Electrochemical and Related Phenomena under Weightless Conditions: I . Flowing Electrolyte Thermocells

Abstract

A flowing electrolyte thermogalvanic cell (Cu, ) has been studied under weightless conditions via drop‐tower experiments. Unexplained perturbations have been observed in the output potential in both the time‐dependent (emf build‐up) and quasi‐stationary state regions over a wide range of experimental conditions. Exhaustive control experiments as well as the general and over‐all reproducibility of perturbations per se in a large number of trials rule out oscillations in the hydraulic system as well as random transients as factors responsible for the observed phenomena. Stationary electrolyte systems including thermocells, concentration cells, and a Daniell cell, exhibited similar perturbations during the transition.The addition of urea was found to dampen the marked oscillations normally shown by a copper thermocell at the same output potential. The result is important in view of the known decreased ultrasonic attenuation and increased sound velocity caused by urea addition to water. At ambient temperatures the electrolytic conductivity of freshly prepared urea‐cupric sulfate solutions gradually increases and in subsequent drops the zero‐gravity induced oscillations reappear.Copper thermocells utilizing nonaqueous solvents (acetonitrile or absolute methanol) exhibit a voltage decrease (several millivolts) but the time/potential curve continues on its original course after impact. The potential of concentration cells (with linear and nonlinear gradients) increases (several millivolts in 0.7 sec), then decays to its initial value prior to impact; cells with linear gradients exhibit relatively larger changes. Inversion tests are also described. Daniell cells (1.09v at 20°C) show a similar behavior except that the voltage increase is about 40 mv.To understand better the influence of the transition on physico‐chemical processes, the electrochemical measurements were supplemented (with the appropriate controls) by a study of diffusional phenomena, heterogeneous and homogeneous chemical reactions. In all cases increased rates were observed and are attributed to enhanced ion mobility during weightlessness. On the basis of these experiments it must be concluded that an interaction exists between chemically reacting systems and gravitational fields.