A Study For Preparation Of Si₃N₄ Nanowires By High Temperature Nitridation Of Recovered Sawdust Silicon

Due to the excellent mechanical and photoelectric properties,Si₃N₄ nanowires have a wide range of applications in many fields such as nanocomposites,solar cells and optoelectronic devices.In existing several ways of preparation of silicon nitride nanotubes,such as carbon thermal reduction method,thermal evaporation method,pioneer body heat method,combustion synthesis methods such as common problems of high cost,difficult to control product size.In general,Si₃N₄ powder can be produced in large quantities by direct high-temperature nitriding of silicon powder,but only a small amount of Si₃N₄ nanowires can be produced.In this paper,a new direct nitride method was proposed to fabricate?-Si₃N₄ nanowires with silica sawdust powder,which is difficult to be effectively used in the photovoltaic field,to provide data and theoretical support for the expansion of industrial production of Si₃N₄ nanowires.A large number of?-Si₃N₄ nanowires with diameters of less than 60nm and length of centimeter were obtained on the surface of the powders by optimizing the nitriding method and adjusting the nitriding process parameters,using NH₃ pretreatment process in the flow of N₂/H₂(95:5)mixture atmosphere at 1350?.Among them,Although NH₃pretreatment can obviously improve the yield of Si₃N₄ nanowires,it is not conducive to their growth.Nitrogen mixed with 5%H₂ as nitridation atmosphere can better support the growth of products.In the temperature range from 1300?to 1380?,with the rise of reaction temperature,the yield of Si₃N₄ nanowires increased first and then decreased,and the product morphology was obviously different.At 1350?,the product yield was the highest and the morphology was the best.For different holding time,with the extension of holding time,the yield and length of nanowire products showed an increasing trend.However,for the raw materials of the experimental volume,the 5h nitriding time showed the best product morphology and more uniform diameter size.Under the conditions of different heating rates,the slower the heating rate is,the more conducive to the crystallization of silicon nitride.However,if the heating rate is over5?/min,the surface morphology of the product nanowires gradually becomes rough with the acceleration of the heating rate,and accompanied by the appearance of Si₂N₂O components.Through the literature research and thermodynamic calculation,found that:under the condition of 1350?,difficult to form and participate in silicon vapor and liquid silicon nitride,silicon nitride to participate in solid state reaction products not nanowires in morphology,and participate in the Si O gas nitriding reaction while gibbs free energy?G is greater than zero,but can be formed through Si₃N₄ location of O₂consumption,promote the reaction.In addition,the nitriding reaction with Si O gas is easier to realize the synthesis of?phase.Based on thermodynamic analysis and experimental characterization results,prediction,this method under the nucleation of nanowires products relies mainly on the highly reactive nitrogen atoms of NH₃produced at high temperature,and the growth of nanowires products rely mainly on the surface of coating a layer of amorphous oxide,oxide layer have the effect of collection,adsorption reaction gas,through the way of vapor deposition growth nitriding silicon nanowires.Although the amorphous oxide layer exists on the surface of the products,it can be removed by simple pickling process.