Citation: Lu Wen-Qing, Jin An-Ding, Zhu Xiao-Lei, Zhou Zhi-Hua, Huang Jin-Fan. Kinetics of Crystal Nucleation in 2,2,3-trimethylbutane C7H16[J]. Acta Physico-Chimica Sinica, 1997, 13(12): 1101-1107. doi: 10.3866/PKU.WHXB19971209
2，2，3-三甲基丁烷(C7H16)晶体的成核动力学
用XRD研究了2，2，3-三甲基丁烷（C7H16）（TMB）的高温固相I，运用凝聚态物质相变动力学的电子衍射技术探测了直径约为13nm的TMB簇合物的冻结行为. 实验中采用了玻璃Laval喷咀（30号），Ne为载气，样品为TMB蒸汽，混合气中TMB的摩尔分数为0.10，样品总压力为2.48×105Pa, 样品的起始温度为313K，通过超声膨胀产生簇合物. 在相同的膨胀条件下用飞行管试验求出簇合物的速度从而求出时标.在7.9μs的间隙中电子衍射跟踪了冻结过程，在约170K的冻结温度下平均大小为5500个分子左右的簇合物以3.5×1028m-3•s-1的成核速率冻结成固相I. 如果根据Tumbull, Fisher和Buckle的经典成核理论解释观测的成核速率，则固相I和过冷液体之间在170K的界面自由能的估计值为4.05kJ•m2. 形成临界晶核后估计的生长速率表明本实验中观测的成核过程对应着簇合物是单核冻结成固相I的单晶.
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关键词:
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超声气流膨胀
- / 三甲基丁烷簇的相和大小
- / 成核速率
- / 界面自由基
English
Kinetics of Crystal Nucleation in 2,2,3-trimethylbutane C7H16
High temperature solid phase I of 2,2,3-trimethylbutane(C7H16)(TMB) was investigated by X-ray powder diffraction. The electron diffraction technique for observing the kinetics of phase transitions in the condensed matter has been applied to study the freezing of TMB clusters with diameter of~13nm. Cluster beams were generated from the supersonically expanded TMB vapor with mole fraction of 0.01 in neon carrier gas. The freezing evolution was monitored by electron diffraction in interval of 7-9 μs. Clusters with an average size of ~5,500 molecules were observed to freeze into the solid phase I at a nucleation rate of 3.5 × 1028 m-3•s- 1 at the freezing temperature of clusters, ～170K. The estimated growth rate of postcritical nuclei indicates that the observed nucleation in the present experiment corresponds to mononuclear freezing of the clusters into single crystals of solid phase I.
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