Thermal and spectroscopic measurements of the interactions of oleic acid with surfaces of aluminum, magnesium and Al-Mg alloys

Differential scanning calorimetry and Fourier transform IR reflectance spectroscopy have been used to study the interactions of oleic acid with the surfaces of aluminum, magnesium and Al-Mg alloys. Measurements were made in both air and argon from 150 to 575 °C. The magnesium content of the alloys ranged from 2.6 to 10.7 wt.% and samples were examined in the form of fine powders or smooth plates. A few experiments were also conducted using granular magnesium and aluminium oxides to assist in evaluating the role of surface oxides in the reactions. The IR reflectance signals at about 1590 and 1450 cm^-1 showed the formation of magnesium oleate in the various magnesium samples at 175 to 300 °C. With the alloy series there was a marked trend towards greater absorbance of these bands with increase in the magnesium content. Little or no evidence was obtained for the formation of aluminum oleate from IR spectra while thermal measurements showed enthalpy changes of -1050 and -650 cal g^-1 respectively for magnesium and aluminium grains in reactions with the acid in air over the range from 150 to 575 °C. Supplementary details of the surface properties of samples were obtained from profilometric, nitrogen adsorption and electron spectroscopy for chemical analysis measurements. Some preliminary work is described in which alloys were laminated to high density polyethylene in an attempt to assess the influence of surface composition on joint strengths.