SOLUTE POLARIZATION DURING PLANAR FREEZING OF AQUEOUS SALT-SOLUTIONS
SOLUTE POLARIZATION DURING PLANAR FREEZING OF AQUEOUS SALT-SOLUTIONS
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DOI：
10.1016/s0017-9310(83)80179-3
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发表时间：
1983-01-01
影响因子：
5.2
通讯作者：
WOLLHOVER, K
中科院分区：
文献类型：
--
作者：
KORBER, C;SCHEIWE, MW;WOLLHOVER, K
本文分析了具有平面固液界面的二元盐水溶液在单向冻结过程中的溶质再分配。低温显微镜配备了一个专门设计的冷冻阶段产生一个明确的温度分布和界面传播动力学类似的大型系统的板状几何形状。连接显微镜分光光度计，通过透射光进行浓度测量。NaMnO 4的水溶液，表现出在525 nm处的最大吸收，并具有相图，以及质量扩散特性，非常类似于NaCl在水中，被用作样品溶液。该方法的一个主要优点是定量测量和观察相结合，允许视觉控制的冰锋的形状，因此从平面冻结到更高的结构的过渡。在一维冻结过程中记录了浓度分布的光度扫描，界面传播速率在1和10 μm s-1之间。结果表明，浓度分布的“陡度”随着时间和生长速度的增加而增加。在初始过渡过程中，计算结果与描述恒定冰锋速度下纯物质扩散的数学模型吻合较好。平面界面的不稳定性导致枝晶击穿总是发生在共晶或稳态条件下达到。
An analysis of solute redistribution in binary aqueous salt solutions during unidirectional freezing with a planar solid-liquid interface is presented. A cryomicroscope was equipped with a specially designed freezing stage yielding a well-defined temperature distribution and interface propagation kinetics similar to large systems of plate-like geometry. A microscope spectrophotometer was attached for concentration measurements by means of transmitted light. Aqueous solutions of NaMnO4, exhibiting a maximum absorption at 525 nm and having a phase diagram, as well as mass diffusion properties, very similar to NaCl in water, were used as sample solutions. A major advantage of the method is the combination of quantitative measurements and observation allowing a visual control of the shape of the ice front, and hence of the transition from planar freezing to higher structures. Photometricscans of concentration profiles were recorded duringone-dimensional freezing with interface propagation rates between 1 and 10 μm s−1. It was shown that the ‘steepness’ of the concentration distributions increased with both time and growth velocity. During the initial transient, the results agree well with amathematical model describing pure mass diffusion at constant ice front velocity. Instabilities of the planar interface resulting in dendritic breakdown always occurred before eutectic or steady-state conditions were reached.