The aim of this study was to evaluate the effect of alumina (Al₂O₃) additive and sintering temperature on the microstructural, physical, mechanical, and in vitro bioactivity properties of hydroxyapatite (HA). The composites consisting of 2.5 and 5 wt% Al₂O₃ and monolithic HA were uniaxially pelleted at 350 MPa with the size of ∅11 and 11 mm² and sintered at five different temperatures ranging from 900 to 1300 °C for 4 h. A series of thermal analysis methods and tests were used to evaluate both phase changes that occurred during sintering and the physical/mechanical properties of the sintered samples. The bioactivity property of the samples having the highest compressive strength value was investigated in a simulated body fluid (SBF) solution for 3, 7, 15, and 30 days. Results showed that HA without Al₂O₃ had started to decompose at 1200 °C, and the addition of Al₂O₃ led to the reduction of decomposition temperature from 1200 to 900 °C. However, the main phase was HA for all the sintered samples. The highest mechanical strength values were 130.20 ± 6.22, 60.27 ± 9.93, and 0.96 ± 0.05 MPa m^1/2 for compressive strength, three-point bending strength, and fracture toughness, respectively, for monolithic HA when it was sintered at 1100 °C. All of these mechanical strength values of monolithic HA were improved higher than the rate of 60% as the grain growth of HA was inhibited by the addition of Al₂O₃. The highest mechanical strength values of HA–Al₂O₃ composites were obtained for the samples sintered at 1200 °C when the densification rate reached 90%. In vitro investigations showed that Al₂O₃ led to a reduction in the in vitro bioactivity of HA, but it could be used in the human body since its surface is coated by apatite layers when in vitro time reached 30 days.

中文翻译：

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氧化铝添加剂和烧结温度对羟基磷灰石-氧化铝复合材料的微观结构，物理，机械和生物活性的影响

这项研究的目的是评估氧化铝（Al ₂ O ₃）添加剂和烧结温度对羟基磷灰石（HA）的微观结构，物理，机械和体外生物活性的影响。将由2.5和5 wt％的Al ₂ O ₃和单块HA组成的复合材料在350 MPa下单轴造粒，尺寸分别为∅11和11 mm ²并在900至1300°C的五个不同温度下烧结4小时。使用了一系列热分析方法和测试来评估烧结过程中发生的相变以及烧结样品的物理/机械性能。在模拟体液（SBF）溶液中研究了3天，7天，15天和30天具有最高抗压强度值的样品的生物活性。结果表明，不含Al ₂ O _3的HA在1200°C时开始分解，并加入Al ₂ O ₃导致分解温度从1200降低到900°C。但是，所有烧结样品的主要相均为HA。整体HA在1100°C烧结时的最高机械强度分别为130.20±6.22、60.27±9.93和0.96±0.05 MPa m ^1/2，分别为抗压强度，三点弯曲强度和断裂韧性。 。由于加入Al ₂ O ₃抑制了HA的晶粒长大，因此整体HA的所有这些机械强度值均提高了60％以上。HA–Al ₂ O ₃的最高机械强度值当致密化率达到90％时，获得了在1200°C烧结的样品的复合材料。体外研究表明，Al ₂ O ₃导致HA的体外生物活性降低，但由于在体外培养时间达到30天时其表面被磷灰石层覆盖，因此可用于人体。