Synthesis And Study Of The α-Alumina Platelets

Flaky alumina is widely used in the field of composite materials, cosmetics and pearl pigment, etc, because it has special two-dimensional structure and excellent physical and chemical properties. However, it is very strict for its usability. The particle size and crystal morphology have an important influence on the use of flaky alumina. Therefore, in this thesis, we carried out depth research relate to synthesis Flaky alumina powder by high temperature solid state method and molten salt sysnthesis. The powder was mainly characterized by XRD, DSC-TG, SEM techniques.Flaky α-Al₂O₃ was synthesized by high-temperature solid phase method introducing Al F3 to alumina precursor. The effects of Al F3 additive, calcination temperature, holding time on the phase transformation and morphology of the prepared flaky α-Al₂O₃ were investigated. The results show that unstable crystalline alumina at 900 ℃ converts to stable α-Al₂O₃ with 10% Al F3 additive, Al F3 can significantly reduce the phase transformation temperature of alumina; With the increase in the amount of Al F3, morphology of alumina by the flocculent into worm-like, eventually become platelet morphology. When The calcination temperature is 1200 ℃, holding time 3h, aluminum fluoride dosage 20%, the large and thin flaky α-Al₂O₃ were prepared, but the morphology of α-Al₂O₃ are irregular.Flaky alumina was prepared by a molten salt synthesis method. Firstly, the effects of the different source of aluminum, calcining conditions, molten salt species and ratio on the morphology and size of α-Al₂O₃ powders were investigated.The best results indicated that when Al2（SO4）3·18H2O was used as source of aluminum, the ratio of molten salt and aluminum salt is set to 4:1, the flaky alumina powders with uniform morphology, uniform large particle size were synthesized with molten salt synthesis method after six hours calcination at 1200℃. Secondly, under the best experimental conditions, the effects of nanosized α-Al₂O₃ seeds, platelet α-Al₂O₃ seeds, additives on the morphology and size of α-Al₂O₃ powders were also investigated in detail. The experimental results show that the platelet α-Al₂O₃ size reduces obviously with increasing nanosized α-Al₂O₃ seeds content; As the Platelet α-Al₂O₃ seeds are added,a significantly increase in the platelet α-Al₂O₃ size occurs; Nevertheless, the amplitude of platelet size increase becomes smaller with increasing platelet α-Al₂O₃ seeds content. The irregular morphology of platelet α-Al₂O₃ can be obtained by adding the Na3PO4·12 H2 O additives, however, the thickness of them is decrease.The diameter of the flaky α-Al₂O₃ reduced and then increased with the increasing contents of Ti Cl4 and TBOT additives, finaly they showed the tendency to reduce. While the diameter of the flaky α-Al₂O₃ with adding Ti O2 additives always reduce. The thickness showed out the tendency of increasing for all three titanium-containing additives. It is worth mentioning that the hexagon shape of particles from hexagon into polygon or even roundness shapes with the contents of three titanium-containing additives at 8%.