Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degreesC, the A-type carbonate hydroxyapatite was crystallized at 635 degreesC in particles of similar size (40-120 nm) with no internal porosity. At a higher temperature (900 degreesC) a sintering process took place, resulting in network of a larger particles, consisting of HAp and P-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degreesC with an activation energy of 62.7-72.2 kcal mol(-1). (C) 2003 Elsevier Science (USA). All rights reserved.