Preparation of SiC Porous Ceramics by Crystalline Silicon Cutting Waste

SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30%,40%,by mass) on the phase composition,microstructure,sintering properties,cold compressive strength and thermal shock resistance of as-prepared Si C porous ceramics were investigated. The results show that:( 1) addition of NH4HCO3 remarkably influences the apparent porosity and cold compressive strength of specimens. The apparent porosity achieves its maximum value( 63. 40%) when 40% NH4HCO3 is added,while the minimum cold compressive strength is 4. 77 MPa;( 2) the specimen with 40% NH4HCO3 has the best thermal shock resistance. The thermal cycling times between1 000 ℃ to room temperature reach 62;( 3) the addition of NH4HCO3 does not remarkably affect the phase composition of the specimens;( 4) the specimens include a large number of SiC particles and a small amount of SiC whiskers.

Effects of Pore-forming Agents on Properties of Silicon Carbide Porous Ceramics Prepared from Crystalline Silicon Cutting Waste

SiC powder was rapidly synthesized in an induction furnace with crystalline silicon cutting waste and active carbon as raw materials,and then SiC porous ceramics were prepared at 1600 t for 4 h with carbon embedded using the powder as raw material,the starch and the graphite as pore-forming agents.Effects of additions of different pore-forming agents on the phase composition,microstructures,physical properties,and cold crushing strength of the porous ceramics were investigated.The results show that the main crystalline phases of the synthetic powder areα-S iC(6H-SiC)andβ-SiC(3C-SiC).The phase composition of the porous ceramics includesα-S iC(6H-SiC),β-SiC(3C-SiC),FeSi,quartz and Si2N20.The apparent porosity and closed porosity of the porous ceramics prepared by adding starch are higher,and the cold compressive strength of the porous ceramics added with graphite is higher.As increasing the additions of the starch,the apparent porosity,closed porosity and linear shrinkage ratio of the porous ceramics increase,and the bulk density decreases correspondingly.When 20 mass%starch is added,the apparent porosity,closed porosity,linear shrinkage ratio and cold compressive strength are 57.05%,2.03%,5.10%and 10.20 MPa,respectively.

Recovery of high purity silicon from SoG crystalline silicon cutting slurry waste

The composition and size distribution of cutting waste were characterized. The Si-rich powders were obtained from the cutting waste using a physical sedimentation process, and then further purified by removing impurity using acid leaching. The effects of process parameters such as acid leaching time, temperature and the ratio of solid to liquid on the purification efficiency were investigated, and the parameters were optimized. Afterwards, the high-purity Si ingot was obtained by melting the Si-rich powders in vacuum furnace. Finally, the high purity Si with 99.96%Si, 1.1×10^-6 boron （B）, and 4.0×10^-6 phosphorus （P） were obtained. The results indicate that it is feasible to extract high-purity Si, and further produce SoG-Si from the cutting slurry waste.

Coupling magnetic particles with flocculants to enhance demulsification and separation of waste cutting emulsion for engineering applications

Magnetic particles were coupled with a flocculant to enhance the demulsification and separation of waste cutting emulsions.The optimal magnetic particle size and critical magnetic field conditions were investigated to achieve large-scale engineering application of magnetic demulsification separation for waste cutting emulsion treatment.The micro-scale magnetic particles were found to show comparable effects to nano-scale magnetic particles on enhancing the demulsification and separation of cutting emulsions,which are beneficial for broadening the selectivity of low-cost magnetic particles.The critical magnetic separation region was determined to be an area 40 mm from the magnetic field source.Compared to the flocculant demulsification,the magnetic demulsification separation exhibited a significant advantage in accelerating flocs-water separation by decreasing the separation time of flocs from 180-240 min to less than 15 min,compressing the flocs by reducing the floc volume ratio from 60%-90%to lower than 20%,and showing excellent adaptability to the variable properties of waste cutting emulsions.Coupled with the design of the magnetic disk separator,continuous demulsification separation of the waste cutting emulsion was achieved at 1.0 t/hr for at least 10 hr to obtain clear effluent with 81%chemical oxygen demand removal and 89%turbidity reduction.This study demonstrates the feasibility of applying magnetic demulsification separation to large-scale continuous treatment of waste emulsion.Moreover,it addresses the flocs-water separation problems that occur in practical flocculant demulsification engineering applications.

Scalable synthesis of N-doped Si/G@voids@C with porous structures for high-performance anode of lithium-ion batteries

The co-utilization of silicon(Si) and graphite(G) has been considered as the preferred strategy to achieve high energy density anode materials,but the effective synergistic integration of Si and graphite is still a challenge and it is necessary to find a scheme to accommodate the large-scale production of Si/graphite anodes.In this work,silicon cutting waste from the photovoltaic industry was used as raw material,mixed with graphite,pitch,and polyvinylpyrrolidone,and subjected to high-energy ball milling.The mixture was then heated in an Ar atmosphere for the carbon coating,and the resulting Si/graphite/carbon(Si/G/C) composite was etched to remove the thicker SiOx layer formed on the Si surface to allow the pores between the Si and the carbon matrix to obtain Si@voids/G@C.Benefiting from the integrated structural design and the significantly enhanced electronic conductivity,the Si/G@voids@C composite exhibited the first dischargespecific capacity of 2530 mAh·g^(-1) with an initial coulombic efficiency(ICE) of 86.7%,and the remaining capacity exceeded 1000 mAh·g^(-1) after 550 cycles at 1.5A·g^(-1).Notably,full lithium-ion batteries with a Si/G@voids@C anode and LiFePO_4 cathode delivered a stable capacity of 140 mAh·g^(-1).The synthesis method is facile and cost-effective,providing an integration strategy for Si and G with a potential scheme for large-scale commercial applications.