High-purity Si Powder Research Articles

Simultaneous preparation of high-purity silicides, eutectic Si/MSi2 (M: Nb, Ta, Mo, or W) alloys, and silicon through the separation of Si–M solvents using electromagnetic directional crystallization

• Refractory silicides and eutectic Si/MSi 2 (M: Nb, Ta, Mo, or W) alloys were prepared by separation Si–M solvent. • High-purity silicon can be obtained by acid leaching of eutectic Si/MSi 2 alloy. • A new approach for simultaneous preparation of high-purity refractory silicides, eutectic Si/MSi 2 alloys, and Si. • Mechanism separation and impurity removal of Si–M alloy was discussed. Refractory silicides, eutectic Si/MSi 2 (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/MSi 2 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 MSi 2 (NbSi 2 , TaSi 2 , MoSi 2 , or WSi 2 ) and eutectic Si/MSi 2 (Si/NbSi 2 , Si/TaSi 2 , Si/MoSi 2 , or Si/WSi 2 ) alloys are precipitated in sequence because the crystallization temperature of MSi 2 is higher than that of the eutectic Si/MSi 2 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 MSi 2 and eutectic Si/MSi 2 alloys. In addition, as the eutectic Si/MSi 2 alloys consist of Si and MSi 2 phases, high-purity Si powders (>99.98%) can be obtained by separating the Si and MSi 2 phases using acid leaching. The results indicate the feasibility of the new approach in preparing refractory silicides, eutectic Si/MSi 2 alloys, and high-purity Si.

Recovery of high purity Si from kerf-loss Si slurry waste by flotation method using PEA collector

Separation and recovery of high-purity Si powder from kerf-loss Si slurry waste is a critical challenge for the photovoltaic industry. A green surfactant poly (propylene glycol) bis (2-aminopropyl ether) (PEA) was employed as a collector to facilitate the separation of Si and SiC from kerf-loss Si waste during flotation process. Single flotation tests of Si and SiC were conducted using 5 × 10−6 mol/L PEA, respectively. The separation efficiencies of Si and SiC in conjunction with PEA adsorption mechanism were investigated. It was found that the maximum recoveries rate of SiC and Si were 90.59% (pH 9.00) and 80.93% (pH 1.96), respectively. Furthermore, the maximum Si grade was determined as 92.31% at pH 8.95 for the sinking part of the mixture generating excellent floatability and selectivity. Zeta potential measurements, FT-IR spectra, and XPS analyses demonstrated that PEA was present on the surface of Si and SiC through electrostatic and hydrogen-bond interactions. The adsorption mechanism was explained based on the results. This research provides an efficient and environmentally friendly route for the separation and recovery of high purity silicon from kerf-loss Si waste.

Purification of Metallurgical Grade Silicon Via the Mg-Si Alloy Refining and Acid Leaching Process

A novel process by combining Mg-Si alloy refining and acid leaching was suggested to purify metallurgical grade Si (MG-Si) in this paper. The proposed process was mainly composed of three steps, such as electromagnetic solidification, evaporation, and acid leaching. The results show that the precipitated Mg2Si crystals in the Mg-Si melt were successfully separated and enriched at the bottom of the sample because of the electromagnetic stirring and temperature gradient. Then, a porous structure Si with pore sizes ranging from nanometer- to micrometer-scale was obtained by evaporating Mg from the Mg2Si crystals. Finally, the high-purity Si powders with a purity of 99.995% were prepared by employing a successive acid leaching process. Most of the impurities (B, P, Fe, Ca, Ti, Ni, V, Cu) can be removed to less than 1 ppmw after the leaching process, indicating that an efficient elimination of impurities can be achieved with the help of the porous structure. Although bits of Mg was contained in the purified Si, it is expected to be eliminated by using a vacuum directional solidification. During the process, most of the magnesium can be recycled for cyclic utilization, which should be beneficial for the cost reduction. Therefore, it could be proposed that an efficient method of Si purification was obtained, which may be a valuable idea for the fabrication of solar grade silicon (SoG-Si).

A novel approach to prepare high-purity Si and Si/TiSi2 materials simultaneously using Ti-bearing blast furnace slag

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.

Recovery of silicon powder from kerf loss slurry waste using superconducting high gradient magnetic separation technology

A major challenge in recycling of silicon powder from kerf loss slurry waste is the complete removal of metal particles. The traditional acid leaching method is costly and not green. In this paper, a novel approach to recover high-purity Si from the kerf loss slurry waste of solar grade silicon was investigated. The metal impurities were removed with superconducting high gradient magnetic separation technology. The effects of process parameters such as magnetic flux density, slurry density, and slurry flow velocity on the removal efficiency were investigated, and the parameters were optimized. In one lot of control experiments, the silicon content was increased from 90.91 to 95.83%, iron content reduced from 3.24 to 0.57%, and aluminum content from 2.44 to 1.51% under the optimum conditions of magnetic flux density of 4.0 T, slurry density of 20 g/L, and slurry flow velocity of 500 mL/min. The result indicates that the superconducting high gradient magnetic separation technology is a feasible purifying method, and the magnetic separation concentrate could be used as an intermediate product for high-purity Si powder.

Optimization of Binder Burnout for Reaction Bonded Si<sub>3</sub>N<sub>4</sub> Substrate Fabrication by Tape Casting Method

It is a challenge from an industrial point of view to fabricate silicon nitride substrates with high thermal conductivity and good mechanical properties for power devices from high-purity Si scrap powder by means of thick film processes such as tape casting. We characterize the residual carbon and oxygen content after the binder burnout followed by nitridation as a function of the temperature in the temperature range of 300°C - 700°C and the atmosphere in a green tape sample which consists of high-purity Si powder and polymer binders such as polyvinyl butyral and dioctyl phthalate. The optimum condition of binder burnout is suggested in terms of the binder removal temperature and atmosphere. If considering nitridation, the burnout of the organic binder in air compared to that in a nitrogen atmosphere could offer an advantage when fabricating reaction-bonded Si 3 N 4 substrates for power devices to enable low carbon and oxygen contents in green tape samples.

자전 연소 합성법에 의한 고순도 실리콘 분말제조

High purity Si powder was prepared in the system of SiO₂-Mg combustion reaction. Various conditions of combustion reaction and leaching were investigated. As the particle size of Mg decreased and the compaction pressure increased the quantity of the unreacted powder was decreased. In the acid leaching of MgO, increasing particle size, reaction temperature, rotating speed and reaction time made leaching effect low. Final Si powder produced by combustion and leaching reaction, has a high purity of 99.9% with irregular shape.

Synthesis of Reaction Bonded Silicon Nitride from High Purity Si Powders

ABSTRACTSignificantly improved reaction kinetics and properties have been realized for reaction bonded Si3N4 (RBSN) by using Si powders having unusual physical and chemical characteristics combined with clean, oxygen-free processing conditions. For instance, complete nitridation can be achieved in < 1 h at 1150°C or < 100 m at 1250°C without pre-nucleation, or < 1 h at 1100°C with pre-nucleation. These compare with normal schedules of ∼100 h at 1470-1500°C. Resulting strengths (up to 870 MPa) and oxidation resistances of the RBSN essentially equal those of fully dense Si3N4 even though RBSN includes 25% open porosity. The results show that every aspect of the process, ranging from powder synthesis to < ppm levels of oxygen in the nitriding atmosphere, have demonstrable effects on the reaction kinetics and the resulting properties of the parts. With careful processing, reaction formed ceramics can compete advantageously with fully dense counterparts.

Kinetics of α- and β-Si3N4 formation from oxide-free high-purity Si powder

Available kinetic data for the nitridation of high-purity oxide-free Si powder are analysed. The analysis suggests that the α- and β-phases of Si3N4 are formed by separate and parallel reaction paths, and kinetic expressions for their formation are reported. The formation of the α-phase follows first-order kinetics, while the β-phase is formed by a phase-boundary-controlled rate law. These conclusions are consistent with other kinetic and micrographic analyses reported in the literature.

Oxidation and Fracture Strength of High‐Purity Reaction‐Bonded Silicon Nitride

Reaction‐bonded Si3N4 (RBSN) made from high‐purity Si powder is unusually resistant to degradation caused by exposures to air for up to 50 h at temperatures up to 1400°C. The weight gain during oxidation of this SiH4‐originating RBSN is approximately 10 times less than conventional RBSN. Contrary to normally observed strength degradations, room‐temperature strengths of this high‐purity, oxidized RBSN (avg = 435 MPa, max. = 668 MPa) remained at their unusually high, as‐processed levels after 1000° and 1400°C oxidizing exposures. Fracture toughness values were unaffected by oxidation (KIC= 2.3 to 2.4 MPa · m1/2). This superior oxidation resistance results from the high purity and the small diameter pore channels (0.01 to 0.06 μm) achieved in this SiH4‐originating RBSN.