Phosphate Inhibition Effect on Chloride-Induced Crevice Corrosion of Alloy 22

ABSTRACTAlloy 22 has been extensively studied regarding its crevice corrosion (CC) resistance both in pure chloride solutions and in solutions containing different oxyanions that may act as inhibitors of crevice corrosion. The scope of this work was to study the general and localized corrosion behavior of Alloy 22 when phosphate ions were added to a 1 M NaCl solution at 90°C. Results from the electrochemical tests indicate that the size of the passive potential range and the localized corrosion repassivation potential value increased in the presence of phosphate ions. Results from creviced specimens showed a strong inhibition effect of phosphate ions on the chloride induced crevice corrosion of Alloy 22. The critical molar concentration ratio (RCRIT = [phosphate]/[Cl]) to inhibit crevice corrosion was 0.3.

Novel Non-Phosphorous Antiscalants for Inhibition of Calcium Phosphate and Calcium Sulfate Precipitation

A copolymer of acrylic acid (AA)/allylpolyethoxy carboxylate (APEC) was synthesized, characterized and examined as a non-phosphorous antiscalant for industrial cooling-water. Its ability to prevent calcium phosphate and sulfate precipitation was compared with inhibitory power of acrylic acid (AA)/allylpolyethoxy sulfate (APES) and polyamino polyether methylenephosphonate (PAPEMP). Results indicate that the presence of these antiscalants does reduce the extend of calcium phosphate and sulfate precepitation and AA/APEC exhibits the best performance with 99.59% calcium-phosphate inhibition when the dosage of AA/APEC was 6 mg/L and 82.88% calcium-sulfate inhibition at the dosage of 3 mg/L AA/APEC. AA/APEC has also been proven to be an effective inhibitor for calcium phosphate and calcium sulfate even at elevated solution temperature, pH and Ca2+concentration.