INVERSE GAS-CHROMATOGRAPHIC STUDY OF TREATED ALUMINUM SURFACES

Inverse gas chromatography (IGC) was used to study the surfaces of aluminum powder which had been pretreated by (1) etching in aqueous base, (2) etching in aqueous base and washing the powder to neutral pH, and (3) etching in a dichromate/sulfuric acid solution. n-Alkanes, benzene, and their perfluorinated analogues were used as IGC probe molecules. The perfluoroalkanes were less strongly adsorbed on the base-treated sample than the corresponding n-alkanes but were more strongly adsorbed on the acid-neutralized and chromic acid etched samples. Plots of RT In V(g)-degrees versus the logarithm of the probe vapor pressure showed that the perfluorinated alkane line was below the reference n-alkane line for the base-treated column and above the reference line for the other two columns. Free energies of nondispersive interactions determined from these plots are consistent with the behavior of benzene as a weak acid and suggest that perfluorobenzene may be acting as a weakly basic probe. The dispersive component of the surface free energy for the chromic acid etched aluminum is 15-20% higher than those for the other two materials.