Research On Mullite Whisker Reinforced Al-Si Refractory Castable Matrix

(1)By adding different content of crystalline AlF₃to the aluminum-silicon castable,focus on the effect of the addition of crystalline AlF₃on the mechanical properties of the mullite whisker toughened aluminum-silicon castable,and determine the optimal addition amount of AlF₃;（2）Add NH4F and Al（NO₃）₃·H₂O to the aluminum-silicon castable,and prepare different content of AlF3 in situ,focusing on the effect of in-situ synthesis of AlF₃on the properties of mullite whisker toughened aluminum-silicon castable,And determine the best in-situ content of AlF₃;（3）Based on Chapter（2）Experiment,different sintering temperatures are used for heat treatment of alumina-silica.The focus is on the effect of temperature on the properties of in-situ mullite whiskers to enhance the performance of alumina-silica.Add crystalline AlF₃as an additive to generate mullite whiskers in situ to toughen alumina-silica.The research found that:Crystalline AlF₃is conducive to the formation of mullite whiskers,but the addition amount should not be too much;when the addition amount of crystalline AlF₃gradually increases,the aspect ratio of mullite whiskers shows a trend of first increasing and then decreasing.And when the addition of AlF₃is 2wt.%,the maximum aspect ratio is 10.42.When AlF₃is added in too much amount,too much gas phase fluoride and fluorine gas will cause the growth direction of mullite to grow in two-dimensional direction,resulting in sheet-like structure of mullite,and the sheet-like structure cannot form a toughened structure,thereby reducing The strength of the specimen.Whiskers will interweave each other to form a grid structure.The whisker aspect ratio will directly affect the strength of the aluminum-silicon castable.When the addition amount of AlF₃is 2wt.%,the flexural strength of the sample reaches the maximum value,which is 34.72 MPa.Add NH₄F and Al（NO₃）₃·9H₂O as additives to prepare AlF₃in situ;then use AlF3 to generate mullite whiskers in situ to toughen aluminum-silicon castable.The research found that:The in-situ synthesis of AlF₃is conducive to the formation of mullite whiskers.With the increase in the in-situ production of AlF₃,the aspect ratio of mullite whiskers first increases and then decreases.When it is 1wt.%,the aspect ratio reaches the maximum value of 11.22;A large number of needle-like slender mullite whiskers can make the whiskers intertwined to form a network structure to form a mechanically toughened structure;when the in-situ synthesis of AlF₃is 1wt.%,the flexural strength at room temperature reaches the maximum.The maximum flexural strength at room temperature is 35.92MPa.Because the whiskers have the ability to block crack growth and release the stress at the crack tip,when the in-situ synthesis of AlF₃is 1wt.%,the residual flexural strength of the sample after 5,10,and15 thermal shocks still performs best.Add NH₄F and Al（NO₃）₃·9H₂O as additives to prepare AlF₃in situ;The mullite whisker toughened aluminum-silicon castable was generated in situ at different sintering temperatures.The study found that as the temperature rises,the sintering performance of the sample gradually appears,and the density of the sample first decreases and then increases.When the sintering temperature is 1600℃,The sample is the densest,and due to the sinterability of the sample and the toughening mechanism of the whiskers,the flexural strength of the sample reaches the maximum at room temperature,and the maximum value is 33.4Mpa.Because the formation of whiskers leads to a suitable porosity of the product,a suitable porosity will enhance the thermal shock resistance of the sample.When the sintering temperature is1400℃,the residual flexural strength of the sample after two thermal shocks reaches the maximum value.The value is 2.35MPa.