Static Corrosion Tests Research Articles

Aluminum alloys with improved high temperature aqueous corrosion resistance

Several aluminum alloys with differing nickel/iron ratios underwent less corrosion at 350° than at 260° C. From the results of a study of their behavior within this temperature range, the composition Al-1 w/o Ni-0.5 w/o Fe-0.1 w/o Ti (A288) was chosen for further investigation. The temperature at which improved corrosion behavior of this alloy was obtained depended on its silicon content, ranging from 315° C for 10 ppm Si to 360° C for 150 ppm Si. Static corrosion tests of A288 at 260°, 290° C and 350° C indicated no “breakaway” phenomenon during about 200 days exposure to water. Moderate extrapolation of the reported data could best be accomplished by assuming a linear behavior at 350° and nearly parabolic behavior for the two lower temperatures. Under dynamic conditions (315° C, 18 ft/sec, low ratio of Al surface to system volume) the new alloy exhibited a constant corrosion rate of 4.2 mil per year, a considerable improvement over the older X8001 alloy. As in static tests, there was little or no improvement noted for A288 over X8001 in a one month dynamic test at 260° C. The application of stress during corrosion did not increase the intergranular penetration of A288. No unusual or accelerated corrosion was found for A288 in a boiling test with a heat flux of 42 watts/cm 2 at 252° C, 600 psi. Significant increases in high temperature tensile strength were obtained by adding small amounts of zirconium and chromium to the basic A288 composition. The creep resistance of the best alloy at 4000 psi-290° C was poor. Experiments designed to probe the mechanism of corrosion indicated that the corrosion barrier for low silicon alloys at 350° C was concentrated at or near the metal-oxide interface and that the deleterious effect of silicon was shared by other members of its periodic group. Chemical analyses showed that for low-silicon alloys at 350° C, the inner layer of corrosion product was enriched in iron and nickel, whereas the loose outer layer was depleted in these elements. At 290° C, the iron and nickel in the product were equal to the concentrations calculated from the composition of the alloy. For alloys containing more silicon, the corrosion product formed at 350° C was enriched in silicon.

Corrosion Resistance of Dense, Impermeable Silicon Carbide

Abstract Corrosion data are presented for dense, impermeable silicon carbide in various media. Results are given for static corrosion tests in aqueous solutions of acids, alkalies, and salts; in fu...