Closure to “Discussion of ‘The Affect of Arsenic on the Dealloying of α‐Brass’ [M. J. Pryor and Kar‐Kheng Giam (pp. 2157–2163, Vol. 129, No. 10)]”

Abstract

R. J. Jais 42 and S. M. M. de De Micheli: 43 In this paper and in the preceding one, 44 the authors present interesting information about the mechanism of the selective dissolution of Cu alloys. We have carried out a research on dealloying offl~ Cu-A1 alloys in NaC1 solutions atpH = 1 andpH = 6.5 at 0.7 and 1.25VH. During polarization, there appeared insoluble corrosion products which were identified as atacamite (Cu2(OH)3CI) and as CuC1. Thick layers (-100 ~m) of Cu, similar in aspect to Fig. 3 (b) in the paper under discussion, were found on the substrate when corrosion products were not immediately removed from the attacked surface after the completion of each experiment. When this cleaning was performed, discontinuous thin films of Cu (-2 ~m) were detected by means of SEM and EDAX observations in the cross section of the samples. Anodic currents of about 0.1 A/cm ~ were recorded during polarization, irrespective of the Cu layer characteristics. Metallographic studies of the cross sections of the thick layers showed that no relation existed between the substructure of the substrate and the substructure of the layer where Cu crystals quite smaller than the grains of the original alloy were observed. As it was pointed out by M. J. Pryor and Kar-Kheng Glare, cathodic deposition of Cu is not possible at high anodic potentials. Taking into account this consideration as well as the experimental results described above, the corrosion features of BjCu-A1 alloys in NaC1 solutions at 0.7 and 1.25Va could be explained by supposing that Cu crystals were formed after polarization, as a result of the reduction of Cu salts which were in contact with the surface of the samples at the corrosion potential in the presence of air. In this case, selective leaching of A1 would not be the mechanism of dealloying. Could the authors give us their opinion hbout this interpretation?presence of very small amounts of arsenic either in the metal or in the solution as oxyanions.For the foregoing reasons, we do not believe that the origin of the dealloyed layer at positive potentials in our study was related to the disproportionation of cuprous chloride.

1,2,4,5 tetrazo spiro (5,4) decane‐3 thione as a corrosion inhibitor for arsenical aluminium brass in 3.5% NaCl solution

“…Aluminium brass is finding extensive use as the tube material for condensers and heat exchangers making use of sea or brackish water as the coolant (Habib and Amin, 1992;Narain and Asad, 1992;Shalaby et al, 1996;Epler and Castle, 1979;Castle and Parvizi, 1986). Incorporation of arsenic and/or phosphorus as the minor alloying additive is found to bring down the occurrence of dealloying attack (Pryor and Glam, 1982;Mazza and Torchio, 1983). The greater resistance of aluminium brass may be attributed to the presence of an aluminium compound which has a passivating effect (Baccaria and Poggi, 1988;Baccaria et al, 1989).…”