Scale formation on polypropylene and copper tubes.

摘要

The scaling behaviors of polypropylene and copper were compared quantitatively under accelerated conditions (distilled water or high supersaturation) and more realistic conditions (potable water and low supersaturation). In addition, the effect of surface roughness on scaling on polypropylene surfaces was studied.; Polypropylene tubes, with different degrees of root mean square roughness on the inner surfaces created by machining with abrasives, were exposed to a laminar flow of distilled water supersaturated with respect to CaCO 3. Nucleation site density, i.e. the number of crystals per unit surface area, on the machined surfaces was two to ten times that on the native surfaces. However, the nucleation site density was not correlated to the roughness of the samples. These results suggest that nanometer-sized surface imperfections (e.g. steps and grooves) formed during the roughening process, rather than roughness, are responsible for the enhanced nucleation on the machined PP surfaces.; Scaling behaviors on polypropylene and copper were compared by exposing the surfaces to laminar flows of distilled water and potable water highly supersaturated with respect to CaCO3 (supersaturation, S > 9) for 0.5 to 4 hours, and distilled water mildly supersaturated (S = 4.8) for 1.5 to 15 hours. The scaling rate of polypropylene was at least 40 higher than that of copper after exposure to the distilled water at S ¿ 9. The scaling rates of polypropylene and copper were not statistically different after exposure to either mildly supersaturated distilled water (S = 4.8) or highly supersaturated potable water.; Polypropylene and copper tubes were also exposed to a laminar flow of mildly supersaturated potable water at 40°C (S = 5 with respect to CaCO3) for 1 to 8 weeks. Calcium phosphate was a major component of the calcium-rich scale deposit, a result that is linked to the presence of trace amount of phosphate ions in the water and the inhibiting effect (for CaCO3 formation) of other ions present. Under these conditions, Cu oxidizes and scales at a higher rate than PP.