Fabrication Of Silicon Nanowire From Fly Ash

Silicon nanowire, as a one-dimensional function material, has attracted so muchattention for its good stablity of semiconductor, electronic transport properties andphotoelectric effect. However, the preparation methods of silicon nanowires have theirown defects, which cost too much energy and time and not suit for industrialization. In thispaper, a novel and inexpensive method has been introduced to fabricate silicon nanowire.Ultrafine SiO₂powders, which were extracted from fly ash of Datang power plant byalkaline leaching, were materials to fabricate SiO₂nanofibers. Then silica nanofibers havebeen reduction of silicon nanowire by magnesiothermic reduction. The main results aresumarized as follow.1. Ultrafine SiO₂powders as the silicon source, different polymer PAN and PVP asthe organic carrier. By exploring the different experimental parameters, compositenanofibers have been fabricated through combining sol-gel and electrospinning.Comparison of results, the optimal reaction conditions has been determined that PAN asthe polymer carriers, the molar ratio of SiO₂/PAN is1:1.2. In order to remove the organic polymer and choose the best curing temperature, thecomposite were calcined at different temperature in furnace. The nanofibers was heatedfrom room temperature to240℃at a rate of5℃/min in air, then in high purity nitrogenatmosphere the nanofibers has been calcined at1000℃for4h at a heating rate of2℃/min from240℃to1000℃. Finally the fibers were heated from1000℃to1200℃ata rate of2℃/min and held at that temperature for2h, then cool down to the roomtemperature in air.3. In this paper, a new method to synthesis of silicon nanowire has been reported. Inthe experiment, two different reducing agents active carbon and magnesium have beenchoosed. In the furnace different ration of reductant have been added to optimize thereaction condition. The results showed that only SiC has been produced after the activatedcarbon react with silica.And silica nanofibers and magnesium have been transferred into aceramic boat, and the mole ratio of Mg/SiO₂is23:1. Such ceramic boat was pushed into a tubefurnace, which the furnace was filled with nitrogen. The temperature of ceramic boat washeated to650℃at a rate of10℃/min, and then held at this temperature for2h. The composite materials were immersed in HCl solution and HF solution, respectively, to getthe pure silicon nanowire. Silicon nanowires electrodes were fabricated by spreading theslurry on current collector. The electrode has been tested in galvanostatic charge-dischargeexperiments to investigate the application of silicon nanowires in lithium-ion batteriers.