**4. Enhancements in the sinterability of HA/ZrO2 ceramic composites**

To overcome the problem of grain growth, unconventional sintering and densification techniques have been proposed. The literature shows that dense HA bodies can be produced by a range of thermal treatments in addition to pressureless air sintering such as conventional HIP, microwave and SPS. However, the application of high temperatures during processing may cause decomposition of the principal components.

To minimize these reactions, some efforts have been made toward reducing the sintering temperature and holding time. Simple economical routes to microstructural improvement are therefore worth investigating. One alternative is the use the sol-gel process to synthesize a large variety of compositions carefully doped with additional phases, allowing obtain HA nanosized particles and a greater control of the morphology and microstructure of the derived HA/ZrO2 compacts.
