Structure Analysis Of Silica Fume And Preparation Of Silica Fume-Magnesium Cement Material

As a kind of inorganic non-metallic micro-nano powder,industrial waste silica fume has been widely used in composite materials,refractories and building materials.Because silica fume is amorphous particles formed by rapid temperature drop and condensation,the further purification and application of silica fume are restricted by the problems of complex structure and poor dispersion.?1?The silica fume was treated by water washing magnetic separation,water flow classification,microwave acid leaching and high temperature calcination.The results show that the silica fume treated by water washing magnetic separation,water flow classification and microwave acid leaching only removes some impurities of Fe₃O₄,free carbon and metal oxides in the silica fume.The crystalline state of silica fume is changed by calcining silica fume at high temperature.At 800 ^oC,the silica fume transforms from amorphous glass phase to cristobalite phase.Through fitting analysis of silica fume impurity,it has been found out that in addition to SiO₂,silica fumealsocontaincompoundslike?SiO₂?_0.694?Na₂O?_0.306,?K,Ca?₂[Mg₄.3Fe_0.7][Si_7.2Al_0.8O₂₂]?OH?₂,Mg₃H₂?SiO₃?₄ as well as small amount of CaO,MgO and other mineralizer.?2?Silica fume was thermally treated to 700-1100°C in air to transform it into crystals and cause it to reach the metastable cristobalite state.when the treatment temperature reaches 800°C,the silica fume undergoes a displacive phase transformation and begins to nucleate.At 1100°C,the silica fume fully converts to cristobalite.Alkali metal impurity compounds in the silica fume promote the phase transformation of silica fume.?3?KH-570 silane coupling agent was used to modify the surface of silica fume under acidic conditions.The oil absorption value of the modified silica fume was significantly reduced,and the hydroxyl number on the surface was sharply reduced.The molecule of KH-570 silane coupling agent was successfully grafted on the surface of silica fume in the form of chemical bonds.The agglomeration of silica fume was reduced and the dispersion was improved.KH-570 silane coupling agent mainly passed through Surface-OH forms hydrogen bond association and is adsorbed on the surface of silica fume particles.?4?The silica fume-magnesium oxychloride cement with different content of silica fume was prepared by using silica fume and magnesium oxychloride cement.It was found that the compressive strength,immersion and sulfate softening coefficients of magnesium oxychloride cement samples were 78.85 MPa,0.72 and 0.76respectively when the mass ratio of MgO:MgCl₂:H₂O was 7:1:15.When the content of silica fume is 30%,its compressive strength,water resistance and sulfate corrosion resistance are the best,the compressive strength is 83.45 Mpa,and the softening coefficients are 0.74 and 0.78,respectively.In addition,the use of industrial waste silica fume to prepare silica fume-magnesium oxychloride cement can significantly reduce the preparation cost of magnesium oxychloride cement materials and increase the added value of silica fume.