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Visualizing Different Crystalline States during the Infrared Imaging of Calcium Phosphates
Vibrational Spectroscopy ( IF 2.5 ) Pub Date : 2020-05-01 , DOI: 10.1016/j.vibspec.2020.103045
Vuk Uskoković 1
Affiliation  

Abstract Methods utilizing relatively simple mathematical operations during physical analyses to enable the visualization of otherwise invisible correlations and effects are of particular appeal to researchers and students in pedagogical settings. At the same time, discerning the amorphous phase from its crystalline counterpart in materials is challenging with the use of vibrational spectroscopy and is nowhere as straightforward as in phase composition analytical methods such as X-ray diffraction. A method is demonstrated for the use of first- and second-order differentiation of Fourier transform infrared spectra of calcium phosphates to distinguish their amorphous states from the crystalline ones based on the exact line positioning rather than on comparatively vaguer band broadening and splitting effects. The study utilizes a kinetic approach, focusing on the comparison of spectral features of amorphous precursors annealed in air at different temperatures or aged for different periods of time in an aqueous solution until transforming to one or a mixture of crystalline phases, including hydroxyapatite and α- and β-tricalcium phosphate. One of the findings challenges the concept of the nucleation lag time preceding the crystallization from amorphous precursors as a “dead” period and derives a finite degree of constructive changes occurring at the atomic scale in its course. The differential method for highlighting spectral differences depending on the sample crystallinity allows for monitoring in situ the process of conversion of the amorphous calcium phosphate phase to its crystalline analogue(s). One such method can be of practical significance for synthetic solid state chemists testing for the chemical stability and/or concentration of the reactive amorphous phase in these materials, but also for biologists measuring the maturity of bone and medical researchers evaluating its phase composition and, thus, the state of metabolic and mechanical stability.

中文翻译:

磷酸钙红外成像过程中不同晶态的可视化

摘要 在物理分析过程中利用相对简单的数学运算来实现其他不可见的相关性和效果的可视化的方法对教学环境中的研究人员和学生特别有吸引力。同时,使用振动光谱法将材料中的非晶相与其结晶对应物区分开来具有挑战性,并且没有像 X 射线衍射等相组成分析方法那样简单。演示了一种使用磷酸钙的傅里叶变换红外光谱的一阶和二阶微分的方法,以基于精确的线定位而不是相对模糊的带展宽和分裂效应来区分它们的无定形状态和结晶状态。该研究采用动力学方法,重点比较了无定形前体在不同温度下在空气中退火或在水溶液中老化不同时间直到转变为一种或多种结晶相的光谱特征,包括羟基磷灰石和α-和β-磷酸三钙。其中一项发现挑战了将无定形前体结晶之前的成核滞后时间作为“死”期的概念,并得出在其过程中在原子尺度上发生的有限程度的建设性变化。根据样品结晶度突出光谱差异的微分方法允许在原位监测无定形磷酸钙相转化为其结晶类似物的过程。
更新日期:2020-05-01
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