Preparation of A Plate-like Particle of Calcium Aluminosilicate via Layered Double Hydroxide

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A plate-like inorganic particle composed of non-toxic and low price materials has received considerable attention in recent years. However, the preparation of a plate-like inorganic particle is known to be generally difficult. In this study, Ca-Al-NO_3 layered double hydroxide (LDH) was synthesized as a precursor and intercalation technique was used for the preparation of Ca-Al-SiO_4 LDH. The precursor was synthesized by the direct reaction of powdered quick lime (CaO) with NaAlO_2 in alkaline aqueous solution. It was found that the Ca-Al--NO_3 LDH (d_<0030>0.87 nm, Ca_<0.72>Al_<0.28>(OH)_2(NO_3)_<0.14>(OH)_<0.14>(0.52H_2O)) particle with hexagonal plate-like shape and 1〜4 μm in diameter size was formed at the optimum condition : Ca/Al ratio 3, synthesis temperature 323 K (1 h), aging temperature 373 K (2 h). By the hydrothermal treatment of the LDH at 473 K for 0.5〜2 h, the particle diameter was increased to 10〜20 μm. Then, the ion-exchange of NO_3^-ion in these LDHs with silicate ion was carried out at 298 K and the resulting LDHs Ca_<0.72>Al_<0.28>(OH)_2(SiO_4)_<0.074>(0.43H_2O)) was heated at 573〜1,173 K for 0.5 h. During the intercalation and hydrothermal treatments, the plate-like particle shape was maintained and the crystalline material of gehlenite (Ca_2Al_2SiO_7) as main phase was obtained. In conclusion, we succeeded the preparation of a plate-like particle of calcium aluminosilicate from non-toxic and low price materials such as limestone and NaAlO_2.