Effect of Solids Loadings, Sintering Temperatures and Sintering Periods on Microstructure of Hydroxyapatite

Abstract

Attributed to its biocompatibility and osteoconductivity, hydroxyapatite (HAp, Ca10(PO4)6(OH)2) has been extensively utilized as a bioactive material. As the implant material, HAp is required to be fabricated into a porous form. The present study was therefore aimed at synthesizing HAp powder by solution combustion technique and at fabricating porous HAp specimens. Calcium nitrate and ammonium dihydrogenphosphate (NH4H2PO4), with Ca/P ratio equal to 2.3, were used as initial reagents in the HAp synthesis process. X-ray diffraction analysis confirmed that HAp was present as the primary phase, while minor secondary phases, Tri-calcium phosphaste (TCP) and CaO, were also observed. To prepare porous specimens, HAp slip with solids loadings ranging from 15 to 25 vol% was cast into acrylic molds and sintered. The sintering temperatures were 1350°C and 1450°C, and sintering periods ranged from 2 to 4 hours. Results from microstructural analysis revealed that high solids loadings, sintering temperatures and sintering periods resulted in decreasing of porosity. Porosity in the range between 30 and 90%, which was in an acceptable range for orthopedic applications, was observed.