Residual chlorine prevents full densification of flash sintered yttria-stabilized zirconia ceramics

Abstract

The densification of yttria-stabilized zirconia (YSZ) during flash sintering is strongly dependent on the amount of residual chlorine in the sintered bodies. The residual chlorine, present as a remnant from powder synthesis, hinders densification after it is trapped and vaporized in the rapidly closing pores, limiting the final density at around 87 – 93% of theoretical. We show that this phenomenon is likely to affect all YSZ powders synthesized from chloride precursors unless the residual chlorine is reduced to ≤ 0.03 wt% before the onset of the flash sintering. This can be universally achieved by thermal purification of green bodies at a high temperature or by chemical purification in ammonium hydroxide. Furthermore, added binder in commercially available Tosoh zirconia TZ-powders (TZ-3YB, TZ-3YB-E) helps to significantly reduce chlorine content during binder burnout which in turn allows flash sintering into a high density even without green body purification.