Chow Laurence C, Sun Limin, Hockey Bernard
American Dental Association Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD 20899.
National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
J Res Natl Inst Stand Technol. 2004 Dec 1;109(6):543-51. doi: 10.6028/jres.109.041. Print 2004 Nov-Dec.
In previous studies nano sized hydroxyapatite (HA) particles were prepared by solgel or precipitation methods, in which the products were washed by aqueous or non-aqueous liquids to remove impurities or undesired components. The washing is know to modify the surfaces of the cystalline particles. This study evaluated properties of nano HA materials prepared by a spray drying method in which the HA product was not exposed to any liquid after its formation. The spray drying apparatus consisted of a nozzle that sprayed an acidic calcium phosphate solution in the form of a fine mist into a stream of filtered air flowing through a heated glass column. The water and volatile acid were evaporated by the time the mist reached the end of the column, and the fine particles were collected by an electrostatic precipitator. Powder x ray diffraction patterns suggested the material was amorphous, exhibiting a single broad peak at 30.5° 2θ. However, high resolution transmission electron microscopic analysis showed that the particles, some of which were 5 nm in size, exhibited well ordered HA lattice fringes. Small area diffraction patterns were indicative of HA. Fourier transfer infrared spectroscopy showed patterns of typical of HA with small amounts of HPO4 (2-). The thermodynamic solubility product of the nano HA was 3.3 × 10(-94) compared to 1 × 10(-117) for macro scale crystalline HA. These results showed that a spray drying technique can be used to prepare nanometer sized crystalline HA that have significantly different physicochemical properties than those of its bulk-scale counterpart.
在先前的研究中，纳米级羟基磷灰石（HA）颗粒是通过溶胶 - 凝胶法或沉淀法制备的，其中产物用含水或非水液体洗涤以去除杂质或不需要的成分。已知这种洗涤会改变结晶颗粒的表面。本研究评估了通过喷雾干燥法制备的纳米HA材料的性能，在该方法中，HA产物形成后未暴露于任何液体。喷雾干燥装置由一个喷嘴组成，该喷嘴将酸性磷酸钙溶液以细雾形式喷入流经加热玻璃柱的过滤空气流中。当雾到达柱的末端时，水和挥发性酸被蒸发，细颗粒通过静电除尘器收集。粉末X射线衍射图谱表明该材料是无定形的，在2θ为30.5°处呈现一个宽峰。然而，高分辨率透射电子显微镜分析表明，这些颗粒（其中一些尺寸为5nm）呈现出有序的HA晶格条纹。小面积衍射图谱表明是HA。傅里叶变换红外光谱显示出具有少量HPO4（2 - ）的典型HA图谱。纳米HA的热力学溶解度积为3.3×10（-94），而宏观尺度结晶HA的溶解度积为1×10（-117）。这些结果表明，喷雾干燥技术可用于制备具有与其宏观对应物显著不同的物理化学性质的纳米级结晶HA。
