The master sintering curve approach was extended theoretically to the Field-Assisted Sintering Technique (or SPS). Experimental data from constant heating rate testing confirm the general applicability of this framework. An apparent activation energy of similar to 290 kJ/mol was found for ultrafine alumina below 1200 A degrees C. As alumina densifies by grain boundary diffusion in the present conditions, this low value of the apparent activation energy might be due to thermal gradients in the specimens induced by rapid heating.