Li leaching from lithium carbonate-primer: An emerging perspective of transport pathway development

Studies of Li depletion in sections of a Li ₂ CO ₃ -primer comprising a polyurethane binder, MgO, TiO ₂ , BaSO ₄ in addition to Li ₂ CO _3, were performed using a combination of particle induced γ-ray and X-ray emission spectroscopies along with SEM/EDS analysis. A mixture of depletion behaviours was observed. At the earliest stages (to around 48 h)initial release was confined to the surface. At longer times (168 h)voids developed deeper into the primer and after 500 h Li ₂ CO ₃ dissolution was observed at places throughout the thickness of the primer to the metal/primer interface. Microscopic transport pathways formed which involved all large inorganic particles. SEM showed that rupture of the polyurethane matrix contributed to network formation. Finite element analysis indicated that rupture may be due to internal stresses around particles isolated in the polyurethane matrix and associated with water uptake. Thus the transport network seemed to be generated by chemical dissolution at the particle/polymer interface and may be enhanced by mechanical degradation due to internal mechanical stresses. The release kinetics of the Li ₂ CO ₃ inhibitor from the primer was followed as a function of time and the data analysed according to a release behaviour of t ⁿ . There was very rapid initial release of Li followed by a slower release of Mg and to a lesser extent Ba. The value of n varied significant with time, but showed a mixture of Fickian release and direct dissolution for Mg and Ba at intermediate times, but transport through a pore network at longer times. The leaching data was interpreted in terms of local transport networks that developed in the primer with time.