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

近年来，一种由无毒廉价材料组成的板状无机颗粒受到了广泛的关注。然而，制备板状无机粒子通常是困难的。本研究以Ca-Al-NO_3层状双氢氧化物（LDH）为前驱体，采用插层技术制备Ca-Al-SiO_4 LDH。采用粉状生石灰（CaO）与NaAlO_2在碱性水溶液中直接反应的方法合成了该前驱体。结果表明，在Ca/Al比为3、合成温度为323 K （1 h）、时效温度为373 K （2 h）的最佳条件下，可制得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))六方片状、直径为1 ~ 4 μm的Ca-Al—NO_3 LDH颗粒。经473 K水热处理0.5 ~ 2 h， LDH颗粒直径增大到10 ~ 20 μm。然后，在298 K的温度下，将这些LDHs中的NO_3^-离子与硅酸盐离子进行离子交换，得到的LDHs Ca_<0.72>Al_<0.28>(OH)_2（SiO_4)_<0.074>(0.43H_2O)）在573 ~ 1173 K的温度下加热0.5 h。在插层和水热处理过程中，保持了板状颗粒的形状，得到了以钙长石（Ca_2Al_2SiO_7）为主相的晶状材料。综上所述，我们成功地用石灰石和NaAlO_2等无毒价廉的材料制备了硅酸铝钙板状颗粒。

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.