The role of Cu(I) in the process of forming Cu2-xS coatings by a chemical route

The interaction of the Cu2O absorbed with Na2Sn (n = 1-4), during formation of the Cu2-xS coatings has been investigated by cyclic voltammetry. The summarized reaction of this process has been shown to correspond to the equation. Na2Sn + Cu2Oad + H2O --> Cu2Sad + (n-1) S degrees + 2NaOH, where S degrees/Cu=(n-1)/2. Such a stoichiometry of reaction can be explain ed by the formation of an intermediate - the adsorbed polysulphide of Cu(I) - and by its subsequent decomposition into Cu2S and S degrees. When a thicker coating is being formed, i.e., when the surface being coated is repeatedly immersed into an ammoniate solution of Cu(I) and S degrees f ully bouned: S(ad)degrees + 2Cu(+) --> CuS + Cu2+. At the same time due to different solubility products (L = 2.5.10(-48) and 6.3.10(-36) for Cu2S anti CuS respectively), an exchange CuSad + 2 (1-x) Cu+ --> Cu2-xSad + (1-x)Cu2occurs. After formation of Cu2+, parallel processes characteristic for the interact ion of Cu(II) with Na2Sn, start to take place, during which SD is also form ed.