Silicon Kerf Research Articles

Fabrication and properties of silica/mullite porous ceramic by foam-gelcasting process using silicon kerf waste as raw material

Silica/mullite porous ceramic with high porosity and low density was fabricated via foam-gelcasting with silicon kerf waste and corundum powder as raw materials. The effects of solid loading on porosity, bulk density, compressive strength, thermal conductivity and microstructure were systematically investigated. The porosity of porous ceramics decreased from 84.1% to 25.4%, bulk density increased from 0.67 to 1.78 g cm−3, compressive strength increased from 3.60 to 20.54 MPa and thermal conductivity increased from 0.204 to 0.892 W (m K)−1 as the solid loading increased from 50 to 65 wt%. Moreover, the relationship between microstructure and mechanical properties was discussed in detail.

Thermodynamic study on the carbothermal nitridation synthesis of silicon nitride using silicon kerf loss

A novel way to produce the silicon nitride using cheaper silicon kerf loss instead of expensive pure silicon as a raw material has been studied through thermodynamic analysis and Gibbs free energy minimization method. The mass fraction of Si3N4 in products increases with increasing the temperature at atmospheric pressure with mole ratio of carbon to oxygen of 1:1. More content of carbon added in silicon kerf loss, the less content of Si2N2O and the more content of SiC formed in the product. In addition, the pressure parameter obviously influences the composition of nitridation products, which can be attributed to lots of gas-phase reactions existing in the nitridation process. With the pressure increased, the mass fraction of Si3N4 decreases below 1500 °C, while it increases above 1500 °C. In conclusion, the optimal products contain Si3N4 of 95.6 mass%, Si2N2O of 1.7 mass% and SiC of 2.7 mass%, which formed at 1032 °C and 1 × 10−5 bar with mole ratio of carbon to oxygen of 1:3.

Recycling of silicon kerf waste for preparation of porous SiCw/SiC membrane supports by in situ synthesis

AbstractRecycling has enormous economic benefits and practical significance under the context of gradually increasing solid wastes. In order to recycle and reuse the silicon kerf waste, in this work, porous SiCw/SiC ceramics were successfully prepared by in situ synthesis from silicon kerf waste and fired at 1400‐1500°C for 4 hours. The results showed that these porous ceramics, reinforced by the interlocking whisker, revealed high apparent porosity (48.02%‐51.76%) and cold compressive strength (5.68‐9.54 MPa). Furthermore, the practicable pore size (2.09‐2.53 μm) and decent durability showed the potential of these porous ceramics as membrane supports. This work verified the possibility of the SiC‐based ceramics prepared from the silicon kerf waste.

An efficient way of recycling silicon kerf waste for synthesis of high‐quality SiC

AbstractIn this paper, an efficient approach of recycling and reutilizing of silicon kerf waste (SKW) to prepare high‐quality silicon carbide (SiC) by carbothermic reduction method is reported. SKW used as silicon source and petroleum coke as carbon source were submitted to the induction furnace for high‐temperature smelting. The effects and mechanism of smelting temperatures and time on micro morphology, crystal structure, and purity of the obtained high‐quality SiC were studied by X‐ray diffractometry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) as well as the Raman and photoluminescence (PL) analyses. Raman and PL analyses have verified the existence of SiC crystal types as 6H and 3C. The SEM and energy dispersive X‐ray spectroscopy results show that the SiC particles size increases with the increasing smelting time and demonstrate that the iron impurity was enriched at the edges of SiC which can be easily removed by the subsequent acid leaching. The enrichment process can be accelerated by the increase of temperature. In addition, the carbothermic reduction mechanism of SKW was studied in detail. The obtained SiC powder after purification can reach 98.7% through this new method, which is of low cost, high efficiency, and environment friendly.

A metallurgical route to upgrade silicon kerf derived from diamond-wire slicing process

Silicon kerf generated during the diamond-wire slicing process contains various impurities and are considered industrial waste. In order to utilize the waste, a feasible process to purify silicon kerf by a combination of slag treatment and acid leaching was developed. The results demonstrated that the Na2OSiO2 slag refining can effectively enhance the yield of the silicon kerf, and the Si yield was found to be 63.2%. The combined processes were able to reduce the total concentration of major impurities (Fe, Al, Ca, Ni, B, and P) from 6998 to 58 ppmw with a removal efficiency of 99.2%. The purity of the recovered Si was upgraded to from 93.3% to 99.98%. The mechanism suggests that impurity removal was facilitated by both the oxidation and the segregation of impurities to intermetallic precipitate phases. These precipitates can then be eliminated by acid leaching, and the extraction process of metallic impurities was mainly dominated by the surface chemical reaction.

Silicon anodes for lithium-ion batteries produced from recovered kerf powders

Silicon kerf waste from a photovoltaic silicon production process is assessed as an anode material for application as a lithium ion battery anode. In contrast to previous studies, the Si-kerf is used as-produced, with no chemical treatment or physical processing beyond solvent PEG removal. The as-produced Si-kerf performed as well as, or better than, previously reported Si-kerf anodes and is found to outperform a cleaned Si-kerf sample from blade sawing with a larger particle size. This highlights the advantage of the diamond wire cutting process, which yields relatively small particles. In half-cell testing, a cycle life >300 cycles at a capacity of 1000 mAh g−1 is achieved with high levels of FEC addition. Full-cell testing against an NMC 442 cathode resulted in specific capacities up to 150 mAh g−1 (NMC). A relatively high degree of lithium consumption arising from repeated SEI formation is present. It is concluded that pure Si-kerf is unsuitable for commercial application in Li-ion cells.

Porous silica/mullite ceramics prepared by foam-gelcasting using silicon kerf waste as raw material

Porous silica/mullite ceramics with high porosity, sufficient compressive strength and low thermal conductivity were successfully prepared by foam-gelcasting method using silicon kerf waste as raw material. Microstructures of the as-prepared porous ceramics were found complex, depicting large-sized spherical pores, circular window pores, and small-sized pores present on internal walls. Effects of temperature on porosity, bulk density, compressive strength, and thermal conductivity were investigated. The thermal conductivity of the samples with a bulk density of 0.65 g/cm3, a porosity of 86.7%, and a compressive strength of 3.19 MPa was 0.178 W/(m·K), indicating that it can be used in the field of thermal insulation materials.

Recycling and reuse of kerf-loss silicon from diamond wire sawing for photovoltaic industry

With the rapid growth of the global photovoltaic (PV) industry, the waste from PV industry cannot be ignored, especially the solid wastes from silicon kerf loss and the used quartz crucibles from silicon casting. The silicon kerf loss during wafer sawing was nearly 160,000 tonnes and the used crucible waste was nearly 70,000 tonnes in 2017. With the transition of wafering technology from the slurry-based wire to diamond wire sawing, recycling and reuse of kerf-loss silicon have become more feasible due to the lower impurity contents. In this paper, we aimed to find a simple approach to recycle the kerf loss and identify the purity for reuse. We first analyzed the contents of the as-received kerf-loss silicon from the industry. Then, suitable acids and refining procedure were proposed. The metals, especially nickel, could be easily reduced to several ppmw, boron and phosphorous to sub-ppmw, and carbon to several hundred ppmw, while oxygen was less than 5 wt%. Although the purity of the recycled silicon was not sufficient for casting feedstock, it had a comparable purity of about 5 N with the commercial silicon nitride releasing agent and crucibles used in silicon casting for solar cells. Because the nitride crucibles could be reused a few times for casting, the used crucible waste could be significantly reduced as well.

Separation and purification of silicon from cutting kerf-loss slurry waste by electromagnetic and slag treatment technology

The recovery of silicon from cutting kerf-loss slurry waste for the polycrystalline silicon production has been becoming a meaningful and urgent issue. In this paper, a united method of combining electromagnetic separation and slag treatment technology was used to separate and purify silicon from silicon kerf. The low melting compound of Na3AlF6 is added to the synthetic binary CaO-SiO2 slag, which can improve the separation effect of silicon from slag phase. The mechanism of physical separation and chemical purification of silicon from cutting kerf-loss slurry waste was investigated. The experimental results show that the electromagnetic stirring has an obvious effect for silicon separation in spite of no slag addition. The addition of CaO-SiO2 or CaO-SiO2-Na3AlF6 slag can further improve the separation rate of silicon. The purity of separated silicon is about 99.47% after the synthetic CaO-SiO2-Na3AlF6 slag treatment and reaches 99.98% followed by a vacuum directional solidification treatment. The recovered silicon from cutting kerf-loss slurry waste by this method can meet the purity requirement to the raw materials for silicon ingot casting.

The impact of damage etching on fracture strength of diamond wire sawn monocrystalline silicon wafers for photovoltaics use

To reduce silicon kerf loss, we have cut silicon bricks into wafers using a thin diamond wire (the diameter of core wire: 80 µm, the average size of abrasives: 10 µm). Damages caused by diamond wire sawing are responsible to have an asymmetry in fracture strength, a lower strength in parallel bending and a higher strength in perpendicular bending to the saw marks. To elucidate the asymmetry to the depth of subsurface damage, front and backside surfaces of wafers are etched in 3, 5, and 10 µm depth by 24% KOH aqueous solution. By etching 3 and 5 µm, the strength are enhanced by a factor of 1.96 and 2.9 times in parallel bending and by 1.03 and 1.31 times in perpendicular bending compared to bare wafers. Etching more than 5 µm removes the asymmetry, showing the equal strength in the bending in both directions. We cystallographically consider several fracture mechanisms of bare and etched wafers through the observation of each fracture surface.

Recycling Si-kerf from photovoltaics: A very promising route to thermoelectrics

Large scale photovoltaic technology require Si wafers and cutting process has the significant disadvantage of disposing typically more than 50% of high purity material as waste kerf. Recycling silicon kerf is of increasing interest, focusing on various applications such as batteries, heat exchangers, color glasses etc. In this work, the case of thermoelectric material production is proposed and explored. Slurry waste from cutting Si wafers was processed, aiming to obtain powders with high Si concentration for the preparation of thermoelectric silicides. Mg2Si1-x-ySnxGey based materials were prepared using processed Si-kerf and their properties were evaluated. Structural features, as well as thermoelectric performance of the silicides are presented and compared to previously synthesized materials using a high purity Si source. A quite high figure-of-merit value of these multiphase materials was achieved, reaching up to 1.3 for the Sn-rich and 1 for the Si-rich compositions at 800 K.

Clean enhancing elimination of boron from silicon kerf using Na2O-SiO2 slag treatment

Abstract Silicon kerf waste can be used as a secondary resource for the recovery of high purity silicon for solar cells production. Boron is amongst the most deleterious impurities in silicon and its concentration should be strictly controlled. Slag treatment is considered an effective method to extract impurities, especially boron, from silicon kerf. The study investigated the feasibility and optimization of a process for producing high-purity silicon from sawing waste by slag treatment. The slag system studied was Na2O-SiO2 and the effects of holding time, slag composition, and slag:kerf ratio on boron distribution were investigated. The optimum conditions for refining of silicon kerf at 1923 K were found to be a slag of 65 wt.% Na2O−35 wt.% SiO2 and treatment for 30 min. This resulted in reduction of boron concentration in silicon from 8.6 to 1.0 ppmw, corresponding to a removal efficiency of 88%. Investigation of the boron transfer mechanism indicated that mass transfer of boron in slag is likely the rate controlling step of the overall process. The mass transfer coefficients for boron in silicon and slag were 3.6 × 10−6 cm⋅s−1 and 5.8 × 10−6 cm s−1, respectively.

Fabrication of Si2N2O ceramic with silicon kerf waste as raw material

SiC and Si in silicon kerf waste of photo-voltaic (PV) industry produced by a slurry technology are difficult to be separated for recycling due to their similar density and particle sizes. In this work, silicon kerf waste after removing the glycol and metal was characterized, then used as raw material for producing Si2N2O ceramics. In the silicon kerf waste, besides SiC and Si, amorphous SiO2 exist because of the reaction of Si with water during the storage time. Thermodynamic calculation showed that, ascribing to the reaction of Si, N2 with SiO2 and the reaction of SiC, N2 with SiO2 at high temperature in N2 atmosphere, the Si was exhausted and the SiC was decreased to form the Si2N2O. With the content of sintering additives increasing, the porosity of the samples was decreased, the bulk density was increased, and the strength of the samples was increased. It would be a reasonable method for fully utilizing the silicon kerf waste to fabricate Si2N2O composite ceramic without separating the SiC and Si.

Anodes for Lithium Ion Batteries Produced from Recovered Silicon Powders

Lithium Ion Batteries (LIB) offers the highest energy density among rechargeable batteries technologies. However, improvement in materials are needed for LIB in order to increase energy density, safety, durability, decrease cost and allow the further deployment of technologies like electric vehicles and energy storage. One way to improve these batteries is to develop new electrodes, both cathode and anode, resulting in higher energy density. Graphite is today used as anode materials, but Silicon has been extensive studied due to their approximately 10 times higher gravimetrical capacity. However, it is well known that silicon has challenges related to volume expansion during (de)lithiation upon cycling. Several proposed solutions, like nanostructuring, nanowires, encapsulation etc. have been proposed. Here we present initial work, using Silicon kerf (recovered Silicon powders from cutting of silicon ingots). Silicon kerf was delivered by the ECOSOLAR partner Garbo S.r.l. and the materials were cleaned to remove most of the impurities. The electrochemical performance of Silicon kerf was investigated in half cells. The silicon was mixed with Super C 65 carbon black as conducting agent and Na CMC as binder. Na CMC was dissolved in an aqueous solution containing KOH and citric acid at pH 3 to facilitate chemical bonding between the binder and the active material. Electrodes were fabricated by tape casting on plain Cu foil as current collector. Casts with varying thickness were produced to investigate the effect of electrode loading. C2016 coin cells was prepared using electrolyte consisted of 1M LiPF6 dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 by vol) added 5 wt% FEC (fluoroethylene carbonate). Initial studies for using silicon kerf as a source for high capacity anode materials in lithium ion batteries has demonstrated that kerf should be evaluated further to determine the long time cycling stability of this materials. The materials were evaluated both to determine the maximum capacity and stability using capacity limited cycling. The electrodes using Si kerf were stable for 150 cycles during capacity limited cycling using a loading of 0.6 mg/cm3 and a bit lower cycle stability for electrodes with higher loading. It must be highlighted that the electrode structures and composition, electrolyte composition etc. has not been optimized. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 679692.

Carbon elimination from silicon kerf: Thermogravimetric analysis and mechanistic considerations

40% of ultrapure silicon is lost as kerf during slicing to produce wafers. Kerf is currently not being recycled due to engineering challenges and costs associated with removing its abundant impurities. Carbon left behind from the lubricant remains as one of the most difficult contaminants to remove in kerf without significant silicon oxidation. The present work enables to better understand the mechanism of carbon elimination in kerf which can aid the design of better processes for kef recycling and low cost photovoltaics. In this paper, we studied the kinetics of carbon elimination from silicon kerf in two atmospheres: air and N2, under a regime of no-diffusion-limitation. We report the apparent activation energy in both atmospheres using three methods: Kissinger, and two isoconversional approaches. In both atmospheres, a bimodal apparent activation energy is observed, suggesting a two stage process. A reaction mechanism is proposed in which (a) C-C and C-O bond cleavage reactions occur in parallel with polymer formation; (b) at higher temperatures, this polymer fully degrades in air but leaves a tarry residue in N2 that accounts for about 12% of the initial total carbon.

Use of a thermal plasma process to recycle silicon kerf loss to solar-grade silicon feedstock

Abstract The objective of this study was to recycle the dust generated in the slicing of silicon wafers (silicon kerf) by means of a two-stage thermal plasma process. In the first stage, the silicon particles are injected in a plasma jet where silicon oxides and carbon impurities are removed by vaporization. In the second stage, the purified silicon droplets are collected in a silicon bath maintained in a hot-wall crucible. The optimal operating conditions for reduction were determined by injecting into the plasma jet a commercial silicon powder of known degree of oxidation and measuring the attained degree of reduction. Also, silicon powders from wafer slicing were processed in the two-stage plasma set-up. The results of these tests showed that the deoxidation rate of the final silicon ingot was as high as 80% and the initial carbon concentration decreased by 85%. The purification was essentially controlled by the residence time of particles in the hottest zones of the plasma jet and the partial pressure of oxygen in the processing atmosphere.

Elimination of Carbon Contamination from Silicon Kerf Using a Furnace Aerosol Reactor Methodology

Approximately 40% of the refined silicon is lost as sawdust (kerf) during the cutting process while producing wafers. Attempts have been made to recycle this kerf, but abundant impurities such as carbon (∼13000 ppm) burden its recovery. Using conventional bulk heating methods to remove carbon requires long residence time and inevitably causes silicon oxidation. This makes the treated kerf unsuitable for further processing and reuse. A novel aerosol method that is effective for selective carbon removal from silicon kerf at low residence times is described. The design of the aerosol process is supported by thermogravimetric analysis of kerf that provides insights into kinetics of the carbon removal process. At 900 °C in an air atmosphere carbon was removed below detection levels at a residence time of 6 s. Under the same conditions in a nitrogen atmosphere, 90% elimination of carbon was measured. Minimal oxidation of the Si sample was observed under these conditions.

Recycling of kerf loss silicon derived from diamond-wire saw cutting process by chemical approach

Treatment processes of the kerf loss silicon using a chemical approach, hydrobromination reaction, have been investigated. Since the kerf loss silicon is generated in the cutting process of silicon ingot using a diamond wire saw, the sample in a form of wet cake was composed of fine particles of silicon kerf, cutting lubricant, and metallic impurities. The removal efficiency of lubricant and metal impurities using acetone and acid solutions, respectively, were examined by thermal and elemental analyses. The heat treatment was necessary, rather than the washing with acetone, for complete removal of the lubricant from the sample. After being treated successively with organic solvent (acetone) and acid (HNO3 and HCl), the dry sample obtained at each step was exposed to HBr gas in a flow reactor heated at 400°C. The reactivity was evaluated with respect to the conversion of HBr. The HBr conversion was much higher with the use of kerf silicon that did not experience acid treatment. Furthermore, the metal impurity concentration without acid treatment after the reaction was much lower than that with acid treatment. Further, to examine the impact of abrasive grain on the purity of the obtained products, diamond particles were intentionally added to the silicon sample. The presence of diamond gave little influence on the metal impurities in products, indicating that the operation of hydrobromination can eliminate the important steps adopted in the traditional purification process for kerf loss silicon with the acid treatment of metallurgical approach.

Characterization of Silicon Kerf and the Effect of Grinding on the Synthesis of SiC Powder

Characterization of silicon kerf from photovoltaic silicon-wafer production was carried out. Also, SiC powder was synthesized using high purity silicon kerf by varying grinding conditions. With increase of grinding time, surface of the silicon was oxidized to form silicon oxide. Also, it was observed that the unreacted silicon oxide and free silicon amount in the SiC powder increases with an increasing grinding times, even though silicon particle size of the starting material is decreased.