Department of Physics, New Jersey Institute of Technology, Newark, New Jersey 07102, USA.
J Chem Phys. 2009 Oct 28;131(16):164115. doi: 10.1063/1.3254322.
A typical nucleation-growth process is considered: a system is quenched into a supersaturated state with a small critical radius r( *) (-) and is allowed to nucleate during a finite time interval t(n), after which the supersaturation is abruptly reduced to a fixed value with a larger critical radius r( *) (+). The size-distribution of nucleated particles f(r,t) further evolves due to their deterministic growth and decay for r larger or smaller than r( *) (+), respectively. A general analytic expressions for f(r,t) is obtained, and it is shown that after a large growth time t this distribution approaches an asymptotic shape determined by two dimensionless parameters, lambda related to t(n), and Lambda=r( *) (+)/r( *) (-). This shape is strongly asymmetric with an exponential and double-exponential cutoffs at small and large sizes, respectively, and with a broad near-flat top in case of a long pulse. Conversely, for a short pulse the distribution acquires a distinct maximum at r=r(max)(t) and approaches a universal shape exp[zeta-e(zeta)], with zeta proportional to r-r(max), independent of the pulse duration. General asymptotic predictions are examined in terms of Zeldovich-Frenkel nucleation model where the entire transient behavior can be described in terms of the Lambert W function. Modifications for the Turnbull-Fisher model are also considered, and analytics is compared with exact numerics. Results are expected to have direct implementations in analysis of two-step annealing crystallization experiments, although other applications might be anticipated due to universality of the nucleation pulse technique.
通常认为成核-生长过程是这样的:将系统在有限时间间隔 t(n) 内淬火到具有小临界半径 r() (-) 的过饱和状态,之后将过饱和度突然降低到具有较大临界半径 r() (+) 的固定值。在 r 大于或小于 r() (+) 的情况下,由于成核粒子的确定性生长和衰减,成核粒子的大小分布 f(r,t) 进一步演化。得到了 f(r,t) 的一般解析表达式,并表明在较大的生长时间 t 之后,该分布接近由两个无量纲参数确定的渐近形状,参数 lambda 与 t(n) 有关,参数 Lambda=r() (+)/r(*) (-)。这种形状具有强烈的不对称性,在小尺寸和大尺寸处分别具有指数和双指数截止,在长脉冲的情况下具有宽阔的近平顶。相反,对于短脉冲,分布在 r=r(max)(t) 处具有明显的最大值,并接近通用形状 exp[zeta-e(zeta)],其中 zeta 与 r-r(max) 成正比,与脉冲持续时间无关。根据 Zeldovich-Frenkel 成核模型检验了一般的渐近预测,其中整个瞬态行为可以用 Lambert W 函数来描述。还考虑了 Turnbull-Fisher 模型的修改,并且将分析与精确数值进行了比较。由于成核脉冲技术的普遍性,预计这些结果将直接应用于两步退火结晶实验的分析中,尽管可能会有其他应用。