Silicon nitride ceramics with SiO₂, CaO, and MgO as sintering aids were investigated in view of biomedical applications. In the current study, samples with four different compositions were pressureless sintered at 1750^°C for 1 h under a nitrogen atmosphere. The samples were evaluated concerning densification, microstructure, mechanical properties, and in vitro bioactivity. Microstructures with elongated β-Si₃N₄ grains dispersed in an intergranular phase and with densities from 78.77 to 97.14% of the theoretical density were obtained. Higher contents of SiO₂ resulted in the best densification and mechanical properties. Besides, replacements of CaO by MgO in the initial compositions affected Young's modulus and in vitro bioactivity. Considering the samples with relative density higher than 94.14%, those with lower values of Young's modulus had lower SiO₂/MgO ratios. After immersion in SBF (Simulated Body Fluid), the samples with high porosity and/or partial replacements of CaO by MgO had their surfaces coated with a layer rich in calcium and phosphorus, morphologically similar to hydroxyapatite. Hence, producing silicon nitride ceramics with the potential to be used as orthopedic implants must consider ideal amounts of additives. In this article, the best combination of mechanical properties and mineralization capability was reached by the composition with low content of MgO, and high content of SiO₂ and CaO.

中文翻译：

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添加 SiO2、CaO 和 MgO 的氮化硅陶瓷的机械性能和体外生物活性

鉴于生物医学应用，研究了以SiO ₂ 、CaO和MgO作为烧结助剂的氮化硅陶瓷。在目前的研究中，具有四种不同成分的样品在氮气气氛下在 1750 ^{°C下无压烧结 1 小时。}对样品的致密化、微观结构、机械性能和体外生物活性进行了评估。获得了具有细长β-Si ₃ N ₄晶粒分散在晶间相中且密度为理论密度的78.77％至97.14％的微观结构。_{SiO 2}含量较高导致最佳的致密化和机械性能。此外，在初始组合物中用 MgO 替代 CaO 会影响杨氏模量和体外生物活性。考虑相对密度高于94.14%的样品，杨氏模量值较低的样品SiO _2较低/MgO 比率。在浸入 SBF（模拟体液）后，具有高孔隙率和/或部分用 MgO 替代 CaO 的样品的表面涂有富含钙和磷的层，其形态类似于羟基磷灰石。因此，生产具有用作骨科植入物潜力的氮化硅陶瓷必须考虑添加剂的理想量。在本文中，MgO含量低，SiO ₂和CaO含量高的组成达到了机械性能和矿化能力的最佳组合。