MOLECULAR-SCALE STRUCTURE OF THE CATION MODIFIED MUSCOVITE MICA BASAL-PLANE

The muscovite mica basal plane surface was investigated directly with atomic force microscopy (AFM), zeta potential, and contact angle meaus rements after H+, Li+, K+, and Mg2+ ion exchange followed by heating a t a temperature of 300 degrees C. Typical AFM images of the H- and K-m ica showed an ideal array of light spots corresponding to one to five oxygen ions on the surface crystallographic layer of the muscovite mic a. No spots were observed in the cavity surrounded by the light spots. In particular, the ideal image of H-mica, which should correspond to a bare basal plane where no interlayer cation exists, indicated that t he calcination did not damage the mica basal plane. In the images of t he Li- and Mg-micas, a significant irregular array of the light spots corresponding to the oxygen ions and small spots in the hexagonal cavi ty of the mica basal plane could be observed. Furthermore, the zeta po tential of the H- and K-mica basal planes showed identical values to t he freshly cleaved mica basal plane, while the zeta potential of Li- a nd Mg-mica basal planes were much lower in magnitude than freshly clea ved mica. These results substantiate that Li+ and Mg2+ ions were irrev ersibly fixed in the hexagonal cavity on the mica basal plane, resulti ng in neutralization of negative charge. However, the K+ ions could no t be fixed in the hexagonal cavity. Such a cation-fixation process ref lects the relative size of dehydrated cations and the size of the char acteristic hexagonal cavity in the mica basal plane.