Carbon and sintering of oxides: Densification kinetics vary by orders of magnitude

Advanced ceramics manufacturing (e.g., non-conventional sintering, additive manufacturing…) often introduces carbonaceous species into oxides. Herein, we investigate the carbon impact on the densification kinetics in model systems (Al2O3 and Y2O3-stabilized ZrO2). While the influence of carbon may be limited in the case of pressure-assisted densification, its impact in pressure-less processes is significant: the addition of ≈ 0.5 wt% of carbon delays consolidation by hundreds of degrees Celsius. Such an effect is also visible when the carbon doping occurs after pre-sintering, i.e., after the formation of the first necks and grain boundaries. Besides densification, grain growth is substantially affected. The observed change in the densification kinetics is consistent with a decreasein the driving force induced by the carbon adsorption on the powder surface, although additional effects might also occur. These results are of particular relevance given that different sources of carbon are emerging in ceramic processing from additive manufacturing to non-conventional sintering.