The Study And Preparation Of Mullite Whiskers Via Industrial Solid Waste

Mullite （3A1₂O₃·2SiO₂） whisker is needle-like structure mullitemonocrystal, it possesses the performance of mullite, but has the bettermechanical property, the thermostability, the antioxidant, the thermal shockresistance, low thermal expansion, high strength at high temperature and highshear elasticity. For these reasons, as one of the excellent addition for theceramic, the development of mullite whiskers would be used in the field ofmachinery, electron and fuel.Fly ash and coal gangue are one massive solid discharge of industrial,the chemical composition are A1₂O₃and SiO₂. Fly ash is the fine ash fromexhaust gas of burned coal. Years slagging at present in China, the discharge offly ash had reached30million tons, and the slagging would increase. So muchfly ash would pollute the air, and it is harm to bodies. Coal gangue is solid wasteduring the coal mining and one of the black rock, who has low carbon content,the1000million tons has stored up so far. So much coal gangue would occupythe cultivated land, and cause fire hazard. Therefore, the recycling of industrialwaste to produce valuable materials attracts a great deal interest from scientistsalike.At present, the preparation methods of mullite whisker mainly containsfiring the powders, sol-gel, mineral decompose, dope the oxide, growing in situand molten-salt method. But the methods of sol-gel and mineral decompose areprejudice industrialization produce, because of complex process and highsynthesis temperature. However, the method of molten-salt possessessimpleness, applicability, low cost and others advantage. On the other side, themolten-salt combine the advantage of solution synthesis and solid synthesis, themolten-salt is mobile phase during the reaction, because of the low viscosity,these in favour of the growing of whiskers, and the morphology of the product.In this study, the industrial waste of fly ash and coal gangue are used asraw materials, aluminum sulfate as replenishers of Al₂O₃, Na₂（SO₄）, KCl andNaCl are used as molten-salt, the better micro-morphology of mullite whiskersare obtained. The phase formation and microstructure of the as synthesized whiskers were characterized via differential scanning calorimetry （DSC）, X-raypowder diffraction （XRD） and scanning electron microscopy （SEM）.The results indicate that the dispersed uniformly with high purity and aspectratio>15（40-70nm in diameter） mullite whiskers are synthesized via fly ash asraw materials at1000℃for3h, the molar ration of Al₂O₃and SiO₂is1.5with50wt%Na₂SO₄. When the coal gangue are used as raw materials, at1100℃for3h, the molar of Al₂O₃and SiO₂is1.5and the mass ratio of Na₂SO₄is65%, thehigh purity mullite whiskers were synthesized, the aspect ratio>30（35-65nm indiameter）.