| Contents Notes |
"From both laboratory and field investigations it has been found that protective films can be formed or deposited on lead and asbestos-cement pipes. The purpose of the present project was to determine the chemical and/or crystalographic composition of surface films on these pipes. Both laboratory and field samples of lead were investigated by Raman and infrared spectroscopy. A number of laboratory samples were investigated in situ using laser-excited Raman spectroscopy. A limited number of field samples of asbestos-cement pipes were studied using infrared spectroscopy. In addition, surface films from field samples of galvanized iron pipes were measured. The results on lead pipes indicate that the surface films are primarily composed of lead monoxide, PbO. This compound exists in two crystalographic forms, orthorhombic and tetragonal. The latter should be the stable form under ambient conditions; however, orthorhombic is "stabilized" by some types of impurities and is the dominant form present at pH values below 7. Due to its unstable nature, orthorhombic PbO has a strong tendency to enter the water column. The stable tetragonal form of PbO was observed at pH values greater than 7.5. This form appears to be much more protective of the surface, i.e., it acts as a protective film. Variations in the chemical composition of asbestos-cement pipes make it impossible to identify the composition of surface films using spectroscopic techniques; however, surface films on field samples of galvanized iron were identified as zinc carbonates using jnfrared spectroscopy." |
