Spatiotemporal Patterns in Electrochemically Reacting System

摘要-哈德逊- 9710259 将对电流随时间和沿着电极表面的位置变化的条件下的电化学反应进行实验研究。 时空模式发生在许多条件下，在其他类型的反应系统，包括液相和气相反应，气固非均相反应，生化反应等电化学反应，如那些正在考虑在这里，不均匀的表面是典型的动态条件下。 非均匀性对反应的总速率以及系统动力学有很强的影响。 然而，在电化学时空图案上的信息很少，并且可用的信息在很大程度上限于有限的特殊情况，其中图案既可见又缓慢移动。 应开发一个实验装置来研究这些时空模式;使用电极阵列，以便可以在反应表面的许多位置独立测量电流或反应速率。 由于在每个电极处测量电流，并且由于每个位置处的采样率可以很高，比如每个通道5000 Hz，因此该方法适用于大范围条件下的所有类型的电化学反应。 阵列将具有各种配置，包括正方形、六边形和指状图案。 通过改变阵列中电极的数量、单个电极的尺寸或电极之间的间隔来改变反应表面的长度尺度。 将通过改变阵列中某些电极的电位来研究表面不均匀性或起搏器的影响 铁在硫酸中的溶解是一个具有代表性和重要性的电溶解反应。 将在两个参数范围内研究该反应。 在第一种情况下，发生低频主动-被动振荡;周期的快速激活和较慢的钝化阶段都是通过波穿过电极表面而发生的。 将进行表面波现象和随着电势改变而在图案之间发生的时空分叉的研究。 还将使用显微镜和摄像机直接观察缓慢移动的钝化波。 将建立数学模型。

ABSTRACT - Hudson - 9710259 Experimental studies will be carried out on electrochemical reactions under conditions in which the current changes with both time and position along the electrode surface. Spatiotemporat patterns occur under many conditions in other types of reacting systems including liquid and gas phase reactions, gas-solid heterogeneous reactions, biochemical reactions, etc. During electrochemical reactions, such as those being considered here, nonuniform surfaces are typical under dynamic conditions. The nonuniformities have a strong effect on the overall rate of reaction as well as the system dynamics. However, very little information is available on spatiotemporal patterns in electrochemistry and that which is available is restricted largely to limited, special cases in which the patterns are both visible and slow moving. An experimental setup shall be developed to study these spatiotemporal patterns; arrays of electrodes are used so that the current, or rate of reaction, can be measured independently at many locations on the reaction surface. Since the current is measured at each electrode and since the sampling rate at each location can be high, say 5000 Hz per channel, the method is applicable to all types of electrochemical reactions over a large range of conditions. The arrays will be in various configurations including square, hexagonal, and fing patterns. The length scale of the reaction surface is varied by changing the number of electrodes in an array, the size of the individual electrodes, or the spacing among the electrodes. The effect of surface nonunifonnities or pacemakers will be studied by varying the potential of some of the electrodes in the array A representative and important electrodissolution reaction, the dissolution of iron in sulfuric acid will be studied. This reaction will be investigated in two parameter ranges. In the first, low frequency active-passive oscillations occur; both the fast activation and the slower passivation phases of the cycle occur by the passage of waves across the electrode surface. A study of surface wave phenomena and the spatiotemporal bifurcations which occur among patterns as the potential is changed will be carried out. Direct visual observations using microscope and video camera of the slowly moving passivation waves will also be made. Mathematical models will be developed.