![]() In column B, place the value -4.34 from 0 to 6.0. If necessary, conduct a sort in A to place 6.1 properly. įill column A with pH values from 0 to 14 in steps of 1, adding the value of 6.1. The pE° change with pOH and therefore, with pH, with a slope of unity because although there is a two-electron change, two OH are produced. The pE° will remain unchanged with pH until the value at which Ni(OH)2(s) begins to precipitate from a solution in which = 1 The following equations will be considered. Let us consider the effect of pH on pEjjj. The areas between the lines represent regions in which one species predominates and are labeled accordingly. The resultant diagrams consist of a series of appropriately drawn line segments. Ī great deal of information about redox systems can be conveyed efficiently by Pourbaix diagrams in which pE° values for various oxidation states are plotted against pH or another relevant variable such as log, (2.48) gives the same result if either acid or alkaline solution is selected. (2.48) for an alkaline solution and compute the Eh and Eq. (2.32), the Nemst equation gives the hydrogen potential as Įxample 2.10 Drive eq. Consider the hydrogen evolution reaction at standard conditions (T = 25 ☌, Po = 1 atm) įrom eq. The constmction of the E-pH Pourbaix diagram for water and oxygen is straightforward. There are several difficulties with using the Pourbaix diagram to predict the stability of copper during polishing, specifically Ĭomplexing ions alter the Pourbaix diagram by moving the boundaries of the stability regions and adding new stability regions/ An example of a slurry where copper is immune to corrosion is given in Section 4.2.4. Without a chemical component, the polish becomes strictly mechanical polishing (MP). If there is no oxidation of the metal, there is no chemical component to the polish. The second reason the region of stability is important is that if the metal falls in the region of immunity (the Cu region), it is thermodynamically impossible for the metal to dissolve into solution or form a solid oxidation product. In 1 vol% NH4OH, for example, Cu ions are complexed by NHj according to Boundary lines in such diagrams divide the areas of stability for different phases and are derived from the use of Nemst equation Ĭopper polish slurry formations may contain dissolved NH, ig) to complex the copper ions and increase copper solubility. ��ȳa ��FbYAx�ÎJ?����ʒe]�s/cɚ�b��-)�̥#�����a��� �ˌ������x,h���Ō�Ң ����9�kKM�������'��`%�)��c>j�ɼ�SJq.Pourbaix diagrams, or pH- potential diagrams, have been constructed to facilitate the prediction of the various phases (reactions and reaction products) that are stable in an aqueous electrochemical system at equilibrium. Source : )/Rect/Subj(Typewritten Text)/Subtype/FreeText/T(Parithy)/Type/Annot>endobj112 0 objendobj113 0 obj/ProcSet>/Subtype/Form/Type/XObject>stream ![]()
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