SURFACE FREE-ENERGY COMPONENTS OF CALCIUM-CARBONATE AND THEIR CHANGESDUE TO RADIOFREQUENCY ELECTRIC-FIELD TREATMENT

Surface free energy components for calcium carbonate were determined u sing a thin-layer wicking technique based on Washburn's equation. It w as found that the Lifshitz-van der Waals interaction for this solid, g amma(S)LW is 48.0 mJ/m2, and the acid-base electron donor parameter, g amma(S-), equals 79.0 mJ/m2, while no value for the electron acceptor parameter, gamma(S)+, was detected. These results show that calcium ca rbonate possesses a strong monopolar surface. After the thin layer of calcium carbonate was treated with a radiofrequency electric field (44 MHz, 60 V nonloaded peak-to-peak amplitude) for 15 or 25 min, the ele ctron donor parameter decreased to 40.7 and 63.9 mJ/m2, and small elec tron acceptor parameters appeared, 1.34 and 1.77 mJ/m2, respectively. At present, no idea can be put forward for the smaller changes in the gamma(S)- parameter for the surface treated for the longer time with t he RF field. However, it is postulated that the observed changes in ac id-base interactions (hydrogen bonding) are due to some rearrangements of the surface hydroxyl groups and/or the adsorbed water molecules, l eading to their partial mutual saturation, as this type of interaction is complementary. (C) 1994 Academic Press, Inc.