Static electrification by electrolytic processes

Abstract

If one regards a metal in contact with a liquid of high dielectric constant such as water, in which acids, bases or salts, i.e., electrolytes are soluble and dissociated, the metal immersed in the liquid will tend to go into solution in the form of ions. Depending on the nature of the dissolved substances in the liquid and the nature of the metal, the metal will tend to go into solution as positive ions, or reacting with the solution, it may go into solution in the form of complex negative ions. The action is most strongly pronounced in water, although liquified NH₃ gas acts in an analogous fashion. When solution takes place, the process continues until under the action of the kinetic bombardment by the ions and of the field of the charge acquired by the charged metal, the metal takes on a specific potential leading to equilibrium between processes of solution and precipitation of ions on the surface. The potential depends on the nature of the metal and the concentration of ions, or dissolved salts, in the solution. Many metals like Zn or the alkali atoms are strongly metallic and tend to send their own positive ions into solution. Other metals, like Al will, in slightly acid solution, go in as positive metal ions, in this case as trivalent Al⁺⁺⁺ ions, but in an alkaline NaOH solution will dissolve as Na₃AlO₃, sending the negative ions ${{H}_{2}}AlO_{3}^{-}$ , $HAlO_{3}^{=}$ , and $AlO_{3}^{\equiv }$ into solution. At a certain hydrogen ion concentration, e.g. pH, Al metal exposed to an aqueous solution is quite inert. This is called its iso-electric point at which it sends neither one ion nor the other into solution. Any neutral metal either at its iso-electric point, or that is inert to its environment while not contributing ions, may receive ions of the solution gaining charge until it is in equilibrium with its environment as regards liberation and resolution of the ions as influenced by the charge. For example, Cu in a dilute HC1 solution or Pt in the presence of H⁺ ions, will receive these, gaining a positive charge and leaving the liquid negative. It does not take a high concentration of dissolved acid to yield considerable charge.