From Rate Measurements to Mechanistic Data for Condensed Matter Reactions: A Case Study Using the Crystallization of [Zn(OH2)6][ZnCl4]
From Rate Measurements to Mechanistic Data for Condensed Matter Reactions: A Case Study Using the Crystallization of [Zn(OH2)6][ZnCl4]
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从凝聚态反应的速率测量到机理数据：使用 [Zn(OH2)6][ZnCl4] 结晶的案例研究
DOI：
10.3390/cryst7010011
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发表时间：
2016
影响因子：
8.6
通讯作者：
James D. Martin
中科院分区：
文献类型：
--
作者：
Berkley G. Hillis;Bradley P. Losey;James Weng;N. Ghaleb;F. Hou;James D. Martin
的结晶的动力学的R = 3水合氯化锌，[Zn（OH 2）6][ZnCl 4]，测定的时间分辨同步辐射X射线衍射，时间分辨中子衍射，并通过差示扫描量热法。结果表明，使用经典的Kolmogorov，约翰逊，Mehl，Avrami（KJMA）动力学模型的速率数据的分析提供了从根本上不同的速率常数等效的反应条件。重新引入的动力学模型，使用我们最近开发的改进的KJMA模型（M-KJMA），通过每种方法测量的样品的量，它表明，这些不同的速率测量技术可以给内在的，材料特定的速率常数，相边界的速度，Vpb。然后将这些数据与直接光学测量的结晶前沿速度进行比较。时间分辨衍射方法独特地监测液体反应物的损失和结晶产物的形成，证明该水合物相的结晶不通过中间相进行。温度依赖的vpb数据，然后很好地拟合过渡区理论提取激活参数。这些表明，该结晶反应的限速组分是水合的沃茨（或质子）进入晶格的限制位置的有序化，导致大的负活化熵。
The kinetics of crystallization of the R = 3 hydrate of zinc chloride, [Zn(OH2)6][ZnCl4], is measured by time-resolved synchrotron x-ray diffraction, time-resolved neutron diffraction, and by differential scanning calorimetry. It is shown that analysis of the rate data using the classic Kolmogorov, Johnson, Mehl, Avrami (KJMA) kinetic model affords radically different rate constants for equivalent reaction conditions. Reintroducing the amount of sample measured by each method into the kinetic model, using our recently developed modified-KJMA model (M-KJMA), it is shown that each of these diverse rate measurement techniques can give the intrinsic, material specific rate constant, the velocity of the phase boundary, vpb. These data are then compared to the velocity of the crystallization front directly measured optically. The time-resolved diffraction methods uniquely monitor the loss of the liquid reactant and formation of the crystalline product demonstrating that the crystallization of this hydrate phase proceeds through no intermediate phases. The temperature dependent vpb data are then well fit to transition zone theory to extract activation parameters. These demonstrate that the rate-limiting component to this crystallization reaction is the ordering of the waters (or protons) of hydration into restricted positions of the crystalline lattice resulting in large negative entropy of activation.