Role of conduction and convection heat transfer during rapid crack-free sintering of bulk ceramic with low thermal conductivity

Rapid sintering is nowadays a domain of novel methods such as spark plasma sintering (SPS) or flash sintering. These methods deal with special heating and, therefore, it is difficult to describe obtained results by a conventional pressure-less sintering mechanism. This work deals with specially designed pressure-less rapid sintering furnace, which allows heating rates on level of hundreds degrees per minute. Sample with volume over 30 cm3 from low thermally conductive tetragonal zirconia stabilized with 3 mol% Y2O3 (3Y-TZP) was rapidly sintered to relative density of 86% without crack formation. Experimental data were used for numerical calculations of conduction/convection heat transfer. Obtained results reveal that the maximum temperature in the sample does not exceed 1200 °C if only heating by conduction and convection is considered. Our results indicate that during rapid sintering of low thermally conductive materials radiation heat transfer is dominant in both conventional and SPS conditions.