STUDY OF ADSORPTION AND DESORPTION PROCESSES OF HEDP ON LOW-ALLOYED STEEL BY RADIOACTIVE LABELING

In our experiments ''solution'' and ''electrode'' methods were applied . The quantities of the inhibitor on the electrode surface adsorbed at various potentials and HEDP concentrations were studied. The quantity adsorbed was the same at each potential, but varied with the concentr ation of HEDP, therefore, all experiments were performed at the corros ion potential (-720 mV/SSCE). Inhibitor distribution was studied on th e electrode surface and found to be uniform within limits of error. De sorption and heterogeneous molecule exchange of the inhibitor was inve stigated in four series of experiments. In the first, second and fourt h series of desorption experiments the radioactivity of the electrode surface showed no change. In the third series, however, some change co uld be detected, where HEDP molecules took part in a heterogeneous mol ecule exchange reaction. The exchange of HEDP molecules was reversible on the surface of low-alloyed steel. The quantity adsorbed as a funct ion of inhibitor concentration could be determined with adsorption iso therm, e.g., the Langmuir isotherm, from the adsorption data of the la belled compound and/or the data of weight loss measurements. From the three isotherms the roughness factor (about 6-8) was also calculable.