Interstratification in expandable mica produced by cation-exchange treatment

Kyushu National Industrial Research Institute, Tosu, Japan

A unique interstratified expandable mica was obtained by cation exchange treatments using an expandable mica synthesized from talc. The ²³ Na 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 (super +) : one was exchangeable and the other was not exchangeable. Half of the Na (super +) per unit cell of the expandable mica was replaced with Mg (super 2+) by cation exchange treatments. The X-ray powder diffraction (XRD) analysis of the Mg (super 2+) exchanged expandable mica, after heating at 73 degrees C, indicated that Na (super +) in the interlayer sheets was exchanged with Mg (super 2+) in every second layer and that it had an interstratified structure with a 12.5-Aa layer thickness and a 9.6-Aa layer thickness. The structure of the Mg (super 2+) -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 (super -) , but the other had a different stacking sequence from talc and no structural OH (super -) .

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