Spatiotemporal Patterns in Electrochemically Reacting System

实验研究将在电流沿电极表面随时间和位置变化的条件下进行电化学反应。在其他类型的反应系统中，包括液相和气相反应、气固非均相反应、生化反应等，在许多条件下都会出现时空模式。在电化学反应过程中，如这里所考虑的，在动态条件下，非均匀表面是典型的。这种不均匀性对反应的总速率和系统动力学都有很大的影响。然而，关于电化学时空模式的信息非常少，而且这些信息主要局限于模式既可见又缓慢移动的有限特殊情况。需要建立实验装置来研究这些时空模式；电极阵列的使用，使电流，或反应速率，可以独立地测量在许多位置的反应表面。由于在每个电极上测量电流，并且由于每个位置的采样率可以很高，例如每个通道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。这些阵列将有不同的配置，包括正方形、六边形和圆形。反应表面的长度尺度可以通过改变阵列中电极的数量、单个电极的大小或电极之间的间距来改变。通过改变阵列中某些电极的电位来研究表面不均匀性对起搏器的影响。一个具有代表性和重要意义的电溶解反应，铁在硫酸中的溶解将被研究。该反应将在两个参数范围内进行研究。首先，低频主动式无源振荡发生；这个循环的快速激活阶段和缓慢钝化阶段都是通过电极表面的波的通过而发生的。对表面波现象和随着电位变化而发生的模式间时空分岔进行了研究。使用显微镜和摄像机对缓慢移动的钝化波进行直接的目视观察。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.