A structural study of size-dependent lattice variation: In situ X-ray diffraction of the growth of goethite nanoparticles from 2-line ferrihydrite
A structural study of size-dependent lattice variation: In situ X-ray diffraction of the growth of goethite nanoparticles from 2-line ferrihydrite
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DOI：
10.2138/am-2020-7217
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发表时间：
2020-05-01
影响因子：
3.1
通讯作者：
Chen, Si Athena
中科院分区：
文献类型：
--
作者：
Heaney, Peter J.;Oxman, Matthew J.;Chen, Si Athena
与大多数天然金属不同，当微晶尺寸接近纳米级时，金属氧化物的晶胞倾向于膨胀。在这里，我们回顾了不同的模型，占这种行为，我们目前的结构分析针铁矿（α-FeOOH）微晶从类似于10到类似于30 nm。针铁矿的研究在连续的颗粒生长过程中，通过水热转化的2线水铁矿在pH值为13.6，在80，90，和100摄氏度，使用时间分辨，角色散同步X射线衍射。将Ferrihydrite凝胶注入具有低背景散射的聚酰亚胺毛细管中，增加了用于检测加热后成核的针铁矿纳米晶体的衍射的灵敏度。Rietveld分析使晶体学和动力学数据的高分辨率提取成为可能。针铁矿的晶粒尺寸随时间以相似的速率增加，为所有temperature.With增加晶粒尺寸，针铁矿晶胞体积减小，主要是由于收缩沿着c轴，方向的紧密堆积（空间群Pnma）。我们引入纳米尺度的收缩系数（CNC）作为一个类似的热膨胀系数（CTE）比较的晶格应变对针铁矿和其他金属氧化物的晶粒尺寸的依赖性，我们认为，纳米尺度诱导的晶体膨胀是定量类似的针铁矿加热时产生的。此外，我们的一级动力学模型的基础上的Johnson-Mehl-Avrami-Kolmogorov（JMAK）方程得到的活化能为72.74 +/- 0.2 kJ/mol的水铁矿针铁矿的转化，低于报道的值为赤铁矿成核和生长。
Unlike most native metals, the unit cells of metal oxides tend to expand when crystallite sizes approach the nanoscale. Here we review different models that account for this behavior, and we present structural analyses for goethite (alpha-FeOOH) crystallites from similar to 10 to similar to 30 nm. The goethite was investigated during continuous particle growth via the hydrothermal transformation of 2-line ferrihydrite at pH 13.6 at 80, 90, and 100 degrees C using time-resolved, angle-dispersive synchrotron X-ray diffraction. Ferrihydrite gels were injected into polyimide capillaries with low background scattering, increasing the sensitivity for detecting diffraction from goethite nanocrystals that nucleated upon heating. Rietveld analysis enabled high-resolution extraction of crystallographic and kinetic data. Crystallite sizes for goethite increased with time at similar rates for all temperatures.With increasing crystallite size, goethite unit-cell volumes decreased, primarily as a result of contraction along the c-axis, the direction of closest-packing (space group Pnma). We introduce the coefficient of nanoscale contraction (CNC) as an analog to the coefficient of thermal expansion (CTE) to compare the dependence of lattice strain on crystallite size for goethite and other metal oxides, and we argue that nanoscale-induced crystallographic expansion is quantitatively similar to that produced when goethite is heated. In addition, our first-order kinetic model based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation yielded an activation energy for the transformation of ferrihydrite to goethite of 72.74 +/- 0.2 kJ/mol, below reported values for hematite nucleation and growth.