抄録
A hydrotalcite-type layered double hydroxide Al2Li (OH)6 [Fe (CN)6] 1/4·nH2O (Fe (CN)6-LDH) was synthesized by a coprecipitation method and its thermal change under oxidizing and reducing atmospheres were investigated. The synthesized Fe (CN)6-LDH consisted of plate shaped particles of 0.1-0.2μm in size and the lattice parameters were those of a hexagonal cell with a=5.06 and c=31.92Å. The interlayer spacing between the LDH octahedral layers was estimated to be 5.8Å and was occupied by 0.25 [Fe (CN)6] 4- anions and 1.8H2O as the above chemical formula. The [Fe (CN)6] 4- anions in the interlayers were octahedral in structure and oriented with their individual 3-fold axes perpendicular to the LDH layers. The specific surface area measured by the BET method using N2 gas as the adsorbate was 108.9m2/g. The Fe (CN) 6-LDH decomposed upon firing up to 260°C and changed into LiAl5O8 and Li2CO3, and finally into LiAl5O8 and α-LiAlO2 at higher temperatures. For sample fired under an oxidizing atmosphere of flowing dry air the Fe component in the Fe (CN)6-LDH incorporated into LiAl5O8 by substituting for Al atoms whereas it segregated and dispersed in the samples as fine particles by firing under a reducing atmosphere of flowing H2 gas. The resulting particles were γ-Fe2O3 in the samples fired at temperatures between 450° and 490°C and α-Fe above 500°C. The γ-Fe2O3 particles were several nm in size but increased rapidly upon elevating the firing temperature, up to submicron meter in α-Fe particles.
