One of the critical factors in advanced ceramics is synthesizing the starting powder. Therefore in the last few years many different methods of synthesis of nanosized alumina powders were developed. Unfortunately, very often the synthesized nanopowder is not the thermodynamically stable phase. Hence, the phase transformations occurs during sintering process.  The transformation into the stable α-Al₂O₃ goes through the stages of nucleation, transformation to a phase and coalescence of α-nuclei. During densification a intragranular pores are closed so to achieve fully densification in the final stage of sintering the holding time and temperatures must be increased. But the kinetics of transformation and in the  consequence the microstructure can be enhanced by the addition of α-seeds that act as a nucleation sites for phase transformation.

In this work a commercially available δ-alumina powder (NanoTek) with average particle size 47nm was seeded by 1, 1.5 and 2wt% of α-Al₂O₃ (TM-DAR, Taimei Chemicals, Japan). Obtained samples were sintered in different temperatures. Next the influence of addition of  α-Al₂O₃ on the transformation, microstructural development and densification was studied. The researches showed that the unseeded samples have lower sintered densities although the green densities of seeded and unseeded samples were similar. The transformation temperature and the microstructure of seeded samples after sintering also was improved

This work was financially supported by Ministry of Science and Higher Education: Grant No. N205 009 31 / 0353

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