Research On The Synthesis And Mechanism Of Magnesium Borate And Aluminum Borate Whiskers

Borate whisker is a new type of inorganic nonmetallic materials,it has excellent properties of high temperature resistance,high heat resistance,corrosion resistance,good mechanical strength,light weight,high hardness and high elastic modulus.It has been widely used in the field of composite material synthesis.In this paper,the magnesium borate whisker and aluminum borate whisker were prepared by sol-gel method and high temperature cosolvent method,respectively.The properties of the products were studied by changing the type and proportion of raw materials,the pH of the solution,the synthesis temperature,the calcination time and the heating rate.The composition,structure,microstructure and growth mechanism of magnesium borate whisker and aluminum borate whisker under different conditions were characterized by X-ray diffraction(XRD),scanning electric microscopy(SEM),infrared spectroscopy(FT-IR)and siumltaneous thermal analysis(DSC and TG).Then compared with the above methods,the results are as follows:(1)The magnesium borate prepared by sol-gel method with citric acid is almost pure phase,and the obtained whiskers have more yield and better on morphology;we found the best proportion is magnesium nitrate:complexant=1:1 by adjusting the ratio of magnesium borate and complexing agent;increasing the pH of the solution did not get the better morphology of magnesium borate nanorods;the process of preparing magnesium borate by sol-gel method was autocatalytic.(2)In the preparation process of the magnesium borate by high temperature cosolvent dry method,the purity,crystallinity,infrared characteristic peak intensity and the length diameter ratio of magnesium borate whisker decreased with the increase of boric acid.When the ratio of boron and magnesium is 1:1,the product has high purity and uniform whisker morphology.In the preparation process of the magnesium borate by high temperature cosolvent wet method,the ratio of boron and magnesium and synthesis temperature also affected the composition and morphology of the product,but the influence on the structure is not obvious.When the ratio of boron and magnesium is 1.5:1 and synthesis temperature is 800℃,the purity and morphology of magnesium borate whisker is better.Contrasting the composition,morphology and structure of the product,we found the wet method can produce better magnesium borate whisker.And the process of preparing magnesium borate by wet method and dry method all follows the dissolution-precipitation(SLS)mechanism.(3)Aluminum borate obtained by the high temperature cosolvent dry method is Al18B4O33,and it obtained by the wet method is Al4B2O9.We contrasted the composition,morphology,structure and yield of the whisker,and found a fat that the wet method could produce better aluminum borate whisker than dry method.Besides,the yield of the whisker is so high by using alum in high temperature cosolvent dry method and the ratio of boron and aluminum and synthesis temperature affected the composition and morphology of the product.When the ratio of boron and aluminum is 3:9 and synthesis temperature is 1000℃,the whisker has high purity and better uniformity.Holding time also influenced the morphology and performance of the whisker and the optimum holding time is 1h by contrast.The synthesis temperature of the reaction could be greatly reduced by the wet method,and the optimum ratio is 1.5:1,the optimum synthesis temperature is 800℃.And the dry method follows the mechanism of liquid-solid(LS),the process of preparing aluminum borate by wet method was the dissolution-precipitation(SLS)process.