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Effect of Cooling Rate on Freezing of Wool-Water Mixtures

机译：冷却速率对羊毛水混合物冻结的影响

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摘要

The effect of the cooling rate on freezing of a wool-water system is studied using DSC at cooling rates (CR) that vary from 1.25 to 40 K/min. By means of centrifugation, an equilibrium quantity of interstitial water in the fibers (W_s) is determined to be 0.48 g/g of wool. Two samples with different water contents are used: sample A is more than W_s, i.e., W_c = 0.54, and sample B is 0.43 g/g of wool. Characteristic shape changes in a broad exotherm ranging from temperatures of about 230 to 260 K are observed in DSC curves, A freezing mechanism of interstitial water is proposed on the basis of supercooling. The swollen wool is assumed to be a dispersion system consisting of domains defined as structurally favored sites, permitting water migration for ice crystal growth. The shape change with CR can be explained by differences in the freezing temperature of water of different volumes in the domains. Kissinger's equation is applicable to this crystallization process. Values of activation energy for both A and B samples are nearly the same, about -115 kJ/mol. Activation energy is considered to be the sum of the two terms for crystallization and migration of water, and the latter value is presumed to be about 49 kJ/mol. The important finding is that ice crystals in sample A cooled at 1.25 K/min contain an amount of water corresponding to about 38.2% of the so-called "nonfreezing water" W_u, which remains unfrozen at a CR above 5 K/min.
机译：使用DSC在1.25至40 K / min的冷却速率（CR）下研究了冷却速率对羊毛-水系统冻结的影响。通过离心，确定纤维中的间隙水的平衡量（W_s）为0.48g / g羊毛。使用两个具有不同水含量的样品：样品A大于W_s，即W_c = 0.54，而样品B为0.43 g / g羊毛。在DSC曲线中观察到温度在约230至260 K的宽幅放热中的特征形状变化。在过冷的基础上，提出了间隙水的冻结机理。溶胀的羊毛被认为是由定义为结构上有利位置的区域组成的分散系统，允许水迁移以生长冰晶。 CR引起的形状变化可以通过域中不同体积的水的冷冻温度差异来解释。基辛格方程式适用于该结晶过程。 A和B样品的活化能值几乎相同，约为-115 kJ / mol。活化能被认为是水的结晶和迁移的两项的总和，并且后者的值被推定为约49 kJ / mol。重要的发现是，以1.25 K / min的速度冷却的样品A中的冰晶所含的水量约为所谓的“非冷冻水” W_u的38.2％，该水在CR高于5 K / min时仍未冻结。

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