Control of layer charge has been undertaken for expandable fluorine micas utilizing a fixation method with interlayer A13+ cations and the conception of effective layer charge (E. L. C. ) have been brought. Sodium-fluorine mica having layer charge of 0.8 (Na
0.8Mg
2.2Li
0.8Si
4O
10F
2) and it's Li+-exchanged form, i. e. Li-fluorine mica, were used as mothe r crystals for layer charge-controlling. Partially exchanged Al
3+in Li-mica is completely fixed into hexagonal holes of silicate layer and loses it's exchangeability upon heating at 500 °C, so that the net negative charge, i. e. E. L. C., which is defined as the difference between the original layer charge and the fixed Al
3+-positive charge per unit silicate layer, is controllable with interlayer cation ratios of Al
3+/Li+. The partially Al
3+-exchanged Li-micas show limited swelling but they recover free swelling upon heating at 500 °C. This is caused by the remaining interlayer Li+ cations and reduction of layer charge through Al3+-fixation. The content of intercalated hydroxoaluminum polycations decreases linearly with decreasing E. L. C., indicating that the intercalated pillar density is controllable for cross-linked mica complexes. Thermal durability of the complexes decreases with decreasing E. L. C. because the pillar density in the complexes having smaller values of E. L. C. is too low to stabilize the intercalated structure at high temperatures, resulting in the collapse of regular stacking sequences and the smaller quantity of micropores in interlayer region of the complexes. The basal spacings of the complexes heated at 500 °C are 17.7 A, not depending on E. L. C., while specific surface areas and micropore volumes of them show dependency on E. L. C. due to the changes of pillar density and the difference of thermal behaviors of intercalated substances, showing a maximum at E. L. C. of 0.5.
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