Removal Of Silicon Research Articles

Numerical simulation of thermal-flow-magnetic coupling dynamics during P-type monocrystalline silicon removal in electrical discharge machining

To investigate the mechanisms underlying material removal and crater formation on semiconductor silicon in electrical discharge machining (EDM), this study presents a comprehensive thermal-flow-magnetic coupling simulation model, taking into account the synergistic effects of temperature, fluid dynamics and electromagnetic fields. Utilizing the model, the removal dynamics of P-type monocrystalline silicon within a monopulse discharge interval were meticulously simulated. Subsequently, the crater formation mechanism, as well as variations in the temperature and velocity fields, were thoroughly examined. The simulation model’s validity is experimentally confirmed. Findings indicate that an augmentation in pulse duration and thermal energy input precipitates a progressive expansion of the heat-affected zone in silicon. Concurrently, the temperature field’s expanse and the melting-vaporization frontier extend accordingly. The material undergoes instantaneous vaporization upon exposure to the high-temperature heat source. The volumetric expansion of the vapor is substantial, engendering a thermal explosive force that has a significant impact on the molten material. Ejection of material is attributed to the interplay between thermal explosive forces and electromagnetic influences. Experimental observations show that the morphology and dimensions of the simulated crater closely match those of the experimental crater, affirming the model’s capability to elucidate the crater formation mechanism in EDM processes.

Comprehensive recovery of valuable elements from vanadium precipitation liquor using selective impurity removal-reduction precipitation process

The vanadium precipitation liquor produced by the vanadium slag extraction process contains various valuable elements, which are not utilized at high value. In this paper, chromium is recovered through aluminum salt impurity removal - chemical reduction precipitation method. Moreover, the ammonia nitrogen and sodium sulfur in the vanadium precipitation liquor are recovered by stripping and crystallization, thereby achieving comprehensive resource recovery and utilization. The aluminum salt slag removal reduction chemical precipitation method is used to separate Cr from Si, Ca and V impurities. As a result, the obtained Cr2O3 product has a purity of 98.20%, the chromium recovery efficiency is 97.58%, and the silicon removal efficiency reaches 99.66%. The ammonia nitrogen was recovered by stripping, which would be reused to the vanadium precipitation process, with an ammonia nitrogen stripping efficiency of 98%. The purity of NH4Cl is 99.13% and meets the 99-level national standard. The Na2SO4 was recovered by evaporation concentration - crystallization method, which would be reused to the vanadium slag roasting process, with a Na2SO4 recovery efficiency of 88.38%. And the purity of Na2SO4 is 98.85%, which meets the industrial standard for Class II Na2SO4 products. The final solution after comprehensive recovery of valuable elements would be reused to the leaching process, thereby achieving water circulation. This process realizes the high-value utilization of chromium, ammonia, nitrogen, sodium and sulfur, and has no wastewater discharge and is an environment-friendly route.

A Study on the Removal of Impurity Elements Silicon and Zinc from Rubidium Chloride by Vacuum Distillation.

With the rapid development of high and new technology, rubidium and its compounds show broad application prospect and market demand with their unique characteristics. At present, the production of rubidium metal is mainly prepared by calcium thermal reduction of rubidium chloride. Rubidium metal obtained by reduction requires multi-step vacuum distillation to obtain high-purity rubidium metal. The purity of rubidium metal depends on the purity of the raw material rubidium chloride. Rubidium metal is relatively active and is easy to oxidize and explode in air. Therefore, a method combining vacuum decomposition and vacuum distillation to reduce impurity elements in rubidium chloride from raw materials is proposed in this paper. The experimental results show that under the conditions of pressure of 5-10 Pa, distillation temperature of 823 K and vacuum distillation time of 60 min, the contents of Si and Zn impurities are reduced from 1206 mg/kg and 310 mg/kg to less than 0.1 mg/kg, and the removal rates are 99.99% and 99.97%, respectively. Rubidium chloride has almost no loss, and through one-step vacuum distillation, the impurity elements silicon and zinc can be deeply removed, reducing the flammability and explosiveness, high cost, long process and other problems caused by the subsequent preparation of high-purity rubidium metal.

Experimental Research on Deep Silicon Removal in Spent SCR Catalysts

In this research, hydrofluoric acid (HF) was used as a leaching agent to remove silicon impurities from titanium dioxide powder regenerated from a spent SCR catalyst. Further, the effects of HF concentration, liquid–solid ratio, leaching temperature, and leaching time on the leaching rate of regenerated titanium dioxide powder were investigated. The results revealed that the leaching rate of silicon in alkali-leached samples could reach 99.47% under the following conditions: 4% HF concentration, a leaching temperature of 50 °C, and a liquid–solid ratio of 5:1. When compared under identical experimental conditions, the silicon leaching rate in the alkali leached sample using HF surpassed that of the spent SCR catalyst. This suggests that high-temperature alkali leaching led to the degradation of the catalyst and the glass fiber within it, rendering this process more favorable for silicon leaching.

Numerical investigations of water jet-guided laser cutting of silicon

To investigate the interaction mechanism between a laser, water jet, and substrate, a model is developed to simulate the temperature field evolution and removal process during water jet-guided laser (WJGL) cutting of silicon. The model accounted for the temperature-dependent properties of the silicon absorption coefficient, as well as the physical processes of solid-liquid-gas phase change. A three-dimensional finite volume model of WJGL cutting of silicon is created, incorporating laser energy input, water jet impact-cooling, and silicon phase transition and removal. The volume of fluid (VOF) method is employed to trace the interphase interface and obtain the groove shape. The validity of the model is verified by comparing simulation results with experimental data. The simulation results show that the groove cross section is characterized by a “V” shape. The groove depth nonlinearly increases from 52 to 385 μm with an increasing number of cuts. Additionally, the residual temperature of the silicon substrate rises from 837 to 1345 K as the number of scans increases from 1 to 10. The findings offer valuable insights into WJGL cutting research, specifically shedding light on the intricate details of the laser-water jet-substrate interaction mechanism.

Recovery of tungsten from spent selective catalytic reduction catalyst by sulfuric acid precipitation and evaporation crystallization method

AbstractBACKGROUNDSelective catalytic reduction (SCR) can effectively handle NOx from flue gas in coal‐fired power plants. However, as the core part of the SCR method, V2O5–WO3/TiO2 catalyst has a limited operational life in the complex flue gas environment. The recovery of rare metals from spent catalyst would not only bring economic benefits but also solve environmental problems. The process of reducing acid leaching and further roasting‐water leaching could realize the efficient recycling of vanadium, tungsten and titanium.RESULTSAfter reducing acid leaching and roasting‐water leaching to treat spent SCR catalyst, the obtained solution containing tungsten was used as the raw material in this study. The optimal pH value of solution for removal of silicon and aluminum impurities was 9.2–9.5. The best tungsten precipitation conditions were shown as follows: a tungsten concentration of 30 g L−1, a sulfuric acid concentration of 8 mol L−1, reaction temperature of 70 °C and reaction time of 2 h. Under the optimal tungsten precipitation conditions, the tungsten precipitation efficiency can reach 92.53%. Finally, in order to further improve the purity of the crude H2WO4, the crude H2WO4 was fully dissolved in ammonia, followed by filtration and evaporation crystallization to obtain 5(NH4)2O.12WO3.5H2O (APT) crystals with a purity of 93.05 wt%. The crystallization efficiency of APT was 73.37% at 60 °C for 2 h with a rotor speed of 400 rpm.CONCLUSIONThese results indicated that a higher purity of APT crystals can be obtained by the steps of removing silicon and aluminum, precipitation of tungsten by sulfuric acid, ammonia dissolution and evaporation crystallization. © 2023 Society of Chemical Industry (SCI).

Insights into Interfacial Mechanism of CeO2/Silicon and Atomic-Scale Removal Process during Chemo-Mechanical Grinding of Silicon.

Chemo-mechanical grinding (CMG) is a valid processing method to achieve a low-damage surface of silicon. However, the atomic interfacial mechanism during the CMG is still unclear. Herein, the CMG process of silicon was investigated using first principles and frictional wear tests in which the effects of pressure and speed on the interfacial reaction were comprehensively analyzed. Simulations showed that the formation and breakage of chemical bonds occurred at the CeO2/silicon interface during CMG, and the newly formed chemical bonds were stronger than those on the silicon surface. Also, it was found that the pressure and speed improved the materials removal rate by means of accelerating the interfacial chemical reactions, which is also verified by frictional wear tests. This study provides new insights into the atomic interfacial mechanism during silicon CMG.

Study on preparation of ultra-clean coal from bituminous coal using the ionic liquid extraction

ABSTRACT In order to realize clean and efficient utilization of low rank coal, ultra-clean coal preparation is an important method. A clean and efficient method of producing ultra-clean coal is urgently needed, given the high environmental impact and corrosiveness of the chemicals used in the traditional chemical preparation of ultra-clean coal. In this study, ultra-clean coal was prepared by leaching using acidic imidazole ionic liquids, and the effects of temperature, time and concentration on the reaction process were investigated. The ash composition of the sample and the ash removal mechanism under the ionic liquid were revealed, and the evolution law of the microstructure and functional group characteristics was clarified. The research showed that the concentration and temperature had a large influence on the ash content of the product during the leaching process, and the reaction time had a small influence. The minimum ash content of the ultra-clean coal could reach 0.89% (dry basis). In the ionic liquid system, iron, calcium and magnesium in the coal were effectively removed, the iron oxide content was significantly reduced and calcium salts except calcium sulfate were effectively removed, while periclase was almost completely removed. However, the removal of silicon and aluminum was poor. Most of the alumina and silica remained in the ultra-clean coal. Extracted coal had more cracks and rougher surface than raw coal, the BET surface area decreased from 2.8579 to 2.4032. Under the influence of ionic liquid, the Aar/Aal ratio, which evaluates the aromaticity of coal, increased from 0.3702 to 0.8569, indicating that the aromaticity of coal was significantly improved. The CH2/CH3 ratio describing the length and branching degree of aliphatic chains in coal decreased from 4.0849 to 3.1516 which showed that ionic liquids can effectively reduce the length of aliphatic side chains, weakening the coal’s oxidizing activity. The pyrolysis curve of coal shifted to the high temperature zone and the peak temperature increased, indicating the effect of ionic liquids on the chemical stability of coal.

Clean removal of silicon (IV) and vanadium (V) from high concentration chromium (VI) solutions in the chromate production processes

How to effectively and environmentally purify chromate solutions containing impurities such as silicon and vanadium, and avoid the generation of Cr(VI)-containing residues are important issues to be solved urgently. Herein, a novel Cr2O3∙2.7H2O adsorbent with stable three-dimensional nanoflower structure was fabricated using the hydrothermal method, which was successfully implemented in the removal of Si(IV) and V(V) from dichromate system. Batch adsorption experiments revealed that the saturated adsorption capacity of Si(IV) was 140.06 mg/g at pH 9 and 132.98 mg/g V(V) at pH 2. Furthermore, density functional theory (DFT) calculations revealed that V(V) anionic species exhibited high adsorption energies (−990.70 kJ/mol, −697.10 kJ/mol) and small adsorption distances from the β-CrOOH(012) (≈1.89 Å, 1.98 Å), verifying the selective adsorption of Cr2O3∙2.7H2O on V(V) in Cr(VI)–Si(IV)–V(V) ternary systems. The integrated mechanisms of electrostatic interaction, coordination, polymerization and precipitation for the removal behaviors were proposed via FT-IR, XPS and DFT calculations. In the real Na2Cr2O7 complex solutions, the simultaneous removal rates of 88.48% Si(IV) and 80% V(V) were achieved, with optimal adsorption conditions at a pH of 8 and a temperature of 333 K. Furthermore, the desorbed Cr2O3∙2.7H2O can be effectively converted into high-value nano Cr2O3, indicating the potential of this new green adsorbent. Therefore, this study not only imparts theoretical and practical insights into the purification of chromate solutions but also contributes to the advancement of cleaner chromium compound production by facilitating the high-value conversion of the adsorbent.

Removal of Silicon from Magnesite by Flotation: Influence of Particle Size and Mechanical Mechanism.

The feasibility of producing high-density sintered magnesia with a one-step sintering method was investigated by utilizing finely ground magnesite as raw materials for direct flotation. The mechanism of flotation desilication of microfine grain magnesite was investigated by combining microstructure and chemical properties. The results showed that dodecylamine (DDA) has a sorting effect on magnesite reverse flotation desilication. Under the premise of 150 mg/L sodium polyacrylate (PAANa) as an inhibitor and 300 mg/L DDA as a collector, the content and recovery rate of MgO can reach 83.91% and 78.78%, respectively. When sodium oleate (NaOL) was used as a collector, the recovery rate of MgO was only 49.22%; therefore, it is unsuitable for magnesite purification. The flotation effect was affected because MgO particles and SiO2 particles agglomerated in the flotation process. The flotation agent cannot work for a single element but works for the mineral agglomerate. While collecting Si elements, the agglomerated MgO was also brought into the froth layer, making flotation impossible.

Removal of hardness and silicon by precipitation from reverse osmosis influent: Process optimization and economic analysis

The removal of hardness and silicon in the reverse osmosis influent is urgently desirable in view of wastewater purification and reuse. However, the development of cost-effective method reducing the hardness and silicon to low level is challenging. Herein, the single step process and double step precipitation process were proposed, aiming at minimize the adverse effect of influent wastewater on reverse osmosis membranes. The optimal dosages of precipitants (FeCl3 and MgCl2) and the effects of pH values and time were investigated. In the double step process, the concentrations of total hardness and silicon reached the lowest values (11.0 mg·L−1 and 2.1 mg·L−1) by adding 400 mg·L−1 MgCl2 and 300 mg·L−1 FeCl3. Subsequently, four schemes for the wastewater treatment were proposed, which scheme D using both FeCl3 and MgCl2 as precipitants obtained the lowest cost (1.20 $·t−1). This work could provide technological support for removing total hardness and silicon from industrial wastewater and industrial wastewater recycling.

Mitigating silica fouling in electro-electrodialysis: Anode compartment modification and process intensification approaches

Electro-electrodialysis (EED) based causticization of industrial (agro-based paper mills) green liquor experiences severe silicate fouling issues (especially in anode compartment) resulting frequent shutdown, dismantling, cleaning and reassembling challenges. Therefore, continuous causticization through EED process becomes difficult. Appropriate design modification of the anode compartment along with periodic silica removal could overcome frequent shutdown issues, and execution of EED process for longer duration. The novel mechanism of silicon removal using EED process by the precipitant is also presented. Their treatment performances in removing silicon were statistically evaluated and confirmed by instrumental techniques. Using modified design and 200 cm2 of membrane area, 500 mL of 2.56 mol·L−1 of NaOH (92% Na+ ion recovery) could be produced in 4 h by electrolyzing 500 mL of industrial green liquor under constant current density, 60 mA·cm−2. Proposed modification could result ∼21% improvement in caustic recovery/energy consumption compared to unmodified anode compartment. With improve the performance which is the average current efficiency 74.5% and energy consumption 4.42 kWh·kg−1, was recorded.

Optimization of Silicon Selective Leaching with Glycerol Using Response Surface Methodology (RSM)

Selective removal of silicon might open-up the possibility of reusing silicon-contaminated spent catalyst. Unfortunately, study regarding this topic is still scarce. The effect of important parameters such as leaching treatment time and temperature was investigated, and the process conditions were optimized using response surface methodology (RSM) based on central composite design (CCD). Based on analysis of variance (ANOVA) results, leaching treatment time was found to be the most significant parameter, followed by temperature. Higher temperature and longer treatment time were satisfactorily enough for efficient silicon leaching from spent catalyst. The obtained quadratic model (R2 = 0.995) shows a good correlation between the predicted values and experimental data. The optimum condition for silicon leaching was identified to be a temperature of 213.3°C and a treatment time of 5.83 hours.

Textured p-type crystalline silicon surfaces obtained by multi-step plasma process for SHJ solar cells

P-type monocrystalline silicon wafers were textured by means of a multi-step plasma etching technique with the aim of greatly reducing their reflectance and effectively exploiting the highest possible amount of solar radiation in heterojunction photovoltaic devices. Suitable surface morphologies, characterized by high light scattering, have to be obtained without damaging the c-Si electrical properties. For this reason, some aspects of the plasma etching process have been studied and improved. Modifications have been made to obtain both “cleaner” processes and energetically lower ion bombardment. By operating at high pressure (0.4 mbar), a process controlled by diffusion of reactive species towards the substrate was favoured. Another innovative aspect consisted in two “reconditioning” plasma processes of the Si surface before the actual silicon removal step with SF6 /O2 gas mixtures. A strong reduction in the average optical reflection down to 5% was obtained coupled with a minority carriers lifetime (τeff) of about 950 μs, value comparable to that of the untreated silicon. An interesting surface morphology, consisting in “U" shaped cavities, was obtained. Texture irregularities were easily removed by acid etching. The moderate depth of the cavities is very promising for an effective passivation with a-Si:H thin films.

Mechanical effect of abrasives on silicon surface in chemo-mechanical grinding

To obtain high-quality surfaces and subsurfaces of ground silicon wafers, chemo-mechanical grinding (CMG) for silicon has been developed by inducing chemical reactions into grinding. Chemical reactions between abrasives and silicon during CMG process have been proved in previous studies. The mechanical effect of abrasives in CMG process is not fully understood. To investigate abrasives’ mechanical effect on material removal and subsurface damage of silicon in CMG process, silicon nanoscratching experiments with CeO2 indenter under a progressive normal load were conducted, and microtopographies of scratch surface and subsurface were observed. For comparison, silicon nanoscratching experiments with diamond indenter were also conducted. Finite element models of silicon nanoscratching with CeO2 and diamond indenters were built to investigate the relationship between stress distribution and damage evolution of silicon. Experimental investigations and simulation results indicate that no obvious material removal of silicon or serious subsurface damage is generated by CeO2 indenter's mechanical action because the wear of CeO2 indenter leads to the release of the stress on silicon. Material removal of silicon during CMG process relies on chemical reactions between soft abrasives and silicon other than stress on silicon generated by soft abrasives.

A novel cationic collector for silicon removal from collophane using reverse flotation under acidic conditions

A novel cationic collector for silicon removal from collophane using reverse flotation under acidic conditions

LONG-TERM MICROVASCULAR REMODELING AND CYSTIC CHANGES AFTER RETINAL DETACHMENT TREATED WITH SILICON OIL TAMPONADE.

To determine the long-term microvascular alterations associated with macular cystic changes after retinal detachment surgery with silicone oil tamponade. The results of two optical coherence tomography angiographies performed at 11 months and 38 months after silicone removal were retrospectively analyzed for 30 eyes. The data were compared between both measurements and between eyes with macular cysts (MC+) and without macular cysts (MC-). Two patterns of cysts were identified and compared: cysts exclusively involving the inner nuclear layer (INLc) and cysts present in all retinal layers. At both end points, 20 eyes (67%) presented with macular cysts, 12 of them (40%) had INLc. At the first end point, vascular density of superficial capillary plexus was higher and superficial foveal avascular zone was smaller in MC+ eyes than in MC- eyes (P = 0.04 and P = 0.017, respectively). At the second end point, vascular density of superficial capillary plexus significantly decreased in MC+ eyes as compared with the first end point (P < 0.001) and superficial foveal avascular zone enlarged (P < 0.001). Macular central thickness decreased between follow-ups only in eyes with INLc (P < 0.01). The final best-corrected visual acuity was better in eyes with INLc than in eyes with cysts present in all retinal layers (P < 0.01). There was no difference between the final best-corrected visual acuity in eyes with INLc and MC- eyes. Macular cysts are a common finding long after silicon removal. Vascular remodeling seems characterized by an initial increase of the vascular density of superficial capillary plexus in eyes with cysts, which is followed by its progressive decrease. The INLc is the most common pattern of cysts. They are associated with a progressive decrease of the central macular thickness without visual impairment.

Material removal on silicon towards atomic and close-to-atomic scale by infrared femtosecond laser

Ultrashort laser pulse is a widely used tool for high precision machining. However, the understanding on its minimum removal is still unclear. In this paper, single laser pulse (232 fs at 1030 nm) is used to study material removal of silicon from its (001) surface at near threshold fluence. The damage threshold, effective attenuation length, removal depth and ablation morphology are investigated systematically using atomic force microscopy. The minimum material removal of down to 1 nm is observed experimentally. A novel molecular dynamics method coupled with two temperature model is developed to reveal multiphoton ionization and explore the dynamic process. Results show that laser-induced plasma plays important role in the interaction process. The ablation crater is generated by plasma ejection and the outer rim around the crater is formed by the recoil pressure due to high pressure plasma expanding.

Reliability Treatment of Silicon in Oilfield Wastewater by Electrocoagulation

Scaling caused by silicate in oilfield wastewater gathering system pipelines can cause serious pipeline blockage. Therefore, this study adopts facile, effective and environment friendly electrocoagulation method to remove the silicon in oilfield wastewater. After confirming the level of factors through single factor experiments, the optimal scheme for electrocoagulation was selected by orthogonal experiments and verification tests, the silicon content would be dramatically decreased from 81.51 mg/L to 21.88 mg/L when pH = 6, reaction time = 20 min, current density = 27 mA/cm2 and wastewater temperature = 35 °C. In addition, the silicon removal rate would reach up to 85.90% when the pH of oilfield wastewater was kept as its original condition without changing other optimal factors; such an enhanced silicon removal effect could be attributed to the calcium ions chemical coagulation after the mechanism investigation.

Complexity of clay minerals and its effects on silicon dynamics in hypersaline coastal wetland soils, Brazil

Context Tidal dynamics and high evaporative rates in hypersaline tidal flat (HTF) soils favour a range of clay reactions and the formation of complex clay assemblages. HTFs have a geochemical environment conducive to mineral reactions, and therefore, clay mineral alteration controls essential nutrients in coastal wetlands. Aims The crystallochemical characteristics of clay minerals from two HTFs were studied to provide insights into the complexity of fine clay assemblages in HTF soils and their effects on Si biogeochemistry. Methods The fine clay fraction (&lt;0.2 μm) from these HTFs were investigated using X-ray diffraction (XRD) modelling, XRF, FTIR, TEM–EDS, and silicon sequential extractions. Key results The results have indicated the presence of endmembers and R0 mixed-layered minerals such as kaolinite, smectite, illite, kaolinite–smectite (K–S), kaolinite–illite (K–I), illite–smectite (I–S), and illite–vermiculite (I–V). In general, K–S was the dominant mineral in the samples, occurring in a range of kaolinite layers. Alteration of detrital kaolinite to other mixed-layered minerals occurs in soils, leading to silicon removal from the soil solution because of mineral genesis. There is Mg enrichment at the expense of Al in the samples, and bio-opal appears to be the source of Si for the kaolinite alteration process. Conclusions Our findings indicate that clay authigenesis is an important factor controlling Si dynamics in HTF soils, acting as a sink of Si during the formation of new clay phases. Implications Chemical reactions involving clay minerals are critical for deepening our understanding of the biogeochemistry of wetland soils.