Influence of heating rate on two-step sintering behaviour of different hydroxyapatite nanopowders

Abstract

Producing of dense nanostructured calcium phosphate-based bioceramics represents a challenging issue in biomaterial science. High volume fraction of energetically rich grain boundaries contributes to improved attachment of chemical species, which are important in the processes of bone tissue regeneration. Beside that, nanostructured ceramics exhibited better mechanical properties due to changed fracture path. The process of presureless sintering is the most compatible route for industrial fabrication of dense bioceramic materials, but it is often connected with accelerated grain growth in final sintering stage. In the method of two-step sintering (TSS) the difference between kinetics of grain boundary diffusion and grain boundary migration is used to obtain almost full dense, nanostructured ceramics. However, designing of proper sintering parameters is very important in every sintering technique employed. In this study, hydroxyapatite nanopowders were synthesized by different methods, precisely, chemical precipitation and hydrothermal processing of precipitate. The prepared powders were pressed in pellets and heated with different heating rates (2, 5, 10 ºC/min), with short isothermal dwell at certain temperature range. From that shrinkage curves the appropriate conditions were selected to design TSS experiments. The impact of heating rate on final density, phase composition, average grain size and microstructural uniformity is discussed. Furthermore, mechanical properties were determined.