Vacuum Metallurgy Research Articles

Simulation and experimental study of temperature and mass distributions of indium metal in vacuum evaporation

The temperature field and spatial distribution of metal vapor (i.e., flow field) are critical for the purity and direct yield of metals. However, it is impossible to accurately determine the temperature field and distribution of the metal vapor in a vacuum furnace. This study developed a surface-to-surface thermal radiation and volume of fluid multiphase flow coupling model. The temperature distribution and mass distribution of indium vapor in the vertical vacuum furnace at different temperatures from 1423 to 1573 K under the condition of 1 Pa were obtained. The reliability of the model was verified by experimental data obtained under the same conditions as the simulation. The temperature difference between the inside and outside of the condensing plate was 30–45 K in the temperature interval of 1423–1573 K. The temperature difference between the inside wall and the center of the condensing plate was 10 K. The simulation results of indium vapor mass distribution match with the experimental values; the overall temperature error is 5%, and the volatility error is less than 15%. The model developed in this study can be used to predict the temperature field and metal vapor distribution in a vacuum furnace, which will significantly reduce experimental exploration and accurately guide the production practice of vacuum metallurgy. This will expand the application of vacuum metallurgy technology in metal purification, material preparation, waste recycling, and other industries. This can effectively reduce exploratory experiments in the process of vacuum distillation to prepare high-purity metals, reduce the consumption of resources and energy in the experiment and production process, and achieve clean production.

Effect of Ca Addition on Inclusions of Welding Heat-Affected Zone in Pressure Vessel Steels

Pressure vessel steels are used in the manufacture of tanks for the storage of gases, chemical materials and oil. To meet the increasing production demands, high-wire-energy welding is widely used in the manufacture of pressure vessel steels. This means that the weldability of pressure vessel steels needs to be improved. Therefore, in order to reveal the microalloying effect of Ca in pressure vessel steel, this study took a commonly used pressure vessel steel as the research object, and three groups of experimental steels with different Ca mass fractions were prepared using vacuum metallurgy, controlled rolling and controlled cooling. Welding heat simulation technology was used to simulate the welding heat of experimental steel and the welding heat-affected zone (HAZ) was investigated. The inclusions of the welding HAZ in the experimental steels were observed by using a metallographic microscope and scanning electron microscope (SEM). The mechanism of intragranular acicular ferrite (IAF) nucleation induced by the inclusions containing Ca elements in the welding HAZ of pressure vessel steels was also discussed. The research results show that the addition of Ca increased the number density of effective inclusions in the welding HAZ of the experimental steel up to 535.60 pieces/mm2. The addition of the Ca element was beneficial for producing more pinning inclusions in the experimental steel welding HAZ under the experimental conditions, and the inclusions were mainly elliptical oxide complex inclusions of Ca-Si with a size of about 2 μm. Meanwhile, Al2O3 and MnS were precipitated. After the addition of Ca elements, Mn-poor regions appeared around the inclusions containing Ca in the welding HAZ. IAF nucleation was mainly induced by the local compositional change mechanism and supplemented by the stress–strain energy mechanism and inert interface energy mechanism. This study provides a valuable reference for optimizing the welding process of pressure vessel steels and is of great importance for understanding the IAF nucleation mechanism of Ca-containing inclusions in the welding HAZ of pressure vessel steels.

Effect of Mg Addition on Inclusions in the Welding Heat-Affected Zone of Pressure Vessel Steels

With the development of the pressure vessel industry, high-energy wire welding has a great future. However, this means higher demands on the weldability of pressure vessel steels. Controlling inclusions via oxidative metallurgy is a reliable method of improving the weldability of pressure vessel steels. Hence, in this paper, experimental steels with different Mg element mass fractions were prepared using vacuum metallurgy. Simulated welding for high-heat input welding was carried out using the Gleeble-2000 welding thermal simulation test machine. The inclusions in the welding heat-affected zone (HAZ) in the experimental steels were observed using an optical microscope (OM) and scanning electron microscope (SEM). The compositions of the inclusions were analyzed using an energy-dispersive spectrometer (EDS). The research results indicated that the addition of Mg could increase the number density of the inclusions in the welding HAZ. With the addition of Mg from 0 to 5 wt.%, the total number density of the inclusions increased from 133 to 687 pieces/mm2, and the number density of the inclusions with a size of 0–5 μm2 increased from 122 to 579 pieces/mm2. The inclusions in the experimental steel welding HAZ with Mg elements were mainly elliptical composite inclusions composed of (Mg-Zr-O) + MnS. Moreover, MnS precipitated on the surface of the Mg-containing inclusions in the welding HAZ. Intragranular acicular ferrite (IAF) nucleation was primarily induced via the minimum lattice mismatch mechanism, supplemented with stress-strain energy and inert interface energy mechanisms.

In-situ oxygen extraction from TiO2 using laser thermal vacuum metallurgy

One of the greatest challenges for long-term human activities on the Moon is the development of in-situ resource utilization (ISRU) technologies, including in-situ oxygen extraction. In this study, a novel method called laser thermal vacuum metallurgy (LTVM) was proposed for oxygen extraction from lunar regolith, specifically using TiO2 as raw material. Firstly, the theoretical feasibility of oxygen production from TiO2 was elucidated through thermodynamic calculations. Subsequently, the impact of laser power density on the decomposition behavior of TiO2 was investigated. The results demonstrate that through the augmentation of laser power density to elevate temperatures, there is a substantial enhancement observed in both the pyrolysis and vaporization processes of TiO2. Under the conditions of a laser power density of 2.48 kW/cm2, the surface temperature of TiO2 can be maintained at approximately 2175 °C. The resulting pyrolysis products consist of Ti6O11 (8.2 ± 0.5 wt %), Ti5O9 (23.7 ± 0.6 wt %), Ti4O7 (10.9 ± 0.4 wt %), and Ti3O5 (57.2 ± 0.8 wt %). Further combining with the result of gas collection, the estimated oxygen extraction rate is approximately 43.3 L per kilogram of TiO2. Therefore, LTVM holds the potential to provide a new approach for in-situ oxygen extraction from titanium-containing lunar regolith on the Moon.

Measurement and effect of volatilization kinetic parameters in the production of high-purity zinc by vacuum distillation

Vacuum distillation is commonly used for preparing high-purity zinc. However, the pressure of the experimental equipment must be below 1 Pa. Therefore, careful control over the accuracy of the equipment and vacuum system is required. In addition, there is a lack of information concerning the volatilization kinetic parameters for Zn, which makes it difficult to control the temperature and time parameters for the production of high-purity Zn. To solve these issues, the change in the mass of Zn and its evaporation rate (ω) at different temperatures (T) and pressures (P) was measured in real time using the vacuum differential-weight method. Using fitting, mathematical models for ω-T, ω-P, and ω-P-T were obtained, and, thus, other volatilization kinetic parameters, such as the evaporation coefficient and critical pressure, could be derived. The results showed that the critical pressure of Zn with respect to temperature was linear. Crucially, using the optimized parameters, high-purity Zn (6N8) was produced. Thus, this study provides volatilization kinetic parameters for the vacuum distillation of Zn and acts as a reference for improving the technological conditions and equipment production parameters used in Zn vacuum metallurgy.

Vacuum evaporation and expansion of pure metals at high temperature: Application to titanium and zirconium

The evaporation of metallic elements in vacuum metallurgy is an issue of great industrial concern. It is well known that a rarefied gas atmosphere raises the evaporation of the liquid metal at high temperature. The net flux of evaporation must then be accurately predicted i.e. the deviation from the Langmuir law because of the recondensation flux of the metallic vapour on the molten bath. The objective of this study is an experimental and theoretical evaluation of the net evaporation rate in the case of two reactive metals at high temperature, one (Zr) with a low vapour pressure whereas the second (Ti) exhibits a relatively higher vapour pressure. An experimental device has been set up in order to measure under usual industrial conditions (10−2 Pa) the evaporation fluxes as well as the expansion of the metallic vapour. In parallel, a particle simulation of the experiments compares the behaviour of the vapour for weak (Zr) and medium (Ti) collisional regimes. Experimental and numerical results testify to the validity of the Knudsen cosine evaporation law with a n exponent equal to 1 for Zr and 2 for Ti.

Application of modified molecular interaction volume model for phase equilibrium of PbS–Sb2S3 system in vacuum distillation

In this paper, the modified molecular interaction volume model (M-MIVM) was used to calculate the activities of components of the PbS–Sb2S3 binary matte system. On this basis, the vapor-liquid equilibrium (VLE) data of the PbS–Sb2S3 system were calculated by M-MIVM in combination with the theory of vacuum metallurgy and VLE. Additionally, the VLE experiment of the PbS–Sb2S3 binary matte system was conducted to correctly interpret the results of the model. The calculated results of the VLE of the model were consistent with the experimental values, and the VLE calculation of the PbS–Sb2S3 binary matte system by M-MIVM was reliable. This is an effective and convenient method to predict the relationship between product components with temperature and pressure in vacuum distillation of PbS and Sb2S3 mixed melts, providing theoretical guidance for vacuum separation and purification of PbS and Sb2S3.

Recovery of Te for the scrap of Bi2Te3-based alloys by vacuum metallurgy

Every year a large amount of scrap can be produced from the Bi2Te3-based alloys when processing. A clean, new vacuum distillation method is proposed to purify Te from the scrap of Bi2Te3-based alloys. In this work, the saturated vapor pressure, distillation rate and separation coefficient of each metal element in Bi2Te3-based alloys are theoretically analyzed. The effects of distillation temperature and time on the volatilization and condensation behavior of elements are studied under the dynamic vacuum of 0.1 Pa. According to the research results, a multi-stage distillation method is proposed, and Te was purified from 41.53% to 98.88% while the total impurity content was reduced to 1.12% through this procedure. Moreover, Te of the scrap of Bi2Te3-based alloys can be separated and recovered effectively via this three-step vacuum distillation. The results lay the foundation for the industrial purification of Te and provide a low-cost, simple and green recycling process of thermoelectric scrap, which has important practical significance.

Advances in the Safe Disposal and Comprehensive Utilization of Spent Carbon Anode From Aluminum Electrolysis: Prospects for Extraction and Application of Carbon Resources From Hazardous Waste

Spent carbon anode (SCA) is a dangerous solid waste that is continuously discharged from the aluminum electrolysis industry and has a large number of valuable resources and a high risk of environmental pollution. Its safe disposal and resource utilization have become a resource and environmental problem that must be solved urgently. Current methods for SCA disposal include flotation, vacuum metallurgy, physical activation, roasting, bubbling fluidized bed combustion, alkali fusion, alkali leaching, and chemical leaching combined with high temperature graphitization. In this paper, the material composition, resource properties, and environmental risks of SCA are discussed. Working principle, treatment process, advantages and disadvantages of the above methods are also briefly described and compared. Results showed that flotation is the safest disposal and comprehensive utilization technology that is suitable for characteristics of SCA raw materials and has the most large-scale application potential. In addition, characteristics of SCA recovery products are correlated to the recycling of aluminum reduction cells. This technology can alleviate the shortage of high-quality petroleum coke resources in China’s carbon material industry and the high cost of raw materials in aluminum electrolysis industry.

Experimental investigation and modeling of vapor-liquid equilibria for Bi–Zn and Bi–Sn–Zn systems at 10 Pa

For the Bi–Zn and Bi–Sn–Zn systems, vacuum distillation experiments were carried out at 10 Pa. The results show that the content of Zn for the Bi–Zn system in the vapor phase could reach more than 0.999 mol fraction in vacuum distillation. The VLE (vapor-liquid equilibrium) data were correlated using the Tsuboka-Katayama's modification of the Wilson equation (T-K-Wilson). The correlation showed good agreement with experimental data. Thermodynamic consistency tests of experimental data for the binary and ternary systems were presented by the Van Ness method. The results demonstrate that VLE phase diagram is reliable for predicting the process of vacuum distillation for the systems. It provides an efficient way to guide the separation and purification of crude Zn in vacuum metallurgy

Separation and recovery of heavy metals zinc and lead from phosphorus flue dust by vacuum metallurgy

Yellow phosphorous flue dust (YPFD) is a solid waste produced by the yellow phosphorus industry that contains heavy metals such as zinc (Zn) and lead (Pb), causing environmental damage. In this work, a vacuum metallurgy method is proposed to separate and recover Zn and Pb from solid waste YPFD. Under optimized conditions of 1173 K, 30 wt% reductant dosage, 60 min, and 5–10 Pa, the pre-separation of Zn and Pb was realized and the recovery rates of Zn and Pb reached 92.47% and 99.78%, respectively. In addition, gallium (Ga) remained in the residue with little loss, and then recovered by raising the reaction temperature to 1323 K. The recovery rates of Ga reached 87.57%. The principle of metal volatilization under vacuum at different temperatures was also clarified. The thermodynamic calculations of the carbothermal reduction reaction of metal oxides under vacuum were carried out. The analysis of the product obtained at 1173 K showed that Zn and Pb mainly existed in the form of elemental or simple compounds. At 1323 K, Ga in the residue was highly enriched in the condensation zone, which is conducive for the subsequent purification. The whole process is short, there is no waste water, low levels of pollution of emitted, and the technology provides a clean and sustainable way to reuse YPFD.

A vacuum distillation process for separation of antimony trisulfide and lead sulfide from jamesonite

Jamesonite is an important complex antimony mineral which treated by conventional methods have shortcomings, such as sulfur dioxide emission and low antimony and lead recovery. This study applied vacuum metallurgy technology to treat jamesonite. The vacuum decomposition behavior of jamesonite (Pb4FeSb6S14) was investigated, and a two-step vacuum distillation process of separation of antimony trisulfide (Sb2S3) and lead sulfide (PbS) from jamesonite was developed. First of all, the decomposition behavior of Pb4FeSb6S14 under vacuum condition was comprehensively studied. The results indicate it decompose into Sb2S3, PbS and FeS at 823 K under vacuum condition, then, Sb2S3 and PbS volatilize at different temperatures. Based on above results, we investigated the effects of vacuum distillation temperature and time on the recovery of Sb2S3 and PbS as well as the effects of temperature on the purity of them. The results indicate that the optimal temperature for separating Sb2S3 and PbS are 923 K and 1173 K, respectively. Under optimal conditions, up to 98% of Sb2S3 with a purity of 99.17% and up to 99.5% of PbS with a purity of 98.7% could be recovered.

Application of multi-stage vacuum distillation for secondary resource recovery: potential recovery method of cadmium telluride photovoltaic waste

With the widespread use of cadmium telluride solar cells, environmental protection, and effective recycling approaches for solar cell component waste have become topics of concern. As an emerging metal smelting technology, vacuum metallurgy technology has broad application prospects in primary metal refining and the recycling of secondary non-ferrous scraps. Thus, this study proposes a new method for the separation and recovery of rare metals from cadmium telluride waste through sulfur smelting and vacuum distillation. In this process, sulfur is smelted with cadmium telluride to produce tellurium with a high vapor pressure. The tellurium was then separated and purified by multi-stage vacuum distillation. The results show that the tellurium purity can reach up to 99.97% and the tellurium recovery rate was above 99%. The cadmium and sulfur contents in the tellurium were 0.0061% and 0.0194%, respectively. Moreover, the cadmium sulfide produced during the smelting process can be enriched by vacuum distillation, resulting in 99.6% purity. This technology strongly aligns with the “reduce, reuse, and recycle” principle for solid waste, and provides a basis for the sustainable development of the photovoltaic industry.

A novel process for silver enrichment from Kaldo smelting slag of copper anode slime by reduction smelting and vacuum metallurgy

Silver in Kaldo smelting slag of copper anode slime is diffuse and hard to be enriched. In this study, a novel process consisting of reduction smelting and vacuum metallurgy was developed to enrich Ag in Kaldo smelting slag of copper anode slime through laboratory and scale-up experiments. Pb, Bi and Ag in the slag were first enriched in Pb–Bi–Ag alloy by reduction smelting. Results show that when the reduction smelting was conducted for 40min under 1350 °C with the addition of reductant, limestone and iron powder accounting respectively for 10%, 20% and 26% of the raw feed, the recovery of Pb, Bi and Ag was 95.12%, 98.13% and 99.11%, respectively. After the reduction smelting, Ag was separated from Pb and Bi by vacuum distillation based on their difference in vapor pressure. Results show that Pb and Bi in Pb–Bi–Ag alloy were removed under the pressure of 3Pa, distillation temperature of 1000 °C and distillation duration of 2 h. After the vaccum metallurgy process, Ag enrichment ratio is above 9. The scale-up experiment shows that Ag recovery is higher than 98%, and more than 97% of Pb and Bi form Pb–Bi alloy product, which further proves that this novel process is simple but efficient for silver enrichment and separation from Pb and Bi in Kaldo smelting slag of copper anode slime.

A novel method for extracting metal Ag and Cu from high value-added secondary resources by vacuum distillation

The Cu-Ag-Sb alloy produced by oxidation refining of noble lead has a high recovery value because of its high content of Ag and Cu. Vacuum metallurgy has been successfully used in crude metal refining and secondary resource recovery because of its clean and efficient characteristics. In this paper, vacuum distillation is used to treat Cu-Ag-Sb alloy, and the saturated vapor pressure of each metal element in the Cu-Ag-Sb alloy and the Gibbs free energy (ΔG) of the possible decomposition reaction are theoretically analyzed. The effects of temperature and time on the experimental results were investigated by controlling the pressure at 10 Pa, distillation temperature in the range of 1473 ~ 1673 K and distillation time in the range of 4 ~ 7 h. The experimental results show that after 300 kg of Cu-Ag-Sb alloy was subjected to vacuum distillation under the optimized conditions (1573 K, 6 h, and 10 Pa), Ag and Cu were recovered as volatiles and residues, respectively, and their recovery efficiency reached 99.25% and 98.11%; Ag and Cu were effectively separated. This process provides theoretical guidance for the industrial treatment of Cu-Ag-Sb alloys with no waste gas or water, which meets the needs for cleaner production in the metallurgical industry.

The Equilibrium of the System “Gas–Liquid” for Alloy Sn-Sb in Vacuum Distillation

In the processing of lead bullion necessary to separate the metal from impurities – copper, tin, antimony, arsenic, silver, bismuth, and with the possible use of environmentally friendly, technologically effi cient and cost-eff ective high performance vacuum distillation. To analyze the behavior of multicomponent alloy processing, pre-selection of temperature and pressure of the system, evaluate the eff ectiveness of component separation in a vacuum distillation using phase diagrams temperature–composition “of T–h,” pressure–composition “R–x”. The aim of this work was to calculate the equilibrium “gas–liquid” VLE (vapor liquid equilibrium), including the dependence of phase composition on temperature (T-x) and pressure (P-x) for Sn-Sb alloy during vacuum distillation on the basis of the three-dimensional model of molecular interaction MIVM (мolecular interaction volume model), as well as determination of thermodynamic parameters of the process. In the temperature range 823-1073 to the calculated saturated vapor pressure (Pa) Sn (3.32.10–9–8.12.10–5) and Sb (3.954–273.66). High values of the ratio р*Sb / р*Sn = (1190–3.37).106 and separation factor logβSb = 6.25–9.44 create a theoretical background for the selective separation of these metals by vacuum distillation, when the antimony is enriched in the gas phase (βSb > 1), and tin – liquid. The mole fraction of tin in the gas phase уSn = (1–5000).10–9 increases with increasing temperature 823-1073 K and the molar fraction of the metal in the alloy хSn = 0.1–0.9. Using the MIVM model calculated activity coeffi cients of antimony γSb = 0.439–0.992 and tin γSn = 0.433–0.992 for Sn-Sb alloy with diff erent composition in the investigated temperature range. For phase diagrams VLE can be used by the lever rule (rule lines) to help predict quantities of substances, residues and sublimates at a predetermined temperature. For the phase boundary “liquid–gas” Sn-Sb alloy the values of the excess Gibbs energy, enthalpy and entropy: 􀈂 􀜩􀯠 􀮾 = 0.744–2.096 kJ/mol; – = 0.763–2.166 kJ/mol; = 0.0181–0.0891 J/mol.K. VLE phase diagrams alloys provide the necessary information for the design of technological parameters in industrial production, vacuum metallurgy, as well as to predict temperature and pressure process for obtaining Sn – and Sbcontaining products of a given composition

Experimental investigation and modeling of phase equilibria for Cu-Bi and Cu-Bi-Sb alloys in vacuum distillation

The measurements of vapor-liquid equilibrium (VLE) for Cu-Bi and Cu-Bi-Sb alloys in vacuum distillation were performed. We calculated the VLE diagrams of Cu-Bi and Cu-Bi-Sb alloys at 10 Pa by Wilson equation only using binary parameters. Thermodynamic consistency tests of experimental data for the binary and ternary systems were discussed using the Van Ness method. The calculated results are in good agreement with the experimental data. The VLE data can be used for designing the purification process and phase separation of crude copper in vacuum metallurgy.

Application of the modified molecular interaction volume model (M-MIVM) to vapor-liquid phase equilibrium of binary alloys in vacuum distillation

Thermodynamic models such as the Wilson model and molecular interaction volume model (MIVM) are known for their use in the calculation of activity coefficients of symmetric systems like Pb-Sn and Pb-Sb, but are deficient in handling asymmetric systems like Ag-Sn and Cu-Sn. Unfortunately, in metallurgical field, including vacuum metallurgy, the symmetric systems only account for a small part of liquid alloys, while the asymmetric systems take up a majority proportion. To overcome this application limitation of the Wilson model and MIVM in vacuum metallurgy, the modified molecular interaction volume model (M-MIVM) was applied. In contrast with Wilson model and MIVM, the M-MIVM exhibited remarkable superiority in data fitting of activity coefficient of binary asymmetric systems, which effectively increased the accuracy of predicting the activities of the multicomponent systems containing corresponding binary asymmetric systems. Therefore, M-MIVM made possible a more accurate vapor-liquid phase equilibrium diagram of asymmetric systems. In addition, since M-MIVM is a modification of the MIVM, it retains MIVM's capabilities to predict separation coefficient and calculate vapor-liquid equilibrium (VLE) of symmetric systems under quasi-vacuum condition. These identified advantages made M-MIVM, when compared with existing models, to have better accuracy and wider scope of application in vacuum metallurgy.

Sustainable extraction of lead and re-use of valuable metals from lead-rich secondary materials

Traditional lead metallurgy, a highly complicated lead extraction process for valuable metal recovery, has exhausted resources and produced a variety of hazardous wastes that are extremely harmful to the environment and unfavorable to the sustainable development of the lead industry. Vacuum metallurgy has become a promising emerging technology contributing to refining primary metals and the recovery of secondary nonferrous metal wastes. The technology is therefore relevant in the context of a transition to a more environmentally friendly circular economy. There is a growing interest in using vacuum distillation for extraction of Pb and valuable metals recovery from lead-rich secondary materials including crude lead, waste Pb-Sn alloy (WPSA) and lead anode slime (LAS). Results indicated that vacuum extracted lead (99.5% Pb) was obtained from crude lead (92.88%) using the two stage high-low temperature vacuum distillation process. Removals of 99.99% for Cu, 99.50% for Sn, and 98.00% for Ag, were achieved respectively. The valuable metals of Ag, Cu and Sn were recovered and concentrated in the final residue. Vacuum separation results of WPSA demonstrated that the purity of Pb reached 99.4% and recovery of Sn was above 86.0%. A novel integrated smelting-vacuum method is proposed here to reuse LAS. Copper and Ag were successfully enriched in the residues whilst Pb was collected in volatiles. The appropriate vacuum process effectively extracted Pb whilst recycling valuable metals, in a sustainable and environmentally friendly manner.

Comparison of three-pole AMB and HMB for magnetic suspended molecular pump

Molecular pumps have been widely used in the vacuum metallurgy, coating, semiconductor manufacturing and many other fields in which the high vacuum, ultra-clean environment is needed. The application of magnetic bearings can bring many advantages for molecular pump, such as eliminating the friction, decreasing the power loss, lowering the maintenance costs, and increasing the rotating speed and service life. Besides, the magnetic bearings can fundamentally solve the vacuum chamber pollution problem which is caused by the backflow of lubrication oil steam. The three-pole magnetic bearings are the simplest structure of radial magnetic bearings and can be driven by three-phase converter which has the advantages of low costs, small volume and low power loss. In this paper, the performance of the three-pole active magnetic bearing (AMB) and hybrid magnetic bearing (HMB) are compared based on radial force–current characteristics analysis. Firstly, the mathematical model of three-pole AMB and HMB is built by equivalent magnetic circuit model, and the radial force–current characteristics are analyzed. Then, simulation by the three-dimensional (3D) finite element method (FEM) is performed. Finally, the experiment is conducted. The FEM results are consistent with the analytical results, showing that the nonlinearity and coupling of three-pole HMB are lower than three-pole AMB. The reason of causing nonlinearity and coupling is also discussed.