The effects of temperature and pH on the dissolution and passivation processes of copper in carbonate-bicarbonate solutions

Abstract

Foram feitos estudos eletroquímicos de eletrodos de cobre policristalino em soluções de carbonato-bicarbonato, analisando os efeitos da temperatura e do pH, cobrindo uma extensa faixa de composições eletrolíticas num intervalo de 5-65 °C. As condições hidrodinâmicas do sistema também foram consideradas. Os resultados são explicados com base numa modificação das características do filme decorrente dos efeitos de agitação da solução e das temperaturas elevadas. Nestas situações, forma-se uma camada menos hidratada, reduzindo o processo de dissolução. A força iônica torna-se um fator adicional que afeta o estado geral do sistema.Elec tro chem i cal stud ies of polycrystalline cop per elec trodes in car bon ate-bicarbonate solu tions an a lyz ing both tem per a ture and pH ef fects were car ried out, cov er ing a wide range of elec tro lyte com po si tion in the 5-65 °C range. Hy dro dy namic con di tions were also con sid ered. The re sults are ex plained on the ba sis of a mod i fi ca tion of the char ac ter is tics of the film through so lu tion stir ring and high tem per a ture. In this sit u a tion, a less hy drated pas sive layer is obtained, re duc ing the dis so lu tion pro cess. The ionic strength be comes an ad di tional fac tor that af fects the gen eral state of the sys tem. Key words: cop per, pH, tem per a ture, voltammetry In tro duc tionThe be havior of cop per in neu tral and al ka line so lu tions has been stud ied by several au thors [1][2][3][4][5][6][7][8][9][10][11] . There ex ists a general agree ment about the struc ture and com position of prepassive and pas sive films, al though the ki net ics of complex an odic pro cesses can change de pending on po ten tial perturbations, the na ture of ions in so lution [4][5][6][7]9,11 , ionic strength, pH, and hy dro dy namic con di tions [5][6][7][8] . The aim of this study was to at tain in for ma tion about the potentiodynamic be hav ior of cop per in so lu tions containing car bon ate/bi car bon ate ions, cov ering wide ranges of elec trolyte pH, tem per a ture, and ionic strength, in or der to es tab lish their con tri bu tions to the metal dis so lu tion and passivation pro cesses. Ma te rials and MethodsThe elec trochemical equip ment, ex perimental de tails and elec trode treat ment have been pre vi ously de scribed in de tail 7,12 . "Specpure" cop per ro tat ing disks (John son Matthey Chem i cals., 0.15 cm 2 ap par ent area) em bedded in PTFE hold ers were used as the work ing elec trodes.The potentials were measured against a saturated calomel electrode (SCE), but in the text the potential are re ferred to the NHE scale, tak ing into ac count the corrected po ten tial val ues of SCE ac cording to a suit able equation 13 . A large-area plat i num plate was em ployed as the coun ter elec trode.The elec tro lyte so lu tions con sisted of a mix ture of xM KHCO 3 + yM K 2 CO 3 (0.0075 ≤ x ≤ 2.25; 0.0005 ≤ y ≤ 1.5), cov er ing the 8.3-11.6 pH range. They were prepared from an a lyt i cal grade re agents and tri ple-distilled wa ter pre vi ously bo...

Characterization of the Deposition ofn-Octanohydroxamate on Copper Surfaces

“…Kaluzhina and Sieber 29 made similar observations in their voltammograms of copper in 0.02 M/ 0.1 M bicarbonate solutions at slow sweep rates (10 mV s −1 ) but not at fast sweep rates (100 mV s −1 ). Both Ribotta and Folquer 30 and Kaluzhina and Sieber 29 state that the second oxidation peak relates to the formation of CuCO 3 .Cu(OH) 2 , in accordance with the Pourbaix diagram. Kaluzhina and Sieber 29 propose that the behavior observed at lower sweep rates is due to the concurrent formation of a very thin layer of CuO with the CuCO 3 .Cu(OH) 2 initially, that goes on to dissolve when in contact with the electrolyte.…”

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