【作者】 常青；

【导师】 茹红强； Daolun Chen；

【作者基本信息】 东北大学 ， 材料学， 2011， 博士

【摘要】 羟基磷灰石(HA)具有优良的生物相容性、生物活性、骨传导性,因此羟基磷灰石在生物硬组织的修复、替换及提高硬组织的功能方面发挥着越来越重要的作用。但由于羟基磷灰石脆性较大,无法满足机体对其力学性能的要求。虽然最近研究发现通过引进金属钛(Ti)可以提高羟基磷灰石的韧性,但采用的热压等烧结工艺只能作形状简单的制品,且成本高。因此如何低成本获得力学性能优良、形状易控的HA/Ti复合材料成为人们越来越关心的问题。本文针对这一问题,通过向HA/Ti材料中引入铁(Fe),采用低成本的真空烧结工艺制备了新型的HA/Ti-Fe复合材料,并详细研究了该材料的粉体制备、材料烧结、力学性能和生物性能。本研究对于开发新型的HA基复合材料,拓宽其临床的应用等具有重要的理论意义和实际应用价值。采用Ca(NO3)2-P2O5和Ca(OH)2-H3PO4两种反应体系制备HA粉体。在以Ca(NO3)2和P2O5为反应物制备HA粉体的过程中,系统研究了柠檬酸的添加对粉体形成过程、产物杂质相及粉体粒度的影响。结果表明：加入的柠檬酸通过螯合作用改变了HA的形成历程、提高了胶体的稳定性、降低了杂质相CaO的含量,并在一定程度上抑制了粉体的团聚。在以Ca(OH)2和H3P04为反应物制备HA粉体的过程中,研究了反应终点pH值、球磨处理和煅烧温度对粉体相组成和粒度的影响。结果表明：反应终点pH值控制在10.5左右时,可以得到结晶较好、组分单一的HA粉体；采用简单经济的球磨工艺,可有效地打破粉体团聚,减小颗粒尺寸,增加颗粒比表面能；煅烧温度为750℃时,制备的HA粉体结晶度好、纯度高、颗粒细小且分布均匀。通过比较两种体系制备的HA粉体性能,Ca(OH)2-H3PO4体系可制得粒度分布均匀的高纯HA粉体,且该法工艺简单,适合批量制备,本文最终选用该体系制备HA粉体。此外,本实验对Ca(OH)2-H3PO4体系制备的HA粉体的烧结行为进行了研究。结果表明：采用真空烧结工艺,可在1000℃的低温下,获得致密度高达99%的HA陶瓷。根据Ti-Fe二元相图,本文首先确定了Ti和Fe的混合比例为67：33(质量比,w%),通过球磨工艺获得Ti-Fe复合粉体；然后将此复合粉体与Ca(OH)2-H3PO4体系制备的HA粉体混合,通过真空烧结工艺制备了HA/Ti-Fe复合材料。利用X射线衍射仪(XRD)、扫描电镜(SEM)和透射电镜(TEM)分析了HA/Ti-Fe复合材料的相组成和微观组织,研究了Fe的引入和Ti-Fe颗粒的含量对相组成和微观组织的影响,同时考察了Ti-Fe烧结体的微观组织,详细探讨了HA/Ti-Fe复合材料微观组织的形成机理。结果表明：通过真空烧结,可成功获得孔隙率低、致密度较好的HA/Ti-Fe复合材料；Fe的引入有效地抑制了HA的分解及其与Ti的反应,使得主晶相HA和Ti相仍保留在基体中；基体HA中的Ti-Fe增强颗粒呈一种新颖的蛋壳状结构,其中核区主要由Fe组成,壳层主要由Ti组成。在HA/Ti-Fe复合材料制备及微观组织研究的基础上,本文考察了复合材料的力学性能,研究了Ti-Fe颗粒的添加对复合材料力学性能的影响,探讨了复合材料的强韧化机理。结果表明：Ti-Fe颗粒的添加使复合材料的抗弯强度、断裂韧性和循环疲劳寿命均大幅提高。经1000℃C烧结,当Ti-Fe含量为5%时,复合材料的抗弯强度出现最大值(93MPa),与纯HA相比提高了42%；当Ti-Fe含量为15%时,复合材料的断裂韧性达到最大值(1.3MPa.m1/2),较纯HA提高了128%。复合材料的强韧化主要缘于Ti-Fe颗粒蛋壳状的组织结构、分布于壳层的韧性相Ti和Ti-Fe颗粒与HA基体之间具有结合强度良好的界面。Ti-Fe颗粒对复合材料的强韧化机制主要包括：颗粒的桥联增韧、裂纹偏转和裂纹的分叉增韧。本文同时研究了烧结温度对HA/Ti-Fe复合材料微观组织和力学性能的影响。结果表明：烧结温度的变化对微观组织影响较小。当提高烧结温度时,复合材料的致密度、抗弯强度、断裂韧性和循环疲劳寿命随之提高,但当烧结温度为1050℃C时,会加剧HA的分解。因此复合材料的最佳烧结温度为1000℃C。在上述研究基础上,本文还采用SEM立体技术对HA/Ti-Fe复合材料强度断口表面进行了三维重建并通过软件计算出了断口的分形维数,考察了分形维数与力学性能的关系。结果表明：复合材料的强度断口具有良好的分形特征,随着Ti-Fe颗粒含量的增加,复合材料断口的粗糙度增加,分形维数也随之增加；由于材料内部孔隙的存在,复合材料的强度与分形维数不存在定量的关系,但是断裂韧性与分形维数的增量呈正向的线性关系,与Mecholsky-Mackin方程非常吻合。最后采用模拟体液浸泡实验对HA/Ti-Fe复合材料的生物学行为进行了初步评价,研究了其在体液环境中的稳定性和生物活性。结果表明：Fe的引入提高了复合材料在体液环境中的长期稳定性；HA/5%(Ti-33w%Fe)复合材料既具有一定的生物稳定性,也表现出良好的生物活性,表面有类磷酸盐矿物质的沉积；HA/15%(Ti-33w%Fe)复合材料在SBF浸泡过程中几乎没有溶解或沉积发生,表现出极佳的生物稳定性。更多还原

【Abstract】 Hydroxyapatite (HA), due to its remarkable biocompatibility and its high chemical similarity to biological apatite present in human hard tissues, is a widely used biomaterial in clinical applications to repair human hard tissue bone and dentin. However, the successful application of HA ceramics in load-bearing areas is limited because of its low mechanical properties. Up to date, the reinforcement of HA with ductile titanium (Ti) particles via hot pressing has recently attracted much attention. But its high costs and limits on shaping make this method less attractive from both the technical and economical point of view. It is necessary to develop a cost-effective route of fabricating HA/Ti composites with improved strength and fracture toughness. The purpose of this project is, therefore, to synthesize a novel iron-containing HA/titanium composite in an attempt to develop HA-based composites with improved strength and toughness via low-temperature pressureless sintering in vacuum, including the synthesis of HA powders, preparation of the composites, mechanical properties and biological behavior of the composites. The present study might open up a new approach for the development of bio-composites with improved mechanical properties for the load-bearing applications.HA powder was prepared by two kinds of reagent groups which included Ca(NO3)2-P2O5ethanol solution and Ca(OH)2-H3PO4. In the process using Ca(NO3)2-P2O5as starting materials, the influence of citric acid (CA) on the formation process of HA nanopowder, phase purity and particle size were investigated. The results showed that the addition of CA improved the gel’s stability and changed the transformation process of HA from precursors due to the chelating effect of CA. The content of CaO phase in HA nanopowder obtained after addition of CA was reduced substantially in comparison with the powder prepared without using CA. Moreover, CA was also found to be able to suppress the agglomeration of powder particles, leading to the finer HA powders with high dispersibility. In the process using Ca(OH)2-H3PO4as starting materials, the influence of pH value, ball milling and calcination temperature on HA preparation were investigated. The results showed that the obtained HA powders were pure and highly crystallized when pH value was controlled at10.5.It was also found that the particle size was smaller after ball milling. The temperature of750℃was considered as the optimal calcination temperature. To prepare HA powders using Ca(OH)2-H3PO4as starting materials was finally chosen since this method is more cost-effective and easier to control. Besides, the sintering behavior of HA powders prepared by precipitation method was investigated. A relative density of99%could be obtained when the HA powders were pressureless sintered in vacuum at1000℃.A new iron-containing HA/Ti composite was synthesized using obtained HA powders and Ti-Fe particles as starting materials via pressureless sintering in vacuum at a relatively low temperature. The pure Ti and Fe powders, with a ratio of Ti-33w%Fe based on Ti-Fe phase diagram, were mixed by ball-milling to prepare Ti-Fe particles, which were then used to prepare HA/Ti-Fe composites. The influence of the addition of iron on the phase composition and microstructure of the composites were investigated via XRD, SEM and TEM. The results revealed that the addition of iron lessened the decomposition of HA and interaction between HA and Ti as well, which made the desirable Ti phase remain in the matrix. A unique core/shell microstructure of irregularly shaped Ti-Fe reinforcing particles was obtained, which consisted of outer shell of titanium and inner core of iron. This led to a favorable microstructure and good interfacial bonding with the HA matrix.In correlation with the preparation and microstructure of the HA based composites, the mechanical properties of the composites, and especially the underlying strengthening and toughening mechanisms were studied. It was found that the relative density, hardness, and Young’s modulus decreased with increasing amount of Ti-Fe particles, while the flexural strength, fracture toughness, and fatigue resistance increased significantly by the addition of iron. The flexural strength of the composite with5%of Ti-Fe particles which was sintered at1000℃reached the maximum value of93MPa. The fracture toughness of the composite with15%of Ti-Fe particles reached1.3MPa·m1/2. This represented an increase of the flexural strength and fracture toughness by42%and128%in comparison with pure HA, respectively. Such remarkable improvement in the mechanical properties of the composites was mainly due to the presence of more ductile Ti-Fe particles in the form of core/shell structure, coupled with their good bonding with the HA matrix. In the composites the major toughening mechanisms were crack bridging, crack branching and crack deflection. The influence of sintering temperature on the microstructure and mechanical properties of the HA based composites were investigated, too. It was found that the variation of sintering temperature had little effect on the formation of the novel core/shell microstructure, but influenced the mechanical properties. The relative density, flexural strength, fracture toughness and cyclic fatigue resistance were enhanced with increasing sintering temperature. But the decomposition of HA became severe when sintering temperature reached1050℃. Therefore, the optimal sintering temperature was1000℃.The fractal dimension of fracture surfaces of the HA based composites was evaluated using SEM stereoscopy coupled with a3D surface analysis. And the potential relationship between fracture toughness and fractal dimension in the HA based composites was discussed. The fracture surfaces of the HA based composites were observed to exhibit basically fractal characteristics. Both fracture surface roughness and fractal dimension increased with increasing amount of Ti-Fe reinforcing particles. Though no straightforward relation between the flexural strength and fractal dimension could be established due to the presence of porosity, the fracture toughness increased linearly with the square root of fractal dimensional increment (i.e., follows the Mecholsky-Mackin relationship well) due to the presence of more ductile Ti-Fe particles along with the effect of porosity in brittle materials.Finally, the in-vitro biological behavior of the newly-developed HA based composites was studied by immersing the composites in the simulated body fluid (SBF). The addition of iron was found to have a significant influence on the in-vitro biological behavior of the composites. The present results suggested that the stability of the composites in the physiological solution was markedly improved. Precipitation occurred on the surface of HA/5%(Ti-33w%Fe) composite, showing a good combination of physiostability with bioactivity, while HA/15%(Ti-33w%Fe) composite exhibited superior physiostability since there was no obvious change on the surface of HA/15%(Ti-33w%Fe) composite.更多还原