Abstract
Synthesis of Ln3+-substituted tetrasilicic fluorine micas [K1-xLnxMg2-2xLi1+2x(Si4O10)F2; Ln=Ce, Nd, Eu; x=0.0-0.2] was undertaken by solid state reaction and melting methods. Eu3+-substituted mica synthesized by the melting method had the largest solid solubility, i.e., x=0.10. The solid solubility of rare earth ions in mica structure depends on the radius of rare earth cations, resulting in the order Eu3+>Nd3+>Ce3+. Highly Ln3+-substituted fluorine micas were synthesized by ion exchange-fixation method from expandable Nataeniolite [Na0.8Mg2.2Li0.8(Si4O10)F2] and altered tetrasilicic fluorine mica [KxNa1-xMg2.5(Si4O10)F2; x≥0.18]. Homoionic Ln3+-exchanged micas obtained from Na-taeniolite didn't lose their rehydration properties upon heating even at 900°C. The degree in rehydration upon heating for homoionic Ln3+-exchanged micas also decreased in the same order Eu3+>Nd3+>Ce3+. This order is explained in terms of the polarizing power of interlayer Ln3+ ions. However, (Ln3+, K+)-exchanged micas obtained from altered tetrasilicic micas with NaB(C6H5)4 treatment showed complete fixation of interlayer Ln3+ ions upon heating at 400°C, probably due to the effect of residual K+. They lost thoroughly rehydration property. This allows us to synthesize nonexpandable fluorine micas having the highest content of rare earth cations. Ce3+-substituted micas thus obtained showed strong UV-absorptivity.
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