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首页> 外文期刊>Crystal growth & design >Transparent Aggregates of Nanocrystalline Hydroxyapatite
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Transparent Aggregates of Nanocrystalline Hydroxyapatite

机译：纳米晶羟基磷灰石的透明聚集体

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摘要

Assemblies of nanoparticles into transparent aggregates have solicited strong research interest in the form of both crystalline or amorphous aggregates of nanoparticles. In the present work, we make short-range ordered several millimeter-sized transparent aggregates of citrate modified calcium phosphate nanoparticles and discuss the mechanism of their formation. Microparticles of hydroxyapatite (HAP) nanocrystals and amorphous calcium phosphate (ACP) were synthesized with citrate as a growth and assembly modifier. Millimeter-sized transparent aggregates of these microparticles were made with 0 to 7.5% citrate/Ca2+. The degree of crystallinity, i.e., the ratio between nanocrystalline HAP and ACP in the microparticles, was determined by Rietveld refinement of powder X-ray diffraction data with an internal standard. It was found to decrease with increasing citrate concentration. Citrate also reduced the nanocrystallite size at low citrate concentrations. Above similar to 3% added citrate, the crystallite size did not reduce further. Transparent aggregates were obtained by drying a suspension of particles. The aggregates lacked long-range order and in many cases featured spiral fractures partially propagating through the aggregates. The assembly mechanisms were studied by in situ video imaging, polarized optical microscopy, transmission electron microscopy, and confocal microscopy. The transparent aggregates consisted of polydisperse microparticles. The transparent aggregates form due to evaporation, but sedimentation leads to vertical size segregation with larger microparticles preferentially located at the bottom of the sample.
机译：将纳米颗粒组装成透明聚集体以纳米颗粒的结晶或无定形聚集体的形式引起了强烈的研究兴趣。在目前的工作中，我们使柠檬酸盐改性的磷酸钙纳米粒子短程有序地形成了几毫米大小的透明聚集体，并讨论了它们的形成机理。以柠檬酸盐为生长和组装改性剂，合成了羟基磷灰石（HAP）纳米晶体和无定形磷酸钙（ACP）微粒。这些微粒的毫米大小的透明聚集体由0至7.5％柠檬酸盐/ Ca2 +制成。结晶度，即微粒中纳米晶HAP与ACP之间的比例，是通过Rietveld用内标对粉末X射线衍射数据进行精制确定的。发现它随着柠檬酸盐浓度的增加而降低。柠檬酸盐还降低了低柠檬酸盐浓度下的纳米微晶尺寸。超过3％的添加柠檬酸盐，微晶尺寸没有进一步减小。通过干燥颗粒的悬浮液获得透明的聚集体。骨料缺乏远距离有序性，在许多情况下，特征在于螺旋裂缝部分地扩散穿过骨料。通过原位视频成像，偏振光学显微镜，透射电子显微镜和共聚焦显微镜研究了组装机理。透明的聚集体由多分散的微粒组成。透明的聚集体由于蒸发而形成，但是沉淀导致垂直尺寸的分离，较大的微粒优先位于样品底部。

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