| Abstract: | SUMMARIES. To characterize more fully the metal soaps found in paint films or on metal surfaces, several metal soaps were synthesized and their X-ray diffraction pattern and Fourier transform infrared (FTIR) and Raman spectra measured. Metal soaps were obtained from four different fatty acids found in drying oils — two saturated (palmitic and stearic acids) and two misai united (alcic and linolcic acids) — and from capper, zinc and lead, three metals thai arc typically found in metal alloys and paint systems. Data are reported for the fallowing compounds: palmitic acid, stearic acid, oleic acid, linolcic acid, zinc palmitate, zinc stéarate, zinc oleate, zinc linoleate, copper palmitate, copper stéarate, copper oleatc, lead palmitate, lead stéarate and lead oleate. Features that are characteristic oj specific compounds were observed. Soaps obtained from different fatty acids with the same metal ion show differences, as do soaps obtained with the same fatty acid but with different metal ions. Identification is key to understanding how and why metal soaps form on actual objects, and this may lead to preventive measures.
CONCLUSION. Synthesis of pure metal soaps (zinc palmitate, zinc stéarate, zinc oleate, zinc linoleate, copper palmitate, copper stéarate, copper oleate, lead palmitate, lead stéarate and lead oleate) and their characterization by X-ray diffraction, infrared spectroscopy and Raman spectroscopy made it possible to document features that are characteristic of specific compounds. Soaps obtained from different fatty acids with the same metal ion show differences by all techniques, as do soaps obtained with the same fatty acid but with different metal ions. Characterization by X-ray diffraction requires that the soap be in the crystalline form. Also, since the most intense characteristic lines of the various metal soaps are at low angles, patterns must be measured with equipment that can resolve lines in this region. Lines at higher angles are also characteristic to a lesser extent but are much weaker. FTIR spectroscopy provides useful information and does not impose limitations due to the type of instrument used. The position of the carboxylate absorption is related to the metal present in the soap, while weaker absorptions in the 1300-lOOOcm-1 region can be used to determine the fatty acid of the soap. Raman spectroscopy also provides information that makes it possible to differentiate metal soaps. Metal soaps found on artifacts and works of art were characterized based on the data obtained in the current study. However, accretions, efflorescence or inclusions in paint film often consist of mixtures of degradation products and undegraded original materials, making a precise identification of all com¬ponents more difficult. Infrared spectroscopy seems to be best suited tor analysing mixtures of metal soaps; this technique is very sensitive, as long as absorptions from pigments or other compounds do not mask characteristic features as, unfortunately, often hap¬pens. It is hoped that the work presented here will help in the characterization of metal soaps found on actual objects. Identification is key to understanding how and why they form and this may lead to preventive measures. |
|---|
