Characterization of Calcium Ferrite Mono-Nitrate Hydrates and Changes of Their Crystal Structures by pH Control

Abstract

Calcium ferrite mono-nitrate hydrate (hereafter abbreviated as CFMNH) obtained at 60°C by a reaction between Ca (OH) ₂ suspension and Fe (NO₃) ₃ solution was characterized by XRD, FT-IR, DTA-TG and SEM-EDX. The synthesized CFMNH was the puseudo-hexagonal layer compound with basal spacing of 1.04 nm which is equivalent to half of the lattice constant c. By heating CFMNH below 100°C, this basal spacing was decreased from 1.04 nm at room temperature through 0.86 nm at 60°C to 0.80 nm at 100°C. These CFMNHs were also indexed tentatively as puseudo-hexagonal symmetry.
To study change of basal spacing with pH, 1.04 nm CFMNH suspension was stirred for 1 hour at room temperature in various pH solutions adjusted from about 12 to 13 with NaOH. The basal spacing of CFMNH decreased from 1.04 nm to 0.76 nm with increase of pH. The 0.76 nm spacing of CFMNH was finally settled to 0.80 nm by a longer aging process. The three types of CFMNH with different basal spacings were obtained by pH control as well as by thermal dehydration. However, the chemical composition and structure of 0.80 nm CFMNH obtained at room temperature by pH control were different from those of 0.80 nm CFMNH obtained by thermal dehydration in terms of carbonate contents, degree of hydrogen bond and stacking mode of layers.