Abstract
The mixed powders of β-Ca3(PO4)2 (TCP) and DyPO4 with mole ratios (Dy/TCP) 0-1.0 were uniaxially dry-pressed at 50MPa to disks or bars, before cold isostatic pressing at 100MPa. The specimens were fired at 1000-1400°C for 10min-20hrs in air. The phases observed in the fired specimens above 1250°C were α-TCP and HAp for Dy/TCP mole ratio=0-0.01, α-TCP, Dy-containing β-TCP and HAp for Dy/TCP ratio=0.05, Dy-containing β-TCP and HAp for Dy/TCP ratio=0.10-0.35, and Dy-containing β-TCP, DyPO4 and HAp for Dy/TCP ratio=0.40-1.0. The upper solubility limit of Dy in β-TCP was reached when the Dy/TCP ratio was 0.33. The relative density≥95% was achieved when the Dy/TCP ratio was 0.10-0.25 above 1300°C (3hrs). The maximum relative density was 97% at 1300°C, over 98% at 1350-1400°C when the Dy/TCP ratio was 0.18. The sintered specimens (relative density≥95%) could be machined using metallic gravers or dental burs. The reason why the Dy-containing β-TCP ceramics are machinable seems to be due to the easy transgranular fracture of β-TCP grains doped with Dy. The three-point bending strength and Vickers' hardness of the bars sintered at 1300°C for 3hrs were in the range 30-50MPa and 2-3GPa, respectively, when the Dy/TCP ratio was 0.10-0.25. However, increasing firing temperature over 1350°C tended to decrease the bending strength because of grain growth. The linear thermal expansion coefficients were within 11-12×10-6/°C (-900°C). The citric solubility%, which was determined under the condition of 1g of Dy-containing β-TCP powder (fired at 1300°C for 3hrs) and 150ml of 2% citric acid solution at 20°C for 1h, was about 95% when the Dy/TCP ratio was 0.05-0.33.
