam epitaxy (MBE) for random substrates poses a multidimensional challenge and is sometimes controversial. Due to variations in substrates and growth processes, the determination of the deoxidation condition heavily relies on the individual's expertise, yielding inconsistent results. This study employs a machine learning model that integrates interpolation and vision transformer (Interpolation-ViT) techniques. The model utilizes reflection high-energy electron diffraction videos as input to predict the status of the substrate, enabling automated deoxidation within a controlled architecture for various substrates. Furthermore, we highlight the potential of models trained on data from specific MBE equipment to achieve high-accuracy deployment on different pieces of equipment. In contrast to traditional methods, our approach holds exceptional value, as it standardizes deoxidation temperatures across diverse equipment and substrates. This significantly advances the standardization of the semiconductor process. The concepts and methods presented are expected to revolutionize semiconductor manufacturing processes in the optoelectronic and microelectronic industries.

Impact of trace silicon on irradiation hardening and embrittlement of RAFM steel subjected to neutron irradiation

The content of silicon (Si) element in reduced activation ferritic/martensitic (RAFM) steels varies significantly among different candidates of fusion reactor structural materials. Si is not intentionally added to the RAFM steel but rather remains as a residue during the deoxidation process in steel fabrication. To control and reduce the Si content, removing processes and special treatments are required. The additional refining processes significantly increase the cost of steel fabrication. Currently, the role of residual or trace Si in neutron irradiation of steel remains unclear. In the presented study, two 9Cr-2 W RAFM steels with Si contents of 0.1 wt.% and 0.01 wt.% were fabricated and subjected to a neutron irradiation at 563 K with a neutron fluence of 4.8 × 1023m−2. The main results show that 0.1 wt.% Si can contribute to the suppression of irradiation hardening and embrittlement, as evidenced by the reduction in irradiation-increased hardness and yield strength, while maintaining preferable elongation. Microscopic analysis suggests that an appropriate content of Si helps refine the grains in RAFM steel, increases the ductile fracture region of the fracture surface, and effectively reduces the density of dislocation loops induced by neutron irradiation. The findings evidence that retaining a certain amount of trace Si should be an informed and rational choice in the design of RAFM steel.

Study on the Causes and Control Measures of Mg–Al Spinel Inclusions in U75V Heavy Rail Steel

U75V heavy rail steel production uses an aluminum-free deoxidation process; however, large particles of MgO–Al2O3 inclusions form in the steel, which has a great impact on product quality. In this paper, we try to explain how spinel inclusions, which affect the metallurgical quality of heavy rail steel, are produced by thermodynamic and experimental methods, and then determined measures for avoiding such inclusions. The formation mechanism of spinel inclusions in U75V heavy rail steel was determined through the analysis of nozzle clogging in the pouring process and typical inclusions in steel. The results show that there are two types of spinel inclusions in heavy rail steel: one is pure Mg–Al spinel inclusions and the other is Mg–Al spinel inclusions coated with calcium aluminate. The small, pure Mg–Al spinel inclusions were precipitated during the solidification of the molten steel, and the precipitation temperature was related to the composition of the molten steel. The large spinel inclusions were derived from clogging of the submersed nozzle. Mg–Al spinel inclusions coated with calcium aluminate were transformed from CaO–SiO2–Al2O3–MgO complex inclusions in the steel during cooling, and the formation temperature was related to the content of Al2O3 and MgO in the inclusions. The content of Al2O3 and MgO in the inclusions was the key to the formation of the Mg–Al spinel inclusions. Therefore, in order to control the production of spinel inclusions in steel, it is necessary to strictly control the content of impurity elements such as magnesium and aluminum in the alloy auxiliary materials, to reduce the secondary oxidation of liquid steel and to reduce the erosion of refractory materials.

Development of deoxidation process for off-grade titanium sponge using magnesium metal with wire mesh strainer type of crucible

In this study, the deoxidation process for off-grade titanium (Ti) sponge using magnesium (Mg) metal with a wire mesh strainer type of crucible was developed. Ti hydride (TiH2) feedstock, which was prepared by hydrogenating off-grade Ti sponge, was deoxidized using Mg in a molten magnesium chloride–potassium chloride salt at 933 K under an argon and 20% hydrogen (H2) mixed gas atmosphere. After deoxidation, the residual Mg-containing salt was separated in situ from the crucible to investigate the feasibility of minimizing salt loss during the leaching and production of pure TiH2. The results showed that the presence of residual Mg-containing salt inside the crucible strongly influenced whether a mixture of Ti and TiH2 or pure TiH2 was produced. When the salt was not sufficiently separated, a mixture of Ti and TiH2 was obtained and its oxygen (O) concentration was 0.121 mass% under certain conditions. Meanwhile, pure TiH2 was obtained by increasing the H2 gas flow rate during deoxidation. Therefore, these results demonstrate that the decrease of O concentration to below 0.180 mass% and the minimal loss of the salt are feasible.

Ce-doped Mn/Co catalyst: Analysis of performance and mechanism underlying NH3+NO+CO model reaction

In this study, we prepared Mn-Co-Ce catalysts through coprecipitation, analyzed their physicochemical properties through X-ray diffraction, transmission electron microscopy, hydrogen temperature programmed reduction, and X-ray photoelectron spectroscopy, and studied the removal of NO by NH3+CO. The Ce-1.25 catalyst (Mn: Co: Ce molar ratio of 1:3:1.25) exhibited the highest NH3+CO synergistic NOx reduction efficiency. Doping of Ce at appropriate concentrations effectively mitigated the micro-agglomeration of metal particles, increasing the relative content of active species on the catalyst surface, providing more defect sites, and enhancing the electron mobility of the adsorbed species and catalyst. The mechanism of the CO-NH3-selective catalytic reduction (SCR) reaction synergy was revealed as follows. The CO-NO reaction involved the gradual deoxidization and reduction process of nitrate; it was difficult for this reaction to be activated in the later stages, which limited its overall activity. The NH3-SCR reaction on the sample surface followed the Langmuir-Hinshelwood mechanism, while CO oxidation and the CO-NO reaction mainly followed the Eley-Rideal mechanism. In the cooperative reaction process, CO mainly reacted with NO3* to generate NO2*, which was accompanied by direct oxidation of some CO.

Electro-deoxidation behavior of Ca4Ti3O10 in molten CaCl2-NaCl

Ca4Ti3O10 is one of the important minerals enriched by titanium-containing blast furnace slag. The electro-deoxidation behavior of Ca4Ti3O10 was investigated, and titanium metal was successfully prepared in molten CaCl2-NaCl by the FFC Cambridge process. Firstly, the band structure and state density of Ca4Ti3O10 were calculated by the first principle, and the bond-breaking trend was analyzed. Then, the reduction process of Ca4Ti3O10 and the preparation mechanism of titanium were carried out by electrochemical methods. Finally, constant voltage electrolysis experiments were conducted at 900 °C and a voltage of 3.2 V for different durations. The electrolytic products were characterized using XRD, SEM-EDS, and XPS. The results revealed that the reduction process of Ca4Ti3O10 proceeded as follows: Ti4+→Ti3+→Ti2+→Ti+→Ti. The deoxidation path of the product after constant voltage electrolysis was observed as Ca4Ti3O10 → TiO2 → CaTiO3→ TiO2→ Ti2O3 → TiO → Ti2O → Ti. The whole deoxidation process can be divided into three stages: (I) the Ti-Ca bond in Ca4Ti3O10 is broken to form CaTiO3 and TiO2; (II) CaTiO3 and TiO2 are reduced from the surface of the cathode sheet inward to form a Ti-O solid solution; (Ⅲ) Ti-O solid solution is further deoxidized to form Ti metal. This method provides a theoretical basis for the subsequent electrolysis of titanium-rich slag, thereby contributing to developing a more sustainable and efficient method for extracting titanium from enriched titanium slag.

Comment on “Wetting of liquid copper on TC4 titanium alloy and 304 stainless-steel at 1273–1433 K” Materials & design 169 (2019) 107667

In the present paper a few comments on the paper “Wetting of liquid copper on TC4 titanium alloy and 304 stainless-steel at 1273–1433 K” Materials & Design 169 (2019) 107667, have been discussed. The comments are mainly focused on the wetting mechanism. We used the ISD method for characterization of the intrinsic wetting behavior of molten Cu on 304ss. In Sun et al.’s work, they adopt MSD method for characterization. With this respect the obtained data and discussed results are doubtful. For the wetting behavior characterization of metal/metal system, oxide film is a non-negligible factor on both the droplet surface and the substrate surface. To characterize the intrinsic wetting behavior, it is necessary to avoid the involvements of de-oxidation process and the influence of melting process.

Studies on Preparation of Thorium-Based Intermetallics in CaCl2 Melt by Electrochemical De-Oxidation Process

Thorium and its alloys find immense applications in nuclear technology. In the present study, the feasibility of direct electrochemical de-oxidation of mixed ThO2-NiO (7:3 molar ratio) and ThO2-Fe2O3 (7:1.5 molar ratio) to Th7Ni3 and Th7Fe3 intermetallics was investigated for the first time in CaCl2 melt at 900 °C using FFC Cambridge process. Electro-reduction mechanisms of the mixed metal oxides were elucidated by conducting constant voltage electrolysis at 3.1 V cell potential with sintered mixed metal oxides pellet cathode and HD graphite anode in molten CaCl2 for different time intervals. The electrolysed products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis techniques. Reduction of the less stable metal oxide, e.g., NiO or Fe2O3, occurred at the initial phase of electrolysis, and de-oxidation of more stable ThO2 took place in presence of newly formed metallic Ni or Fe in the later stage, leading to the formation of Th7Ni3 or Th7Fe3. Electro-reduction mechanism of ThO2 was evaluated using cyclic voltammetry technique with ThO2 filled Mo cavity electrode, and a single-step reduction of ThO2 to Th was perceived.

Thermodynamics of the Formation of Non-Metallic Inclusions during the Deoxidation of GCr15 Bearing Steel

The non-metallic inclusions in steel mainly come from the deoxidization process of molten steel. Based on the different deoxidization processes of GCr15 bearing steel produced by a domestic steel plant, the single deoxidization curves of Al, Si, and Mn and the compound deoxidization curves of Al-Si and Si-Mn under pure molten iron and GCr15 bearing steel production conditions were calculated with the FactSage 8.1 thermodynamic software. The results show that the deoxidization curves under the two conditions are quite different. At the same time, the Al-Ti deoxidation equilibrium curve under the condition of GCr15 bearing steel was calculated. It was found that when [Ti] < 0.0015% in the steel, the equilibrium deoxidation product was Al2O3, and no titanium oxide was generated. Finally, a thermodynamic calculation and analysis of the effect of rare-earth Ce content on the modification of inclusions in GCr15 bearing steel were carried out. The results showed that when T = 1873 K, the rare-earth Ce treatment of aluminum deoxidized the GCr15 bearing steel; when [Al] = 0.015%, Al2O3 inclusions increased with the increase in [Ce] content, and the evolution path was Al11O18Ce→CeAlO3→Ce2O3. When [Si] = 0.28%, [O] > 50 ppm, and CeCrO3 and [O] 0.012% appeared. CeS inclusions appeared in the steel, and the final equilibrium product was CeS + Ce2O3. When [Ce] < 0.012%, CeS was not produced in the steel, and only Ce2O3 existed.

Study of the Microstructure of 08PS Steel Deoxidized with Standard Ferroalloys and Prospects for Replacing Them with Complex Deoxidants

The annotation This research work is devoted to the study of the microstructure of 08PS steel deoxidized using standard ferroalloys and the prospect of replacing them with complex deoxidifiers. The purpose of the study was to determine the impact of the deoxidation process on the microstructure of steel and to assess the replacement with complex deoxidants. Research methods included metallographic analysis of steel samples and energy dispersion analysis (EDX) to determine the composition of non-metallic inclusions. The analysis was carried out on steel samples before and after deoxidation, the microstructure, the size of non-metallic inclusions and their composition were studied.

Low-oxygen Ti-6Al-4V alloy powder synthesized by an aluminothermic reduction combined with deoxidation process

A novel aluminothermic reduction combined with deoxidation process was developed in this research to prepare low-oxygen Ti-6Al-4V alloy powder. First, with Al and Al-V alloy powders as reducing agents and additives, crude Ti-6Al-4V alloy powder was fabricated by reduction-vacuum distillation using Na2TiF6 as a titanium source. The aluminothermic reduction process was investigated by TG-DSC technique, and the thermal kinetic parameters of the reaction process were calculated by the Kissinger method. The oxygen content of the crude Ti-6Al-4V alloy powder with a coral-like porous structure was detected as 0.366 %. Furthermore, the existential states of the oxygen contained in the crude product powder was analyzed using XPS. The results indicated that the oxygen existed in three chemical states: metal oxides, defective oxygen, and adsorbed oxygen. Therefore, the deoxygenation of the crude Ti-6Al-4V alloy powder with calcium as a deoxidizer was carried out at 900 °C. As a result, the final Ti-6Al-4V powder with an oxygen content of approximately 822 ppm could be obtained. The contents of Ti, Al, V, Fe, and O in the obtained Ti-6Al-4V powders met the requirements of GB/T 3620.1−2016. This work had demonstrated the feasibility of preparing Ti-6Al-4V alloy powder by the novel aluminothermic reduction combined with deoxidation process.

Carbothermal-sulfurization of TiO2 into Ti2SC MAX phase in TiO2/C/FeS2 ternary system

The conventional method for synthesizing Ti2SC depends on the reaction between TiS and TiC, which requires the utilization of costly Ti, TiC, or TiS2 powders. Utilizing TiO2 as the raw material for the synthesis of Ti2SC enables the cost-effective preparation of this compound. However, the optimization of the TiO2/C/XnSm (sulfides) system is of utmost importance when aiming to synthesize Ti2SC through carbothermal-sulfurization of TiO2, as the formation temperature of TiS and TiC greatly depends on the XnSm. In this study, the identification of the thermodynamically dominant region for the formation of TiS and TiC in the TiO2/C/XnSm systems was conducted by utilizing various sulfides (63 types). Considering factors such as the challenges associated with removing by-products, accessibility, and toxicity, FeS2 was ultimately chosen as a highly promising candidate. Thanks to the low melting point of FeS2, Ti3O5, the preliminary carbothermal reduction product of TiO2, has achieved rapid-deep deoxidation and phase reconstruction processes in the molten phase. Meanwhile, unlike the conventional solid-solid sintering reaction, which often results in residual reactants that are challenging to eliminate. This novel one-step phase transformation process that occurs in the molten phase exhibits minimal impurity phases, apart from the by-product Fe. Ti2SC with a purity greater than 99 wt% was obtained when the TiO2/C/FeS2 was pickled to remove Fe after sintering at 1600 °C for 5 min. This work will provide the theoretical basis and a new path for the low-cost preparation of sulfur-containing MAX phases.