Despite the growing interest in the spark plasma sintering (SPS) of uranium dioxide, its sintering mechanisms have yet to be studied in great detail. Herein we propose a direct method to calculate the apparent activation energy for densification, Q_act, and the stress exponent, n, for SPS of nearly stoichiometric UO₂. A set of experiments performed at different heating rates (CHR) and different pressures levels allowed us to calculate Q_act and n, respectively, though we were limited to a theoretical density between 50% to 75 %. The master sintering curve was employed as a complementary method to compare Q_act. The average values were Q_act =96 kJ/mol (CHR), Q_act = 100 kJ/mol (MSC) and n = 1.4. We have therefore proposed grain boundary diffusion coupled with grain boundary sliding as the densification mechanism. The activation energy in SPS tends to be lower compared with that in other processes like conventional sintering (250−450 kJ/mol), creep (350−550 kJ/mol) and hot pressing (222 kJ/mol and 480 kJ/mol).

This decrease could be due to the effect of the electric field combined with the higher heating rates, typical of SPS.

尽管人们对二氧化铀的火花等离子体烧结（SPS）越来越感兴趣，但其烧结机理尚待详细研究。本文中，我们提出了一种直接方法，用于计算接近化学计量比的UO _2的SPS的致密化Q _act的表观活化能Q _act和应力指数n。尽管我们将理论密度限制在50％至75％之间，但在不同的加热速率（CHR）和不同的压力水平下进行的一组实验分别使我们能够计算Q _act和n。采用主烧结曲线作为比较Q_行为的补充方法。平均值是Q _act = 96 kJ / mol（CHR），Q _act = 100 kJ / mol（MSC），n = 1.4。因此，我们提出了结合晶界滑动的晶界扩散作为致密化机制。与传统烧结（250-450 kJ / mol），蠕变（350-550 kJ / mol）和热压（222 kJ / mol和480 kJ / mol）等其他工艺相比，SPS中的活化能趋于降低。 。

这种降低可能是由于电场的影响以及SPS典型的较高加热速率所致。