Study Of Synthesis And Properties Of Tungsten-based Composite Power Nanomaterials

In recent years , with the rapid development of microelectronics and communication industry,the fast growing up of nanomaterials research was stimulated.It is very significantly important for the development and application of nanomaterials to seek new facile synthesis method,exploit new materials system and discover their special function.Tungsten-based materials play an important and unique role in defence and high-tech industries . Owing to the high melting point of tungsten , their applicationsrely on high temperature powder metallurgy processes.Therefore,refinement of their powders to ultrafine or nanometer size is valuable,as this will lower their sintering temperature and improve their properties.Nanomaterials based on tungsten is a kind of advanced materials with many potential application.Tungsten oxide is an n-type semiconductor with wide forbidden band,with excellent photocatalysis,and with application in disposal waste gas and polluted water.Bi₂WO₆ have been studied as a promising sensitive material for NO gas sensors.In this dissertation,we prepared tungsten trioxide and bismuth tungstate nanomaterials using low-cost,facile sodium tungstate as raw material.While in the hydrothermal/solvothermal process,the final particles are usually formed through a dissolution-crystallization process,and the as-prepared products are well-crystallized and in narrow size distribution.Reaction conditions that have important effects on the final products,and have also been discussed in details.We synthesized WO3 through different methods , hydrothermal and solventhermol with tungstic acid precursor prepared from Na₂WO₄.The phases,morphologies,particle size and distribution were analysed and characterized by using XRD,SEM.Ethanol was added in the system as stabilization,it can control the size and disperse of WO3 nanoparticles.And it cannot be used too much,for the Na₂WO₄ has low solubility in water and the solubility will reduce with the increasing of contents of ethanol.Through hydrothermal method,orthorhombic Bi₂WO₆ have been synthesized in the acidic conditions and we got many morphologies such as flower-like,sphere-like and so on.UV-visible diffuse reflection spectra of the prepared Bi₂WO₆ indicated that they had absorption in the visible region,but a blue shift appeared compared to their bulk counterparts.And in the alkaline conditions,we got the tetragonal Bi₁₄W₂O₂₇.With the increase of ethanol,the X-ray diffraction indicated that the intensity reduced,and the width increased.When we used the pure ethanol without water,we got the product which had good absorption of Congo red.After annealing in the muffle at 500℃for 0.5 h,We got pure orthorhombic Bi₂WO₆ when dealt with ethanol and we got 2 kinds of products,orthorhombic Bi₂WO₆ and tetragonal Bi₁₄W₂O₂₇ when precursor hadn't been dealt with ethanol.The ethanol took an important role in the crystallization process.