Control of Composition and Microstructure of Porous Carbonate-Containing Hydroxyapatite by Sintering Under Controlled Atmospheres

Carbonate-containing hydroxyapatite (CHA) is considered a promising material for artificial bones.To obtain CHA porous ceramics with a high carbonate content, two CHA powders (CHA-0.6 and CHA-5.0)containing 0.6 and 5.0 mass% of carbonate, respectively, and having particle sizes of 0.1 and 1.5 μm, were sintered at various temperatures under air, CO₂, and steam atmospheres.Sintering was delayed under CO₂ and steam atmospheres.Both samples were affected by the type of atmosphere in a similar way, but the overall relative density was lower in CHA-5.0.Both samples retained their porous structure with a relatively high carbonate content of 2-3 mass% when sintered at 900-1000 °C under a CO₂ atmosphere.The carbonate content increased to 3-5 mass% when the combination of steam and CO₂ was used as atmospheres at 1000 °C, with the higher carbonate content observed in CHA-5.0.These results demonstrate that porous CHA ceramics with a relatively high carbonate content can be obtained by sintering CHA particles under controlled atmospheric conditions.