Effect of pH on Quality of Calcium Carbonate Film Deposited From Moderately Hard and Hard Water

bition of potable-water-distribution systems is a difficult area in which to apply theory to practice because of the many variables such as the composition and crystalline structure of the metal, concentration and availability of the oxidizing agent, and synergistic effects of ions in solution that may vary in an unknown way throughout the distribution system. There are at least two obvious reasons to inhibit corrosion in cast-iron distribution systems: these are economics and health. It would cost tremendous sums of money (estimated to be $10 billion 15 yr ago)2 to replace the cast-iron pipe presently in use in the US alone. There is also the increased pumping cost caused by corrosion-created pipeline roughness and constriction. The health aspect is more involved because of the aspiration of contaminated ground water through corrosioncaused perforations in the pipeline and the presence of corrosion products that cause increased chlorine demand and form a refuge for microorganism growth. These microorganisms cause taste and odor problems and, if suspended or dissolved in the water, make the water unpalatable for the consumer. These conditions frequently result in the consumer's choosing another water supply that may be untreated or of unsafe bacterial or viral content. Most of the corrosion research conducted to date has been directed toward controlling corrosion in industrial applications, that is, corrosion control of metals in contact with highly corrosive solutions such as sulfuric, nitric, and hydrocholoric acids. The solution to corrosion control in many of these studies has been to develop exotic alloys or add chemical inhibitors. Because of cost, the application of exotic alloys to water-distribution systems has never been considered seriously. In spite of the impressive results obtained from chemical additives in industrial applications, additives fall far short of the mark, when applied to potable-water-distributiori systems, in two important areas. The first is that of cost of treatment for a once-through system; the second is that of the inhibitor's being safe for human consumption at the concentrations required for corrosion control. With the recent concern over pollution of the environment, another problem may be discharge of the