The influence of ammonium lignosulphonate as an expander on the formation of PbSO4 on lead amalgam electrodes

Linear potential sweeps and potentiostatic pulse perturbations have been employed to investigate the influence of the expander ammonium lignosulphonate, on the anodic formation of PbSO4 on lead amalgam electrodes in sulphuric acid solutions at 24 °C. It was found that the expander strongly adsorbs onto the clean amalgam surface thus affecting the formation of the PbSO4 film. The expander increased the charge necessary for passivation, inhibited the cathodic reduction of the film, and produced a more porous film. Evidence is given for the presence of an optimum concentration of expander. Some speculations concerning the mode of action of the expander onto the amalgam surface are presented.