Interstratification in expandable mica produced by cation-exchange treatment

A unique interstratified expandable mica was obtained by cation exchange treatments using an expandable mica synthesized from talc. The Na-23 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of the expandable mica used as a starting material showed that it had 2 kinds of Na+: one was exchangeable and the other was not exchangeable. Half of the Na+ per unit cell of the expandable mica was replaced with Mg2+ by cation exchange treatments. The X-ray powder diffraction (XRD) analysis of the Mg2+-exchanged expandable mica, after heating at 73 degrees C, indicated that Na+ in the interlayer sheets was exchanged with Mg2+ in every second layer and that it had an interstratified structure with a 12.5-Angstrom layer thickness and a 9.6-Angstrom layer thickness. The structure of the Mg2+-exchanged expandable mica was changed into a unique interstratified structure by the calcination at 600 degrees C; one component had a stacking sequence of talc and a small amount of OH-, but the other had a different stacking sequence from talc and no structural OH-.