シリカ源に金属ケイ素を用いたGa, Al-ZSM-5固容体の合成

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Silicalite 1, Ga-ZSM-5, solid solution were hydrothermally synthesized at 185℃ using silicon metal(99.999%)powder as the silica source. Their crystals were commonly spherulites consisting of radial aggregates of needles grown in the direction of c-axis. Dimensions of these spherulites were in the range of 10 to 15μm, and grew up to 18μm with increase of the Al content. It can be considered that the spherulites were formed in solutions with high concentrations as compared with the growth environments of prismatic crystals.The orthorhombic cell edges for products are as follows.Silicalite 1:a=20.103, b=19.950, c=13.436Å Al end-member:a=20.117, b=19.961, c=13.442Å Ga end-member:a=20.145, b=19.989, c=13.456Å The lattice parameters for solid solitions varied between those of the end-members, and approximately increased uniformly with increase of the Ga content. This is brought about by the difference in ionic radius between Al^<3+> and Ga^<3+>ions. With the replacement of Al by Ga, however, the expansion in c-axis was small as compared with those in a-and b-axes. The elongation of c-axis was supposed to be hampered due to rigid link form of chain-type connention composed of 5-rings in the same direction. Silicalite 1 was considerably siliceous at 2x10^5 for SiO_2/Al_2O_3 molar ratio. Al and Ga end-members contained. 6.0Al and 6.0Ga per unit cell, respectively and this Ga content was maximum in this experiment, but it is not clear whether the Al content was maximum or not. All products between the end-members were regarded as an ideal solid solution based from the relationship between the Ga_2O_3 molar fractios (Ga_2O_3/(Al_2O_3+Ga_2O_3)) of the products and those of the starting materials. The (Al+Ga)contents/u. c. of the solid solutions were in narrow range between 5.9 and 6.1, and hence it can be considered that there is no site preference between Al and Ga atoms in ZSM-5 framework.
日本粘土学会の論文
1993-05-25

シリカ源に金属ケイ素を用いたGa, Al-ZSM-5固容体の合成

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