CHANGES IN SWELLING CHARACTERISTICS AND STRUCTURE OF NA-FLUORINE MICAS WITH GA-SUBSTITUTIONS AND AL-SUBSTITUTIONS

Series of Ga- and Al-Substituted Na-fluorine micas NaMg2+xLi1-x(TxSi4-x-yGeyO10) F2 and NaMg2+xLi1-x (TxGe4-x-ySiyO10) F2; x = 0.0-1.0, T = Ga, Al, y = 0, 1, 2, 3, were synthesized. Variations of infrared spectra, lattice constants and swelling properties were studied, and compared with those of corresponding K-series micas. Continuous changes in basal spacing (c.sin-beta) with increasing Ga- and Al-contents proved that there were complete series of solid solutions between the end member micas with an exception of NaMg3 (AlSi3O10) F2. Linear relations between c.sin-beta or b-axis values and mean radius of tetrahedral cation were obtained for Ga- and Al-substituted Na-micas having x-value of 1.0. However, the b-axis values of Na-micas are far smaller than those of corresponding K-analogues, demonstrating that the degree of distortion in tetrahedral rotation angle alpha and octahedral flattening angle psi is determined by the size of interlayer cation as well as that of tetrahedral cation. The values of alpha for Na-micas increased with the amounts of Ga- and Al-substitution. Na-micas lose also their swelling ability with increasing Ga- and Al-substitution. The loss of hydration property of interlayer cation results from the increase of alpha and the change of charge balancing, which increase the stability of interlayer structure.