Interaction between alumina surfaces has been measured using atomic force microscope (AFM). The effects of pH and electrolyte concentration of NaCl on the forec measurement were investigated. At low ionic strenght around 0.0003mol/L, the interaction behaves as long- tanged repulsive force. With the rising of salt concentration, the magnitude of the repulsive force decreases due to compression of the electric double layer. The measured double layer decay lengths were consistent with the theoretical values. The measured force curve of 0.000 3mol.L was forred with DLVO theory with condtant change and constant potential as 8.8mV. The pH value has great influence on the interaction magnitude. A t pH 7.90, the interaction force is attractive. The fitted constant charge data show the isoelectric point of alumina is at 8.2, which is consistent with the results obtained from the eletrophoretic mobility measurement .

Key words: SODIUM CHLORIDE, ALUMINIUM OXIDE, INTERACTIONS