Application of electrical pulsed discharge to metal layer exfoliation from glass substrate of hard-disk platter

The platter, which is the data-storage component of hard-disk drives, contains platinum group metals on a substrate. It is necessary to separate the metal layer from the substrate to recover the platinum group metals and other valuable elements. The separation of the metal layer from the glass substrate were investigated by using two types of pulsed-power generators (PPGs), namely a nanosecond and a microsecond PPG. By conducting repetitive pulse discharges to the platter surface, the metal layer was peeled off and the maximum exfoliation rate reached about 60% for both the nanosecond PPG and the microsecond PPG. The higher the single pulse energy, the higher the exfoliation efficiency. The maximum peeling energy efficiency were 16%/kJ and 30%/kJ for the nanosecond PPG and microsecond PPG, respectively. It was demonstrated that the pulse width affected the formation of the discharge plasma. In the nanosecond PPG, a discharge plasma was formed between the edge of the metal layer and the electrode, whereas in the microsecond PPG, a discharge plasma channel was formed across the metal layer. SEM images of the substrate surface after discharge treatment showed that part of the removed metal layer was molten and reattached to the glass substrate. The reattached particles were spherical with a diameter of ∼10 μm, and were enriched by 20% in terms of ruthenium mass. The exfoliation process of the metal layer by electric pulses and the generation of metal particles were explained.