Kinetic aspects of superfast consolidation of silicon nitride based ceramics by spark plasma sintering
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A newly developed novel rapid densification process named Spark
Plasma Sintering (SPS) has been successfuly applied to compact silicon
nitride based ceramics. In this process the precursor powders are pressed
uniaxially in a carbon die, and an on–off pulsed DC voltage is applied
simultaneously. The current passes through the carbon pressure die as well
as the sample, so that the sample is heated both from the outside and the
inside, which allows very fast heating rates to be applied (up to 600°C min−1).
In addition to heat and pressure this process utilises the self-heating
action caused by spark discharges between the particles, which occurs in the
initial stage of the current–voltage pulse. These processes promote
material transfer and allow the preparation of fully dense compacts of silicon
nitride based ceramics within a few minutes. In this presentation, the phase
transformation sequences during the initial stages of the sintering process,
as well as the consolidation mechanisms are discussed from a kinetic point
of view for Si3N4, β-sialon, and α–β-sialon
composite materials.
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