ИСТИНА

Biomaterials for bone replacement and grafting should possess sufficient strength, be bioresorbable and demonstrate osteoconductive and osteoinductive properties. Nowadays, hydroxyapatite (HA) and tricalcium phosphate (TCP) are the most widespread ceramics for bone grafting at the market. However, their resorption is reported, in some cases, to be not enough. This is why the search for more soluble compounds compared to HA and TCP looks very perspective. A possible way to increase ceramics solubility leads to partial substitution of Ca2+ -ions in Ca3(PO4)2 by alkali cations, like Na+ or/and K+. From this viewpoint, bioceramics based on compositions from Ca3(PO4)2 - CaKPO4 - CaNaPO4 ternary system are promising. At the same time, one should bear in mind that solubility level (resorbability) is depended not only by a reduction of lattice energy but also by microstructure features, what could be controlled by sintering conditions. To control Ca3(PO4)2 - CaKPO4 - CaNaPO4 based ceramic microstructure it is necessary to know possible phase transformations in the system and the way to manage microstructure by sintering schedule or sintering process. CaK0.6Na0.4PO4 was chosen as a model material for sintering experiments due to low volume changing at phase transformation and the presence of all ions in composition. These facts allow to study sintering behaviour interfering factors. In previous work, it was shown that single-phase CaK0.6Na0.4PO4 cannot be sintered to full-dense ceramics by conventional sintering. Large grains and a big amount of intragrain pores were a common feature of the microstructure of the ceramics under study. In this work, CaK0.6Na0.4PO4 was sintered by Spark Plasma Sintering (SPS) and flash-sintering methods. Results showed good microstructure with grain size with order 1-2μm. Pores were predominantly located in grain boundaries. Moreover, flash-sintering of CaK0.6Na0.4PO4 allowed to obtain ceramics below phase transition temperature. The reported study was funded by RFBR, project number 19-38-90199.