Maeda Nobuo, Wells Darrell, Becker Norman C, Hartley Patrick G, Wilson Peter W, Haymet Anthony D J, Kozielski Karen A
CSIRO Materials Science & Engineering, Ian Wark Laboratory, Bayview Avenue, Clayton VIC 3168, Australia.
Rev Sci Instrum. 2011 Jun;82(6):065109. doi: 10.1063/1.3602926.
Nucleation in a supercooled or a supersaturated medium is a stochastic event, and hence statistical analyses are required for the understanding and prediction of such events. The development of reliable statistical methods for quantifying nucleation probability is highly desirable for applications where control of nucleation is required. The nucleation of gas hydrates in supercooled conditions is one such application. We describe the design and development of a high pressure automated lag time apparatus (HP-ALTA) for the statistical study of gas hydrate nucleation and growth at elevated gas pressures. The apparatus allows a small volume (≈150 μl) of water to be cooled at a controlled rate in a pressurized gas atmosphere, and the temperature of gas hydrate nucleation, T(f), to be detected. The instrument then raises the sample temperature under controlled conditions to facilitate dissociation of the gas hydrate before repeating the cooling-nucleation cycle again. This process of forming and dissociating gas hydrates can be automatically repeated for a statistically significant (>100) number of nucleation events. The HP-ALTA can be operated in two modes, one for the detection of hydrate in the bulk of the sample, under a stirring action, and the other for the detection of the formation of hydrate films across the water-gas interface of a quiescent sample. The technique can be applied to the study of several parameters, such as gas pressure, cooling rate and gas composition, on the gas hydrate nucleation probability distribution for supercooled water samples.
在过冷或过饱和介质中的成核是一个随机事件，因此需要进行统计分析来理解和预测此类事件。对于需要控制成核的应用而言，开发可靠的统计方法来量化成核概率是非常必要的。在过冷条件下气体水合物的成核就是这样一种应用。我们描述了一种高压自动滞后时间装置（HP-ALTA）的设计与开发，用于在升高的气体压力下对气体水合物的成核和生长进行统计研究。该装置能使小体积（约150微升）的水在加压气体气氛中以可控速率冷却，并检测气体水合物成核的温度T(f)。然后仪器在可控条件下升高样品温度，以促进气体水合物的分解，之后再重复冷却-成核循环。形成和解离气体水合物的这个过程可以针对具有统计学意义（>100）数量的成核事件自动重复。HP-ALTA可以在两种模式下运行，一种用于在搅拌作用下检测样品主体中的水合物，另一种用于检测静态样品气-水界面上水合物膜的形成。该技术可应用于研究诸如气体压力、冷却速率和气体组成等几个参数对过冷水样品气体水合物成核概率分布的影响。
