Transparent Nanocrystalline Hydroxyapatite Bioceramics Prepared by High Pressure and Room Temperature Compaction

Nanopolycrystalline hydroxyapatite (HAP) ceramics are proposed to possess superior mechanical and optical properties, making them suitable for use as windows for implantable biodevices. However, sintering transparent ceramics typically requires high temperatures to eliminate scattering centers, which often leads to significant grain growth, resulting in coarse micron‐sized grains that increase light scattering and reduce transparency. In this work, the densification process of nanopowder HAP compacts using high pressure without the aid of temperature is explored. High pressure alone can initiate and drive densification in nanopowder HAP compacts. At pressures exceeding 5 GPa, the samples exhibited high transparency and transmission in both infrared and visible wavelengths. By applying high pressure, densification can be achieved without the need for externally applied thermal energy. High‐pressure sintering shows the advantageous in preventing grain growth and promoting the formation of bulk nanostructure ceramics, maintaining the grain size of the initial particles. High‐pressure compaction at room temperature provides a way to prepare highly dense ceramics with nanosized grains while avoiding excessive grain growth.