【作者】 胡晓霞；

【导师】 吕宇鹏；

【作者基本信息】 山东大学 ， 材料学， 2014， 博士

【摘要】 磷酸钙系生物材料广泛用于硬组织修复与重建,其力学性能、溶解行为等是决定其临床应用效果的关键因素。本文采用化学沉淀法制备羟基磷灰石(HA)和非晶磷灰石(ACP)粉末,并研究了传统机械混合法和悬浮液混合法制备ACP/HA复合粉末的物理性质及其在无压烧结、微波烧结和热压烧结过程中的烧结行为。以ACP晶化现象为切入点,将ACP与HA不同的烧结行为和溶解速率相结合,探索该复合烧结体的物理、力学性质与溶解行为。采用化学沉淀法在0℃下合成ACP粉末,Ca/P比、pH值、反应时间是合成ACP的主要影响因素。当Ca/P比为1.50,1.67和2.0时,均能制备出ACP粉末。反应前分别调节Ca,P溶液pH值为11,反应过程中不再进行混合溶液pH值的调节或调节其pH值并保证为11对合成ACP没有明显影响。另外,反应时间控制在30min以内,有利于获得理想的ACP粉末,制备的ACP粉末900℃煅烧后转变为p-TCP。通过机械混合法和悬浮液混合法获得的ACP/HA复合粉末中的ACP形态均为空心球形,直径为20～50nm；前者的HA为直径为100nm的粒状晶粒,后者的HA则为长度为20～40nm的棒状晶粒。由于粉末中HA形态和晶粒尺寸的不同,悬浮液混合法复合粉末的比表面积、总孔体积均比相同成分的机械混合法复合粉末大；复合粉末的比表面积和总孔体积均随ACP含量的升高而增大。另外,悬浮液混合法比机械混合法制备的复合粉末ACP与HA两相达到更小尺度上的分散均匀,这有利于改善材料的烧结性能。ACP/HA复合粉末经无压烧结、微波烧结和热压烧结后,均获得p-TCP/HA双相磷灰石(BCP)陶瓷,所得BCP陶瓷中p-TCP相的质量分数与ACP/HA粉末中ACP的质量分数大致相等,可以通过调节粉末中ACP的含量控制BCP陶瓷的相组成和相含量。无压烧结采用烧结温度为1150℃,保温时间为2h时可获得晶粒尺寸较小、较致密的BCP陶瓷。当ACP/HA粉末中ωACP为0wt.%时,获得晶粒尺寸约1-2μm的纯HA陶瓷；当ωACP为100wt.%时,获得晶粒尺寸约5-10μm的纯p-TCP陶瓷；当ωACP为25,50和75wt.%时,陶瓷中存在大、小两种尺寸的晶粒,且随ωACP的增大,大尺寸的晶粒所占的比例逐渐升高。机械混合体系烧结体中大小两种尺寸的晶粒分别成片分布。这主要是因为机械混合法是将HA与ACP粉末进行混合,混合时基本单元为几微米的颗粒,其尺寸相对较大,难以达到较小尺度上的均匀。随着复合粉末中ωACP的升高,气孔的数量逐渐增多、尺寸逐渐增大。采用悬浮液混合体系烧结体中2～3μm和1μm左右两种尺寸的晶粒均匀分布。这主要是因为此种混合方法是将HA与ACP在制备过程中的悬浮液状态下进行混合,混合过程伴随着机械搅拌,此时的基本单元为几百纳米的团聚体,尺寸相对较小,有利于两相混合均匀。另外,悬浮液混合法制备的复合粉末中随着ωACP的升高((ωACP为100wt.%除外),其烧结体气孔的数量逐渐减少,尺寸逐渐减小。采用微波烧结时,坯体的预烧对材料的相含量或微观结构有一定的影响。预烧不改变烧结体相组成,但提高了悬浮液混合体系烧结体中p-TCP相的含量,并使机械混合体系和悬浮液混合体系烧结体中均出现大量气孔。不同方法获得的相同成分的ACP/HA粉末,采用微波烧结时所得BCP陶瓷的晶粒尺寸不超过1μm。这主要是因为微波烧结的升温速度快,结晶形核驱动力大,形核率高。同时,保温时间较短,晶粒来不及长大。ACP/HA粉末(ωACP=25～75wt.%)经热压烧结后,机械混合体系烧结体中存在大小两种尺寸的晶粒,尺寸分别约为0.5～1μm和2～5μm,晶界平直。悬浮液混合体系烧结体中也存在大小两种尺寸的晶粒,但晶粒尺寸相对较小,分别为小于0.5μm和1～2μm,晶界弯曲。ACP含量为0～75wt.%的范围内,经三种烧结方式获得的机械混合体系烧结体,硬度、断裂韧性、抗压和抗弯强度随着粉末中ACP含量的增大而降低,悬浮液混合体系烧结体则随着粉末中ACP含量的升高而增大。这是由于机械混合体系烧结体致密度随着粉末中ACP含量的升高而减小,而悬浮液混合体系烧结体致密度随着粉末中ACP含量的升高而增大。在一定范围内,材料的力学性能随着致密度的增大而升高。悬浮液混合体系相同成分烧结体的硬度热压烧结最高、微波烧结最低,断裂韧性则是无压烧结最高、微波烧结最低,硬度和断裂韧性的最高值分别为5GPa和1.27MPa.m1/2。烧结体的抗压和抗弯强度为热压烧结最高,微波烧结最低。粉末试样(破碎后粒径315～400μm)经过Tris-HC1缓冲溶液浸泡14天后,粉末试样的失重量随原始粉末中ACP含量的增大而增大。悬浮液混合体系粉末试样的失重量低于相同烧结条件下的机械混合体系粉末试样,且溶解均匀、连续。块体试样经过28天浸泡后,机械混合体系块体试样的失重量也随原始粉末中ACP含量的增大而增大,且表面形成尺寸较大(约2～7μm)、分布不均匀的溶解孔。悬浮液混合体系块体试样的失重量不符合上述变化规律,试样表面形成的溶解孔分散均匀、尺寸较小。这主要是受两相在烧结体中的分散效果、晶粒尺寸和孔体积的共同影响。更多还原

【Abstract】 Calcium phosphate ceramics have become of prime importance for biological applications in the field of hard tissue repair and reconstruction, and their mechanical properties, solution and degradation behaviors, etc. are still immediate areas of research focus. In this work, hydroxyapatite (HA) and amorphous calcium phosphate (ACP) ceramic powder are synthesized by chemical coprecipitation process, and the ACP/HA powder mixture are prepared via mechanically mixing and suspension mixing method, respectively. Moreover, the sintering behaviors of the powder mixture are studied during the ordinary pressureless sintering, microwave sintering and hot-pressing sintering processes. In addition, physical, mechanical and dissolution properties of the sintered bodies are investigated from the view of the crystallization of ACP.The Ca/P ratio, pH value, reaction time are the major factors influencing the nature of the product for the chemical precipitation of ACP. The results show that ACP is formed when the Ca/P ratio of the reacting solution is1.50,1.67and2.0and the ACP would transformed into beta tricalcium phosphate (β-TCP) after the heat treatment at900℃.The adjusting of pH value during the reaction process has not affected the formation of ACP if the pH values of corresponding reacting solution were adjusted to11before the reaction. Additionally, the reaction time kept within30min is advantageous in obtaining of ACP powder.ACP/HA powder mixture with ACP content of25,50and75wt.%are prepared by mechanically mixing and suspension mixing methods. The ACP powder have morphologies of hollow sphere with diameters of20～50μm in both of mechanically and suspension mixing ACP/HA powder mixture, and the HA powder are composed of granular grains with diameters of100nm in the former mixture while rod-like grains with length of20～40nm in the latter. The specific surface area and total pore volume of suspension mixing ACP/HA powder mixture is larger than that of mechanically mixing one with the same composition due to the difference of HA morphology. Moreover, the specific surface areas and total pore volume are increased as the fraction of ACP increased in the powder mixture prepared via the same method.Biphasic calcium phosphate (BCP) ceramics consisting of β-TCP and HA are obtained after the mechanically and suspension mixing ACP/HA powder mixture are sintered via ordinary pressureless sintering, microwave sintering and hot pressing sintering. In addition, the weight ratios of (3-TCP in the BCP ceramics are roughly equal to the weight ratios of ACP in the ACP/HA powder mixture, indicating that the phase content of BCP ceramics can be tailored via the control of ACP content in the powder mixture.Dense BCP ceramics with limited grain size can be generated when the pressureless sintering is carried out at1150℃for2h. The grain size of β-TCP ceramics made from ACP powder and HA ceramics made from HA powder are5μm and1μm, respectively, while BCP ceramics made from the ACP/HA powder mixture with the ACP mass fraction ranging from25to75%consist of two kinds of grain sizes. The larger grains are about5～10μm, the smaller are1～2μm and they distribute inhomogeneously in the pressureless sintered BCP ceramics when the ACP/HA powder mixture are synthesized through mechanically mixing method. Moreover, the amount and size of pore are increased as the ACP content increases. On the contrary, the larger grains are only2～3μm, the smaller are still about1μm and they distribute homogeneously in the BCP ceramics made by suspension mixing ACP/HA powder mixture. The amount and size of pore are decreased as the ACP content increases.Presintering affects the phase content and microstructure of BCP ceramics when microwave sintering is carried out on the ACP/HA bodies. It increase the content of β-TCP phase in the BCP ceramics made by suspension mixing ACP/HA powder and leads to plenty of pores in all of BCP ceramics. The grain sizes are smaller than1μm.Grains with size of5μm and with straight boundaries are found in the hot pressing sintered BCP ceramics made by mechanically mixing ACP/HA powder (ωACP=25～75wt.%). Conversely, grain sizes are not larger than2.5μm if the ACP/HA powder mixture are prepared via suspension mixing method. In addition, there is nearly on pore in all of hot pressing sintered BCP ceramics.In general, the mechanical properties including hardness, fracture toughness and compressive strength of sintered bodies made of suspension mixing powder are all enhanced from those of mechanically mixing powder under the same sintering conditions. Moreover, the mechanical properties of sintered bodies increase as the mass fraction of ACP increased from0to75%in the original suspension mixing powder while the mechanically mixing powder follow the inverse regularity. The hardness and fracture toughness of pressureless sintered bodies made from suspension mixing powder with75wt.%ACP are5GPa and1.27MPa-m1/2.In vitro dissolution experiments of sintered ACP/HA bodies is carried out in Tris-HCl buffer solution, the results show that the weight loss of soaked powder samples (315～400nm) increases as the content of ACP in ACP/HA powder mixture increases. Additionally, the weight loss of powder sample made of suspension mixing method is less than that of mechanically mixing under the same condition after soaked for14days, and the dissolution is homogeneously and continuously. For the bulk samples made of mechanically mixing composite powder, weight loss also increases with the ACP content in the original powder increases after28days immersing. Meanwhile, large sizes of dissolved pores are formed on the surface and distribute inhomogeneously. However, weight loss, for the bulk samples made of suspension mixing composite powder, doesn’t follow the above rule. The dissolved pores on their surface are small and distribute homogeneously, which is mainly influenced by the phase content, grain size and pore volume.更多还原