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Purpose This paper aims to under the laboratory environment, the corrosion behavior of X80 pipeline steel in oilfield injection water in eastern China was studied by immersion test. Design/methodology/approach First, the corrosion product film was immersed in oilfield injection water and the effect on the corrosion behavior and the corrosion reaction mechanism were constantly observed during this period. The effect was displayed by potentiodynamic polarization curve and electrochemical impedance spectrums (EIS) measurements. Second, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to observe and test the corrosion product film immersed in the oilfield water for 30 days. Findings The results indicate that the tendency of metal corrosion becomes weaker at an early stage, but strengthened later, which means the corrosion rate is accelerating. Besides, it is indicated by impedance spectroscopy that with the decreasing of the capacitance arc radius, the reaction resistance is reducing in this progress. Meanwhile, the character of Warburg impedance could be found in EIS, which means that the erosional components are more likely to penetrate the product film to reach the matrix. The corrosion product is mainly composed of the inner Fe3O4 layer and outer shell layer, which contains a large number of calcium carbonate granular deposits. It is this corrosion under fouling that produces severe localized corrosion, forming many etch pits on the metal substrate. Originality/value The experiment chose the X80 steel, the highest-grade pipeline steel used in China, to conduct the static immersion test in the injection water coming from an oilfield in eastern China. Accordingly, the corrosion mechanism and the effect of corrosion product film on the corrosion of pipeline steel were analyzed and discussed.

The extraction of Ti from Ti-bearing blast-furnace slag (TBFS) via aluminothermic reduction to prepare Ti–Si–Al alloy has several promising applications. However, the refractories of the furnace lining can dissolve into the molten slag and change the composition of the slag, not only shortening the life of the refractories, but also influencing the preparation of Ti–Si–Al alloys for industrial applications. The main purpose of this study was to explore the corrosion behavior of refractories (carbon, alumina, and magnesia bricks) and determine the most suitable refractories for the aluminothermic reduction of TBFS. Herein, for the first time, the dissolution equilibrium of refractories during the aluminothermic reduction of TBFS and its effect on aluminothermic reduction were revealed. The results revealed that the alumina and magnesia bricks were more effective for obtaining bulk Ti–Si–Al alloy and avoiding high mass loss of the Ti–Si–Al alloy compared to the carbon bricks. Furthermore, the corrosion of alumina and magnesia bricks increased with an increase in the content of the added CaO; however, the corrosion of the alumina bricks was more severe compared to the magnesia bricks. In addition, the largest extraction ratio of Ti (maximum value: 99.85%) was achieved when magnesia bricks were employed. The results of this study indicate that magnesia bricks are the optimal refractory for the preparation of Ti–Si–Al alloy via the aluminothermic reduction of TBFS. This work provides important experimental information for the industrial application of the aluminothermic reduction of TBFS in the preparation of Ti–Si–Al alloys.

In order to solve the problem of insufficient bearing capacity of existing concrete piles, a type of concrete pile with an additional lengthened strengthening core is designed, by inserting the steel tube through guiding hole and pouring core concrete. To reveal the mechanical performance of the reinforced piles, scale model tests and finite element simulations were performed. The results showed that both the vertical and horizontal bearing capacity increase with the length of the stiffening core. The axial force of the enhanced core is also smaller than conventional concrete piles, and the extended core can share the axial force of the foundation pile to improve the stress distribution of the pile body. These findings point toward a useful and general method for increasing the load capacity of existing concrete piles.

In this work, silicon purifying process based on the novel Cu-catalyzed chemical leaching (CuCCL) treatment has been investigated as a function of different silicon particle size, HF concentration, leaching time, H2O2 concentration, Cu(NO3)2 concentration and leaching temperature. Typical impurity precipitate in silicon was analyzed, which revealed that the main impurities of Fe, Al, Ca, Ti, and V mainly exist as Si2Fe, Si–Fe–Al, Si–Fe–Al–Ca, and Si–Fe–Al–Ti–V phases in the MG-Si feedstock. The results showed that the main impurities Fe, Al, Ca, Ti, and V can be effectively eliminated by the CuCCL treatment, especially for Ca, Ti and V. In the appropriate experiment conditions, the removal of main impurities Fe, Al, Ca, Ti, and V from MG-Si significantly reached to 99.38%, 98.64, 100%, 100%, and 100%, respectively. It was found that the impurities on the silicon facilitated the formation of porous structures during the CuCCL process, and the generated porous structures further exposed more impurities to the acid etchants, which promote the impurity removal from silicon. Furthermore, the leaching behaviors of impurity precipitates in the CuCCL process were obtained through revealing their evolution during deposition and etching steps. The high-efficient silicon purification effect of this study may bring some new strategy for achieving the low-cost solar grade silicon.

Imbibition oil recovery in low permeability fractured reservoirs has been acknowledged as an efficient method to enhance oil recovery. However, the effects of the complex pore structure and the hydraulic pressure in fracture on the fluids transport were not considered comprehensively in any model at pore scale in literature. This paper aims to study the microscopic mechanism of the imbibition process and define the concept of an imbibition unit using mathematical methods. Based on fractal theory, the improved effective porosity, permeability model, mass transfer model, and the fracture control range model of the matrix are derived, considering the effects of surface roughness, heterogeneity of the pore structure, irreducible water and the hydraulic pressure in fracture. The required parameters for model calculation are obtained by the three-dimensional reconstructed CT images, density test experiment and wetting test experiment. Good agreements are achieved between the result calculated by the proposed model and that of the experiment. The sensitivity analysis of the mass transfer model is then conducted and discussed. The results indicate that the cumulative oil recovery during the imbibition process is mainly controlled by the surface fractal dimension ( D s ), the pore pressure gradient ( Δ p), the pore fractal dimension ( D λ ), the hydraulic pressure in the fracture ( P h ), and the tortuosity of the capillary ( τ ). And Δ p, D λ , and P h shows a positive relationship with the cumulative oil recovery, while D s and τ shows a negative influence.

With the rapid increase of photovoltaic (PV) system production and installation, the recycling of end-of-life PV modules has become an important issue. In this paper, the recovery of Si by separating the layers of end-of-life PV modules using KOH-ethanol solution was investigated. Compared with traditional swelling or dissolving reagents (such as benzene and trichloroethylene), KOH-ethanol is a green reagent with low environmental toxicity. The experiments explored the effect of different alkalis, module sizes, temperatures, KOH concentrations, and solid-to-liquid ratios on the separation ratio of the PV modules. The mechanism for separating these layers was also studied. Under optimal conditions, the layers of these PV modules can be completely separated in 3 h, and oxidation of the recovered Si wafer can be controlled. Hence, this method of recycling PV modules is of great significance for environmental protection and resource utilization.

The demand for crystalline silicon wafers is continuing to increase. It is inevitable that high-purity silicon will be lost as loose abrasive slurry silicon powder (LASSP) and diamond wire saw silicon powder (DWSSP) during the process of wafer preparation. For this reason, some advanced processes or methods require further development to solve the problems of the high production cost, silicon wafer shortage, and environmental pollution caused by these silicon resources. Some processes and technologies for silicon recovery and purification from LASSP and DWSSP are comprehensively reviewed in this paper. These investigations inform some anticipated technological trends and required improvements, and encourage the development of technological solutions. Furthermore, the authors propose that high-purity silicon for industrial implementations can be recycled from LASSP and DWSSP via a combined process of an acid leaching pretreatment and a high-temperature treatment. Additionally, some existing deficiencies and areas that require enhancement are also proposed for improved impurity removal and silicon recovery with a higher process efficiency.

This paper proposes a method of recycling and purifying silicon from diamond-wire cutting waste by a combined process of slag refining and electromagnetic stirring. A slagging agent of calcium silicate containing barium oxide was added to the diamond-wire cutting waste. Different experimental conditions were carried out for silicon separation and purification. Owing to the difference of affinity between impurity elements and oxygen, the elements with high oxygen affinity combined with oxygen and changed into oxides, which entered into the slag phase. The separation of silicon and slag in the melt was realized through electromagnetic stirring in a medium frequency induction furnace. The experimental results show that this proposed refining method can remove impurities more effectively from diamond-wire cutting waste. It was also found that the mass ratio of slag to silicon has a significant effect on the separation efficiency of silicon.

The interactions among impurity components in Si-based solution are the important thermodynamic parameters for the purification of silicon materials. A ?same concentration? method was used to determine the activity interaction coefficients of Fe to B and Al to B in the silicon solution. Fe and Al were respectively dissolved into the binary Si-B solution at 1723 K with the holding time of 5 h, 7 h, 9 h, and 11 h. The equilibrium concentrations of Fe, B in the Si-B-Fe system and Al, B in the Si-B-Al system were determined. The interaction coefficients of Fe to B and Al to B were obtained by fitting the solubility data of B, Fe, and Al. The solubility relationships between B and [%Fe], and between B and [%Al] were obtained, respectively. It was found by the SEM and EPMA pictures of the samples that the third component Fe or Al added to the binary Si-B solution was alloyed, which verifies the accuracy of the experimental determination results. The significance of the activity interaction coefficient of B on boron removal from industrial silicon was analyzed.

The thermodynamic properties of impurity components in silicon solutions play an important role in the chemical removal process to the metallurgical route. In this paper, the component activity coefficients and interaction parameters of dilute silicon solutions were estimated by the molecular interaction volume model (MIVM). The activity coefficients (?i) of component i in dilute binary Si-i and ternary Si-i-j solutions at 1687-1873 K were firstly calculated. The concentration dependences of the interaction parameter and activity coefficient were also obtained. The self-interaction parameters (?i,i) for Si-i system were obtained as ?B,B= -2.728-362.031/T, ?Al,Al = 2.157-1876.776/T, ?Fe,Fe= -4.842+14445.926/T and ?P,P = -2.543+13767.036/T. At the same time, the interaction parameters among components B, Al, and Fe in dilute ternary Sii- j solutions were also derived as ?Fe,B=-1.2758-2946.306/T, ?Al,B = 0.7467-9765.9298/T and ?Fe,Al= -1.39677+3319.6803/T. Most important of all, the temperature dependences of the interaction parameters and activity coefficients in dilute Si-i and Si-i-j solutions with a certain i or j concentration were deduced. The results show that the predicted self-interaction parameters of B, Al, Fe, and P in binary silicon solutions reasonably agree with the experimental data. This further shows that MIVM is of reliability and can be expanded to a multi-component dilute silicon solution.

Varieties of pore‐scale numerical and empirical approaches have been proposed to predict the rock permeability when the pore structure is known, for example, microscopic computerized tomography (micro‐CT) technology. A comparative study on these approaches is conducted in this paper. A reference dataset of nine micro‐CT images of porous rocks is generated and processed including artificial sandpacks, tight sandstone, and carbonate. Multiple numerical and empirical approaches are used to compute the absolute permeability of micro‐CT images including the image voxel‐based solver (VBS), pore network model (PNM), Lattice Boltzmann method (LBM), Kozeny‐Carman (K‐C) equation, and Thomeer relation. Computational accuracy and efficiency of different numerical approaches are investigated. The results indicate that good agreements among numerical solvers are achieved for the sample with a homogeneous structure, while the disagreement increases with an increase in heterogeneity and complexity of pore structure. The LBM and VBS solver both have a relative higher computation accuracy, whereas the PNM solver is less accurate due to simplification on the topological structure. The computation efficiency of the different solver is generally computation resources dependent, and the PNM solver is the fastest, followed by VBS and LBM solver. As expected, empirical relation can over‐estimate permeability by a magnification of 50 or more, particularly for those strong heterogeneous structures reported in this study. Nevertheless, empirical relation is still applicable for artificial rocks.

Boron removal is a challenge in the purification of industrial silicon. A new technology for boron removal from silicon using chlorine slag flux refining followed by acid leaching treatment has been investigated and is described herein. The boron in silicon is oxidized by the slag flux and enters into the slag phase. However, some soluble boron remains in the refined silicon, and this can then be further removed by acid leaching treatment. The boron is reduced from 22 parts per million by weight (ppmw) to 1.37 ppmw with removal efficiency of 93.7% through ternary CaO-SiO2-CaCl2 slag flux treatment. After acid leaching treatment, the boron in the refined silicon is further reduced to 0.81 ppmw and the removal efficiency of boron reaches 96.3%. This result shows that this new technology has an obvious role in the further enhancement of boron removal. Using 3 wt.% B-doped silicon alloy as the raw material for purification, the results demonstrate the role of the acid leaching treatment in soluble boron removal from the refined silicon. The oxidization and dissolution behaviors of boron in silicon during the slagging and acid leaching treatment are described and explained.

A new approach was proposed to prepare multi-products, high-purity Si powders, bulk Si, and Si/TiSi2 materials (eutectic Si-Ti), simultaneously using inexpensive low-purity Si (99.3%) and metallurgical waste—Ti-bearing blast furnace slag. TiO2 in Ti-bearing blast furnace slag was first reduced by Si to form a Si-Ti alloy which was then separated into high-purity bulk Si (99.97%) and Si/TiSi2 materials (99.4%) using directional solidification. The bulk Si could be repeatedly recycled as a reductant, or further upgraded to prepare super-pure Si powders (99.995%) after acid leaching. The new approach shows many sustainable and economic benefits, such as no carbon gas emission, low acid consumption and Si loss, recyclable Si reductant, widely-used multi-products employing one approach, and rapid consumption of accumulated Ti-bearing blast furnace slag.

The formation of ZrB2 particles in Al–Si alloys not only improves the properties of the Al–Si alloy but also helps remove B from Si for the preparation of solar-grade Si. A thermodynamic study was ...

The preparation of solar-grade silicon (99.9999 wt%) with low-cost technology is facing challenges. In the present study, a novel metal-catalyzed chemical corrosion (MCCC) method on purifying industrial silicon powder, consisting of HF concentration, corroding temperature, H2O2 concentration and corroding duration were studied. The evolution of typical precipitates phases on the surface of silicon to each etchant were investigate before and after etching with/without MCCC via EPMA (electron probe micro analyzer) equipped with EDS (energy dispersive X-ray spectroscopy). The results showed that numerous microporous structures applied on the surface of silicon powder by MCCC are beneficial for the removal of impurities. After MCCC, the purity of silicon powder can be improved from 99.48 to 99.99 wt%, which is higher than 99.93 wt% obtained without MCCC. It was found that the removal reaction of boron and phosphorus by MCCC from industrial silicon powder in accordance well with the cracking shrinking kinetic model, which was confirmed to be controlled by both of interfacial transfer and diffusion through the product layer process. Furthermore, the chemical reaction mechanism of MCCC was revealed. The impurities deep removal under leaching step would greatly relieve successive impurities removal stress, even shorten the traditional metallurgical routes, which is of great significance to high-effective and clean produce solar grade silicon for industrial use.

A new type of zeolite composite antibacterial agents was prepared by introducing zinc oxide and copper ions into 13X zeolite through the coprecipitation and ion-exchange methods. The structural properties of the tested antibacterial material were characterized and the antibacterial activity was evaluated. In Cu2+/ZnO-13X (CZ-13), zinc oxide and copper ions were either embedded in the interlayer space or dispersed on surface of 13X zeolite. Excellent antimicrobial activity of CZ-13 was observed on Escherichia coli (E. coli) and Staphylococcus aureus (S.aureus). In the case of Cu2+/ZnO-13X, both MIC and MBC against E.coli were 0.2 mg/mL and 0.8 mg/mL. For S.aureus, CZ-13 also showed similar antibacterial properties. The bacterial cells turned from normal rod-shape into irregular shapes after treatment with the tested CZ-13. An increase of the intracellular enzyme activity after CZ-13 addition suggested that the permeability of the cell membrane increased and bacteria were damaged.

Impurity removal is essential for the recovery and regeneration of silicon resources from diamond wire saw powder by metallurgical purification technologies. In this paper, the aluminum was removed from the diamond wire saw powder via a direct HCl leaching method. In order to analyze the removal efficiency of various experimental conditions, certain parameters such as HCl concentration, leaching temperature, reaction time and liquid-solid ratio were also investigated. Particularly, the removal efficiency of Al reached 95.6% under the optimal leaching condition, such as the HCl concentration of 4 mol·L−1, the leaching temperature of 60 °C, the reaction time of 3 h, and the liquid-solid ratio of 10. The shrinking core model and homogeneous model were then respectively utilized to describe the leaching kinetics of the Al removal leaching process. The results indicated that the homogeneous model was more suitable than the shrinking core model. Moreover, the kinetics parameters regarding the reaction orders m=3, n=2.81, the activation energy Ea=97.30kJ mol−1, the frequency factor A=1.11×1014 min−1. Furthermore, the leaching mechanism of Al removal was revealed based on kinetic analysis and materials characterization. This work is of great practical value in terms of regenerating silicon resources from the diamond wire saw powder waste materials with efficient and low cost methods.

A multi-field coupling model of heat-flow-thermal stress was established to investigate the influence of Marangoni effect on the growth quality of multi-crystalline silicon (mc-Si) during the vacuum directional solidification (VDS) process. The simulation results showed that the Marangoni effect has a significant effect on the distribution of temperature and thermal stress as well during the VDS process due to the increased velocity of melts. The enhanced flow incurred more homogeneous temperature distribution of silicon melts and reduced radial temperature gradient, which then leads to the flatter solid/liquid (s/l) interface. However, as temperature gradient of the crystal increased, thermal stress of the silicon ingot was strengthened as a result. The growth quality of crystal was more desirable when adopting a pulling-down rate of 10 µm/s, in which case the (111) surface was advantageous throughout the entire crystal growth process by XRD detection. Finally, the reliability of the numerical simulation result was verified by the experiment.

Large amounts of Ti-bearing blast furnace slag (TBFS), diamond wire saw Si powder (DWSSP), and Al alloy scrap (AAS) are generated annually. Although these are industrial waste, they contain valuable Ti, Si, and Al resources. In this work, a novel process is developed for the simultaneous recycling of Ti, Si, and Al from these three wastes to prepare TiSi2 and Al-Si alloys. TBFS, DWSSP, and CaO (flux) were mixed to form a mixed Ti-Si-slag, which was combined with AAS and underwent reduction smelting at 1823K to prepare Si-Ti-Al alloys. Subsequently, TiSi2 (98.7%) and low-Fe Al-Si (0.64 wt.% Fe) alloys were prepared sequentially by separating the molten Si-Ti-Al melt via electromagnetic directional crystallization with a pull-down rate of 3μm/s. The impurities in the Si-Ti-Al alloy were removed during the separation process by segregation at the boundary of the solid-liquid phase and volatilization. Furthermore, the entire process produces no waste acid or waste gas. Therefore, this work has introduced an efficient and environmentally friendly method for the value-added recycling of Ti, Si, and Al resources from accumulated TBFS, DWSSP, and AAS.

Spent SCR catalyst (SSC), Ti-bearing blast furnace slag (TBFS), and Al alloy scrap (AAS) are industrial wastes that are rich in Ti and Al. To utilize Ti and Al resources in these three wastes, here, an efficient approach is proposed to prepare two useful alloys, Ti5Si3 and Ti5Si4-TiAl3, using the three wastes as raw materials. First, AAS was used as a reductant to extract Ti and Si from the SSC and TBFS and simultaneously prepare Ti-Si-Al alloys. The effect of the crucible (Al2O3 and MgO crucibles) and CaO addition (slagging agent) on Al reduction was investigated, and the results showed that a MgO crucible and the addition of CaO increased the extraction ratio of Ti and Si. Then, Ti5Si3 and Ti5Si4-TiAl3 alloys were prepared sequentially by the separation of molten Ti-Si-Al melt via electromagnetic directional crystallization. Impurities in the Ti-Si-Al alloy were removed during electromagnetic directional crystallization. No carbon, waste acid, and waste gas were discharged throughout the whole production process. This work provides a green, high-efficiency, and low-cost method that also treats accumulated SSC, TBFS, and AAS wastes.

The installed capacity of solar photovoltaic power generation has grown rapidly in the last decades. With the rapid development of the photovoltaic industry, the demand for Si wafers, which are integral to solar cells, has grown dramatically. In the manufacture of Si wafers, the traditional loose abrasive sawing method (LAS) has gradually been replaced by the diamond-wire sawing method (DWS). However, during the diamond-wire wafer sawing process, approximately 35%-40% of the crystalline Si becomes diamond-wire sawing silicon waste (DSSW). Therefore, DSSW represents a resource worth recycling due to its low levels of impurities and high silicon content. Furthermore, recycling prevents DSSW from becoming environmental pollution and eliminates disposal costs. This review provides an overview of the recycling and reutilization of DSSW based on an extensive literature survey. In view of the rapid increase in DSSW production and current purification bottleneck of 5 N, in-situ utilizations may be more feasible, such as the preparation of silicon containing alloys and functional ceramic materials, which not only frees from the complex purification process, but has a huge demand. Finally, based on the review, future prospects are proposed, aiming to identify research directions with significant potential in the resource utilization of DSSW and other silicon wastes.

Hf, Zr, or Ti was employed as additive to enhance removal of the main impurities from metallurgical-grade Si (MG–Si) during the Si–Sn alloy refining process. The microstructure of Si-Sn alloy without/with Zr, Hf, or Ti was observed and analyzed by electron probe microanalysis (EPMA) to investigate the distribution of impurities. Compositions of intermetallic phases precipitated in Sn or among the grain boundaries of Si were quantitatively analyzed using EPMA. The mechanisms of their formation and the removal of impurities are discussed. The results of Si refining showed that the addition of Hf or Zr slightly enhanced the removal of Al. The high refining temperature in the Si-Sn alloy refining process was responsible for the low extraction of B. Most of Zr, Hf, or Ti was removed simultaneously with other impurities during the Si–Sn alloy refining process.

Nanostructures of silicon are gradually becoming hot candidate due to outstanding capability for trapping light and improving conversion efficiency of solar cell. In this paper, silicon nanowires (SiNWs) and silicon inverted pyramid arrays (SiIPs) were introduced on surface of Gr-Si solar cell through silver and copper-catalyzed chemical etching, respectively. The effects of SiNWs and SiIPs on carrier lifetime, optical properties and efficiency of Gr-SiNWs and Gr-SiIPs solar cells were systematically analyzed. The results show that the inverted pyramid arrays have more excellent ability for balancing antireflectance loss and surface area enlargement. The power conversion efficiency (PCE) and carrier lifetime of Gr-SiIPs devices respectively increase by 62% and 34% by comparing with that of Gr-SiNWs solar cells. Finally, the Gr-SiIPs cell with PCE of 5.63% was successfully achieved through nitric acid doping. This work proposes a new strategy to introduce the inverted pyramid arrays for improving the performance of Gr-Si solar cells.

Ti-bearing blast-furnace slag is a metallurgical waste but a promising Ti resource. In this study, Ti and Al–Si alloys can be prepared directly by separating a Ti–Si–Al alloy that was prepared by reducing Ti and Si from Ti-bearing blast-furnace slag with Al. The technology of directional solidification with electromagnetic force was employed to carry out the separation of the Ti–Si–Al alloy. When additions of CaO and Al were 24 wt% and 40 wt%, respectively, the composition of the obtained Ti–Si–Al alloy was 31.8 wt% Ti, 22.7 wt% Si, 28.5 wt% Al, and 10.2 wt% Fe. Ti5Si4, TiSi, Al–Si–Ti (τ2), Al–Si–Fe (τ4), and Al–Si alloys were prepared in sequence after separating the Ti–Si–Al alloy using directional solidification with electromagnetic force. However, when the composition of the Ti–Si–Al alloy was changed to 21.2 wt% Ti, 48.5 wt% Si, 19 wt% Al, and 6.8 wt% Fe, the TiSi2, Si, Al–Si–Fe and Al–Si alloys were prepared in sequence. This study will propose an approach to employ the metallurgical waste, titanium-bearing blast-furnace slag, to prepare Ti and Al–Si alloys.

Impurity removal, the purification process from metallurgical grade silicon (MG-Si) required to obtain solar grade silicon (SoG-Si), is crucial to the preparation of silicon-based solar cells. Some...

Coarse Al-Si alloy is produced from bauxite via carbon electro-thermal reduction method. Silicon and iron-rich phases are two main detrimental impurities in coarse Al-Si alloy, and they can be simultaneously removed by adding Mn under the electromagnetic field. We focus on the influence of different Mn additions, dropping rates, and current intensity on the simultaneous removal efficiency of Si and Fe. Experimental results show that as mole ratio of Mn/Fe reaches more than 0.8, the morphology of iron-rich phases together with silicon changed from harmful acicular-like to the contributing bulks, concentrated at the bottom of Al-Si alloy as intermetallic compounds. Furthermore, when Mn/Fe reaches 1.2 and a lower dropping rate (5 to 25 μm/s) is adopted, both Si and Fe contents in the Al-Si alloy decreased drastically after electromagnetic directional solidification process, reaching 11.42 and 0.4 pct, respectively, with a desirable Fe removal efficiency of 91 pct. Finally, the principle of simultaneously separating Si and removing iron-rich phases from Al-Si alloy is studied deeply.

The Si purification mechanism was investigated by using Al Si solvent with small amounts of V to enhance B removal. The results indicated that a small amount of V enhanced the removal of B from the Al Si melt, as it formed the VBX compound. The VBX was determined to be VB2 via EPMA. The solubility product of the VB2 in the Al-43at. %Si melt at 1273 K and the Al-35at. %Si melt at 1173 K were initially measured experimentally with equilibrium technology, and were determined to be 8.15 × 10 - 11 (1273 K) and 5.97 × 10 - 12 (1173 K). The relationship between the solubility product of VB2 and the liquidus temperature of Al Si melt was estimated, which indicated that an excessive V addition or a lower temperature is needed to enhance the efficiency of B removal from the Al Si melt. Based on the thermodynamic analysis, V was used as an additive in the Si purification process with the Al-35at. % Si solvent that had electromagnetic solidification. The results of the Si purification indicated that a small amount of V could enhance the B removal efficiently and VSi2 was found in eutectic Al Si phase along the Si crystals boundaries. The maximum removal rate of B was about 76%. The supplementary V was completely eliminated together with the B and did not contaminate the refined Si.

A simple and effective method for the removal of impurities from large-sized particle metallurgical-grade silicon (MG-Si) powders based on Cu-catalyzed chemical leaching (CuCCL) has been proposed and discussed. The leaching behaviors of the main metallic impurities (Fe, Al, Ca, Ti, Ni, V and Cu) were investigated using various leaching approaches. The typical precipitates at Si grain boundaries before and after leaching were observed and analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. The leaching results show that the order of impurity removal efficiency, from highest to lowest, is CuCCL > HF-H2O2 leaching > HF leaching. After CuCCL, the total metal impurity concentration can be reduced from 6759 ppmw to 193.41 ppmw. The numerous micro-scale “channels” introduced by CuCCL are beneficial for the removal of impurities, especially for the non-dissolving metal impurities, such as calcium and aluminum. The results indicated that CuCCL is promising as an industrial purification method to produce solar-grade silicon.

In the present work, a continuous growth model of primary silicon from Al-Si melts was established based on the experimental and numerical data to analyze the separation mechanism of primary silicon from Al-Si alloy with high silicon content during electromagnetic directional solidification process. Results show that the separation of primary Si from Al-Si melts depends on the growth rate of primary Si phase and the solidification rate of the melts. Moreover, the separation and enrichment effects of primary Si during the electromagnetic directional solidification process could be improved by enhancing the bottom cooling conditions of crucible and the stirring strength of Al-Si alloy melts. Finally, the distribution and composition of phases and microstructures of the Al-Si alloy after the electromagnetic directional solidification technique were also analyzed and discussed.

The “same activity” method was used to determine the activity interaction coefficient of Al to Fe in a Si-based solution. Al was dissolved into a binary Si-Fe solution at 1663, 1673, 1693 and 1723 K. The solubility of Fe and Al in silicon was determined at different temperatures, and the interaction coefficients of Al to Fe were calculated and obtained by fitting the solubility data of Al and Fe. Scanning Electron Microscopy-Energy Dispersive Spectrometer (SEM-EDS) and Electron Probe Micro Analyzer (EPMA) techniques were used to verify the uniformity of the Si-Fe-Al alloy samples and the reliability of the interaction coefficient obtained by experiments at 1693 and 1723 K. The X-ray Powder Diffraction (XRD) results displayed the phase transformation from FeAl3Si2 to FeAl2.7Si2.3 to Fe3Al0.3Si0.7 with rising dissolution temperature, and crystallographic data of the phases were obtained by Rietveld refinements.

In electromagnetic directional solidification, the silicon phase cannot always be completely separated, resulting in considerable waste of power and silicon. This study investigated the electromagnetic separation of silicon by using electromagnetic induction-heated directional solidification furnaces at varying frequencies. Two frequencies were applied to separate silicon from aluminum–silicon melts. Numerical simulation results indicated that a low frequency (3 kHz) could substantially enhance the separation of silicon from aluminum–silicon melts under an alternating electromagnetic field, which could increase the speed of the melts to 0.92 cm/s. Experimental results showed that separation efficiency could exceed 85% at a pulling rate of 10 μm/s when a furnace at a frequency of 3 kHz was used. This method can potentially meet the requirements of manufacturing low-cost solar cells for industrial use.

The depressing texturation and stubborn directional saw marks on diamond wire sawing (DWS) polysilicon wafers has resulted in severe limitations for the mass application of DWS technology in PV market. Herein, a simple and low-cost copper-assisted chemical etching method was presented to controllably nano-texturing DWS polysilicon wafers. The work firstly reveals the adjustment of anion species in copper salts can readily control the nanostructure during the copper-catalyzed etching process. After etching, the obtained inverted pyramid structure can effectively reduce the reflectivity of the silicon wafer surface, the reflectance can be as low as 5.8% in the wavelength range of 300–1100 nm. Moreover, the surface saw marks are removed after etching, and the novel texture method guarantee the low recombination rates. The effective texturing method shows a promising potential application in the photovoltaic field.

TiSi 2 crystals were successfully obtained via directional solidification separation of a Ti–Si eutectic alloy under electromagnetic stirring. In order to explore the separation mechanism in detail, experiments were conducted using a high-frequency induction furnace at different downward speeds and by varying the thermal parameters of directional solidification (i.e., temperature gradient, cooling rate, and growth rate) of a crucible loaded with Ti–75 wt%Si melt. The results demonstrate that electromagnetic stirring and the thermal parameters of directional solidification played different roles in the crystal separation of TiSi 2 . While the electromagnetic stirring enhanced the migration of TiSi 2 crystals in the Ti–Si melt and mushy zone, low downward rates (5 μm/s) were beneficial for the growth of TiSi 2 crystals and reduced the mushy zone area. Therefore, a low downward rate combined with electromagnetic stirring is favorable for the enrichment of TiSi 2 crystals.

To improve the photocatalytic property and recovery rate of existing ZnO materials, a magnetically separable heterostructure photocatalytic composed of GO sheets and nanohybrid Fe 3 O 4 /ZnO material was synthesized by a simple low-temperature chemical synthesis process. This synthesis enables simultaneous decoration of Fe 3 O 4 /ZnO spheres on both sides of the GO sheets. As a result, the Tauc's plot revealed the band gap of Fe 3 O 4 /ZnO-GO sample decreases to 2.07 eV from 3.38 eV of ZnO. This smaller energy band gap and slower recombination rate of electron-hole pairs greatly improve the photocatalytic activity of the Fe 3 O 4 /ZnO-GO complex through the wider visible light absorption range. The photocatalytic reaction rate of the pure ZnO photocatalyst is 4.84 × 10 −3 min −1 , for Fe 3 O 4 /ZnO composite is 1.564 × 10 −2 min −1 and for Fe 3 O 4 /ZnO-GO composite is 5.558 × 10 −2 min −1 . The stability and recovery rate and photocatalytic property retention also greatly improved from ZnO-only photocatalyst. The photocatalytic reactivity of Fe 3 O 4 /ZnO-GO nanocomposite structure reaches 92.8% efficiency on the first run and was at 75% efficiency after the four cycling.

In order to discuss the effects of transition metals such as Zr, Hf, and Ti on the removal of impurities (B, P, Fe, Al, Ca, Ti, V, Cu, Ni, Mn, Zr, and Hf) in the purification of metallurgical-grade Si (MG-Si) with Al–Si alloy, the impurity phases formed after solidification were investigated by electron probe microanalysis (EPMA) and their removal by acid leaching was performed. EPMA investigation showed that β-Al5FeSi was the main impurity phase aside from Al in the sample without additives. However, after adding Zr, Hf, or Ti, the ZrSi2, HfSi2, or TiSi2 compound dissolved in small amounts of Al was the most observed phase besides β-Al5FeSi and Al. Impurities such as V, Ni, and Mn were more likely to coexist with β-Al5FeSi when Hf or Zr was employed as the impurity getter. However, V preferentially coexisted with TiSi2 when Ti was added. The leaching results showed that the addition of Zr, Hf, or Ti significantly enhanced the extraction of B and slightly enhanced that of other impurities. The added Zr, Hf, and Ti were eliminated efficiently with the other impurities, reaching extraction ratios of 99.998%, 99.9994%, and 99.997%, respectively.

Refractory silicides, eutectic Si/MSi2 (M: Nb, Ta, Mo, or W) alloys, and high-purity silicon are materials that have been used in many high-tech industries. Today, they are prepared using different technologies, i.e., each of them is prepared using an independent technology. This study proposes a new method to simultaneously prepare three high-purity materials (refractory silicides, eutectic Si/MSi2 alloys, and silicon) using electromagnetic directional crystallization. The Si–M (Si–Nb, Si–Ta, Si–Mo, or Si–W) solvents are separated using electromagnetic directional crystallization, and then the MSi2 (NbSi2, TaSi2, MoSi2, or WSi2) and eutectic Si/MSi2 (Si/NbSi2, Si/TaSi2, Si/MoSi2, or Si/WSi2) alloys are precipitated in sequence because the crystallization temperature of MSi2 is higher than that of the eutectic Si/MSi2 alloys. Additionally, owing to the segregation behavior of impurities between the solid and liquid phases, impurities in the Si–M solvents can be eliminated efficiently to prepare high-purity MSi2 and eutectic Si/MSi2 alloys. In addition, as the eutectic Si/MSi2 alloys consist of Si and MSi2 phases, high-purity Si powders (>99.98%) can be obtained by separating the Si and MSi2 phases using acid leaching. The results indicate the feasibility of the new approach in preparing refractory silicides, eutectic Si/MSi2 alloys, and high-purity Si.

The grain size and porosity are two significant parameters to evaluate the properties of the Al alloy. In this work, an electromagnetic-field-enhanced directional solidification process hybridized with the remelting treatment was proposed to refine the grain size of Al alloys and at the same time to remove the residual gas in molten alloys. Furthermore, the effects of several factors on the grain refinement and degassing were investigated. The high induction current is effective for the obtainment of the small homogeneous grain size because of the stirring effect. With the increase of the moving rate, the grain size increased and then decreased due to the nucleation effect. The remelting process enables both the grain refinement and H2 degassing to obtain regular grain orientations. The simulated pressure field, velocity field and H2 gas volume fraction show the mechanism of the bubble transfer in the liquid Aluminum alloy. The pressure field depicts a sharp pressure gradient on the upper side of the bubble. The velocity field indicates an increase in the velocity maximum in the bubble. The shape evolution process of the H2 bubble shows the effect of the interface tension.

With the rapid increase of heat flux and demand for miniaturization of electronic equipment, the traditional heat conduction and convective heat transfer methods could not meet the needs. Therefore, the spray cooling experiment was carried out to obtain the basic heat transfer and cooling process. In this experiment, the spray cooling system was set up to investigate the influence of refrigerant charge on heat transfer performance in steady-state, dynamic heating, and dissipating processes. In a steady-state, the heat transfer coefficient increased with the rise of the refrigerant charge. In the dynamic dissipating process, both heat flux and heat transfer coefficient decreased rapidly after the critical heat flux, and the surface temperature drop point of each refrigerant charge was presented. The optimum refrigerant charge was provided considering the cooling parameters and the system operating performance. When the refrigerant operating pressure was 0.5 MPa, the spray cooling process presented with the higher heat flux, heat transfer coefficient, and cooling efficiency in this experiment. Meanwhile, the suitable surface temperature drop point and more gentle heat flux curves in the nucleate boiling region were obtained. The research results will contribute to the spray cooling system design, which should be operated before departure from the nucleate boiling point for avoiding cooling failure.

A novel water-based rust conversion agent (abbreviated as “TE-GAE”) was firstly synthesized using gallic acid (3,4,5-Trihydroxybenzoic acid, abbreviated as “GA”) and triethanolamine (abbreviated as “TE”) by esterification reaction. A new type of rust conversion coating (abbreviated as “TE-GAE coating”) containing the TE-GAE and additives was also prepared. The structural feature of rust conversion agent TE-GAE was characterized using Fourier transform infrared spectrum (FT-IR). The effect of the synthetic water-based TE-GAE coating on original rust layer were investigated by X-ray diffractometer (XRD) and Scanning electron microscope (SEM). Compared with traditional rust conversion coatings that apply tannic acid and phosphoric acid as rust converters, the as-synthesized integrated TE-GAE coating firstly revolutionized the application method of the anti-corrosion coatings, combined the traditional “primer” and “topcoat” into one, and improved engineering efficiency while ensuring protective effect. Additionally, the adhesion test indicated that the integrated TE-GAE coating presented remarkably strong film adhesion between the coating and steel substrate. Meanwhile, the neutral salt spray test and weather-resistant test showed significant corrosion resistance. Furthermore, a corrosion resistance mechanism including the combined effect of the rust conversion, barrier and corrosion inhibition for the integrated TE-GAE coating was tentatively proposed, which indicating that the rust converter chelates with Fe2+/Fe3+ to form a dense chelating film, extend the penetration path of corrosive medium and delay the occurrence of corrosion process. Thus, such a “green” and “efficient” integrated rust conversion coating is promising for protecting steel from corrosion, which is critical for the sustainable development of functional coating materials.

The present study investigated the effects of adding CH3COOH to HCl and HF used to purify metallurgical-grade Si (MG-Si). After 6 h of leaching MG-Si with an acid mixture consisting of 4 mol L−1 HCl, 3 mol L−1 HF, and 3 mol L−1 CH3COOH at 348 K, the total impurity removal efficiency was 88.5%, exceeding the 81.5% removal efficiency obtained without addition of CH3COOH. The microstructural evolution of Si after etching with the two lixiviants indicated better dissolution of metal impurities in MG-Si when using the HCl-HF-CH3COOH mixture. Furthermore, the leaching kinetics of Fe using the HCl-HF and HCl-HF-CH3COOH mixtures were observed to depend on the interfacial chemical reactions.

Boron separation from metallurgical grade silicon (MG-Si) is still a puzzle for metallurgical route. A purification method to MG-Si using a synthetic CaO-CaCl2 slag (no SiO2 addition) treatment combined with an Ar-O2-H2O gas blowing technique was studied. The mechanism of boron separation from silicon using the synthetic CaO-CaCl2 slag treatment and the Ar-O2-H2O gas blowing was analyzed and elaborated. The results showed that the intermediate product SiO2, generated by the O2 gas blowing, was combined into silicate with CaO slag reagent. Boron in silicon can be separated by both gaseous borides HBO, BOCl and borate CaO·B2O3. It was found that the boron separation can be further improved by separating soluble boron in the refined silicon using the acid leaching treatment. The total separation efficiency of boron in MG-Si reached 94.5% using the combined slag treatment and gas blowing refining technique followed an acid leaching treatment to the refined silicon.

Surfaces nano-texturing has triggered off much attention for trapping sunlight to improve the efficiency of solar cells. Silicon nanowire (SiNWs) arrays, with excellent antireflection performance, will hopefully improve photoelectric conversion of solar cells, however, the deteriorated effective carrier lifetime seriously limits efficiency enhancement of solar devices. Until now, the effect of SiNWs structure on effective carrier lifetime remains unexplored. Herein, the effects of fabrication parameters on the morphology structure and effective carrier lifetime of textured mc-Si were studied in detail. We also firstly discover that the relationship of SiNWs arrays length and effective carrier lifetime shows the negative exponential relation. Moreover, the effects of ethanolic iodine (I–E) concentration, immersion time, and surface pre-conditioning (with and without native oxide) on surface passivation of SiNWs arrays were investigated. It is found that more effective surface passivation could be achieved for the SiNWs arrays with shorter length. Meanwhile, the HF dipping pretreatment is conducive for SiNWs passivation, and which is attributed to Si–Hx termination with lower dissociation energy.

The effects of structural composition, particle size, leaching time, temperature, and liquid–solid ratio on the removal of phosphorus from metallurgical-grade silicon (MG-Si) by acid leaching were investigated. Two specimens with different phase constitutions were studied: crude metallurgical-grade silicon (C-MG-Si), which is reduced from electric arc furnace, with a high content of Al and Ca, and a secondary refined metallurgical-grade silicon (S-MG-Si) obtained after secondary refining in ladle. Using scanning electron microscopy-energy dispersive spectroscopy, the phosphorus-containing phase was only detected in the C-MG-Si grain boundaries. The Si2Al2Ca phase, which was soluble in HCl, showed an affinity for phosphorus, with up to 0.53 wt pct dissolved in this phase. The optimum conditions for acid leaching were grain size, 75-106 μm; leaching time, 6 hours; leaching temperature, 338 K (65 °C); liquid–solid ratio, 6:1; and HCl concentration, 4.0 mol L−1. Using these conditions, the mass fractions of P in C-MG-Si and S-MG-Si were reduced from 105 × 10−6 and 76 × 10−6 to 48 × 10−6 and 61 × 10−6, respectively, with removal efficiencies of 54.3 and 19.7 pct, respectively. Besides, the investigation suggested that adding HF was beneficial for the removal of most impurities. After 6 hours of leaching MG-Si with a mixture composed of 4.0 mol L−1 HCl and 3.0 mol L−1 HF, the purity of C-MG-Si and S-MG-Si were increased from 97.55 and 99.31 pct to 99.91 and 99.87 pct, respectively, with extraction efficiencies of 96.14 and 81.59 pct, respectively. The etching results reveal that the HCl-HF mixture was an effective lixiviant for dissolving impurity inclusions in both C-MG-Si and S-MG-Si.

Zr was employed as an impurity getter to enhance removal of impurities from MG-Si because of its strong affinity for a wide range of impurities. Different lixiviants, HCl + HF, HF and aqua regia, were employed to investigate the leaching behavior of MG-Si at 348 K for 2.5 h with and without Zr addition. Typical precipitates at Si grain boundaries before and after acid leaching were observed and analyzed via scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). The leaching results show that the order of efficiency of the lixiviants, from highest to lowest, is HCl + HF > HF > aqua regia. HCl + HF is the optimal lixiviant for purification of MG-Si with and without Zr addition. The presence of Zr in MG-Si can significantly enhance the efficient extraction of impurities, especially P and Al, which cannot be removed efficiently using conventional hydrometallurgical technologies. The total fraction of impurities removed (Fe, Al, Ca, B, P, Zr, Ti, V, Mn, Cu and Ni) increased from 94.2 to 97.5% after HCl + HF leaching. In addition, 99.9% of the impurity getter Zr was removed, with its concentration decreasing from 50,000 ppmw to 49 ppmw after HCl + HF leaching. The residual amount of Zr in the refined Si can be further removed by directional-solidification purification because of its extremely small segregation coefficient.

Currently, the elimination of Fe from Al-Si alloy for recycling Al-Si scraps, and the purification of Si using Al-Si solvent for recycling Si wafers in solar cells or production of new Si wafers, are two totally different research technologies and topics. A new approach is proposed in this study to combine the two different technologies into a single one which can not only recycle spent Si wafers but also Al-Si scrap simultaneously. The new approach is promising for cost reduction and environmental conservation, because two widely used products, high-purity Si and low Fe eutectic Al-Si alloys, can be prepared simultaneously via electromagnetic directional crystallization. The Al-Si-Fe-(Mn/Cr) melt was separated into a low-Fe eutectic Al-Si alloy (eutectic Al-Si-Fe-(Mn/Cr) alloy) and agglomerated high-purity Si crystals. The critical concentration of Fe (theoretical minimum value of Fe content) in the eutectic Al-Si-Fe-(Mn/Cr) alloys were determined experimentally for the first time, which decreased and increased slightly after the addition of Mn and Cr, respectively. After removing Fe, the residual Fe-containing impurities in the low-Fe eutectic Al-Si-Fe-(Mn/Cr) alloy were modified from their harmful needle-like shape to less harmful Chinese-script-like, and short platelet-like shapes by adding small amounts of Mn and Cr, respectively. After grinding the agglomerated Si crystals and leaching the main impurities, namely Mn, B, Cr , Ca, Al, P, Fe, and Ni, from the Si powders, the purity of Si was upgraded from 99.34% to 99.96%. This new and promising approach can be used for the purifying Si, recycling Si wafers and Al-Si scraps.

A new rust conversion agent based on gallic acid was developed. On this basis, an integrated epoxy rust conversion coating that combined the primer and topcoat of traditional coatings into one was prepared. Compared with the traditional coatings, the integrated epoxy rust conversion coating in this study appeared significant performances: (1) It simplified the construction process, and strengthened the adhesion between rust conversion coating and rust/substrate; (2) In corrosion simulation environments, i.e., the natural environment, water immersion environment and weather-resistant accelerated aging environment, the surface of integrated epoxy rust conversion coating was smooth, and contained fewer holes. Meanwhile, the contact between the coating and substrate or rust was relatively close. Additionally, the corrosion potential and corrosion current density respectively were −0.465 v/7.247 × 10−7 A/cm2, -0.736 v/5.958 × 10−5 A/cm2, and -0.574 v/2.305 × 10−6 A/cm2. (3) The degree of rust conversion was delectable, and rust conversion mechanism showed that the components of original rust were transformed into stable phases, i.e., the phenolic hydroxyls contained in rust conversion agent can form a series of stable complexes with Fe–O–C structure by chelating with iron ion, thus inhibiting further rust expansion.

Slag refining is one of the most effective methods to remove impurities from metallurgical grade silicon. In this paper, ZnO was added to a binary 50% CaO-50% SiO2 slag system with a mass ratio of 2–30% to study the impurities removal from metallurgical grade silicon. The results showed that boron was reduced from 12.94 ppmw to 2.18 ppmw by a 46% CaO-46% SiO2-8% ZnO slag system. Compared to the 50% CaO-50% SiO2 slag system, slag refining with ZnO addition showed a 20% increase in removal efficiency and a 40% increase in the distribution coefficient. After acid leaching, boron was further reduced to 1.52 ppmw with a removal efficiency of 88.25%. By a combined process of slag refining and acid leaching, impurities Al and Fe were reduced from 817 ppmw and 3800 ppmw to 1.2 ppmw and 96 ppmw with removal efficiencies of 99.8% and 97.5%, respectively. The evaporation loss of the generated metallic zinc during slag refining was greater than 99.7%. After acid leaching, the minimum zinc content in silicon was only 4 ppmw.

To select an optimal gas stimulation technique for gas-rich low-permeability coal seams, contrast tests were conducted to study the permeability improvement effects of blasting and hydraulic fracturing techniques based on the same geological units of coal seams. A contrast test of three shaped charge blasting groups with different charging coefficients showed that when the radial decoupling charging coefficient was 1.5, a stress wave with low dominant frequency produced the strongest stimulation effect, and the combined action of the blasting gas and the stress wave on the coal mass effectively increased the volume fraction of gas in the extraction boreholes by 2.0–3.4 times. A contrast test of two hydraulic fracturing groups with different fracture parameters showed that increasing the duration of hydraulic fracturing continuously could effectively compensate for the injected pressure in the target coal seam and increase the gas permeability coefficient of the original coal mass by 6 times. A contrast test between the two permeability improvement techniques, namely, shaped charge blasting and hydraulic fracturing, showed that the effective range of permeability improvement by hydraulic fracturing was 1 m wider than that by shaped charge blasting, and that although shaped charge blasting provided a higher initial peak of the gas volume fraction in the extraction boreholes, the gas volume fraction under hydraulic fracturing had a lower decay rate.

Small amounts of Ti (