高温高圧の水および蒸気によるCu-Zn合金の腐食の研究

Abstract

A corrosion test has been made on Cu-5∼40%Zn alloys in saturated water and steam at 300°, 86 kg/cm2, for 250 hours using autoclave. Specimens were prepared as cold-rolled and annealed strips. All specimens, except those of low-zinc alloys exposed to saturated water, increased in weight with increase of zinc content forming the dark red corrosion product. The effect of corrosion on the tensile strength and the elongation of specimens were remarkable with increase of zinc content of the alloys. From microscopical examination, alloys of low zinc content (Zn=5∼20%) suffered preferred whisker-like corrosion penetrating along and in the grains, under the layer of corrosion product. On the other hand, the alloys of high zinc content (Zn=25∼40%) suffered layer type corrosion. The depth of penetration and thickness of the layer of corrosion increased with increase of zinc content. From X-ray powder diffraction and chemical analysis, corrosion products formed on the surface of the specimens were identified as a mixture of metallic copper and zinc oxide (hexagonal). Annealing treatment of the specimens tried has no perceptible effect on corrosion. As the results of these tests, it is considered that the zinc atoms near the surface of Cu-Zn alloy are selectively oxidized by high temperature water and steam forming the metallic copper and the zinc oxide as the corrosion product.