Abstract: A number of important links in the metallurgical production process are related to interface phenomena, including slag foaming, hot metal desulphurization, refractory erosion, converter blowing, the behavior of inclusions in steel, and so on. Interfacial wettability is an important aspect of the interfacial interaction. By controlling the interfacial wettability between two phases, it is possible to remove inclusions, improve the cleanliness of the molten steel, reduce erosion of the refractory material, improve the life of the lining material, and ensure smooth production and product quality. Thus, it is necessary to analyze interfacial phenomena in ironmaking and steelmaking with respect to interfacial wettability. In general, interfacial wettability can be measured by the contact angle and interfacial tension, and the contact angle and interfacial tension between the molten steel and slag are determined primarily by the surface active element in molten steel and the active surface component in slag. In this study, we analyzed in detail some common phenomena in the steelmaking process from the view of interfacial wettability. With respect to the slag foaming process, we mainly analyzed the effects of the contact angle and interfacial tension on the slag foaming index. To study the hot metal desulphurization process, we considered effects on the desulfurization rate and the utilization and penetration speed of the desulfurizing agent. Regarding the refractory erosion process by molten slag and steel, we primarily studied the effects on the refractory saturation slubility in molten slag, the penetration depth of molten slag in refractory material, and the refractory erosion rate. To study the behavior of inclusions in steel, we considered effects on the nucleation, aggregation, removal, and spatial distribution homogeneity of inclusions. We also summarized the conditions associated with better interfacial wettability with respect to the corresponding phenomena.
Abstract: Iron-based amorphous alloys exhibit many desirable features, such as low coercivity, high permeability, high electrical resistivity, low loss, and good frequency characteristics, which make them a kind of viable energy-saving and environmentally-friendly materials. Their attractive features are due to their isotropic property, small structural correlation dimension, and magnetic anisotropic constant. The interactive coupling between the α-iron (Fe) nanocrystalline phase and amorphous soft magnetic phase further reduces the magnetic anisotropy and magnetostrictive effect of the Fe-based amorphous and nanocrystalline composites. Therefore, Fe-based amorphous and nanocrystalline alloys have a high saturation flux density and high magnetic permeability, and have been widely applied for electric power, electronics, and information transmission and conversion industries. Now, Fe-based amorphous and nanocrystalline alloys have been produced and applied to various areas on a large scale. In this paper, the development histories, situation, and tendency of Fe-based amorphous and nanocrystalline alloyswere briefly summarized. The research results of Fe-based bulk and ribbon amorphous alloys, along with nanocrystalline alloys with high saturation flux density (Bs), were reviewed in detail. The main contents of this paper include the compositions and properties of high-Bs Fe-based bulk and ribbon amorphous alloys; the compositions, structure and properties of high-Bs Fe-based nanocrystalline alloys; and the effects of alloying elements on the magnetic properties. These results will provide valuable insights that can be used for the development of Fe-based soft magnetic materials with a high saturation flux density.
Abstract: Paste backfilling has become an important support technology in green mining construction. The flowability and rheology performance of paste determine whether the slurry can be transported normally. As such, the evaluation of flowability and rheology of paste are important factors in the reliability of paste transportation. Because paste has the three characteristics of fluidity, stability and plasticity, traditional two-phase flow theory cannot effectively analyze its plug flow. However, it is an effective method for analyzing and evaluating the fluidity of the paste based on rheology theory, and the yield stress is an important parameter for evaluating the rheological characteristics of paste. Due to the different properties of the materials in different mines, it is difficult to analyze the factors that influence yield stress. Several experiments have been conducted on a variety of tailings from different mines, including a gradation characterization and influence experiment, a rheology experiment on materials of similar densities, and double-factor rheological experiments based on the concentration and sand ratio. Combined with mesoscopic structure analysis technology, the evolution mechanism of yield stress was studied. The results indicate that the stability coefficient of paste can effectively reflect the gradation, and can also reflect the comprehensive characteristics of the granule and fluid. The yield stress increases significantly with the paste stability coefficient and increases exponentially with the concentration. At the same time, yield stress is characterized by negative exponential growth with density. The error range of this yield stress prediction model for unclassified tailings paste is within 10%. The mesoscopic structure analysis shows that yield stress is mainly controlled by gradation and flocculent structure. The gradation constitutes the foundation for the plasticity and stability of the slurry. The flocculent structure transforms free water into the semi-stable form of adsorptive water, which causes the macro-evolution of the yield stress.
Abstract: The depth and scale of potash mines is currently increasing. Backfill materials with higher homogeneity and greater fluidity property are required to prevent blocking and ensure that filling materials are transported safely to the underground mines. The production of low-cost backfill materials that meet both strength and transportability requirements is therefore extremely important. A potash filling material with steel slag as a cementing agent was prepared to solve the problems caused by potash tailings and brine water in potash mines, such as environmental pollution, resources waste, and potential safety issues. This was also done with the aim of improving the flow and strength properties of potash filling materials by using steel slag as binder because its hydration reaction is slow and durable. The results indicated that the fluidity and late strength met requirements. It was also initially proved that the steel slag fineness and curing temperature had a significant influence on the performance of the filling material. The fluidity of the filler was greater than 200 mm in 8 h and the compressive strength reached 2 MPa in 28 days, which satisfied the performance requirements for the filler. This article mainly focuses on the analysis of the curing mechanism from a microscopic point of view. The results of X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS), thermogravimetry/differential thermal analysis (TG/DTA), and Fourier-transform infrared spectroscopy (FTIR) show that the products of the hydration reactions are primarily C-S-H gels, hydrocalumite (or Friedel's salt), and brucite. They are interspersed with each other so that the density and strength improve. The results show that isomorphous substitution occurs in the microscopic structure of the layered hydrocalumite and hydrotalcite. The Ca2+, Mg2+, Fe2+, Fe3+, Al3+, and Si4+ can replace each other and enable OH-, Cl-, and H2O molecules to be easily absorbed into the interlayer. In this way, impurity ions can be stabilized and stability of the filling material can be improved. The results of this study provide preliminary evidence that steel slag powder can be used as a binder in potash backfill material.
Abstract: High-water-content materials are a new type of inorganic cementitious material. They have been widely used in the mining of underground mined-out areas in recent years. However, the higher filling cost has always been the key limiting factor in their further development and application. Meanwhile, large volumes of industrial waste, such as fly ash, has become a serious environmental problem as well as a wasted resource, at a time when the rational repurposing of industrial waste is of great significance to the developed world. To solve the problems of the high cost of mine-filling material, the wasting of a useful resource, and the environmental pollution caused by large surpluses of industrial waste like fly ash, the physical and mechanical properties, microstructure, and chemical components of high-water-content materials of varying fly ash content were studied. An engineering test model (ETM) mechanics test system, scanning electron microscopy (SEM) scanning device, X-ray diffraction (XRD) diffraction analyzer, and a fly ash modification mechanism were discussed based on the microscopic and phase analysis results. The test results show that:(1) with increasing fly ash content, the setting time of high-water-content materials gradually increases, water content decreases, and bulk remained relatively unchangs; (2) high-water-content materials, with or without fly ash, are elastoplastic materials, and their deformation and failure progress could be divided into pore compaction stage, elastic stage, yield stage, and failure stage; (3) the peak strength, elastic modulus, and deformation modulus of high-water-content materials are reduced with increasing fly ash content, although residual strength is improved; and (4) the most reasonable dosage of fly ash is 15% when strength, modulus and cost are considered. Peak intensity, elastic modulus, and deformation modulus of high-water-content material are reduced by only 25%, 8.6% and 10% at this fly ash dosage, respectively, and the residual strength increased by 50%. Phase and morphology analyses show that the amount of fly ash affects the hydration progress of β-C2S, resulting in reduction of ettringite and an increase in other hydration products. Thus, the homogeneity and integrity of the structure of ettringite are destroyed at different levels, leading, eventually, to a reduction in the compressive strength of high-water-content materials.
Abstract: As a by-product of mining and the extensive production of industrial solid waste, tailing has many types, has a low utilization rate, and seriously affects the surrounding ecological environment. With the protection of natural resources and ecology in China, the traditional methods of obtaining clay and natural stone by mining cultivated land and preparing building materials by utilizing a high-temperature process will be avoided and eliminated gradually. In the face of the increasing demand for construction and decoration materials in the engineering construction sector in the Jing-Jin-Ji region, the use of tailing resources, which are stockpiled in large amounts in Chengde, Hebei Province, for the preparation of baking-free and decorative bricks is characterized by high usage of solid waste, low energy consumption, low environmental pollution, and considerable savings. In this study, for the simple system of molybdenum tailing-cement brick, the press molding process, microstructure, and coloring property after the addition of pigment were investigated. Results show that, for the baking-free brick, the appropriate cement-to-tailing ratio is 0.18~0.25, water-to-solid raw materials ratio for pressing is 0.10, pressing strength is 25 MPa, pressing holding time is 30 s, and brick performance is improved by the step-style pressing mode. After curing for a long time, the relative contents of Ca(OH)2, ettringite, and CaCO3 increase with the increase in the content of cement in the brick samples, whereas the content of mica decreases. If the mass content of cement reaches 25%, then the AFm phase (low sulfur calcium aluminum sulfate) will form. Large quantities of hydrated calcium silicate (C-S-H) gel, ettringite, and Ca(OH)2 can also be observed in the brick samples. The addition of red, yellow, and green pigments of iron oxide type within 9% has only a slight effect on brick strength. By contrast, the addition of blue and black pigments causes strength loss. Thus, their contents should be appropriately controlled within 6% to 9%.
Abstract: Sintering is an important process for the smelting of iron and steel for ironmaking in a blast furnace. However, the sintering process emits air pollutants in the sintering flue gas, especially fine particles and dioxins. In order to study the effects of sintering with precipitator dust on the composition of particulate matter and dioxins in the sintering flue gas, the precipitator dust was purified by a water washing method. The influence of sintering with the precipitator dust before and after the purifying modification was determined by a sintering cup experiment. The flue gas pollutants were then collected by the impact particle sampler and dioxin sampler and the alkali content, heavy metal content and dioxin precursor emissions were determined. The experimental results indicate that potassium (K) and chlorine (Cl) in the precipitator dust are effectively removed by the water washing method. The sintering with the purifying modification and precipitator dust improve the particle size distribution of the sinter and reduce the concentration of particulates and dioxins that are emitted in the flue gas. The K content is higher in the sintered particles, especially the smaller ones, compared to sodium (Na), lead (Pb), and zinc (Zn). Sintering with the precipitator dust after washing significantly reduces the K content of the sinter burden proportion and causes the notable reduction of K in the flue gas particles, particularly in the particle size range of 1.10-2.10 μm. The Cl in the sintering raw material, along with the chlorobenzene and polychlorinated biphenyls that are generated in the sintering process, cause the generation of the dioxins. The sintering with the precipitator dust after washing effectively reduces the content of Cl. The emission of polychlorinated biphenyls is also reduced to 40%, which is beneficial in reducing the concentration of dioxins.
Abstract: Confined spaces are extremely common in industrial production and emergency rescue situations, and are also widely found in the fields of mining, chemistry, metallurgy, construction, aviation, submarines, emergency hedging, and others. Confined space operations and living environments are characterized by small spaces, poor ventilation, lack of oxygen, high temperatures and humidity, and poor lighting and communication. Exposure to this operating environment over even short periods of time causes thermal stress and changes in the oxygen content of the human body, which lead to physical discomforts such as increased heart rate, increased blood pressure, and body temperature changes. As exposure time increases, the human body experiences fatigue, confusion, and other symptoms. The physical fatigue caused by the human body being exposed to confined space environments is the main causal factor in safety accidents. Therefore, a method must be developed to enable objective measurement and rapid determination of physiological fatigue. A 100-min-limit manned experiment was conducted in a confined space to test an objective fatigue measurement method based on the photoplethysmography pulse wave (PPG). An algorithm was then developed to extract PPG signal feature parameters to determine the hemodynamics and circulatory system changes that characterize physiological fatigue. As the most basic physiological signal of the human body, the PPG contains abundant information about hemodynamics and autonomic nervous system circulation. This information is reflected in parameters such as the wave shape, speed, and rhythm. The results indicate that when the human body experiences physiological fatigue, the average period of the PPG signal is significantly greater than that when it is non-fatigued (p<0.001), the vascular resistance increases, and the stroke volume per stroke is significantly decreased. The two types of complexity (KC complexity, high-order KC complexity) of PPG signals were calculated under fatigue and non-fatigue conditions. The calculation results was found for these two complexities to be the same, and the waveforms to be more stable when the body is not fatigued. Therefore, the results demonstrate that the PPG signal can capture the physiological changes of the fatigue state and provide objective measurement and enable rapid judgment regarding physiological fatigue.
Abstract: A bottleneck occurs in the application of bioleaching technology to fluoride-containing ore. The reason for this is that fluorine has a strong inhibitory effect on leaching bacteria with the dissolution of fluorine-containing gangue minerals. In this study, we use the chemical properties of fluorine to convert F ions by adding substances that can form stable complexes with F-, which enables the leaching bacteria to tolerate high fluoride environments. In this research, we studied the inhibition mechanism of fluorine on bacteria, and identified its true toxic form (HF). We found that fluoride exhibited a transmembrane inhibitory effect on bacteria. Under fluoride stress conditions, the concentration of intracellular fluoride was significantly higher than that of a non-fluorinated control group, which was about 18% dry cell. We selected common Fe3+ ions in the bioleaching system, and studied the competitive complex detoxification of Fe3+ to F-. Our thermodynamic analysis results show that Fe3+ can compete with HF in first-order competitive complexation reactions whereby the HF complex structure is converted to FeFn3-n. In the presence of ferric ions, we found that the bacteria could tolerate F-concentrations up to 1.0 g·L-1. Our analysis of the Fe and F complex species indicates that bacteria could grow normally when the concentration of Fe3+ ions was five times greater than that of F- ions. Correspondingly, the proportion of FeF2+ components in the solution was ≥ 45%, and the concentration of free fluoride was 2.87×10-5 mol·L-1. The complexation mechanism shows that as the ratio of F--Fe3+ decreases, the concentration of the ligand is relatively lower. Based on the coordination chemistry, the complex of fluoride and iron moves in a lower coordination direction, and the Fe and F complex species can be controlled by adjusting the concentration ratio of F- and Fe3+ in the medium, therefore making it possible for bacteria to grow in a high-fluorine environment.
Abstract: Preheating and reduction of iron ore fine in a multi-stage continuous fluidized bed (FB), which can improve gas utilization, heat efficiency and decrease production cost of hot metal, is a development direction for ore fine reduction with gas as a reductant. Multi-stage FBs coupled with a gasifier for producing hot metal have been successfully industrialized in Southern Korea. However, progress of FBs for iron ore reduction is slow in China. The reduction fraction and utilization ratio of gas are two important parameters for the iron reduction process. The key to feasible estimation of new technologies and design of parameters in the reduction process and reactors is understanding the influence of various parameters. As a result, the coupling kinetic model of iron oxide reduction and reducing gas oxidation in two-stage FB was established to investigate the influence of technical parameters on reducing the efficiency of iron ore fine in a continuous FB. FeO, which comes from a R2 FB, is reduced in a R1 FB using qualified gas as a reducing gas. Fe2O3, which comes from R3 preheating of a FB, is reduced to FeO in R2 FB using off-gas from a R1 FB. The results are in a good accordance with literature data. The influence of parameters, such as the size of the ore fine and pressure in the FB, on reducing efficiency was investigated according with this model. For the reduction results to be ≥ 85% metallization ratio, ≥ 38% gas utilization rate and 950~1050 m3·t-1 ratio of gas flow to ore mass, the technological conditions are an average ore fine size less than 1.5 mm, FB temperature of 780~800℃, gas reduction potential greater than 93%, volume fraction of inert gas less than 5% average pressure of 3.5×105~4.0×105 Pa, the reciprocal of standing time ug/H of 1.0~1.1 s-1, average retention time in R1 FB of 30 min and average retention time in R2 FB of 20 min.
Abstract: Steel slag is an industrial solid waste generated during the steelmaking process and is an important secondary resource. Since steel slag is rich in aluminosilicates, it can be used to make ceramics. The use of steel slag to prepare ceramics plays an important role in the utilization of it. In this paper, the effect of the sintering temperature and holding time on the sintering process and the densification of products during the preparation of ceramics from steel slag were explored. In particular, low magnesium (Mg) and high Mg samples were chosen for study. The Mg oxide content for the low Mg sample was 2.52% and it was 10.50% for the high Mg sample. Current studies of steel slag ceramics mainly consider the amount of steel slag, the basic formula of the trial, the subsequent performance of the test specimen, the influence of a certain element on the mechanical properties, and the crystal phase of the ceramic. In this work,the preparation of the ceramics with steel slag and clay as main raw materials was considered. By establishing the kinetic description of the sintering process, the sintering activation energy with different magnesium contents could be calculated. The sintering activation energy for the low magnesium and high magnesium ceramic samples was relatively small, and was 36 kJ·mol-1 and 54 kJ·mol-1, respectively. Meanwhile, the densification of the ceramic samples with different magnesium contents was investigated. It is concluded that the material migration mechanism is controlled by surface diffusion when the sintering temperature of the low magnesium sample is 1000℃. At 1100℃, the volume diffusion is the main control mode. When the high magnesium sample is sintered at 1110℃ or higher, the sintering process is mainly controlled by the diffusion of the liquid phase.
Abstract: With the rapid development of computer science, artificial intelligence, big data technology, and various detection technologies, the converter off-gas analysis technology can continuously monitor the reaction process in a basic oxygen furnace without being limited by the size of the converter mouth; this technology can also help save costs thus receive much attention again. The focus of the off-gas analysis technology is to fully extract the information from the converter off-gas data during the steelmaking process, establish the model closely related to the process, and guide the actual steelmaking production. This study investigates the problem of off-gas analysis technology in predicting the carbon content of molten bath at the end of steelmaking process. The fitting model of converter end-point carbon curve avoids the difficulty of accurately determining the initial carbon content of the molten bath. It is assumed that a certain function defines the relationship between the decarburization rate and the carbon content in the molten bath, therefore can be used to predict the carbon content of the bath. The hit rates of the cubic model and the exponential model are 85.9% and 81.2%, respectively, with end-point carbon prediction error of only ±0.02%. Applying the molecular theory, the activity of FeO in slag is calculated to be 0.241 for the slag components of SPHC steel. When the tapping temperature is 1686℃, the critical carbon content of the selective oxidation of C and Fe is 0.033%. Based on the traditional exponential model, the influence of operating parameters such as lance height, top blowing rate and bottom blowing rate is considered, and an exponential model is established based on the bath mixing degree. Compared with other models of off-gas analysis carbon curve fitting, the hit rate of the exponential model based on bath mixing degree is greatly improved. The hit rate of end-point carbon is 88.2% with error of ±0.02%, accounting for 75 heats.
Abstract: A hexagonal α-Al2O3 with good crystallinity and regular morphology was prepared at lower calcination temperature by using boehmite (AlOOH) as precursor and AlF3 seed as additive.The possible mechanisms were investigated by DSC-TG-MS analysis under the condition of AlF3 seed coefficient 2%, which indicates that a transition compound (Al-O-F) promotes the nucleation phase transition of α-Al2O3 through gas-solid reaction, and releases HF simultaneously. Furthermore, the effects of AlF3 coefficient and calcination temperature (T) on the phase, morphology, size, and specific surface area were investigated. Results show that light AlF3 seeds can enhance the crystallinity of α-Al2O3. When the AlF3 coefficient increases from 0.5% to 10%, the hexagonal-shaped structure becomes clear, but its size increases and its specific surface area decreases. Boehmite can completely change into high-crystallinity, hexagonal-shaped α-Al2O3 under the best condition of T=850℃, AlF3 seed coefficient 2%, and constant calcination time of 4 h.
Abstract: Al-doped zinc oxide (AZO) transparent conductive films with different sheet resistances were deposited on the surface of float glass by a room temperature coating technique. The procedure for radar cross section (RCS) measurements for AZO transparent conductive films was established, and the definition of the relative reflectivity based on the RCS mean value was proposed. The electromagnetic scattering characteristics for the AZO transparent conductive films were analyzed by way of the sheet resistance and visible light transmittance. The AZO films with different sheet resistances were tested in the microwave darkroom and RCS curves for the films were obtained with incident frequencies of 10 GHz and 15 GHz and in the HH and VV polarizations modes. The characteristics of the RCS curve distribution in angular domains of 20° and 60° in the nose direction and the characteristics of RCS mean values were analyzed to study the stealth performance for aircraft cockpit glasses. The influence of the sheet resistance on RCS relative reflectivity and visible light transmittance was studied based on RCS test results from the AZO transparent conductive films. When the sheet resistance was small, the distribution of the RCS curves was similar to that of their corresponding metal. When the sheet resistance increased, the RCS mean values in the angular domains of 20° and 60° in the nose direction decreased and the stealth performance was reduced. In addition, the RCS relative reflectivity decreased and the visible light transmittance increased. The rate of the decrease in the relative reflectivity was related to the sheet resistance. It was determined that an appropriate sheet resistance can meet the needs of stealth and lighting simultaneously. The results achieved from darkroom test also proved that upon meeting the requirement of visible light transmittance for aircraft cockpit glasses, the AZO transparent conductive film could provide shaped stealth performance when the value of sheet resistance was between 18 Ω to 45 Ω. When the sheet resistance was 18 Ω, the best performance of AZO appears with a relative reflectivity, Rem2 of 84% and RedB of 0.73 dB.
Abstract: Lamina emergent mechanisms that can realize out-of-plane motion are a kind of compliant mechanisms. They mainly transmit motion, force, and energy through flexible joints; therefore, the design of flexible joints is very important. In the design of flexible joints, the primary requirements are the bending performance and the tensile and compressive properties. However, in general, with the improvement of the bending performance of flexible joints, the tensile and compressive properties deteriorate, and the overall performance of the joints is unable to meet the requirements. To realize joints with better overall performance, tension straps of flexible joints were designed in this study. Based on a flexible joint with high flexibility, a new flexible joint named SS-LEJ was designed. According to the equivalent method, the joint's equivalent spring model was created, and the equations needed to calculate the bending equivalent stiffness of the joints were deduced. In addition, a finite element analysis model was created. The equations were verified by theoretical calculations and ABAQUS simulation analysis. The theoretical calculation and ABAQUS simulation analysis results agree very well. To improve the tensile and compressive properties of SS-LEJ, four kinds of tension straps in different positions and shapes of SST-LEJ were designed. Stress analysis was performed, and the finite element analysis results show that SST3-LEJ and SST4-LEJ are the best two kinds of SST-LEJ. The bending performances and the tensile and compressive properties of SST3-LEJ, SST4-LEJ, SS-LEJ, and inverted bending-orthogonal (IBO) joint were compared. The results show that the bending performances of SST3-LEJ and SST4-LEJ are between those of SS-LEJ and IBO joint, and the tensile and compressive properties of SST3-LEJ and SST4-LEJ are better than those of SS-LEJ and IBO joint. This indicates that the overall performances of SST3-LEJ and SST4-LEJ are better, and the design goal is achieved, which provides an effective method for the design of flexible joints.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
