The thermal treatment had two parts: in the first 30 min most of the organic materials were burnt out, whereas in the second part the eggshell transformation into calcium-oxide was obtained (holding time was 3 h). To synthesize calcium phosphate powders, shells were crushed and milled in a ball milling and an attritor milling set up. The ball milling (Fritsch GmBH) is equipped with alumina balls and bowls, the attritor milling (Union Process) was fitted with zirconia tanks and zirconia balls (∅2 mm). The crushed eggshell was reacted by an exothermic reaction with phosphoric acid. The mixtures were milled for 5 h, at 4000 rpm (attritor milling) or for 10 h at 350 rpm (ball milling), for homogenous mixing and to prevent agglomeration of the calcined. The details of the milling procedure, and the samples are presented in Table 1. HAp powders usually degrade at high temperatures, the most common problem being that the CaO phase appears. After milling, a small amount of (approximately 0.5 g) each type of HAp powders were heat treated at 900 °C for 2 h in air atmosphere (Table 1).