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Molybdenum silicides (Mo–Si) have attracted great interest owing to their good electrical conductivity, ultra-high melting point and well oxidation resistance. In this work, the controllable syntheses of Mo5Si3 and Mo3Si powders by silicothermic reduction of MoS2 in the presence of lime are studied for the first time. The internal mixture composed of MoS2 and Si is wrapped by sufficient CaO. After the reaction is finished, the synthesized molybdenum silicides can be easily separated from the desulfurization layer by peeling off the desulfurization product. The results show that Mo3Si and Mo5Si3 can be prepared at 1500 °C for the samples with the MoS2:Si molar ratio of 1:1.7 and 1:2.33, respectively. In addition, the results show that both SiS2 and SiS can be formed during the heating process. The thermodynamic analysis about the disproportionation reaction of SiS indicates that the existence of SiS2 depends on the partial pressure of SiS (PSiS) and temperature. Moreover, it is demonstrated that SiS2 is preferentially formed under low temperature conditions. As the temperature rises, it is much easier for SiS2 to react with Si to form SiS. Additionally, this work experimentally proves for the first time that SiS gas can directly reduce MoS2 to form MoSi2 and SiS2. Subsequently, the recovery of S in the desulfurization product was studied. S in MoS2 was first captured by CaO in the form of CaS (accompanied by Ca2SiO4 and Si). In order to solve this CaS containing desulfurization product which is detrimental to the environment, CaS in the desulfurization product is react with Fe2O3 and C to form FeS. This work provides new insights into the closed-loop capture and recovery of S in the process of extracting metals or metal compounds from sulfide ores. more...

In this work, the sulfur-free emission route for the synthesis of Mo and Mo2C via carbothermal reduction of MoS2 was proposed. The internal MoS2-C mixture is wrapped by an external desulfurization layer composed of CaO and C. In the internal layer, MoS2 reacted with carbon black and generated Mo, Mo2C (or their mixture), as well as S2, CS2 and CS gas. Both experiments and thermodynamic calculations show that the main gaseous product should be CS2. The sulfur-containing gas produced can be completely captured by the desulfurization layer in the form of CaS. This strategy can avoid the emission of S-containing gas compared with the traditional route. In addition, after removing the unreacted desulfurizer and gently breaking the desulfurization product layer, the molybdenum-containing product can be collected. For the raw material with a MoS2:C molar ratio of 1:1, after reacting at 1600 °C for 4 hours, Mo with carbon and sulfur contents of 0.053 and 0.050 pct is acquired. In addition, Mo2C-dominant product can be obtained after reacting at 1600 °C for 4 hours at a MoS2:C molar ratio of 1:1.52, with the carbon and sulfur contents of 5.878 and 0.049 pct. The above shows that this strategy has the advantages of high-efficiency desulfurization and simple separation of desulfurization product, which is an environment-friendly method for the production of molybdenum additives. more...

Fully dense and magnetically controllable glass ceramics was successfully synthesized by method of hot pressing using CaO-Al2O3-SiO2-Na2O glass powder and Fe3O4 powder as raw materials. The influences of sintering temperature and time, content and particle size of Fe3O4, as well as particle size of glass powder on the densification and magnetic properties of samples were investigated. It was found that the saturation magnetization gradually increased with increasing magnetite content. In addition, the samples containing smaller size magnetite particles had a higher coercivity. However, for samples using smaller size glass powder, magnetite particles could partially dissolve into the glass matrix, which led to the decrease of saturation magnetization and the increase of coercivity. It was also concluded that the precipitation of crystalline phase from smaller size glass powder caused the decrease of degree of densification, and after decreasing the sintering temperature, the degree of densification of product was enhanced. more...

Refractory metal diboride is a kind of excellent ultra-high temperature ceramics and could be applied as thermal shielding material for supersonic aircraft. In this paper, a two-step reaction process for the synthesis of refractory metal diboride powders was proposed using refractory metal oxide, carbon black (C), B4C, and calcium Ca as raw materials. Firstly, the carbothermal reduction reaction between oxides and C was taken place at 1773 K; and then, the reduction product was reacted with B4C and Ca for the purposes of boronization and decarburization. After acidic leaching, pure diboride was prepared. The experimental results indicated that diborides of Ti, Zr, Hf, V, Nb and Ta with low residual carbon content can be prepared by this method. In addition, the inheritance relationship of particle size between raw oxide and finally prepared diboride was revealed. By this method, ultra-fine TiB2 (123 nm) and ZrB2 (76 nm) powders were also successfully prepared, with the raw materials of nano TiO2 and nano ZrO2, respectively. more...

Tungsten borides are special compounds with potential applications in superhard materials, anti-friction materials, and catalytic materials. In this study, a new synthetic method for tungsten boride is proposed using tungsten (W) and boron carbide (B4C) as raw materials. First, the boronization reaction between W and B4C was carried out at a high temperature; then, the boronization products were reacted with calcium to generate CaC2 for decarburization. After acidic leaching of the CaC2 and Ca, pure tungsten boride could be prepared. By investigating the reaction between different ratios of W and B4C, it was found that only pure W2B and WB were synthesized in the current method, and W2B5 could react rapidly with Ca to form WB and CaB6. However, in the absence of a decarburization treatment after the boronization process, carbon-containing WB (C content = 1.2 wt%) and W2B5 (C content = 3.4 wt%) could also be prepared. In addition, it was concluded that the prepared tungsten boride roughly maintained the morphology and particle size of raw W, and ultra-fine tungsten boride could be synthesized with ultra-fine W powder at a low boronization reaction temperature. more...

The influences of atmosphere during processes of melting and heat treatment, heat treatment temperature, Fe3O4 content and basicity on the magnetic properties of magnetite-based glass ceramics were investigated. For sample containing 20 % Fe3O4 melted in different atmospheres, the highest saturation magnetisation was realized in 20vol% air + 80 vol% Ar, due to the fact that ratio of Fe3+ to Fe2+ in melt obtained in this atmosphere was close to 2. However, it was found that the coercivity of glass ceramics was not affected by the melting atmosphere. A high sintering temperature led to the decrease of saturation magnetisation and the increase of coercivity. As increasing Fe3O4 content, the main crystal phase transformed from CaSiO3 to CaFe0.6Al1.3Si1.08O6 and finally to magnetite phase, accompanied by the increase of saturation magnetisation and coercivity. In addition, the increase of basicity caused the decrease of saturation magnetisation and the increase of coercivity. more...

Stainless steel pickling sludge is the precipitate from the neutralization process of stainless steel pickling liquor. Until now, many methods about the harmless treatments of pickling sludge have been developed, and among them the most effective one is to produce Fe-Cr-Ni alloy by carbothermic reduction process. However, the carbon and sulfur (harmful elements for steel) contents of the produced Fe-Cr-Ni alloy are difficult to be controlled, especially for the high-CaSO4 sludge. The current paper proposed a new method to produce the low-carbon and low-sulfur Fe-Cr-Ni-Si alloy by using the high-CaSO4 stainless steel pickling sludge. Firstly, the sludge was pre-reduced by carbon at 1100 °C. Then, the pre-reduced sludge was mixed with silicon powder and reacted at 1550 °C for the deep reduction, separation, and desulfurization. By the current method, the Fe-Cr-Ni-Si alloy with a carbon content of 0.513 wt pct and a sulfur content of 0.003 wt pct was produced. Meanwhile, the Fe, Cr, and Ni contents in alloys were 59.600, 15.440, and 13.570 wt pct, with recovery rates of 97.99, 97.61, and 98.65 pct, respectively. Such an alloy can be used as the alloy additive for stainless steel production. more...

High-quality ferrovanadium nitride (FeV45N, FeV55N and Fe65N) was fabricated using the raw materials of Fe3O4, V2O5 and graphite via carbothermal reduction nitridation method. Compared with the traditional methods, it shortens the production process of ferrovanadium nitride by avoiding the preparation of ferrovanadium. The effects of C/O molar ratio and reaction temperature on phase transition, density, carbon, oxygen and nitrogen contents and microstructure were investigated. The appropriate C/O molar ratio is crucial to obtain the products with high nitrogen content. It is also found that a higher temperature is beneficial for the densification, and the density of the products obtained at 1550 °C is much higher than that at 1500 °C. Moreover, a higher temperature contributes to the increase in nitrogen content owing to the higher reaction kinetics. The carbothermal reduction nitridation method is proved to be a facile route to fabricate cost-effective ferrovanadium nitride and is possible to be applied for industrial production. more...

Due to its distinctive properties and promising applications, one-dimensional Mo2C has received increasing attention in recent years. In this paper, the strategy of two-step topochemical synthesizing one-dimensional Mo2C nanobelts with one-dimensional MoO3 nanobelts as precusor was first proposed. The phase composition, morphology, structure, chemical states, specific surface area and pore size distribution of the synthesized Mo2C were characterized. Firstly, one-dimensional MoO3 nanobelts were synthesized via hydrothermal route. Secondly, Mo2N nanobelts were synthesized by the reduction and nitriding reaction of MoO3 nanobelts via NH3. Finally, one-dimensional Mo2C nanobelts with a width of 100–500 nm and a length of several tens of micrometers were successfully prepared after carbonization of one-dimensional Mo2N nanobelts under a 5%CH4/H2 gas mixture flow at 700 °C for 2 h. Additionally, the prepared one-dimensional Mo2C nanobelts has abundant mesopores on its surface and has a specific surface area of 48.7 m2/g. more...

In this study, the effect of involvement of CaO–Al2O3–SiO2–MgO tundish flux into CaO–SiO2–Al2O3–Na2O–CaF2 mold flux on viscosity and structure of mold flux was investigated through employing the rotating viscometer and associated structure analysis including high resolution Raman spectroscopy and solid-state 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR). The results showed that the viscosity continuously increases with increasing involvement of tundish flux. The apparent activation energy obtained from the temperature dependence of the viscosity presents an increase from 128.5 kJ/mol to 149.1 kJ/mol with increase of involvement ratio from 0 to 0.75. Semi-quantitative analysis using the deconvoluted Raman spectra and 27Al MAS-NMR spectra revealed an increase in amounts of [AlO4] and Si–O–Al units, but in the meanwhile a decrease in amounts of [AlOnF4-n] and [AlO5] units, this indicates the structure transformation from prevalent silicate structure to complex alumino-silicate structure with increasing involvement ratio. A self-developed structurally-based viscosity model can predict the viscosity of mold flux with varying involvement ratio and presents a smallest deviation of 15.8% compared to those prevalent viscosity models despite of the great transformation of the melt from silicate system to alumino-silicate system. more...

High-purity ultrafine W or WC powder was prepared via a two-step process composed of the carbothermic pre-reduction of WO2.9 and the following deep reduction with H2 or carbonization with CH4+H2 mixed gases. The effects of C/WO2.9 molar ratio and temperature on phase composition, morphology, particle size, and impurity content of products were investigated. The results revealed that when the C/WO2.9 ratio was in the range from 2.1:1 to 2.5:1, the carbothermic pre-reduction products consisted of W and a small amount of WO2. With changing C/WO2.9 ratio from 2.1:1 to 2.5:1, the particle sizes were gradually decreased. In order to prepare ultrafine W or WC powder, a relatively high C/WO2.9 ratio and a lower reaction temperature at this stage were preferred. After the second reaction, the final products of ultrafine W and WC powders with a high purity could be obtained, respectively. more...

The mixed alkali effects of Li2O, Na2O, and K2O on viscosity of CaO-SiO2-Al2O3 melts are investigated by rotating cylinder method. It is found that the single addition of Li2O, Na2O, or K2O to CaO-SiO2-Al2O3 melt will reduce the viscosity of melt, regardless of the Al2O3 content, while the degree of reduction follows the sequence of Li2O > Na2O > K2O. For melts containing two alkali oxides, viscosity monotonically decreases when one alkali oxide is replaced by another at all temperature investigated in this paper, but no extrema of viscosity is found like the behavior of electrical conductivity. In addition, the extrema are not found in the slag containing three alkali oxides if changing their relative contents but keeping their total contents constant. Raman spectroscopy is used to illustrate the relationship between viscosity and structure of melt and it is found that degree of polymerization is the major factor affecting the viscosity of melt. more...

In this study, we introduced a facile and efficient method for the large-scale synthesis of porous 2D molybdenum nitrides nanosheets via the topochemical nitridation of MoS2 by NH3 with the assistance of CaO at 750 °C–820 °C. The presence of CaO can noticeably promote the reduction rate of MoS2 by generating CaS. After acidic leaching, porous 2D MoN, a mixture of 2D MoN and Mo2N, as well as Mo2N nanosheets with the thickness of about 7 nm and pore size of about 10.5 nm were successfully prepared at different temperatures. When the temperature increased from 750 °C to 820 °C, the product gradually changed from MoN to Mo2N. Due to the weak Van der Waals forces between the layers of MoS2, the topochemical substitution of S in MoS2 by N led to the exfoliating of layers. The large difference of crystal structures and volume between precursor and product, as well as the high reaction rate led to the formation of porous structure of molybdenum nitrides. more...

The method of calciothermic reduction of B4C was proposed for preparing CaB6. The phase transition and morphology evolution during the reaction were investigated in detail. The experimental results reveal that Ca first reacts with B4C to generate CaB2C2 and CaB6 at a low temperature and that the CaB2C2 subsequently reacts with Ca to produce CaB6 and CaC2 at a high temperature. After the products were leached to remove the byproduct CaC2, pure CaB6 was obtained. The grain size of the prepared CaB6 was 2–3 μm, whereas its particle size was 4–13 μm; it inherited the particle size of B4C. The residual C content of the product was decreased to 1.03wt% after the first reaction at 1173 K for 4 h and the second reaction at 1623 K for 4 h. more...

This paper provides a new method for preparing refractory metal diboride by reducing refractory metal oxide with Calcium hexaboride (CaB6), which is prepared using B4C and calcium as raw materials. For refractory metal powders (M = Ti, Zr, Hf, V, Nb, Ta, Cr) which are expensive and hard to be produced by a simple route, it is more cost-effective to directly use refractory metal oxide to prepare its boride. After reacting at 1473 K for 4 h, CaB6 and refractory metal oxide could completely react to form MB2, CaO and B2O3. The single-phase product with the particle size of sub-micron was obtained after acidic leaching, filtration and drying. CaB6 could be used as a universal reducing agent to prepare metal boride. more...

High purity vanadium nitride (VN) powders were prepared via a two-step process using vanadium trioxide (V2O3) as the raw material. The V2O3 was firstly reduced at 873 K in Ar atmosphere via magnesiothermic reduction reaction to get the mixture of V and MgO, and then the products were further nitrided at 1473 K in N2 atmosphere. Finally, the as-prepared samples were acid-leached to obtain pure VN powders. X-ray diffractometry and field-emission scanning electron microscopy were used to analyze the phase transition and morphological evolution of the samples. The results reveal that the overall morphology of the obtained VN powder retains the morphology of the initial V2O3 powders. After removing MgO by acidic leaching, the porous VN particles can be obtained, with the oxygen content of 0.178 wt.%. Compared with the traditional methods, high purity VN powders with a small amount of oxygen and no carbon can be obtained. more...

Vanadium diboride (VB2) powders with low oxygen content are prepared via a molten-salt-assisted borothermal reduction reaction at 1123 K to 1273 K (850 °C to 1000 °C) using V2O3 and boron powders as the raw materials. The effects of the amount of molten salt and reaction temperature on the phase transition and morphology of the final products are investigated. The results reveal that the addition of molten salt is beneficial for decreasing both the synthesis temperature and particle size of the final products. When the mass ratio of NaCl to reactants is 0.75:1, the VB2 powders prepared at 1173 K (900 °C) have a particle size lower than 100 nm. Too little or too high molten salt addition has a negative impact on the preparation of the VB2 powders. Furthermore, the reaction temperature has an important impact on the morphology and purity of the VB2 particles. An appropriate reaction temperature (1173 K (900 °C)) is beneficial for controlling the size of the VB2 particles in the order of nanoscale and improving the quality of the VB2 powders. more...

In the current study, ultrafine and high-purity tungsten carbide (WC) powders are successfully prepared by a two-step process: carbothermic reduction of WO3 followed by carbonization reaction. The effects of the C/WO3 molar ratio, reaction temperature and reaction time on the phase transition and morphology evolution of the products are investigated. During the carbothermic reduction process, all the oxygen in yellow tungsten trioxide (WO3) is removed by carbon to generate a mixture of W, W2C and WC at 1100 °C; and then the as-prepared powder is mixed with an appropriate content of carbon black and carbonized at 1200 °C. The carbon content in the finally obtained WC powders is almost equal to the theoretical value. Furthermore, it is found that a high C/WO3 molar ratio at the first stage is beneficial for decreasing the particle size of the WC powders. When the C/WO3 molar ratio is 3.5, the single phase WC with a particle size of about 200 nm can be obtained. Therefore, this carbothermic reduction–carburization process may provide a simple, low-cost, and high efficiency route to prepare the WC powders in a large-scale. more...

The submicrometric VB 2 powders are prepared at 1773 K by a boro-carbothermal reduction method using V 2 O 3 , B 4 C and C powders as the raw materials. The effects of reaction temperature and B 4 C content on the phase composition and morphology of the products are investigated. The phase transition and morphological evolution of the products are characterized by X-ray diffraction (XRD) and Field-emission scanning electron microscopy (FE-SEM). The results reveal that firstly V 2 O 3 reacts with B 4 C to generate VB 2 , VC and B 2 O 3 , and then the by-products of VC and B 2 O 3 react with C to produce VB 2 . Owing to the evaporation loss of the B 2 O 3 , excess B 4 C should be added to avoid the formation of the boron deficient phases. Only when the V 2 O 3 /B 4 C/C molar ratio is close to 1:1.26:2, the single-phase VB 2 could be prepared which has the residual carbon and oxygen contents of 0.34 wt% and 1.4 wt%, respectively. The particles of VB 2 powders obtained at 1773 K display a plate-like morphology with a size of approximately 0.1–0.8 µm. more...

The development of a highly efficient and low cost production process is instrumental for the wide application of VO2 and V2O3. In this paper, VO2 and V2O3 powders are successfully prepared via carbothermal reduction of V2O5 in a flowing Ar atmosphere at 973 K and 1423 K, respectively. Compared with the traditional methods, graphite is used as a reductant, which resulted in a low cost. The experimental results show that a high temperature assists in improving the kinetic rate. The phase transformation during the low-temperature reduction process between 948 K and 973 K occurs in the following sequential order: V2O5→V6O13→VO2. When the temperature is 1423 K or 1473 K, the phase transformation can be described as follows: V2O5→V3O5→V2O3. Owing to the shrink of the volume, the as-prepared VO2 and V2O3 particles could not maintain the original micro-morphology of V2O5. Relative to VO2, the as-prepared V2O3 particles are porous. It is also concluded that the V2O3 can be easily oxidized to VO2, when the partial pressure of O2 is in the range of 10−8 atm to 10−1 atm. Therefore, a reasonable reaction temperature and reaction time are important to prepare high purity V2O3. more...

The development of a highly efficient and low-cost production process is instrumental for the wide application of vanadium nitride (VN). The strong affinity of vanadium with carbon and oxygen resulted in the significant difficulty to produce VN with a high purity. In this paper, a novel production route was proposed that involves the magnesiothermic reduction and nitration of vanadium (III) oxide (V2O3) in nitrogen atmosphere with the assistance of magnesium chloride (MgCl2) in the temperature range of 948 K to 1073 K (675 °C to 800 °C). Compared with the traditional methods, there was no contamination of carbon. Meanwhile, oxygen content can be controlled to a low level. Furthermore, VN could be prepared at low temperatures within a short time, which was beneficial for decreasing the particle size of VN. The phase transition and morphological evolution of samples were analyzed by X-ray diffraction and Field-Emission Scanning Electron Microscopy, respectively. The experimental results showed that high temperature assisted in decreasing the residual oxygen content in VN but can decrease the specific surface area. Oxygen content of the obtained VN powder after reacting at 1073 K (800 °C) for 3 hours was 1.36 wt pct. more...

A method of preparing Mo2C via vacuum carbothermic reduction of MoS2 in the temperature range of 1350–1550°C was proposed. The effects of MoS2-to-C molar ratio (α, α = 1:1, 1:1.5, and 1:2.5) and reaction temperature (1350 to 1550°C) on the reaction were studied in detail. The phase transition, morphological evolution, and residual sulfur content of the products were analyzed by X-ray diffraction, field-emission scanning electron microscopy, and carbon–sulfur analysis, respectively. The results showed that the complete decomposition of MoS2 under vacuum is difficult, whereas activated carbon can react with MoS2 under vacuum to generate Mo2C. Meanwhile, higher temperatures and the addition of more carbon accelerated the rate of carbothermic reduction reaction and further decreased the residual sulfur content. From the experimental results, the optimum molar ratio α was concluded to be 1:1.5. more...