Particle Surface Softening as Universal Behaviour during Flash Sintering of Oxide Nano-Powders.

The dissipated electric power in oxide powder compacts, subjected to flash sintering, is several hundreds of W·cm. This power is analyzed considering local softening/melting and transient plasma/liquid formation at the particle contacts due to thermal runaway. The sudden increase in compact electric conductivity and dissipated power referred to current percolation through the softening/liquid formed at the particle contacts, at the percolation threshold. The energy-balance and heat transfer considerations during the transient flash event are consistent with the local heating of the nanoparticle contacts to the ceramic melting temperature, or above it. The formation of the plasma by field emission of electrons is also considered.